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Sample records for beam ct kv

  1. Evaluation of on-board kV cone beam CT (CBCT)-based dose calculation

    NASA Astrophysics Data System (ADS)

    Yang, Yong; Schreibmann, Eduard; Li, Tianfang; Wang, Chuang; Xing, Lei

    2007-02-01

    On-board CBCT images are used to generate patient geometric models to assist patient setup. The image data can also, potentially, be used for dose reconstruction in combination with the fluence maps from treatment plan. Here we evaluate the achievable accuracy in using a kV CBCT for dose calculation. Relative electron density as a function of HU was obtained for both planning CT (pCT) and CBCT using a Catphan-600 calibration phantom. The CBCT calibration stability was monitored weekly for 8 consecutive weeks. A clinical treatment planning system was employed for pCT- and CBCT-based dose calculations and subsequent comparisons. Phantom and patient studies were carried out. In the former study, both Catphan-600 and pelvic phantoms were employed to evaluate the dosimetric performance of the full-fan and half-fan scanning modes. To evaluate the dosimetric influence of motion artefacts commonly seen in CBCT images, the Catphan-600 phantom was scanned with and without cyclic motion using the pCT and CBCT scanners. The doses computed based on the four sets of CT images (pCT and CBCT with/without motion) were compared quantitatively. The patient studies included a lung case and three prostate cases. The lung case was employed to further assess the adverse effect of intra-scan organ motion. Unlike the phantom study, the pCT of a patient is generally acquired at the time of simulation and the anatomy may be different from that of CBCT acquired at the time of treatment delivery because of organ deformation. To tackle the problem, we introduced a set of modified CBCT images (mCBCT) for each patient, which possesses the geometric information of the CBCT but the electronic density distribution mapped from the pCT with the help of a BSpline deformable image registration software. In the patient study, the dose computed with the mCBCT was used as a surrogate of the 'ground truth'. We found that the CBCT electron density calibration curve differs moderately from that of pCT. No

  2. Evaluation of on-board kV cone beam CT (CBCT)-based dose calculation.

    PubMed

    Yang, Yong; Schreibmann, Eduard; Li, Tianfang; Wang, Chuang; Xing, Lei

    2007-02-07

    On-board CBCT images are used to generate patient geometric models to assist patient setup. The image data can also, potentially, be used for dose reconstruction in combination with the fluence maps from treatment plan. Here we evaluate the achievable accuracy in using a kV CBCT for dose calculation. Relative electron density as a function of HU was obtained for both planning CT (pCT) and CBCT using a Catphan-600 calibration phantom. The CBCT calibration stability was monitored weekly for 8 consecutive weeks. A clinical treatment planning system was employed for pCT- and CBCT-based dose calculations and subsequent comparisons. Phantom and patient studies were carried out. In the former study, both Catphan-600 and pelvic phantoms were employed to evaluate the dosimetric performance of the full-fan and half-fan scanning modes. To evaluate the dosimetric influence of motion artefacts commonly seen in CBCT images, the Catphan-600 phantom was scanned with and without cyclic motion using the pCT and CBCT scanners. The doses computed based on the four sets of CT images (pCT and CBCT with/without motion) were compared quantitatively. The patient studies included a lung case and three prostate cases. The lung case was employed to further assess the adverse effect of intra-scan organ motion. Unlike the phantom study, the pCT of a patient is generally acquired at the time of simulation and the anatomy may be different from that of CBCT acquired at the time of treatment delivery because of organ deformation. To tackle the problem, we introduced a set of modified CBCT images (mCBCT) for each patient, which possesses the geometric information of the CBCT but the electronic density distribution mapped from the pCT with the help of a BSpline deformable image registration software. In the patient study, the dose computed with the mCBCT was used as a surrogate of the 'ground truth'. We found that the CBCT electron density calibration curve differs moderately from that of pCT. No

  3. SU-E-J-214: Comparative Assessment On IGRT On Partial Bladder Cancer Treatment Between CT-On-Rails (CTOR) and KV Cone Beam CT (CBCT)

    SciTech Connect

    Lin, T; Ma, C

    2014-06-01

    Purpose: Image-Guided radiation therapy(IGRT) depends on reliable online patient-specific anatomy information to address random and progressive anatomy changes. Large margins have been suggested to bladder cancer treatment due to large daily bladder anatomy variation. KV Cone beam CT(CBCT) has been used in IGRT localization prevalently; however, its lack of soft tissue contrast makes clinicians hesitate to perform daily soft tissue alignment with CBCT for partial bladder cancer treatment. This study compares the localization uncertainties of bladder cancer IGRT using CTon- Rails(CTOR) and CBCT. Methods: Three T2N0M0 bladder cancer patients (total of 66 Gy to partial bladder alone) were localized daily with either CTOR or CBCT for their entire treatment course. A total of 71 sets of CTOR and 22 sets of CBCT images were acquired and registered with original planning CT scans by radiation therapists and approved by radiation oncologists for the daily treatment. CTOR scanning entailed 2mm slice thickness, 0.98mm axial voxel size, 120kVp and 240mAs. CBCT used a half fan pelvis protocol from Varian OBI system with 2mm slice thickness, 0.98axial voxel size, 125kVp, and 680mAs. Daily localization distribution was compared. Accuracy of CTOR and CBCT on partial bladder alignment was also evaluated by comparing bladder PTV coverage. Results: 1cm all around PTV margins were used in every patient except target superior limit margin to 0mm due to bowel constraint. Daily shifts on CTOR averaged to 0.48, 0.24, 0.19 mms(SI,Lat,AP directions); CBCT averaged to 0.43, 0.09, 0.19 mms(SI,Lat,AP directions). The CTOR daily localization showed superior results of V100% of PTV(102% CTOR vs. 89% CBCT) and bowel(Dmax 69.5Gy vs. 78Gy CBCT). CTOR images showed much higher contrast on bladder PTV alignment. Conclusion: CTOR daily localization for IGRT is more dosimetrically beneficial for partial bladder cancer treatment than kV CBCT localization and provided better soft tissue PTV

  4. Evaluation of the effects of sagging shifts on isocenter accuracy and image quality of cone-beam CT from kV on-board imagers.

    PubMed

    Ali, Imad; Ahmad, Salahuddin

    2009-07-17

    To investigate the effects of sagging shifts of three on-board kV imaging systems (OBI) on the isocenter positioning accuracy and image quality of cone-beam CT (CBCT). A cubical phantom having a metal marker in the center that can be aligned with the radiation isocenter was used to measure sagging shifts and their variation with gantry angle on three Varian linacs with kV on-board imaging systems. A marker-tracking algorithm was applied to detect the shadow of the metal marker and localize its center in the two-dimensional cone-beam radiographic projections. This tracking algorithm is based on finding the position of maximum cross-correlation between a region-of-interest from a template image (including the metal marker) and the projections containing the shadow of the metal marker. Sagging shifts were corrected by mapping the center of the metal marker to a reference position for all projections acquired over a full gantry rotation (0-360 degrees). The sag-corrected radiographic projections were then used to reconstruct CBCT using Feldkamp back-projection. A standard quality assurance phantom was used to evaluate the image quality of CBCT before and after sagging correction. Sagging affects both the positioning accuracy of the OBI isocenter and the CBCT image quality. For example, on one linac, the position of the marker on the cone-beam radiographic projections depends on the angular view and has maximal shifts of about 2 mm along the imager x-direction (patient's cross-plane). Sagging produces systematic shifts of the OBI isocenter as large as 1 mm posterior and 1 mm left in patient coordinates relative to the radiation isocenter. Further, it causes spatial distortion and blurring in CBCT image reconstructed from radiographic projections that are not corrected for OBI sagging. CBCT numbers vary by about 1% in full-fan scans and up to 3.5% in half-fan scans because of sagging. In order to achieve better localization accuracy in image-guided radiation therapy

  5. [Image guided radiotherapy with the Cone Beam CT kV (Elekta): experience of the Léon Bérard centre].

    PubMed

    Pommier, P; Gassa, F; Lafay, F; Claude, L

    2009-09-01

    Image guide radiotherapy with the Cone Beam CT kV (CBCT-kV) developed by Elekta has been implemented at the centre Léon Bérard in November 2006. The treatment procedure is presented and detailed for prostate cancer IGRT and non small cell lung cancer (NSCLC) stereotactic radiotherapy (SRT). CBCT-kV is routinely used for SRT, selected paediatric cancers, all prostate carcinomas, primitive brain tumours and head and neck cancers that do not require nodes irradiation. Thirty-five to 40 patients are treated within a daily 11-hours period. The general procedure for 3D images acquisition and their analysis is described. The CBCT-kV permitted to identify about 10% of prostate cancer patients for whom a positioning with bone-based 2D images only would have led to an unacceptable dose distribution for at least one session. SRT is now used routinely for inoperable NSCLC. The easiness of implementing CBCT-kV imaging and its expected medical benefit should lead to a rapid diffusion of this technology that is also submitted to prospective and multicentric medico-economical evaluations.

  6. Dose Calculation on KV Cone Beam CT Images: An Investigation of the Hu-Density Conversion Stability and Dose Accuracy Using the Site-Specific Calibration

    SciTech Connect

    Rong Yi

    2010-10-01

    Precise calibration of Hounsfield units (HU) to electron density (HU-density) is essential to dose calculation. On-board kV cone beam computed tomography (CBCT) imaging is used predominantly for patients' positioning, but will potentially be used for dose calculation. The impacts of varying 3 imaging parameters (mAs, source-imager distance [SID], and cone angle) and phantom size on the HU number accuracy and HU-density calibrations for CBCT imaging were studied. We proposed a site-specific calibration method to achieve higher accuracy in CBCT image-based dose calculation. Three configurations of the Computerized Imaging Reference Systems (CIRS) water equivalent electron density phantom were used to simulate sites including head, lungs, and lower body (abdomen/pelvis). The planning computed tomography (CT) scan was used as the baseline for comparisons. CBCT scans of these phantom configurations were performed using Varian Trilogy{sup TM} system in a precalibrated mode with fixed tube voltage (125 kVp), but varied mAs, SID, and cone angle. An HU-density curve was generated and evaluated for each set of scan parameters. Three HU-density tables generated using different phantom configurations with the same imaging parameter settings were selected for dose calculation on CBCT images for an accuracy comparison. Changing mAs or SID had small impact on HU numbers. For adipose tissue, the HU discrepancy from the baseline was 20 HU in a small phantom, but 5 times lager in a large phantom. Yet, reducing the cone angle significantly decreases the HU discrepancy. The HU-density table was also affected accordingly. By performing dose comparison between CT and CBCT image-based plans, results showed that using the site-specific HU-density tables to calibrate CBCT images of different sites improves the dose accuracy to {approx}2%. Our phantom study showed that CBCT imaging can be a feasible option for dose computation in adaptive radiotherapy approach if the site

  7. Dose calculation on kV cone beam CT images: an investigation of the Hu-density conversion stability and dose accuracy using the site-specific calibration.

    PubMed

    Rong, Yi; Smilowitz, Jennifer; Tewatia, Dinesh; Tomé, Wolfgang A; Paliwal, Bhudatt

    2010-01-01

    Precise calibration of Hounsfield units (HU) to electron density (HU-density) is essential to dose calculation. On-board kV cone beam computed tomography (CBCT) imaging is used predominantly for patients' positioning, but will potentially be used for dose calculation. The impacts of varying 3 imaging parameters (mAs, source-imager distance [SID], and cone angle) and phantom size on the HU number accuracy and HU-density calibrations for CBCT imaging were studied. We proposed a site-specific calibration method to achieve higher accuracy in CBCT image-based dose calculation. Three configurations of the Computerized Imaging Reference Systems (CIRS) water equivalent electron density phantom were used to simulate sites including head, lungs, and lower body (abdomen/pelvis). The planning computed tomography (CT) scan was used as the baseline for comparisons. CBCT scans of these phantom configurations were performed using Varian Trilogy system in a precalibrated mode with fixed tube voltage (125 kVp), but varied mAs, SID, and cone angle. An HU-density curve was generated and evaluated for each set of scan parameters. Three HU-density tables generated using different phantom configurations with the same imaging parameter settings were selected for dose calculation on CBCT images for an accuracy comparison. Changing mAs or SID had small impact on HU numbers. For adipose tissue, the HU discrepancy from the baseline was 20 HU in a small phantom, but 5 times lager in a large phantom. Yet, reducing the cone angle significantly decreases the HU discrepancy. The HU-density table was also affected accordingly. By performing dose comparison between CT and CBCT image-based plans, results showed that using the site-specific HU-density tables to calibrate CBCT images of different sites improves the dose accuracy to approximately 2%. Our phantom study showed that CBCT imaging can be a feasible option for dose computation in adaptive radiotherapy approach if the site-specific calibration

  8. Experimental validation of a Monte Carlo-based kV x-ray projection model for the Varian linac-mounted cone-beam CT imaging system

    NASA Astrophysics Data System (ADS)

    Lazos, Dimitrios; Pokhrel, Damodar; Su, Zhong; Lu, Jun; Williamson, Jeffrey F.

    2008-03-01

    Fast and accurate modeling of cone-beam CT (CBCT) x-ray projection data can improve CBCT image quality either by linearizing projection data for each patient prior to image reconstruction (thereby mitigating detector blur/lag, spectral hardening, and scatter artifacts) or indirectly by supporting rigorous comparative simulation studies of competing image reconstruction and processing algorithms. In this study, we compare Monte Carlo-computed x-ray projections with projections experimentally acquired from our Varian Trilogy CBCT imaging system for phantoms of known design. Our recently developed Monte Carlo photon-transport code, PTRAN, was used to compute primary and scatter projections for cylindrical phantom of known diameter (NA model 76-410) with and without bow-tie filter and antiscatter grid for both full- and half-fan geometries. These simulations were based upon measured 120 kVp spectra, beam profiles, and flat-panel detector (4030CB) point-spread function. Compound Poisson- process noise was simulated based upon measured beam output. Computed projections were compared to flat- and dark-field corrected 4030CB images where scatter profiles were estimated by subtracting narrow axial-from full axial width 4030CB profiles. In agreement with the literature, the difference between simulated and measured projection data is of the order of 6-8%. The measurement of the scatter profiles is affected by the long tails of the detector PSF. Higher accuracy can be achieved mainly by improving the beam modeling and correcting the non linearities induced by the detector PSF.

  9. Monitoring Dosimetric Impact of Weight Loss With Kilovoltage (KV) Cone Beam CT (CBCT) During Parotid-Sparing IMRT and Concurrent Chemotherapy

    SciTech Connect

    Ho, Kean Fatt; Marchant, Tom; Moore, Chris; Webster, Gareth; Rowbottom, Carl; Penington, Hazel; Lee, Lip; Yap, Beng; Sykes, Andrew; Slevin, Nick

    2012-03-01

    Purpose: Parotid-sparing head-and-neck intensity-modulated radiotherapy (IMRT) can reduce long-term xerostomia. However, patients frequently experience weight loss and tumor shrinkage during treatment. We evaluate the use of kilovoltage (kV) cone beam computed tomography (CBCT) for dose monitoring and examine if the dosimetric impact of such changes on the parotid and critical neural structures warrants replanning during treatment. Methods and materials: Ten patients with locally advanced oropharyngeal cancer were treated with contralateral parotid-sparing IMRT concurrently with platinum-based chemotherapy. Mean doses of 65 Gy and 54 Gy were delivered to clinical target volume (CTV)1 and CTV2, respectively, in 30 daily fractions. CBCT was prospectively acquired weekly. Each CBCT was coregistered with the planned isocenter. The spinal cord, brainstem, parotids, larynx, and oral cavity were outlined on each CBCT. Dose distributions were recalculated on the CBCT after correcting the gray scale to provide accurate Hounsfield calibration, using the original IMRT plan configuration. Results: Planned contralateral parotid mean doses were not significantly different to those delivered during treatment (p > 0.1). Ipsilateral and contralateral parotids showed a mean reduction in volume of 29.7% and 28.4%, respectively. There was no significant difference between planned and delivered maximum dose to the brainstem (p = 0.6) or spinal cord (p = 0.2), mean dose to larynx (p = 0.5) and oral cavity (p = 0.8). End-of-treatment mean weight loss was 7.5 kg (8.8% of baseline weight). Despite a {>=}10% weight loss in 5 patients, there was no significant dosimetric change affecting the contralateral parotid and neural structures. Conclusions: Although patient weight loss and parotid volume shrinkage was observed, overall, there was no significant excess dose to the organs at risk. No replanning was felt necessary for this patient cohort, but a larger patient sample will be investigated

  10. SU-E-I-07: Response Characteristics and Signal Conversion Modeling of KV Flat-Panel Detector in Cone Beam CT System

    SciTech Connect

    Wang, Yu; Cao, Ruifen; Pei, Xi; Wang, Hui; Hu, Liqin

    2015-06-15

    Purpose: The flat-panel detector response characteristics are investigated to optimize the scanning parameter considering the image quality and less radiation dose. The signal conversion model is also established to predict the tumor shape and physical thickness changes. Methods: With the ELEKTA XVI system, the planar images of 10cm water phantom were obtained under different image acquisition conditions, including tube voltage, electric current, exposure time and frames. The averaged responses of square area in center were analyzed using Origin8.0. The response characteristics for each scanning parameter were depicted by different fitting types. The transmission measured for 10cm water was compared to Monte Carlo simulation. Using the quadratic calibration method, a series of variable-thickness water phantoms images were acquired to derive the signal conversion model. A 20cm wedge water phantom with 2cm step thickness was used to verify the model. At last, the stability and reproducibility of the model were explored during a four week period. Results: The gray values of image center all decreased with the increase of different image acquisition parameter presets. The fitting types adopted were linear fitting, quadratic polynomial fitting, Gauss fitting and logarithmic fitting with the fitting R-Square 0.992, 0.995, 0.997 and 0.996 respectively. For 10cm water phantom, the transmission measured showed better uniformity than Monte Carlo simulation. The wedge phantom experiment show that the radiological thickness changes prediction error was in the range of (-4mm, 5mm). The signal conversion model remained consistent over a period of four weeks. Conclusion: The flat-panel response decrease with the increase of different scanning parameters. The preferred scanning parameter combination was 100kV, 10mA, 10ms, 15frames. It is suggested that the signal conversion model could effectively be used for tumor shape change and radiological thickness prediction. Supported by

  11. [New methods in the treatment of localized prostate cancer: use of dynamic arc therapy and kV cone-beam CT positioning].

    PubMed

    Szappanos, Szabolcs; Farkas, Róbert; Lőcsei, Zoltán; László, Zoltán; Kalincsák, Judit; Bellyei, Szabolcs; Sebestyén, Zsolt; Csapó, László; Sebestyén, Klára; Halász, Judit; Musch, Zoltán; Beöthe, Tamás; Farkas, László; Mangel, László

    2014-08-10

    Bevezetés: A prosztatarák az idősebb életkor és a fejlett világ daganatos megbetegedése. Lokalizált prosztatarák esetében a műtéti ellátás mellett komoly szerepe van a definitív sugárkezelésnek. Célkitűzés: A szerzők intézetében telepített Novalis TX gyorsító segítségével úgynevezett intenzitásmodulált sugárterápia, annak dinamikus ívbesugárzással elvégzett formája, illetve verifikáció során háromdimenziós lágy szöveti képellenőrzést biztosító, integrált kilovoltos cone-beam komputertomográfiával végzett képvezérelt sugárterápia került bevezetésre, amely módszerekkel szerzett első tapasztalataikat ismertetik a szerzők. Módszer: 2011 decembere és 2013 februárja között, dóziseszkalációt követően, 102 dinamikus ívbesugárzással elvégzett kezelést végeztek, majd 10-10 szelektált, alacsony és magas kockázatú betegnél (átlagéletkor 72,5 év) elkészítették a háromdimenziós konformális besugárzási terveket is. Azonos célterület-lefedettség mellett összevetették a rizikószervek dózisterhelését. Eredmények: A dinamikus ívbesugárzással elvégzett kezelések mellett a rizikószervek szignifikánsan alacsonyabb dózisterhelését érték el, amelyet a kedvező korai mellékhatásprofil is alátámaszt. Következtetések: Az intenzitásmodulált sugárterápia dinamikus ívbesugárzással elvégzett formája biztonsággal alkalmazott standard kezelési módozattá vált a szerzők intézetében. Késői mellékhatások és lokális kontroll további vizsgálata szükséges. Orv. Hetil., 2014, 155(32), 1265–1272.

  12. An algorithm to extract three-dimensional motion by marker tracking in the kV projections from an on-board imager: four-dimensional cone-beam CT and tumor tracking implications.

    PubMed

    Ali, Imad; Alsbou, Nesreen; Herman, Terence; Ahmad, Salahuddin

    2011-02-01

    The purpose of this work is to extract three-dimensional (3D) motion trajectories of internal implanted and external skin-attached markers from kV cone-beam projections and reduce image artifact from patient motion in cone-beam computed tomography (CBCT) from on-board imager. Cone beam radiographic projections were acquired for a mobile phantom and liver patients with internal implanted and external skin-attached markers. An algorithm was developed to automatically find the positions of the markers in the projections. It uses normalized cross-correlation between a template image of a metal seed marker and the projections to find the marker position. From these positions and time-tagged angular views, the marker 3D motion trajectory was obtained over a time interval of nearly one minute, which is the time required for scanning. This marker trajectory was used to remap the pixels of the projections to eliminate motion. Then, the motion-corrected projections were used to reconstruct CBCT. An algorithm was developed to extract 3D motion trajectories of internal and external markers from cone-beam projections using a kV monoscopic on-board imager. This algorithm was tested and validated using a mobile phantom and patients with liver masses that had radio-markers implanted in the tumor and attached to the skin. The extracted motion trajectories were used to investigate motion correlation between internal and external markers in liver patients. Image artifacts from respiratory motion were reduced in CBCT reconstructed from cone-beam projections that were preprocessed to remove motion shifts obtained from marker tracking. With this method, motion-related image artifacts such as blurring and spatial distortion were reduced, and contrast and position resolutions were improved significantly in CBCT reconstructed from motion-corrected projections. Furthermore, correlated internal and external marker 3D-motion tracks obtained from the kV projections might be useful for 4DCBCT

  13. [Radiation output evaluation of kilovoltage cone beam CT unit].

    PubMed

    Wang, Yunlai; Liao, Xiongfei; Ge, Ruigang

    2011-09-01

    To evaluate the radiation output and stability of linac-integrated kV cone beam CT unit. Air kermas in radiographic mode were measured with 0.6 cc ion chamber and Unidos electrometer for Synergy-integrated XVI kV cone beam CT unit. Air kermas vs image frames were measured in fluoroscopic mode. Output stability and depth doses were measured. The air kerma increased quadratically with the increased tube voltage, while increasing linearly with the tube current, exposure time, and number of frames. The radiation output stability and its change with the gantry angle were within +/-1%. The percentage depth dose increased with higher tube voltage. The radiation output of XVI is stable. The radiation outputs change considerably with the preset parameters. Parameters should be optimally chosen to reduce the patient dose.

  14. Cardiac cone-beam CT

    SciTech Connect

    Manzke, Robert . E-mail: robert.manzke@philips.com

    2005-10-15

    This doctoral thesis addresses imaging of the heart with retrospectively gated helical cone-beam computed tomography (CT). A thorough review of the CT reconstruction literature is presented in combination with a historic overview of cardiac CT imaging and a brief introduction to other cardiac imaging modalities. The thesis includes a comprehensive chapter about the theory of CT reconstruction, familiarizing the reader with the problem of cone-beam reconstruction. The anatomic and dynamic properties of the heart are outlined and techniques to derive the gating information are reviewed. With the extended cardiac reconstruction (ECR) framework, a new approach is presented for the heart-rate-adaptive gated helical cardiac cone-beam CT reconstruction. Reconstruction assessment criteria such as the temporal resolution, the homogeneity in terms of the cardiac phase, and the smoothness at cycle-to-cycle transitions are developed. Several reconstruction optimization approaches are described: An approach for the heart-rate-adaptive optimization of the temporal resolution is presented. Streak artifacts at cycle-to-cycle transitions can be minimized by using an improved cardiac weighting scheme. The optimal quiescent cardiac phase for the reconstruction can be determined automatically with the motion map technique. Results for all optimization procedures applied to ECR are presented and discussed based on patient and phantom data. The ECR algorithm is analyzed for larger detector arrays of future cone-beam systems throughout an extensive simulation study based on a four-dimensional cardiac CT phantom. The results of the scientific work are summarized and an outlook proposing future directions is given. The presented thesis is available for public download at www.cardiac-ct.net.

  15. SU-E-I-23: A General KV Constrained Optimization of CNR for CT Abdominal Imaging

    SciTech Connect

    Weir, V; Zhang, J

    2015-06-15

    Purpose: While Tube current modulation has been well accepted for CT dose reduction, kV adjusting in clinical settings is still at its early stage. This is mainly due to the limited kV options of most current CT scanners. kV adjusting can potentially reduce radiation dose and optimize image quality. This study is to optimize CT abdomen imaging acquisition based on the assumption of a continuous kV, with the goal to provide the best contrast to noise ratio (CNR). Methods: For a given dose (CTDIvol) level, the CNRs at different kV and pitches were measured with an ACR GAMMEX phantom. The phantom was scanned in a Siemens Sensation 64 scanner and a GE VCT 64 scanner. A constrained mathematical optimization was used to find the kV which led to the highest CNR for the anatomy and pitch setting. Parametric equations were obtained from polynomial fitting of plots of kVs vs CNRs. A suitable constraint region for optimization was chosen. Subsequent optimization yielded a peak CNR at a particular kV for different collimations and pitch setting. Results: The constrained mathematical optimization approach yields kV of 114.83 and 113.46, with CNRs of 1.27 and 1.11 at the pitch of 1.2 and 1.4, respectively, for the Siemens Sensation 64 scanner with the collimation of 32 x 0.625mm. An optimized kV of 134.25 and 1.51 CNR is obtained for a GE VCT 64 slice scanner with a collimation of 32 x 0.625mm and a pitch of 0.969. At 0.516 pitch and 32 x 0.625 mm an optimized kV of 133.75 and a CNR of 1.14 was found for the GE VCT 64 slice scanner. Conclusion: CNR in CT image acquisition can be further optimized with a continuous kV option instead of current discrete or fixed kV settings. A continuous kV option is a key for individualized CT protocols.

  16. Feasibility of Dose Reduction Using Novel Denoising Techniques for Low kV (80 kV) CT Enterography: Optimization and Validation

    PubMed Central

    Guimarães, Luís S; Fletcher, Joel G; Yu, Lifeng; Huprich, James E; Fidler, Jeff L.; Manduca, Armando; Ramirez-Giraldo, Juan Carlos; Holmes, David R.; McCollough, Cynthia H

    2010-01-01

    Rational and Objectives To optimize and validate projection space denoising (PSDN) strategies for application to 80 kV computed tomography (CT) data to achieve 50% dose reduction. Materials and Methods This retrospective HIPAA-compliant study had IRB approval. We utilized 80 kV image data (mean CTDIvol 7.9 mGy) obtained from dual-source dual-energy CTE exams in 42 patients. For each exam, nine 80 kV image datasets were reconstructed using PSDN (3 levels of intensity) ± image-based denoising and compared to commercial reconstruction kernels. For optimization, qualitative analysis selected optimal denoising strategies, with quantitative analysis measuring image contrast, noise and sharpness (FWHM bowel wall thickness, maximum CT number gradient). For validation, two radiologists examined image quality, comparing low-dose 80 kV optimally denoised images to full dose mixed kV images. Results PSDN algorithms generated the best 80 kV image quality (41/42 patients), while the commercial kernels produced the worst (39/42, p < 0.001). Overall 80 kV PSDN approaches resulted in higher contrast (mean 332 HU vs. 290 HU), slightly less noise (mean 20 HU vs. 26 HU), but slightly decreased images sharpness (relative bowel wall thickness, 1.069 vs. 1.000) compared to full-dose mixed kV images. Mean image quality scores for full-dose CTE images was 4.9 compared to 4.5 for optimally-denoised half-dose 80 kV CTE images, and 3.1 for non-denoised 80 kV CTE images (p<0.001). Conclusion Optimized denoising strategies improve the quality of 80 kV CT enterography images such that CT data obtained at 50% of routine dose levels approaches the image quality of full-dose exams. PMID:20832023

  17. The adaptation of megavoltage cone beam CT for use in standard radiotherapy treatment planning

    NASA Astrophysics Data System (ADS)

    Thomas, T. Hannah Mary; Devakumar, D.; Purnima, S.; Ravindran, B. Paul

    2009-04-01

    Potential areas where megavoltage computed tomography (MVCT) could be used are second- and third-phase treatment planning in 3D conformal radiotherapy and IMRT, adaptive radiation therapy, single fraction palliative treatment and for the treatment of patients with metal prostheses. A feasibility study was done on using MV cone beam CT (CBCT) images generated by proprietary 3D reconstruction software based on the FDK algorithm for megavoltage treatment planning. The reconstructed images were converted to a DICOM file set. The pixel values of megavoltage cone beam computed tomography (MV CBCT) were rescaled to those of kV CT for use with a treatment planning system. A calibration phantom was designed and developed for verification of geometric accuracy and CT number calibration. The distance measured between two marker points on the CBCT image and the physical dimension on the phantom were in good agreement. Point dose verification for a 10 cm × 10 cm beam at a gantry angle of 0° and SAD of 100 cm were performed for a 6 MV beam for both kV and MV CBCT images. The point doses were found to vary between ±6.1% of the dose calculated from the kV CT image. The isodose curves for 6 MV for both kV CT and MV CBCT images were within 2% and 3 mm distance-to-agreement. A plan with three beams was performed on MV CBCT, simulating a treatment plan for cancer of the pituitary. The distribution obtained was compared with those corresponding to that obtained using the kV CT. This study has shown that treatment planning with MV cone beam CT images is feasible.

  18. The adaptation of megavoltage cone beam CT for use in standard radiotherapy treatment planning.

    PubMed

    Thomas, T Hannah Mary; Devakumar, D; Purnima, S; Ravindran, B Paul

    2009-04-07

    Potential areas where megavoltage computed tomography (MVCT) could be used are second- and third-phase treatment planning in 3D conformal radiotherapy and IMRT, adaptive radiation therapy, single fraction palliative treatment and for the treatment of patients with metal prostheses. A feasibility study was done on using MV cone beam CT (CBCT) images generated by proprietary 3D reconstruction software based on the FDK algorithm for megavoltage treatment planning. The reconstructed images were converted to a DICOM file set. The pixel values of megavoltage cone beam computed tomography (MV CBCT) were rescaled to those of kV CT for use with a treatment planning system. A calibration phantom was designed and developed for verification of geometric accuracy and CT number calibration. The distance measured between two marker points on the CBCT image and the physical dimension on the phantom were in good agreement. Point dose verification for a 10 cm x 10 cm beam at a gantry angle of 0 degrees and SAD of 100 cm were performed for a 6 MV beam for both kV and MV CBCT images. The point doses were found to vary between +/-6.1% of the dose calculated from the kV CT image. The isodose curves for 6 MV for both kV CT and MV CBCT images were within 2% and 3 mm distance-to-agreement. A plan with three beams was performed on MV CBCT, simulating a treatment plan for cancer of the pituitary. The distribution obtained was compared with those corresponding to that obtained using the kV CT. This study has shown that treatment planning with MV cone beam CT images is feasible.

  19. Commissioning kilovoltage cone-beam CT beams in a radiation therapy treatment planning system.

    PubMed

    Alaei, Parham; Spezi, Emiliano

    2012-11-08

    The feasibility of accounting of the dose from kilovoltage cone-beam CT in treatment planning has been discussed previously for a single cone-beam CT (CBCT) beam from one manufacturer. Modeling the beams and computing the dose from the full set of beams produced by a kilovoltage cone-beam CT system requires extensive beam data collection and verification, and is the purpose of this work. The beams generated by Elekta X-ray volume imaging (XVI) kilovoltage CBCT (kV CBCT) system for various cassettes and filters have been modeled in the Philips Pinnacle treatment planning system (TPS) and used to compute dose to stack and anthropomorphic phantoms. The results were then compared to measurements made using thermoluminescent dosimeters (TLDs) and Monte Carlo (MC) simulations. The agreement between modeled and measured depth-dose and cross profiles is within 2% at depths beyond 1 cm for depth-dose curves, and for regions within the beam (excluding penumbra) for cross profiles. The agreements between TPS-calculated doses, TLD measurements, and Monte Carlo simulations are generally within 5% in the stack phantom and 10% in the anthropomorphic phantom, with larger variations observed for some of the measurement/calculation points. Dose computation using modeled beams is reasonably accurate, except for regions that include bony anatomy. Inclusion of this dose in treatment plans can lead to more accurate dose prediction, especially when the doses to organs at risk are of importance.

  20. Engineering of beam direct conversion for a 120-kV, 1-MW ion beam

    NASA Technical Reports Server (NTRS)

    Barr, W. L.; Doggett, J. N.; Hamilton, G. W.; Kinney, J. D.; Moir, R. W.

    1977-01-01

    Practical systems for beam direct conversion are required to recover the energy from ion beams at high efficiency and at very high beam power densities in the environment of a high-power neutral-injection system. Such an experiment is now in progress using a 120-kV beam with a maximum total current of 20 A. After neutralization, the H(+) component to be recovered will have a power of approximately 1 MW. A system testing these concepts has been designed and tested at 15 kV, 2 kW in preparation for the full-power tests. The engineering problems involved in the full-power tests affect electron suppression, gas pumping, voltage holding, diagnostics, and measurement conditions. Planning for future experiments at higher power includes the use of cryopumping and electron suppression by a magnetic field rather than by an electrostatic field. Beam direct conversion for large fusion experiments and reactors will save millions of dollars in the cost of power supplies and electricity and will dispose of the charged beam under conditions that may not be possible by other techniques.

  1. Minimizing image noise in on-board CT reconstruction using both kilovoltage and megavoltage beam projections.

    PubMed

    Zhang, Junan; Yin, Fang-Fang

    2007-09-01

    We studied a recently proposed aggregated CT reconstruction technique which combines the complementary advantages of kilovoltage (kV) and megavoltage (MV) x-ray imaging. Various phantoms were imaged to study the effects of beam orientations and geometry of the imaging object on image quality of reconstructed CT. It was shown that the quality of aggregated CT was correlated with both kV and MV beam orientations and the degree of this correlation depended upon the geometry of the imaging object. The results indicated that the optimal orientations were those when kV beams pass through the thinner portion and MV beams pass through the thicker portion of the imaging object. A special preprocessing procedure was also developed to perform contrast conversions between kV and MV information prior to image reconstruction. The performance of two reconstruction methods, one filtered backprojection method and one iterative method, were compared. The effects of projection number, beam truncation, and contrast conversion on the CT image quality were investigated.

  2. Feasibility study on effect and stability of adaptive radiotherapy on kilovoltage cone beam CT.

    PubMed

    Yadav, Poonam; Ramasubramanian, Velayudham; Paliwal, Bhudatt R

    2011-09-01

    We have analyzed the stability of CT to density curve of kilovoltage cone-beam computerized tomography (kV CBCT) imaging modality over the period of six months. We also, investigated the viability of using image value to density table (IVDT) generated at different time, for adaptive radiotherapy treatment planning. The consequences of target volume change and the efficacy of kV CBCT for adaptive planning issues is investigated. MATERIALS AND METHODS.: Standard electron density phantom was used to establish CT to electron density calibrations curve. The CT to density curve for the CBCT images were observed for the period of six months. The kV CBCT scans used for adaptive planning was acquired with an on-board imager system mounted on a "Trilogy" linear accelerator. kV CBCT images were acquired for daily setup registration. The effect of variations in CT to density curve was studied on two clinical cases: prostate and lung. The soft tissue contouring is superior in kV CBCT scans in comparison to mega voltage CT (MVCT) scans. The CT to density curve for the CBCT images was found steady over six months. Due to difficulty in attaining the reproducibility in daily setup for the prostate treatment, there is a day-to-day difference in dose to the rectum and bladder. There is no need for generating a new CT to density curve for the adaptive planning on the kV CBCT images. Also, it is viable to perform the adaptive planning to check the dose to target and organ at risk (OAR) without performing a new kV CT scan, which will reduce the dose to the patient.

  3. Accuracy in automatic image registration between MV cone beam computed tomography and planning kV computed tomography in image guided radiotherapy.

    PubMed

    Kanakavelu, Nithya; Samuel, E James Jebaseelan

    2016-01-01

    To verify the accuracy of automatic image registration (IR) between the planning kilo voltage computed tomography (kV CT) and megavoltage cone beam computed tomography (MV CBCT) datasets using phantom and patient images. The automatic IR between MV CBCT and planning kV CT is a fast solution for performing online image guided radiotherapy (IGRT). The IR accuracy has to be verified periodically as it directly affects patient setup accuracy. The automatic IR accuracy was evaluated using image quality phantom acquired with different kV CT slice thickness, different MV CBCT acquisition MUs and reconstruction slice size and thickness. The IR accuracy was also evaluated on patient images on different anatomical sites such as brain, head & neck, thorax and pelvis. The uncertainty in the automatic registration was assessed by introducing known offset to kV CT dataset and compared with the registration results. The result with the phantom images was within 2 mm in all three translational directions. The accuracy in automatic IR using patient images was within 2 mm in most of the cases. 3 mm planning kV CT slice thickness was sufficient to perform automatic IR successfully within 2 mm accuracy. The MV CBCT reconstruction parameters such as slice thickness and slice size had no effect on the registration accuracy. This study shows that the automatic IR is accurate within 2 mm and provides confidence in performing them between planning kV CT and MV CBCT image datasets for online image guided radiotherapy.

  4. Enhancement of image quality with a fast iterative scatter and beam hardening correction method for kV CBCT.

    PubMed

    Reitz, Irmtraud; Hesse, Bernd-Michael; Nill, Simeon; Tücking, Thomas; Oelfke, Uwe

    2009-01-01

    The problem of the enormous amount of scattered radiation in kV CBCT (kilo voltage cone beam computer tomography) is addressed. Scatter causes undesirable streak- and cup-artifacts and results in a quantitative inaccuracy of reconstructed CT numbers, so that an accurate dose calculation might be impossible. Image contrast is also significantly reduced. Therefore we checked whether an appropriate implementation of the fast iterative scatter correction algorithm we have developed for MV (mega voltage) CBCT reduces the scatter contribution in a kV CBCT as well. This scatter correction method is based on a superposition of pre-calculated Monte Carlo generated pencil beam scatter kernels. The algorithm requires only a system calibration by measuring homogeneous slab phantoms with known water-equivalent thicknesses. In this study we compare scatter corrected CBCT images of several phantoms to the fan beam CT images acquired with a reduced cone angle (a slice-thickness of 14 mm in the isocenter) at the same system. Additional measurements at a different CBCT system were made (different energy spectrum and phantom-to-detector distance) and a first order approach of a fast beam hardening correction will be introduced. The observed image quality of the scatter corrected CBCT images is comparable concerning resolution, noise and contrast-to-noise ratio to the images acquired in fan beam geometry. Compared to the CBCT without any corrections the contrast of the contrast-and-resolution phantom with scatter correction and additional beam hardening correction is improved by a factor of about 1.5. The reconstructed attenuation coefficients and the CT numbers of the scatter corrected CBCT images are close to the values of the images acquired in fan beam geometry for the most pronounced tissue types. Only for extreme dense tissue types like cortical bone we see a difference in CT numbers of 5.2%, which can be improved to 4.4% with the additional beam hardening correction. Cupping is

  5. Imaging doses from the Elekta Synergy X-ray cone beam CT system.

    PubMed

    Amer, A; Marchant, T; Sykes, J; Czajka, J; Moore, C

    2007-06-01

    The Elekta Synergy is a radiotherapy treatment machine with integrated kilovoltage (kV) X-ray imaging system capable of producing cone beam CT (CBCT) images of the patient in the treatment position. The aim of this study is to assess the additional imaging dose. Cone beam CT dose index (CBDI) is introduced and measured inside standard CTDI phantoms for several sites (head: 100 kV, 38 mAs, lung: 120 kV, 152 mAs and pelvis: 130 kV, 456 mAs). The measured weighted doses were compared with thermoluminescent dosimeter (TLD) measurements at various locations in a Rando phantom and at patients' surfaces. The measured CBDIs in-air at the isocentre were 9.2 mGy 100 mAs(-1), 7.3 mGy 100 mAs(-1) and 5.3 mGy 100 mAs(-1) for 130 kV, 120 kV and 100 kV, respectively. The body phantom weighted CBDI were 5.5 mGy 100 mAs(-1) and 3.8 mGy 100 mAs(-1 )for 130 kV and 120 kV. The head phantom weighted CBDI was 4.3 mGy 100 mAs(-1) for 100 kV. The weighted doses for the Christie Hospital CBCT imaging techniques were 1.6 mGy, 6 mGy and 22 mGy for the head, lung and pelvis. The measured CBDIs were used to estimate the total effective dose for the Synergy system using the ImPACT CT Patient Dosimetry Calculator. Measured CBCT doses using the Christie Hospital protocols are low for head and lung scans whether compared with electronic portal imaging (EPI), commonly used for treatment verification, or single and multiple slice CT. For the pelvis, doses are similar to EPI but higher than CT. Repeated use of CBCT for treatment verification is likely and hence the total patient dose needs to be carefully considered. It is important to consider further development of low dose CBCT techniques to keep additional doses as low as reasonably practicable.

  6. How do kV and mAs affect CT lesion detection performance?

    NASA Astrophysics Data System (ADS)

    Huda, W.; Ogden, K. M.; Shah, K.; Jadoo, C.; Scalzetti, E. M.; Lavallee, R. L.; Roskopf, M. L.

    2007-03-01

    The purpose of this study was to investigate how output (mAs) and x-ray tube voltage (kV) affect lesion detection in CT imaging. An adult Rando phantom was scanned on a GE LightSpeed CT scanner at x-ray tube voltages from 80 to 140 kV, and outputs from 90 to 360 mAs. Axial images of the abdomen were reconstructed and viewed on a high quality monitor at a soft tissue display setting. We measured detection of 2.5 to 12.5 mm sized lesions using a 2 Alternate Forced Choice (2-AFC) experimental paradigm that determined lesion contrast (I) corresponding to a 92% accuracy (I 92%) of lesion detection. Plots of log(I 92%) versus log(lesion size) were all approximately linear. The slope of the contrast detail curve was ~ -1.0 at 90 mAs, close to the value predicted by the Rose model, but monotonically decreased with increasing mAs to a value of ~ -0.7 at 360 mAs. Increasing the x-ray tube output by a factor of four improved lesion detection by a factor of 1.9 for the smallest lesion (2.5 mm), close to the value predicted by the Rose model, but only by a factor of 1.2 for largest lesion (12.5 mm). Increasing the kV monotonically decreased the contrast detail slopes from -1.02 at 80 kV to -0.71 at 140 kV. Increasing the x-ray tube voltage from 80 to 140 kV improved lesion detection by a factor of 2.8 for the smallest lesion (2.5 mm), but only by a factor of 1.7 for largest lesion (12.5 mm). We conclude that: (i) quantum mottle is an important factor for low contrast lesion detection in images of anthropomorphic phantoms; (ii) x-ray tube voltage has a much greater influence on lesion detection performance than x-ray tube output; (iii) the Rose model only predicts CT lesion detection performance at low x-ray tube outputs (90 mAs) and for small lesions (2.5 mm).

  7. Algorithm for X-ray scatter, beam-hardening, and beam profile correction in diagnostic (kilovoltage) and treatment (megavoltage) cone beam CT.

    PubMed

    Maltz, Jonathan S; Gangadharan, Bijumon; Bose, Supratik; Hristov, Dimitre H; Faddegon, Bruce A; Paidi, Ajay; Bani-Hashemi, Ali R

    2008-12-01

    Quantitative reconstruction of cone beam X-ray computed tomography (CT) datasets requires accurate modeling of scatter, beam-hardening, beam profile, and detector response. Typically, commercial imaging systems use fast empirical corrections that are designed to reduce visible artifacts due to incomplete modeling of the image formation process. In contrast, Monte Carlo (MC) methods are much more accurate but are relatively slow. Scatter kernel superposition (SKS) methods offer a balance between accuracy and computational practicality. We show how a single SKS algorithm can be employed to correct both kilovoltage (kV) energy (diagnostic) and megavoltage (MV) energy (treatment) X-ray images. Using MC models of kV and MV imaging systems, we map intensities recorded on an amorphous silicon flat panel detector to water-equivalent thicknesses (WETs). Scattergrams are derived from acquired projection images using scatter kernels indexed by the local WET values and are then iteratively refined using a scatter magnitude bounding scheme that allows the algorithm to accommodate the very high scatter-to-primary ratios encountered in kV imaging. The algorithm recovers radiological thicknesses to within 9% of the true value at both kV and megavolt energies. Nonuniformity in CT reconstructions of homogeneous phantoms is reduced by an average of 76% over a wide range of beam energies and phantom geometries.

  8. Sci—Thur AM: YIS - 09: Validation of a General Empirically-Based Beam Model for kV X-ray Sources

    SciTech Connect

    Poirier, Y.; Sommerville, M.; Johnstone, C.D.; Gräfe, J.; Nygren, I.; Jacso, F.; Khan, R.; Villareal-Barajas, J.E.; Tambasco, M.

    2014-08-15

    Purpose: To present an empirically-based beam model for computing dose deposited by kilovoltage (kV) x-rays and validate it for radiographic, CT, CBCT, superficial, and orthovoltage kV sources. Method and Materials: We modeled a wide variety of imaging (radiographic, CT, CBCT) and therapeutic (superficial, orthovoltage) kV x-ray sources. The model characterizes spatial variations of the fluence and spectrum independently. The spectrum is derived by matching measured values of the half value layer (HVL) and nominal peak potential (kVp) to computationally-derived spectra while the fluence is derived from in-air relative dose measurements. This model relies only on empirical values and requires no knowledge of proprietary source specifications or other theoretical aspects of the kV x-ray source. To validate the model, we compared measured doses to values computed using our previously validated in-house kV dose computation software, kVDoseCalc. The dose was measured in homogeneous and anthropomorphic phantoms using ionization chambers and LiF thermoluminescent detectors (TLDs), respectively. Results: The maximum difference between measured and computed dose measurements was within 2.6%, 3.6%, 2.0%, 4.8%, and 4.0% for the modeled radiographic, CT, CBCT, superficial, and the orthovoltage sources, respectively. In the anthropomorphic phantom, the computed CBCT dose generally agreed with TLD measurements, with an average difference and standard deviation ranging from 2.4 ± 6.0% to 5.7 ± 10.3% depending on the imaging technique. Most (42/62) measured TLD doses were within 10% of computed values. Conclusions: The proposed model can be used to accurately characterize a wide variety of kV x-ray sources using only empirical values.

  9. SU-E-I-06: A Dose Calculation Algorithm for KV Diagnostic Imaging Beams by Empirical Modeling

    SciTech Connect

    Chacko, M; Aldoohan, S; Sonnad, J; Ahmad, S; Ali, I

    2015-06-15

    Purpose: To develop accurate three-dimensional (3D) empirical dose calculation model for kV diagnostic beams for different radiographic and CT imaging techniques. Methods: Dose was modeled using photon attenuation measured using depth dose (DD), scatter radiation of the source and medium, and off-axis ratio (OAR) profiles. Measurements were performed using single-diode in water and a diode-array detector (MapCHECK2) with kV on-board imagers (OBI) integrated with Varian TrueBeam and Trilogy linacs. The dose parameters were measured for three energies: 80, 100, and 125 kVp with and without bowtie filters using field sizes 1×1–40×40 cm2 and depths 0–20 cm in water tank. Results: The measured DD decreased with depth in water because of photon attenuation, while it increased with field size due to increased scatter radiation from medium. DD curves varied with energy and filters where they increased with higher energies and beam hardening from half-fan and full-fan bowtie filters. Scatter radiation factors increased with field sizes and higher energies. The OAR was with 3% for beam profiles within the flat dose regions. The heal effect of this kV OBI system was within 6% from the central axis value at different depths. The presence of bowtie filters attenuated measured dose off-axis by as much as 80% at the edges of large beams. The model dose predictions were verified with measured doses using single point diode and ionization chamber or two-dimensional diode-array detectors inserted in solid water phantoms. Conclusion: This empirical model enables fast and accurate 3D dose calculation in water within 5% in regions with near charge-particle equilibrium conditions outside buildup region and penumbra. It considers accurately scatter radiation contribution in water which is superior to air-kerma or CTDI dose measurements used usually in dose calculation for diagnostic imaging beams. Considering heterogeneity corrections in this model will enable patient specific dose

  10. Empirical beam hardening correction (EBHC) for CT.

    PubMed

    Kyriakou, Yiannis; Meyer, Esther; Prell, Daniel; Kachelriess, Marc

    2010-10-01

    Due to x-ray beam polychromaticity and scattered radiation, attenuation measurements tend to be underestimated. Cupping and beam hardening artifacts become apparent in the reconstructed CT images. If only one material such as water, for example, is present, these artifacts can be reduced by precorrecting the rawdata. Higher order beam hardening artifacts, as they result when a mixture of materials such as water and bone, or water and bone and iodine is present, require an iterative beam hardening correction where the image is segmented into different materials and those are forward projected to obtain new rawdata. Typically, the forward projection must correctly model the beam polychromaticity and account for all physical effects, including the energy dependence of the assumed materials in the patient, the detector response, and others. We propose a new algorithm that does not require any knowledge about spectra or attenuation coefficients and that does not need to be calibrated. The proposed method corrects beam hardening in single energy CT data. The only a priori knowledge entering EBHC is the segmentation of the object into different materials. Materials other than water are segmented from the original image, e.g., by using simple thresholding. Then, a (monochromatic) forward projection of these other materials is performed. The measured rawdata and the forward projected material-specific rawdata are monomially combined (e.g., multiplied or squared) and reconstructed to yield a set of correction volumes. These are then linearly combined and added to the original volume. The combination weights are determined to maximize the flatness of the new and corrected volume. EBHC is evaluated using data acquired with a modern cone-beam dual-source spiral CT scanner (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany), with a modern dual-source micro-CT scanner (Tomo-Scope Synergy Twin, CT Imaging GmbH, Erlangen, Germany), and with a modern C-arm CT scanner

  11. Empirical beam hardening correction (EBHC) for CT.

    PubMed

    Kyriakou, Yiannis; Meyer, Esther; Prell, Daniel; Kachelrieß, Marc

    2010-10-01

    Due to x-ray beam polychromaticity and scattered radiation, attenuation measurements tend to be underestimated. Cupping and beam hardening artifacts become apparent in the reconstructed CT images. If only one material such as water, for example, is present, these artifacts can be reduced by precorrecting the rawdata. Higher order beam hardening artifacts, as they result when a mixture of materials such as water and bone, or water and bone and iodine is present, require an iterative beam hardening correction where the image is segmented into different materials and those are forward projected to obtain new rawdata. Typically, the forward projection must correctly model the beam polychromaticity and account for all physical effects, including the energy dependence of the assumed materials in the patient, the detector response, and others. We propose a new algorithm that does not require any knowledge about spectra or attenuation coefficients and that does not need to be calibrated. The proposed method corrects beam hardening in single energy CT data. The onlya priori knowledge entering EBHC is the segmentation of the object into different materials. Materials other than water are segmented from the original image, e.g., by using simple thresholding. Then, a (monochromatic) forward projection of these other materials is performed. The measured rawdata and the forward projected material-specific rawdata are monomially combined (e.g., multiplied or squared) and reconstructed to yield a set of correction volumes. These are then linearly combined and added to the original volume. The combination weights are determined to maximize the flatness of the new and corrected volume. EBHC is evaluated using data acquired with a modern cone-beam dual-source spiral CT scanner (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany), with a modern dual-source micro-CT scanner (TomoScope Synergy Twin, CT Imaging GmbH, Erlangen, Germany), and with a modern C-arm CT scanner

  12. Empirical beam hardening correction (EBHC) for CT

    SciTech Connect

    Kyriakou, Yiannis; Meyer, Esther; Prell, Daniel; Kachelriess, Marc

    2010-10-15

    Purpose: Due to x-ray beam polychromaticity and scattered radiation, attenuation measurements tend to be underestimated. Cupping and beam hardening artifacts become apparent in the reconstructed CT images. If only one material such as water, for example, is present, these artifacts can be reduced by precorrecting the rawdata. Higher order beam hardening artifacts, as they result when a mixture of materials such as water and bone, or water and bone and iodine is present, require an iterative beam hardening correction where the image is segmented into different materials and those are forward projected to obtain new rawdata. Typically, the forward projection must correctly model the beam polychromaticity and account for all physical effects, including the energy dependence of the assumed materials in the patient, the detector response, and others. We propose a new algorithm that does not require any knowledge about spectra or attenuation coefficients and that does not need to be calibrated. The proposed method corrects beam hardening in single energy CT data. Methods: The only a priori knowledge entering EBHC is the segmentation of the object into different materials. Materials other than water are segmented from the original image, e.g., by using simple thresholding. Then, a (monochromatic) forward projection of these other materials is performed. The measured rawdata and the forward projected material-specific rawdata are monomially combined (e.g., multiplied or squared) and reconstructed to yield a set of correction volumes. These are then linearly combined and added to the original volume. The combination weights are determined to maximize the flatness of the new and corrected volume. EBHC is evaluated using data acquired with a modern cone-beam dual-source spiral CT scanner (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany), with a modern dual-source micro-CT scanner (TomoScope Synergy Twin, CT Imaging GmbH, Erlangen, Germany), and with a modern

  13. Spectroscopic determination of the composition of a 50 kV hydrogen diagnostic neutral beam

    SciTech Connect

    Feng, X.; Nornberg, M. D. Den Hartog, D. J.; Oliva, S. P.; Craig, D.

    2016-11-15

    A grating spectrometer with an electron multiplying charge-coupled device camera is used to diagnose a 50 kV, 5 A, 20 ms hydrogen diagnostic neutral beam. The ion source density is determined from Stark broadened H{sub β} emission and the spectrum of Doppler-shifted H{sub α} emission is used to quantify the fraction of ions at full, half, and one-third beam energy under a variety of operating conditions including fueling gas pressure and arc discharge current. Beam current is optimized at low-density conditions in the ion source while the energy fractions are found to be steady over most operating conditions.

  14. Spectroscopic determination of the composition of a 50 kV hydrogen diagnostic neutral beam

    NASA Astrophysics Data System (ADS)

    Feng, X.; Nornberg, M. D.; Craig, D.; Den Hartog, D. J.; Oliva, S. P.

    2016-11-01

    A grating spectrometer with an electron multiplying charge-coupled device camera is used to diagnose a 50 kV, 5 A, 20 ms hydrogen diagnostic neutral beam. The ion source density is determined from Stark broadened Hβ emission and the spectrum of Doppler-shifted Hα emission is used to quantify the fraction of ions at full, half, and one-third beam energy under a variety of operating conditions including fueling gas pressure and arc discharge current. Beam current is optimized at low-density conditions in the ion source while the energy fractions are found to be steady over most operating conditions.

  15. Collimated electron beam accelerated at 12 kV from a Penning discharge

    SciTech Connect

    Toader, D.; Oane, M.; Ticoş, C. M.

    2015-01-15

    A pulsed electron beam accelerated at 12 kV with a duration of 40 μs per pulse is obtained from a Penning discharge with a hollow anode and two cathodes. The electrons are extracted through a hole in one of the cathodes and focused by a pair of coils. The electron beam has a diameter of a few mm in the cross section, while the beam current reaches peak values of 400 mA, depending on the magnetic field inside the focussing coils. This relatively inexpensive and compact device is suitable for the irradiation of small material samples placed in high vacuum.

  16. 130 kV High-Resolution Electron Beam Lithography System for Sub-10-nm Nanofabrication

    NASA Astrophysics Data System (ADS)

    Okino, Teruaki; Kuba, Yukio; Shibata, Masahiro; Ohyi, Hideyuki

    2013-06-01

    An electron beam lithography (EBL) system, CABL-UH, with a 130 kV high acceleration voltage has been developed that succeeded in minimizing beam size by minimizing Coulomb blur. This system has a short single-stage electron beam (EB) gun with an alignment function of two extractor centers to minimize Coulomb blur. This gun has also succeeded in thoroughly avoiding microdischarges. By adopting this EB gun and many other techniques, high resolution and long-term high stability have been achieved and an extremely fine pattern (4 nm line) has been delineated.

  17. A technique for on-board CT reconstruction using both kilovoltage and megavoltage beam projections for 3D treatment verification

    SciTech Connect

    Yin Fangfang; Guan Huaiqun; Lu Wenkai

    2005-09-15

    The technologies with kilovoltage (kV) and megavoltage (MV) imaging in the treatment room are now available for image-guided radiation therapy to improve patient setup and target localization accuracy. However, development of strategies to efficiently and effectively implement these technologies for patient treatment remains challenging. This study proposed an aggregated technique for on-board CT reconstruction using combination of kV and MV beam projections to improve the data acquisition efficiency and image quality. These projections were acquired in the treatment room at the patient treatment position with a new kV imaging device installed on the accelerator gantry, orthogonal to the existing MV portal imaging device. The projection images for a head phantom and a contrast phantom were acquired using both the On-Board Imager{sup TM} kV imaging device and the MV portal imager mounted orthogonally on the gantry of a Varian Clinac{sup TM} 21EX linear accelerator. MV projections were converted into kV information prior to the aggregated CT reconstruction. The multilevel scheme algebraic-reconstruction technique was used to reconstruct CT images involving either full, truncated, or a combination of both full and truncated projections. An adaptive reconstruction method was also applied, based on the limited numbers of kV projections and truncated MV projections, to enhance the anatomical information around the treatment volume and to minimize the radiation dose. The effects of the total number of projections, the combination of kV and MV projections, and the beam truncation of MV projections on the details of reconstructed kV/MV CT images were also investigated.

  18. A technique for on-board CT reconstruction using both kilovoltage and megavoltage beam projections for 3D treatment verification.

    PubMed

    Yin, Fang-Fang; Guan, Huaiqun; Lu, Wenkai

    2005-09-01

    The technologies with kilovoltage (kV) and megavoltage (MV) imaging in the treatment room are now available for image-guided radiation therapy to improve patient setup and target localization accuracy. However, development of strategies to efficiently and effectively implement these technologies for patient treatment remains challenging. This study proposed an aggregated technique for on-board CT reconstruction using combination of kV and MV beam projections to improve the data acquisition efficiency and image quality. These projections were acquired in the treatment room at the patient treatment position with a new kV imaging device installed on the accelerator gantry, orthogonal to the existing MV portal imaging device. The projection images for a head phantom and a contrast phantom were acquired using both the On-Board Imager kV imaging device and the MV portal imager mounted orthogonally on the gantry of a Varian Clinac 21EX linear accelerator. MV projections were converted into kV information prior to the aggregated CT reconstruction. The multilevel scheme algebraic-reconstruction technique was used to reconstruct CT images involving either full, truncated, or a combination of both full and truncated projections. An adaptive reconstruction method was also applied, based on the limited numbers of kV projections and truncated MV projections, to enhance the anatomical information around the treatment volume and to minimize the radiation dose. The effects of the total number of projections, the combination of kV and MV projections, and the beam truncation of MV projections on the details of reconstructed kV/MV CT images were also investigated.

  19. SU-E-I-29: Care KV: Dose It Influence Radiation Dose in Non-Contrast Examination of CT Abdomen/pelvis?

    SciTech Connect

    Zhang, J; Ganesh, H; Weir, V

    2015-06-15

    Purpose: CARE kV is a tool that automatically recommends optimal kV setting for individual patient for specific CT examination. The use of CARE kV depends on topogram and the user-selected contrast behavior. CARE kV is expected to reduce radiation dose while improving image quality. However, this may work only for certain groups of patients and/or certain CT examinations. This study is to investigate the effects of CARE kV on radiation dose of non-contrast examination of CT abdomen/pelvis. Methods: Radiation dose (CTDIvol and DLP) from patients who underwent abdomen/pelvis non-contrast examination with and without CARE kV were retrospectively reviewed. All patients were scanned in the same scanner (Siemens Somatom AS64). To mitigate any possible influences due to technologists’ unfamiliarity with the CARE kV, the data with CARE kV were retrieved 1.5 years after the start of CARE kV usage. T-test was used for significant difference in radiation dose. Results: Volume CTDIs and DLPs from 18 patients before and 24 patients after the use of CARE kV were obtained in a duration of one month. There is a slight increase in both average CTDIvol and average DLP with CARE kV compared to those without CARE kV (25.52 mGy vs. 22.65 mGy for CTDIvol; 1265.81 mGy-cm vs. 1199.19 mGy-cm). Statistically there was no significant difference. Without CARE kV, 140 kV was used in 9 of 18 patients, while with CARE KV, 140 kV was used in 15 of 24 patients. 80kV was not used in either group. Conclusion: The use of CARE kV may save time for protocol optimization and minimize variability among technologists. Radiation dose reduction was not observed in non-contrast examinations of CT abdomen/pelvis. This was partially because our CT protocols were tailored according to patient size before CARE kV and partially because of large size patients.

  20. Development of resist process for 5-KV multi-beam technology

    NASA Astrophysics Data System (ADS)

    Icard, B.; Rio, D.; Veltman, P.; Kampherbeek, B.; Constancias, C.; Pain, L.

    2009-03-01

    E-beam Maskless activities raised a lot of interest in the past years from semiconductor companies strongly concerned by the constant cost increase of masked-based lithography (1). Beginning of 2008, the European Commission started an integrated program called "MAGIC", Maskless lithography for IC manufacturing, which pushes the development and the insertion of the European multi-beam technology (2) in the semiconductor industry. This project supports also to develop the infrastructure for the use of this technology, including resist processes, data processing and proximity corrections. Within MAGIC, MAPPER develops its low energy (5keV) massively parallel concept (3). Compared to a standard single E-Beam machine working classically at 50kV, this low accelerating voltage requires the use of thin resist film to deal with the lower penetration depth of the electrons. This paper presents the resist development status, including Chemically Amplified Resist and non-CAR platforms. Comparisons of the performances of these resist platforms in terms of resolution, sensitivity, roughness and stability are detailed, including their potential integration into CMOS technological flow. Finally, a first review of the state of the art of resist performance for patterning at 5kV will be performed. Based on the level of achievements presented in this paper, a discussion is also engaged about the needs of resist developments to fulfill industry targets in 2011.

  1. [Dual energy CT angiography of the carotid arteries: quality, bone subtraction, and radiation dosage using tube voltage 80/140 kV versus 100/140 kV].

    PubMed

    Santos Armentia, E; Tardáguila de la Fuente, G; Castellón Plaza, D; Delgado Sánchez-Gracián, C; Prada González, R; Fernández Fernández, L; Tardáguila Montero, F

    2014-01-01

    To study the differences in vascular image quality, bone subtraction, and dose of radiation of dual energy CT angiography of the supraaortic trunks using different tube voltages. We reviewed the CT angiograms of the supraaortic trunks in 46 patients acquired with a 128-slice dual source CT scanner using two voltage protocols (80/140 kV and 100/140 kV). The "head bone removal" tool was used for postprocessing. We divided the arteries into 15 segments. In each segment, we evaluated the image quality of the vessels and the effectiveness of bone removal in multiplanar reconstructions (MPR) and in maximum intensity projections (MIP) with each protocol, analyzing the trabecular and cortical bones separately. We also evaluated the dose of radiation received. Of the 46 patients, 13 were studied using 80/140 kV and 33 with 100/140 kV. There were no significant differences between the two groups in age or sex. Image quality in four segments was better in the group examined with 100/140 kV. Cortical bone removal in MPR and MIP and trabecular bone removal in MIP were also better in the group examined with 100/140 kV. The dose of radiation received was significantly higher in the group examined with 100/140 kV (1.16 mSv with 80/140 kV vs. 1.59 mSv with 100/140 kV). Using 100/140 kV increases the dose of radiation but improves the quality of the study of arterial segments and bone subtraction. Copyright © 2011 SERAM. Published by Elsevier Espana. All rights reserved.

  2. HECTOR: A 240kV micro-CT setup optimized for research

    NASA Astrophysics Data System (ADS)

    Masschaele, Bert; Dierick, Manuel; Van Loo, Denis; Boone, Matthieu N.; Brabant, Loes; Pauwels, Elin; Cnudde, Veerle; Van Hoorebeke, Luc

    2013-10-01

    X-ray micro-CT has become a very powerful and common tool for non-destructive three-dimensional (3D) visualization and analysis of objects. Many systems are commercially available, but they are typically limited in terms of operational freedom both from a mechanical point of view as well as for acquisition routines. HECTOR is the latest system developed by the Ghent University Centre for X-ray Tomography (http://www.ugct.ugent.be) in collaboration with X-Ray Engineering (XRE bvba, Ghent, Belgium). It consists of a mechanical setup with nine motorized axes and a modular acquisition software package and combines a microfocus directional target X-ray source up to 240 kV with a large flat-panel detector. Provisions are made to install a line-detector for a maximal operational range. The system can accommodate samples up to 80 kg, 1 m long and 80 cm in diameter while it is also suited for high resolution (down to 4 μm) tomography. The bi-directional detector tiling is suited for large samples while the variable source-detector distance optimizes the signal to noise ratio (SNR) for every type of sample, even with peripheral equipment such as compression stages or climate chambers. The large vertical travel of 1 m can be used for helical scanning and a vertical detector rotation axis allows laminography experiments. The setup is installed in a large concrete bunker to allow accommodation of peripheral equipment such as pumps, chillers, etc., which can be integrated in the modular acquisition software to obtain a maximal correlation between the environmental control and the CT data taken. The acquisition software does not only allow good coupling with the peripheral equipment but its scripting feature is also particularly interesting for testing new and exotic acquisition routines.

  3. Assessment of image quality and dose calculation accuracy on kV CBCT, MV CBCT, and MV CT images for urgent palliative radiotherapy treatments.

    PubMed

    Held, Mareike; Cremers, Florian; Sneed, Penny K; Braunstein, Steve; Fogh, Shannon E; Nakamura, Jean; Barani, Igor; Perez-Andujar, Angelica; Pouliot, Jean; Morin, Olivier

    2016-03-08

    A clinical workflow was developed for urgent palliative radiotherapy treatments that integrates patient simulation, planning, quality assurance, and treatment in one 30-minute session. This has been successfully tested and implemented clinically on a linac with MV CBCT capabilities. To make this approach available to all clin-ics equipped with common imaging systems, dose calculation accuracy based on treatment sites was assessed for other imaging units. We evaluated the feasibility of palliative treatment planning using on-board imaging with respect to image quality and technical challenges. The purpose was to test multiple systems using their commercial setup, disregarding any additional in-house development. kV CT, kV CBCT, MV CBCT, and MV CT images of water and anthropomorphic phantoms were acquired on five different imaging units (Philips MX8000 CT Scanner, and Varian TrueBeam, Elekta VersaHD, Siemens Artiste, and Accuray Tomotherapy linacs). Image quality (noise, contrast, uniformity, spatial resolution) was evaluated and compared across all machines. Using individual image value to density calibrations, dose calculation accuracies for simple treatment plans were assessed for the same phantom images. Finally, image artifacts on clinical patient images were evaluated and compared among the machines. Image contrast to visualize bony anatomy was sufficient on all machines. Despite a high noise level and low contrast, MV CT images provided the most accurate treatment plans relative to kV CT-based planning. Spatial resolution was poorest for MV CBCT, but did not limit the visualization of small anatomical structures. A comparison of treatment plans showed that monitor units calculated based on a prescription point were within 5% difference relative to kV CT-based plans for all machines and all studied treatment sites (brain, neck, and pelvis). Local dose differences > 5% were found near the phantom edges. The gamma index for 3%/3 mm criteria was ≥ 95% in most

  4. Assessment of image quality and dose calculation accuracy on kV CBCT, MV CBCT, and MV CT images for urgent palliative radiotherapy treatments.

    PubMed

    Held, Mareike; Cremers, Florian; Sneed, Penny K; Braunstein, Steve; Fogh, Shannon E; Nakamura, Jean; Barani, Igor; Perez-Andujar, Angelica; Pouliot, Jean; Morin, Olivier

    2016-03-01

    A clinical workflow was developed for urgent palliative radiotherapy treatments that integrates patient simulation, planning, quality assurance, and treatment in one 30-minute session. This has been successfully tested and implemented clinically on a linac with MV CBCT capabilities. To make this approach available to all clinics equipped with common imaging systems, dose calculation accuracy based on treatment sites was assessed for other imaging units. We evaluated the feasibility of palliative treatment planning using on-board imaging with respect to image quality and technical challenges. The purpose was to test multiple systems using their commercial setup, disregarding any additional in-house development. kV CT, kV CBCT, MV CBCT, and MV CT images of water and anthropomorphic phantoms were acquired on five different imaging units (Philips MX8000 CT Scanner, and Varian TrueBeam, Elekta VersaHD, Siemens Artiste, and Accuray Tomotherapy linacs). Image quality (noise, contrast, uniformity, spatial resolution) was evaluated and compared across all machines. Using individual image value to density calibrations, dose calculation accuracies for simple treatment plans were assessed for the same phantom images. Finally, image artifacts on clinical patient images were evaluated and compared among the machines. Image contrast to visualize bony anatomy was sufficient on all machines. Despite a high noise level and low contrast, MV CT images provided the most accurate treatment plans relative to kV CT-based planning. Spatial resolution was poorest for MV CBCT, but did not limit the visualization of small anatomical structures. A comparison of treatment plans showed that monitor units calculated based on a prescription point were within 5% difference relative to kV CT-based plans for all machines and all studied treatment sites (brain, neck, and pelvis). Local dose differences >5% were found near the phantom edges. The gamma index for 3%/3 mm criteria was ≥95% in most cases

  5. Dynamic bowtie for fan-beam CT.

    PubMed

    Liu, Fenglin; Wang, Ge; Cong, Wenxiang; Hsieh, Scott S; Pelc, Norbert J

    2013-01-01

    A bowtie is a filter used to shape an x-ray beam and equalize its flux reaching different detector channels. For development of spectral CT with energy discriminating photon-counting (EDPC) detectors, here we propose and evaluate a dynamic bowtie for performance optimization based on a patient model or a scout scan. With a mechanical rotation of a dynamic bowtie and an adaptive adjustment of an x-ray source flux, an x-ray beam intensity profile can be modulated. First, a mathematical model for dynamic bowtie filtering is established for an elliptical section in fan-beam geometry, and the contour of the optimal bowtie is derived. Then, numerical simulation is performed to compare the performance of the dynamic bowtie in the cases of an ideal phantom and a realistic cross-section relative to the counterparts without any bowtie and with a fixed bowtie respectively. Our dynamic bowtie can equalize the expected numbers of photons in the case of an ideal phantom. In practical cases, our dynamic bowtie can effectively reduce the dynamic range of detected signals inside the field of view. Although our design is optimized for an elliptical phantom, the resultant dynamic bowtie can be applied to a real fan-beam scan if the underlying cross-section can be approximated as an ellipse. Furthermore, our design methodology can be applied to specify an optimized dynamic bowtie for any cross-section of a patient, preferably using rapid prototyping technology.

  6. Patient radiation doses for electron beam CT

    SciTech Connect

    Castellano, Isabel A.; Dance, David R.; Skinner, Claire L.; Evans, Phil M.

    2005-08-15

    A Monte Carlo based computer model has been developed for electron beam computed tomography (EBCT) to calculate organ and effective doses in a humanoid hermaphrodite phantom. The program has been validated by comparison with experimental measurements of the CT dose index in standard head and body CT dose phantoms; agreement to better than 8% has been found. The robustness of the model has been established by varying the input parameters. The amount of energy deposited at the 12:00 position of the standard body CT dose phantom is most susceptible to rotation angle, whereas that in the central region is strongly influenced by the beam quality. The program has been used to investigate the changes in organ absorbed doses arising from partial and full rotation about supine and prone subjects. Superficial organs experience the largest changes in absorbed dose with a change in subject orientation and for partial rotation. Effective doses for typical clinical scan protocols have been calculated and compared with values obtained using existing dosimetry techniques based on full rotation. Calculations which make use of Monte Carlo conversion factors for the scanner that best matches the EBCT dosimetric characteristics consistently overestimate the effective dose in supine subjects by typically 20%, and underestimate the effective dose in prone subjects by typically 13%. These factors can therefore be used to correct values obtained in this way. Empirical dosimetric techniques based on the dose-length product yield errors as great as 77%. This is due to the sensitivity of the dose length product to individual scan lengths. The magnitude of these errors is reduced if empirical dosimetric techniques based on the average absorbed dose in the irradiated volume (CTDI{sub vol}) are used. Therefore conversion factors specific to EBCT have been calculated to convert the CTDI{sub vol} to an effective dose.

  7. Beam property measurement of a 300-kV ion source test stand for a 1-MV electrostatic accelerator

    NASA Astrophysics Data System (ADS)

    Park, Sae-Hoon; Kim, Dae-Il; Kim, Yu-Seok

    2016-09-01

    The KOMAC (Korea Multi-purpose Accelerator Complex) has been developing a 300-kV ion source test stand for a 1-MV electrostatic accelerator for industrial purposes. A RF ion source was operated at 200 MHz with its matching circuit. The beam profile and emittance were measured behind an accelerating column to confirm the beam property from the RF ion source. The beam profile was measured at the end of the accelerating tube and at the beam dump by using a beam profile monitor (BPM) and wire scanner. An Allison-type emittance scanner was installed behind the beam profile monitor (BPM) to measure the beam density in phase space. The measurement results for the beam profile and emittance are presented in this paper.

  8. CT thermometry for cone-beam CT guided ablation

    NASA Astrophysics Data System (ADS)

    DeStefano, Zachary; Abi-Jaoudeh, Nadine; Li, Ming; Wood, Bradford J.; Summers, Ronald M.; Yao, Jianhua

    2016-03-01

    Monitoring temperature during a cone-beam CT (CBCT) guided ablation procedure is important for prevention of over-treatment and under-treatment. In order to accomplish ideal temperature monitoring, a thermometry map must be generated. Previously, this was attempted using CBCT scans of a pig shoulder undergoing ablation.1 We are extending this work by using CBCT scans of real patients and incorporating more processing steps. We register the scans before comparing them due to the movement and deformation of organs. We then automatically locate the needle tip and the ablation zone. We employ a robust change metric due to image noise and artifacts. This change metric takes windows around each pixel and uses an equation inspired by Time Delay Analysis to calculate the error between windows with the assumption that there is an ideal spatial offset. Once the change map is generated, we correlate change data with measured temperature data at the key points in the region. This allows us to transform our change map into a thermal map. This thermal map is then able to provide an estimate as to the size and temperature of the ablation zone. We evaluated our procedure on a data set of 12 patients who had a total of 24 ablation procedures performed. We were able to generate reasonable thermal maps with varying degrees of accuracy. The average error ranged from 2.7 to 16.2 degrees Celsius. In addition to providing estimates of the size of the ablation zone for surgical guidance, 3D visualizations of the ablation zone and needle are also produced.

  9. Scattering intensities for a white beam (120 kV) presenting a semi-empirical model to preview scattered beams

    NASA Astrophysics Data System (ADS)

    Gonçalves, O. D.; Boldt, S.; Kasch, K. U.

    2016-09-01

    This work aims at measuring the scattering cross sections for white beams and the verification of a semi-empirical model predicting scattered energy spectra of an X-ray beam produced by an industrial X-ray tube (Pantack Sievert, 120 kV, tungsten target) incident on a water sample. Both, theoretical and semi-empirical results presented are based on the form factor approach with results well corresponding to performed measurements. The elastic (Rayleigh) scattering cross sections are based on Thomson scattering with a form factor correction as published by Morin (1982). The inelastic (Compton) contribution is based on the Klein Nishina equation (Klein and Nishina, 1929) multiplied by the incoherent scattering factors calculated by Hubbel et al. (1975). Two major results are presented: first, the experimental integrated in energy cross sections corresponds with theoretical cross sections obtained at the mean energy of the measured scattered spectra at a given angle. Secondly, the measured scattered spectra at a given angle correspond to those obtained utilizing the semi-empirical model as proposed here. A good correspondence of experimental results and model predictions can be shown. The latter, therefore, proves to be a useful method to calculate the scattering contributions in a number of applications as for example cone beam tomography.

  10. Personalized Assessment of kV Cone Beam Computed Tomography Doses in Image-guided Radiotherapy of Pediatric Cancer Patients

    SciTech Connect

    Zhang Yibao; Yan Yulong; Nath, Ravinder; Bao Shanglian; Deng Jun

    2012-08-01

    Purpose: To develop a quantitative method for the estimation of kV cone beam computed tomography (kVCBCT) doses in pediatric patients undergoing image-guided radiotherapy. Methods and Materials: Forty-two children were retrospectively analyzed in subgroups of different scanned regions: one group in the head-and-neck and the other group in the pelvis. Critical structures in planning CT images were delineated on an Eclipse treatment planning system before being converted into CT phantoms for Monte Carlo simulations. A benchmarked EGS4 Monte Carlo code was used to calculate three-dimensional dose distributions of kVCBCT scans with full-fan high-quality head or half-fan pelvis protocols predefined by the manufacturer. Based on planning CT images and structures exported in DICOM RT format, occipital-frontal circumferences (OFC) were calculated for head-and-neck patients using DICOMan software. Similarly, hip circumferences (HIP) were acquired for the pelvic group. Correlations between mean organ doses and age, weight, OFC, and HIP values were analyzed with SigmaPlot software suite, where regression performances were analyzed with relative dose differences (RDD) and coefficients of determination (R{sup 2}). Results: kVCBCT-contributed mean doses to all critical structures decreased monotonically with studied parameters, with a steeper decrease in the pelvis than in the head. Empirical functions have been developed for a dose estimation of the major organs at risk in the head and pelvis, respectively. If evaluated with physical parameters other than age, a mean RDD of up to 7.9% was observed for all the structures in our population of 42 patients. Conclusions: kVCBCT doses are highly correlated with patient size. According to this study, weight can be used as a primary index for dose assessment in both head and pelvis scans, while OFC and HIP may serve as secondary indices for dose estimation in corresponding regions. With the proposed empirical functions, it is possible

  11. Evaluating the image quality of cone beam CT acquired during rotational delivery

    PubMed Central

    Maria Das, K J; Maria Midunvaleja, K; Gowtham Raj, D; Agarwal, Arpita; Velmurugan, J; Kumar, Shaleen

    2015-01-01

    Objective: The aim of this work was to evaluate the quality of kilovoltage (kV) cone beam CT (CBCT) images acquired during arc delivery. Methods: Arc plans were delivered on a Catphan® 600 phantom (The Phantom Laboratory Inc., Salem, NY), and kV CBCT images were acquired during the treatment. The megavoltage (MV) scatter effect on kV CBCT image quality was evaluated using parameters such as Hounsfield unit (HU) accuracy, spatial resolution, contrast-to-noise ratio (CNR) and spatial non-uniformity (SNU). These CBCT images were compared with reference scans acquired with the same acquisition parameters without MV “beam on”. This evaluation was carried out for different photon beams (6 and 15 MV), arc types (half vs full arc), static field sizes (10 × 10 and 25 × 25 cm2) and source-to-imager distances (SID) (150 and 170 cm). Results and Conclusion: HU accuracy, CNR and SNU were considerably affected by MV scatter, and this effect was increased with increasing field size and decreasing photon energy, whereas the spatial resolution was almost unchanged. The MV scatter effect was observed to be more for full-rotation arc delivery than for half-arc delivery. In addition, increasing the SID resulted in decreased MV scatter effect and improved the image quality. Advances in knowledge: Nowadays, volumetric modulated arc therapy (VMAT) is increasingly used in clinics, and this arc therapy enables us to acquire CBCT imaging simultaneously. But, the main issue of concurrent imaging is the “MV scatter” effect on CBCT imaging. This study aims to experimentally quantify the effect of MV scatter on CBCT image quality. PMID:26226396

  12. 6 GHz Microwave Power-Beaming Demonstration with 6-kV Rectenna and Ion-Breeze Thruster

    NASA Astrophysics Data System (ADS)

    Cummings, T.; Janssen, J.; Karnesky, J.; Laks, D.; Santillo, M.; Strause, B.; Myrabo, L. N.; Alden, A.; Bouliane, P.; Zhang, M.

    2004-03-01

    On 14 April 2003 at the Communications Research Center (CRC) in Ottawa, Ontario, a 5.85-GHz transmitter beamed 3-kW of microwave power to a remote rectifying antenna (i.e., rectenna) that delivered 6-kV to a special `Ion-Breeze' Engine (IBE). Three of CRC's 26.5-cm by 31-cm rectennas were connected in series to provide the ~6-kV output. RPI's low-voltage IBE thrusters performed well in a ``world's first'' power-beaming demonstration with rectennas and endoatmospheric ion-propulsion engines. The successful tests were a low-tech, proof-of-concept demonstration for the future full-sized MicroWave Lightcraft (MWLC) and its air breathing `loiter' propulsion mode. Additional IBE experiments investigated the feasibility of producing flight control forces on the MWLC. The objective was to torque the charged hull for `pitch' or `roll' maneuvers. The torquing demonstration was entirely successful.

  13. [Patient positioning using in-room kV CT for image-guided radiotherapy (IGRT) of prostate cancer].

    PubMed

    Kliton, Jorgo; Agoston, Péter; Major, Tibor; Polgár, Csaba

    2012-09-01

    The purpose of the study was to evaluate accuracy of patients' set up verified by kV CT-on-rails system and compare automatic and manual image registration of planning and verification kVCT-s. Between January 2001 and March 2011, at ten patients with prostate cancer the clinical target volumes (CTVs) for prostate (CTV-PROS), and prostate plus caudal 1 cm of seminal vesicles (CTV-PVS) with or without pelvic lymph node region were contoured on the treatment planning CT, according to risk category of the patient. Planning target volumes (PTVs) were created with 1 cm margin extended around the CTVs in each direction. The isocentre was marked on the skin with three radiopaque markers. After the set up, treatment couch with the patient was turned by 180 degree and images were acquired of the region of the isocentre with a kV helical CT-on-rails system (treatment CT). An image registration software was used to co-register planning and treatment CT images. Automatic CT image co-registration was followed by manual co-registration taking into account the CTV-PROS contour and soft tissue informations. Deviations of the isocentres in lateral (LAT), longitudinal (LONG) and vertical (VERT) directions were recorded after each image co-registration. Corresponding data were compared using the t-probe. Systematic (S) and random (s) errors of the set up were calculated. Adequate PTV to CTV margins were calculated by van Herk's formula (2.5xS + 0,7xs). Overall 252 deviations were analysed on fourty-two CT series of 10 patients. The mean errors of the set up with automatic and manual image co-registrations were 0.19 cm and 0.07 cm (p=0.001) in LAT, 0.05 cm and 0.03 cm (p=0.07) in LONG and 0.16 cm and 0.22 cm (p=0.16) in VERT directions, respectively. The systematic errors of the set up for automatic and manual image registrations were 0.22 cm and 0.26 cm in LAT, 0.17 cm and 0.18 cm in LONG, 0.25 cm and 0.26 cm in VERT directions, respectively. The random errors of the set up for

  14. Third-generation Dual-source CT for Head and Neck CT Angiography with 70 kV Tube Voltage and 20-25 ml Contrast Medium in Patients With Body Weight Lower than 75 kg.

    PubMed

    Chen, Yu; Zhu, Yuanli; Xue, Huadan; Wang, Yun; Li, Yumei; Zhang, Zhuhua; Jin, Zhengyu

    2017-02-20

    Objective To investigate the image quality of head and neck CT angiography (CTA)using the third-generation dual-source CT combined with 70 kV tube voltage and 20-25 ml contrast medium (CM),and evaluate the effects of venous artifacts arising from the CM on the ipsilateral side of injection. Methods Totally 40 consecutive patients with suspected vascular diseases and body weight lower than 75 kg prospectively underwent head and neck CTA examination using the third-generation dual-source CT. CTA was performed with a third-generation dual-source CT system. Patients were randomly divived into 70 kV group (n=20)and 100 kV group (n=20). The 70 kV group used 20-25 ml CM and advanced modeled iterative reconstruction technique,and the 100 kV group used 40 ml CM and filtered back projection. Venous artifacts and CM residues were evaluated by a 3-point scale (1=excellent,3=poor),respectively. Results The effective dose of 70 kV group decreased 58% compared to 100 kV group (t=-18.14,P<0.001).In the 70 kV group,16 patients (80.0%)presented with venous artifacts and six of them (37.5%,6/16)affected the adjacent arteries. In the 100 kV group,19 patients (95.0%)presented with venous artifacts,and seven of them (36.8%,7/19)affected the adjacent arteries (Z=-0.878,P=0.380). In the 70 kV group,13 patients (65.0%)presented with obvious CM residues and two of them (15.3%,2/13)prolonged into the superior vena cava (SVC). In the 100 kV group,19 patients(95.0%)presented with obvious CM residues,and thirteen of them(68.4%,13/19)prolonged into the SVC (Z=-3.654,P<0.001). Conclusion Compared with the 100 kV,the third-generation dual-source CT for head and neck CTA,combined with 70 kV and 20-25 ml CM,can remarkably decrease the radiation dose,along with reduced CM residues and comparable venous artifacts.

  15. Cone Beam CT vs. Fan Beam CT: A Comparison of Image Quality and Dose Delivered Between Two Differing CT Imaging Modalities.

    PubMed

    Lechuga, Lawrence; Weidlich, Georg A

    2016-09-12

    A comparison of image quality and dose delivered between two differing computed tomography (CT) imaging modalities-fan beam and cone beam-was performed. A literature review of quantitative analyses for various image quality aspects such as uniformity, signal-to-noise ratio, artifact presence, spatial resolution, modulation transfer function (MTF), and low contrast resolution was generated. With these aspects quantified, cone beam computed tomography (CBCT) shows a superior spatial resolution to that of fan beam, while fan beam shows a greater ability to produce clear and anatomically correct images with better soft tissue differentiation. The results indicate that fan beam CT produces superior images to that of on-board imaging (OBI) cone beam CT systems, while providing a considerably less dose to the patient.

  16. [Accurate 3D free-form registration between fan-beam CT and cone-beam CT].

    PubMed

    Liang, Yueqiang; Xu, Hongbing; Li, Baosheng; Li, Hongsheng; Yang, Fujun

    2012-06-01

    Because the X-ray scatters, the CT numbers in cone-beam CT cannot exactly correspond to the electron densities. This, therefore, results in registration error when the intensity-based registration algorithm is used to register planning fan-beam CT and cone-beam CT. In order to reduce the registration error, we have developed an accurate gradient-based registration algorithm. The gradient-based deformable registration problem is described as a minimization of energy functional. Through the calculus of variations and Gauss-Seidel finite difference method, we derived the iterative formula of the deformable registration. The algorithm was implemented by GPU through OpenCL framework, with which the registration time was greatly reduced. Our experimental results showed that the proposed gradient-based registration algorithm could register more accurately the clinical cone-beam CT and fan-beam CT images compared with the intensity-based algorithm. The GPU-accelerated algorithm meets the real-time requirement in the online adaptive radiotherapy.

  17. SU-E-J-27: Effects of Metal Artifacts of KV and MV CT Images on Structure Delineation and Tissue Electron/Mass Density Calculation.

    PubMed

    He, T; Tanyi, J; Crilly, R; Laub, W

    2012-06-01

    To quantitatively evaluate effects of image artifacts of hip prostheses on the accuracy of structure delineation and tissue density calculation on kV and MV CT images. Five hip prostheses made of stainless steel, titanium and cobalt chrome alloys were positioned inside a water tank and scanned respectively on a Philips CT and a Tomotherapy Hi-Art unit. Prostheses were positioned to mimic single and bilateral implantations. Rods of tissue materials of lung, water and bone were placed at locations next and distal to metal implants near femoral head, neck and stem of prostheses. kV and MV CT scans were repeated for each placement. On CT images, cross-sectional outlines of metal implants and tissue rods were delineated. Densities of rod materials were determined and compared to the true values. Metal artifacts were severe on kV CTs and minimal on MV CTs. Cross-sectional outlines of metal implants and tissue rods on kV CTs were severely distorted by artifacts while those on MV CTs remained clearly identifiable. For kV CTs, deviations of measured tissue density from true value were up to 51.3%, 30.6% and 40.9% respectively for lung, bone and solid water. The magnitude of deviation was generally larger at locations closer to metal implants and greater with bilateral implants than single implant. For MV CTs, deviations of measured density from true value were less than 6% for all three tissue materials either with single or bilateral implants. Magnitude of deviation appeared to be uniform and independent of locations relative to metal implants. High Z metal artifacts on kV CTs can have severe impact on the accuracy of structure delineation and tissue density calculation, while on MV CTs, the impact is substantially less and insignificant. MV CTs should be considered for treatment planning on patients with high Z metal implants. © 2012 American Association of Physicists in Medicine.

  18. Dose reduction in dynamic CT stress myocardial perfusion imaging: comparison of 80-kV/370-mAs and 100-kV/300-mAs protocols.

    PubMed

    Fujita, Makiko; Kitagawa, Kakuya; Ito, Tatsuro; Shiraishi, Yasuyuki; Kurobe, Yusuke; Nagata, Motonori; Ishida, Masaki; Sakuma, Hajime

    2014-03-01

    To determine the effect of reduced 80-kV tube voltage with increased 370-mAs tube current on radiation dose, image quality and estimated myocardial blood flow (MBF) of dynamic CT stress myocardial perfusion imaging (CTP) in patients with a normal body mass index (BMI) compared with a 100-kV and 300-mAs protocol. Thirty patients with a normal BMI (<25 kg/m(2)) with known or suspected coronary artery disease underwent adenosine-stress dual-source dynamic CTP. Patients were randomised to 80-kV/370-mAs (n = 15) or 100-kV/300-mAs (n = 15) imaging. Maximal enhancement and noise of the left ventricular (LV) cavity, contrast-to-noise ratio (CNR) and MBF of the two groups were compared. Imaging with 80-kV/370-mAs instead of 100-kV/300-mAs was associated with 40% lower radiation dose (mean dose-length product, 359 ± 66 vs 628 ± 112 mGy[Symbol: see text]cm; P < 0.001 ) with no significant difference in CNR (34.5 ± 13.4 vs 33.5 ± 10.4; P = 0.81) or MBF in non-ischaemic myocardium (0.95 ± 0.20 vs 0.99 ± 0.25 ml/min/g; P = 0.66). Studies obtained using 80-kV/370-mAs were associated with 30.9% higher maximal enhancement (804 ± 204 vs 614 ± 115 HU; P < 0.005), and 31.2% greater noise (22.7 ± 3.5 vs 17.4 ± 2.6; P < 0.001). Dynamic CTP using 80-kV/370-mA instead of 100-kV/300-mAs allowed 40% dose reduction without compromising image quality or MBF. Tube voltage of 80-kV should be considered for individuals with a normal BMI. • CT stress perfusion imaging (CTP) is increasingly used to assess myocardial function. • Dynamic CTP is feasible at 80-kV in patients with normal BMI. • An 80-kV/370-mAs protocol allows 40% dose reduction compared with 100-kV/300-mAs. • Contrast-to-noise ratio and myocardial blood flow of the two protocols were comparable.

  19. Cone Beam CT vs. Fan Beam CT: A Comparison of Image Quality and Dose Delivered Between Two Differing CT Imaging Modalities

    PubMed Central

    Weidlich, Georg A.

    2016-01-01

    A comparison of image quality and dose delivered between two differing computed tomography (CT) imaging modalities—fan beam and cone beam—was performed. A literature review of quantitative analyses for various image quality aspects such as uniformity, signal-to-noise ratio, artifact presence, spatial resolution, modulation transfer function (MTF), and low contrast resolution was generated. With these aspects quantified, cone beam computed tomography (CBCT) shows a superior spatial resolution to that of fan beam, while fan beam shows a greater ability to produce clear and anatomically correct images with better soft tissue differentiation. The results indicate that fan beam CT produces superior images to that of on-board imaging (OBI) cone beam CT systems, while providing a considerably less dose to the patient. PMID:27752404

  20. Effects of High Volume MOSFET Usage on Dosimetry in Pediatric CT, Pediatric Lens of the Eye Dose Reduction Using Siemens Care kV, & Designing Quality Assurance of a Cesium Calibration Source

    NASA Astrophysics Data System (ADS)

    Smith, Aaron Kenneth

    Project 1: Effects of High Volume MOSFET Usage on Dosimetry in Pediatric CT: Purpose: The objective of this study was to determine if using large numbers of Metal-Oxide-Semiconducting-Field-Effect Transistors, MOSFETs, effects the results of dosimetry studies done with pediatric phantoms due to the attenuation properties of the MOSFETs. The two primary focuses of the study were first to experimentally determine the degree to which high numbers of MOSFET detectors attenuate an X-ray beam of Computed Tomography (CT) quality and second, to experimentally verify the effect that the large number of MOSFETs have on dose in a pediatric phantom undergoing a routine CT examination. Materials and Methods: A Precision X-Ray X-Rad 320 set to 120kVp with an effective half value layer of 7.30mm aluminum was used in concert with a tissue equivalent block phantom and several used MOSFET cables to determine the attenuation properties of the MOSFET cables by measuring the dose (via a 0.18cc ion chamber) given to a point in the center of the phantom in a 0.5 min exposure with a variety of MOSFET arrangements. After the attenuating properties of the cables were known, a GE Discovery 750 CT scanner was employed using a routine chest CT protocol in concert with a 10-year-old Atom Dosimetry Phantom and MOSFET dosimeters in 5 different locations in and on the phantom (upper left lung (ULL), upper right lung (URL), lower left lung (LLL), lower right lung (LRL), and the center of the chest to represent skin dose). Twenty-eight used MOSFET cables were arranged and taped on the chest of the phantom to cover 30% of the circumference of the phantom (19.2 cm). Scans using tube current modulation and not using tube current modulation were taken at 30, 20, 10, and 0% circumference coverage and 28 MOSFETs bundled and laid to the side of the phantom. The dose to the various MOSFET locations in and on the chest were calculated and the image quality was accessed in several of these situations by

  1. Current role of hybrid CT/angiography system compared with C-arm cone beam CT for interventional oncology

    PubMed Central

    Arai, Y; Inaba, Y; Inoue, M; Nishiofuku, H; Anai, H; Hori, S; Sakaguchi, H; Kichikawa, K

    2014-01-01

    Hybrid CT/angiography (angiography) system and C-arm cone beam CT provide cross-sectional imaging as an adjunct to angiography. Current interventional oncological procedures can be conducted precisely using these two technologies. In this article, several cases using a hybrid CT/angiography system are shown first, and then the advantages and disadvantages of the hybrid CT/angiography and C-arm cone beam CT are discussed with literature reviews. PMID:24968749

  2. Current role of hybrid CT/angiography system compared with C-arm cone beam CT for interventional oncology.

    PubMed

    Tanaka, T; Arai, Y; Inaba, Y; Inoue, M; Nishiofuku, H; Anai, H; Hori, S; Sakaguchi, H; Kichikawa, K

    2014-09-01

    Hybrid CT/angiography (angiography) system and C-arm cone beam CT provide cross-sectional imaging as an adjunct to angiography. Current interventional oncological procedures can be conducted precisely using these two technologies. In this article, several cases using a hybrid CT/angiography system are shown first, and then the advantages and disadvantages of the hybrid CT/angiography and C-arm cone beam CT are discussed with literature reviews.

  3. [Dosimetric calibration of CT pencil chamber in cobalt beams].

    PubMed

    Li, Yi; Wang, Junliang; Wang, Yunlai

    2014-01-01

    To explore the dose-length product calibration method for pencil ionization chamber in cobalt beams. The PTW TM30009 ionization chamber was placed into the central hole of T40017 head phantom and irradiated 60 s in 20 cm x 20 cm cobalt beam. The charge was collected with UNIDOS electrometer. Absorbed doses were measured with TM30013 0.6 mL farmer-type chamber under the same condition. The CT chamber calibration factor was expressed in dose-length product. Dose linearity and spatial response were also investigated. The calibration factor in dose-length product was derived from measured data. Dose linearity and spatial response were good in cobalt beams. It is feasible to calibrate the CT chamber in cobalt beams for patient dose evaluation in MVCT.

  4. Beam hardening correction for sparse-view CT reconstruction

    NASA Astrophysics Data System (ADS)

    Liu, Wenlei; Rong, Junyan; Gao, Peng; Liao, Qimei; Lu, HongBing

    2015-03-01

    Beam hardening, which is caused by spectrum polychromatism of the X-ray beam, may result in various artifacts in the reconstructed image and degrade image quality. The artifacts would be further aggravated for the sparse-view reconstruction due to insufficient sampling data. Considering the advantages of the total-variation (TV) minimization in CT reconstruction with sparse-view data, in this paper, we propose a beam hardening correction method for sparse-view CT reconstruction based on Brabant's modeling. In this correction model for beam hardening, the attenuation coefficient of each voxel at the effective energy is modeled and estimated linearly, and can be applied in an iterative framework, such as simultaneous algebraic reconstruction technique (SART). By integrating the correction model into the forward projector of the algebraic reconstruction technique (ART), the TV minimization can recover images when only a limited number of projections are available. The proposed method does not need prior information about the beam spectrum. Preliminary validation using Monte Carlo simulations indicates that the proposed method can provide better reconstructed images from sparse-view projection data, with effective suppression of artifacts caused by beam hardening. With appropriate modeling of other degrading effects such as photon scattering, the proposed framework may provide a new way for low-dose CT imaging.

  5. SU-E-J-14: A Comparison of a 2.5MV Imaging Beam to KV and 6MV Imaging Beams

    SciTech Connect

    Nitsch, P; Robertson, D; Balter, P

    2015-06-15

    Purpose: To compare image quality metrics and dose of TrueBeam V2.0’s 2.5MV imaging beam and kV and 6MV images. Methods: To evaluate the MV image quality, the Standard Imaging QC-3 and Varian Las Vegas (LV) phantoms were imaged using the ‘quality’ and ‘low dose’ modes and then processed using RIT113 V6.3. The LEEDS phantom was used to evaluate the kV image quality. The signal to noise ratio (SNR) was also evaluated in patient images using Matlab. In addition, dose per image was evaluated at a depth of 5cm using solid water for a 28.6 cm × 28.6 cm field size, which is representative of the largest jaw settings at an SID of 150cm. Results: The 2.5MV images had lower dose than the 6 MV images and a contrast to noise ratio (CNR) about 1.4 times higher, when evaluated using the QC-3. When energy was held constant but dose varied, the different modes, ‘low dose’ and ‘quality’, showed less than an 8% difference in CNR. The ‘quality’ modes demonstrated better spatial resolution than the ‘low dose’; however, even with the ‘low dose’ all line pairs were distinct except for the 0.75lp/mm on the 2.5MV. The LV phantom was used to measure low contrast detectability and showed similar results to the QC-3. Several patient images all confirmed that SNR were highest in kV images followed by 2.5MV and then 6MV. Qualitatively, for anatomical areas with large variability in thickness, like lateral head and necks, 2.5MV images show more anatomy, such as shoulder position, than kV images. Conclusions: The kV images clearly provide the best image metrics per unit dose. The 2.5MV beam showed excellent contrast at a lower dose than 6MV and may be superior to kV for difficult to image areas that include large changes in anatomical thickness. P Balter: Varian, Sun Nuclear, Philips, CPRIT.

  6. Development and validation of a measurement-based source model for kilovoltage cone-beam CT Monte Carlo dosimetry simulations

    PubMed Central

    McMillan, Kyle; McNitt-Gray, Michael; Ruan, Dan

    2013-01-01

    Purpose: The purpose of this study is to adapt an equivalent source model originally developed for conventional CT Monte Carlo dose quantification to the radiation oncology context and validate its application for evaluating concomitant dose incurred by a kilovoltage (kV) cone-beam CT (CBCT) system integrated into a linear accelerator. Methods: In order to properly characterize beams from the integrated kV CBCT system, the authors have adapted a previously developed equivalent source model consisting of an equivalent spectrum module that takes into account intrinsic filtration and an equivalent filter module characterizing the added bowtie filtration. An equivalent spectrum was generated for an 80, 100, and 125 kVp beam with beam energy characterized by half-value layer measurements. An equivalent filter description was generated from bowtie profile measurements for both the full- and half-bowtie. Equivalent source models for each combination of equivalent spectrum and filter were incorporated into the Monte Carlo software package MCNPX. Monte Carlo simulations were then validated against in-phantom measurements for both the radiographic and CBCT mode of operation of the kV CBCT system. Radiographic and CBCT imaging dose was measured for a variety of protocols at various locations within a body (32 cm in diameter) and head (16 cm in diameter) CTDI phantom. The in-phantom radiographic and CBCT dose was simulated at all measurement locations and converted to absolute dose using normalization factors calculated from air scan measurements and corresponding simulations. The simulated results were compared with the physical measurements and their discrepancies were assessed quantitatively. Results: Strong agreement was observed between in-phantom simulations and measurements. For the radiographic protocols, simulations uniformly underestimated measurements by 0.54%–5.14% (mean difference = −3.07%, SD = 1.60%). For the CBCT protocols, simulations uniformly

  7. Calibration free beam hardening correction for cardiac CT perfusion imaging

    NASA Astrophysics Data System (ADS)

    Levi, Jacob; Fahmi, Rachid; Eck, Brendan L.; Fares, Anas; Wu, Hao; Vembar, Mani; Dhanantwari, Amar; Bezerra, Hiram G.; Wilson, David L.

    2016-03-01

    Myocardial perfusion imaging using CT (MPI-CT) and coronary CTA have the potential to make CT an ideal noninvasive gate-keeper for invasive coronary angiography. However, beam hardening artifacts (BHA) prevent accurate blood flow calculation in MPI-CT. BH Correction (BHC) methods require either energy-sensitive CT, not widely available, or typically a calibration-based method. We developed a calibration-free, automatic BHC (ABHC) method suitable for MPI-CT. The algorithm works with any BHC method and iteratively determines model parameters using proposed BHA-specific cost function. In this work, we use the polynomial BHC extended to three materials. The image is segmented into soft tissue, bone, and iodine images, based on mean HU and temporal enhancement. Forward projections of bone and iodine images are obtained, and in each iteration polynomial correction is applied. Corrections are then back projected and combined to obtain the current iteration's BHC image. This process is iterated until cost is minimized. We evaluate the algorithm on simulated and physical phantom images and on preclinical MPI-CT data. The scans were obtained on a prototype spectral detector CT (SDCT) scanner (Philips Healthcare). Mono-energetic reconstructed images were used as the reference. In the simulated phantom, BH streak artifacts were reduced from 12+/-2HU to 1+/-1HU and cupping was reduced by 81%. Similarly, in physical phantom, BH streak artifacts were reduced from 48+/-6HU to 1+/-5HU and cupping was reduced by 86%. In preclinical MPI-CT images, BHA was reduced from 28+/-6 HU to less than 4+/-4HU at peak enhancement. Results suggest that the algorithm can be used to reduce BHA in conventional CT and improve MPI-CT accuracy.

  8. Dedicated Cone-Beam CT System for Extremity Imaging

    PubMed Central

    Al Muhit, Abdullah; Zbijewski, Wojciech; Thawait, Gaurav K.; Stayman, J. Webster; Packard, Nathan; Senn, Robert; Yang, Dong; Foos, David H.; Yorkston, John; Siewerdsen, Jeffrey H.

    2014-01-01

    Purpose To provide initial assessment of image quality and dose for a cone-beam computed tomographic (CT) scanner dedicated to extremity imaging. Materials and Methods A prototype cone-beam CT scanner has been developed for imaging the extremities, including the weight-bearing lower extremities. Initial technical assessment included evaluation of radiation dose measured as a function of kilovolt peak and tube output (in milliampere seconds), contrast resolution assessed in terms of the signal difference–to-noise ratio (SDNR), spatial resolution semiquantitatively assessed by using a line-pair module from a phantom, and qualitative evaluation of cadaver images for potential diagnostic value and image artifacts by an expert CT observer (musculoskeletal radiologist). Results The dose for a nominal scan protocol (80 kVp, 108 mAs) was 9 mGy (absolute dose measured at the center of a CT dose index phantom). SDNR was maximized with the 80-kVp scan technique, and contrast resolution was sufficient for visualization of muscle, fat, ligaments and/or tendons, cartilage joint space, and bone. Spatial resolution in the axial plane exceeded 15 line pairs per centimeter. Streaks associated with x-ray scatter (in thicker regions of the patient—eg, the knee), beam hardening (about cortical bone—eg, the femoral shaft), and cone-beam artifacts (at joint space surfaces oriented along the scanning plane—eg, the interphalangeal joints) presented a slight impediment to visualization. Cadaver images (elbow, hand, knee, and foot) demonstrated excellent visibility of bone detail and good soft-tissue visibility suitable to a broad spectrum of musculoskeletal indications. Conclusion A dedicated extremity cone-beam CT scanner capable of imaging upper and lower extremities (including weight-bearing examinations) provides sufficient image quality and favorable dose characteristics to warrant further evaluation for clinical use. © RSNA, 2013 Online supplemental material is available for

  9. Reduction of beam hardening artifacts in cone-beam CT imaging via SMART-RECON algorithm

    NASA Astrophysics Data System (ADS)

    Li, Yinsheng; Garrett, John; Chen, Guang-Hong

    2016-03-01

    When an automatic exposure control is introduced in C-arm cone beam CT data acquisition, the spectral inconsistencies between acquired projection data are exacerbated. As a result, conventional water/bone correction schemes are not as effective as in conventional diagnostic x-ray CT acquisitions with a fixed tube potential. In this paper, a new method was proposed to reconstruct several images with different degrees of spectral consistency and thus different levels of beam hardening artifacts. The new method relies neither on prior knowledge of the x-ray beam spectrum nor on prior compositional information of the imaging object. Numerical simulations were used to validate the algorithm.

  10. TU-EF-204-08: Dose Efficiency of Added Beam-Shaping Filter with Varied Attenuation Levels in Lung-Cancer Screening CT

    SciTech Connect

    Ma, C; Yu, L; Vrieze, T; Leng, S; Fletcher, J; McCollough, C

    2015-06-15

    Purpose: Added filtration such as tin filter has the potential to improve dose efficiency of x-ray beam in lung-cancer screening CT. However, dose efficiency with added beam filtration is highly dependent on patient attenuation level. In this phantom study, we evaluated the image quality at different tube voltages with and without added tin filter when attenuation level varies. Methods: A 30 x 20 cm anthropomorphic thorax phantom with three added extension rings were used to simulate small (S), medium (M), large (L), and extra-large (XL) adult patients. These phantoms were scanned on a 192-slice CT scanner (Force, Siemens) at 100 and 120kV without tin filtration, and 100 and 150 kV with tin filtration (100Sn and 150Sn), at multiple dose levels at each kV. Images were reconstructed using iterative reconstruction (ADMIRE, Siemens). Radiation dose was measured with a 0.6 cc ion chamber in the middle and peripheral areas of the phantom. Image quality was assessed using mean image noise at uniform areas in the central region and lung. Radiation dose that is required for each kV to match the noise in a routine lung-cancer CT screening technique (120kV, 25 quality reference mAs) was calculated. Results: At each of the four phantom sizes, 100Sn had the lowest noise in both soft tissue and lung. Compared with 120 kV, 100Sn saved 39%–60% dose for the same noise, depending on phantom size. For the XL phantom (50 by 40 cm), 150Sn provided images with the least beam-hardening artifact in peripheral region. Conclusion: For thoracic CT, added tin filtration can provide considerable dose reduction compared with 120 kV. 100Sn provides better dose efficiencies for all phantom sizes, while 150Sn provides better image quality in peripheral region for extra-large patients. Drs.Joel G. Fletcher and Cynthia H. McCollough receive research support from Siemens Healthcare.

  11. Cardiac cone-beam CT volume reconstruction using ART

    SciTech Connect

    Nielsen, T.; Manzke, R.; Proksa, R.; Grass, M.

    2005-04-01

    Modern computed tomography systems allow volume imaging of the heart. Up to now, approximately two-dimensional (2D) and 3D algorithms based on filtered backprojection are used for the reconstruction. These algorithms become more sensitive to artifacts when the cone angle of the x-ray beam increases as it is the current trend of computed tomography (CT) technology. In this paper, we investigate the potential of iterative reconstruction based on the algebraic reconstruction technique (ART) for helical cardiac cone-beam CT. Iterative reconstruction has the advantages that it takes the cone angle into account exactly and that it can be combined with retrospective cardiac gating fairly easily. We introduce a modified ART algorithm for cardiac CT reconstruction. We apply it to clinical cardiac data from a 16-slice CT scanner and compare the images to those obtained with a current analytical reconstruction method. In a second part, we investigate the potential of iterative reconstruction for a large area detector with 256 slices. For the clinical cases, iterative reconstruction produces excellent images of diagnostic quality. For the large area detector, iterative reconstruction produces images superior to analytical reconstruction in terms of cone-beam artifacts.

  12. Quality control and patient dosimetry in dental cone beam CT.

    PubMed

    Vassileva, J; Stoyanov, D

    2010-01-01

    This paper presents the initial experience in performing quality control and patient dose measurements in a cone beam computed tomography (CT) scanner (ILUMA Ultra, IMTEC Imaging, USA) for oral and maxillofacial radiology. The X-ray tube and the generator were tested first, including the kVp accuracy and precision, and the half-value layer (HVL). The following tests specific for panoramic dental systems were also performed: tube output, beam size and beam alignment to the detector. The tests specific for CT included measurements of noise and CT numbers in water and in air, as well as the homogeneity of CT numbers. The most appropriate dose quantity was found to be the air kerma-area product (KAP) measured with a KAP-metre installed at the tube exit. KAP values were found to vary from 110 to 185 microGy m(2) for available adult protocols and to be 54 microGy m(2) for the paediatric protocol. The effective dose calculated with the software PCXMC (STUK, Finland) was 0.05 mSv for children and 0.09-0.16 mSv for adults.

  13. Automated planning of breast radiotherapy using cone beam CT imaging

    SciTech Connect

    Amit, Guy; Purdie, Thomas G.

    2015-02-15

    Purpose: Develop and clinically validate a methodology for using cone beam computed tomography (CBCT) imaging in an automated treatment planning framework for breast IMRT. Methods: A technique for intensity correction of CBCT images was developed and evaluated. The technique is based on histogram matching of CBCT image sets, using information from “similar” planning CT image sets from a database of paired CBCT and CT image sets (n = 38). Automated treatment plans were generated for a testing subset (n = 15) on the planning CT and the corrected CBCT. The plans generated on the corrected CBCT were compared to the CT-based plans in terms of beam parameters, dosimetric indices, and dose distributions. Results: The corrected CBCT images showed considerable similarity to their corresponding planning CTs (average mutual information 1.0±0.1, average sum of absolute differences 185 ± 38). The automated CBCT-based plans were clinically acceptable, as well as equivalent to the CT-based plans with average gantry angle difference of 0.99°±1.1°, target volume overlap index (Dice) of 0.89±0.04 although with slightly higher maximum target doses (4482±90 vs 4560±84, P < 0.05). Gamma index analysis (3%, 3 mm) showed that the CBCT-based plans had the same dose distribution as plans calculated with the same beams on the registered planning CTs (average gamma index 0.12±0.04, gamma <1 in 99.4%±0.3%). Conclusions: The proposed method demonstrates the potential for a clinically feasible and efficient online adaptive breast IMRT planning method based on CBCT imaging, integrating automation.

  14. Practical patient dosimetry for partial rotation cone beam CT

    PubMed Central

    Podnieks, E C; Negus, I S

    2012-01-01

    Objectives This work investigates the validity of estimating effective dose for cone beam CT (CBCT) exposures from the weighted CT dose index (CTDIW) and irradiated length. Methods Measurements were made within cylindrical poly(methyl methacrylate) (PMMA) phantoms measuring 14 cm and 28 cm in length and 32 cm in diameter for the 200° DynaCT acquisition on the Siemens Artis zee fluoroscopy unit (Siemens Medical Solutions, Erlangen, Germany). An interpolated average dose was calculated to account for the partial rotation. Organ and effective doses were estimated by modelling projections in the Monte Carlo software programme PCXMC (STUK, Helsinki, Finland). Results The CTDIW was found to closely approximate the interpolated average dose if the positions of the measured doses reflected the X-ray beam rotation. The average dose was found to increase by 8% when the phantom length was increased from 14 to 28 cm. Using the interpolated average dose and the irradiated length for effective dose calculations gave similar values to PCXMC when a double-length (28-cm) CT dose index phantom was irradiated. Simplifying the estimation of effective dose with PCXMC by modelling just 4 projections around the abdomen gave effective doses that were only 7% different to those given when 41 projections were modelled. Calculated doses to key organs within the beam varied by as much as 27%. Conclusion Estimating effective dose from the CTDIW and the irradiated length is sufficiently accurate for CBCT if the chamber positions are considered carefully. A conversion factor can be used only if a single CT dose index phantom is available. The estimation of organ doses requires a large number of modelled projections in PCXMC. PMID:21304011

  15. Development of a 3D CT scanner using cone beam

    NASA Astrophysics Data System (ADS)

    Endo, Masahiro; Kamagata, Nozomu; Sato, Kazumasa; Hattori, Yuichi; Kobayashi, Shigeo; Mizuno, Shinichi; Jimbo, Masao; Kusakabe, Masahiro

    1995-05-01

    In order to acquire 3D data of high contrast objects such as bone, lung and vessels enhanced by contrast media for use in 3D image processing, we have developed a 3D CT-scanner using cone beam x ray. The 3D CT-scanner consists of a gantry and a patient couch. The gantry consists of an x-ray tube designed for cone beam CT and a large area two-dimensional detector mounted on a single frame and rotated around an object in 12 seconds. The large area detector consists of a fluorescent plate and a charge coupled device video camera. The size of detection area was 600 mm X 450 mm capable of covering the total chest. While an x-ray tube was rotated around an object, pulsed x ray was exposed 30 times a second and 360 projected images were collected in a 12 second scan. A 256 X 256 X 256 matrix image (1.25 mm X 1.25 mm X 1.25 mm voxel) was reconstructed by a high-speed reconstruction engine. Reconstruction time was approximately 6 minutes. Cylindrical water phantoms, anesthetized rabbits with or without contrast media, and a Japanese macaque were scanned with the 3D CT-scanner. The results seem promising because they show high spatial resolution in three directions, though there existed several point to be improved. Possible improvements are discussed.

  16. Upright cone beam CT imaging using the onboard imager

    SciTech Connect

    Fave, Xenia Martin, Rachael; Yang, Jinzhong; Balter, Peter; Court, Laurence; Carvalho, Luis; Pan, Tinsu

    2014-06-15

    Purpose: Many patients could benefit from being treated in an upright position. The objectives of this study were to determine whether cone beam computed tomography (CBCT) could be used to acquire upright images for treatment planning and to demonstrate whether reconstruction of upright images maintained accurate geometry and Hounsfield units (HUs). Methods: A TrueBeam linac was programmed in developer mode to take upright CBCT images. The gantry head was positioned at 0°, and the couch was rotated to 270°. The x-ray source and detector arms were extended to their lateral positions. The x-ray source and gantry remained stationary as fluoroscopic projections were taken and the couch was rotated from 270° to 90°. The x-ray tube current was normalized to deposit the same dose (measured using a calibrated Farmer ion chamber) as that received during a clinical helical CT scan to the center of a cylindrical, polyethylene phantom. To extend the field of view, two couch rotation scans were taken with the detector offset 15 cm superiorly and then 15 cm inferiorly. The images from these two scans were stitched together before reconstruction. Upright reconstructions were compared to reconstructions from simulation CT scans of the same phantoms. Two methods were investigated for correcting the HUs, including direct calibration and mapping the values from a simulation CT. Results: Overall geometry, spatial linearity, and high contrast resolution were maintained in upright reconstructions. Some artifacts were created and HU accuracy was compromised; however, these limitations could be removed by mapping the HUs from a simulation CT to the upright reconstruction for treatment planning. Conclusions: The feasibility of using the TrueBeam linac to take upright CBCT images was demonstrated. This technique is straightforward to implement and could be of enormous benefit to patients with thoracic tumors or those who find a supine position difficult to endure.

  17. Dose calculation using megavoltage cone-beam CT

    SciTech Connect

    Morin, Olivier . E-mail: Morin@radonc17.ucsf.edu; Chen, Josephine; Aubin, Michele; Gillis, Amy; Aubry, Jean-Francois; Bose, Supratik; Chen Hong; Descovich, Martina; Xia Ping; Pouliot, Jean

    2007-03-15

    Purpose: To demonstrate the feasibility of performing dose calculation on megavoltage cone-beam CT (MVCBCT) of head-and-neck patients in order to track the dosimetric errors produced by anatomic changes. Methods and Materials: A simple geometric model was developed using a head-size water cylinder to correct an observed cupping artifact occurring with MVCBCT. The uniformity-corrected MVCBCT was calibrated for physical density. Beam arrangements and weights from the initial treatment plans defined using the conventional CT were applied to the MVCBCT image, and the dose distribution was recalculated. The dosimetric inaccuracies caused by the cupping artifact were evaluated on the water phantom images. An ideal test patient with no observable anatomic changes and a patient imaged with both CT and MVCBCT before and after considerable weight loss were used to clinically validate MVCBCT for dose calculation and to determine the dosimetric impact of large anatomic changes. Results: The nonuniformity of a head-size water phantom ({approx}30%) causes a dosimetric error of less than 5%. The uniformity correction method developed greatly reduces the cupping artifact, resulting in dosimetric inaccuracies of less than 1%. For the clinical cases, the agreement between the dose distributions calculated using MVCBCT and CT was better than 3% and 3 mm where all tissue was encompassed within the MVCBCT. Dose-volume histograms from the dose calculations on CT and MVCBCT were in excellent agreement. Conclusion: MVCBCT can be used to estimate the dosimetric impact of changing anatomy on several structures in the head-and-neck region.

  18. Fast 3D multiple fan-beam CT systems

    NASA Astrophysics Data System (ADS)

    Kohlbrenner, Adrian; Haemmerle, Stefan; Laib, Andres; Koller, Bruno; Ruegsegger, Peter

    1999-09-01

    Two fast, CCD-based three-dimensional CT scanners for in vivo applications have been developed. One is designed for small laboratory animals and has a voxel size of 20 micrometer, while the other, having a voxel size of 80 micrometer, is used for human examinations. Both instruments make use of a novel multiple fan-beam technique: radiation from a line-focus X-ray tube is divided into a stack of fan-beams by a 28 micrometer pitch foil collimator. The resulting wedge-shaped X-ray field is the key to the instrument's high scanning speed and allows to position the sample close to the X-ray source, which makes it possible to build compact CT systems. In contrast to cone- beam scanners, the multiple fan-beam scanner relies on standard fan-beam algorithms, thereby eliminating inaccuracies in the reconstruction process. The projections from one single rotation are acquired within 2 min and are subsequently reconstructed into a 1024 X 1024 X 255 voxel array. Hence a single rotation about the sample delivers a 3D image containing a quarter of a billion voxels. Such volumetric images are 6.6 mm in height and can be stacked on top of each other. An area CCD sensor bonded to a fiber-optic light guide acts as a detector. Since no image intensifier, conventional optics or tapers are used throughout the system, the image is virtually distortion free. The scanner's high scanning speed and high resolution at moderately low radiation dose are the basis for reliable time serial measurements and analyses.

  19. Beam hardening and partial beam hardening of the bowtie filter: Effects on dosimetric applications in CT

    NASA Astrophysics Data System (ADS)

    Lopez-Rendon, X.; Zhang, G.; Bosmans, H.; Oyen, R.; Zanca, F.

    2014-03-01

    Purpose: To estimate the consequences on dosimetric applications when a CT bowtie filter is modeled by means of full beam hardening versus partial beam hardening. Method: A model of source and filtration for a CT scanner as developed by Turner et. al. [1] was implemented. Specific exposures were measured with the stationary CT X-ray tube in order to assess the equivalent thickness of Al of the bowtie filter as a function of the fan angle. Using these thicknesses, the primary beam attenuation factors were calculated from the energy dependent photon mass attenuation coefficients and used to include beam hardening in the spectrum. This was compared to a potentially less computationally intensive approach, which accounts only partially for beam hardening, by giving the photon spectrum a global (energy independent) fan angle specific weighting factor. Percentage differences between the two methods were quantified by calculating the dose in air after passing several water equivalent thicknesses representative for patients having different BMI. Specifically, the maximum water equivalent thickness of the lateral and anterior-posterior dimension and of the corresponding (half) effective diameter were assessed. Results: The largest percentage differences were found for the thickest part of the bowtie filter and they increased with patient size. For a normal size patient they ranged from 5.5% at half effective diameter to 16.1% for the lateral dimension; for the most obese patient they ranged from 7.7% to 19.3%, respectively. For a complete simulation of one rotation of the x-ray tube, the proposed method was 12% faster than the complete simulation of the bowtie filter. Conclusion: The need for simulating the beam hardening of the bow tie filter in Monte Carlo platforms for CT dosimetry will depend on the required accuracy.

  20. Investigation of gated cone-beam CT to reduce respiratory motion blurring

    PubMed Central

    Kincaid, Russell E.; Yorke, Ellen D.; Goodman, Karyn A.; Rimner, Andreas; Wu, Abraham J.; Mageras, Gig S.

    2013-01-01

    Purpose: Methods of reducing respiratory motion blurring in cone-beam CT (CBCT) have been limited to lung where soft tissue contrast is large. Respiration-correlated cone-beam CT uses slow continuous gantry rotation but image quality is limited by uneven projection spacing. This study investigates the efficacy of a novel gated CBCT technique. Methods: In gated CBCT, the linac is programmed such that gantry rotation and kV image acquisition occur within a gate around end expiration and are triggered by an external respiratory monitor. Standard CBCT and gated CBCT scans are performed in 22 patients (11 thoracic, 11 abdominal) and a respiration-correlated CT (RCCT) scan, acquired on a standard CT scanner, from the same day serves as a criterion standard. Image quality is compared by calculating contrast-to-noise ratios (CNR) for tumors in lung, gastroesophageal junction (GEJ) tissue, and pancreas tissue, relative to surrounding background tissue. Congruence between the object in the CBCT images and that in the RCCT is measured by calculating the optimized normalized cross-correlation (NCC) following CBCT-to-RCCT rigid registrations. Results: Gated CBCT results in reduced motion artifacts relative to standard CBCT, with better visualization of tumors in lung, and of abdominal organs including GEJ, pancreas, and organs at risk. CNR of lung tumors is larger in gated CBCT in 6 of 11 cases relative to standard CBCT. A paired two-tailed t-test of lung patient mean CNR shows no statistical significance (p = 0.133). In 4 of 5 cases where CNR is not increased, lung tumor motion observed in RCCT is small (range 1.3–5.2 mm). CNR is increased and becomes statistically significant for 6 out of 7 lung patients with > 5 mm tumor motion (p = 0.044). CNR is larger in gated CBCT in 5 of 7 GEJ cases and 3 of 4 pancreas cases (p = 0.082 and 0.192). Gated CBCT yields improvement with lower NCC relative to standard CBCT in 10 of 11, 7 of 7, and 3 of 4 patients for lung, GEJ, and pancreas

  1. Segmentation-free empirical beam hardening correction for CT.

    PubMed

    Schüller, Sören; Sawall, Stefan; Stannigel, Kai; Hülsbusch, Markus; Ulrici, Johannes; Hell, Erich; Kachelrieß, Marc

    2015-02-01

    The polychromatic nature of the x-ray beams and their effects on the reconstructed image are often disregarded during standard image reconstruction. This leads to cupping and beam hardening artifacts inside the reconstructed volume. To correct for a general cupping, methods like water precorrection exist. They correct the hardening of the spectrum during the penetration of the measured object only for the major tissue class. In contrast, more complex artifacts like streaks between dense objects need other techniques of correction. If using only the information of one single energy scan, there are two types of corrections. The first one is a physical approach. Thereby, artifacts can be reproduced and corrected within the original reconstruction by using assumptions in a polychromatic forward projector. These assumptions could be the used spectrum, the detector response, the physical attenuation and scatter properties of the intersected materials. A second method is an empirical approach, which does not rely on much prior knowledge. This so-called empirical beam hardening correction (EBHC) and the previously mentioned physical-based technique are both relying on a segmentation of the present tissues inside the patient. The difficulty thereby is that beam hardening by itself, scatter, and other effects, which diminish the image quality also disturb the correct tissue classification and thereby reduce the accuracy of the two known classes of correction techniques. The herein proposed method works similar to the empirical beam hardening correction but does not require a tissue segmentation and therefore shows improvements on image data, which are highly degraded by noise and artifacts. Furthermore, the new algorithm is designed in a way that no additional calibration or parameter fitting is needed. To overcome the segmentation of tissues, the authors propose a histogram deformation of their primary reconstructed CT image. This step is essential for the proposed

  2. Segmentation-free empirical beam hardening correction for CT

    SciTech Connect

    Schüller, Sören; Sawall, Stefan; Stannigel, Kai; Hülsbusch, Markus; Ulrici, Johannes; Hell, Erich; Kachelrieß, Marc

    2015-02-15

    Purpose: The polychromatic nature of the x-ray beams and their effects on the reconstructed image are often disregarded during standard image reconstruction. This leads to cupping and beam hardening artifacts inside the reconstructed volume. To correct for a general cupping, methods like water precorrection exist. They correct the hardening of the spectrum during the penetration of the measured object only for the major tissue class. In contrast, more complex artifacts like streaks between dense objects need other techniques of correction. If using only the information of one single energy scan, there are two types of corrections. The first one is a physical approach. Thereby, artifacts can be reproduced and corrected within the original reconstruction by using assumptions in a polychromatic forward projector. These assumptions could be the used spectrum, the detector response, the physical attenuation and scatter properties of the intersected materials. A second method is an empirical approach, which does not rely on much prior knowledge. This so-called empirical beam hardening correction (EBHC) and the previously mentioned physical-based technique are both relying on a segmentation of the present tissues inside the patient. The difficulty thereby is that beam hardening by itself, scatter, and other effects, which diminish the image quality also disturb the correct tissue classification and thereby reduce the accuracy of the two known classes of correction techniques. The herein proposed method works similar to the empirical beam hardening correction but does not require a tissue segmentation and therefore shows improvements on image data, which are highly degraded by noise and artifacts. Furthermore, the new algorithm is designed in a way that no additional calibration or parameter fitting is needed. Methods: To overcome the segmentation of tissues, the authors propose a histogram deformation of their primary reconstructed CT image. This step is essential for the

  3. Evaluation of dose from kV cone-beam computed tomography during radiotherapy: a comparison of methodologies

    NASA Astrophysics Data System (ADS)

    Buckley, J.; Wilkinson, D.; Malaroda, A.; Metcalfe, P.

    2017-01-01

    Three alternative methodologies to the Computed-Tomography Dose Index for the evaluation of Cone-Beam Computed Tomography dose are compared, the Cone-Beam Dose Index, IAEA Human Health Report No. 5 recommended methodology and the AAPM Task Group 111 recommended methodology. The protocols were evaluated for Pelvis and Thorax scan modes on Varian® On-Board Imager and Truebeam kV XI imaging systems. The weighted planar average dose was highest for the AAPM methodology across all scans, with the CBDI being the second highest overall. A 17.96% and 1.14% decrease from the TG-111 protocol to the IAEA and CBDI protocols for the Pelvis mode and 18.15% and 13.10% decrease for the Thorax mode were observed for the XI system. For the OBI system, the variation was 16.46% and 7.14% for Pelvis mode and 15.93% to the CBDI protocol in Thorax mode respectively.

  4. Use of MV and kV imager correlation for maintaining continuous real-time 3D internal marker tracking during beam interruptions.

    PubMed

    Wiersma, R D; Riaz, N; Dieterich, Sonja; Suh, Yelin; Xing, L

    2009-01-07

    The integration of onboard kV imaging together with a MV electronic portal imaging device (EPID) on linear accelerators (LINAC) can provide an easy to implement real-time 3D organ position monitoring solution for treatment delivery. Currently, real-time MV-kV tracking has only been demonstrated by simultaneous imagining by both MV and kV imaging devices. However, modalities such as step-and-shoot IMRT (SS-IMRT), which inherently contain MV beam interruptions, can lead to loss of target information necessary for 3D localization. Additionally, continuous kV imaging throughout the treatment delivery can lead to high levels of imaging dose to the patient. This work demonstrates for the first time how full 3D target tracking can be maintained even in the presence of such beam interruption, or MV/kV beam interleave, by use of a relatively simple correlation model together with MV-kV tracking. A moving correlation model was constructed using both present and prior positions of the marker in the available MV or kV image to compute the position of the marker on the interrupted imager. A commercially available radiotherapy system, equipped with both MV and kV imaging devices, was used to deliver typical SS-IMRT lung treatment plans to a 4D phantom containing internally embedded metallic markers. To simulate actual lung tumor motion, previous recorded 4D lung patient motion data were used. Lung tumor motion data of five separate patients were inputted into the 4D phantom, and typical SS-IMRT lung plans were delivered to simulate actual clinical deliveries. Application of the correlation model to SS-IMRT lung treatment deliveries was found to be an effective solution for maintaining continuous 3D tracking during 'step' beam interruptions. For deliveries involving five or more gantry angles with 50 or more fields per plan, the positional errors were found to have < or =1 mm root mean squared error (RMSE) in all three spatial directions. In addition to increasing the robustness

  5. Use of MV and kV imager correlation for maintaining continuous real-time 3D internal marker tracking during beam interruptions

    NASA Astrophysics Data System (ADS)

    Wiersma, R. D.; Riaz, N.; Dieterich, Sonja; Suh, Yelin; Xing, L.

    2009-01-01

    The integration of onboard kV imaging together with a MV electronic portal imaging device (EPID) on linear accelerators (LINAC) can provide an easy to implement real-time 3D organ position monitoring solution for treatment delivery. Currently, real-time MV-kV tracking has only been demonstrated by simultaneous imagining by both MV and kV imaging devices. However, modalities such as step-and-shoot IMRT (SS-IMRT), which inherently contain MV beam interruptions, can lead to loss of target information necessary for 3D localization. Additionally, continuous kV imaging throughout the treatment delivery can lead to high levels of imaging dose to the patient. This work demonstrates for the first time how full 3D target tracking can be maintained even in the presence of such beam interruption, or MV/kV beam interleave, by use of a relatively simple correlation model together with MV-kV tracking. A moving correlation model was constructed using both present and prior positions of the marker in the available MV or kV image to compute the position of the marker on the interrupted imager. A commercially available radiotherapy system, equipped with both MV and kV imaging devices, was used to deliver typical SS-IMRT lung treatment plans to a 4D phantom containing internally embedded metallic markers. To simulate actual lung tumor motion, previous recorded 4D lung patient motion data were used. Lung tumor motion data of five separate patients were inputted into the 4D phantom, and typical SS-IMRT lung plans were delivered to simulate actual clinical deliveries. Application of the correlation model to SS-IMRT lung treatment deliveries was found to be an effective solution for maintaining continuous 3D tracking during 'step' beam interruptions. For deliveries involving five or more gantry angles with 50 or more fields per plan, the positional errors were found to have <=1 mm root mean squared error (RMSE) in all three spatial directions. In addition to increasing the robustness of

  6. Deformable planning CT to cone-beam CT image registration in head-and-neck cancer

    SciTech Connect

    Hou Jidong; Guerrero, Mariana; Chen, Wenjuan; D'Souza, Warren D.

    2011-04-15

    Purpose: The purpose of this work was to implement and validate a deformable CT to cone-beam computed tomography (CBCT) image registration method in head-and-neck cancer to eventually facilitate automatic target delineation on CBCT. Methods: Twelve head-and-neck cancer patients underwent a planning CT and weekly CBCT during the 5-7 week treatment period. The 12 planning CT images (moving images) of these patients were registered to their weekly CBCT images (fixed images) via the symmetric force Demons algorithm and using a multiresolution scheme. Histogram matching was used to compensate for the intensity difference between the two types of images. Using nine known anatomic points as registration targets, the accuracy of the registration was evaluated using the target registration error (TRE). In addition, region-of-interest (ROI) contours drawn on the planning CT were morphed to the CBCT images and the volume overlap index (VOI) between registered contours and manually delineated contours was evaluated. Results: The mean TRE value of the nine target points was less than 3.0 mm, the slice thickness of the planning CT. Of the 369 target points evaluated for registration accuracy, the average TRE value was 2.6{+-}0.6 mm. The mean TRE for bony tissue targets was 2.4{+-}0.2 mm, while the mean TRE for soft tissue targets was 2.8{+-}0.2 mm. The average VOI between the registered and manually delineated ROI contours was 76.2{+-}4.6%, which is consistent with that reported in previous studies. Conclusions: The authors have implemented and validated a deformable image registration method to register planning CT images to weekly CBCT images in head-and-neck cancer cases. The accuracy of the TRE values suggests that they can be used as a promising tool for automatic target delineation on CBCT.

  7. Image quality of flat-panel cone beam CT

    NASA Astrophysics Data System (ADS)

    Rose, Georg; Wiegert, Jens; Schaefer, Dirk; Fiedler, Klaus; Conrads, Norbert; Timmer, Jan; Rasche, Volker; Noordhoek, Niels; Klotz, Erhard; Koppe, Reiner

    2003-06-01

    We present results on 3D image quality in terms of spatial resolution (MTF) and low contrast detectability, obtained on a flat dynamic X-ray detector (FD) based cone-beam CT (CB-CT) setup. Experiments have been performed on a high precision bench-top system with rotating object table, fixed X-ray tube and 176 x 176 mm2 active detector area (Trixell Pixium 4800). Several objects, including CT performance-, MTF- and pelvis phantoms, have been scanned under various conditions, including a high dose setup in order to explore the 3D performance limits. Under these optimal conditions, the system is capable of resolving less than 1% (~10 HU) contrast in a water background. Within a pelvis phantom, even inserts of muscle and fat equivalent are clearly distinguishable. This also holds for fast acquisitions of up to 40 fps. Focusing on the spatial resolution, we obtain an almost isotropic three-dimensional resolution of up to 30 lp/cm at 10% modulation.

  8. Deformable Image Registration of CT and Truncated Cone-beam CT for Adaptive Radiation Therapy*

    PubMed Central

    Zhen, Xin; Yan, Hao; Zhou, Linghong; Jia, Xun; Jiang, Steve B.

    2013-01-01

    Truncation of a cone-beam computed tomography (CBCT) image, mainly caused by the limited field of view (FOV) of CBCT imaging, poses challenges to the problem of deformable image registration (DIR) between CT and CBCT images in adaptive radiation therapy (ART). The missing information outside the CBCT FOV usually causes incorrect deformations when a conventional DIR algorithm is utilized, which may introduce significant errors in subsequent operations such as dose calculation. In this paper, based on the observation that the missing information in the CBCT image domain does exist in the projection image domain, we propose to solve this problem by developing a hybrid deformation/reconstruction algorithm. As opposed to deforming the CT image to match the truncated CBCT image, the CT image is deformed such that its projections match all the corresponding projection images for the CBCT image. An iterative forward-backward projection algorithm is developed. Six head-and-neck cancer patient cases are used to evaluate our algorithm, five with simulated truncation and one with real truncation. It is found that our method can accurately register the CT image to the truncated CBCT image and is robust against image truncation when the portion of the truncated image is less than 40% of the total image. PMID:24169817

  9. Deformable image registration of CT and truncated cone-beam CT for adaptive radiation therapy

    NASA Astrophysics Data System (ADS)

    Zhen, Xin; Yan, Hao; Zhou, Linghong; Jia, Xun; Jiang, Steve B.

    2013-11-01

    Truncation of a cone-beam computed tomography (CBCT) image, mainly caused by the limited field of view (FOV) of CBCT imaging, poses challenges to the problem of deformable image registration (DIR) between computed tomography (CT) and CBCT images in adaptive radiation therapy (ART). The missing information outside the CBCT FOV usually causes incorrect deformations when a conventional DIR algorithm is utilized, which may introduce significant errors in subsequent operations such as dose calculation. In this paper, based on the observation that the missing information in the CBCT image domain does exist in the projection image domain, we propose to solve this problem by developing a hybrid deformation/reconstruction algorithm. As opposed to deforming the CT image to match the truncated CBCT image, the CT image is deformed such that its projections match all the corresponding projection images for the CBCT image. An iterative forward-backward projection algorithm is developed. Six head-and-neck cancer patient cases are used to evaluate our algorithm, five with simulated truncation and one with real truncation. It is found that our method can accurately register the CT image to the truncated CBCT image and is robust against image truncation when the portion of the truncated image is less than 40% of the total image. Part of this work was presented at the 54th AAPM Annual Meeting (Charlotte, NC, USA, 29 July-2 August 2012).

  10. CT to Cone-beam CT Deformable Registration With Simultaneous Intensity Correction

    PubMed Central

    Zhen, Xin; Gu, Xuejun; Yan, Hao; Zhou, Linghong; Jia, Xun; Jiang, Steve B.

    2012-01-01

    Computed tomography (CT) to cone-beam computed tomography (CBCT) deformable image registration (DIR) is a crucial step in adaptive radiation therapy. Current intensity-based registration algorithms, such as demons, may fail in the context of CT-CBCT DIR because of inconsistent intensities between the two modalities. In this paper, we propose a variant of demons, called Deformation with Intensity Simultaneously Corrected (DISC), to deal with CT-CBCT DIR. DISC distinguishes itself from the original demons algorithm by performing an adaptive intensity correction step on the CBCT image at every iteration step of the demons registration. Specifically, the intensity correction of a voxel in CBCT is achieved by matching the first and the second moments of the voxel intensities inside a patch around the voxel with those on the CT image. It is expected that such a strategy can remove artifacts in the CBCT image, as well as ensuring the intensity consistency between the two modalities. DISC is implemented on computer graphics processing units (GPUs) in compute unified device architecture (CUDA) programming environment. The performance of DISC is evaluated on a simulated patient case and six clinical head-and-neck cancer patient data. It is found that DISC is robust against the CBCT artifacts and intensity inconsistency and significantly improves the registration accuracy when compared with the original demons. PMID:23032638

  11. Demons deformable registration of CT and cone-beam CT using an iterative intensity matching approach

    SciTech Connect

    Nithiananthan, Sajendra; Schafer, Sebastian; Uneri, Ali; and others

    2011-04-15

    Purpose: A method of intensity-based deformable registration of CT and cone-beam CT (CBCT) images is described, in which intensity correction occurs simultaneously within the iterative registration process. The method preserves the speed and simplicity of the popular Demons algorithm while providing robustness and accuracy in the presence of large mismatch between CT and CBCT voxel values (''intensity''). Methods: A variant of the Demons algorithm was developed in which an estimate of the relationship between CT and CBCT intensity values for specific materials in the image is computed at each iteration based on the set of currently overlapping voxels. This tissue-specific intensity correction is then used to estimate the registration output for that iteration and the process is repeated. The robustness of the method was tested in CBCT images of a cadaveric head exhibiting a broad range of simulated intensity variations associated with x-ray scatter, object truncation, and/or errors in the reconstruction algorithm. The accuracy of CT-CBCT registration was also measured in six real cases, exhibiting deformations ranging from simple to complex during surgery or radiotherapy guided by a CBCT-capable C-arm or linear accelerator, respectively. Results: The iterative intensity matching approach was robust against all levels of intensity variation examined, including spatially varying errors in voxel value of a factor of 2 or more, as can be encountered in cases of high x-ray scatter. Registration accuracy without intensity matching degraded severely with increasing magnitude of intensity error and introduced image distortion. A single histogram match performed prior to registration alleviated some of these effects but was also prone to image distortion and was quantifiably less robust and accurate than the iterative approach. Within the six case registration accuracy study, iterative intensity matching Demons reduced mean TRE to (2.5{+-}2.8) mm compared to (3.5{+-}3.0) mm

  12. Demons deformable registration of CT and cone-beam CT using an iterative intensity matching approach

    PubMed Central

    Nithiananthan, Sajendra; Schafer, Sebastian; Uneri, Ali; Mirota, Daniel J.; Stayman, J. Webster; Zbijewski, Wojciech; Brock, Kristy K.; Daly, Michael J.; Chan, Harley; Irish, Jonathan C.; Siewerdsen, Jeffrey H.

    2011-01-01

    Purpose: A method of intensity-based deformable registration of CT and cone-beam CT (CBCT) images is described, in which intensity correction occurs simultaneously within the iterative registration process. The method preserves the speed and simplicity of the popular Demons algorithm while providing robustness and accuracy in the presence of large mismatch between CT and CBCT voxel values (“intensity”). Methods: A variant of the Demons algorithm was developed in which an estimate of the relationship between CT and CBCT intensity values for specific materials in the image is computed at each iteration based on the set of currently overlapping voxels. This tissue-specific intensity correction is then used to estimate the registration output for that iteration and the process is repeated. The robustness of the method was tested in CBCT images of a cadaveric head exhibiting a broad range of simulated intensity variations associated with x-ray scatter, object truncation, and∕or errors in the reconstruction algorithm. The accuracy of CT-CBCT registration was also measured in six real cases, exhibiting deformations ranging from simple to complex during surgery or radiotherapy guided by a CBCT-capable C-arm or linear accelerator, respectively. Results: The iterative intensity matching approach was robust against all levels of intensity variation examined, including spatially varying errors in voxel value of a factor of 2 or more, as can be encountered in cases of high x-ray scatter. Registration accuracy without intensity matching degraded severely with increasing magnitude of intensity error and introduced image distortion. A single histogram match performed prior to registration alleviated some of these effects but was also prone to image distortion and was quantifiably less robust and accurate than the iterative approach. Within the six case registration accuracy study, iterative intensity matching Demons reduced mean TRE to (2.5±2.8) mm compared to (3.5±3.0) mm

  13. Demons deformable registration of CT and cone-beam CT using an iterative intensity matching approach.

    PubMed

    Nithiananthan, Sajendra; Schafer, Sebastian; Uneri, Ali; Mirota, Daniel J; Stayman, J Webster; Zbijewski, Wojciech; Brock, Kristy K; Daly, Michael J; Chan, Harley; Irish, Jonathan C; Siewerdsen, Jeffrey H

    2011-04-01

    A method of intensity-based deformable registration of CT and cone-beam CT (CBCT) images is described, in which intensity correction occurs simultaneously within the iterative registration process. The method preserves the speed and simplicity of the popular Demons algorithm while providing robustness and accuracy in the presence of large mismatch between CT and CBCT voxel values ("intensity"). A variant of the Demons algorithm was developed in which an estimate of the relationship between CT and CBCT intensity values for specific materials in the image is computed at each iteration based on the set of currently overlapping voxels. This tissue-specific intensity correction is then used to estimate the registration output for that iteration and the process is repeated. The robustness of the method was tested in CBCT images of a cadaveric head exhibiting a broad range of simulated intensity variations associated with x-ray scatter, object truncation, and/or errors in the reconstruction algorithm. The accuracy of CT-CBCT registration was also measured in six real cases, exhibiting deformations ranging from simple to complex during surgery or radiotherapy guided by a CBCT-capable C-arm or linear accelerator, respectively. The iterative intensity matching approach was robust against all levels of intensity variation examined, including spatially varying errors in voxel value of a factor of 2 or more, as can be encountered in cases of high x-ray scatter. Registration accuracy without intensity matching degraded severely with increasing magnitude of intensity error and introduced image distortion. A single histogram match performed prior to registration alleviated some of these effects but was also prone to image distortion and was quantifiably less robust and accurate than the iterative approach. Within the six case registration accuracy study, iterative intensity matching Demons reduced mean TRE to (2.5 +/- 2.8) mm compared to (3.5 +/- 3.0) mm with rigid registration. A

  14. Appropriate patient selection at abdominal dual-energy CT using 80 kV: relationship between patient size, image noise, and image quality.

    PubMed

    Guimarães, Luís S; Fletcher, Joel G; Harmsen, William S; Yu, Lifeng; Siddiki, Hassan; Melton, Zachary; Huprich, James E; Hough, David; Hartman, Robert; McCollough, Cynthia H

    2010-12-01

    To determine the computed tomographic (CT) detector configuration, patient size, and image noise limitations that will result in acceptable image quality of 80-kV images obtained at abdominal dual-energy CT. The Institutional Review Board approved this HIPAA-compliant retrospective study from archival material from patients consenting to the use of medical records for research purposes. A retrospective review of contrast material-enhanced abdominal dual-energy CT scans in 116 consecutive patients was performed. Three gastrointestinal radiologists noted detector configuration and graded image quality and artifacts at specified levels-midliver, midpancreas, midkidneys, and terminal ileum-by using two five-point scales. In addition, an organ-specific enhancement-to-noise ratio and background noise were measured in each patient. Patient size was measured by using the longest linear dimension at the level of interest, weight, lean body weight, body mass index, and body surface area. Detector configuration, patient sizes, and image noise levels that resulted in unacceptable image quality and artifact rankings (score of 4 or higher) were determined by using multivariate logistic regression. A 14 × 1.2-mm detector configuration resulted in fewer images with unacceptable quality than did the 64 × 0.6-mm configuration at all anatomic levels (P = .004, .01, and .02 for liver, pancreas, and kidneys, respectively). Image acceptability for the kidneys and ileum was significantly greater than that for the liver for all readers and detector configurations (P < .001). For the 14 × 1.2-mm detector configuration, patient longest linear dimensions yielding acceptable image quality across readers ranged from 34.9 to 35.8 cm at the four anatomic levels. An 80-kV abdominal CT can be performed with appropriate diagnostic quality in a substantial percentage of the population, but it is not recommended beyond the described patient size for each anatomic level. The 14 × 1.2-mm detector

  15. Orthogonal-rotating tetrahedral scanning for cone-beam CT

    NASA Astrophysics Data System (ADS)

    Ye, Ivan B.; Wang, Ge

    2012-10-01

    In this article, a cone-beam CT scanning mode is designed assuming four x-ray sources and a spherical sample. The x-ray sources are mounted at the vertices of a regular tetrahedron. On the circumsphere of the tetrahedron, four detection panels are mounted opposite to each vertex. To avoid x-ray interference, the largest half angle of each x-ray cone beam is 27°22', while the radius of the largest ball fully covered by all the cone beams is 0.460, when the radius of the circumsphere is 1. Several scanning schemes are proposed which consist of two rotations about orthogonal axes, such that each quarter turn provides sufficient data for theoretically exact and stable reconstruction. This design can be used in biomedical or industrial settings, such as when a sequence of reconstructions of an object is desired. Similar scanning schemes based on other regular or irregular polyhedra and various rotation speeds are also discussed.

  16. Deformable registration of CT and cone-beam CT with local intensity matching.

    PubMed

    Park, Seyoun; Plishker, William; Quon, Harry; Wong, John; Shekhar, Raj; Lee, Junghoon

    2017-02-07

    Cone-beam CT (CBCT) is a widely used intra-operative imaging modality in image-guided radiotherapy and surgery. A short scan followed by a filtered-backprojection is typically used for CBCT reconstruction. While data on the mid-plane (plane of source-detector rotation) is complete, off-mid-planes undergo different information deficiency and the computed reconstructions are approximate. This causes different reconstruction artifacts at off-mid-planes depending on slice locations, and therefore impedes accurate registration between CT and CBCT. In this paper, we propose a method to accurately register CT and CBCT by iteratively matching local CT and CBCT intensities. We correct CBCT intensities by matching local intensity histograms slice by slice in conjunction with intensity-based deformable registration. The correction-registration steps are repeated in an alternating way until the result image converges. We integrate the intensity matching into three different deformable registration methods, B-spline, demons, and optical flow that are widely used for CT-CBCT registration. All three registration methods were implemented on a graphics processing unit for efficient parallel computation. We tested the proposed methods on twenty five head and neck cancer cases and compared the performance with state-of-the-art registration methods. Normalized cross correlation (NCC), structural similarity index (SSIM), and target registration error (TRE) were computed to evaluate the registration performance. Our method produced overall NCC of 0.96, SSIM of 0.94, and TRE of 2.26 → 2.27 mm, outperforming existing methods by 9%, 12%, and 27%, respectively. Experimental results also show that our method performs consistently and is more accurate than existing algorithms, and also computationally efficient.

  17. Deformable registration of CT and cone-beam CT with local intensity matching

    NASA Astrophysics Data System (ADS)

    Park, Seyoun; Plishker, William; Quon, Harry; Wong, John; Shekhar, Raj; Lee, Junghoon

    2017-02-01

    Cone-beam CT (CBCT) is a widely used intra-operative imaging modality in image-guided radiotherapy and surgery. A short scan followed by a filtered-backprojection is typically used for CBCT reconstruction. While data on the mid-plane (plane of source-detector rotation) is complete, off-mid-planes undergo different information deficiency and the computed reconstructions are approximate. This causes different reconstruction artifacts at off-mid-planes depending on slice locations, and therefore impedes accurate registration between CT and CBCT. In this paper, we propose a method to accurately register CT and CBCT by iteratively matching local CT and CBCT intensities. We correct CBCT intensities by matching local intensity histograms slice by slice in conjunction with intensity-based deformable registration. The correction-registration steps are repeated in an alternating way until the result image converges. We integrate the intensity matching into three different deformable registration methods, B-spline, demons, and optical flow that are widely used for CT-CBCT registration. All three registration methods were implemented on a graphics processing unit for efficient parallel computation. We tested the proposed methods on twenty five head and neck cancer cases and compared the performance with state-of-the-art registration methods. Normalized cross correlation (NCC), structural similarity index (SSIM), and target registration error (TRE) were computed to evaluate the registration performance. Our method produced overall NCC of 0.96, SSIM of 0.94, and TRE of 2.26 → 2.27 mm, outperforming existing methods by 9%, 12%, and 27%, respectively. Experimental results also show that our method performs consistently and is more accurate than existing algorithms, and also computationally efficient.

  18. Multiscale registration of planning CT and daily cone beam CT images for adaptive radiation therapy

    SciTech Connect

    Paquin, Dana; Levy, Doron; Xing Lei

    2009-01-15

    Adaptive radiation therapy (ART) is the incorporation of daily images in the radiotherapy treatment process so that the treatment plan can be evaluated and modified to maximize the amount of radiation dose to the tumor while minimizing the amount of radiation delivered to healthy tissue. Registration of planning images with daily images is thus an important component of ART. In this article, the authors report their research on multiscale registration of planning computed tomography (CT) images with daily cone beam CT (CBCT) images. The multiscale algorithm is based on the hierarchical multiscale image decomposition of E. Tadmor, S. Nezzar, and L. Vese [Multiscale Model. Simul. 2(4), pp. 554-579 (2004)]. Registration is achieved by decomposing the images to be registered into a series of scales using the (BV, L{sup 2}) decomposition and initially registering the coarsest scales of the image using a landmark-based registration algorithm. The resulting transformation is then used as a starting point to deformably register the next coarse scales with one another. This procedure is iterated at each stage using the transformation computed by the previous scale registration as the starting point for the current registration. The authors present the results of studies of rectum, head-neck, and prostate CT-CBCT registration, and validate their registration method quantitatively using synthetic results in which the exact transformations our known, and qualitatively using clinical deformations in which the exact results are not known.

  19. Cone beam CT: a current overview of devices

    PubMed Central

    Nemtoi, A; Czink, C; Haba, D; Gahleitner, A

    2013-01-01

    The purpose of this study was to review and compare the properties of all the available cone beam CT (CBCT) devices offered on the market, while focusing especially on Europe. In this study, we included all the different commonly used CBCT devices currently available on the European market. Information about the properties of each device was obtained from the manufacturers’ official available data, which was later confirmed by their representatives in cases where it was necessary. The main features of a total of 47 CBCT devices that are currently marketed by 20 companies were presented, compared and discussed in this study. All these CBCT devices differ in specific properties according to the companies that produce them. The summarized technical data from a large number of CBCT devices currently on the market offer a wide range of imaging possibilities in the oral and maxillofacial region. PMID:23818529

  20. Intracranial physiological calcifications evaluated with cone beam CT.

    PubMed

    Sedghizadeh, P P; Nguyen, M; Enciso, R

    2012-12-01

    The purpose of this study was to evaluate cone beam CT (CBCT) scans for the presence of physiological and pathological intracranial calcifications. CBCT scans from male and female patients that met our ascertainment criteria were evaluated retrospectively (n=500) for the presence of either physiological or pathological intracranial calcifications. Out of the 500 patients evaluated, 176 had evidence of intracranial physiological calcification (35.2% prevalence), and none had evidence of pathological calcification. There was a 3:2 male-to-female ratio and no ethnic predilection; the ages of affected patients ranged from 13 years to 82 years with a mean age of 52 years. The majority of calcifications appeared in the pineal/habenular region (80%), with some also appearing in the choroid plexus region bilaterally (12%), and a smaller subset appearing in the petroclinoid ligament region bilaterally (8%). Intracranial physiological calcifications can be a common finding on CBCT scans, whereas pathological intracranial calcifications are rare.

  1. Cone beam CT: a current overview of devices.

    PubMed

    Nemtoi, A; Czink, C; Haba, D; Gahleitner, A

    2013-01-01

    The purpose of this study was to review and compare the properties of all the available cone beam CT (CBCT) devices offered on the market, while focusing especially on Europe. In this study, we included all the different commonly used CBCT devices currently available on the European market. Information about the properties of each device was obtained from the manufacturers' official available data, which was later confirmed by their representatives in cases where it was necessary. The main features of a total of 47 CBCT devices that are currently marketed by 20 companies were presented, compared and discussed in this study. All these CBCT devices differ in specific properties according to the companies that produce them. The summarized technical data from a large number of CBCT devices currently on the market offer a wide range of imaging possibilities in the oral and maxillofacial region.

  2. Computer aided breast density evaluation in cone beam breast CT

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaohua; Ning, Ruola

    2011-03-01

    Cone Beam Breast CT is a three-dimensional breast imaging modality with high contrast resolution and no tissue overlap. With these advantages, it is possible to measure volumetric breast density accurately and quantitatively with CBBCT 3D images. Three major breast components need to be segmented: skin, fat and glandular tissue. In this research, a modified morphological processing is applied to the CBBCT images to detect and remove the skin of the breast. After the skin is removed, a 2-step fuzzy clustering scheme is applied to the CBBCT image volume to adaptively cluster the image voxels into fat and glandular tissue areas based on the intensity of each voxel. Finally, the CBBCT breast volume images are divided into three categories: skin, fat and glands. Clinical data is used and the quantitative CBBCT breast density evaluation results are compared with the mammogram-based BIRADS breast density categories.

  3. Dual resolution cone beam breast CT: A feasibility study

    PubMed Central

    Chen, Lingyun; Shen, Youtao; Lai, Chao-Jen; Han, Tao; Zhong, Yuncheng; Ge, Shuaiping; Liu, Xinming; Wang, Tianpeng; Yang, Wei T.; Whitman, Gary J.; Shaw, Chris C.

    2009-01-01

    Purpose: In this study, the authors investigated the feasibility of a dual resolution volume-of-interest (VOI) cone beam breast CT technique and compared two implementation approaches in terms of dose saving and scatter reduction. Methods: With this technique, a lead VOI mask with an opening is inserted between the x-ray source and the breast to deliver x-ray exposure to the VOI while blocking x rays outside the VOI. A CCD detector is used to collect the high resolution projection data of the VOI. Low resolution cone beam CT (CBCT) images of the entire breast, acquired with a flat panel (FP) detector, were used to calculate the projection data outside the VOI with the ray-tracing reprojection method. The Feldkamp–Davis–Kress filtered backprojection algorithm was used to reconstruct the dual resolution 3D images. Breast phantoms with 180 μm and smaller microcalcifications (MCs) were imaged with both FP and FP-CCD dual resolution CBCT systems, respectively. Two approaches of implementing the dual resolution technique, breast-centered approach and VOI-centered approach, were investigated and evaluated for dose saving and scatter reduction with Monte Carlo simulation using a GEANT4 package. Results: The results showed that the breast-centered approach saved more breast absorbed dose than did VOI-centered approach with similar scatter reduction. The MCs in fatty breast phantom, which were invisible with FP CBCT scan, became visible with the FP-CCD dual resolution CBCT scan. Conclusions: These results indicate potential improvement of the image quality inside the VOI with reduced breast dose both inside and outside the VOI. PMID:19810473

  4. Dual resolution cone beam breast CT: a feasibility study.

    PubMed

    Chen, Lingyun; Shen, Youtao; Lai, Chao-Jen; Han, Tao; Zhong, Yuncheng; Ge, Shuaiping; Liu, Xinming; Wang, Tianpeng; Yang, Wei T; Whitman, Gary J; Shaw, Chris C

    2009-09-01

    In this study, the authors investigated the feasibility of a dual resolution volume-of-interest (VOI) cone beam breast CT technique and compared two implementation approaches in terms of dose saving and scatter reduction. With this technique, a lead VOI mask with an opening is inserted between the x-ray source and the breast to deliver x-ray exposure to the VOI while blocking x rays outside the VOI. A CCD detector is used to collect the high resolution projection data of the VOI. Low resolution cone beam CT (CBCT) images of the entire breast, acquired with a flat panel (FP) detector, were used to calculate the projection data outside the VOI with the ray-tracing reprojection method. The Feldkamp-Davis-Kress filtered backprojection algorithm was used to reconstruct the dual resolution 3D images. Breast phantoms with 180 microm and smaller microcalcifications (MCs) were imaged with both FP and FP-CCD dual resolution CBCT systems, respectively. Two approaches of implementing the dual resolution technique, breast-centered approach and VOI-centered approach, were investigated and evaluated for dose saving and scatter reduction with Monte Carlo simulation using a GEANT4 package. The results showed that the breast-centered approach saved more breast absorbed dose than did VOI-centered approach with similar scatter reduction. The MCs in fatty breast phantom, which were invisible with FP CBCT scan, became visible with the FP-CCD dual resolution CBCT scan. These results indicate potential improvement of the image quality inside the VOI with reduced breast dose both inside and outside the VOI.

  5. Iodine contrast cone beam CT imaging of breast cancer

    NASA Astrophysics Data System (ADS)

    Partain, Larry; Prionas, Stavros; Seppi, Edward; Virshup, Gary; Roos, Gerhard; Sutherland, Robert; Boone, John

    2007-03-01

    An iodine contrast agent, in conjunction with an X-ray cone beam CT imaging system, was used to clearly image three, biopsy verified, cancer lesions in two patients. The lesions were approximately in the 10 mm to 6 mm diameter range. Additional regions were also enhanced with approximate dimensions down to 1 mm or less in diameter. A flat panel detector, with 194 μm pixels in 2 x 2 binning mode, was used to obtain 500 projection images at 30 fps with an 80 kVp X-ray system operating at 112 mAs, for an 8-9 mGy dose - equivalent to two view mammography for these women. The patients were positioned prone, while the gantry rotated in the horizontal plane around the uncompressed, pendant breasts. This gantry rotated 360 degrees during the patient's 16.6 sec breath hold. A volume of 100 cc of 320 mg/ml iodine-contrast was power injected at 4 cc/sec, via catheter into the arm vein of the patient. The resulting 512 x 512 x 300 cone beam CT data set of Feldkamp reconstructed ~(0.3 mm) 3 voxels were analyzed. An interval of voxel contrast values, characteristic of the regions with iodine contrast enhancement, were used with surface rendering to clearly identify up to a total of 13 highlighted volumes. This included the three largest lesions, that were previously biopsied and confirmed to be malignant. The other ten highlighted regions, of smaller diameters, are likely areas of increased contrast trapping unrelated to cancer angiogenesis. However the technique itself is capable of resolving lesions that small.

  6. Effective dose from cone beam CT examinations in dentistry.

    PubMed

    Roberts, J A; Drage, N A; Davies, J; Thomas, D W

    2009-01-01

    Cone beam CT (CBCT) is becoming an increasingly utilized imaging modality for dental examinations in the UK. Previous studies have presented little information on patient dose for the range of fields of view (FOVs) that can be utilized. The purpose of the study was therefore to calculate the effective dose delivered to the patient during a selection of CBCT examinations performed in dentistry. In particular, the i-CAT CBCT scanner was investigated for several imaging protocols commonly used in clinical practice. A Rando phantom containing thermoluminescent dosemeters was scanned. Using both the 1990 and recently approved 2007 International Commission on Radiological Protection recommended tissue weighting factors, effective doses were calculated. The doses (E(1990), E(2007)) were: full FOV head (92.8 microSv, 206.2 microSv); 13 cm scan of the jaws (39.5 microSv, 133.9 microSv); 6 cm high-resolution mandible (47.2 microSv, 188.5 microSv); 6 cm high-resolution maxilla (18.5 microSv, 93.3 microSv); 6 cm standard mandible (23.9 microSv, 96.2 microSv); and 6 cm standard maxilla (9.7 microSv, 58.9 microSv). The doses from CBCT are low compared with conventional CT but significantly higher than conventional dental radiography techniques.

  7. Cone beam CT tumor vasculature dynamic study (Murine model)

    NASA Astrophysics Data System (ADS)

    Yang, Dong; Ning, Ruola; Conover, David; Ricardo, Betancourt; Liu, Shaohua

    2008-03-01

    Tumor angiogenesis is the process by which new blood vessels are formed from the existing vessels in a tumor to promote tumor growth. Tumor angiogenesis has important implications in the diagnosis and treatment of various solid tumors. Flat panel detector based cone beam CT opens up a new way for detection of tumors, and tumor angiogenesis associated with functional CBCT has the potential to provide more information than traditional functional CT due to more overall coverage during the same scanning period and the reconstruction being isotropic resulting in a more accurate 3D volume intensity measurement. A functional study was conducted by using CBCT to determine the degree of the enhancement within the tumor after injecting the contrast agent intravenously. For typical doses of contrast material, the amount of enhancement is proportional to the concentration of this material within the region of interest. A series of images obtained at one location over time allows generation of time-attenuation data from which a number of semi-quantitative parameters, such as enhancement rate, can be determined. An in vivo mice study with and without mammo tumor was conducted on our prototype CBCT system, and half scan scheme is used to determine the time-intensity curve within the VOI of the mouse. The CBCT has an x-ray tube, a gantry with slip ring technology, and a 40×30 cm Varian Paxscan 4030CB real time FPD.

  8. Cone beam CT for dental and maxillofacial imaging: dose matters.

    PubMed

    Pauwels, Ruben

    2015-07-01

    The widespread use of cone-beam CT (CBCT) in dentistry has led to increasing concern regarding justification and optimisation of CBCT exposures. When used as a substitute to multidetector CT (MDCT), CBCT can lead to significant dose reduction; however, low-dose protocols of current-generation MDCTs show that there is an overlap between CBCT and MDCT doses. More importantly, although the 3D information provided by CBCT can often lead to improved diagnosis and treatment compared with 2D radiographs, a routine or excessive use of CBCT would lead to a substantial increase of the collective patient dose. The potential use of CBCT for paediatric patients (e.g. developmental disorders, trauma and orthodontic treatment planning) further increases concern regarding its proper application. This paper provides an overview of justification and optimisation issues in dental and maxillofacial CBCT. The radiation dose in CBCT will be briefly reviewed. The European Commission's Evidence Based Guidelines prepared by the SEDENTEXCT Project Consortium will be summarised, and (in)appropriate use of CBCT will be illustrated for various dental applications.

  9. A ray-tracing backprojection algorithm for cone beam CT

    NASA Astrophysics Data System (ADS)

    Lu, Jun; Pan, Tinsu

    2007-03-01

    We have developed a ray-tracing backprojection (RTB) to back-project all the detector pixels into the image domain of cone beam CT (CBCT). The underlying mathematic framework is the FDK reconstruction. In this method, every ray recorded by the flat panel detector is traced back into the image space. In each voxel of the imaging domain, all the rays contributing to the formation of the CT image are summed together weighted by each rays' intersection length with the voxel. The RTB is similar to a reverse process of x-ray transmission imaging, as opposed to the conventional voxel-driven backprojection (VDB). In the RTB, we avoided interpolation and pixel binning approximations, achieved better spatial resolution and eliminated some image artifacts. We have successfully applied the RTB in phantom studies on the Varian On Board Imager CBCT. The images of the Catphan CTP404 module show more accurate representation of the oblique ramps in the measurement of slice thickness, and more accurate determination of slice thickness with the RTB than with VDB. The RTB also shows higher spatial resolution than the VDB in the studies of a high contrast resolution phantom.

  10. Deformable registration of CT and cone-beam CT by local CBCT intensity correction

    NASA Astrophysics Data System (ADS)

    Park, Seyoun; Plishker, William; Shekhar, Raj; Quon, Harry; Wong, John; Lee, Junghoon

    2015-03-01

    In this paper, we propose a method to accurately register CT to cone-beam CT (CBCT) by iteratively correcting local CBCT intensity. CBCT is a widely used intra-operative imaging modality in image-guided radiotherapy and surgery. A short scan followed by a filtered-backprojection is typically used for CBCT reconstruction. While data on the mid-plane (plane of source-detector rotation) is complete, off-mid-planes undergo different information deficiency and the computed reconstructions are approximate. This causes different reconstruction artifacts at off-mid-planes depending on slice locations, and therefore impedes accurate registration between CT and CBCT. To address this issue, we correct CBCT intensities by matching local intensity histograms slice by slice in conjunction with intensity-based deformable registration. This correction-registration step is repeated until the result image converges. We tested the proposed method on eight head-and-neck cancer cases and compared its performance with state-of-the-art registration methods, Bspline, demons, and optical flow, which are widely used for CT-CBCT registration. Normalized mutual-information (NMI), normalized cross-correlation (NCC), and structural similarity (SSIM) were computed as similarity measures for the performance evaluation. Our method produced overall NMI of 0.59, NCC of 0.96, and SSIM of 0.93, outperforming existing methods by 3.6%, 2.4%, and 2.8% in terms of NMI, NCC, and SSIM scores, respectively. Experimental results show that our method is more consistent and roust than existing algorithms, and also computationally efficient with faster convergence.

  11. Carotid CT-angiography: low versus standard volume contrast media and low kV protocol for 128-slice MDCT.

    PubMed

    Kayan, Mustafa; Köroğlu, Mert; Yeşildağ, Ahmet; Ceylan, Ergun; Aktaş, Aykut Recep; Yasar, Selçuk; Aynali, Giray; Parlak, Cem; Munduz, Mehmet; Gürses, Cemil

    2012-09-01

    Availability and utilization of computed tomography angiography has been increasing recently. We aimed to assess the effectiveness of low amount of contrast media and low kV value in order to reduce possible side effects of contrast media and to provide optimization of kV value in the evaluation of the carotid artery with multi-detector computed tomography angiography. Forty one patients were randomized into two groups. Contrast media was administered at a dose of 1 ml/kg in group A patients and of 0.5 ml/kg in group B patients. kV value of 120 in group A and 100 in group B were chosen. Bolus tracking technique was used. Attenuation values of certain arterial segments were measured, and values over 200 HU were considered as significant. North American Symptomatic Carotid Endartherectomy Trial criteria were utilized in the evaluation of stenosis. Image quality in arterial segments of all cases was found to be sufficient for diagnosis. Arterial attenuation values were found to be higher in group B than group A. When compared separately in all arterial segments, there was no statistically significant difference between the groups. For stenosis, 615 arterial segments were evaluated. Moderate stenosis in eight segments and severe stenosis in three segments were identified in group A. Occlusion in three segments, severe stenosis in three segments, and moderate stenosis in 25 segments were detected in group B. Better image quality can be obtained, and the amount of contrast media can be reduced using low kV technique in carotid artery multi-detector computed tomography angiography examination. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

  12. TH-C-18A-10: The Influence of Tube Current On X-Ray Focal Spot Size for 70 KV CT Imaging

    SciTech Connect

    Duan, X; Grimes, J; Yu, L; Leng, S; McCollough, C

    2014-06-15

    Purpose: Focal spot blooming is an increase in the focal spot size at increased tube current and/or decreased tube potential. In this work, we evaluated the influence of tube current on the focal spot size at low kV for two CT systems, one of which used a tube designed to reduce blooming effects. Methods: A slit camera (10 micron slit) was used to measure focal spot size on two CT scanners from the same manufacturer (Siemens Somatom Force and Definition Flash) at 70 kV and low, medium and maximum tube currents, according to the capabilities of each system (Force: 100, 800 and 1300 mA; Flash: 100, 200 and 500 mA). Exposures were made with a stationary tube in service mode using a raised stand without table movement or flying focal spot technique. Focal spot size, nominally 0.8 and 1.2 mm, respectively, was measured parallel and perpendicular to the cathode-anode axis by calculating the full-width-at-half-maximum of the slit profile recording using computed radiographic plates. Results: Focal spot sizes perpendicular to the anode-cathode axis increased at the maximum mA by 5.7% on the Force and 39.1% on the Flash relative to that at the minimal mA, even though the mA was increased 13-fold on the Force and only 5- fold on the Flash. Focal spot size increased parallel to the anode-cathode axis by 70.4% on Force and 40.9% on Flash. Conclusion: For CT protocols using low kV, high mA is typically required. These protocols are relevant in children and smaller adults, and for dual-energy scanning. Technical measures to limit focal spot blooming are important in these settings to avoid reduced spatial resolution. The x-ray tube on a recently-introduced scanner appears to greatly reduce blooming effects, even at very high mA values. CHM has research support from Siemens Healthcare.

  13. Computed tomography dose assessment for a 160 mm wide, 320 detector row, cone beam CT scanner.

    PubMed

    Geleijns, J; Salvadó Artells, M; de Bruin, P W; Matter, R; Muramatsu, Y; McNitt-Gray, M F

    2009-05-21

    Computed tomography (CT) dosimetry should be adapted to the rapid developments in CT technology. Recently a 160 mm wide, 320 detector row, cone beam CT scanner that challenges the existing Computed Tomography Dose Index (CTDI) dosimetry paradigm was introduced. The purpose of this study was to assess dosimetric characteristics of this cone beam scanner, to study the appropriateness of existing CT dose metrics and to suggest a pragmatic approach for CT dosimetry for cone beam scanners. Dose measurements with a small Farmer-type ionization chamber and with 100 mm and 300 mm long pencil ionization chambers were performed free in air to characterize the cone beam. According to the most common dose metric in CT, namely CTDI, measurements were also performed in 150 mm and 350 mm long CT head and CT body dose phantoms with 100 mm and 300 mm long pencil ionization chambers, respectively. To explore effects that cannot be measured with ionization chambers, Monte Carlo (MC) simulations of the dose distribution in 150 mm, 350 mm and 700 mm long CT head and CT body phantoms were performed. To overcome inconsistencies in the definition of CTDI100 for the 160 mm wide cone beam CT scanner, doses were also expressed as the average absorbed dose within the pencil chamber (D100). Measurements free in air revealed excellent correspondence between CTDI300air and D100air, while CTDI100air substantially underestimates CTDI300air. Results of measurements in CT dose phantoms and corresponding MC simulations at centre and peripheral positions were weighted and revealed good agreement between CTDI300w, D100w and CTDI600w, while CTDI100w substantially underestimates CTDI300w. D100w provides a pragmatic metric for characterizing the dose of the 160 mm wide cone beam CT scanner. This quantity can be measured with the widely available 100 mm pencil ionization chamber within 150 mm long CT dose phantoms. CTDI300w measured in 350 mm long CT dose phantoms serves as an appropriate standard of

  14. Auto calibration of a cone-beam-CT

    SciTech Connect

    Gross, Daniel; Heil, Ulrich; Schulze, Ralf; Schoemer, Elmar; Schwanecke, Ulrich

    2012-10-15

    Purpose: This paper introduces a novel autocalibration method for cone-beam-CTs (CBCT) or flat-panel CTs, assuming a perfect rotation. The method is based on ellipse-fitting. Autocalibration refers to accurate recovery of the geometric alignment of a CBCT device from projection images alone, without any manual measurements. Methods: The authors use test objects containing small arbitrarily positioned radio-opaque markers. No information regarding the relative positions of the markers is used. In practice, the authors use three to eight metal ball bearings (diameter of 1 mm), e.g., positioned roughly in a vertical line such that their projection image curves on the detector preferably form large ellipses over the circular orbit. From this ellipse-to-curve mapping and also from its inversion the authors derive an explicit formula. Nonlinear optimization based on this mapping enables them to determine the six relevant parameters of the system up to the device rotation angle, which is sufficient to define the geometry of a CBCT-machine assuming a perfect rotational movement. These parameters also include out-of-plane rotations. The authors evaluate their method by simulation based on data used in two similar approaches [L. Smekal, M. Kachelriess, S. E, and K. Wa, 'Geometric misalignment and calibration in cone-beam tomography,' Med. Phys. 31(12), 3242-3266 (2004); K. Yang, A. L. C. Kwan, D. F. Miller, and J. M. Boone, 'A geometric calibration method for cone beam CT systems,' Med. Phys. 33(6), 1695-1706 (2006)]. This allows a direct comparison of accuracy. Furthermore, the authors present real-world 3D reconstructions of a dry human spine segment and an electronic device. The reconstructions were computed from projections taken with a commercial dental CBCT device having two different focus-to-detector distances that were both calibrated with their method. The authors compare their reconstruction with a reconstruction computed by the manufacturer of the CBCT device to

  15. Auto calibration of a cone-beam-CT.

    PubMed

    Gross, Daniel; Heil, Ulrich; Schulze, Ralf; Schoemer, Elmar; Schwanecke, Ulrich

    2012-10-01

    This paper introduces a novel autocalibration method for cone-beam-CTs (CBCT) or flat-panel CTs, assuming a perfect rotation. The method is based on ellipse-fitting. Autocalibration refers to accurate recovery of the geometric alignment of a CBCT device from projection images alone, without any manual measurements. The authors use test objects containing small arbitrarily positioned radio-opaque markers. No information regarding the relative positions of the markers is used. In practice, the authors use three to eight metal ball bearings (diameter of 1 mm), e.g., positioned roughly in a vertical line such that their projection image curves on the detector preferably form large ellipses over the circular orbit. From this ellipse-to-curve mapping and also from its inversion the authors derive an explicit formula. Nonlinear optimization based on this mapping enables them to determine the six relevant parameters of the system up to the device rotation angle, which is sufficient to define the geometry of a CBCT-machine assuming a perfect rotational movement. These parameters also include out-of-plane rotations. The authors evaluate their method by simulation based on data used in two similar approaches [L. Smekal, M. Kachelriess, S. E, and K. Wa, "Geometric misalignment and calibration in cone-beam tomography," Med. Phys. 31(12), 3242-3266 (2004); K. Yang, A. L. C. Kwan, D. F. Miller, and J. M. Boone, "A geometric calibration method for cone beam CT systems," Med. Phys. 33(6), 1695-1706 (2006)]. This allows a direct comparison of accuracy. Furthermore, the authors present real-world 3D reconstructions of a dry human spine segment and an electronic device. The reconstructions were computed from projections taken with a commercial dental CBCT device having two different focus-to-detector distances that were both calibrated with their method. The authors compare their reconstruction with a reconstruction computed by the manufacturer of the CBCT device to demonstrate the

  16. Algorithm for x-ray beam hardening and scatter correction in low-dose cone-beam CT: phantom studies

    NASA Astrophysics Data System (ADS)

    Liu, Wenlei; Rong, Junyan; Gao, Peng; Liao, Qimei; Lu, HongBing

    2016-03-01

    X-ray scatter poses a significant limitation to image quality in cone-beam CT (CBCT), as well as beam hardening, resulting in image artifacts, contrast reduction, and lack of CT number accuracy. Meanwhile the x-ray radiation dose is also non-ignorable. Considerable scatter or beam hardening correction methods have been developed, independently, and rarely combined with low-dose CT reconstruction. In this paper, we combine scatter suppression with beam hardening correction for sparse-view CT reconstruction to improve CT image quality and reduce CT radiation. Firstly, scatter was measured, estimated, and removed using measurement-based methods, assuming that signal in the lead blocker shadow is only attributable to x-ray scatter. Secondly, beam hardening was modeled by estimating an equivalent attenuation coefficient at the effective energy, which was integrated into the forward projector of the algebraic reconstruction technique (ART). Finally, the compressed sensing (CS) iterative reconstruction is carried out for sparse-view CT reconstruction to reduce the CT radiation. Preliminary Monte Carlo simulated experiments indicate that with only about 25% of conventional dose, our method reduces the magnitude of cupping artifact by a factor of 6.1, increases the contrast by a factor of 1.4 and the CNR by a factor of 15. The proposed method could provide good reconstructed image from a few view projections, with effective suppression of artifacts caused by scatter and beam hardening, as well as reducing the radiation dose. With this proposed framework and modeling, it may provide a new way for low-dose CT imaging.

  17. Cone Beam CT Versus Multislice CT: Radiologic Diagnostic Agreement in the Postoperative Assessment of Cochlear Implantation.

    PubMed

    Razafindranaly, Victor; Truy, Eric; Pialat, Jean-Baptiste; Martinon, Amanda; Bourhis, Magali; Boublay, Nawele; Faure, Frédéric; Ltaïef-Boudrigua, Aïcha

    2016-10-01

    To evaluate the diagnostic concordance between multislice computed tomography (MSCT) and cone beam computed tomography (CBCT) in the early postoperative assessment of patients after cochlear implantation. Prospective, randomized, single-center, interventional, pilot study on the diagnostic performance of a medical device. Tertiary referral center. Patients aged over 18 years requiring a computed tomographic (CT) scan after cochlear implant surgery. Nine patients were implanted with electrode arrays from three different manufacturers, including one bilateral. High-resolution MSCT and CBCT were then performed, and two experienced radiologists blinded to the imaging modality evaluated the randomized images, twice. Concordance between MSCT and CBCT for assessing the scalar position (tympani or vestibuli) of the electrodes. Secondary outcome measures were also studied: length of the intracochlear electrode array, percentage of implanted cochlea, number of intracochlear electrodes, and radiation doses. There was a good agreement between both CT scanners in determining the scalar position and estimating the number of implanted electrodes and percentage of implanted cochlea. CBCT had a lower radiation exposure. The CBCT appears to be a useful tool for postoperative assessment of cochlear implanted adult patients and is comparable to the conventional scanner in determining the scalar position, with lower radiation exposure.

  18. Conversion coefficients for the estimation of effective dose in cone-beam CT

    PubMed Central

    Kim, Dong-Soo; Rashsuren, Oyuntugs

    2014-01-01

    Purpose To determine the conversion coefficients (CCs) from the dose-area product (DAP) value to effective dose in cone-beam CT. Materials and Methods A CBCT scanner with four fields of view (FOV) was used. Using two exposure settings of the adult standard and low dose exposure, DAP values were measured with a DAP meter in C mode (200mm×179 mm), P mode (154 mm×154 mm), I mode (102 mm×102 mm), and D mode (51 mm×51 mm). The effective doses were also investigated at each mode using an adult male head and neck phantom and thermoluminescent chips. Linear regressive analysis of the DAP and effective dose values was used to calculate the CCs for each CBCT examination. Results For the C mode, the P mode at the maxilla, and the P mode at the mandible, the CCs were 0.049 µSv/mGycm2, 0.067 µSv/mGycm2, and 0.064 µSv/mGycm2, respectively. For the I mode, the CCs at the maxilla and mandible were 0.076 µSv/mGycm2 and 0.095 µSv/mGycm2, respectively. For the D mode at the maxillary incisors, molars, and mandibular molars, the CCs were 0.038 µSv/mGycm2, 0.041 µSv/mGycm2, and 0.146 µSv/mGycm2, respectively. Conclusion The CCs in one CBCT device with fixed 80 kV ranged from 0.038 µSv/mGycm2 to 0.146 µSv/mGycm2 according to the imaging modes and irradiated region and were highest for the D mode at the mandibular molar. PMID:24701455

  19. Application of 70 kV Third-generation High-pitch Dual-source Coronary CT Angiography in Patients with Different Body Mass Index.

    PubMed

    Yi, Yan; Cao, Jian; Lin, Lu; Kong, Lingyan; Jiang, Shu; Li, Xiao; Liu, Peijun; Wang, Ming; Wang, Man; Wang, Yun; Jin, Zhengyu; Wang, Yining

    2017-02-20

    Objective  To investigate the optimized range of body mass index (BMI) selection for patients undergoing 70 kV high-pitch dual-source coronary CT angiography (CCTA) on the third-generation dual-source CT (DSCT). Methods  Patients undergoing prospective high-pitch ultra-low contrast media (CM) CCTA on the third-generation DSCT using the automatic tube voltage selection at 70 kV were included and divided into three groups:group A,with BMI≤24 kg/m(2);group B,with 24 kg/m(2)0.05). Subjective image quality in group A(Z=2.91,P=0.004) and B(Z=2.27,P=0.021) were both significantly better than that in group C. Conclusion  The ultra-low tube voltage (70 kV) combined with ultra-low CM CCTA protocol on third-generation high-pitch DSCT may be better for patients with BMI<28 kg/m2 than those with BMI ≥28 kg/m(2) in China.

  20. Dependence Of The Computerized Tomography (CT) Number - Electron Density Relationship On Patient Size And X-Ray Beam Filtration For Fan Beam CT Scanners

    NASA Astrophysics Data System (ADS)

    Masterson, M. E.; Thomason, C. L.; McGary, R.; Hunt, M. A.; Simpson, L. D.; Miller, D. W.; Laughlin, J. S.

    1981-07-01

    The applicability of quantitative information contained in CT scans to diagnostic radiology and to radiation therapy treatment planning and the heterogeneity problem has been recognized by members of the radiological community and by manufacturers. Determination of the relationship between electron density and CT number is important for these applications. As CT technology has evolved, CT number generation has changed. CT number variation was limited in the early water bag systems. However, later generation "air" scanners may exhibit variation in CT numbers across a reconstructed image which are re-lated to positioning within the scan circle and scan field size. Results of experimental investigations using tissue-equivalent phantoms of different cross-sectional shapes and areas on the Technicare Delta 2020 are presented. Investigations also cover the effect of "shaped" and "flat" x-ray beam filters. A variation in CT number is demonstrated on this fan beam geometry scanner for phantoms of different sizes and for different scan circle diameters. An explanation of these effects is given. Differences of as much as 20% in determination of tissue electron density relative to water under different experimental conditions are obtained and reported. A family of curves (electron density vs. CT number) is presented for different patient cross-sectional areas and different scanner settings.

  1. Intracranial physiological calcifications evaluated with cone beam CT

    PubMed Central

    Sedghizadeh, P P; Nguyen, M; Enciso, R

    2012-01-01

    Objectives The purpose of this study was to evaluate cone beam CT (CBCT) scans for the presence of physiological and pathological intracranial calcifications. Methods CBCT scans from male and female patients that met our ascertainment criteria were evaluated retrospectively (n = 500) for the presence of either physiological or pathological intracranial calcifications. Results Out of the 500 patients evaluated, 176 had evidence of intracranial physiological calcification (35.2% prevalence), and none had evidence of pathological calcification. There was a 3:2 male-to-female ratio and no ethnic predilection; the ages of affected patients ranged from 13 years to 82 years with a mean age of 52 years. The majority of calcifications appeared in the pineal/habenular region (80%), with some also appearing in the choroid plexus region bilaterally (12%), and a smaller subset appearing in the petroclinoid ligament region bilaterally (8%). Conclusions Intracranial physiological calcifications can be a common finding on CBCT scans, whereas pathological intracranial calcifications are rare. PMID:22842632

  2. Effective doses from cone beam CT investigation of the jaws

    PubMed Central

    Davies, J; Johnson, B; Drage, NA

    2012-01-01

    Objectives The purpose of the study was to calculate the effective dose delivered to the patient undergoing cone beam (CB) CT of the jaws and maxillofacial complex using the i-CAT Next Generation CBCT scanner (Imaging Sciences International, Hatfield, PA). Methods A RANDO® phantom (The Phantom Laboratory, Salem, NY) containing thermoluminence dosemeters were scanned 10 times for each of the 6 imaging protocols. Effective doses for each protocol were calculated using the 1990 and approved 2007 International Commission on Radiological Protection (ICRP) recommended tissue weighting factors (E1990, E2007). Results The effective dose for E1990 and E2007, respectively, were: full field of view (FOV) of the head, 47 μSv and 78 μSv; 13 cm scan of the jaws, 44 μSv and 77 μSv; 6 cm standard mandible, 35 μSv and 58 μSv; 6 cm high resolution mandible, 69 μSv and 113 μSv; 6 cm standard maxilla, 18 μSv and 32 μSv; and 6 cm high resolution maxilla, 35 μSv and 60 μSv. Conclusions Using the new generation of CBCT scanner, the effective dose is lower than the original generation machine for a similar FOV using the ICRP 2007 tissue weighting factors. PMID:22184626

  3. Effective dose span of ten different cone beam CT devices.

    PubMed

    Rottke, D; Patzelt, S; Poxleitner, P; Schulze, D

    2013-01-01

    Evaluation and reduction of dose are important issues. Since cone beam CT (CBCT) has been established now not just in dentistry, the number of acquired examinations continues to rise. Unfortunately, it is very difficult to compare the doses of available devices on the market owing to different exposition parameters, volumes and geometries. The aim of this study was to evaluate the spans of effective doses (EDs) of ten different CBCT devices. 48 thermoluminescent dosemeters were placed in 24 sites in a RANDO(®) head phantom. Protocols with lowest exposition parameters and protocols with highest exposition parameters were performed for each of the ten devices. The ED was calculated from the measured energy doses according to the International Commission on Radiological Protection 2007 recommendations for each protocol and device, and the statistical values were evaluated afterwards. The calculation of the ED resulted in values between 17.2 µSv and 396 µSv for the ten devices. The mean values for protocols with lowest and highest exposition parameters were 31.6 µSv and 209 µSv, respectively. It was not the aim of this study to evaluate the image quality depending on different exposition parameters but to define the spans of EDs in which different CBCT devices work. There is a wide span of ED for different CBCT devices depending on the selected exposition parameters, required spatial resolution and many other factors.

  4. Effective dose span of ten different cone beam CT devices

    PubMed Central

    Rottke, D; Patzelt, S; Poxleitner, P; Schulze, D

    2013-01-01

    Objectives: Evaluation and reduction of dose are important issues. Since cone beam CT (CBCT) has been established now not just in dentistry, the number of acquired examinations continues to rise. Unfortunately, it is very difficult to compare the doses of available devices on the market owing to different exposition parameters, volumes and geometries. The aim of this study was to evaluate the spans of effective doses (EDs) of ten different CBCT devices. Methods: 48 thermoluminescent dosemeters were placed in 24 sites in a RANDO® head phantom. Protocols with lowest exposition parameters and protocols with highest exposition parameters were performed for each of the ten devices. The ED was calculated from the measured energy doses according to the International Commission on Radiological Protection 2007 recommendations for each protocol and device, and the statistical values were evaluated afterwards. Results: The calculation of the ED resulted in values between 17.2 µSv and 396 µSv for the ten devices. The mean values for protocols with lowest and highest exposition parameters were 31.6 µSv and 209 µSv, respectively. Conclusions: It was not the aim of this study to evaluate the image quality depending on different exposition parameters but to define the spans of EDs in which different CBCT devices work. There is a wide span of ED for different CBCT devices depending on the selected exposition parameters, required spatial resolution and many other factors. PMID:23584925

  5. Streak artifact reduction in cardiac cone beam CT

    NASA Astrophysics Data System (ADS)

    Shechter, Gilad; Naveh, Galit; Lessick, Jonathan; Altman, Ami

    2005-04-01

    Cone beam reconstructed cardiac CT images suffer from characteristic streak artifacts that affect the quality of coronary artery imaging. These artifacts arise from inhomogeneous distribution of noise. While in non-tagged reconstruction inhomogeneity of noise distribution is mainly due to anisotropy of the attenuation of the scanned object (e.g. shoulders), in cardiac imaging it is largely influenced by the non-uniform distribution of the acquired data used for reconstructing the heart at a given phase. We use a cardiac adaptive filter to reduce these streaks. In difference to previous methods of adaptive filtering that locally smooth data points on the basis of their attenuation values, our filter is applied as a function of the noise distribution of the data as it is used in the phase selective reconstruction. We have reconstructed trans-axial images without adaptive filtering, with a regular adaptive filter and with the cardiac adaptive filter. With the cardiac adaptive filter significant reduction of streaks is achieved, and thus image quality is improved. The coronary vessel is much more pronounced in the cardiac adaptive filtered images, in slab MIP the main coronary artery branches are more visible, and non-calcified plaque is better differentiated from vessel wall. This improvement is accomplished without altering significantly the border definition of calcified plaques.

  6. Evaluation of patient dose using a virtual CT scanner: Applications to 4DCT simulation and Kilovoltage cone-beam imaging

    NASA Astrophysics Data System (ADS)

    DeMarco, J. J.; McNitt-Gray, M. F.; Cagnon, C. H.; Angel, E.; Agazaryan, N.; Zankl, M.

    2008-02-01

    This work evaluates the effects of patient size on radiation dose from simulation imaging studies such as four-dimensional computed tomography (4DCT) and kilovoltage cone-beam computed tomography (kV-CBCT). 4DCT studies are scans that include temporal information, frequently incorporating highly over-sampled imaging series necessary for retrospective sorting as a function of respiratory phase. This type of imaging study can result in a significant dose increase to the patient due to the slower table speed as compared with a conventional axial or helical scan protocol. Kilovoltage cone-beam imaging is a relatively new imaging technique that requires an on-board kilovoltage x-ray tube and a flat-panel detector. Instead of porting individual reference fields, the kV tube and flat-panel detector are rotated about the patient producing a cone-beam CT data set (kV-CBCT). To perform these investigations, we used Monte Carlo simulation methods with detailed models of adult patients and virtual source models of multidetector computed tomography (MDCT) scanners. The GSF family of three-dimensional, voxelized patient models, were implemented as input files using the Monte Carlo code MCNPX. The adult patient models represent a range of patient sizes and have all radiosensitive organs previously identified and segmented. Simulated 4DCT scans of each voxelized patient model were performed using a multi-detector CT source model that includes scanner specific spectra, bow-tie filtration, and helical source path. Standard MCNPX tally functions were applied to each model to estimate absolute organ dose based upon an air-kerma normalization measurement for nominal scanner operating parameters.

  7. Presentation of floating mass transducer and Vibroplasty couplers on CT and cone beam CT.

    PubMed

    Mlynski, Robert; Nguyen, Thi Dao; Plontke, Stefan K; Kösling, Sabrina

    2014-04-01

    Various titanium coupling elements, Vibroplasty Couplers, maintaining the attachment of the Floating Mass Transducer (FMT) of the active middle ear implant Vibrant Soundbridge (VSB) to the round window, the stapes suprastructure or the stapes footplate are in use to optimally transfer energy from the FMT to the inner ear fluids. In certain cases it is of interest to radiologically verify the correct position of the FMT coupler assembly. The imaging appearance of FMT connected to these couplers, however, is not well known. The aim of this study was to present the radiological appearance of correctly positioned Vibroplasty Couplers together with the FMT using two different imaging techniques. Vibroplasty Couplers were attached to the FMT of a Vibrant Soundbridge and implanted in formalin fixed human temporal bones. Five FMT coupler assemblies were implanted in different positions: conventionally to the incus, a Bell-Coupler, a CliP-Coupler, a Round Window-Coupler and an Oval Window-Coupler. High spatial resolution imaging with Multi-Detector CT (MDCT) and Cone Beam CT (CBCT) was performed in each specimen. Images were blind evaluated by two radiologists on a visual basis. Middle ear details, identification of FMT and coupler, position of FMT coupler assembly and artefacts were assessed. CBCT showed a better spatial resolution and a higher visual image quality than MDCT, but there was no significant advantage over MDCT in delineating the structures or the temporal bone of the FMT Coupler assemblies. The FMT with its coupler element could be clearly identified in the two imaging techniques. The correct positioning of the FMT and all types of couplers could be demonstrated. Both methods, MDCT and CBCT, are appropriate methods for postoperative localization of FMT in combination with Vibroplasty Couplers and for verifying their correct position. If CBCT is available, this method is recommended due to the better spatial resolution and less metal artifacts.

  8. Dedicated Cone-Beam Breast CT: Feasibility Study with Surgical Mastectomy Specimens

    PubMed Central

    Yang, Wei Tse; Carkaci, Selin; Chen, Lingyun; Lai, Chao-Jen; Sahin, Aysegul; Whitman, Gary J.; Shaw, Chris C.

    2010-01-01

    OBJECTIVE The purpose of this study was to investigate the feasibility of diagnostic breast imaging using a flat-panel detector-based cone-beam CT system. CONCLUSION Imaging of 12 mastectomy specimens was performed at 50–80 kVp with a voxel size of 145 or 290 μm. Our study shows that cone-beam breast CT images have exceptional tissue contrast and can potentially reduce examination time with comparable radiation dose. PMID:18029864

  9. Measurement of cone beam CT coincidence with megavoltage isocentre and image sharpness using the QUASAR™ Penta-Guide phantom

    NASA Astrophysics Data System (ADS)

    Sykes, J. R.; Lindsay, R.; Dean, C. J.; Brettle, D. S.; Magee, D. R.; Thwaites, D. I.

    2008-10-01

    For image-guided radiotherapy (IGRT) systems based on cone beam CT (CBCT) integrated into a linear accelerator, the reproducible alignment of imager to x-ray source is critical to the registration of both the x-ray-volumetric image with the megavoltage (MV) beam isocentre and image sharpness. An enhanced method of determining the CBCT to MV isocentre alignment using the QUASAR™ Penta-Guide phantom was developed which improved both precision and accuracy. This was benchmarked against our existing method which used software and a ball-bearing (BB) phantom provided by Elekta. Additionally, a method of measuring an image sharpness metric (MTF50) from the edge response function of a spherical air cavity within the Penta-Guide phantom was developed and its sensitivity was tested by simulating misalignments of the kV imager. Reproducibility testing of the enhanced Penta-Guide method demonstrated a systematic error of <0.2 mm when compared to the BB method with near equivalent random error (s = 0.15 mm). The mean MTF50 for five measurements was 0.278 ± 0.004 lp mm-1 with no applied misalignment. Simulated misalignments exhibited a clear peak in the MTF50 enabling misalignments greater than 0.4 mm to be detected. The Penta-Guide phantom can be used to precisely measure CBCT MV coincidence and image sharpness on CBCT-IGRT systems.

  10. Measurement of cone beam CT coincidence with megavoltage isocentre and image sharpness using the QUASAR Penta-Guide phantom.

    PubMed

    Sykes, J R; Lindsay, R; Dean, C J; Brettle, D S; Magee, D R; Thwaites, D I

    2008-10-07

    For image-guided radiotherapy (IGRT) systems based on cone beam CT (CBCT) integrated into a linear accelerator, the reproducible alignment of imager to x-ray source is critical to the registration of both the x-ray-volumetric image with the megavoltage (MV) beam isocentre and image sharpness. An enhanced method of determining the CBCT to MV isocentre alignment using the QUASAR Penta-Guide phantom was developed which improved both precision and accuracy. This was benchmarked against our existing method which used software and a ball-bearing (BB) phantom provided by Elekta. Additionally, a method of measuring an image sharpness metric (MTF(50)) from the edge response function of a spherical air cavity within the Penta-Guide phantom was developed and its sensitivity was tested by simulating misalignments of the kV imager. Reproducibility testing of the enhanced Penta-Guide method demonstrated a systematic error of <0.2 mm when compared to the BB method with near equivalent random error (s=0.15 mm). The mean MTF(50) for five measurements was 0.278+/-0.004 lp mm(-1) with no applied misalignment. Simulated misalignments exhibited a clear peak in the MTF(50) enabling misalignments greater than 0.4 mm to be detected. The Penta-Guide phantom can be used to precisely measure CBCT-MV coincidence and image sharpness on CBCT-IGRT systems.

  11. Image-Guided Radiotherapy (IGRT) for Prostate Cancer Comparing kV Imaging of Fiducial Markers With Cone Beam Computed Tomography (CBCT)

    SciTech Connect

    Barney, Brandon M.; Lee, R. Jeffrey; Handrahan, Diana; Welsh, Keith T.; Cook, J. Taylor; Sause, William T.

    2011-05-01

    Purpose: To present our single-institution experience with image-guided radiotherapy comparing fiducial markers and cone-beam computed tomography (CBCT) for daily localization of prostate cancer. Methods and Materials: From April 2007 to October 2008, 36 patients with prostate cancer received intensity-modulated radiotherapy with daily localization by use of implanted fiducials. Orthogonal kilovoltage (kV) portal imaging preceded all 1244 treatments. Cone-beam computed tomography images were also obtained before 286 treatments (23%). Shifts in the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) dimensions were made from kV fiducial imaging. Cone-beam computed tomography shifts based on soft tissues were recorded. Shifts were compared by use of Bland-Altman limits of agreement. Mean and standard deviation of absolute differences were also compared. A difference of 5 mm or less was acceptable. Subsets including start date, body mass index, and prostate size were analyzed. Results: Of 286 treatments, 81 (28%) resulted in a greater than 5.0-mm difference in one or more dimensions. Mean differences in the AP, SI, and LR dimensions were 3.4 {+-} 2.6 mm, 3.1 {+-} 2.7 mm, and 1.3 {+-} 1.6 mm, respectively. Most deviations occurred in the posterior (fiducials, 78%; CBCT, 59%), superior (79%, 61%), and left (57%, 63%) directions. Bland-Altman 95% confidence intervals were -4.0 to 9.3 mm for AP, -9.0 to 5.3 mm for SI, and -4.1 to 3.9 mm for LR. The percentages of shift agreements within {+-}5 mm were 72.4% for AP, 72.7% for SI, and 97.2% for LR. Correlation between imaging techniques was not altered by time, body mass index, or prostate size. Conclusions: Cone-beam computed tomography and kV fiducial imaging are similar; however, more than one-fourth of CBCT and kV shifts differed enough to affect target coverage. This was even more pronounced with smaller margins (3 mm). Fiducial imaging requires less daily physician input, is less time-consuming, and is

  12. Scatter correction for cone-beam CT in radiation therapy

    PubMed Central

    Zhu, Lei; Xie, Yaoqin; Wang, Jing; Xing, Lei

    2009-01-01

    Cone-beam CT (CBCT) is being increasingly used in modern radiation therapy for patient setup and adaptive replanning. However, due to the large volume of x-ray illumination, scatter becomes a rather serious problem and is considered as one of the fundamental limitations of CBCT image quality. Many scatter correction algorithms have been proposed in literature, while a standard practical solution still remains elusive. In radiation therapy, the same patient is scanned repetitively during a course of treatment, a natural question to ask is whether one can obtain the scatter distribution on the first day of treatment and then use the data for scatter correction in the subsequent scans on different days. To realize this scatter removal scheme, two technical pieces must be in place: (i) A strategy to obtain the scatter distribution in on-board CBCT imaging and (ii) a method to spatially match a prior scatter distribution with the on-treatment CBCT projection data for scatter subtraction. In this work, simple solutions to the two problems are provided. A partially blocked CBCT is used to extract the scatter distribution. The x-ray beam blocker has a strip pattern, such that partial volume can still be accurately reconstructed and the whole-field scatter distribution can be estimated from the detected signals in the shadow regions using interpolation∕extrapolation. In the subsequent scans, the patient transformation is determined using a rigid registration of the conventional CBCT and the prior partial CBCT. From the derived patient transformation, the measured scatter is then modified to adapt the new on-treatment patient geometry for scatter correction. The proposed method is evaluated using physical experiments on a clinical CBCT system. On the Catphan©600 phantom, the errors in Hounsfield unit (HU) in the selected regions of interest are reduced from about 350 to below 50 HU; on an anthropomorphic phantom, the error is reduced from 15.7% to 5.4%. The proposed

  13. Scatter correction for cone-beam CT in radiation therapy

    SciTech Connect

    Zhu Lei; Xie Yaoqin; Wang Jing; Xing Lei

    2009-06-15

    Cone-beam CT (CBCT) is being increasingly used in modern radiation therapy for patient setup and adaptive replanning. However, due to the large volume of x-ray illumination, scatter becomes a rather serious problem and is considered as one of the fundamental limitations of CBCT image quality. Many scatter correction algorithms have been proposed in literature, while a standard practical solution still remains elusive. In radiation therapy, the same patient is scanned repetitively during a course of treatment, a natural question to ask is whether one can obtain the scatter distribution on the first day of treatment and then use the data for scatter correction in the subsequent scans on different days. To realize this scatter removal scheme, two technical pieces must be in place: (i) A strategy to obtain the scatter distribution in on-board CBCT imaging and (ii) a method to spatially match a prior scatter distribution with the on-treatment CBCT projection data for scatter subtraction. In this work, simple solutions to the two problems are provided. A partially blocked CBCT is used to extract the scatter distribution. The x-ray beam blocker has a strip pattern, such that partial volume can still be accurately reconstructed and the whole-field scatter distribution can be estimated from the detected signals in the shadow regions using interpolation/extrapolation. In the subsequent scans, the patient transformation is determined using a rigid registration of the conventional CBCT and the prior partial CBCT. From the derived patient transformation, the measured scatter is then modified to adapt the new on-treatment patient geometry for scatter correction. The proposed method is evaluated using physical experiments on a clinical CBCT system. On the Catphan(c)600 phantom, the errors in Hounsfield unit (HU) in the selected regions of interest are reduced from about 350 to below 50 HU; on an anthropomorphic phantom, the error is reduced from 15.7% to 5.4%. The proposed method

  14. Accurate patient dosimetry of kilovoltage cone-beam CT in radiation therapy

    SciTech Connect

    Ding, George X.; Duggan, Dennis M.; Coffey, Charles W.

    2008-03-15

    The increased utilization of x-ray imaging in image-guided radiotherapy has dramatically improved the radiation treatment and the lives of cancer patients. Daily imaging procedures, such as cone-beam computed tomography (CBCT), for patient setup may significantly increase the dose to the patient's normal tissues. This study investigates the dosimetry from a kilovoltage (kV) CBCT for real patient geometries. Monte Carlo simulations were used to study the kV beams from a Varian on-board imager integrated into the Trilogy accelerator. The Monte Carlo calculated results were benchmarked against measurements and good agreement was obtained. The authors developed a novel method to calibrate Monte Carlo simulated beams with measurements using an ionization chamber in which the air-kerma calibration factors are obtained from an Accredited Dosimetry Calibration Laboratory. The authors have introduced a new Monte Carlo calibration factor, f{sub MCcal}, which is determined from the calibration procedure. The accuracy of the new method was validated by experiment. When a Monte Carlo simulated beam has been calibrated, the simulated beam can be used to accurately predict absolute dose distributions in the irradiated media. Using this method the authors calculated dose distributions to patient anatomies from a typical CBCT acquisition for different treatment sites, such as head and neck, lung, and pelvis. Their results have shown that, from a typical head and neck CBCT, doses to soft tissues, such as eye, spinal cord, and brain can be up to 8, 6, and 5 cGy, respectively. The dose to the bone, due to the photoelectric effect, can be as much as 25 cGy, about three times the dose to the soft tissue. The study provides detailed information on the additional doses to the normal tissues of a patient from a typical kV CBCT acquisition. The methodology of the Monte Carlo beam calibration developed and introduced in this study allows the user to calculate both relative and absolute

  15. 4D cone beam CT via spatiotemporal tensor framelet

    SciTech Connect

    Gao, Hao; Li, Ruijiang; Xing, Lei; Lin, Yuting

    2012-11-15

    Purpose: On-board 4D cone beam CT (4DCBCT) offers respiratory phase-resolved volumetric imaging, and improves the accuracy of target localization in image guided radiation therapy. However, the clinical utility of this technique has been greatly impeded by its degraded image quality, prolonged imaging time, and increased imaging dose. The purpose of this letter is to develop a novel iterative 4DCBCT reconstruction method for improved image quality, increased imaging speed, and reduced imaging dose. Methods: The essence of this work is to introduce the spatiotemporal tensor framelet (STF), a high-dimensional tensor generalization of the 1D framelet for 4DCBCT, to effectively take into account of highly correlated and redundant features of the patient anatomy during respiration, in a multilevel fashion with multibasis sparsifying transform. The STF-based algorithm is implemented on a GPU platform for improved computational efficiency. To evaluate the method, 4DCBCT full-fan scans were acquired within 30 s, with a gantry rotation of 200°; STF is also compared with a state-of-art reconstruction method via spatiotemporal total variation regularization. Results: Both the simulation and experimental results demonstrate that STF-based reconstruction achieved superior image quality. The reconstruction of 20 respiratory phases took less than 10 min on an NVIDIA Tesla C2070 GPU card. The STF codes are available at https://sites.google.com/site/spatiotemporaltensorframelet . Conclusions: By effectively utilizing the spatiotemporal coherence of the patient anatomy among different respiratory phases in a multilevel fashion with multibasis sparsifying transform, the proposed STF method potentially enables fast and low-dose 4DCBCT with improved image quality.

  16. Characterization and correction of beam-hardening artifacts during dynamic volume CT assessment of myocardial perfusion.

    PubMed

    Kitagawa, Kakuya; George, Richard T; Arbab-Zadeh, Armin; Lima, João A C; Lardo, Albert C

    2010-07-01

    To fully characterize beam-hardening effects caused by iodinated contrast medium in the left ventricular (LV) cavity and aorta in the assessment of myocardial perfusion at computed tomography (CT) and to validate a beam-hardening artifact correction algorithm that considers fluid-filled vessels and chambers important sources of beam hardening. The Johns Hopkins University animal care and use committee approved all procedures. An anatomically correct LV and myocardial phantom to characterize beam-hardening artifacts was designed. Following validation in the phantom, the beam-hardening correction (BHC) algorithm was applied to 256-detector row dynamic volume CT images in a canine ischemia model (n = 5) during adenosine stress, and the effect of beam hardening was determined by comparing regional dynamic volume CT perfusion metrics (myocardial upslope normalized by maximum LV blood pool attenuation) with microsphere-derived myocardial blood flow (MBF). A paired Student t test was used to compare continuous variables from the same subject but under different conditions, while linear regression analysis was performed to estimate the slope and statistical significance of the relationship between CT-derived perfusion metrics and microsphere-derived MBF. Beam-hardening artifacts were successfully reproduced in phantom studies and were eliminated with the BHC algorithm. The correlation coefficient of CT-derived perfusion metrics and microsphere-derived MBF improved from 0.60 to 0.74 (P > .05) following correction in the animal model. Beam-hardening artifacts confound dynamic volume CT assessment of myocardial perfusion. Application of the BHC algorithm is helpful for improving accuracy of myocardial perfusion at dynamic volume CT.

  17. Fast kilovoltage/megavoltage (kVMV) breathhold cone-beam CT for image-guided radiotherapy of lung cancer

    NASA Astrophysics Data System (ADS)

    Wertz, Hansjoerg; Stsepankou, Dzmitry; Blessing, Manuel; Rossi, Michael; Knox, Chris; Brown, Kevin; Gros, Uwe; Boda-Heggemann, Judit; Walter, Cornelia; Hesser, Juergen; Lohr, Frank; Wenz, Frederik

    2010-08-01

    Long image acquisition times of 60-120 s for cone-beam CT (CBCT) limit the number of patients with lung cancer who can undergo volume image guidance under breathhold. We developed a low-dose dual-energy kilovoltage-megavoltage-cone-beam CT (kVMV-CBCT) based on a clinical treatment unit reducing imaging time to <=15 s. Simultaneous kVMV-imaging was achieved by dedicated synchronization hardware controlling the output of the linear accelerator (linac) based on detector panel readout signals, preventing imaging artifacts from interference of the linac's MV-irradiation and panel readouts. Optimization was performed to minimize the imaging dose. Single MV-projections, reconstructed MV-CBCT images and images of simultaneous 90° kV- and 90° MV-CBCT (180° kVMV-CBCT) were acquired with different parameters. Image quality and imaging dose were evaluated and compared to kV-imaging. Hardware-based kVMV synchronization resulted in artifact-free projections. A combined 180° kVMV-CBCT scan with a total MV-dose of 5 monitor units was acquired in 15 s and with sufficient image quality. The resolution was 5-6 line pairs cm-1 (Catphan phantom). The combined kVMV-scan dose was equivalent to a kV-radiation scan dose of ~33 mGy. kVMV-CBCT based on a standard linac is promising and can provide ultra-fast online volume image guidance with low imaging dose and sufficient image quality for fast and accurate patient positioning for patients with lung cancer under breathhold.

  18. Imaging task-based optimal kV and mA selection for CT radiation dose reduction: from filtered backprojection (FBP) to statistical model based iterative reconstruction (MBIR)

    NASA Astrophysics Data System (ADS)

    Li, Ke; Gomez-Cardona, Daniel; Lubner, Meghan G.; Pickhardt, Perry J.; Chen, Guang-Hong

    2015-03-01

    Optimal selections of tube potential (kV) and tube current (mA) are essential in maximizing the diagnostic potential of a given CT technology while minimizing radiation dose. The use of a lower tube potential may improve image contrast, but may also require a significantly higher tube current to compensate for the rapid decrease of tube output at lower tube potentials. Therefore, the selection of kV and mA should take those kinds of constraints as well as the specific diagnostic imaging task in to consideration. For conventional quasi-linear CT systems employing linear filtered back-projection (FBP) image reconstruction algorithm, the optimization of kV-mA combinations are relatively straightforward, as neither spatial resolution nor noise texture has significant dependence on kV and mA settings. In these cases, zero-frequency analysis such as contrast-to-noise ratio (CNR) or normalized CNR by dose (CNRD) can be used for optimal kV-mA selection. The recently introduced statistical model-based iterative reconstruction (MBIR) method, however, has introduced new challenges to optimal kV and mA selection, as both spatial resolution and noise texture become closely correlated with kV and mA. In this work, a task-based approach based on modern signal detection theory and the corresponding frequency-dependent analysis has been proposed to perform the kV and mA optimization for both FBP and MBIR. By performing exhaustive measurements of task-based detectability index through the technically accessible kV-mA parameter space, iso-detectability contours were generated and overlaid on top of iso-dose contours, from which the kV-mA pair that minimize dose yet still achieving the desired detectability level can be identified.

  19. Single-slice reconstruction method for helical cone-beam differential phase-contrast CT.

    PubMed

    Fu, Jian; Chen, Liyuan

    2014-01-01

    X-ray phase-contrast computed tomography (PC-CT) can provide the internal structure information of biomedical specimens with high-quality cross-section images and has become an invaluable analysis tool. Here a simple and fast reconstruction algorithm is reported for helical cone-beam differential PC-CT (DPC-CT), which is called the DPC-CB-SSRB algorithm. It combines the existing CB-SSRB method of helical cone-beam absorption-contrast CT with the differential nature of DPC imaging. The reconstruction can be performed using 2D fan-beam filtered back projection algorithm with the Hilbert imaginary filter. The quality of the results for large helical pitches is surprisingly good. In particular, with this algorithm comparable quality is obtained using helical cone-beam DPC-CT data with a normalized pitch of 10 to that obtained using the traditional inter-row interpolation reconstruction with a normalized pitch of 2. This method will push the future medical helical cone-beam DPC-CT imaging applications.

  20. Dual-source multi-energy CT with triple or quadruple x-ray beams

    NASA Astrophysics Data System (ADS)

    Yu, Lifeng; Li, Zhoubo; Leng, Shuai; McCollough, Cynthia H.

    2016-03-01

    Energy-resolved photon-counting CT (PCCT) is promising for material decomposition with multi-contrast agents. However, corrections for non-idealities of PCCT detectors are required, which are still active research areas. In addition, PCCT is associated with very high cost due to lack of mass production. In this work, we proposed an alternative approach to performing multi-energy CT, which was achieved by acquiring triple or quadruple x-ray beam measurements on a dual-source CT scanner. This strategy was based on a "Twin Beam" design on a single-source scanner for dual-energy CT. Examples of beam filters and spectra for triple and quadruple x-ray beam were provided. Computer simulation studies were performed to evaluate the accuracy of material decomposition for multi-contrast mixtures using both tri-beam and quadruple-beam configurations. The proposed strategy can be readily implemented on a dual-source scanner, which may allow material decomposition of multi-contrast agents to be performed on clinical CT scanners with energy-integrating detector.

  1. Identification of dental root canals and their medial line from micro-CT and cone-beam CT records

    PubMed Central

    2012-01-01

    Background Shape of the dental root canal is highly patient specific. Automated identification methods of the medial line of dental root canals and the reproduction of their 3D shape can be beneficial for planning endodontic interventions as severely curved root canals or multi-rooted teeth may pose treatment challenges. Accurate shape information of the root canals may also be used by manufacturers of endodontic instruments in order to make more efficient clinical tools. Method Novel image processing procedures dedicated to the automated detection of the medial axis of the root canal from dental micro-CT and cone-beam CT records are developed. For micro-CT, the 3D model of the root canal is built up from several hundred parallel cross sections, using image enhancement, histogram based fuzzy c-means clustering, center point detection in the segmented slice, three dimensional inner surface reconstruction, and potential field driven curve skeleton extraction in three dimensions. Cone-beam CT records are processed with image enhancement filters and fuzzy chain based regional segmentation, followed by the reconstruction of the root canal surface and detecting its skeleton via a mesh contraction algorithm. Results The proposed medial line identification and root canal detection algorithms are validated on clinical data sets. 25 micro-CT and 36 cone-beam-CT records are used in the validation procedure. The overall success rate of the automatic dental root canal identification was about 92% in both procedures. The algorithms proved to be accurate enough for endodontic therapy planning. Conclusions Accurate medial line identification and shape detection algorithms of dental root canal have been developed. Different procedures are defined for micro-CT and cone-beam CT records. The automated execution of the subsequent processing steps allows easy application of the algorithms in the dental care. The output data of the image processing procedures is suitable for mathematical

  2. Beam hardening and smoothing correction effects on performance of micro-ct SkyScan 1173 for imaging low contrast density materials

    NASA Astrophysics Data System (ADS)

    Sriwayu, Wa Ode; Haryanto, Freddy; Khotimah, Siti Nurul; Latief, Fourier Dzar Eljabbar

    2015-04-01

    We have designed and fabricated phantom mimicking breast cancer composition known as a region that has low contrast density. The used compositions are a microcalcifications, fatty tissues and tumor mass by using Al2O3, C27H46O, and hard nylon materials. Besides, phantom also has a part to calculate low cost criteria /CNR (Contrast to Noise Ratio). Uniformity will be measured at water distillation medium located in a part of phantom scale contrast. Phantom will be imaged by using micro ct-sky scan 1173 high energy type, and then also can be quantified CT number to examine SkyScan 1173 performance in imaging low contrast density materials. Evaluation of CT number is done at technique configuration parameter using voltage of 30 kV, exposure 0.160 mAs, and camera resolution 560x560 pixel, the effect of image quality to reconstruction process is evaluated by varying image processing parameters in the form of beam hardening corrections with amount of 25%, 66% and100% with each smoothing level S10,S2 and S7. To obtain the better high quality image, the adjustment of beam hardening correction should be 66% and smoothing level reach maximal value at level 10.

  3. Reducing radiation dose to the female breast during CT coronary angiography: A simulation study comparing breast shielding, angular tube current modulation, reduced kV, and partial angle protocols using an unknown-location signal-detectability metric

    SciTech Connect

    Rupcich, Franco; Gilat Schmidt, Taly; Badal, Andreu; Popescu, Lucretiu M.; Kyprianou, Iacovos

    2013-08-15

    Purpose: The authors compared the performance of five protocols intended to reduce dose to the breast during computed tomography (CT) coronary angiography scans using a model observer unknown-location signal-detectability metric.Methods: The authors simulated CT images of an anthropomorphic female thorax phantom for a 120 kV reference protocol and five “dose reduction” protocols intended to reduce dose to the breast: 120 kV partial angle (posteriorly centered), 120 kV tube-current modulated (TCM), 120 kV with shielded breasts, 80 kV, and 80 kV partial angle (posteriorly centered). Two image quality tasks were investigated: the detection and localization of 4-mm, 3.25 mg/ml and 1-mm, 6.0 mg/ml iodine contrast signals randomly located in the heart region. For each protocol, the authors plotted the signal detectability, as quantified by the area under the exponentially transformed free response characteristic curve estimator (A-caret{sub FE}), as well as noise and contrast-to-noise ratio (CNR) versus breast and lung dose. In addition, the authors quantified each protocol's dose performance as the percent difference in dose relative to the reference protocol achieved while maintaining equivalent A-caret{sub FE}.Results: For the 4-mm signal-size task, the 80 kV full scan and 80 kV partial angle protocols decreased dose to the breast (80.5% and 85.3%, respectively) and lung (80.5% and 76.7%, respectively) with A-caret{sub FE} = 0.96, but also resulted in an approximate three-fold increase in image noise. The 120 kV partial protocol reduced dose to the breast (17.6%) at the expense of increased lung dose (25.3%). The TCM algorithm decreased dose to the breast (6.0%) and lung (10.4%). Breast shielding increased breast dose (67.8%) and lung dose (103.4%). The 80 kV and 80 kV partial protocols demonstrated greater dose reductions for the 4-mm task than for the 1-mm task, and the shielded protocol showed a larger increase in dose for the 4-mm task than for the 1-mm task

  4. Region-of-interest image reconstruction with intensity weighting in circular cone-beam CT for image-guided radiation therapy.

    PubMed

    Cho, Seungryong; Pearson, Erik; Pelizzari, Charles A; Pan, Xiaochuan

    2009-04-01

    Imaging plays a vital role in radiation therapy and with recent advances in technology considerable emphasis has been placed on cone-beam CT (CBCT). Attaching a kV x-ray source and a flat panel detector directly to the linear accelerator gantry has enabled progress in target localization techniques, which can include daily CBCT setup scans for some treatments. However, with an increasing number of CT scans there is also an increasing concern for patient exposure. An intensity-weighted region-of-interest (IWROI) technique, which has the potential to greatly reduce CBCT dose, in conjunction with the chord-based backprojection-filtration (BPF) reconstruction algorithm, has been developed and its feasibility in clinical use is demonstrated in this article. A nonuniform filter is placed in the x-ray beam to create regions of two different beam intensities. In this manner, regions outside the target area can be given a reduced dose but still visualized with a lower contrast to noise ratio. Image artifacts due to transverse data truncation, which would have occurred in conventional reconstruction algorithms, are avoided and image noise levels of the low- and high-intensity regions are well controlled by use of the chord-based BPF reconstruction algorithm. The proposed IWROI technique can play an important role in image-guided radiation therapy.

  5. EGS_cbct: Simulation of a fan beam CT and RMI phantom for measured HU verification.

    PubMed

    van Eeden, Dete; du Plessis, Freek

    2016-10-01

    A mathematical 3D model of an existing computed tomography (CT) scanner was created and used in the EGSnrc-based BEAMnrc and egs_cbct Monte Carlo codes. Simulated transmission dose profiles of a RMI-465 phantom were analysed to verify Hounsfield numbers against measured data obtained from the CT scanner. The modelled CT unit is based on the design of a Toshiba Aquilion 16 LB CT scanner. As a first step, BEAMnrc simulated the X-ray tube, filters, and secondary collimation to obtain phase space data of the X-ray beam. A bowtie filter was included to create a more uniform beam intensity and to remove the beam hardening effects. In a second step the Interactive Data Language (IDL) code was used to build an EGSPHANT file that contained the RMI phantom which was used in egs_cbct simulations. After simulation a series of profiles were sampled from the detector model and the Feldkamp-Davis-Kress (FDK) algorithm was used to reconstruct transversal images. The results were tested against measured data obtained from CT scans. The egs_cbct code can be used for the simulation of a fan beam CT unit. The calculated bowtie filter ensured a uniform flux on the detectors. Good correlation between measured and simulated CT numbers was obtained. In principle, Monte Carlo codes such as egs_cbct can model a fan beam CT unit. After reconstruction, the images contained Hounsfield values comparable to measured data. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  6. Evaluation of the OSC-TV iterative reconstruction algorithm for cone-beam optical CT

    SciTech Connect

    Matenine, Dmitri Mascolo-Fortin, Julia; Goussard, Yves

    2015-11-15

    Purpose: The present work evaluates an iterative reconstruction approach, namely, the ordered subsets convex (OSC) algorithm with regularization via total variation (TV) minimization in the field of cone-beam optical computed tomography (optical CT). One of the uses of optical CT is gel-based 3D dosimetry for radiation therapy, where it is employed to map dose distributions in radiosensitive gels. Model-based iterative reconstruction may improve optical CT image quality and contribute to a wider use of optical CT in clinical gel dosimetry. Methods: This algorithm was evaluated using experimental data acquired by a cone-beam optical CT system, as well as complementary numerical simulations. A fast GPU implementation of OSC-TV was used to achieve reconstruction times comparable to those of conventional filtered backprojection. Images obtained via OSC-TV were compared with the corresponding filtered backprojections. Spatial resolution and uniformity phantoms were scanned and respective reconstructions were subject to evaluation of the modulation transfer function, image uniformity, and accuracy. The artifacts due to refraction and total signal loss from opaque objects were also studied. Results: The cone-beam optical CT data reconstructions showed that OSC-TV outperforms filtered backprojection in terms of image quality, thanks to a model-based simulation of the photon attenuation process. It was shown to significantly improve the image spatial resolution and reduce image noise. The accuracy of the estimation of linear attenuation coefficients remained similar to that obtained via filtered backprojection. Certain image artifacts due to opaque objects were reduced. Nevertheless, the common artifact due to the gel container walls could not be eliminated. Conclusions: The use of iterative reconstruction improves cone-beam optical CT image quality in many ways. The comparisons between OSC-TV and filtered backprojection presented in this paper demonstrate that OSC-TV can

  7. Evaluation of the OSC-TV iterative reconstruction algorithm for cone-beam optical CT.

    PubMed

    Matenine, Dmitri; Mascolo-Fortin, Julia; Goussard, Yves; Després, Philippe

    2015-11-01

    The present work evaluates an iterative reconstruction approach, namely, the ordered subsets convex (OSC) algorithm with regularization via total variation (TV) minimization in the field of cone-beam optical computed tomography (optical CT). One of the uses of optical CT is gel-based 3D dosimetry for radiation therapy, where it is employed to map dose distributions in radiosensitive gels. Model-based iterative reconstruction may improve optical CT image quality and contribute to a wider use of optical CT in clinical gel dosimetry. This algorithm was evaluated using experimental data acquired by a cone-beam optical CT system, as well as complementary numerical simulations. A fast GPU implementation of OSC-TV was used to achieve reconstruction times comparable to those of conventional filtered backprojection. Images obtained via OSC-TV were compared with the corresponding filtered backprojections. Spatial resolution and uniformity phantoms were scanned and respective reconstructions were subject to evaluation of the modulation transfer function, image uniformity, and accuracy. The artifacts due to refraction and total signal loss from opaque objects were also studied. The cone-beam optical CT data reconstructions showed that OSC-TV outperforms filtered backprojection in terms of image quality, thanks to a model-based simulation of the photon attenuation process. It was shown to significantly improve the image spatial resolution and reduce image noise. The accuracy of the estimation of linear attenuation coefficients remained similar to that obtained via filtered backprojection. Certain image artifacts due to opaque objects were reduced. Nevertheless, the common artifact due to the gel container walls could not be eliminated. The use of iterative reconstruction improves cone-beam optical CT image quality in many ways. The comparisons between OSC-TV and filtered backprojection presented in this paper demonstrate that OSC-TV can potentially improve the rendering of

  8. TU-EF-204-03: Task-Based KV and MAs Optimization for Radiation Dose Reduction in CT: From FBP to Statistical Model-Based Iterative Reconstruction (MBIR)

    SciTech Connect

    Gomez-Cardona, D; Li, K; Lubner, M G; Pickhardt, P J; Chen, G-H

    2015-06-15

    Purpose: The introduction of the highly nonlinear MBIR algorithm to clinical CT systems has made CNR an invalid metric for kV optimization. The purpose of this work was to develop a task-based framework to unify kV and mAs optimization for both FBP- and MBIR-based CT systems. Methods: The kV-mAs optimization was formulated as a constrained minimization problem: to select kV and mAs to minimize dose under the constraint of maintaining the detection performance as clinically prescribed. To experimentally solve this optimization problem, exhaustive measurements of detectability index (d’) for a hepatic lesion detection task were performed at 15 different mA levels and 4 kV levels using an anthropomorphic phantom. The measured d’ values were used to generate an iso-detectability map; similarly, dose levels recorded at different kV-mAs combinations were used to generate an iso-dose map. The iso-detectability map was overlaid on top of the iso-dose map so that for a prescribed detectability level d’, the optimal kV-mA can be determined from the crossing between the d’ contour and the dose contour that corresponds to the minimum dose. Results: Taking d’=16 as an example: the kV-mAs combinations on the measured iso-d’ line of MBIR are 80–150 (3.8), 100–140 (6.6), 120–150 (11.3), and 140–160 (17.2), where values in the parentheses are measured dose values. As a Result, the optimal kV was 80 and optimal mA was 150. In comparison, the optimal kV and mA for FBP were 100 and 500, which corresponded to a dose level of 24 mGy. Results of in vivo animal experiments were consistent with the phantom results. Conclusion: A new method to optimize kV and mAs selection has been developed. This method is applicable to both linear and nonlinear CT systems such as those using MBIR. Additional dose savings can be achieved by combining MBIR with this method. This work was partially supported by an NIH grant R01CA169331 and GE Healthcare. K. Li, D. Gomez-Cardona, M. G

  9. Dual-Source Multi-Energy CT with Triple or Quadruple X-ray Beams.

    PubMed

    Yu, Lifeng; Leng, Shuai; McCollough, Cynthia H

    2016-02-01

    Energy-resolved photon-counting CT (PCCT) is promising for material decomposition with multi-contrast agents. However, corrections for non-idealities of PCCT detectors are required, which are still active research areas. In addition, PCCT is associated with very high cost due to lack of mass production. In this work, we proposed an alternative approach to performing multi-energy CT, which was achieved by acquiring triple or quadruple x-ray beam measurements on a dual-source CT scanner. This strategy was based on a "Twin Beam" design on a single-source scanner for dual-energy CT. Examples of beam filters and spectra for triple and quadruple x-ray beam were provided. Computer simulation studies were performed to evaluate the accuracy of material decomposition for multi-contrast mixtures using a tri-beam configuration. The proposed strategy can be readily implemented on a dual-source scanner, which may allow material decomposition of multi-contrast agents to be performed on clinical CT scanners with energy-integrating detector.

  10. Metal Artifact Reduction for Polychromatic X-ray CT Based on a Beam-Hardening Corrector.

    PubMed

    Park, Hyoung Suk; Hwang, Dosik; Seo, Jin Keun

    2016-02-01

    This paper proposes a new method to correct beam hardening artifacts caused by the presence of metal in polychromatic X-ray computed tomography (CT) without degrading the intact anatomical images. Metal artifacts due to beam-hardening, which are a consequence of X-ray beam polychromaticity, are becoming an increasingly important issue affecting CT scanning as medical implants become more common in a generally aging population. The associated higher-order beam-hardening factors can be corrected via analysis of the mismatch between measured sinogram data and the ideal forward projectors in CT reconstruction by considering the known geometry of high-attenuation objects. Without prior knowledge of the spectrum parameters or energy-dependent attenuation coefficients, the proposed correction allows the background CT image (i.e., the image before its corruption by metal artifacts) to be extracted from the uncorrected CT image. Computer simulations and phantom experiments demonstrate the effectiveness of the proposed method to alleviate beam hardening artifacts.

  11. WE-D-9A-02: Automated Landmark-Guided CT to Cone-Beam CT Deformable Image Registration

    SciTech Connect

    Kearney, V; Gu, X; Chen, S; Jiang, L; Liu, H; Chiu, T; Yordy, J; Nedzi, L; Mao, W

    2014-06-15

    Purpose: The anatomical changes that occur between the simulation CT and daily cone-beam CT (CBCT) are investigated using an automated landmark-guided deformable image registration (LDIR) algorithm with simultaneous intensity correction. LDIR was designed to be accurate in the presence of tissue intensity mismatch and heavy noise contamination. Method: An auto-landmark generation algorithm was used in conjunction with a local small volume (LSV) gradient matching search engine to map corresponding landmarks between the CBCT and planning CT. The LSVs offsets were used to perform an initial deformation, generate landmarks, and correct local intensity mismatch. The landmarks act as stabilizing controlpoints in the Demons objective function. The accuracy of the LDIR algorithm was evaluated on one synthetic case with ground truth and data of ten head and neck cancer patients. The deformation vector field (DVF) accuracy was accessed using a synthetic case. The Root mean square error of the 3D canny edge (RMSECE), mutual information (MI), and feature similarity index metric (FSIM) were used to access the accuracy of LDIR on the patient data. The quality of the corresponding deformed contours was verified by an attending physician. Results: The resulting 90 percentile DVF error for the synthetic case was within 5.63mm for the original demons algorithm, 2.84mm for intensity correction alone, 2.45mm using controlpoints without intensity correction, and 1.48 mm for the LDIR algorithm. For the five patients the mean RMSECE of the original CT, Demons deformed CT, intensity corrected Demons CT, control-point stabilized deformed CT, and LDIR CT was 0.24, 0.26, 0.20, 0.20, and 0.16 respectively. Conclusion: LDIR is accurate in the presence of multimodal intensity mismatch and CBCT noise contamination. Since LDIR is GPU based it can be implemented with minimal additional strain on clinical resources. This project has been supported by a CPRIT individual investigator award RP11032.

  12. Assessment of non-invasive chronic fungal rhinosinusitis by cone beam CT: comparison with multidetector CT findings.

    PubMed

    Yamauchi, Tomohiko; Tani, Akiko; Yokoyama, Shuji; Ogawa, Hiroshi

    2017-08-09

    To investigate the accuracy of cone beam CT (CBCT) to diagnose non-invasive chronic fungal rhinosinusitis. Preoperative CT evaluation of non-invasive chronic fungal rhinosinusitis was performed by CBCT (3D Accuitomo 170(®)) and traditional multidetector CT (MDCT) (Aquilion 32(®)) in 13 and 38 patients with non-invasive chronic fungal maxillary sinusitis, respectively, in different facilities. Detection of intrasinus calcification was compared between these two groups. Detection of intrasinus calcification in patients with non-invasive chronic fungal maxillary sinusitis was higher in the MDCT group (84.2%) than the CBCT group (46.2%). CBCT is inferior to MDCT in detection of intrasinus calcification in patients with non-invasive chronic fungal maxillary sinusitis. CBCT is frequently used in the screening of the paranasal lesion, but it is not enough to evaluate non-invasive chronic fungal maxillary sinusitis alone. Retrospective study.

  13. Physical dose distribution due to multi-sliced kV X-ray beam in labeled tissue-like media: an experimental approach.

    PubMed

    Ghasemi, M; Kakuee, O R; Fathollahi, V; Shahvar, A; Mohati, M; Ghafoori, M

    2011-02-01

    Radiotherapy remains a major modality of cancer therapy. Thanks to high flux and high brilliance of synchrotron-generated X-ray, laboratory research with planar microscopically thin X-ray beam promise exciting new opportunities for treatment of cancer. High tolerance of normal tissues at doses up to several hundred Gy in a single dose fraction and preferential damage of tumors at very high doses have been uniquely observed in animal models exposed to microbeams. The fact that beams as thick as 0.68 mm could retain a part of these effects, opens the possibility that the required beam can be produced by high power X-ray tubes besides a dedicated synchrotron. Fortunately, dose distribution due to kilovolt X-rays could be enhanced by the introduction of high-Z contrast agents to tissue-like media. In this work, dose deposition in a phantom--partially loaded with Au and I as contrast agents--irradiated by multi-sliced kV X-ray beam was experimentally investigated in the peak and valley regions both on the surface and in the depth of phantom. The results of experimental dosimetry using Gaf-chromic films were compared with corresponding Monte-Carlo simulation. Relative reduction in the deposited dose in the peak regions downstream the area containing contrast agents in comparison with the adjacent areas was experimentally observed.

  14. Cone beam CT findings of retromolar canals: Report of cases and literature review

    PubMed Central

    Han, Sang-Sun

    2013-01-01

    A retromolar canal is an anatomical variation in the mandible. As it includes the neurovascular bundle, local anesthetic insufficiency can occur, and an injury of the retromolar canal during dental surgery in the mandible may result in excessive bleeding, paresthesia, and traumatic neuroma. Using imaging analysis software, we evaluated the cone-beam computed tomography (CT) images of two Korean patients who presented with retromolar canals. Retromolar canals were detectable on the sagittal and cross-sectional images of cone-beam CT, but not on the panoramic radiographs of the patients. Therefore, the clinician should pay particular attention to the identification of retromolar canals by preoperative radiographic examination, and additional cone beam CT scanning would be recommended. PMID:24380072

  15. Dynamic cone beam CT angiography of carotid and cerebral arteries using canine model

    SciTech Connect

    Cai Weixing; Zhao Binghui; Conover, David; Liu Jiangkun; Ning Ruola

    2012-01-15

    Purpose: This research is designed to develop and evaluate a flat-panel detector-based dynamic cone beam CT system for dynamic angiography imaging, which is able to provide both dynamic functional information and dynamic anatomic information from one multirevolution cone beam CT scan. Methods: A dynamic cone beam CT scan acquired projections over four revolutions within a time window of 40 s after contrast agent injection through a femoral vein to cover the entire wash-in and wash-out phases. A dynamic cone beam CT reconstruction algorithm was utilized and a novel recovery method was developed to correct the time-enhancement curve of contrast flow. From the same data set, both projection-based subtraction and reconstruction-based subtraction approaches were utilized and compared to remove the background tissues and visualize the 3D vascular structure to provide the dynamic anatomic information. Results: Through computer simulations, the new recovery algorithm for dynamic time-enhancement curves was optimized and showed excellent accuracy to recover the actual contrast flow. Canine model experiments also indicated that the recovered time-enhancement curves from dynamic cone beam CT imaging agreed well with that of an IV-digital subtraction angiography (DSA) study. The dynamic vascular structures reconstructed using both projection-based subtraction and reconstruction-based subtraction were almost identical as the differences between them were comparable to the background noise level. At the enhancement peak, all the major carotid and cerebral arteries and the Circle of Willis could be clearly observed. Conclusions: The proposed dynamic cone beam CT approach can accurately recover the actual contrast flow, and dynamic anatomic imaging can be obtained with high isotropic 3D resolution. This approach is promising for diagnosis and treatment planning of vascular diseases and strokes.

  16. CT based treatment planning system of proton beam therapy for ocular melanoma

    NASA Astrophysics Data System (ADS)

    Nakano, Takashi; Kanai, Tatsuaki; Furukawa, Shigeo; Shibayama, Kouichi; Sato, Sinichiro; Hiraoka, Takeshi; Morita, Shinroku; Tsujii, Hirohiko

    2003-09-01

    A computed tomography (CT) based treatment planning system of proton beam therapy was established specially for ocular melanoma treatment. A technique of collimated proton beams with maximum energy of 70 MeV are applied for treatment for ocular melanoma. The vertical proton beam line has a range modulator for spreading beams out, a multi-leaf collimator, an aperture, light beam localizer, field light, and X-ray verification system. The treatment planning program includes; eye model, selecting the best direction of gaze, designing the shape of aperture, determining the proton range and range modulation necessary to encompass the target volume, and indicating the relative positions of the eyes, beam center and creation of beam aperture. Tumor contours are extracted from CT/MRI images of 1 mm thickness by assistant by various information of fundus photography and ultrasonography. The CT image-based treatment system for ocular melanoma is useful for Japanese patients as having thick choroid membrane in terms of dose sparing to skin and normal organs in the eye. The characteristics of the system and merits/demerits were reported.

  17. Simulation of mammograms and tomosynthesis imaging with cone beam breast CT images

    NASA Astrophysics Data System (ADS)

    Han, Tao; Shaw, Chris C.; Chen, Lingyun; Lai, Chao-jen; Liu, Xinming; Wang, Tianpeng

    2008-03-01

    The use of mammography techniques for the screening and diagnosis of breast cancers has been limited by the overlapping of cancer symptoms with normal tissue structures. To overcome this problem, two methods have been developed and actively investigated recently: digital tomosynthesis mammography and cone beam breast CT. Comparison study with these three techniques will be helpful to understand their difference and further might be supervise the direction of breast imaging. This paper describes and discusses about a technique using a general-purpose PC cluster to develop a parallel computer simulation model to simulate mammograms and tomosynthesis imaging with cone beam CT images of a mastectomy breast specimen. The breast model used in simulating mammography and tomosynthesis was developed by re-scaling the CT numbers of cone beam CT images from 80kVp to 20 kev. The compression of breast was simulated by deformation of the breast model. Re-projection software with parallel computation was developed and used to compute projection images of this simulated compressed breast for a stationary detector and a linearly shifted x-ray source. The resulting images were then used to reconstruct tomosynthesis mammograms using shift-and-add algorithms. It was found that MCs in cone beam CT images were not visible in regular mammograms but faintly visible in tomosynthesis images. The scatter signal and noise property needs to be simulated and incorporated in the future.

  18. Point spread function modeling and image restoration for cone-beam CT

    NASA Astrophysics Data System (ADS)

    Zhang, Hua; Huang, Kui-Dong; Shi, Yi-Kai; Xu, Zhe

    2015-03-01

    X-ray cone-beam computed tomography (CT) has such notable features as high efficiency and precision, and is widely used in the fields of medical imaging and industrial non-destructive testing, but the inherent imaging degradation reduces the quality of CT images. Aimed at the problems of projection image degradation and restoration in cone-beam CT, a point spread function (PSF) modeling method is proposed first. The general PSF model of cone-beam CT is established, and based on it, the PSF under arbitrary scanning conditions can be calculated directly for projection image restoration without the additional measurement, which greatly improved the application convenience of cone-beam CT. Secondly, a projection image restoration algorithm based on pre-filtering and pre-segmentation is proposed, which can make the edge contours in projection images and slice images clearer after restoration, and control the noise in the equivalent level to the original images. Finally, the experiments verified the feasibility and effectiveness of the proposed methods. Supported by National Science and Technology Major Project of the Ministry of Industry and Information Technology of China (2012ZX04007021), Young Scientists Fund of National Natural Science Foundation of China (51105315), Natural Science Basic Research Program of Shaanxi Province of China (2013JM7003) and Northwestern Polytechnical University Foundation for Fundamental Research (JC20120226, 3102014KYJD022)

  19. Dual-Source Multi-Energy CT with Triple or Quadruple X-ray Beams

    PubMed Central

    Yu, Lifeng; Leng, Shuai; McCollough, Cynthia H.

    2016-01-01

    Energy-resolved photon-counting CT (PCCT) is promising for material decomposition with multi-contrast agents. However, corrections for non-idealities of PCCT detectors are required, which are still active research areas. In addition, PCCT is associated with very high cost due to lack of mass production. In this work, we proposed an alternative approach to performing multi-energy CT, which was achieved by acquiring triple or quadruple x-ray beam measurements on a dual-source CT scanner. This strategy was based on a “Twin Beam” design on a single-source scanner for dual-energy CT. Examples of beam filters and spectra for triple and quadruple x-ray beam were provided. Computer simulation studies were performed to evaluate the accuracy of material decomposition for multi-contrast mixtures using a tri-beam configuration. The proposed strategy can be readily implemented on a dual-source scanner, which may allow material decomposition of multi-contrast agents to be performed on clinical CT scanners with energy-integrating detector. PMID:27330237

  20. Region-of-interest reconstruction for a cone-beam dental CT with a circular trajectory

    NASA Astrophysics Data System (ADS)

    Hu, Zhanli; Zou, Jing; Gui, Jianbao; Zheng, Hairong; Xia, Dan

    2013-04-01

    Dental CT is the most appropriate and accurate device for preoperative evaluation of dental implantation. It can demonstrate the quantity of bone in three dimensions (3D), the location of important adjacent anatomic structures and the quality of available bone with minimal geometric distortion. Nevertheless, with the rapid increase of dental CT examinations, we are facing the problem of dose reduction without loss of image quality. In this work, backprojection-filtration (BPF) and Feldkamp-Davis-Kress (FDK) algorithm was applied to reconstruct the 3D full image and region-of-interest (ROI) image from complete and truncated circular cone-beam data respectively by computer-simulation. In addition, the BPF algorithm was evaluated based on the 3D ROI-image reconstruction from real data, which was acquired from our developed circular cone-beam prototype dental CT system. The results demonstrated that the ROI-image quality reconstructed from truncated data using the BPF algorithm was comparable to that reconstructed from complete data. The FDK algorithm, however, created artifacts while reconstructing ROI-image. Thus it can be seen, for circular cone-beam dental CT, reducing scanning angular range of the BPF algorithm used for ROI-image reconstruction are helpful for reducing the radiation dose and scanning time. Finally, an analytical method was developed for estimation of the ROI projection area on the detector before CT scanning, which would help doctors to roughly estimate the total radiation dose before the CT examination.

  1. Dosimetric feasibility of cone-beam CT-based treatment planning compared to CT-based treatment planning

    SciTech Connect

    Yoo, Sua . E-mail: sua.yoo@duke.edu; Yin, F.-F.

    2006-12-01

    Purpose: Cone-beam computed tomography (CBCT) images are currently used for positioning verification. However, it is yet unknown whether CBCT could be used in dose calculation for replanning in adaptive radiation therapy. This study investigates the dosimetric feasibility of CBCT-based treatment planning. Methods and Materials: Hounsfield unit (HU) values and profiles of Catphan, homogeneous/inhomogeneous phantoms, and various tissue regions of patients in CBCT images were compared to those in CT. The dosimetric consequence of the HU variation was investigated by comparing CBCT-based treatment plans to conventional CT-based plans for both phantoms and patients. Results: The maximum HU difference between CBCT and CT of Catphan was 34 HU in the Teflon. The differences in other materials were less than 10 HU. The profiles for the homogeneous phantoms in CBCT displayed reduced HU values up to 150 HU in the peripheral regions compared to those in CT. The scatter and artifacts in CBCT became severe surrounding inhomogeneous tissues with reduced HU values up to 200 HU. The MU/cGy differences were less than 1% for most phantom cases. The isodose distributions between CBCT-based and CT-based plans agreed very well. However, the discrepancy was larger when CBCT was scanned without a bowtie filter than with bowtie filter. Also, up to 3% dosimetric error was observed in the plans for the inhomogeneous phantom. In the patient studies, the discrepancies of isodose lines between CT-based and CBCT-based plans, both 3D and IMRT, were less than 2 mm. Again, larger discrepancy occurred for the lung cancer patients. Conclusion: This study demonstrated the feasibility of CBCT-based treatment planning. CBCT-based treatment plans were dosimetrically comparable to CT-based treatment plans. Dosimetric data in the inhomogeneous tissue regions should be carefully validated.

  2. Cone beam CT assisted re-treatment of class 3 invasive cervical resorption

    PubMed Central

    Krishnan, Unni; Moule, Alex J; Alawadhi, Abdulwahab

    2015-01-01

    Invasive cervical root resorption is an uncommon external root resorption which initiates at the cervical aspect of the tooth. This case report involves a case of cervical root resorption which was initially misdiagnosed and managed as cervical root caries. It was later diagnosed with cone beam CT and the lesion microsurgically removed and restored with resin modified glass ionomer cement. The importance of increasing awareness of this uncommon pathology and the role of cone beam CT in mapping the extent of the lesion is emphasised. PMID:25795743

  3. Single-scan scatter correction for cone-beam CT using a stationary beam blocker: a preliminary study

    NASA Astrophysics Data System (ADS)

    Niu, Tianye; Zhu, Lei

    2011-03-01

    The performance of cone-beam CT (CBCT) is greatly limited by scatter artifacts. The existing measurement-based methods have promising advantages as a standard scatter correction solution, except that they currently require multiple scans or moving the beam blocker during data acquisition to compensate for the missing primary data. These approaches are therefore unpractical in clinical applications. In this work, we propose a new measurement-based scatter correction method to achieve accurate reconstruction with one single scan and a stationary beam blocker, two seemingly incompatible features which enable simple and effective scatter correction without increase of scan time or patient dose. Based on CT reconstruction theory, we distribute the blocked areas over one projection where primary signals are considered to be redundant in a full scan. The CT image quality is not degraded even with primary loss. Scatter is accurately estimated by interpolation and scatter-corrected CT images are obtained using an FDK-based reconstruction. In a Monte Carlo simulation study, we first optimize the beam blocker geometry using projections on the Shepp-Logan phantom and then carry out a complete simulation of a CBCT scan on a water phantom. With the scatter-to-primary ratio around 1.0, our method reduces the CT number error from 293 to 2.9 Hounsfield unit (HU) around the phantom center. The proposed approach is further evaluated on a CBCT tabletop system. On the Catphan©600 phantom, the reconstruction error is reduced from 202 to 10 HU in the selected region of interest after the proposed correction.

  4. Comparison of cone-beam CT-guided and CT fluoroscopy-guided transthoracic needle biopsy of lung nodules.

    PubMed

    Rotolo, Nicola; Floridi, Chiara; Imperatori, Andrea; Fontana, Federico; Ierardi, Anna Maria; Mangini, Monica; Arlant, Veronica; De Marchi, Giuseppe; Novario, Raffaele; Dominioni, Lorenzo; Fugazzola, Carlo; Carrafiello, Gianpaolo

    2016-02-01

    To compare the diagnostic performance of cone-beam CT (CBCT)-guided and CT fluoroscopy (fluoro-CT)-guided technique for transthoracic needle biopsy (TNB) of lung nodules. The hospital records of 319 consecutive patients undergoing 324 TNBs of lung nodules in a single radiology unit in 2009-2013 were retrospectively evaluated. The newly introduced CBCT technology was used to biopsy 123 nodules; 201 nodules were biopsied by conventional fluoro-CT-guided technique. We assessed the performance of the two biopsy systems for diagnosis of malignancy and the radiation exposure. Nodules biopsied by CBCT-guided and by fluoro-CT-guided technique had similar characteristics: size, 20 ± 6.5 mm (mean ± standard deviation) vs. 20 ± 6.8 mm (p = 0.845); depth from pleura, 15 ± 15 mm vs. 15 ± 16 mm (p = 0.595); malignant, 60% vs. 66% (p = 0.378). After a learning period, the newly introduced CBCT-guided biopsy system and the conventional fluoro-CT-guided system showed similar sensitivity (95% and 92%), specificity (100% and 100%), accuracy for diagnosis of malignancy (96% and 94%), and delivered non-significantly different median effective doses [11.1 mSv (95 % CI 8.9-16.0) vs. 14.5 mSv (95% CI 9.5-18.1); p = 0.330]. The CBCT-guided and fluoro-CT-guided systems for lung nodule biopsy are similar in terms of diagnostic performance and effective dose, and may be alternatively used to optimize the available technological resources. • CBCT-guided and fluoro-CT-guided lung nodule biopsy provided high and similar diagnostic accuracy. • Effective dose from CBCT-guided and fluoro-CT-guided lung nodule biopsy was similar. • To optimize resources, CBCT-guided lung nodule biopsy may be an alternative to fluoro-CT-guided.

  5. A curve-filtered FDK (C-FDK) reconstruction algorithm for circular cone-beam CT.

    PubMed

    Li, Liang; Xing, Yuxiang; Chen, Zhiqiang; Zhang, Li; Kang, Kejun

    2011-01-01

    Circular cone-beam CT is one of the most popular configurations in both medical and industrial applications. The FDK algorithm is the most popular method for circular cone-beam CT. However, with increasing cone-angle the cone-beam artifacts associated with the FDK algorithm deteriorate because the circular trajectory does not satisfy the data sufficiency condition. Along with an experimental evaluation and verification, this paper proposed a curve-filtered FDK (C-FDK) algorithm. First, cone-parallel projections are rebinned from the native cone-beam geometry in two separate directions. C-FDK rebins and filters projections along different curves from T-FDK in the centrally virtual detector plane. Then, numerical experiments are done to validate the effectiveness of the proposed algorithm by comparing with both FDK and T-FDK reconstruction. Without any other extra trajectories supplemental to the circular orbit, C-FDK has a visible image quality improvement.

  6. Lifetime Measurements of High Polarization Strained-Superlattice Gallium Arsenide at Beam Current > 1 Milliamp using a New 100kV Load Lock Photogun

    SciTech Connect

    J. M. Grames; P. A. Adderley; J. Brittian; J. Clark; J. Hansknecht; D. Machie; M. Poelker; M. L. Stutzman; R. Suleiman; K. E. L. Surles-Law

    2007-08-01

    A new 100 kV GaAs DC Load Lock Photogun has been constructed at Jefferson Laboratory, with improvements for photocathode preparation and for operation in a high voltage, ultra-high vacuum environment. Although difficult to gauge directly, we believe that the new gun design has better vacuum conditions compared to the previous gun design, as evidenced by longer photocathode lifetime, that is, the amount of charge extracted before the quantum efficiency of the photocathode drops by 1/e of the initial value via the ion back-bombardment mechanism. Photocathode lifetime measurements at DC beam intensity of up to 10 mA have been performed to benchmark operation of the new gun and for fundamental studies of the use of GaAs photocathodes at high average current*. These measurements demonstrate photocathode lifetime longer than one million Coulombs per square centimeter at a beam intensity higher than 1 mA. The photogun has been reconfigured with a high polarization strained superlattice photocathode (GaAs/GaAsP) and a mode-locked Ti:Sapphire laser operating near band-gap. Photocathode lifetime measurements at beam intensity greater than 1 mA are measured and presented for comparison.

  7. Region-of-interest image reconstruction in circular cone-beam microCT

    SciTech Connect

    Cho, Seungryong; Bian, Junguo; Pelizzari, Charles A.; Chen, C.-T.; He, T.-C.; Pan Xiaochuan

    2007-12-15

    Cone-beam microcomputed tomography (microCT) is one of the most popular choices for small animal imaging which is becoming an important tool for studying animal models with transplanted diseases. Region-of-interest (ROI) imaging techniques in CT, which can reconstruct an ROI image from the projection data set of the ROI, can be used not only for reducing imaging-radiation exposure to the subject and scatters to the detector but also for potentially increasing spatial resolution of the reconstructed images. Increasing spatial resolution in microCT images can facilitate improved accuracy in many assessment tasks. A method proposed previously for increasing CT image spatial resolution entails the exploitation of the geometric magnification in cone-beam CT. Due to finite detector size, however, this method can lead to data truncation for a large geometric magnification. The Feldkamp-Davis-Kress (FDK) algorithm yields images with artifacts when truncated data are used, whereas the recently developed backprojection filtration (BPF) algorithm is capable of reconstructing ROI images without truncation artifacts from truncated cone-beam data. We apply the BPF algorithm to reconstructing ROI images from truncated data of three different objects acquired by our circular cone-beam microCT system. Reconstructed images by use of the FDK and BPF algorithms from both truncated and nontruncated cone-beam data are compared. The results of the experimental studies demonstrate that, from certain truncated data, the BPF algorithm can reconstruct ROI images with quality comparable to that reconstructed from nontruncated data. In contrast, the FDK algorithm yields ROI images with truncation artifacts. Therefore, an implication of the studies is that, when truncated data are acquired with a configuration of a large geometric magnification, the BPF algorithm can be used for effective enhancement of the spatial resolution of a ROI image.

  8. Comparison of full-scan and half-scan for cone beam breast CT imaging

    NASA Astrophysics Data System (ADS)

    Chen, Lingyun; Shaw, Chris C.; Lai, Chao-jen; Altunbas, Mustafa C.; Wang, Tianpeng; Tu, Shu-ju; Liu, Xinming

    2006-03-01

    The half-scan cone beam technique, requiring a scan for 180° plus detector width only, can help achieve both shorter scan time as well as higher exposure in each individual projection image. This purpose of this paper is to investigate whether half-scan cone beam CT technique can provide acceptable images for clinical application. The half-scan cone beam reconstruction algorithm uses modified Parker's weighting function and reconstructs from slightly more than half of the projection views for full-scan, giving out promising results. A rotation phantom, stationary gantry bench top system was built to conduct experiments to evaluate half-scan cone beam breast CT technique. A post-mastectomy breast specimen, a stack of lunch meat slices embedded with various sizes of calcifications and a polycarbonate phantom inserted with glandular and adipose tissue equivalents are imaged and reconstructed for comparison study. A subset of full-scan projection images of a mastectomy specimen were extracted and used as the half-scan projection data for reconstruction. The results show half-scan reconstruction algorithm for cone beam breast CT images does not significantly degrade image quality when compared with the images of same or even half the radiation dose level. Our results are encouraging, emphasizing the potential advantages in the use of half-scan technique for cone beam breast imaging.

  9. SU-E-I-15: Quantitative Evaluation of Dose Distributions From Axial, Helical and Cone-Beam CT Imaging by Measurement Using a Two-Dimensional Diode-Array Detector

    SciTech Connect

    Chacko, M; Aldoohan, S; Sonnad, J; Ahmad, S; Ali, I

    2015-06-15

    Purpose: To evaluate quantitatively dose distributions from helical, axial and cone-beam CT clinical imaging techniques by measurement using a two-dimensional (2D) diode-array detector. Methods: 2D-dose distributions from selected clinical protocols used for axial, helical and cone-beam CT imaging were measured using a diode-array detector (MapCheck2). The MapCheck2 is composed from solid state diode detectors that are arranged in horizontal and vertical lines with a spacing of 10 mm. A GE-Light-Speed CT-simulator was used to acquire axial and helical CT images and a kV on-board-imager integrated with a Varian TrueBeam-STx machine was used to acquire cone-beam CT (CBCT) images. Results: The dose distributions from axial, helical and cone-beam CT were non-uniform over the region-of-interest with strong spatial and angular dependence. In axial CT, a large dose gradient was measured that decreased from lateral sides to the middle of the phantom due to large superficial dose at the side of the phantom in comparison with larger beam attenuation at the center. The dose decreased at the superior and inferior regions in comparison to the center of the phantom in axial CT. An asymmetry was found between the right-left or superior-inferior sides of the phantom which possibly to angular dependence in the dose distributions. The dose level and distribution varied from one imaging technique into another. For the pelvis technique, axial CT deposited a mean dose of 3.67 cGy, helical CT deposited a mean dose of 1.59 cGy, and CBCT deposited a mean dose of 1.62 cGy. Conclusions: MapCheck2 provides a robust tool to measure directly 2D-dose distributions for CT imaging with high spatial resolution detectors in comparison with ionization chamber that provides a single point measurement or an average dose to the phantom. The dose distributions measured with MapCheck2 consider medium heterogeneity and can represent specific patient dose.

  10. SU-E-J-99: Reconstruction of Cone Beam CT Image Using Volumetric Modulated Arc Therapy Exit Beams

    SciTech Connect

    Jeong, K; Goddard, L; Savacool, M; Mynampati, D; Godoy Scripes, P; Tome', W; Kuo, H; Basavatia, A; Hong, L; Yaparpalvi, R; Kalnicki, S

    2014-06-01

    Purpose: To test the possibility of obtaining an image of the treated volume during volumetric modulated arc therapy (VMAT) with exit beams. Method: Using a Varian Clinac 21EX and MVCT detector the following three sets of detector projection data were obtained for cone beam CT reconstruction with and without a Catphan 504 phantom. 1) 72 projection images from 20 × 16 cm{sup 2} open beam with 3 MUs, 2) 72 projection images from 20 × 16 cm{sup 2} MLC closed beam with 14 MUs. 3) 137 projection images from a test RapicArc QA plan. All projection images were obtained in ‘integrated image’ mode. We used OSCaR code to reconstruct the cone beam CT images. No attempts were made to reduce scatter or artifacts. Results: With projection set 1) we obtained a good quality MV CBCT image by optimizing the reconstruction parameters. Using projection set 2) we were not able to obtain a CBCT image of the phantom, which was determined to be due to the variation of interleaf leakage with gantry angle. From projection set 3), we were able to obtain a weak but meaningful signal in the image, especially in the target area where open beam signals were dominant. This finding suggests that one might be able to acquire CBCT images with rough body shape and some details inside the irradiated target area. Conclusion: Obtaining patient images using the VMAT exit beam is challenging but possible. We were able to determine sources of image degradation such as gantry angle dependent interleaf leakage and beams with a large scatter component. We are actively working on improving image quality.

  11. The effect of beam purity and scanner complexity on proton CT accuracy.

    PubMed

    Piersimoni, P; Ramos-Méndez, J; Geoghegan, T; Bashkirov, V A; Schulte, R W; Faddegon, B A

    2017-01-01

    To determine the dependence of the accuracy in reconstruction of relative stopping power (RSP) with proton computerized tomography (pCT) scans on the purity of the proton beam and the technological complexity of the pCT scanner using standard phantoms and a digital representation of a pediatric patient. The Monte Carlo method was applied to simulate the pCT scanner, using both a pure proton beam (uniform 200 MeV mono-energetic, parallel beam) and the Northwestern Medicine Chicago Proton Center (NMCPC) clinical beam in uniform scanning mode. The accuracy of the simulation was validated with measurements performed at NMCPC including reconstructed RSP images obtained with a preclinical prototype pCT scanner. The pCT scanner energy detector was then simulated in three configurations of increasing complexity: an ideal totally absorbing detector, a single stage detector and a multi-stage detector. A set of 15 cm diameter water cylinders containing either water alone or inserts of different material, size, and position were simulated at 90 projection angles (4° steps) for the pure and clinical proton beams and the three pCT configurations. A pCT image of the head of a detailed digital pediatric phantom was also reconstructed from the simulated pCT scan with the prototype detector. The RSP error increased for all configurations for insert sizes under 7.5 mm in radius, with a sharp increase below 5 mm in radius, attributed to a limit in spatial resolution. The highest accuracy achievable using the current pCT calibration step phantom and reconstruction algorithm, calculated for the ideal case of a pure beam with totally absorbing energy detector, was 1.3% error in RSP for inserts of 5 mm radius or more, 0.7 mm in range for the 2.5 mm radius inserts, or better. When the highest complexity of the scanner geometry was introduced, some artifacts arose in the reconstructed images, particularly in the center of the phantom. Replacing the step phantom used for calibration with a

  12. Percutaneous Bone Biopsies: Comparison between Flat-Panel Cone-Beam CT and CT-Scan Guidance

    SciTech Connect

    Tselikas, Lambros Joskin, Julien; Roquet, Florian; Farouil, Geoffroy; Dreuil, Serge; Hakimé, Antoine Teriitehau, Christophe; Auperin, Anne; Baere, Thierry de Deschamps, Frederic

    2015-02-15

    PurposeThis study was designed to compare the accuracy of targeting and the radiation dose of bone biopsies performed either under fluoroscopic guidance using a cone-beam CT with real-time 3D image fusion software (FP-CBCT-guidance) or under conventional computed tomography guidance (CT-guidance).MethodsSixty-eight consecutive patients with a bone lesion were prospectively included. The bone biopsies were scheduled under FP-CBCT-guidance or under CT-guidance according to operating room availability. Thirty-four patients underwent a bone biopsy under FP-CBCT and 34 under CT-guidance. We prospectively compared the two guidance modalities for their technical success, accuracy, puncture time, and pathological success rate. Patient and physician radiation doses also were compared.ResultsAll biopsies were technically successful, with both guidance modalities. Accuracy was significantly better using FP-CBCT-guidance (3 and 5 mm respectively: p = 0.003). There was no significant difference in puncture time (32 and 31 min respectively, p = 0.51) nor in pathological results (88 and 88 % of pathological success respectively, p = 1). Patient radiation doses were significantly lower with FP-CBCT (45 vs. 136 mSv, p < 0.0001). The percentage of operators who received a dose higher than 0.001 mSv (dosimeter detection dose threshold) was lower with FP-CBCT than CT-guidance (27 vs. 59 %, p = 0.01).ConclusionsFP-CBCT-guidance for bone biopsy is accurate and reduces patient and operator radiation doses compared with CT-guidance.

  13. Cone-Beam CT Localization of Internal Target Volumes for Stereotactic Body Radiotherapy of Lung Lesions

    SciTech Connect

    Wang Zhiheng Wu, Q. Jackie; Marks, Lawrence B.; Larrier, Nicole; Yin Fangfang

    2007-12-01

    Purpose: In this study, we investigate a technique of matching internal target volumes (ITVs) in four-dimensional (4D) simulation computed tomography (CT) to the composite target volume in free-breathing on-board cone-beam (CB) CT. The technique is illustrated by using both phantom and patient cases. Methods and Materials: A dynamic phantom with a target ball simulating respiratory motion with various amplitude and cycle times was used to verify localization accuracy. The dynamic phantom was scanned using simulation CT with a phase-based retrospective sorting technique. The ITV was then determined based on 10 sets of sorted images. The size and epicenter of the ITV identified from 4D simulation CT images and the composite target volume identified from on-board CBCT images were compared to assess localization accuracy. Similarly, for two clinical cases of patients with lung cancer, ITVs defined from 4D simulation CT images and CBCT images were compared. Results: For the phantom, localization accuracy between the ITV in 4D simulation CT and the composite target volume in CBCT was within 1 mm, and ITV was within 8.7%. For patient cases, ITVs on simulation CT and CBCT were within 8.0%. Conclusion: This study shows that CBCT is a useful tool to localize ITV for targets affected by respiratory motion. Verification of the ITV from 4D simulation CT using on-board free-breathing CBCT is feasible for the target localization of lung tumors.

  14. ASSESSMENT OF EFFECTIVE DOSE FROM CONE BEAM CT IMAGING IN SPECT/CT EXAMINATION IN COMPARISON WITH OTHER MODALITIES.

    PubMed

    Tonkopi, Elena; Ross, Andrew A

    2016-12-01

    The aim of this study was to assess radiation dose from the cone beam computed tomography (CBCT) component of single photon emission tomography/computed tomography (SPECT/CT) examinations and to compare it with the radiopharmaceutical related dose as well as dose from multidetector computed tomography (MDCT). Effective dose (ED) from computed tomography (CT) was estimated using dose-length product values and anatomy-specific conversion factors. The contribution from the SPECT component was evaluated using ED per unit administered activity for the radiopharmaceuticals listed in the International Commission on Radiological Protection Publications 80 and 106. With the exception of cardiac studies (0.11 mSv), the CBCT dose (3.96-6.04 mSv) was similar to that from the radiopharmaceutical accounting for 29-56 % of the total ED from the examination. In comparison with MDCT examinations, the CBCT dose was 48 and 42 % lower for abdomen/pelvis and chest/abdomen/pelvis scans, respectively, while in the chest the CBCT scan resulted in higher dose (23 %). Radiation dose from the CT component should be taken into consideration when evaluating total SPECT/CT patient dose. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  15. The application of cone-beam CT in the aging of bone calluses: a new perspective?

    PubMed

    Cappella, A; Amadasi, A; Gaudio, D; Gibelli, D; Borgonovo, S; Di Giancamillo, M; Cattaneo, C

    2013-11-01

    In the forensic and anthropological fields, the assessment of the age of a bone callus can be crucial for a correct analysis of injuries in the skeleton. To our knowledge, the studies which have focused on this topic are mainly clinical and still leave much to be desired for forensic purposes, particularly in looking for better methods for aging calluses in view of criminalistic applications. This study aims at evaluating the aid cone-beam CT can give in the investigation of the inner structure of fractures and calluses, thus acquiring a better knowledge of the process of bone remodeling. A total of 13 fractures (three without callus formation and ten with visible callus) of known age from cadavers were subjected to radiological investigations with digital radiography (DR) (conventional radiography) and cone-beam CT with the major aim of investigating the differences between DR and tomographic images when studying the inner and outer structures of bone healing. Results showed how with cone-beam CT the structure of the callus is clearly visible with higher specificity and definition and much more information on mineralization in different sections and planes. These results could lay the foundation for new perspectives on bone callus evaluation and aging with cone-beam CT, a user-friendly and skillful technique which in some instances can also be used extensively on the living (e.g., in cases of child abuse) with reduced exposition to radiation.

  16. Fan-beam monochromatic x-ray CT using fluorescent x rays excited by synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Toyofuku, Fukai; Tokumori, Kenji; Kanda, Shigenobu; Higashida, Yoshiharu; Ohki, Masafumi; Cho, Tetsuji; Nishimura, Katsuyuki; Hyodo, Kazuyuki; Ando, Masami; Uyama, Chikao

    1999-10-01

    Monochromatic x-ray CT has several advantages over conventional CT, which utilizes bremsstrahlung white x-rays from an x-ray tube. Although various types of monochromatic x-ray CT systems using synchrotron radiation have been developed using a parallel x-ray beam for imaging of small samples with a high spatial resolution, imaging of large objects such as the human body have not been developed yet. We have developed a fan-beam monochromatic x-ray CT using fluorescent x-rays generated by irradiating metal targets by synchrotron radiation. A CdTe linear array detector of 512 mm sensitive width was used in the photon counting mode. We made phantom experiments using fluorescent x-rays ranging from 32 to 75 keV. Monochromatic x-ray CT images of a cylindrical lucite phantom filled with several contrast media have been obtained. Measured CT numbers are compared with linear attenuation coefficients, and they showed a good linearity over a wide range of contrast media concentrations.

  17. Cone beam CT in orthodontics: the current picture.

    PubMed

    Makdissi, Jimmy

    2013-03-01

    The introduction of cone beam computed tomography (CBCT) technology to dentistry and orthodontics revolutionized the diagnosis, treatment and monitoring of orthodontic patients. This review article discusses the use of CBCT in diagnosis and treatment planning in orthodontics. The steps required to install and operate a CBCT facility within the orthodontic practice as well as the challenges are highlighted. The available guidelines in relation to the clinical applications of CBCT in orthodontics are explored.

  18. Tetrahedron beam computed tomography (TBCT): a new design of volumetric CT system.

    PubMed

    Zhang, Tiezhi; Schulze, Derek; Xu, Xiaochao; Kim, Joshua

    2009-06-07

    Volumetric CT imaging systems usually comprise a point x-ray source and a 2D detector. Flat panel imager (FPI)-based cone beam CT (CBCT) has become an important online imaging modality for image-guided radiotherapy and intervention. However, due to excessive scatter photons and inferior detector performance, the image quality of current CBCT is significantly inferior to diagnostic fan-beam CT. We propose a novel tetrahedron beam computed tomography (TBCT) imaging system which consists of a linear scan x-ray source and a linear x-ray detector array. The linear x-ray tube and detector array are aligned perpendicular and parallel to the rotation plane, respectively. The x-ray beams are narrowly collimated into fan beams and focused on the linear detector array. The linear detector and linear x-ray source form a 'tetrahedron' volume instead of a 'cone' volume. TBCT is similar to CBCT in image reconstruction geometry; however, its image quality will be significantly superior to that of CBCT due to its scatter rejection mechanism and the use of high-performance discrete x-ray detectors. In this paper, we describe the design of the TBCT system for image-guided radiotherapy and some results of preliminary studies.

  19. Cone beam CT for diagnosis and treatment planning in trauma cases.

    PubMed

    Palomo, Leena; Palomo, J Martin

    2009-10-01

    Three-dimensional imaging offers many advantages in making diagnoses and planning treatment. This article focuses on cone beam CT (CBCT) for making diagnoses and planning treatment in trauma-related cases. CBCT equipment is smaller and less expensive than traditional medical CT equipment and is tailored to address challenges specific to the dentoalveolar environment. Like medical CT, CBCT offers a three-dimensional view that conventional two-dimensional dental radiography fails to provide. CBCT combines the strengths of medical CT with those of conventional dental radiography to accommodate unique diagnostic and treatment-planning applications that have particular utility in dentoalveolar trauma cases. CBCT is useful, for example, in identifying tooth fractures relative to surrounding alveolar bone, in determining alveolar fracture location and morphology, in analyzing ridge-defect height and width, and in imaging temporomandibular joints. Treatment-planning applications include those involving extraction of fractured teeth, placement of implants, exposure of impacted teeth, and analyses of airways.

  20. SU-E-J-32: Dosimetric Evaluation Based On Pre-Treatment Cone Beam CT for Spine Stereotactic Body Radiotherapy: Does Region of Interest Focus Matter?

    SciTech Connect

    Magnelli, A; Xia, P

    2015-06-15

    Purpose: Spine stereotactic body radiotherapy requires very conformal dose distributions and precise delivery. Prior to treatment, a KV cone-beam CT (KV-CBCT) is registered to the planning CT to provide image-guided positional corrections, which depend on selection of the region of interest (ROI) because of imperfect patient positioning and anatomical deformation. Our objective is to determine the dosimetric impact of ROI selections. Methods: Twelve patients were selected for this study with the treatment regions varied from C-spine to T-spine. For each patient, the KV-CBCT was registered to the planning CT three times using distinct ROIs: one encompassing the entire patient, a large ROI containing large bony anatomy, and a small target-focused ROI. Each registered CBCT volume, saved as an aligned dataset, was then sent to the planning system. The treated plan was applied to each dataset and dose was recalculated. The tumor dose coverage (percentage of target volume receiving prescription dose), maximum point dose to 0.03 cc of the spinal cord, and dose to 10% of the spinal cord volume (V10) for each alignment were compared to the original plan. Results: The average magnitude of tumor coverage deviation was 3.9%±5.8% with external contour, 1.5%±1.1% with large ROI, 1.3%±1.1% with small ROI. Spinal cord V10 deviation from plan was 6.6%±6.6% with external contour, 3.5%±3.1% with large ROI, and 1.2%±1.0% with small ROI. Spinal cord max point dose deviation from plan was: 12.2%±13.3% with external contour, 8.5%±8.4% with large ROI, and 3.7%±2.8% with small ROI. Conclusion: A small ROI focused on the target results in the smallest deviation from planned dose to target and cord although rotations at large distances from the targets were observed. It is recommended that image fusion during CBCT focus narrowly on the target volume to minimize dosimetric error. Improvement in patient setups may further reduce residual errors.

  1. Cone-Beam Computed Tomography (CBCT) Versus CT in Lung Ablation Procedure: Which is Faster?

    SciTech Connect

    Cazzato, Roberto Luigi Battistuzzi, Jean-Benoit Catena, Vittorio; Grasso, Rosario Francesco Zobel, Bruno Beomonte; Schena, Emiliano; Buy, Xavier Palussiere, Jean

    2015-10-15

    AimTo compare cone-beam CT (CBCT) versus computed tomography (CT) guidance in terms of time needed to target and place the radiofrequency ablation (RFA) electrode on lung tumours.Materials and MethodsPatients at our institution who received CBCT- or CT-guided RFA for primary or metastatic lung tumours were retrospectively included. Time required to target and place the RFA electrode within the lesion was registered and compared across the two groups. Lesions were stratified into three groups according to their size (<10, 10–20, >20 mm). Occurrences of electrode repositioning, repositioning time, RFA complications, and local recurrence after RFA were also reported.ResultsForty tumours (22 under CT, 18 under CBCT guidance) were treated in 27 patients (19 male, 8 female, median age 67.25 ± 9.13 years). Thirty RFA sessions (16 under CBCT and 14 under CT guidance) were performed. Multivariable linear regression analysis showed that CBCT was faster than CT to target and place the electrode within the tumour independently from its size (β = −9.45, t = −3.09, p = 0.004). Electrode repositioning was required in 10/22 (45.4 %) tumours under CT guidance and 5/18 (27.8 %) tumours under CBCT guidance. Pneumothoraces occurred in 6/14 (42.8 %) sessions under CT guidance and in 6/16 (37.5 %) sessions under CBCT guidance. Two recurrences were noted for tumours receiving CBCT-guided RFA (2/17, 11.7 %) and three after CT-guided RFA (3/19, 15.8 %).ConclusionCBCT with live 3D needle guidance is a useful technique for percutaneous lung ablation. Despite lesion size, CBCT allows faster lung RFA than CT.

  2. Influence of anatomical location on CT numbers in cone beam computed tomography.

    PubMed

    Oliveira, Matheus L; Tosoni, Guilherme M; Lindsey, David H; Mendoza, Kristopher; Tetradis, Sotirios; Mallya, Sanjay M

    2013-04-01

    To assess the influence of anatomical location on computed tomography (CT) numbers in mid- and full field of view (FOV) cone beam computed tomography (CBCT) scans. Polypropylene tubes with varying concentrations of dipotassium hydrogen phosphate (K₂HPO₄) solutions (50-1200 mg/mL) were imaged within the incisor, premolar, and molar dental sockets of a human skull phantom. CBCT scans were acquired using the NewTom 3G and NewTom 5G units. The CT numbers of the K₂HPO₄ phantoms were measured, and the relationship between CT numbers and K₂HPO₄ concentration was examined. The measured CT numbers of the K₂HPO₄ phantoms were compared between anatomical sites. At all six anatomical locations, there was a strong linear relationship between CT numbers and K₂HPO₄ concentration (R(2)>0.93). However, the absolute CT numbers varied considerably with the anatomical location. The relationship between CT numbers and object density is not uniform through the dental arch on CBCT scans. Copyright © 2013 Elsevier Inc. All rights reserved.

  3. Determination of size-specific exposure settings in dental cone-beam CT.

    PubMed

    Pauwels, Ruben; Jacobs, Reinhilde; Bogaerts, Ria; Bosmans, Hilde; Panmekiate, Soontra

    2017-01-01

    To estimate the possible reduction of tube output as a function of head size in dental cone-beam computed tomography (CBCT). A 16 cm PMMA phantom, containing a central and six peripheral columns filled with PMMA, was used to represent an average adult male head. The phantom was scanned using CBCT, with 0-6 peripheral columns having been removed in order to simulate varying head sizes. For five kV settings (70-90 kV), the mAs required to reach a predetermined image noise level was determined, and corresponding radiation doses were derived. Results were expressed as a function of head size, age, and gender, based on growth reference charts. The use of 90 kV consistently resulted in the largest relative dose reduction. A potential mAs reduction ranging from 7 % to 50 % was seen for the different simulated head sizes, showing an exponential relation between head size and mAs. An optimized exposure protocol based on head circumference or age/gender is proposed. A considerable dose reduction, through reduction of the mAs rather than the kV, is possible for small-sized patients in CBCT, including children and females. Size-specific exposure protocols should be clinically implemented. • Fixed exposure settings in CBCT results in overexposure for smaller patients • For children, considerable dose reduction is possible without compromising image quality • A reduction in mAs is more dose-efficient than a kV reduction • An optimized exposure protocol was proposed based on phantom measurements • This protocol should be validated in a clinical setting.

  4. An index of beam hardening artifact for two-dimensional cone-beam CT tomographic images: establishment and preliminary evaluation

    NASA Astrophysics Data System (ADS)

    Yuan, Fusong; Lv, Peijun; Yang, Huifang; Wang, Yong; Sun, Yuchun

    2015-07-01

    Objectives: Based on the pixel gray value measurements, establish a beam-hardening artifacts index of the cone-beam CT tomographic image, and preliminarily evaluate its applicability. Methods: The 5mm-diameter metal ball and resin ball were fixed on the light-cured resin base plate respectively, while four vitro molars were fixed above and below the ball, on the left and right respectively, which have 10mm distance with the metal ball. Then, cone beam CT was used to scan the fixed base plate twice. The same layer tomographic images were selected from the two data and imported into the Photoshop software. The circle boundary was built through the determination of the center and radius of the circle, according to the artifact-free images section. Grayscale measurement tools were used to measure the internal boundary gray value G0, gray value G1 and G2 of 1mm and 20mm artifacts outside the circular boundary, the length L1 of the arc with artifacts in the circular boundary, the circumference L2. Hardening artifacts index was set A = (G1 / G0) * 0.5 + (G2 / G1) * 0.4 + (L2 / L1) * 0.1. Then, the A values of metal and resin materials were calculated respectively. Results: The A value of cobalt-chromium alloy material is 1, and resin material is 0. Conclusion: The A value reflects comprehensively the three factors of hardening artifacts influencing normal oral tissue image sharpness of cone beam CT. The three factors include relative gray value, the decay rate and range of artifacts.

  5. Dynamic bowtie filter for cone-beam/multi-slice CT.

    PubMed

    Liu, Fenglin; Yang, Qingsong; Cong, Wenxiang; Wang, Ge

    2014-01-01

    A pre-patient attenuator ("bowtie filter" or "bowtie") is used to modulate an incoming x-ray beam as a function of the angle of the x-ray with respect to a patient to balance the photon flux on a detector array. While the current dynamic bowtie design is focused on fan-beam geometry, in this study we propose a methodology for dynamic bowtie design in multi-slice/cone-beam geometry. The proposed 3D dynamic bowtie is an extension of the 2D prior art. The 3D bowtie consists of a highly attenuating bowtie (HB) filled in with heavy liquid and a weakly attenuating bowtie (WB) immersed in the liquid of the HB. The HB targets a balanced flux distribution on a detector array when no object is in the field of view (FOV). The WB compensates for an object in the FOV, and hence is a scaled-down version of the object. The WB is rotated and translated in synchrony with the source rotation and patient translation so that the overall flux balance is maintained on the detector array. First, the mathematical models of different scanning modes are established for an elliptical water phantom. Then, a numerical simulation study is performed to compare the performance of the scanning modes in the cases of the water phantom and a patient cross-section without any bowtie and with a dynamic bowtie. The dynamic bowtie can equalize the numbers of detected photons in the case of the water phantom. In practical cases, the dynamic bowtie can effectively reduce the dynamic range of detected signals inside the FOV. Furthermore, the WB can be individualized using a 3D printing technique as the gold standard. We have extended the dynamic bowtie concept from 2D to 3D by using highly attenuating liquid and moving a scale-reduced negative copy of an object being scanned. Our methodology can be applied to reduce radiation dose and facilitate photon-counting detection.

  6. Dynamic Bowtie Filter for Cone-Beam/Multi-Slice CT

    PubMed Central

    Liu, Fenglin; Yang, Qingsong; Cong, Wenxiang; Wang, Ge

    2014-01-01

    A pre-patient attenuator (“bowtie filter” or “bowtie”) is used to modulate an incoming x-ray beam as a function of the angle of the x-ray with respect to a patient to balance the photon flux on a detector array. While the current dynamic bowtie design is focused on fan-beam geometry, in this study we propose a methodology for dynamic bowtie design in multi-slice/cone-beam geometry. The proposed 3D dynamic bowtie is an extension of the 2D prior art. The 3D bowtie consists of a highly attenuating bowtie (HB) filled in with heavy liquid and a weakly attenuating bowtie (WB) immersed in the liquid of the HB. The HB targets a balanced flux distribution on a detector array when no object is in the field of view (FOV). The WB compensates for an object in the FOV, and hence is a scaled-down version of the object. The WB is rotated and translated in synchrony with the source rotation and patient translation so that the overall flux balance is maintained on the detector array. First, the mathematical models of different scanning modes are established for an elliptical water phantom. Then, a numerical simulation study is performed to compare the performance of the scanning modes in the cases of the water phantom and a patient cross-section without any bowtie and with a dynamic bowtie. The dynamic bowtie can equalize the numbers of detected photons in the case of the water phantom. In practical cases, the dynamic bowtie can effectively reduce the dynamic range of detected signals inside the FOV. Furthermore, the WB can be individualized using a 3D printing technique as the gold standard. We have extended the dynamic bowtie concept from 2D to 3D by using highly attenuating liquid and moving a scale-reduced negative copy of an object being scanned. Our methodology can be applied to reduce radiation dose and facilitate photon-counting detection. PMID:25051067

  7. Evaluation of accuracy of 3D reconstruction images using multi-detector CT and cone-beam CT

    PubMed Central

    Kim, Mija; YI, Won-Jin; Heo, Min-Suk; Lee, Sam-Sun; Choi, Soon-Chul

    2012-01-01

    Purpose This study was performed to determine the accuracy of linear measurements on three-dimensional (3D) images using multi-detector computed tomography (MDCT) and cone-beam computed tomography (CBCT). Materials and Methods MDCT and CBCT were performed using 24 dry skulls. Twenty-one measurements were taken on the dry skulls using digital caliper. Both types of CT data were imported into OnDemand software and identification of landmarks on the 3D surface rendering images and calculation of linear measurements were performed. Reproducibility of the measurements was assessed using repeated measures ANOVA and ICC, and the measurements were statistically compared using a Student t-test. Results All assessments under the direct measurement and image-based measurements on the 3D CT surface rendering images using MDCT and CBCT showed no statistically difference under the ICC examination. The measurements showed no differences between the direct measurements of dry skull and the image-based measurements on the 3D CT surface rendering images (P>.05). Conclusion Three-dimensional reconstructed surface rendering images using MDCT and CBCT would be appropriate for 3D measurements. PMID:22474645

  8. Kv5, Kv6, Kv8, and Kv9 subunits: No simple silent bystanders

    PubMed Central

    2016-01-01

    Members of the electrically silent voltage-gated K+ (Kv) subfamilies (Kv5, Kv6, Kv8, and Kv9, collectively identified as electrically silent voltage-gated K+ channel [KvS] subunits) do not form functional homotetrameric channels but assemble with Kv2 subunits into heterotetrameric Kv2/KvS channels with unique biophysical properties. Unlike the ubiquitously expressed Kv2 subunits, KvS subunits show a more restricted expression. This raises the possibility that Kv2/KvS heterotetramers have tissue-specific functions, making them potential targets for the development of novel therapeutic strategies. Here, I provide an overview of the expression of KvS subunits in different tissues and discuss their proposed role in various physiological and pathophysiological processes. This overview demonstrates the importance of KvS subunits and Kv2/KvS heterotetramers in vivo and the importance of considering KvS subunits and Kv2/KvS heterotetramers in the development of novel treatments. PMID:26755771

  9. Analytical cone-beam reconstruction using a multi-source inverse geometry CT system

    NASA Astrophysics Data System (ADS)

    Yin, Zhye; De Man, Bruno; Pack, Jed

    2007-03-01

    In a 3rd generation CT system, a single source projects the entire field of view (FOV) onto a large detector opposite the source. In multi-source CT imaging, a multitude of sources sequentially project a part of the FOV on a much smaller detector. These sources may be distributed in both the trans-axial and axial directions in order to jointly cover the entire FOV. Scan data from multiple sources in the axial direction provide complementary information, which is not available in a conventional single-source CT system. In this work, an analytical 3D cone-beam reconstruction algorithm for multi-source CT is proposed. This approach has three distinctive features. First, multi-source data are re-binned transaxially to multiple offset third-generation datasets. Second, data points in sinograms from multiple source sets are either accepted or rejected for contribution to the backprojection of a given voxel. Third, instead of using a ramp filter, a Hilbert transform is combined with a parallel derivative to form the filtering mechanism. Phantom simulations are performed using a multi-source CT geometry and compared to conventional 3rd generation CT geometry. We show that multi-source CT can extend the axial scan coverage to 120mm without cone-beam artifacts, while a third-generation geometry results in compromised image quality at 60mm of axial coverage. Moreover, given that the cone-angle in the proposed geometry is limited to 7 degrees, there are no degrading effects such as the Heel effect and scattered radiation, unlike in a third-generation geometry with comparable coverage. An additional benefit is the uniform flux profile resulting in uniform image noise throughout the FOV and a uniform dose absorption profile.

  10. FFT and cone-beam CT reconstruction on graphics hardware

    NASA Astrophysics Data System (ADS)

    Després, Philippe; Sun, Mingshan; Hasegawa, Bruce H.; Prevrhal, Sven

    2007-03-01

    Graphics processing units (GPUs) are increasingly used for general purpose calculations. Their pipelined architecture can be exploited to accelerate various parallelizable algorithms. Medical imaging applications are inherently well suited to benefit from the development of GPU-based computational platforms. We evaluate in this work the potential of GPUs to improve the execution speed of two common medical imaging tasks, namely Fourier transforms and tomographic reconstructions. A two-dimensional fast Fourier transform (FFT) algorithm was GPU-implemented and compared, in terms of execution speed, to two popular CPU-based FFT routines. Similarly, the Feldkamp, David and Kress (FDK) algorithm for cone-beam tomographic reconstruction was implemented on the GPU and its performance compared to a CPU version. Different reconstruction strategies were employed to assess the performance of various GPU memory layouts. For the specific hardware used, GPU implementations of the FFT were up to 20 times faster than their CPU counterparts, but slower than highly optimized CPU versions of the algorithm. Tomographic reconstructions were faster on the GPU by a factor up to 30, allowing 256 3 voxel reconstructions of 256 projections in about 20 seconds. Overall, GPUs are an attractive alternative to other imaging-dedicated computing hardware like application-specific integrated circuits (ASICs) and field programmable gate arrays (FPGAs) in terms of cost, simplicity and versatility. With the development of simpler language extensions and programming interfaces, GPUs are likely to become essential tools in medical imaging.

  11. Noise suppression in scatter correction for cone-beam CT

    PubMed Central

    Zhu, Lei; Wang, Jing; Xing, Lei

    2009-01-01

    Scatter correction is crucial to the quality of reconstructed images in x-ray cone-beam computed tomography (CBCT). Most of existing scatter correction methods assume smooth scatter distributions. The high-frequency scatter noise remains in the projection images even after a perfect scatter correction. In this paper, using a clinical CBCT system and a measurement-based scatter correction, the authors show that a scatter correction alone does not provide satisfactory image quality and the loss of the contrast-to-noise ratio (CNR) of the scatter corrected image may overwrite the benefit of scatter removal. To circumvent the problem and truly gain from scatter correction, an effective scatter noise suppression method must be in place. They analyze the noise properties in the projections after scatter correction and propose to use a penalized weighted least-squares (PWLS) algorithm to reduce the noise in the reconstructed images. Experimental results on an evaluation phantom (Catphan©600) show that the proposed algorithm further reduces the reconstruction error in a scatter corrected image from 10.6% to 1.7% and increases the CNR by a factor of 3.6. Significant image quality improvement is also shown in the results on an anthropomorphic phantom, in which the global noise level is reduced and the local streaking artifacts around bones are suppressed. PMID:19378735

  12. Poster — Thur Eve — 06: Dose assessment of cone beam CT imaging protocols as part of SPECT/CT examinations

    SciTech Connect

    Tonkopi, E; Ross, AA

    2014-08-15

    Purpose: To assess radiation dose from the cone beam CT (CBCT) component of SPECT/CT studies and to compare with other CT examinations performed in our institution. Methods: We used an anthropomorphic chest phantom and the 6 cc ion chamber to measure entrance breast dose for several CBCT and diagnostic CT acquisition protocols. The CBCT effective dose was calculated with ImPACT software; the CT effective dose was evaluated from the DLP value and conversion factor, dependent on the anatomic region. The RADAR medical procedure radiation dose calculator was used to assess the nuclear medicine component of exam dose. Results: The entrance dose to the breast measured with the anthropomorphic phantom was 0.48 mGy and 9.41 mGy for cardiac and chest CBCT scans; and 4.59 mGy for diagnostic thoracic CT. The effective doses were 0.2 mSv, 3.2 mSv and 2.8 mSv respectively. For a small patient represented by the anthropomorphic phantom, the dose from the diagnostic CT was lower than from the CBCT scan, as a result of the exposure reduction options available on modern CT scanners. The CBCT protocols used the same fixed scanning techniques. The diagnostic CT dose based on the patient data was 35% higher than the phantom dose. For most SPECT/CT studies the dose from the CBCT component was comparable with the dose from the radiopharmaceutical. Conclusions: The patient radiation dose from the cone beam CT scan can be higher than that from a diagnostic CT and should be taken into consideration in evaluating total SPECT/CT patient dose.

  13. In vivo verification of proton beam path by using post-treatment PET/CT imaging

    SciTech Connect

    Hsi, Wen C.; Indelicato, Daniel J.; Vargas, Carlos; Duvvuri, Srividya; Li Zuofeng; Palta, Jatinder

    2009-09-15

    Purpose: The purpose of this study is to establish the in vivo verification of proton beam path by using proton-activated positron emission distributions. Methods: A total of 50 PET/CT imaging studies were performed on ten prostate cancer patients immediately after daily proton therapy treatment through a single lateral portal. The PET/CT and planning CT were registered by matching the pelvic bones, and the beam path of delivered protons was defined in vivo by the positron emission distribution seen only within the pelvic bones, referred to as the PET-defined beam path. Because of the patient position correction at each fraction, the marker-defined beam path, determined by the centroid of implanted markers seen in the post-treatment (post-Tx) CT, is used for the planned beam path. The angular variation and discordance between the PET- and marker-defined paths were derived to investigate the intrafraction prostate motion. For studies with large discordance, the relative location between the centroid and pelvic bones seen in the post-Tx CT was examined. The PET/CT studies are categorized for distinguishing the prostate motion that occurred before or after beam delivery. The post-PET CT was acquired after PET imaging to investigate prostate motion due to physiological changes during the extended PET acquisition. Results: The less than 2 deg. of angular variation indicates that the patient roll was minimal within the immobilization device. Thirty of the 50 studies with small discordance, referred as good cases, show a consistent alignment between the field edges and the positron emission distributions from the entrance to the distal edge. For those good cases, average displacements are 0.6 and 1.3 mm along the anterior-posterior (D{sub AP}) and superior-inferior (D{sub SI}) directions, respectively, with 1.6 mm standard deviations in both directions. For the remaining 20 studies demonstrating a large discordance (more than 6 mm in either D{sub AP} or D{sub SI}), 13

  14. TH-A-18C-06: A Scatter Elimination Scheme for Cone Beam CT Using An Oscillating Narrow Beam

    SciTech Connect

    Yan, H; Folkerts, M; Jia, X; Jiang, S; Xu, Y

    2014-06-15

    Purpose: While cone beam CT (CBCT) has been widely used in image guided radiation therapy, its low image quality, primarily caused by scattered x-rays, hinders advanced clinical applications, e.g., CBCT based on-line adaptive re-planning. We propose in this abstract a new scheme called oscillating narrow beam CBCT (ONB-CBCT) to eliminate scatter signals. Methods: ONB-CBCT consists of two major components. 1) Oscillating narrow beam (ONB) scan and 2) partitioned flat panel containing multiple individual detector strips and their own readouts. Both the beam oscillation and detector partition are along the superior-inferior (SI) direction. During data acquisition, at a given projection, the narrow beam sweep through the detector region, and different portions of the detector acquires projection data in synchrony with the narrow beam. ONB can be generated by a rotating slit collimator design with conventional tube with single focal spot, or by directly using a new source with multiple focal spots. A proof-of-principle study via Monte Carlo simulation is conducted to demonstrate the feasibility of ONB-CBCT. Results: As the beam becomes narrower, more and more scatter signals are eliminated. For the case with a bowtie filter and using 15 ONBs, the maximum and the average intensity error due to scatter are below 20 and 10 HU, respectively. Conclusion: ONB yields a narrowed exposure field at each snapshot and hence an inherently negligible scatter effect. Meanwhile, the individualized detector units guarantee high frame rate detection and hence a same large volume coverage as that in conventional CBCT. In summary, ONB-CBCT is a promising design to achieve high-quality CBCT imaging. This study is supported in part by NIH (1R01CA154747-01)

  15. MR cone-beam CT fusion image overlay for fluoroscopically guided percutaneous biopsies in pediatric patients.

    PubMed

    Thakor, Avnesh S; Patel, Premal A; Gu, Richard; Rea, Vanessa; Amaral, Joao; Connolly, Bairbre L

    2016-03-01

    Lesions only visible on magnetic resonance (MR) imaging cannot easily be targeted for image-guided biopsy using ultrasound or X-rays but instead require MR guidance with MR-compatible needles and long procedure times (acquisition of multiple MR sequences). We developed an alternative method for performing these difficult biopsies in a standard interventional suite, by fusing MR with cone-beam CT images. The MR cone-beam CT fusion image is then used as an overlay to guide a biopsy needle to the target area under live fluoroscopic guidance. Advantages of this technique include (i) the ability for it to be performed in a conventional interventional suite, (ii) three-dimensional planning of the needle trajectory using cross-sectional imaging, (iii) real-time fluoroscopic guidance for needle trajectory correction and (iv) targeting within heterogeneous lesions based on MR signal characteristics to maximize the potential biopsy yield.

  16. SU-E-J-135: Feasibility of Using Quantitative Cone Beam CT for Proton Adaptive Planning

    SciTech Connect

    Jingqian, W; Wang, Q; Zhang, X; Wen, Z; Zhu, X; Frank, S; Li, H; Tsui, T; Zhu, L; Wei, J

    2015-06-15

    Purpose: To investigate the feasibility of using scatter corrected cone beam CT (CBCT) for proton adaptive planning. Methods: Phantom study was used to evaluate the CT number difference between the planning CT (pCT), quantitative CBCT (qCBCT) with scatter correction and calibrated Hounsfield units using adaptive scatter kernel superposition (ASKS) technique, and raw CBCT (rCBCT). After confirming the CT number accuracy, prostate patients, each with a pCT and several sets of weekly CBCT, were investigated for this study. Spot scanning proton treatment plans were independently generated on pCT, qCBCT and rCBCT. The treatment plans were then recalculated on all images. Dose-volume-histogram (DVH) parameters and gamma analysis were used to compare between dose distributions. Results: Phantom study suggested that Hounsfield unit accuracy for different materials are within 20 HU for qCBCT and over 250 HU for rCBCT. For prostate patients, proton dose could be calculated accurately on qCBCT but not on rCBCT. When the original plan was recalculated on qCBCT, tumor coverage was maintained when anatomy was consistent with pCT. However, large dose variance was observed when patient anatomy change. Adaptive plan using qCBCT was able to recover tumor coverage and reduce dose to normal tissue. Conclusion: It is feasible to use qu antitative CBCT (qCBCT) with scatter correction and calibrated Hounsfield units for proton dose calculation and adaptive planning in proton therapy. Partly supported by Varian Medical Systems.

  17. Three-rooted premolar analyzed by high-resolution and cone beam CT.

    PubMed

    Marca, Caroline; Dummer, Paul M H; Bryant, Susan; Vier-Pelisser, Fabiana Vieira; Só, Marcus Vinicius Reis; Fontanella, Vania; Dutra, Vinicius D'avila; de Figueiredo, José Antonio Poli

    2013-07-01

    The aim of this study was to analyze the variations in canal and root cross-sectional area in three-rooted maxillary premolars between high-resolution computed tomography (μCT) and cone beam computed tomography (CBCT). Sixteen extracted maxillary premolars with three distinct roots and fully formed apices were scanned using μCT and CBCT. Photoshop CS software was used to measure root and canal cross-sectional areas at the most cervical and the most apical points of each root third in images obtained using the two tomographic computed (CT) techniques, and at 30 root sections equidistant from both root ends using μCT images. Canal and root areas were compared between each method using the Student t test for paired samples and 95 % confidence intervals. Images using μCT were sharper than those obtained using CBCT. There were statistically significant differences in mean area measurements of roots and canals between the μCT and CBCT techniques (P < 0.05). Root and canal areas had similar variations in cross-sectional μCT images and became proportionally smaller in a cervical to apical direction as the cementodentinal junction was approached, from where the area then increased apically. Although variation was similar in the roots and canals under study, CBCT produced poorer image details than μCT. Although CBCT is a strong diagnosis tool, it still needs improvement to provide accuracy in details of the root canal system, especially in cases with anatomical variations, such as the three-rooted maxillary premolars.

  18. Dental cone beam CT image quality possibly reduced by patient movement.

    PubMed

    Donaldson, K; O'Connor, S; Heath, N

    2013-01-01

    Patient artefacts in dental cone beam CT scans can happen for various reasons. These range from artefacts from metal restorations to movement. An audit was carried out in the Glasgow Dental Hospital analysing how many scans showed signs of "motion artefact", and then to assess if there was any correlation between patient age and movement artefacts. Specific age demographics were then analysed to see if these cohorts were at a higher risk of "movement artefacts".

  19. [The study of associated reconstruction using MV linear accelerator and cone-beam CT].

    PubMed

    Liu, Zun-gang; Zhao, Jun; Zhuang, Tian-ge

    2006-07-01

    In this paper, we proposed a new scan mode and image reconstruction method, which combines the data from both the linear accelerator and the cone-beam CT to reconstruct the volume with a limited rotation angle and low sampling rate. The classical filtered backprojection method and the iterative method are utilized to reconstruct the volume. The reconstruction results of the two methods are compared with each other with a relavant anlysis given here.

  20. SparseCT: interrupted-beam acquisition and sparse reconstruction for radiation dose reduction

    NASA Astrophysics Data System (ADS)

    Koesters, Thomas; Knoll, Florian; Sodickson, Aaron; Sodickson, Daniel K.; Otazo, Ricardo

    2017-03-01

    State-of-the-art low-dose CT methods reduce the x-ray tube current and use iterative reconstruction methods to denoise the resulting images. However, due to compromises between denoising and image quality, only moderate dose reductions up to 30-40% are accepted in clinical practice. An alternative approach is to reduce the number of x-ray projections and use compressed sensing to reconstruct the full-tube-current undersampled data. This idea was recognized in the early days of compressed sensing and proposals for CT dose reduction appeared soon afterwards. However, no practical means of undersampling has yet been demonstrated in the challenging environment of a rapidly rotating CT gantry. In this work, we propose a moving multislit collimator as a practical incoherent undersampling scheme for compressed sensing CT and evaluate its application for radiation dose reduction. The proposed collimator is composed of narrow slits and moves linearly along the slice dimension (z), to interrupt the incident beam in different slices for each x-ray tube angle (θ). The reduced projection dataset is then reconstructed using a sparse approach, where 3D image gradients are employed to enforce sparsity. The effects of the collimator slits on the beam profile were measured and represented as a continuous slice profile. SparseCT was tested using retrospective undersampling and compared against commercial current-reduction techniques on phantoms and in vivo studies. Initial results suggest that SparseCT may enable higher performance than current-reduction, particularly for high dose reduction factors.

  1. Can fan beam iCT accurately predict indirect decompression in MISS fusion procedures?

    PubMed

    Janssen, Insa; Lang, Gernot; Navarro-Ramirez, Rodrigo; Jada, Ajit; Berlin, Connor; Hilis, Aaron; Zubkov, Micaella; Gandevia, Lena; Härtl, Roger

    2017-08-07

    Recently, a novel mobile intraoperative fan-beam CT (iFBCT) was introduced, allowing for real time navigation and immediate intraoperative evaluation of neural decompression in spine surgery. This study sought to investigate whether intraoperatively assessed neural decompression during minimally invasive spine surgery (MISS) has a predictive value for clinical and radiographic outcome. A retrospective study of patients undergoing iCT-guided extreme lateral interbody fusion (XLIF) or transforaminal lumbar interbody fusion (TLIF) was conducted. Pre- (1) and intraoperative (after cage implantation; 2), postoperative (3), and follow-up (4) radiographic and clinical parameters obtained from X-rays or CT were quantified. 34 patients (41 spinal segments) were analyzed. iCT-based navigation was successfully accomplished in all patients. Radiographic parameters, revealed significant improvement from preoperatively to intraoperatively after cage implantation in both MISS procedures (XLIF/TLIF) (p≤0.05). Radiological parameters for both MISS fusion procedures did not reveal significant differences to the assessed radiographic measures at follow-up (P>0.05). Radiological outcome values did not decrease when compared intraoperatively (after cage implantation) to latest follow-up. Utilization of intraoperative fan-beam CT is capable of assessing neural decompression intraoperatively with high accuracy allowing for precise prediction of radiological outcome and earliest possible feedback during MISS fusion procedures. These findings are highly valuable for routine practice and future investigations towards finding a threshold for neural decompression that translates into clinical improvement. If sufficient neural decompression has been confirmed with iCT imaging studies, additional postoperative and/or follow-up imaging studies might no longer be required if patients remain asymptomatic. Copyright © 2017 Elsevier Inc. All rights reserved.

  2. Actively triggered 4d cone-beam CT acquisition

    SciTech Connect

    Fast, Martin F.; Wisotzky, Eric; Oelfke, Uwe; Nill, Simeon

    2013-09-15

    Purpose: 4d cone-beam computed tomography (CBCT) scans are usually reconstructed by extracting the motion information from the 2d projections or an external surrogate signal, and binning the individual projections into multiple respiratory phases. In this “after-the-fact” binning approach, however, projections are unevenly distributed over respiratory phases resulting in inefficient utilization of imaging dose. To avoid excess dose in certain respiratory phases, and poor image quality due to a lack of projections in others, the authors have developed a novel 4d CBCT acquisition framework which actively triggers 2d projections based on the forward-predicted position of the tumor.Methods: The forward-prediction of the tumor position was independently established using either (i) an electromagnetic (EM) tracking system based on implanted EM-transponders which act as a surrogate for the tumor position, or (ii) an external motion sensor measuring the chest-wall displacement and correlating this external motion to the phase-shifted diaphragm motion derived from the acquired images. In order to avoid EM-induced artifacts in the imaging detector, the authors devised a simple but effective “Faraday” shielding cage. The authors demonstrated the feasibility of their acquisition strategy by scanning an anthropomorphic lung phantom moving on 1d or 2d sinusoidal trajectories.Results: With both tumor position devices, the authors were able to acquire 4d CBCTs free of motion blurring. For scans based on the EM tracking system, reconstruction artifacts stemming from the presence of the EM-array and the EM-transponders were greatly reduced using newly developed correction algorithms. By tuning the imaging frequency independently for each respiratory phase prior to acquisition, it was possible to harmonize the number of projections over respiratory phases. Depending on the breathing period (3.5 or 5 s) and the gantry rotation time (4 or 5 min), between ∼90 and 145

  3. Accuracy of linear intraoral measurements using cone beam CT and multidetector CT: a tale of two CTs

    PubMed Central

    Patcas, R; Markic, G; Müller, L; Ullrich, O; Peltomäki, T; Kellenberger, C J; Karlo, C A

    2012-01-01

    Objectives The aim was to compare the accuracy of linear bone measurements of cone beam CT (CBCT) with multidetector CT (MDCT) and validate intraoral soft-tissue measurements in CBCT. Methods Comparable views of CBCT and MDCT were obtained from eight intact cadaveric heads. The anatomical positions of the gingival margin and the buccal alveolar bone ridge were determined. Image measurements (CBCT/MDCT) were performed upon multiplanar reformatted data sets and compared with the anatomical measurements; the number of non-assessable sites (NASs) was evaluated. Results Radiological measurements were accurate with a mean difference from anatomical measurements of 0.14 mm (CBCT) and 0.23 mm (MDCT). These differences were statistically not significant, but the limits of agreement for bone measurements were broader in MDCT (−1.35 mm; 1.82 mm) than in CBCT (−0.93 mm; 1.21 mm). The limits of agreement for soft-tissue measurements in CBCT were smaller (−0.77 mm; 1.07 mm), indicating a slightly higher accuracy. More NASs occurred in MDCT (14.5%) than in CBCT (8.3%). Conclusions CBCT is slightly more reliable for linear measurements than MDCT and less affected by metal artefacts. CBCT accuracy of linear intraoral soft-tissue measurements is similar to the accuracy of bone measurements. PMID:22554987

  4. Dose calculation accuracy using cone-beam CT (CBCT) for pelvic adaptive radiotherapy

    NASA Astrophysics Data System (ADS)

    Guan, Huaiqun; Dong, Hang

    2009-10-01

    This study is to evaluate the dose calculation accuracy using Varian's cone-beam CT (CBCT) for pelvic adaptive radiotherapy. We first calibrated the Hounsfield Unit (HU) to electron density (ED) for CBCT using a mini CT QC phantom embedded into an IMRT QA phantom. We then used a Catphan 500 with an annulus around it to check the calibration. The combined CT QC and IMRT phantom provided correct HU calibration, but not Catphan with an annulus. For the latter, not only was the Teflon an incorrect substitute for bone, but the inserts were also too small to provide correct HUs for air and bone. For the former, three different scan ranges (6 cm, 12 cm and 20.8 cm) were used to investigate the HU dependence on the amount of scatter. To evaluate the dose calculation accuracy, CBCT and plan-CT for a pelvic phantom were acquired and registered. The single field plan, 3D conformal and IMRT plans were created on both CT sets. Without inhomogeneity correction, the two CT generated nearly the same plan. With inhomogeneity correction, the dosimetric difference between the two CT was mainly from the HU calibration difference. The dosimetric difference for 6 MV was found to be the largest for the single lateral field plan (maximum 6.7%), less for the 3D conformal plan (maximum 3.3%) and the least for the IMRT plan (maximum 2.5%). Differences for 18 MV were generally 1-2% less. For a single lateral field, calibration with 20.8 cm achieved the minimum dosimetric difference. For 3D and IMRT plans, calibration with a 12 cm range resulted in better accuracy. Because Catphan is the standard QA phantom for the on-board imager (OBI) device, we specifically recommend not using it for the HU calibration of CBCT.

  5. Dose calculation accuracy using cone-beam CT (CBCT) for pelvic adaptive radiotherapy.

    PubMed

    Guan, Huaiqun; Dong, Hang

    2009-10-21

    This study is to evaluate the dose calculation accuracy using Varian's cone-beam CT (CBCT) for pelvic adaptive radiotherapy. We first calibrated the Hounsfield Unit (HU) to electron density (ED) for CBCT using a mini CT QC phantom embedded into an IMRT QA phantom. We then used a Catphan 500 with an annulus around it to check the calibration. The combined CT QC and IMRT phantom provided correct HU calibration, but not Catphan with an annulus. For the latter, not only was the Teflon an incorrect substitute for bone, but the inserts were also too small to provide correct HUs for air and bone. For the former, three different scan ranges (6 cm, 12 cm and 20.8 cm) were used to investigate the HU dependence on the amount of scatter. To evaluate the dose calculation accuracy, CBCT and plan-CT for a pelvic phantom were acquired and registered. The single field plan, 3D conformal and IMRT plans were created on both CT sets. Without inhomogeneity correction, the two CT generated nearly the same plan. With inhomogeneity correction, the dosimetric difference between the two CT was mainly from the HU calibration difference. The dosimetric difference for 6 MV was found to be the largest for the single lateral field plan (maximum 6.7%), less for the 3D conformal plan (maximum 3.3%) and the least for the IMRT plan (maximum 2.5%). Differences for 18 MV were generally 1-2% less. For a single lateral field, calibration with 20.8 cm achieved the minimum dosimetric difference. For 3D and IMRT plans, calibration with a 12 cm range resulted in better accuracy. Because Catphan is the standard QA phantom for the on-board imager (OBI) device, we specifically recommend not using it for the HU calibration of CBCT.

  6. Investigation of the dose distribution for a cone beam CT system dedicated to breast imaging.

    PubMed

    Lanconelli, Nico; Mettivier, Giovanni; Lo Meo, Sergio; Russo, Paolo

    2013-06-01

    Cone-beam breast Computed Tomography (bCT) is an X-ray imaging technique for breast cancer diagnosis, in principle capable of delivering a much more homogeneous dose spatial pattern to the breast volume than conventional mammography, at dose levels comparable to two-view mammography. We present an investigation of the three-dimensional dose distribution for a cone-beam CT system dedicated to breast imaging. We employed Monte Carlo simulations for estimating the dose deposited within a breast phantom having a hemiellipsoidal shape placed on a cylinder of 3.5 cm thickness that simulates the chest wall. This phantom represents a pendulant breast in a bCT exam with the average diameter at chest wall, assumed to correspond to a 5-cm-thick compressed breast in mammography. The phantom is irradiated in a circular orbit with an X-ray cone beam selected from four different techniques: 50, 60, 70, and 80 kVp from a tube with tungsten anode, 1.8 mm Al inherent filtration and additional filtration of 0.2 mm Cu. Using the Monte Carlo code GEANT4 we simulated a system similar to the experimental apparatus available in our lab. Simulations were performed at a constant free-in-air air kerma at the isocenter (1 μGy); the corresponding total number of photon histories per scan was 288 million at 80 kVp. We found that the more energetic beams provide a more uniform dose distribution than at low energy: the 50 kVp beam presents a frequency distribution of absorbed dose values with a coefficient of variation almost double than that for the 80 kVp beam. This is confirmed by the analysis of the relative dose profiles along the radial (i.e. parallel to the "chest wall") and longitudinal (i.e. from "chest wall" to "nipple") directions. Maximum radial deviations are on the order of 25% for the 80 kVp beam, whereas for the 50 kVp beam variations around 43% were observed, with the lowest dose values being found along the central longitudinal axis of the phantom. Copyright © 2012

  7. Experimental Scatter Correction Methods in Industrial X-Ray Cone-Beam CT

    NASA Astrophysics Data System (ADS)

    Schörner, K.; Goldammer, M.; Stephan, J.

    2011-06-01

    Scattered radiation presents a major source of image degradation in industrial cone-beam computed tomography systems. Scatter artifacts introduce streaks, cupping and a loss of contrast in the reconstructed CT-volumes. In order to overcome scatter artifacts, we present two complementary experimental correction methods: the beam-stop array (BSA) and an inverse technique we call beam-hole array (BHA). Both correction methods are examined in comparative measurements where it is shown that the aperture-based BHA technique has practical and scatter-reducing advantages over the BSA. The proposed BHA correction method is successfully applied to a large-scale industrial specimen whereby scatter artifacts are reduced and contrast is enhanced significantly.

  8. Electron stripping processes of H{sup −} ion beam in the 80 kV high voltage extraction column and low energy beam transport line at LANSCE

    SciTech Connect

    Draganic, I. N.

    2016-02-15

    Basic vacuum calculations were performed for various operating conditions of the Los Alamos National Neutron Science H{sup −} Cockcroft-Walton (CW) injector and the Ion Source Test Stand (ISTS). The vacuum pressure was estimated for both the CW and ISTS at five different points: (1) inside the H{sup −} ion source, (2) in front of the Pierce electrode, (3) at the extraction electrode, (4) at the column electrode, and (5) at the ground electrode. A static vacuum analysis of residual gases and the working hydrogen gas was completed for the normal ion source working regime. Gas density and partial pressure were estimated for the injected hydrogen gas. The attenuation of H{sup −} beam current and generation of electron current in the high voltage acceleration columns and low energy beam transport lines were calculated. The interaction of H{sup −} ions on molecular hydrogen (H{sub 2}) is discussed as a dominant collision process in describing electron stripping rates. These results are used to estimate the observed increase in the ratio of electrons to H{sup −} ion beam in the ISTS beam transport line.

  9. Electron stripping processes of H- ion beam in the 80 kV high voltage extraction column and low energy beam transport line at LANSCE

    NASA Astrophysics Data System (ADS)

    Draganic, I. N.

    2016-02-01

    Basic vacuum calculations were performed for various operating conditions of the Los Alamos National Neutron Science H- Cockcroft-Walton (CW) injector and the Ion Source Test Stand (ISTS). The vacuum pressure was estimated for both the CW and ISTS at five different points: (1) inside the H- ion source, (2) in front of the Pierce electrode, (3) at the extraction electrode, (4) at the column electrode, and (5) at the ground electrode. A static vacuum analysis of residual gases and the working hydrogen gas was completed for the normal ion source working regime. Gas density and partial pressure were estimated for the injected hydrogen gas. The attenuation of H- beam current and generation of electron current in the high voltage acceleration columns and low energy beam transport lines were calculated. The interaction of H- ions on molecular hydrogen (H2) is discussed as a dominant collision process in describing electron stripping rates. These results are used to estimate the observed increase in the ratio of electrons to H- ion beam in the ISTS beam transport line.

  10. Three-dimensional cone-beam region-of-interest (ROI) CT reconstruction

    NASA Astrophysics Data System (ADS)

    Liu, Ruijie Rachel

    2001-06-01

    ROI cone-beam (CB) CT is proposed in this thesis as a new technique in which a set of partially filtered ROI images is used for CT reconstruction. It can be used in neural surgery as fluoroscopy 3D CT images with reduced dose outside the ROL Depending on the contrast resolution requirement of the CT images and therefore the thickness of the ROI filter, the dose can be reduced by 50%-70%. In this study, the shape of the ROI is rectangular in the middle of the image. In order to do CB reconstruction, the image distortion has to be corrected, because all the images were acquired by the image intensifier (II) where distortion occurs. We proposed a new method, named as super-global (SG) model with a set of parameters, to do distortion correction for all the images in a rotational run. The SG model is carefully tested and compared with the conventional global correction method Study shows that it is an accurate efficient method for the distortion correction of images acquired by rotational C-arms. The intensity of ROI images has to be equalized within and without ROI after distortion correction. First, the edge is detected; then equalization factors are applied to the filtered areas. Now the distortion-free and intensity-equalized images are used for CB backprojection to reconstruct the 3D CT images by Feldkamp algorithm. This algorithm is tested by a mathematical phantom reconstruction. Iso-center correction and uniform scattering subtraction is discussed and applied in the experimental phantom reconstruction. We took images of a phantom and a rabbit with and without contrast medium injection, and with and without ROI filtration. Their 3D CT images were obtained. For the rabbit, vascular CT images were obtained by subtracting CT images with contrast medium from those without contrast. The CT images of the ROI edges are in good shape, and no obvious artifact is observed. Though the filtered area has higher noise, its intensify is equalized pretty well with that of the

  11. GPU-accelerated regularized iterative reconstruction for few-view cone beam CT

    SciTech Connect

    Matenine, Dmitri; Goussard, Yves

    2015-04-15

    Purpose: The present work proposes an iterative reconstruction technique designed for x-ray transmission computed tomography (CT). The main objective is to provide a model-based solution to the cone-beam CT reconstruction problem, yielding accurate low-dose images via few-views acquisitions in clinically acceptable time frames. Methods: The proposed technique combines a modified ordered subsets convex (OSC) algorithm and the total variation minimization (TV) regularization technique and is called OSC-TV. The number of subsets of each OSC iteration follows a reduction pattern in order to ensure the best performance of the regularization method. Considering the high computational cost of the algorithm, it is implemented on a graphics processing unit, using parallelization to accelerate computations. Results: The reconstructions were performed on computer-simulated as well as human pelvic cone-beam CT projection data and image quality was assessed. In terms of convergence and image quality, OSC-TV performs well in reconstruction of low-dose cone-beam CT data obtained via a few-view acquisition protocol. It compares favorably to the few-view TV-regularized projections onto convex sets (POCS-TV) algorithm. It also appears to be a viable alternative to full-dataset filtered backprojection. Execution times are of 1–2 min and are compatible with the typical clinical workflow for nonreal-time applications. Conclusions: Considering the image quality and execution times, this method may be useful for reconstruction of low-dose clinical acquisitions. It may be of particular benefit to patients who undergo multiple acquisitions by reducing the overall imaging radiation dose and associated risks.

  12. GPU-accelerated regularized iterative reconstruction for few-view cone beam CT.

    PubMed

    Matenine, Dmitri; Goussard, Yves; Després, Philippe

    2015-04-01

    The present work proposes an iterative reconstruction technique designed for x-ray transmission computed tomography (CT). The main objective is to provide a model-based solution to the cone-beam CT reconstruction problem, yielding accurate low-dose images via few-views acquisitions in clinically acceptable time frames. The proposed technique combines a modified ordered subsets convex (OSC) algorithm and the total variation minimization (TV) regularization technique and is called OSC-TV. The number of subsets of each OSC iteration follows a reduction pattern in order to ensure the best performance of the regularization method. Considering the high computational cost of the algorithm, it is implemented on a graphics processing unit, using parallelization to accelerate computations. The reconstructions were performed on computer-simulated as well as human pelvic cone-beam CT projection data and image quality was assessed. In terms of convergence and image quality, OSC-TV performs well in reconstruction of low-dose cone-beam CT data obtained via a few-view acquisition protocol. It compares favorably to the few-view TV-regularized projections onto convex sets (POCS-TV) algorithm. It also appears to be a viable alternative to full-dataset filtered backprojection. Execution times are of 1-2 min and are compatible with the typical clinical workflow for nonreal-time applications. Considering the image quality and execution times, this method may be useful for reconstruction of low-dose clinical acquisitions. It may be of particular benefit to patients who undergo multiple acquisitions by reducing the overall imaging radiation dose and associated risks.

  13. Enlarged longitudinal dose profiles in cone-beam CT and the need for modified dosimetry

    SciTech Connect

    Mori, Shinichiro; Endo, Masahiro; Nishizawa, Kanae; Tsunoo, Takanori; Aoyama, Takahiko; Fujiwara, Hideaki; Murase, Kenya

    2005-04-01

    In order to examine phantom length necessary to assess radiation dose delivered to patients in cone-beam CT with an enlarged beamwidth, we measured dose profiles in cylindrical phantoms of sufficient length using a prototype 256-slice CT-scanner developed at our institute. Dose profiles parallel to the rotation axis were measured at the central and peripheral positions in PMMA (polymethylmethacrylate) phantoms of 160 or 320 mm diameter and 900 mm length. For practical application, we joined unit cylinders (150 mm long) together to provide phantoms of 900 mm length. Dose profiles were measured with a pin photodiode sensor having a sensitive region of approximately 2.8x2.8 mm{sup 2} and 2.7 mm thickness. Beamwidths of the scanner were varied from 20 to 138 mm. Dose profile integrals (DPI) were calculated using the measured dose profiles for various beamwidths and integration ranges. For the body phantom (320-mm-diam phantom), 76% of the DPI was represented for a 20 mm beamwidth and 60% was represented for a 138 mm beamwidth if dose profiles were integrated over a 100 mm range, while more than 90% of the DPI was represented for beamwidths between 20 and 138 mm if integration was carried out over a 300 mm range. The phantom length and integration range for dosimetry of cone-beam CT needed to be more than 300 mm to represent more than 90% of the DPI for the body phantom with the beamwidth of more than 20 mm. Although we reached this conclusion using the prototype 256-slice CT-scanner, it may be applied to other multislice CT-scanners as well.

  14. Effect of temperature on beam damage of asbestos fibers in the transmission electron microscope (TEM) at 100kV.

    PubMed

    Martin, Joannie; Beauparlant, Martin; Sauvé, Sébastien; L'Espérance, Gilles

    2017-03-01

    Damage to asbestos fibers by the transmission electron microscope (TEM) electron beam is a known limitation of this powerful method of analysis. Although it is often considered only in terms of loss of crystallinity, recent studies have shown that the damage may also change the elemental composition of fibers, thus causing significant identification errors. In this study, the main objective was to assess whether temperature is a factor influencing damage to asbestos fibers and, if so, how it can be used to minimize damage. It was found that lowering the temperature to 123K can inhibit, for a given time, the manifestation of the damage. The significant decrease of atom diffusion at low temperature momentarily prevents mass loss, greatly reducing the possibility of misidentification of anthophyllite asbestos fibers. The results obtained in this study strongly suggest that the predominant mechanism damage is probably related to the induced-electric-field model relegating radiolysis to the status of a subsidiary damage mechanism. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. 3D In Vivo Dosimetry Using Megavoltage Cone-Beam CT and EPID Dosimetry

    SciTech Connect

    Elmpt, Wouter van Nijsten, Sebastiaan; Petit, Steven; Mijnheer, Ben; Lambin, Philippe; Dekker, Andre

    2009-04-01

    Purpose: To develop a method that reconstructs, independently of previous (planning) information, the dose delivered to patients by combining in-room imaging with transit dose measurements during treatment. Methods and Materials: A megavoltage cone-beam CT scan of the patient anatomy was acquired with the patient in treatment position. During treatment, delivered fields were measured behind the patient with an electronic portal imaging device. The dose information in these images was back-projected through the cone-beam CT scan and used for Monte Carlo simulation of the dose distribution inside the cone-beam CT scan. Validation was performed using various phantoms for conformal and IMRT plans. Clinical applicability is shown for a head-and-neck cancer patient treated with IMRT. Results: For single IMRT beams and a seven-field IMRT step-and-shoot plan, the dose distribution was reconstructed within 3%/3mm compared with the measured or planned dose. A three-dimensional conformal plan, verified using eight point-dose measurements, resulted in a difference of 1.3 {+-} 3.3% (1 SD) compared with the reconstructed dose. For the patient case, planned and reconstructed dose distribution was within 3%/3mm for about 95% of the points within the 20% isodose line. Reconstructed mean dose values, obtained from dose-volume histograms, were within 3% of prescribed values for target volumes and normal tissues. Conclusions: We present a new method that verifies the dose delivered to a patient by combining in-room imaging with the transit dose measured during treatment. This verification procedure opens possibilities for offline adaptive radiotherapy and dose-guided radiotherapy strategies taking into account the dose distribution delivered during treatment sessions.

  16. Method for measuring the intensity profile of a CT fan-beam filter

    NASA Astrophysics Data System (ADS)

    Whiting, Bruce R.; Dohatcu, Andreea

    2014-03-01

    Research on CT systems often requires knowledge of intensity as a function of angle in the fan-beam, due to the presence of bowtie filters, for studies such as dose reduction simulation, Monte Carlo dose calculations, or statistical reconstruction algorithms. Since manufacturers consider the x-ray bowtie filter design to be proprietary information, several methods have been proposed to measure the beam intensity profile independently: 1) calculate statistical properties of noise in acquired sinograms (requires access to raw data files, which is also vendor proprietary); 2) measure the waveform of a dosimeter located away from the isocenter (requires dosimeter equipment costing > 10K). We present a novel method that is inexpensive (parts costing 100 from any hardware store, using Gafchromic film at $3 per measurement), requires no proprietary information, and can be performed in a few minutes. A fixture is built from perforated steel tubing, which forms an aperture that selectively samples the intensity at a particular fan-beam angle in a rotating gantry. Two exposures (1× and 2×) are made and self-developing radiochromic film (Gafchromic XR- Ashland Inc.) is then scanned on an inexpensive PC document scanner. An analysis method is described that linearizes the measurements for relative exposure. The resultant profile is corrected for geometric effects (1/LΛ2 fall-off, gantry dwell time) and background exposure, providing a noninvasive estimate of the CT fan-beam intensity present in an operational CT system. This method will allow researchers to conveniently measure parameters required for modeling the effects of bowtie filters in clinical scanners.

  17. Investigation of dosimetric variations of liver radiotherapy using deformable registration of planning CT and cone-beam CT.

    PubMed

    Huang, Pu; Yu, Gang; Chen, Jinhu; Ma, Changsheng; Qin, Shaohua; Yin, Yong; Liang, Yueqiang; Li, Hongsheng; Li, Dengwang

    2017-01-01

    Many patients with technically unresectable or medically inoperable hepatocellular carcinoma (HCC) had hepatic anatomy variations as a result of interfraction deformation during fractionated radiotherapy. We conducted this retrospective study to investigate interfractional normal liver dosimetric consequences via reconstructing weekly dose in HCC patients. Twenty-three patients with HCC received conventional fractionated three-dimensional conformal radiation therapy (3DCRT) were enrolled in this retrospective investigation. Among them, seven patients had been diagnosed of radiation-induced liver disease (RILD) and the other 16 patients had good prognosis after treatment course. The cone-beam CT (CBCT) scans were acquired once weekly for each patient throughout the treatment, deformable image registration (DIR) of planning CT (pCT) and CBCT was performed to acquire modified CBCT (mCBCT), and the structural contours were propagated by the DIR. The same plan was applied to mCBCT to perform dose calculation. Weekly dose distribution was displayed on the pCT dose space and compared using dose difference, target coverage, and dose volume histograms. Statistical analysis was performed to identify the significant dosimetric variations. Among the 23 patients, the three weekly normal liver D50 increased by 0.2 Gy, 4.2 Gy, and 4.7 Gy, respectively, for patients with RILD, and 1.0 Gy, 2.7 Gy, and 3.1 Gy, respectively, for patients without RILD. Mean dose to the normal liver (Dmean) increased by 0.5 Gy, 2.6 Gy, and 4.0 Gy, respectively, for patients with RILD, and 0.4 Gy, 3.1 Gy, and 3.4 Gy, respectively, for patients without RILD. Regarding patients with RILD, the average values of the third weekly D50 and Dmean were both over hepatic radiation tolerance, while the values of patients without RILD were below. The dosimetric consequence showed that the liver dose between patients with and without RILD were different relative to the planned dose, and the RILD patients suffered

  18. Target delineation for radiosurgery of a small brain arteriovenous malformation using high-resolution contrast-enhanced cone beam CT.

    PubMed

    van der Bom, Imramsjah M J; Gounis, Matthew J; Ding, Linda; Kühn, Anna Luisa; Goff, David; Puri, Ajit S; Wakhloo, Ajay K

    2014-06-01

    Three years following endovascular embolization of a 3 mm ruptured arteriovenous malformation (AVM) of the left superior colliculus in a 42-year-old man, digital subtraction angiography showed continuous regrowth of the lesion. Thin-slice MRI acquired for treatment planning did not show the AVM nidus. The patient was brought back to the angiography suite for high-resolution contrast-enhanced cone beam CT (VasoCT) acquired using an angiographic c-arm system. The lesion and nidus were visualized with VasoCT. MRI, CT and VasoCT data were transferred to radiation planning software and mutually co-registered. The nidus was annotated for radiation on VasoCT data by an experienced neurointerventional radiologist and a dose/treatment plan was completed. Due to image registration, the treatment area could be directly adopted into the MRI and CT data. The AVM was completely obliterated 10 months following completion of the radiosurgery treatment.

  19. Target delineation for radiosurgery of a small brain arteriovenous malformation using high-resolution contrast-enhanced cone beam CT.

    PubMed

    van der Bom, Imramsjah M J; Gounis, Matthew J; Ding, Linda; Kühn, Anna Luisa; Goff, David; Puri, Ajit S; Wakhloo, Ajay K

    2013-08-14

    Three years following endovascular embolization of a 3 mm ruptured arteriovenous malformation (AVM) of the left superior colliculus in a 42-year-old man, digital subtraction angiography showed continuous regrowth of the lesion. Thin-slice MRI acquired for treatment planning did not show the AVM nidus. The patient was brought back to the angiography suite for high-resolution contrast-enhanced cone beam CT (VasoCT) acquired using an angiographic c-arm system. The lesion and nidus were visualized with VasoCT. MRI, CT and VasoCT data were transferred to radiation planning software and mutually co-registered. The nidus was annotated for radiation on VasoCT data by an experienced neurointerventional radiologist and a dose/treatment plan was completed. Due to image registration, the treatment area could be directly adopted into the MRI and CT data. The AVM was completely obliterated 10 months following completion of the radiosurgery treatment.

  20. X-Ray Scatter Correction on Soft Tissue Images for Portable Cone Beam CT.

    PubMed

    Aootaphao, Sorapong; Thongvigitmanee, Saowapak S; Rajruangrabin, Jartuwat; Thanasupsombat, Chalinee; Srivongsa, Tanapon; Thajchayapong, Pairash

    2016-01-01

    Soft tissue images from portable cone beam computed tomography (CBCT) scanners can be used for diagnosis and detection of tumor, cancer, intracerebral hemorrhage, and so forth. Due to large field of view, X-ray scattering which is the main cause of artifacts degrades image quality, such as cupping artifacts, CT number inaccuracy, and low contrast, especially on soft tissue images. In this work, we propose the X-ray scatter correction method for improving soft tissue images. The X-ray scatter correction scheme to estimate X-ray scatter signals is based on the deconvolution technique using the maximum likelihood estimation maximization (MLEM) method. The scatter kernels are obtained by simulating the PMMA sheet on the Monte Carlo simulation (MCS) software. In the experiment, we used the QRM phantom to quantitatively compare with fan-beam CT (FBCT) data in terms of CT number values, contrast to noise ratio, cupping artifacts, and low contrast detectability. Moreover, the PH3 angiography phantom was also used to mimic human soft tissues in the brain. The reconstructed images with our proposed scatter correction show significant improvement on image quality. Thus the proposed scatter correction technique has high potential to detect soft tissues in the brain.

  1. Analysis of Cone-Beam Artifacts in off-Centered Circular CT for Four Reconstruction Methods

    PubMed Central

    Peyrin, F.; Sappey-Marinier, D.

    2006-01-01

    Cone-beam (CB) acquisition is increasingly used for truly three-dimensional X-ray computerized tomography (CT). However, tomographic reconstruction from data collected along a circular trajectory with the popular Feldkamp algorithm is known to produce the so-called CB artifacts. These artifacts result from the incompleteness of the source trajectory and the resulting missing data in the Radon space increasing with the distance to the plane containing the source orbit. In the context of the development of integrated PET/CT microscanners, we introduced a novel off-centered circular CT cone-beam geometry. We proposed a generalized Feldkamp formula (α-FDK) adapted to this geometry, but reconstructions suffer from increased CB artifacts. In this paper, we evaluate and compare four different reconstruction methods for correcting CB artifacts in off-centered geometry. We consider the α-FDK algorithm, the shift-variant FBP method derived from the T-FDK, an FBP method based on the Grangeat formula, and an iterative algebraic method (SART). The results show that the low contrast artifacts can be efficiently corrected by the shift-variant method and the SART method to achieve good quality images at the expense of increased computation time, but the geometrical deformations are still not compensated for by these techniques. PMID:23165048

  2. SU-E-T-416: VMAT Dose Calculations Using Cone Beam CT Images: A Preliminary Study

    SciTech Connect

    Yu, S; Sehgal, V; Kuo, J; Daroui, P; Ramsinghani, N; Al-Ghazi, M

    2014-06-01

    Purpose: Cone beam CT (CBCT) images have been used routinely for patient positioning throughout the treatment course. However, use of CBCT for dose calculation is still investigational. The purpose of this study is to assess the utility of CBCT images for Volumetric Modulated Arc Therapy (VMAT) plan dose calculation. Methods: A CATPHAN 504 phantom (The Phantom Laboratory, Salem, NY) was used to compare the dosimetric and geometric accuracy between conventional CT and CBCT (in both full and half fan modes). Hounsfield units (HU) profiles at different density areas were evaluated. A C shape target that surrounds a central avoidance structure was created and a VMAT plan was generated on the CT images and copied to the CBCT phantom images. Patient studies included three brain patients, and one head and neck (H'N) patient. VMAT plans generated on the patients treatment planning CT was applied to CBCT images obtained during the first treatment. Isodose distributions and dosevolume- histograms (DVHs) were compared. Results: For the phantom study, the HU difference between CT and CBCT is within 100 (maximum 96 HU for Teflon CBCT images in full fan mode). The impact of these differences on the calculated dose distributions was clinically insignificant. In both phantom and patient studies, target DVHs based on CBCT images were in excellent agreement with those based on planning CT images. Mean, Median, near minimum (D98%), and near maximum (D2%) doses agreed within 0-2.5%. A slightly larger discrepancy is observed in the patient studies compared to that seen in the phantom study, (0-1% vs. 0 - 2.5%). Conclusion: CBCT images can be used to accurately predict dosimetric results, without any HU correction. It is feasible to use CBCT to evaluate the actual dose delivered at each fraction. The dosimetric consequences resulting from tumor response and patient geometry changes could be monitored.

  3. Experimental realization of fluence field modulated CT using digital beam attenuation

    PubMed Central

    Szczykutowicz, TP; Mistretta, CA

    2014-01-01

    Purpose Tailoring CT scan acquisition parameters to individual patients is a topic of much research in the CT imaging community. It is now common place to find automatically adjusted tube current options for modern CT scanners. In addition, the use of beam shaping filters, commonly called bowtie filters, is available on most CT systems and allows for different body regions to receive different incident x-ray fluence distributions. However, no method currently exists which allows for the form of the incident x-ray fluence distribution to change as a function of view angle. This study represents the first experimental realization of fluence field modulated CT (FFMCT) for a c-arm geometry CT scan. Methods: X-ray fluence modulation is accomplished using a digital beam attenuator (DBA). The device is composed of 10 iron wedge pairs that modulate the thickness of iron x-rays must traverse before reaching a patient. Using this device, experimental data was taken using a Siemens Zeego c-arm scanner. Scans were performed on a cylindrical polyethylene phantom and on two different sections of an anthropomorphic phantom. The DBA was used to equalize the x-ray fluence striking the detector for each scan. Non DBA, or “flat field” scans were also acquired of the same phantom objects for comparison. In addition, a scan was performed in which the DBA was used to enable volume of interest (VOI) imaging. In VOI, only a small sub-volume within a patient receives full dose and the rest of the patient receives a much lower dose. Data corrections unique to using a piece-wise constant modulator were also developed. Results The feasibility of FFMCT implemented using a DBA device has been demonstrated. Initial results suggest dose reductions of up to 3.6 times relative to “flat field” CT. In addition to dose reduction, the DBA enables a large improvement in image noise uniformity and the ability to provide regionally enhanced signal to noise using VOI imaging techniques. Conclusions

  4. SU-D-207-06: Clinical Validations of Shading Correction for Cone-Beam CT Using Planning CT as a Prior

    SciTech Connect

    Tsui, T; Zhu, L; Wei, J

    2015-06-15

    Purpose: Current cone-beam CT (CBCT) images contain severe shading artifacts mainly due to scatter, hindering their quantitative use in current radiation therapy. We have previously proposed an effective shading correction method for CBCT using planning CT (pCT) as prior knowledge. In this work, we investigate the method robustness via statistical analyses on studies of a large patient group and compare the performance with that of a state-of-the-art method implemented on the current commercial radiation therapy machine -- the Varian Truebeam system. Methods: Since radiotherapy patients routinely undergo multiple-detector CT (MDCT) scans in the planning procedure, we use the high-quality pCT as “free” prior knowledge for CBCT image improvement. The CBCT image with no correction is first spatially registered with the pCT. Primary CBCT projections are estimated via forward projections of the registered image. The low frequency errors in the projections, which stem from mainly scatter, are estimated by filtering the difference between original line integral and the estimated scatter projections. The corrected CBCT image is then reconstructed from the scatter corrected projections. The proposed method is evaluated on 40 cancer patients. Results: On all patient images, we compare errors on CT number, spatial non-uniformity (SNU) and image contrast, using pCT as the ground truth. T-tests show that our algorithm improves over the Varian method on CBCT accuracies of CT number and SNU with 90% confident. The average CT number error is reduced from 54.8 HU on the Varian method to 40.9 HU, and the SNU error is reduced from 7.7% to 3.8%. There is no obvious improvement on image contrast. Conclusion: Large-group patient studies show that the proposed pCT-based algorithm outperforms the Varian method of the Truebeam system on CBCT shading correction, by providing CBCT images with higher CT number accuracy and greater image uniformity.

  5. Passive breath gating equipment for cone beam CT-guided RapidArc gastric cancer treatments.

    PubMed

    Hu, Weigang; Li, Guichao; Ye, Jinsong; Wang, Jiazhou; Peng, Jiayuan; Gong, Min; Yu, Xiaoli; Studentski, Matthew T; Xiao, Ying; Zhang, Zhen

    2015-01-01

    To report preliminary results of passive breath gating (PBG) equipment for cone-beam CT image-guided gated RapidArc gastric cancer treatments. Home-developed PBG equipment integrated with the real-time position management system (RPM) for passive patient breath hold was used in CT simulation, online partial breath hold (PBH) CBCT acquisition, and breath-hold gating (BHG) RapidArc delivery. The treatment was discontinuously delivered with beam on during BH and beam off for free breathing (FB). Pretreatment verification PBH CBCT was obtained with the PBG-RPM system. Additionally, the reproducibility of the gating accuracy was evaluated. A total of 375 fractions of breath-hold gating RapidArc treatments were successfully delivered and 233 PBH CBCTs were available for analysis. The PBH CBCT images were acquired with 2-3 breath holds and 1-2 FB breaks. The imaging time was the same for PBH CBCT and conventional FB CBCT (60s). Compared to FB CBCT, the motion artifacts seen in PBH CBCT images were remarkably reduced. The average BHG RapidArc delivery time was 103 s for one 270-degree arc and 269 s for two full arcs. The PBG-RPM based PBH CBCT verification and BHG RapidArc delivery was successfully implemented clinically. The BHG RapidArc treatment was accomplished using a conventional RapidArc machine with high delivery efficiency. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  6. Individualized volume CT dose index determined by cross-sectional area and mean density of the body to achieve uniform image noise of contrast-enhanced pediatric chest CT obtained at variable kV levels and with combined tube current modulation.

    PubMed

    Goo, Hyun Woo

    2011-07-01

    A practical body-size adaptive protocol providing uniform image noise at various kV levels is not available for pediatric CT. To develop a practical contrast-enhanced pediatric chest CT protocol providing uniform image noise by using an individualized volume CT dose index (CTDIvol) determined by the cross-sectional area and density of the body at variable kV levels and with combined tube current modulation. A total of 137 patients (mean age, 7.6 years) underwent contrast-enhanced pediatric chest CT based on body weight. From the CTDIvol, image noise, and area and mean density of the cross-section at the lung base in the weight-based group, the best fit equation was estimated with a very high correlation coefficient (γ(2) = 0.86, P < 0.001). For the next study, 177 patients (mean age, 7.9 years; the CTDIvol group) underwent contrast-enhanced pediatric chest CT with the CTDIvol determined individually by the best fit equation. CTDIvol values on the dose report after CT scanning, noise differences from the target noise, areas, and mean densities were compared between these two groups. The CTDIvol values (mean ± standard deviation, 1.6 ± 0.7 mGy) and the noise differences from the target noise (1.1 ± 0.9 HU) of the CTDIvol group were significantly lower than those of the weight-based group (2.0 ± 1.0 mGy, 1.8 ± 1.4 HU) (P < 0.001). In contrast, no statistically significant difference was found in area (317.0 ± 136.8 cm(2) vs. 326.3 ± 124.8 cm(2)), mean density (-212.9 ± 53.1 HU vs. -221.1 ± 56.3 HU), and image noise (13.8 ± 2.3 vs. 13.6 ± 1.7 HU) between the weight-based and the CTDIvol groups (P > 0.05). Contrast-enhanced pediatric chest CT with the CTDIvol determined individually by the cross-sectional area and density of the body provides more uniform noise and better dose adaptation to body habitus than does weight-based CT at variable kV levels and with combined tube current modulation.

  7. SimDoseCT: dose reporting software based on Monte Carlo simulation for a 320 detector-row cone-beam CT scanner and ICRP computational adult phantoms

    NASA Astrophysics Data System (ADS)

    Cros, Maria; Joemai, Raoul M. S.; Geleijns, Jacob; Molina, Diego; Salvadó, Marçal

    2017-08-01

    This study aims to develop and test software for assessing and reporting doses for standard patients undergoing computed tomography (CT) examinations in a 320 detector-row cone-beam scanner. The software, called SimDoseCT, is based on the Monte Carlo (MC) simulation code, which was developed to calculate organ doses and effective doses in ICRP anthropomorphic adult reference computational phantoms for acquisitions with the Aquilion ONE CT scanner (Toshiba). MC simulation was validated by comparing CTDI measurements within standard CT dose phantoms with results from simulation under the same conditions. SimDoseCT consists of a graphical user interface connected to a MySQL database, which contains the look-up-tables that were generated with MC simulations for volumetric acquisitions at different scan positions along the phantom using any tube voltage, bow tie filter, focal spot and nine different beam widths. Two different methods were developed to estimate organ doses and effective doses from acquisitions using other available beam widths in the scanner. A correction factor was used to estimate doses in helical acquisitions. Hence, the user can select any available protocol in the Aquilion ONE scanner for a standard adult male or female and obtain the dose results through the software interface. Agreement within 9% between CTDI measurements and simulations allowed the validation of the MC program. Additionally, the algorithm for dose reporting in SimDoseCT was validated by comparing dose results from this tool with those obtained from MC simulations for three volumetric acquisitions (head, thorax and abdomen). The comparison was repeated using eight different collimations and also for another collimation in a helical abdomen examination. The results showed differences of 0.1 mSv or less for absolute dose in most organs and also in the effective dose calculation. The software provides a suitable tool for dose assessment in standard adult patients undergoing CT

  8. SimDoseCT: dose reporting software based on Monte Carlo simulation for a 320 detector-row cone-beam CT scanner and ICRP computational adult phantoms.

    PubMed

    Cros, Maria; Joemai, Raoul M S; Geleijns, Jacob; Molina, Diego; Salvadó, Marçal

    2017-07-17

    This study aims to develop and test software for assessing and reporting doses for standard patients undergoing computed tomography (CT) examinations in a 320 detector-row cone-beam scanner. The software, called SimDoseCT, is based on the Monte Carlo (MC) simulation code, which was developed to calculate organ doses and effective doses in ICRP anthropomorphic adult reference computational phantoms for acquisitions with the Aquilion ONE CT scanner (Toshiba). MC simulation was validated by comparing CTDI measurements within standard CT dose phantoms with results from simulation under the same conditions. SimDoseCT consists of a graphical user interface connected to a MySQL database, which contains the look-up-tables that were generated with MC simulations for volumetric acquisitions at different scan positions along the phantom using any tube voltage, bow tie filter, focal spot and nine different beam widths. Two different methods were developed to estimate organ doses and effective doses from acquisitions using other available beam widths in the scanner. A correction factor was used to estimate doses in helical acquisitions. Hence, the user can select any available protocol in the Aquilion ONE scanner for a standard adult male or female and obtain the dose results through the software interface. Agreement within 9% between CTDI measurements and simulations allowed the validation of the MC program. Additionally, the algorithm for dose reporting in SimDoseCT was validated by comparing dose results from this tool with those obtained from MC simulations for three volumetric acquisitions (head, thorax and abdomen). The comparison was repeated using eight different collimations and also for another collimation in a helical abdomen examination. The results showed differences of 0.1 mSv or less for absolute dose in most organs and also in the effective dose calculation. The software provides a suitable tool for dose assessment in standard adult patients undergoing CT

  9. Characterization and correction of cupping effect artefacts in cone beam CT

    PubMed Central

    Hunter, AK; McDavid, WD

    2012-01-01

    Objective The purpose of this study was to demonstrate and correct the cupping effect artefact that occurs owing to the presence of beam hardening and scatter radiation during image acquisition in cone beam CT (CBCT). Methods A uniform aluminium cylinder (6061) was used to demonstrate the cupping effect artefact on the Planmeca Promax 3D CBCT unit (Planmeca OY, Helsinki, Finland). The cupping effect was studied using a line profile plot of the grey level values using ImageJ software (National Institutes of Health, Bethesda, MD). A hardware-based correction method using copper pre-filtration was used to address this artefact caused by beam hardening and a software-based subtraction algorithm was used to address scatter contamination. Results The hardware-based correction used to address the effects of beam hardening suppressed the cupping effect artefact but did not eliminate it. The software-based correction used to address the effects of scatter resulted in elimination of the cupping effect artefact. Conclusion Compensating for the presence of beam hardening and scatter radiation improves grey level uniformity in CBCT. PMID:22378754

  10. Characterization and correction of cupping effect artefacts in cone beam CT.

    PubMed

    Hunter, A K; McDavid, W D

    2012-03-01

    The purpose of this study was to demonstrate and correct the cupping effect artefact that occurs owing to the presence of beam hardening and scatter radiation during image acquisition in cone beam CT (CBCT). A uniform aluminium cylinder (6061) was used to demonstrate the cupping effect artefact on the Planmeca Promax 3D CBCT unit (Planmeca OY, Helsinki, Finland). The cupping effect was studied using a line profile plot of the grey level values using ImageJ software (National Institutes of Health, Bethesda, MD). A hardware-based correction method using copper pre-filtration was used to address this artefact caused by beam hardening and a software-based subtraction algorithm was used to address scatter contamination. The hardware-based correction used to address the effects of beam hardening suppressed the cupping effect artefact but did not eliminate it. The software-based correction used to address the effects of scatter resulted in elimination of the cupping effect artefact. Compensating for the presence of beam hardening and scatter radiation improves grey level uniformity in CBCT.

  11. Evaluation of flat panel detector cone beam CT breast imaging with different sizes of breast phantoms

    NASA Astrophysics Data System (ADS)

    Ning, Ruola; Conover, David; Lu, Xianghua; Zhang, Yan; Yu, Yong; Schiffhauer, Linda; Cullinan, Jeanne

    2005-04-01

    The sensitivity to detect small breast cancers and the specificity of conventional mammography (CM) remain limited owing to an overlap in the appearances of lesions and surrounding structure. We propose to address the limitations accompanying CM using flat panel detector (FPD)-based cone beam CT breast imaging (CBCTBI). The purpose of the study is to determine optimal x-ray operation ranges for different sizes of normal breasts and corresponding glandular dose levels. The current CBCT prototype consists of a modified GE HighSpeed Advantage CT gantry, an x-ray tube, a Varian PaxScan 4030CB FPD, a CT table and a PC. Two uncompressed breast phantoms, with the diameters of 10.8 and 13.8 cm, consist of three inserts: a layer of silicone jell simulating a background structure, a lucite plate on which five simulated carcinomas are mounted, and a plate on which six calcifications are attached. With a single scan, 300 projections were acquired for all phantom scans. The optimal x-ray techniques for different phantom sizes were determined. The total mean glandular doses for different size phantoms were measured using a CT pencil ionization chamber. With the optimal x-ray techniques that result in the maximal dose efficiency for the different tissue thickness, the image quality with two different phantoms was evaluated. The results demonstrate that the CBCTBI can detect a few millimeter-size simulated carcinoma and ~ 0.2 mm calcification with clinically acceptable mean glandular doses for different size breasts.

  12. [Periinterventional cone-beam-CT: application at transarterial chemoembolization of liver tumors].

    PubMed

    Adamus, R; Uder, M; Wilhelm, M; Loose, R W

    2011-07-01

    Periinterventional Cone-Beam CT (CBCT) today is a valuable tool in complex radiological interventions. Only little experience exists about CBCT in transarterial chemoembolisations (TACE) of liver tumors. 25 patients underwent periinterventional CBCT. We used a C-arc DSA with 30 × 40 cm flat panel detector. Image data with axial, coronal and 3D-reconstruction were acquired by 217° rotation in 8 seconds. In all 25 cases CBCT had an influence on the TACE regarding the decision which vessels to catheterize, the amount of retention of the embolisation agent or an abort because of insufficient vascularisation. In comparison with DSA alone, CBCT allows a better visualisation of tumour vessels, simplifies selective catheterisation, the decision whether an embolisation is possible and enables a good visualisation of Lipiodol retention. Hence, CBCT is a helpful periinterventional tool but cannot substitute CT and MRI in follow up.

  13. Implant planning and placement using optical scanning and cone beam CT technology.

    PubMed

    van der Zel, Jef M

    2008-08-01

    There is a growing interest in minimally invasive implant therapy as a standard prosthodontic treatment, providing complete restoration of occlusal function. A new treatment method (CADDIMA), which combines both computerized tomographic (CT) and optical laser-scan data for planning and design of surgical guides, implant abutments, and prosthetic devices, is described. Imaging using a "NewTom 3G" cone beam CT scanner and a modified laser triangulation scanner "D200c" is discussed, as are impression and surgical guide fabrication, which allow for flapless, precise implant placement and an accurate provisional prosthesis. The new approach gives the operator full control over the design of the implant prosthesis for planning of proper occlusal relations and shows promise for further evaluation.

  14. Scattered radiation in flat-detector based cone-beam CT: analysis of voxelized patient simulations

    NASA Astrophysics Data System (ADS)

    Wiegert, Jens; Bertram, Matthias

    2006-03-01

    This paper presents a systematic assessment of scattered radiation in flat-detector based cone-beam CT. The analysis is based on simulated scatter projections of voxelized CT images of different body regions allowing to accurately quantify scattered radiation of realistic and clinically relevant patient geometries. Using analytically computed primary projection data of high spatial resolution in combination with Monte-Carlo simulated scattered radiation, practically noise-free reference data sets are computed with and without inclusion of scatter. The impact of scatter is studied both in the projection data and in the reconstructed volume for the head, thorax, and pelvis regions. Currently available anti-scatter grid geometries do not sufficiently compensate scatter induced cupping and streak artifacts, requiring additional software-based scatter correction. The required accuracy of scatter compensation approaches increases with increasing patient size.

  15. Motion compensation for cone-beam CT using Fourier consistency conditions

    NASA Astrophysics Data System (ADS)

    Berger, M.; Xia, Y.; Aichinger, W.; Mentl, K.; Unberath, M.; Aichert, A.; Riess, C.; Hornegger, J.; Fahrig, R.; Maier, A.

    2017-09-01

    In cone-beam CT, involuntary patient motion and inaccurate or irreproducible scanner motion substantially degrades image quality. To avoid artifacts this motion needs to be estimated and compensated during image reconstruction. In previous work we showed that Fourier consistency conditions (FCC) can be used in fan-beam CT to estimate motion in the sinogram domain. This work extends the FCC to 3\\text{D} cone-beam CT. We derive an efficient cost function to compensate for 3\\text{D} motion using 2\\text{D} detector translations. The extended FCC method have been tested with five translational motion patterns, using a challenging numerical phantom. We evaluated the root-mean-square-error and the structural-similarity-index between motion corrected and motion-free reconstructions. Additionally, we computed the mean-absolute-difference (MAD) between the estimated and the ground-truth motion. The practical applicability of the method is demonstrated by application to respiratory motion estimation in rotational angiography, but also to motion correction for weight-bearing imaging of knees. Where the latter makes use of a specifically modified FCC version which is robust to axial truncation. The results show a great reduction of motion artifacts. Accurate estimation results were achieved with a maximum MAD value of 708 μm and 1184 μm for motion along the vertical and horizontal detector direction, respectively. The image quality of reconstructions obtained with the proposed method is close to that of motion corrected reconstructions based on the ground-truth motion. Simulations using noise-free and noisy data demonstrate that FCC are robust to noise. Even high-frequency motion was accurately estimated leading to a considerable reduction of streaking artifacts. The method is purely image-based and therefore independent of any auxiliary data.

  16. SU-E-J-43: Deformed Planning CT as An Electron Density Substitute for Cone-Beam CT

    SciTech Connect

    Mishra, K; Godley, A

    2014-06-01

    Purpose: To confirm that deforming the planning CT to the daily Cone-Beam CTs (CBCT) can provide suitable electron density for adaptive planning. We quantify the dosimetric difference between plans calculated on deformed planning CTs (DPCT) and daily CT-on-rails images (CTOR). CTOR is used as a test of the method as CTOR already contains accurate electron density to compare against. Methods: Five prostate only IMRT patients, each with five CTOR images, were selected and re-planned on Panther (Prowess Inc.) with a uniform 5 mm PTV expansion, prescribed 78 Gy. The planning CT was deformed to match each CTOR using ABAS (Elekta Inc.). Contours were drawn on the CTOR, and copied to the DPCT. The original treatment plan was copied to both the CTOR and DPCT, keeping the center of the prostate as the isocenter. The plans were then calculated using the collapsed cone heterogeneous dose engine of Prowess and typical DVH planning parameters used to compare them. Results: Each DPCT was visually compared to its CTOR with no differences observed. The agreement of the copied CTOR contours with the DPCT anatomy further demonstrated the deformation accuracy. The plans calculated using CTOR and DPCT were compared. Over the 25 plan pairs, the average difference between them for prostate D100, D98 and D95 were 0.5%, 0.2%, and 0.2%; PTV D98, D95 and mean dose: 0.3%, 0.2% and 0.3%; bladder V70, V60 and mean dose: 1.1%, 0.7%, and 0.2%; and rectum mean dose: 0.3%. (D100 is the dose covering 100% of the target; V70 is the volume of the organ receiving 70 Gy). Conclusion: We observe negligible difference between the dose calculated on the DPCT and the CTOR, implying that deformed planning CTs are a suitable substitute for electron density. The method can now be applied to CBCTs. Research version of Panther provided by Prowess Inc. Research version of ABAS provided by Elekta Inc.

  17. Development of high-resolution x-ray CT system using parallel beam geometry

    SciTech Connect

    Yoneyama, Akio Baba, Rika; Hyodo, Kazuyuki; Takeda, Tohoru; Nakano, Haruhisa; Maki, Koutaro; Sumitani, Kazushi; Hirai, Yasuharu

    2016-01-28

    For fine three-dimensional observations of large biomedical and organic material samples, we developed a high-resolution X-ray CT system. The system consists of a sample positioner, a 5-μm scintillator, microscopy lenses, and a water-cooled sCMOS detector. Parallel beam geometry was adopted to attain a field of view of a few mm square. A fine three-dimensional image of birch branch was obtained using a 9-keV X-ray at BL16XU of SPring-8 in Japan. The spatial resolution estimated from the line profile of a sectional image was about 3 μm.

  18. Automated volume of interest delineation and rendering of cone beam CT images in interventional cardiology

    NASA Astrophysics Data System (ADS)

    Lorenz, Cristian; Schäfer, Dirk; Eshuis, Peter; Carroll, John; Grass, Michael

    2012-02-01

    Interventional C-arm systems allow the efficient acquisition of 3D cone beam CT images. They can be used for intervention planning, navigation, and outcome assessment. We present a fast and completely automated volume of interest (VOI) delineation for cardiac interventions, covering the whole visceral cavity including mediastinum and lungs but leaving out rib-cage and spine. The problem is addressed in a model based approach. The procedure has been evaluated on 22 patient cases and achieves an average surface error below 2mm. The method is able to cope with varying image intensities, varying truncations due to the limited reconstruction volume, and partially with heavy metal and motion artifacts.

  19. Development of high-resolution x-ray CT system using parallel beam geometry

    NASA Astrophysics Data System (ADS)

    Yoneyama, Akio; Baba, Rika; Hyodo, Kazuyuki; Takeda, Tohoru; Nakano, Haruhisa; Maki, Koutaro; Sumitani, Kazushi; Hirai, Yasuharu

    2016-01-01

    For fine three-dimensional observations of large biomedical and organic material samples, we developed a high-resolution X-ray CT system. The system consists of a sample positioner, a 5-μm scintillator, microscopy lenses, and a water-cooled sCMOS detector. Parallel beam geometry was adopted to attain a field of view of a few mm square. A fine three-dimensional image of birch branch was obtained using a 9-keV X-ray at BL16XU of SPring-8 in Japan. The spatial resolution estimated from the line profile of a sectional image was about 3 μm.

  20. Local filtration based scatter correction for cone-beam CT using primary modulation.

    PubMed

    Zhu, Lei

    2016-11-01

    Excessive scatter contamination fundamentally limits the image quality of cone-beam CT (CBCT), hindering its quantitative use in clinical applications. The author has previously proposed an effective scatter correction method for CBCT using primary modulation. A Fourier transform-based algorithm (FTPM) was implemented to estimate scatter from modulated projections, with a few limitations including the assumption of uniform modulation frequency and magnitude that becomes less accurate in the presence of beam-hardening and other nonideal effects. This paper aims to overcome the above drawbacks by developing a new algorithm for the primary modulation method with improved accuracy and reliability. Incident x-ray intensities for each detector pixel with and without the interception of the modulator blocker are estimated from a modulated flat-field image. A new signal relationship is then developed to obtain a first scatter estimate from a modulated projection using a spatially varying modulation distribution. The method empirically adjusts the effective modulation magnitude for each projection ray to account for the beam-hardening effects. Estimated scatter signals with high expected errors are discarded in the generation of the final scatter distribution. The author proposes a technique of local filtration to accelerate major portions of the signal processing, and the new algorithm is referred to as local filtration based primary modulation (LFPM). The study on the Catphan® 600 phantom shows that LFPM effectively removes scatter-induced cupping artifacts on CBCT images and reduces the CT image error from 222 to 15 HU. In addition, the image contrast on eight contrast rods of the phantom is enhanced by a factor of 2 on average. On an anthropomorphic head phantom, LFPM reduces the CT image error from 153 to 18 HU and eliminates the streak artifacts observed on the result of FTPM with substantially improved image uniformity. On the Rando® phantom, LFPM reduces the CT

  1. Investigation of uncertainties in image registration of cone beam CT to CT on an image-guided radiotherapy system.

    PubMed

    Sykes, J R; Brettle, D S; Magee, D R; Thwaites, D I

    2009-12-21

    Methods of measuring uncertainties in rigid body image registration of fan beam computed tomography (FBCT) to cone beam CT (CBCT) have been developed for automatic image registration algorithms in a commercial image guidance system (Synergy, Elekta, UK). The relationships between image registration uncertainty and both imaging dose and image resolution have been investigated with an anthropomorphic skull phantom and further measurements performed with patient images of the head. A new metric of target registration error is proposed. The metric calculates the mean distance traversed by a set of equi-spaced points on the surface of a 5 cm sphere, centred at the isocentre when transformed by the residual error of registration. Studies aimed at giving practical guidance on the use of the Synergy automated image registration, including choice of algorithm and use of the Clipbox are reported. The chamfer-matching algorithm was found to be highly robust to the increased noise induced by low-dose acquisitions. This would allow the imaging dose to be reduced from the current clinical norm of 2 mGy to 0.2 mGy without a clinically significant loss of accuracy. A study of the effect of FBCT slice thickness/spacing and CBCT voxel size showed that 2.5 mm and 1 mm, respectively, gave acceptable image registration performance. Registration failures were highly infrequent if the misalignment was typical of normal clinical set-up errors and these were easily identified. The standard deviation of translational registration errors, measured with patient images, was 0.5 mm on the surface of a 5 cm sphere centred on the treatment centre. The chamfer algorithm is suitable for routine clinical use with minimal need for close inspection of image misalignment.

  2. Investigation of uncertainties in image registration of cone beam CT to CT on an image-guided radiotherapy system

    NASA Astrophysics Data System (ADS)

    Sykes, J. R.; Brettle, D. S.; Magee, D. R.; Thwaites, D. I.

    2009-12-01

    Methods of measuring uncertainties in rigid body image registration of fan beam computed tomography (FBCT) to cone beam CT (CBCT) have been developed for automatic image registration algorithms in a commercial image guidance system (Synergy, Elekta, UK). The relationships between image registration uncertainty and both imaging dose and image resolution have been investigated with an anthropomorphic skull phantom and further measurements performed with patient images of the head. A new metric of target registration error is proposed. The metric calculates the mean distance traversed by a set of equi-spaced points on the surface of a 5 cm sphere, centred at the isocentre when transformed by the residual error of registration. Studies aimed at giving practical guidance on the use of the Synergy automated image registration, including choice of algorithm and use of the Clipbox are reported. The chamfer-matching algorithm was found to be highly robust to the increased noise induced by low-dose acquisitions. This would allow the imaging dose to be reduced from the current clinical norm of 2 mGy to 0.2 mGy without a clinically significant loss of accuracy. A study of the effect of FBCT slice thickness/spacing and CBCT voxel size showed that 2.5 mm and 1 mm, respectively, gave acceptable image registration performance. Registration failures were highly infrequent if the misalignment was typical of normal clinical set-up errors and these were easily identified. The standard deviation of translational registration errors, measured with patient images, was 0.5 mm on the surface of a 5 cm sphere centred on the treatment centre. The chamfer algorithm is suitable for routine clinical use with minimal need for close inspection of image misalignment.

  3. Improving image accuracy of region-of-interest in cone-beam CT using prior image.

    PubMed

    Lee, Jiseoc; Kim, Jin Sung; Cho, Seungryong

    2014-03-06

    In diagnostic follow-ups of diseases, such as calcium scoring in kidney or fat content assessment in liver using repeated CT scans, quantitatively accurate and consistent CT values are desirable at a low cost of radiation dose to the patient. Region of-interest (ROI) imaging technique is considered a reasonable dose reduction method in CT scans for its shielding geometry outside the ROI. However, image artifacts in the reconstructed images caused by missing data outside the ROI may degrade overall image quality and, more importantly, can decrease image accuracy of the ROI substantially. In this study, we propose a method to increase image accuracy of the ROI and to reduce imaging radiation dose via utilizing the outside ROI data from prior scans in the repeated CT applications. We performed both numerical and experimental studies to validate our proposed method. In a numerical study, we used an XCAT phantom with its liver and stomach changing their sizes from one scan to another. Image accuracy of the liver has been improved as the error decreased from 44.4 HU to -0.1 HU by the proposed method, compared to an existing method of data extrapolation to compensate for the missing data outside the ROI. Repeated cone-beam CT (CBCT) images of a patient who went through daily CBCT scans for radiation therapy were also used to demonstrate the performance of the proposed method experimentally. The results showed improved image accuracy inside the ROI. The magnitude of error decreased from -73.2 HU to 18 HU, and effectively reduced image artifacts throughout the entire image.

  4. Design and optimization of a dedicated cone-beam CT system for musculoskeletal extremities imaging

    NASA Astrophysics Data System (ADS)

    Zbijewski, W.; De Jean, P.; Prakash, P.; Ding, Y.; Stayman, J. W.; Packard, N.; Senn, R.; Yang, D.; Yorkston, J.; Machado, A.; Carrino, J. A.; Siewerdsen, J. H.

    2011-03-01

    The design, initial imaging performance, and model-based optimization of a dedicated cone-beam CT (CBCT) scanner for musculoskeletal extremities is presented. The system offers a compact scanner that complements conventional CT and MR by providing sub-mm isotropic spatial resolution, the ability to image weight-bearing extremities, and the capability for integrated real-time fluoroscopy and digital radiography. The scanner employs a flat-panel detector and a fixed anode x-ray source and has a field of view of ~ (20x20x20) cm3. The gantry allows a "standing" configuration for imaging of weight-bearing lower extremities and a "sitting" configuration for imaging of upper extremities and unloaded lower extremities. Cascaded systems analysis guided the selection of x-ray technique (e.g., kVp, filtration, and dose) and system design (e.g., magnification factor), yielding input-quantum-limited performance at detector signal of 100 times the electronic noise, while maintaining patient dose below 5 mGy (a factor of ~2-3 less than conventional CT). A magnification of 1.3 optimized tradeoffs between source and detector blur for a 0.5 mm focal spot. A custom antiscatter grid demonstrated significant reduction of artifacts without loss of contrast-to-noise ratio or increase in dose. Image quality in cadaveric specimens was assessed on a CBCT bench, demonstrating exquisite bone detail, visualization of intra-articular morphology, and soft-tissue visibility approaching that of diagnostic CT. The capability to image loaded extremities and conduct multi-modality CBCT/fluoroscopy with improved workflow compared to whole-body CT could be of value in a broad spectrum of applications, including orthopaedics, rheumatology, surgical planning, and treatment assessment. A clinical prototype has been constructed for deployment in pilot study trials.

  5. SU-E-T-161: Evaluation of Dose Calculation Based On Cone-Beam CT

    SciTech Connect

    Abe, T; Nakazawa, T; Saitou, Y; Nakata, A; Yano, M; Tateoka, K; Fujimoto, K; Sakata, K

    2014-06-01

    Purpose: The purpose of this study is to convert pixel values in cone-beam CT (CBCT) using histograms of pixel values in the simulation CT (sim-CT) and the CBCT images and to evaluate the accuracy of dose calculation based on the CBCT. Methods: The sim-CT and CBCT images immediately before the treatment of 10 prostate cancer patients were acquired. Because of insufficient calibration of the pixel values in the CBCT, it is difficult to be directly used for dose calculation. The pixel values in the CBCT images were converted using an in-house program. A 7 fields treatment plans (original plan) created on the sim-CT images were applied to the CBCT images and the dose distributions were re-calculated with same monitor units (MUs). These prescription doses were compared with those of original plans. Results: In the results of the pixel values conversion in the CBCT images,the mean differences of pixel values for the prostate,subcutaneous adipose, muscle and right-femur were −10.78±34.60, 11.78±41.06, 29.49±36.99 and 0.14±31.15 respectively. In the results of the calculated doses, the mean differences of prescription doses for 7 fields were 4.13±0.95%, 0.34±0.86%, −0.05±0.55%, 1.35±0.98%, 1.77±0.56%, 0.89±0.69% and 1.69±0.71% respectively and as a whole, the difference of prescription dose was 1.54±0.4%. Conclusion: The dose calculation on the CBCT images achieve an accuracy of <2% by using this pixel values conversion program. This may enable implementation of efficient adaptive radiotherapy.

  6. Optimal slice thickness for cone-beam CT with on-board imager

    PubMed Central

    Seet, KYT; Barghi, A; Yartsev, S; Van Dyk, J

    2010-01-01

    Purpose: To find the optimal slice thickness (Δτ) setting for patient registration with kilovoltage cone-beam CT (kVCBCT) on the Varian On Board Imager (OBI) system by investigating the relationship of slice thickness to automatic registration accuracy and contrast-to-noise ratio. Materials and method: Automatic registration was performed on kVCBCT studies of the head and pelvis of a RANDO anthropomorphic phantom. Images were reconstructed with 1.0 ≤ Δτ (mm) ≤ 5.0 at 1.0 mm increments. The phantoms were offset by a known amount, and the suggested shifts were compared to the known shifts by calculating the residual error. A uniform cylindrical phantom with cylindrical inserts of various known CT numbers was scanned with kVCBCT at 1.0 ≤ Δτ (mm) ≤ 5.0 at increments of 0.5 mm. The contrast-to-noise ratios for the inserts were measured at each Δτ. Results: For the planning CT slice thickness used in this study, there was no significant difference in residual error below a threshold equal to the planning CT slice thickness. For Δτ > 3.0 mm, residual error increased for both the head and pelvis phantom studies. The contrast-to-noise ratio is proportional to slice thickness until Δτ = 2.5 mm. Beyond this point, the contrast-to-noise ratio was not affected by Δτ. Conclusion: Automatic registration accuracy is greatest when 1.0 ≤ Δτ (mm) ≤ 3.0 is used. Contrast-to-noise ratio is optimal for the 2.5 ≤ Δτ (mm) ≤ 5.0 range. Therefore 2.5 ≤ Δτ (mm) ≤ 3.0 is recommended for kVCBCT patient registration where the planning CT is 3.0 mm. PMID:21611047

  7. Poster — Thur Eve — 10: Partial kV CBCT, complete kV CBCT and EPID in breast treatment: a dose comparison study for skin, breasts, heart and lungs

    SciTech Connect

    Roussin, E; Archambault, L K; Wierzbicki, W

    2014-08-15

    The advantages of kilovoltage cone beam CT (kV CBCT) imaging over electronic portal imaging device (EPID) such as accurate 3D anatomy, soft tissue visualization, fast rigid registration and enhanced precision on patient positioning has lead to its increasing use in clinics. The benefits of this imaging technique are at the cost of increasing the dose to healthy surrounding organs. Our center has moved toward the use of daily partial rotation kV CBCT to restrict the dose to healthy tissues. This study aims to better quantify radiation doses from different image-guidance techniques such as tangential EPID, complete and partial kV CBCT for breast treatments. Cross-calibrated ionization chambers and kV calibrated Gafchromic films were used to measure the dose to the heart, lungs, breasts and skin. It was found that performing partial kV CBCT decreases the heart dose by about 36%, the lungs dose by 31%, the contralateral breast dose by 41% and the ipsilateral breast dose by 43% when compared to a full rotation CBCT. The skin dose measured for a full rotation CBCT was about 0.8 cGy for the contralateral breast and about 0.3 cGy for the ipsilateral breast. The study is still ongoing and results on skin doses for partial rotation kV CBCT as well as for tangential EPID images are upcoming.

  8. Quantitative evaluation of beam-hardening artefact correction in dual-energy CT myocardial perfusion imaging.

    PubMed

    Bucher, Andreas M; Wichmann, Julian L; Schoepf, U Joseph; Wolla, Christopher D; Canstein, Christian; McQuiston, Andrew D; Krazinski, Aleksander W; De Cecco, Carlo N; Meinel, Felix G; Vogl, Thomas J; Geyer, Lucas L

    2016-09-01

    To assess quantitatively the impact of a novel reconstruction algorithm ("kernel") with beam-hardening correction (BHC) on beam-hardening artefacts of the myocardium at dual-energy CT myocardial perfusion imaging (DE-CTMPI). Rest-series of DE-CTMPI examinations from 14 patients were retrospectively analyzed. Six image series were reconstructed for each patient: a) 100 kV, b) 140 kV, and c) linearly blended MIX0.5, each with BHC (D33f kernel) and without (D30f kernel). Seven hundred and fifty-six myocardial regions were assessed. Seven equal regions of interest divided the myocardium in the axial section. Three subdivisions were created within these regions in areas prone to BHA. Reports of SPECT studies performed within 30 days of CT examination were used to confirm the presence and location of true perfusion defects. Paired student t-test was used for statistical evaluation. Overall mean myocardial attenuation was lower using BHC (D30f: 87.3 ± 24.1 HU; D33f: 85.5 ± 21.5 HU; p = 0.009). Overall relative difference from average myocardial attenuation (RDMA) was more homogeneous using BHC (D30f: -0.3 ± 11.4 %; D33f: 0.1 ± 10.1 %; p < 0.001). Changes in RDMA were greatest in the posterobasal myocardium (D30f: -16.2 ± 10.0 %; D33f: 3.4 ± 10.7 %; p < 0.001). A dedicated reconstruction algorithm with BHC can significantly reduce beam-hardening artefacts in DE-CTMPI. • Beam-hardening artefacts (BHA) cause interference with attenuation-based CT myocardial perfusion assessment (CTMPI). • BHA occur mostly in the posterobasal left ventricular wall. • Beam-hardening correction homogenized and decreased mean myocardial attenuation. • BHC can help avoid false-positive findings and increase specificity of static CTMPI.

  9. Enhancement of breast calcification visualization and detection using a modified PG method in Cone Beam Breast CT.

    PubMed

    Liu, Jiangkun; Ning, Ruola; Cai, Weixing; Benitez, Ricardo Betancourt

    2012-01-01

    Cone Beam Breast CT is a promising diagnostic modality in breast imaging. Its isotropic 3D spatial resolution enhances the characterization of micro-calcifications in breasts that might not be easily distinguishable in mammography. However, due to dose level considerations, it is beneficial to further enhance the visualization of calcifications in Cone Beam Breast CT images that might be masked by noise. In this work, the Papoulis-Gerchberg method was modified and implemented in Cone Beam Breast CT images to improve the visualization and detectability of calcifications. First, the PG method was modified and applied to the projections acquired during the scanning process; its effects on the reconstructed images were analyzed by measuring the Modulation Transfer Function and the Noise Power Spectrum. Second, Cone Beam Breast CT images acquired at different dose levels were pre-processed using this technique to enhance the visualization of calcification. Finally, a computer-aided diagnostic algorithm was utilized to evaluate the efficacy of this method to improve calcification detectability. The results demonstrated that this technique can effectively improve image quality by improving the Modulation Transfer Function with a minor increase in noise level. Consequently, the visualization and detectability of calcifications were improved in Cone Beam Breast CT images. This technique was also proved to be useful in reducing the x-ray dose without degrading visualization and detectability of calcifications.

  10. Enhancement of Breast Calcification Visualization and Detection Using a Modified PG Method in Cone Beam Breast CT

    PubMed Central

    Liu, Jiangkun; Cai, Weixing; Benitez, Ricardo Betancourt

    2012-01-01

    Cone Beam Breast CT is a promising diagnostic modality in breast imaging. Its isotropic 3D spatial resolution enhances the characterization of micro-calcifications in breasts that might not be easily distinguishable in mammography. However, due to dose level considerations, it is beneficial to further enhance the visualization of calcifications in Cone Beam Breast CT images that might be masked by noise. In this work, the Papoulis-Gerchberg method was modified and implemented in Cone Beam Breast CT images to improve the visualization and detectability of calcifications. First, the PG method was modified and applied to the projections acquired during the scanning process; its effects on the reconstructed images were analyzed by measuring the Modulation Transfer Function and the Noise Power Spectrum. Second, Cone Beam Breast CT images acquired at different dose levels were pre-processed using this technique to enhance the visualization of calcification. Finally, a computer-aided diagnostic algorithm was utilized to evaluate the efficacy of this method to improve calcification detectability. The results demonstrated that this technique can effectively improve image quality by improving the Modulation Transfer Function with a minor increase in noise level. Consequently, the visualization and detectability of calcifications were improved in Cone Beam Breast CT images. This technique was also proved to be useful in reducing the x-ray dose without degrading visualization and detectability of calcifications. PMID:22398591

  11. Development of a quality control program for a cone beam CT imaging system

    NASA Astrophysics Data System (ADS)

    Betancourt Benítez, Ricardo; Ning, Ruola; Conover, David; Zhang, Yan; Cai, Weixing

    2008-03-01

    Routine quality control assessments of medical equipment are crucial for an accurate patient medical treatment as well as for the safety of the patient and staff involved. These regular evaluations become especially important when dealing with radiation-emitting equipment. Therefore, a quality control (QC) program has been developed to quantitatively evaluate imaging systems by measuring standard parameters related to image quality such as the Modulation Transfer Function (MTF), the Noise Power Spectrum (NPS), uniformity, linearity and noise level among others. First, the methods of evaluating the aforementioned parameters have been investigated using a cone beam CT imaging system. Different exposure techniques, phantoms, acquisition modes of the flat panel detector (FPD) and reconstruction algorithms relevant to a clinical environment were all included in this investigation. Second, using the results of the first part of this study, a set of parameters for the QC program was established that yields both, an accurate depiction of the system image quality and an integrated program for easy and practical implementation. Lastly, this QC program will be implemented and practiced in our cone beam CT imaging system. The results using our available phantoms demonstrate that the QC program is adequate to evaluate stability and image quality of this system since it provides comparable parameters to other QC programs.

  12. Cone beam CT evaluation of the presence of anatomic accessory canals in the jaws

    PubMed Central

    Eshak, M; Brooks, S; Abdel-Wahed, N

    2014-01-01

    Objectives: To assess the prevalence, location and anatomical course of accessory canals of the jaws using cone beam CT. Methods: A retrospective analysis of 4200 successive cone beam CT scans, for patients of both genders and ages ranging from 7 to 88 years, was performed. They were exposed at the School of Dentistry, University of Michigan, Ann Arbor, MI. After applying the exclusion criteria (the presence of severe ridge resorption, pre-existing implants, a previously reported history of craniofacial malformations or syndromes, a previous history of trauma or surgery, inadequate image quality and subsequent scans from the same individuals), 4051 scans were ultimately included in this study. Results: Of the 4051 scans (2306 females and 1745 males) that qualified for inclusion in this study, accessory canals were identified in 1737 cases (42.9%; 1004 females and 733 males). 532 scans were in the maxilla (13.1%; 296 females and 236 males) and 1205 in the mandible (29.8%; 708 females and 497 males). Conclusions: A network of accessory canals bringing into communication the inner and outer cortical plates of the jaws was identified. In light of these findings, clinicians should carefully assess for the presence of accessory canals prior to any surgical intervention to decrease the risk for complications. PMID:24670010

  13. Does cone beam CT actually ameliorate stab wound analysis in bone?

    PubMed

    Gaudio, D; Di Giancamillo, M; Gibelli, D; Galassi, A; Cerutti, E; Cattaneo, C

    2014-01-01

    This study aims at verifying the potential of a recent radiological technology, cone beam CT (CBCT), for the reproduction of digital 3D models which may allow the user to verify the inner morphology of sharp force wounds within the bone tissue. Several sharp force wounds were produced by both single and double cutting edge weapons on cancellous and cortical bone, and then acquired by cone beam CT scan. The lesions were analysed by different software (a DICOM file viewer and reverse engineering software). Results verified the limited performances of such technology for lesions made on cortical bone, whereas on cancellous bone reliable models were obtained, and the precise morphology within the bone tissues was visible. On the basis of such results, a method for differential diagnosis between cutmarks by sharp tools with a single and two cutting edges can be proposed. On the other hand, the metrical computerised analysis of lesions highlights a clear increase of error range for measurements under 3 mm. Metric data taken by different operators shows a strong dispersion (% relative standard deviation). This pilot study shows that the use of CBCT technology can improve the investigation of morphological stab wounds on cancellous bone. Conversely metric analysis of the lesions as well as morphological analysis of wound dimension under 3 mm do not seem to be reliable.

  14. Accurate Coregistration between Ultra-High-Resolution Micro-SPECT and Circular Cone-Beam Micro-CT Scanners.

    PubMed

    Ji, Changguo; van der Have, Frans; Gratama van Andel, Hugo; Ramakers, Ruud; Beekman, Freek

    2010-01-01

    Introduction. Spatially registering SPECT with CT makes it possible to anatomically localize SPECT tracers. In this study, an accurate method for the coregistration of ultra-high-resolution SPECT volumes and multiple cone-beam CT volumes is developed and validated, which does not require markers during animal scanning. Methods. Transferable animal beds were developed with an accurate mounting interface. Simple calibration phantoms make it possible to obtain both the spatial transformation matrix for stitching multiple CT scans of different parts of the animal and to register SPECT and CT. The spatial transformation for image coregistration is calculated once using Horn's matching algorithm. Animal images can then be coregistered without using markers. Results. For mouse-sized objects, average coregistration errors between SPECT and CT in X, Y, and Z directions are within 0.04 mm, 0.10 mm, and 0.19 mm, respectively. For rat-sized objects, these numbers are 0.22 mm, 0.14 mm, and 0.28 mm. Average 3D coregistration errors were within 0.24 mm and 0.42 mm for mouse and rat imaging, respectively. Conclusion. Extending the field-of-view of cone-beam CT by stitching is improved by prior registration of the CT volumes. The accuracy of registration between SPECT and CT is typically better than the image resolution of current ultra-high-resolution SPECT.

  15. Simulations and experimental feasibility study of fan-beam coherent-scatter CT

    NASA Astrophysics Data System (ADS)

    Harding, Adrian; Schlomka, Jens-Peter; Harding, Geoffrey L.

    2002-11-01

    Fan-beam coherent scatter computer tomography (CSCT) has been employed to obtain 2-dimensional images of spatially resolved diffraction patterns in order to supplement CT images in material discrimination. A Monte Carlo simulation tool DiPhoS (Diagnostic Photon Simulation) was used to create 2-dimensional scatter projection data sets of high-contrast water and Lucite phantom objects with plastic inserts. The results were used as input to a reconstruction routine based on a novel simultaneous iterative reconstruction technique (SIRT). At the same time an experimental demonstrator was assembled to confirm the simulations by measurements and to show the feasibility of coherent scatter CT. It consisted of a 4.5kW constant power X-ray tube, a rotatable object plate and a vertical detector column that could be panned around the object. Spatial resolution was ensured by mechanical collimation. Phantoms similar to those simulated were measured and reconstructed and the contrast achieved by CSCT between the materials under examination substantially exceeded that achieved in CT. A further step was taken by examining an animal tissue sample in the same way, the results of which show remarkable contrast between muscle, cartilage and fat, suggesting that CSCT can also be used in a medical scenario.

  16. Tooth labeling in cone-beam CT using deep convolutional neural network for forensic identification

    NASA Astrophysics Data System (ADS)

    Miki, Yuma; Muramatsu, Chisako; Hayashi, Tatsuro; Zhou, Xiangrong; Hara, Takeshi; Katsumata, Akitoshi; Fujita, Hiroshi

    2017-03-01

    In large disasters, dental record plays an important role in forensic identification. However, filing dental charts for corpses is not an easy task for general dentists. Moreover, it is laborious and time-consuming work in cases of large scale disasters. We have been investigating a tooth labeling method on dental cone-beam CT images for the purpose of automatic filing of dental charts. In our method, individual tooth in CT images are detected and classified into seven tooth types using deep convolutional neural network. We employed the fully convolutional network using AlexNet architecture for detecting each tooth and applied our previous method using regular AlexNet for classifying the detected teeth into 7 tooth types. From 52 CT volumes obtained by two imaging systems, five images each were randomly selected as test data, and the remaining 42 cases were used as training data. The result showed the tooth detection accuracy of 77.4% with the average false detection of 5.8 per image. The result indicates the potential utility of the proposed method for automatic recording of dental information.

  17. Improving the accuracy of CT dimensional metrology by a novel beam hardening correction method

    NASA Astrophysics Data System (ADS)

    Zhang, Xiang; Li, Lei; Zhang, Feng; Xi, Xiaoqi; Deng, Lin; Yan, Bin

    2015-01-01

    Its powerful nondestructive characteristics are attracting more and more research into the study of computed tomography (CT) for dimensional metrology, which offers a practical alternative to the common measurement methods. However, the inaccuracy and uncertainty severely limit the further utilization of CT for dimensional metrology due to many factors, among which the beam hardening (BH) effect plays a vital role. This paper mainly focuses on eliminating the influence of the BH effect in the accuracy of CT dimensional metrology. To correct the BH effect, a novel exponential correction model is proposed. The parameters of the model are determined by minimizing the gray entropy of the reconstructed volume. In order to maintain the consistency and contrast of the corrected volume, a punishment term is added to the cost function, enabling more accurate measurement results to be obtained by the simple global threshold method. The proposed method is efficient, and especially suited to the case where there is a large difference in gray value between material and background. Different spheres with known diameters are used to verify the accuracy of dimensional measurement. Both simulation and real experimental results demonstrate the improvement in measurement precision. Moreover, a more complex workpiece is also tested to show that the proposed method is of general feasibility.

  18. An investigation into factors affecting electron density calibration for a megavoltage cone-beam CT system.

    PubMed

    Hughes, Jessica; Holloway, Lois C; Quinn, Alexandra; Fielding, Andrew

    2012-09-06

    There is a growing interest in the use of megavoltage cone-beam computed tomography (MV CBCT) data for radiotherapy treatment planning. To calculate accurate dose distributions, knowledge of the electron density (ED) of the tissues being irradiated is required. In the case of MV CBCT, it is necessary to determine a calibration-relating CT number to ED, utilizing the photon beam produced for MV CBCT. A number of different parameters can affect this calibration. This study was undertaken on the Siemens MV CBCT system, MVision, to evaluate the effect of the following parameters on the reconstructed CT pixel value to ED calibration: the number of monitor units (MUs) used (5, 8, 15 and 60 MUs), the image reconstruction filter (head and neck, and pelvis), reconstruction matrix size (256 by 256 and 512 by 512), and the addition of extra solid water surrounding the ED phantom. A Gammex electron density CT phantom containing EDs from 0.292 to 1.707 was imaged under each of these conditions. The linear relationship between MV CBCT pixel value and ED was demonstrated for all MU settings and over the range of EDs. Changes in MU number did not dramatically alter the MV CBCT ED calibration. The use of different reconstruction filters was found to affect the MV CBCT ED calibration, as was the addition of solid water surrounding the phantom. Dose distributions from treatment plans calculated with simulated image data from a 15 MU head and neck reconstruction filter MV CBCT image and a MV CBCT ED calibration curve from the image data parameters and a 15 MU pelvis reconstruction filter showed small and clinically insignificant differences. Thus, the use of a single MV CBCT ED calibration curve is unlikely to result in any clinical differences. However, to ensure minimal uncertainties in dose reporting, MV CBCT ED calibration measurements could be carried out using parameter-specific calibration measurements.

  19. Optimizing 4D cone-beam CT acquisition protocol for external beam radiotherapy

    SciTech Connect

    Li Tianfang; Xing Lei . E-mail: lei@reyes.stanford.edu

    2007-03-15

    Purpose: Four-dimensional cone-beam computed tomography (4D-CBCT) imaging is sensitive to parameters such as gantry rotation speed, number of gantry rotations, X-ray pulse rate, and tube current, as well as a patient's breathing pattern. The aim of this study is to optimize the image acquisition on a patient-specific basis while minimizing the scan time and the radiation dose. Methods and Materials: More than 60 sets of 4D-CBCT images, each with a temporal resolution of 10 phases, were acquired using multiple-gantry rotation and slow-gantry rotation techniques. The image quality was quantified with a relative root mean-square error (RE) and correlated with various acquisition settings; specifically, varying gantry rotation speed, varying both the rotation speed and the number of rotations, and varying both the rotation speed and tube current to keep the radiation exposure constant. These experiments were repeated for three different respiratory periods. Results: With similar radiation dose, 4D-CBCT images acquired with low current and low rotation speed have better quality over images obtained with high current and high rotation speed. In general, a one-rotation low-speed scan is superior to a two-rotation double-speed scan, even though they provide the same number of projections. Furthermore, it is found that the image quality behaves monotonically with the relative speed as defined by the gantry rotation speed and the patient respiratory period. Conclusions: The RE curves established in this work can be used to predict the 4D-CBCT image quality before a scan. This allows the acquisition protocol to be optimized individually to balance the desired quality with the associated scanning time and patient radiation dose.

  20. 4D-Imaging of the Lung: Reproducibility of Lesion Size and Displacement on Helical CT, MRI, and Cone Beam CT in a Ventilated Ex Vivo System

    SciTech Connect

    Biederer, Juergen Dinkel, Julien; Remmert, Gregor; Jetter, Siri; Nill, Simeon; Moser, Torsten; Bendl, Rolf; Thierfelder, Carsten; Fabel, Michael; Oelfke, Uwe; Bock, Michael; Plathow, Christian; Bolte, Hendrik; Welzel, Thomas; Hoffmann, Beata; Hartmann, Guenter; Schlegel, Wolfgang; Debus, Juergen; Heller, Martin

    2009-03-01

    Purpose: Four-dimensional (4D) imaging is a key to motion-adapted radiotherapy of lung tumors. We evaluated in a ventilated ex vivo system how size and displacement of artificial pulmonary nodules are reproduced with helical 4D-CT, 4D-MRI, and linac-integrated cone beam CT (CBCT). Methods and Materials: Four porcine lungs with 18 agarose nodules (mean diameters 1.3-1.9 cm), were ventilated inside a chest phantom at 8/min and subject to 4D-CT (collimation 24 x 1.2 mm, pitch 0.1, slice/increment 24x10{sup 2}/1.5/0.8 mm, pitch 0.1, temporal resolution 0.5 s), 4D-MRI (echo-shared dynamic three-dimensional-flash; repetition/echo time 2.13/0.72 ms, voxel size 2.7 x 2.7 x 4.0 mm, temporal resolution 1.4 s) and linac-integrated 4D-CBCT (720 projections, 3-min rotation, temporal resolution {approx}1 s). Static CT without respiration served as control. Three observers recorded lesion size (RECIST-diameters x/y/z) and axial displacement. Interobserver- and interphase-variation coefficients (IO/IP VC) of measurements indicated reproducibility. Results: Mean x/y/z lesion diameters in cm were equal on static and dynamic CT (1.88/1.87; 1.30/1.39; 1.71/1.73; p > 0.05), but appeared larger on MRI and CBCT (2.06/1.95 [p < 0.05 vs. CT]; 1.47/1.28 [MRI vs. CT/CBCT p < 0.05]; 1.86/1.83 [CT vs. CBCT p < 0.05]). Interobserver-VC for lesion sizes were 2.54-4.47% (CT), 2.29-4.48% (4D-CT); 5.44-6.22% (MRI) and 4.86-6.97% (CBCT). Interphase-VC for lesion sizes ranged from 2.28% (4D-CT) to 10.0% (CBCT). Mean displacement in cm decreased from static CT (1.65) to 4D-CT (1.40), CBCT (1.23) and MRI (1.16). Conclusions: Lesion sizes are exactly reproduced with 4D-CT but overestimated on 4D-MRI and CBCT with a larger variability due to limited temporal and spatial resolution. All 4D-modalities underestimate lesion displacement.

  1. 4D-Imaging of the lung: reproducibility of lesion size and displacement on helical CT, MRI, and cone beam CT in a ventilated ex vivo system.

    PubMed

    Biederer, Juergen; Dinkel, Julien; Remmert, Gregor; Jetter, Siri; Nill, Simeon; Moser, Torsten; Bendl, Rolf; Thierfelder, Carsten; Fabel, Michael; Oelfke, Uwe; Bock, Michael; Plathow, Christian; Bolte, Hendrik; Welzel, Thomas; Hoffmann, Beata; Hartmann, Günter; Schlegel, Wolfgang; Debus, Jürgen; Heller, Martin; Kauczor, Hans-Ulrich

    2009-03-01

    Four-dimensional (4D) imaging is a key to motion-adapted radiotherapy of lung tumors. We evaluated in a ventilated ex vivo system how size and displacement of artificial pulmonary nodules are reproduced with helical 4D-CT, 4D-MRI, and linac-integrated cone beam CT (CBCT). Four porcine lungs with 18 agarose nodules (mean diameters 1.3-1.9 cm), were ventilated inside a chest phantom at 8/min and subject to 4D-CT (collimation 24 x 1.2 mm, pitch 0.1, slice/increment 24 x 10(2)/1.5/0.8 mm, pitch 0.1, temporal resolution 0.5 s), 4D-MRI (echo-shared dynamic three-dimensional-flash; repetition/echo time 2.13/0.72 ms, voxel size 2.7 x 2.7 x 4.0 mm, temporal resolution 1.4 s) and linac-integrated 4D-CBCT (720 projections, 3-min rotation, temporal resolution approximately 1 s). Static CT without respiration served as control. Three observers recorded lesion size (RECIST-diameters x/y/z) and axial displacement. Interobserver- and interphase-variation coefficients (IO/IP VC) of measurements indicated reproducibility. Mean x/y/z lesion diameters in cm were equal on static and dynamic CT (1.88/1.87; 1.30/1.39; 1.71/1.73; p > 0.05), but appeared larger on MRI and CBCT (2.06/1.95 [p < 0.05 vs. CT]; 1.47/1.28 [MRI vs. CT/CBCT p < 0.05]; 1.86/1.83 [CT vs. CBCT p < 0.05]). Interobserver-VC for lesion sizes were 2.54-4.47% (CT), 2.29-4.48% (4D-CT); 5.44-6.22% (MRI) and 4.86-6.97% (CBCT). Interphase-VC for lesion sizes ranged from 2.28% (4D-CT) to 10.0% (CBCT). Mean displacement in cm decreased from static CT (1.65) to 4D-CT (1.40), CBCT (1.23) and MRI (1.16). Lesion sizes are exactly reproduced with 4D-CT but overestimated on 4D-MRI and CBCT with a larger variability due to limited temporal and spatial resolution. All 4D-modalities underestimate lesion displacement.

  2. Validation of a deformable image registration technique for cone beam CT-based dose verification

    SciTech Connect

    Moteabbed, M. Sharp, G. C.; Wang, Y.; Trofimov, A.; Efstathiou, J. A.; Lu, H.-M.

    2015-01-15

    Purpose: As radiation therapy evolves toward more adaptive techniques, image guidance plays an increasingly important role, not only in patient setup but also in monitoring the delivered dose and adapting the treatment to patient changes. This study aimed to validate a method for evaluation of delivered intensity modulated radiotherapy (IMRT) dose based on multimodal deformable image registration (DIR) for prostate treatments. Methods: A pelvic phantom was scanned with CT and cone-beam computed tomography (CBCT). Both images were digitally deformed using two realistic patient-based deformation fields. The original CT was then registered to the deformed CBCT resulting in a secondary deformed CT. The registration quality was assessed as the ability of the DIR method to recover the artificially induced deformations. The primary and secondary deformed CT images as well as vector fields were compared to evaluate the efficacy of the registration method and it’s suitability to be used for dose calculation. PLASTIMATCH, a free and open source software was used for deformable image registration. A B-spline algorithm with optimized parameters was used to achieve the best registration quality. Geometric image evaluation was performed through voxel-based Hounsfield unit (HU) and vector field comparison. For dosimetric evaluation, IMRT treatment plans were created and optimized on the original CT image and recomputed on the two warped images to be compared. The dose volume histograms were compared for the warped structures that were identical in both warped images. This procedure was repeated for the phantom with full, half full, and empty bladder. Results: The results indicated mean HU differences of up to 120 between registered and ground-truth deformed CT images. However, when the CBCT intensities were calibrated using a region of interest (ROI)-based calibration curve, these differences were reduced by up to 60%. Similarly, the mean differences in average vector field

  3. Validation of a deformable image registration technique for cone beam CT-based dose verification

    PubMed Central

    Moteabbed, M.; Sharp, G. C.; Wang, Y.; Trofimov, A.; Efstathiou, J. A.; Lu, H.-M.

    2015-01-01

    Purpose: As radiation therapy evolves toward more adaptive techniques, image guidance plays an increasingly important role, not only in patient setup but also in monitoring the delivered dose and adapting the treatment to patient changes. This study aimed to validate a method for evaluation of delivered intensity modulated radiotherapy (IMRT) dose based on multimodal deformable image registration (dir) for prostate treatments. Methods: A pelvic phantom was scanned with CT and cone-beam computed tomography (CBCT). Both images were digitally deformed using two realistic patient-based deformation fields. The original CT was then registered to the deformed CBCT resulting in a secondary deformed CT. The registration quality was assessed as the ability of the dir method to recover the artificially induced deformations. The primary and secondary deformed CT images as well as vector fields were compared to evaluate the efficacy of the registration method and it’s suitability to be used for dose calculation. plastimatch, a free and open source software was used for deformable image registration. A B-spline algorithm with optimized parameters was used to achieve the best registration quality. Geometric image evaluation was performed through voxel-based Hounsfield unit (HU) and vector field comparison. For dosimetric evaluation, IMRT treatment plans were created and optimized on the original CT image and recomputed on the two warped images to be compared. The dose volume histograms were compared for the warped structures that were identical in both warped images. This procedure was repeated for the phantom with full, half full, and empty bladder. Results: The results indicated mean HU differences of up to 120 between registered and ground-truth deformed CT images. However, when the CBCT intensities were calibrated using a region of interest (ROI)-based calibration curve, these differences were reduced by up to 60%. Similarly, the mean differences in average vector field

  4. WE-G-18A-06: Sinogram Restoration in Helical Cone-Beam CT

    SciTech Connect

    Little, K; Riviere, P La

    2014-06-15

    Purpose: To extend CT sinogram restoration, which has been shown in 2D to reduce noise and to correct for geometric effects and other degradations at a low computational cost, from 2D to a 3D helical cone-beam geometry. Methods: A method for calculating sinogram degradation coefficients for a helical cone-beam geometry was proposed. These values were used to perform penalized-likelihood sinogram restoration on simulated data that were generated from the FORBILD thorax phantom. Sinogram restorations were performed using both a quadratic penalty and the edge-preserving Huber penalty. After sinogram restoration, Fourier-based analytical methods were used to obtain reconstructions. Resolution-variance trade-offs were investigated for several locations within the reconstructions for the purpose of comparing sinogram restoration to no restoration. In order to compare potential differences, reconstructions were performed using different groups of neighbors in the penalty, two analytical reconstruction methods (Katsevich and single-slice rebinning), and differing helical pitches. Results: The resolution-variance properties of reconstructions restored using sinogram restoration with a Huber penalty outperformed those of reconstructions with no restoration. However, the use of a quadratic sinogram restoration penalty did not lead to an improvement over performing no restoration at the outer regions of the phantom. Application of the Huber penalty to neighbors both within a view and across views did not perform as well as only applying the penalty to neighbors within a view. General improvements in resolution-variance properties using sinogram restoration with the Huber penalty were not dependent on the reconstruction method used or the magnitude of the helical pitch. Conclusion: Sinogram restoration for noise and degradation effects for helical cone-beam CT is feasible and should be able to be applied to clinical data. When applied with the edge-preserving Huber penalty

  5. Effect of voxel size on the accuracy of 3D reconstructions with cone beam CT

    PubMed Central

    Maret, D; Telmon, N; Peters, O A; Lepage, B; Treil, J; Inglèse, J M; Peyre, A; Kahn, J L; Sixou, M

    2012-01-01

    Objectives The various types of cone beam CT (CBCT) differ in several technical characteristics, notably their spatial resolution, which is defined by the acquisition voxel size. However, data are still lacking on the effects of voxel size on the metric accuracy of three-dimensional (3D) reconstructions. This study was designed to assess the effect of isotropic voxel size on the 3D reconstruction accuracy and reproducibility of CBCT data. Methods The study sample comprised 70 teeth (from the Institut d’Anatomie Normale, Strasbourg, France). The teeth were scanned with a KODAK 9500 3D® CBCT (Carestream Health, Inc., Marne-la-Vallée, France), which has two voxel sizes: 200 µm (CBCT 200 µm group) and 300 µm (CBCT 300 µm group). These teeth had also been scanned with the KODAK 9000 3D® CBCT (Carestream Health, Inc.) (CBCT 76 µm group) and the SCANCO Medical micro-CT XtremeCT (SCANCO Medical, Brüttisellen, Switzerland) (micro-CT 41 µm group) considered as references. After semi-automatic segmentation with AMIRA® software (Visualization Sciences Group, Burlington, MA), tooth volumetric measurements were obtained. Results The Bland–Altman method showed no difference in tooth volumes despite a slight underestimation for the CBCT 200 µm and 300 µm groups compared with the two reference groups. The underestimation was statistically significant for the volumetric measurements of the CBCT 300 µm group relative to the two reference groups (Passing–Bablok method). Conclusions CBCT is not only a tool that helps in diagnosis and detection but it has the complementary advantage of being a measuring instrument, the accuracy of which appears connected to the size of the voxels. Future applications of such measurements with CBCT are discussed. PMID:23166362

  6. Effect of voxel size on the accuracy of 3D reconstructions with cone beam CT.

    PubMed

    Maret, D; Telmon, N; Peters, O A; Lepage, B; Treil, J; Inglèse, J M; Peyre, A; Kahn, J L; Sixou, M

    2012-12-01

    The various types of cone beam CT (CBCT) differ in several technical characteristics, notably their spatial resolution, which is defined by the acquisition voxel size. However, data are still lacking on the effects of voxel size on the metric accuracy of three-dimensional (3D) reconstructions. This study was designed to assess the effect of isotropic voxel size on the 3D reconstruction accuracy and reproducibility of CBCT data. The study sample comprised 70 teeth (from the Institut d'Anatomie Normale, Strasbourg, France). The teeth were scanned with a KODAK 9500 3D® CBCT (Carestream Health, Inc., Marne-la-Vallée, France), which has two voxel sizes: 200 µm (CBCT 200 µm group) and 300 µm (CBCT 300 µm group). These teeth had also been scanned with the KODAK 9000 3D® CBCT (Carestream Health, Inc.) (CBCT 76 µm group) and the SCANCO Medical micro-CT XtremeCT (SCANCO Medical, Brüttisellen, Switzerland) (micro-CT 41 µm group) considered as references. After semi-automatic segmentation with AMIRA® software (Visualization Sciences Group, Burlington, MA), tooth volumetric measurements were obtained. The Bland-Altman method showed no difference in tooth volumes despite a slight underestimation for the CBCT 200 µm and 300 µm groups compared with the two reference groups. The underestimation was statistically significant for the volumetric measurements of the CBCT 300 µm group relative to the two reference groups (Passing-Bablok method). CBCT is not only a tool that helps in diagnosis and detection but it has the complementary advantage of being a measuring instrument, the accuracy of which appears connected to the size of the voxels. Future applications of such measurements with CBCT are discussed.

  7. Classification of teeth in cone-beam CT using deep convolutional neural network.

    PubMed

    Miki, Yuma; Muramatsu, Chisako; Hayashi, Tatsuro; Zhou, Xiangrong; Hara, Takeshi; Katsumata, Akitoshi; Fujita, Hiroshi

    2017-01-01

    Dental records play an important role in forensic identification. To this end, postmortem dental findings and teeth conditions are recorded in a dental chart and compared with those of antemortem records. However, most dentists are inexperienced at recording the dental chart for corpses, and it is a physically and mentally laborious task, especially in large scale disasters. Our goal is to automate the dental filing process by using dental x-ray images. In this study, we investigated the application of a deep convolutional neural network (DCNN) for classifying tooth types on dental cone-beam computed tomography (CT) images. Regions of interest (ROIs) including single teeth were extracted from CT slices. Fifty two CT volumes were randomly divided into 42 training and 10 test cases, and the ROIs obtained from the training cases were used for training the DCNN. For examining the sampling effect, random sampling was performed 3 times, and training and testing were repeated. We used the AlexNet network architecture provided in the Caffe framework, which consists of 5 convolution layers, 3 pooling layers, and 2 full connection layers. For reducing the overtraining effect, we augmented the data by image rotation and intensity transformation. The test ROIs were classified into 7 tooth types by the trained network. The average classification accuracy using the augmented training data by image rotation and intensity transformation was 88.8%. Compared with the result without data augmentation, data augmentation resulted in an approximately 5% improvement in classification accuracy. This indicates that the further improvement can be expected by expanding the CT dataset. Unlike the conventional methods, the proposed method is advantageous in obtaining high classification accuracy without the need for precise tooth segmentation. The proposed tooth classification method can be useful in automatic filing of dental charts for forensic identification.

  8. Design and development of C-arm based cone-beam CT for image-guided interventions: initial results

    NASA Astrophysics Data System (ADS)

    Chen, Guang-Hong; Zambelli, Joseph; Nett, Brian E.; Supanich, Mark; Riddell, Cyril; Belanger, Barry; Mistretta, Charles A.

    2006-03-01

    X-ray cone-beam computed tomography (CBCT) is of importance in image-guided intervention (IGI) and image-guided radiation therapy (IGRT). In this paper, we present a cone-beam CT data acquisition system using a GE INNOVA 4100 (GE Healthcare Technologies, Waukesha, Wisconsin) clinical system. This new cone-beam data acquisition mode was developed for research purposes without interfering with any clinical function of the system. It provides us a basic imaging pipeline for more advanced cone-beam data acquisition methods. It also provides us a platform to study and overcome the limiting factors such as cone-beam artifacts and limiting low contrast resolution in current C-arm based cone-beam CT systems. A geometrical calibration method was developed to experimentally determine parameters of the scanning geometry to correct the image reconstruction for geometric non-idealities. Extensive phantom studies and some small animal studies have been conducted to evaluate the performance of our cone-beam CT data acquisition system.

  9. Usefulness of a lead shielding device for reducing the radiation dose to tissues outside the primary beams during CT.

    PubMed

    Chung, Jae-Joon; Cho, Eun-Suk; Kang, Sung Min; Yu, Jeong-Sik; Kim, Dae Jung; Kim, Joo Hee

    2014-12-01

    This study was done to investigate the efficacy of a lead shield in protecting the tissues outside the primary beams, such as the breast and thyroid, by measurement of the entrance skin dose during CT of the brain, neck, abdomen, and lumbar spine. Institutional Review Board approval was obtained. This study included 150 patients (male:female 25:125, age range 15-45 years). In females, brain, lumbar spine, and abdominal CT scans, pre-/post-contrast neck CT scans, and post-contrast liver dynamic CT scans were performed. In males, brain CT scans only were performed. Breast shielding was performed in all females, and thyroid shielding was conducted in patients with brain CT. During all CT studies, the left breast or left thyroid was shielded using a lead shield, and the contralateral side was left unshielded. Thus, each breast or thyroid measurement had its own control for the same demographic data. The efficacy of the shielding of both breasts and thyroids during CT was assessed. During brain, abdominal, lumbar, pre-/post-contrast neck, and post-contrast liver dynamic CT, 33.5, 26.0, 17.4, 26.5, and 16.2 % of the breast skin dose were reduced, respectively. During brain CT, the thyroid skin dose was reduced by 17.9 % (females) and 20.6 % (males). There were statistically significant differences in the skin doses of shielded organs (p < 0.05). Breast shielding during neck and liver dynamic CT was the most effective compared with breast or thyroid shielding during other CT scans. We recommend breast shielding during neck and liver dynamic CT in young female patients to avoid unnecessary radiation exposure.

  10. SU-E-J-103: Setup Errors Analysis by Cone-Beam CT (CBCT)-Based Imaged-Guided Intensity Modulated Radiotherapy for Esophageal Cancer

    SciTech Connect

    Yang, H; Wang, W; Hu, W; Chen, X; Wang, X; Yu, C

    2014-06-01

    Purpose: To quantify setup errors by pretreatment kilovolt cone-beam computed tomography(KV-CBCT) scans for middle or distal esophageal carcinoma patients. Methods: Fifty-two consecutive middle or distal esophageal carcinoma patients who underwent IMRT were included this study. A planning CT scan using a big-bore CT simulator was performed in the treatment position and was used as the reference scan for image registration with CBCT. CBCT scans(On-Board Imaging v1. 5 system, Varian Medical Systems) were acquired daily during the first treatment week. A total of 260 CBCT scans was assessed with a registration clip box defined around the PTV-thorax in the reference scan based on(nine CBCTs per patient) bony anatomy using Offline Review software v10.0(Varian Medical Systems). The anterior-posterior(AP), left-right(LR), superiorinferior( SI) corrections were recorded. The systematic and random errors were calculated. The CTV-to-PTV margins in each CBCT frequency was based on the Van Herk formula (2.5Σ+0.7σ). Results: The SD of systematic error (Σ) was 2.0mm, 2.3mm, 3.8mm in the AP, LR and SI directions, respectively. The average random error (σ) was 1.6mm, 2.4mm, 4.1mm in the AP, LR and SI directions, respectively. The CTV-to-PTV safety margin was 6.1mm, 7.5mm, 12.3mm in the AP, LR and SI directions based on van Herk formula. Conclusion: Our data recommend the use of 6 mm, 8mm, and 12 mm for esophageal carcinoma patient setup in AP, LR, SI directions, respectively.

  11. The value of cone beam CT in assessing and managing a dilated odontome of a maxillary canine.

    PubMed

    Wall, Aoibheann; Ng, Suk; Djemal, Serpil

    2015-03-01

    A case of an unusual anomaly in a maxillary canine is described. A deep enamel invagination resulted in pulpal necrosis, longstanding infection and development of an associated radicular cyst. Diagnostic X-ray imaging was invaluable in demonstrating the complex root anatomy of the dilated odontome. In particular, a cone beam CT scan helped in the formulation of an appropriate treatment plan. Clinical Relevance: Three-dimensional imaging using cone beam CT was valuable in this case to demonstrate the complicated anatomy of a rare dental anomaly, and to help plan treatment.

  12. Bone Forming Potential of An-Organic Bovine Bone Graft: A Cone Beam CT study.

    PubMed

    Uzbek, Usman Haider; Rahman, Shaifulizan Ab; Alam, Mohammad Khursheed; Gillani, Syed Wasif

    2014-12-01

    An-organic bovine bone graft is a xenograft with the potential of bone formation. The aim of this study was to evaluate the bone density using cone beam computed tomography scans around functional endosseous implant in the region of both augmented maxillary sinus with the an-organic bovine bone graft and the alveolar bone over which the graft was placed to provide space for the implants. Sterile freeze dried bovine bone graft produced by National Tissue Bank, University Sains, Malaysia was used for stage-1 implant placement with maxillary sinus augmentation in a total of 19 subjects with 19 implants. The age of all subjects ranged between 40-60 years with a mean age 51±4.70. All subjects underwent a follow up CT scan using PlanmecaPromax 3D(®) Cone beam computed tomography scanner at the Radiology department, Hospital University Sains, Malaysia. The collected data was then analysed to evaluate bone density in Hounsfield Units using PlanmecaRomexis" Imaging Software 2.2(®) which is specialized accompanying software of the cone beam computed tomography machine. There was bone formation seen at the site of the augmented sinus. A significant increase (p<0.005) in bone density was reported at the augmented site compared to the bone density of the existing alveolar bone. An-organic bovine bone graft is an osteoconductive material that can be used for the purpose of maxillary sinus augmentation.

  13. Dose distribution for dental cone beam CT and its implication for defining a dose index

    PubMed Central

    Pauwels, R; Theodorakou, C; Walker, A; Bosmans, H; Jacobs, R; Horner, K; Bogaerts, R

    2012-01-01

    Objectives To characterize the dose distribution for a range of cone beam CT (CBCT) units, investigating different field of view sizes, central and off-axis geometries, full or partial rotations of the X-ray tube and different clinically applied beam qualities. The implications of the dose distributions on the definition and practicality of a CBCT dose index were assessed. Methods Dose measurements on CBCT devices were performed by scanning cylindrical head-size water and polymethyl methacrylate phantoms, using thermoluminescent dosemeters, a small-volume ion chamber and radiochromic films. Results It was found that the dose distribution can be asymmetrical for dental CBCT exposures throughout a homogeneous phantom, owing to an asymmetrical positioning of the isocentre and/or partial rotation of the X-ray source. Furthermore, the scatter tail along the z-axis was found to have a distinct shape, generally resulting in a strong drop (90%) in absorbed dose outside the primary beam. Conclusions There is no optimal dose index available owing to the complicated exposure geometry of CBCT and the practical aspects of quality control measurements. Practical validation of different possible dose indices is needed, as well as the definition of conversion factors to patient dose. PMID:22752320

  14. Bone Forming Potential of An-Organic Bovine Bone Graft: A Cone Beam CT study

    PubMed Central

    Rahman, Shaifulizan AB.; Alam, Mohammad Khursheed; Gillani, Syed Wasif

    2014-01-01

    Purpose: An-organic bovine bone graft is a xenograft with the potential of bone formation. The aim of this study was to evaluate the bone density using cone beam computed tomography scans around functional endosseous implant in the region of both augmented maxillary sinus with the an-organic bovine bone graft and the alveolar bone over which the graft was placed to provide space for the implants. Materials and Methods: Sterile freeze dried bovine bone graft produced by National Tissue Bank, University Sains, Malaysia was used for stage-1 implant placement with maxillary sinus augmentation in a total of 19 subjects with 19 implants. The age of all subjects ranged between 40-60 years with a mean age 51±4.70. All subjects underwent a follow up CT scan using PlanmecaPromax 3D® Cone beam computed tomography scanner at the Radiology department, Hospital University Sains, Malaysia. The collected data was then analysed to evaluate bone density in Hounsfield Units using PlanmecaRomexis” Imaging Software 2.2® which is specialized accompanying software of the cone beam computed tomography machine. Results: There was bone formation seen at the site of the augmented sinus. A significant increase (p<0.005) in bone density was reported at the augmented site compared to the bone density of the existing alveolar bone. Conclusion: An-organic bovine bone graft is an osteoconductive material that can be used for the purpose of maxillary sinus augmentation. PMID:25654037

  15. Beam-specific planning target volumes incorporating 4D CT for pencil beam scanning proton therapy of thoracic tumors.

    PubMed

    Lin, Liyong; Kang, Minglei; Huang, Sheng; Mayer, Rulon; Thomas, Andrew; Solberg, Timothy D; McDonough, James E; Simone, Charles B

    2015-11-08

    The purpose of this study is to determine whether organ sparing and target coverage can be simultaneously maintained for pencil beam scanning (PBS) proton therapy treatment of thoracic tumors in the presence of motion, stopping power uncertainties, and patient setup variations. Ten consecutive patients that were previously treated with proton therapy to 66.6/1.8 Gy (RBE) using double scattering (DS) were replanned with PBS. Minimum and maximum intensity images from 4D CT were used to introduce flexible smearing in the determination of the beam specific PTV (BSPTV). Datasets from eight 4D CT phases, using ± 3% uncertainty in stopping power and ± 3 mm uncertainty in patient setup in each direction, were used to create 8 × 12 × 10 = 960 PBS plans for the evaluation of 10 patients. Plans were normalized to provide identical coverage between DS and PBS. The average lung V20, V5, and mean doses were reduced from 29.0%, 35.0%, and 16.4 Gy with DS to 24.6%, 30.6%, and 14.1 Gy with PBS, respectively. The average heart V30 and V45 were reduced from 10.4% and 7.5% in DS to 8.1% and 5.4% for PBS, respectively. Furthermore, the maximum spinal cord, esophagus, and heart doses were decreased from 37.1 Gy, 71.7 Gy, and 69.2 Gy with DS to 31.3 Gy, 67.9 Gy, and 64.6 Gy with PBS. The conformity index (CI), homogeneity index (HI), and global maximal dose were improved from 3.2, 0.08, 77.4 Gy with DS to 2.8, 0.04, and 72.1 Gy with PBS. All differences are statistically significant, with p-values <0.05, with the exception of the heart V45 (p = 0.146). PBS with BSPTV achieves better organ sparing and improves target coverage using a repainting method for the treatment of thoracic tumors. Incorporating motion-related uncertainties is essential.

  16. Beam-specific planning target volumes incorporating 4D CT for pencil beam scanning proton therapy of thoracic tumors.

    PubMed

    Lin, Liyong; Kang, Minglei; Huang, Sheng; Mayer, Rulon; Thomas, Andrew; Solberg, Timothy D; McDonough, James E; Simone, Charles B

    2015-11-01

    The purpose of this study is to determine whether organ sparing and target coverage can be simultaneously maintained for pencil beam scanning (PBS) proton therapy treatment of thoracic tumors in the presence of motion, stopping power uncertainties, and patient setup variations. Ten consecutive patients that were previously treated with proton therapy to 66.6/1.8 Gy (RBE) using double scattering (DS) were replanned with PBS. Minimum and maximum intensity images from 4D CT were used to introduce flexible smearing in the determination of the beam specific PTV (BSPTV). Datasets from eight 4D CT phases, using ±3% uncertainty in stopping power and ±3 mm uncertainty in patient setup in each direction, were used to create 8×12×10=960 PBS plans for the evaluation of 10 patients. Plans were normalized to provide identical coverage between DS and PBS. The average lung V20, V5, and mean doses were reduced from 29.0%, 35.0%, and 16.4 Gy with DS to 24.6%, 30.6%, and 14.1 Gy with PBS, respectively. The average heart V30 and V45 were reduced from 10.4% and 7.5% in DS to 8.1% and 5.4% for PBS, respectively. Furthermore, the maximum spinal cord, esophagus, and heart doses were decreased from 37.1 Gy, 71.7 Gy, and 69.2 Gy with DS to 31.3 Gy, 67.9 Gy, and 64.6 Gy with PBS. The conformity index (CI), homogeneity index (HI), and global maximal dose were improved from 3.2, 0.08, 77.4 Gy with DS to 2.8, 0.04, and 72.1 Gy with PBS. All differences are statistically significant, with p-values <0.05, with the exception of the heart V45 (p=0.146). PBS with BSPTV achieves better organ sparing and improves target coverage using a repainting method for the treatment of thoracic tumors. Incorporating motion-related uncertainties is essential. PACS number: 87.55.D.

  17. Relationship between low tube voltage (70 kV) and the iodine delivery rate (IDR) in CT angiography: An experimental in-vivo study

    PubMed Central

    Pietsch, Hubertus; Korporaal, Johannes G.; Haberland, Ulrike; Mahnken, Andreas H.; Flohr, Thomas G.; Uder, Michael; Jost, Gregor

    2017-01-01

    Objective Very short acquisition times and the use of low-kV protocols in CTA demand modifications in the contrast media (CM) injection regimen. The aim of this study was to optimize the use of CM delivery parameters in thoraco-abdominal CTA in a porcine model. Materials and methods Six pigs (55–68 kg) were examined with a dynamic CTA protocol (454 mm scan length, 2.5 s temporal resolution, 70 s total acquisition time). Four CM injection protocols were applied in a randomized order. 120 kV CTA protocol: (A) 300 mg iodine/kg bodyweight (bw), IDR = 1.5 g/s (flow = 5 mL/s), injection time (ti) 12 s (60 kg bw). 70 kV CTA protocols: 150 mg iodine/kg bw: (B) IDR = 0.75 g/s (flow = 2.5 mL/s), ti = 12 s (60 kg bw); (C) IDR = 1.5 g/s (flow = 5 mL/s), ti = 12 s (60 kg bw); (D) IDR = 3.0 g/s (flow = 10 mL/s), ti = 3 s (60 kg bw). The complete CM bolus shape was monitored by creating time attenuation curves (TAC) in different vascular territories. Based on the TAC, the time to peak (TTP) and the peak enhancement were determined. The diagnostic window (relative enhancement > 300 HU), was calculated and compared to visual inspection of the corresponding CTA data sets. Results The average relative arterial peak enhancements after baseline correction were 358.6 HU (A), 356.6 HU (B), 464.0 HU (C), and 477.6 HU (D). The TTP decreased with increasing IDR and decreasing ti, protocols A and B did not differ significantly (systemic arteries, p = 0.843; pulmonary arteries, p = 0.183). The delay time for bolus tracking (trigger level 100 HU; target enhancement 300 HU) for single-phase CTA was comparable for protocol A and B (3.9, 4.3 s) and C and D (2.4, 2.0 s). The scan window time frame was comparable for the different protocols by visual inspection of the different CTA data sets and by analyzing the TAC. Conclusions All protocols provided sufficient arterial enhancement. The use of a 70 kV CTA protocol is recommended because of a 50% reduction of total CM volume and a 50% reduced

  18. Empirical binary tomography calibration (EBTC) for the precorrection of beam hardening and scatter for flat panel CT

    SciTech Connect

    Grimmer, Rainer; Kachelriess, Marc

    2011-04-15

    Purpose: Scatter and beam hardening are prominent artifacts in x-ray CT. Currently, there is no precorrection method that inherently accounts for tube voltage modulation and shaped prefiltration. Methods: A method for self-calibration based on binary tomography of homogeneous objects, which was proposed by B. Li et al. [''A novel beam hardening correction method for computed tomography,'' in Proceedings of the IEEE/ICME International Conference on Complex Medical Engineering CME 2007, pp. 891-895, 23-27 May 2007], has been generalized in order to use this information to preprocess scans of other, nonbinary objects, e.g., to reduce artifacts in medical CT applications. Further on, the method was extended to handle scatter besides beam hardening and to allow for detector pixel-specific and ray-specific precorrections. This implies that the empirical binary tomography calibration (EBTC) technique is sensitive to spectral effects as they are induced by the heel effect, by shaped prefiltration, or by scanners with tube voltage modulation. The presented method models the beam hardening correction by using a rational function, while the scatter component is modeled using the pep model of B. Ohnesorge et al. [''Efficient object scatter correction algorithm for third and fourth generation CT scanners,'' Eur. Radiol. 9(3), 563-569 (1999)]. A smoothness constraint is applied to the parameter space to regularize the underdetermined system of nonlinear equations. The parameters determined are then used to precorrect CT scans. Results: EBTC was evaluated using simulated data of a flat panel cone-beam CT scanner with tube voltage modulation and bow-tie prefiltration and using real data of a flat panel cone-beam CT scanner. In simulation studies, where the ground truth is known, the authors' correction model proved to be highly accurate and was able to reduce beam hardening by 97% and scatter by about 75%. Reconstructions of measured data showed significantly less artifacts than

  19. Empirical binary tomography calibration (EBTC) for the precorrection of beam hardening and scatter for flat panel CT.

    PubMed

    Grimmer, Rainer; Kachelriess, Marc

    2011-04-01

    Scatter and beam hardening are prominent artifacts in x-ray CT. Currently, there is no precorrection method that inherently accounts for tube voltage modulation and shaped prefiltration. A method for self-calibration based on binary tomography of homogeneous objects, which was proposed by B. Li et al. ["A novel beam hardening correction method for computed tomography," in Proceedings of the IEEE/ICME International Conference on Complex Medical Engineering CME 2007, pp. 891-895, 23-27 May 2007], has been generalized in order to use this information to preprocess scans of other, nonbinary objects, e.g., to reduce artifacts in medical CT applications. Further on, the method was extended to handle scatter besides beam hardening and to allow for detector pixel-specific and ray-specific precorrections. This implies that the empirical binary tomography calibration (EBTC) technique is sensitive to spectral effects as they are induced by the heel effect, by shaped prefiltration, or by scanners with tube voltage modulation. The presented method models the beam hardening correction by using a rational function, while the scatter component is modeled using the pep model of B. Ohnesorge et al. ["Efficient object scatter correction algorithm for third and fourth generation CT scanners," Eur. Radiol. 9(3), 563-569 (1999)]. A smoothness constraint is applied to the parameter space to regularize the underdetermined system of nonlinear equations. The parameters determined are then used to precorrect CT scans. EBTC was evaluated using simulated data of a flat panel cone-beam CT scanner with tube voltage modulation and bow-tie prefiltration and using real data of a flat panel cone-beam CT scanner. In simulation studies, where the ground truth is known, the authors' correction model proved to be highly accurate and was able to reduce beam hardening by 97% and scatter by about 75%. Reconstructions of measured data showed significantly less artifacts than the standard reconstruction

  20. Dacryocystography using cone beam CT in patients with lacrimal drainage system obstruction.

    PubMed

    Tschopp, Markus; Bornstein, Michael M; Sendi, Pedram; Jacobs, Reinhilde; Goldblum, David

    2014-01-01

    To assess the usefulness of cone beam CT (CBCT) for dacryocystography (DCG) using either direct syringing or passive application of contrast medium. Ten consecutive patients with epiphora who had CBCT-DCG in a sitting position were retrospectively analyzed. CBCT-DCGs were performed using 2 techniques: direct syringing with contrast medium or using the passive technique, where patients received 3 drops of contrast medium into the conjunctival sac before CBCT-DCG. Clinical and radiologic diagnoses were compared for both groups. The 10 patients (men = 3) had a mean age of 63.2 years. Both techniques proved to be simple procedures with good delineation of the bone, soft tissue, and the contrast medium in the lacrimal system. No side effects were noted. CBCT-DCG is a useful alternative to determine the localization of stenosis in patients with chronic epiphora.

  1. Limited-angle reverse helical cone-beam CT for pipeline with low rank decomposition

    NASA Astrophysics Data System (ADS)

    Wu, Dong; Zeng, Li

    2014-10-01

    In this paper, tomographic imaging of pipeline in service by cone-beam computed tomography (CBCT) is studied. With the developed scanning strategy and image model, the quality of reconstructed image is improved. First, a limited-angle reverse helical scanning strategy based on C-arm computed tomography (C-arm CT) is developed for the projection data acquisition of pipeline in service. Then, an image model which considering the resemblance among slices of pipeline is developed. Finally, split Bregman method based algorithm is implemented in solving the model aforementioned. Preliminary results of simulation experiments show that the projection data acquisition strategy and reconstruction method are efficient and feasible, and our method is superior to Feldkamp-Davis-Kress (FDK) algorithm and simultaneous algebraic reconstruction technique (SART).

  2. [Application of elastic registration based on Demons algorithm in cone beam CT].

    PubMed

    Pang, Haowen; Sun, Xiaoyang

    2014-02-01

    We applied Demons and accelerated Demons elastic registration algorithm in radiotherapy cone beam CT (CBCT) images, We provided software support for real-time understanding of organ changes during radiotherapy. We wrote a 3D CBCT image elastic registration program using Matlab software, and we tested and verified the images of two patients with cervical cancer 3D CBCT images for elastic registration, based on the classic Demons algorithm, minimum mean square error (MSE) decreased 59.7%, correlation coefficient (CC) increased 11.0%. While for the accelerated Demons algorithm, MSE decreased 40.1%, CC increased 7.2%. The experimental verification with two methods of Demons algorithm obtained the desired results, but the small difference appeared to be lack of precision, and the total registration time was a little long. All these problems need to be further improved for accuracy and reducing of time.

  3. Reconstruction of a cone-beam CT image via forward iterative projection matching

    SciTech Connect

    Brock, R. Scott; Docef, Alen; Murphy, Martin J.

    2010-12-15

    Purpose: To demonstrate the feasibility of reconstructing a cone-beam CT (CBCT) image by deformably altering a prior fan-beam CT (FBCT) image such that it matches the anatomy portrayed in the CBCT projection data set. Methods: A prior FBCT image of the patient is assumed to be available as a source image. A CBCT projection data set is obtained and used as a target image set. A parametrized deformation model is applied to the source FBCT image, digitally reconstructed radiographs (DRRs) that emulate the CBCT projection image geometry are calculated and compared to the target CBCT projection data, and the deformation model parameters are adjusted iteratively until the DRRs optimally match the CBCT projection data set. The resulting deformed FBCT image is hypothesized to be an accurate representation of the patient's anatomy imaged by the CBCT system. The process is demonstrated via numerical simulation. A known deformation is applied to a prior FBCT image and used to create a synthetic set of CBCT target projections. The iterative projection matching process is then applied to reconstruct the deformation represented in the synthetic target projections; the reconstructed deformation is then compared to the known deformation. The sensitivity of the process to the number of projections and the DRR/CBCT projection mismatch is explored by systematically adding noise to and perturbing the contrast of the target projections relative to the iterated source DRRs and by reducing the number of projections. Results: When there is no noise or contrast mismatch in the CBCT projection images, a set of 64 projections allows the known deformed CT image to be reconstructed to within a nRMS error of 1% and the known deformation to within a nRMS error of 7%. A CT image nRMS error of less than 4% is maintained at noise levels up to 3% of the mean projection intensity, at which the deformation error is 13%. At 1% noise level, the number of projections can be reduced to 8 while maintaining

  4. A quality assurance program for image quality of cone-beam CT guidance in radiation therapy

    SciTech Connect

    Bissonnette, Jean-Pierre; Moseley, Douglas J.; Jaffray, David A.

    2008-05-15

    The clinical introduction of volumetric x-ray image-guided radiotherapy systems necessitates formal commissioning of the hardware and image-guided processes to be used and drafts quality assurance (QA) for both hardware and processes. Satisfying both requirements provides confidence on the system's ability to manage geometric variations in patient setup and internal organ motion. As these systems become a routine clinical modality, the authors present data from their QA program tracking the image quality performance of ten volumetric systems over a period of 3 years. These data are subsequently used to establish evidence-based tolerances for a QA program. The volumetric imaging systems used in this work combines a linear accelerator with conventional x-ray tube and an amorphous silicon flat-panel detector mounted orthogonally from the accelerator central beam axis, in a cone-beam computed tomography (CBCT) configuration. In the spirit of the AAPM Report No. 74, the present work presents the image quality portion of their QA program; the aspects of the QA protocol addressing imaging geometry have been presented elsewhere. Specifically, the authors are presenting data demonstrating the high linearity of CT numbers, the uniformity of axial reconstructions, and the high contrast spatial resolution of ten CBCT systems (1-2 mm) from two commercial vendors. They are also presenting data accumulated over the period of several months demonstrating the long-term stability of the flat-panel detector and of the distances measured on reconstructed volumetric images. Their tests demonstrate that each specific CBCT system has unique performance. In addition, scattered x rays are shown to influence the imaging performance in terms of spatial resolution, axial reconstruction uniformity, and the linearity of CT numbers.

  5. A quality assurance program for image quality of cone-beam CT guidance in radiation therapy.

    PubMed

    Bissonnette, Jean-Pierre; Moseley, Douglas J; Jaffray, David A

    2008-05-01

    The clinical introduction of volumetric x-ray image-guided radiotherapy systems necessitates formal commissioning of the hardware and image-guided processes to be used and drafts quality assurance (QA) for both hardware and processes. Satisfying both requirements provides confidence on the system's ability to manage geometric variations in patient setup and internal organ motion. As these systems become a routine clinical modality, the authors present data from their QA program tracking the image quality performance of ten volumetric systems over a period of 3 years. These data are subsequently used to establish evidence-based tolerances for a QA program. The volumetric imaging systems used in this work combines a linear accelerator with conventional x-ray tube and an amorphous silicon flat-panel detector mounted orthogonally from the accelerator central beam axis, in a cone-beam computed tomography (CBCT) configuration. In the spirit of the AAPM Report No. 74, the present work presents the image quality portion of their QA program; the aspects of the QA protocol addressing imaging geometry have been presented elsewhere. Specifically, the authors are presenting data demonstrating the high linearity of CT numbers, the uniformity of axial reconstructions, and the high contrast spatial resolution of ten CBCT systems (1-2 mm) from two commercial vendors. They are also presenting data accumulated over the period of several months demonstrating the long-term stability of the flat-panel detector and of the distances measured on reconstructed volumetric images. Their tests demonstrate that each specific CBCT system has unique performance. In addition, scattered x rays are shown to influence the imaging performance in terms of spatial resolution, axial reconstruction uniformity, and the linearity of CT numbers.

  6. Automatic tracking of implanted fiducial markers in cone beam CT projection images

    SciTech Connect

    Marchant, T. E.; Skalski, A.; Matuszewski, B. J.

    2012-03-15

    Purpose: This paper describes a novel method for simultaneous intrafraction tracking of multiple fiducial markers. Although the proposed method is generic and can be adopted for a number of applications including fluoroscopy based patient position monitoring and gated radiotherapy, the tracking results presented in this paper are specific to tracking fiducial markers in a sequence of cone beam CT projection images. Methods: The proposed method is accurate and robust thanks to utilizing the mean shift and random sampling principles, respectively. The performance of the proposed method was evaluated with qualitative and quantitative methods, using data from two pancreatic and one prostate cancer patients and a moving phantom. The ground truth, for quantitative evaluation, was calculated based on manual tracking preformed by three observers. Results: The average dispersion of marker position error calculated from the tracking results for pancreas data (six markers tracked over 640 frames, 3840 marker identifications) was 0.25 mm (at iscoenter), compared with an average dispersion for the manual ground truth estimated at 0.22 mm. For prostate data (three markers tracked over 366 frames, 1098 marker identifications), the average error was 0.34 mm. The estimated tracking error in the pancreas data was < 1 mm (2 pixels) in 97.6% of cases where nearby image clutter was detected and in 100.0% of cases with no nearby image clutter. Conclusions: The proposed method has accuracy comparable to that of manual tracking and, in combination with the proposed batch postprocessing, superior robustness. Marker tracking in cone beam CT (CBCT) projections is useful for a variety of purposes, such as providing data for assessment of intrafraction motion, target tracking during rotational treatment delivery, motion correction of CBCT, and phase sorting for 4D CBCT.

  7. Modulation transfer function determination using the edge technique for cone-beam micro-CT

    NASA Astrophysics Data System (ADS)

    Rong, Junyan; Liu, Wenlei; Gao, Peng; Liao, Qimei; Lu, Hongbing

    2016-03-01

    Evaluating spatial resolution is an essential work for cone-beam computed tomography (CBCT) manufacturers, prototype designers or equipment users. To investigate the cross-sectional spatial resolution for different transaxial slices with CBCT, the slanted edge technique with a 3D slanted edge phantom are proposed and implemented on a prototype cone-beam micro-CT. Three transaxial slices with different cone angles are under investigation. An over-sampled edge response function (ERF) is firstly generated from the intensity of the slightly tiled air to plastic edge in each row of the transaxial reconstruction image. Then the oversampled ESF is binned and smoothed. The derivative of the binned and smoothed ERF gives the line spread function (LSF). At last the presampled modulation transfer function (MTF) is calculated by taking the modulus of the Fourier transform of the LSF. The spatial resolution is quantified with the spatial frequencies at 10% MTF level and full-width-half-maximum (FWHM) value. The spatial frequencies at 10% of MTFs are 3.1+/-0.08mm-1, 3.0+/-0.05mm-1, and 3.2+/-0.04mm-1 for the three transaxial slices at cone angles of 3.8°, 0°, and -3.8° respectively. The corresponding FWHMs are 252.8μm, 261.7μm and 253.6μm. Results indicate that cross-sectional spatial resolution has no much differences when transaxial slices being 3.8° away from z=0 plane for the prototype conebeam micro-CT.

  8. The influence of bowtie filtration on x-ray photons distribution in cone beam CT

    NASA Astrophysics Data System (ADS)

    Jiang, Shanghai; Feng, Peng; Wei, Biao; He, Peng; Deng, Luzhen; Zhang, Wei

    2015-10-01

    Bowtie filters are used to modulate an incoming x-ray beam as a function of the angle of the x-ray to balance the photon flux on a detector array. Because of their key roles in radiation dose reduction and multi-energy imaging, bowtie filters have attracted a major attention in modern X-ray computed tomography (CT). However, few researches are concerned on the effects of the structure and materials for the bowtie filter in the Cone Beam CT (CBCT). In this study, the influence of bowtie filters' structure and materials on X-ray photons distribution are analyzed using Monte Carlo (MC) simulations by MCNP5 code. In the current model, the phantom was radiated by virtual X-ray source (its' energy spectrum calculated by SpekCalc program) filtered using bowtie, then all photons were collected through array photoncounting detectors. In the process above, two bowtie filters' parameters which include center thickness (B), edge thickness (controlled by A), changed respectively. Two kinds of situation are simulated: 1) A=0.036, B=1, 2, 3, 4, 5, 6mm and the material is aluminum; 2) A=0.016, 0.036, 0.056, 0.076, 0.096, B=2mm and the material is aluminum. All the X-ray photons' distribution are measured through MCNP. The results show that reduction in center thickness and edge thickness can reduce the number of background photons in CBCT. Our preliminary research shows that structure parameters of bowtie filter can influence X-ray photons, furthermore, radiation dose distribution, which provide some evidences in design of bowtie filter for reducing radiation dose in CBCT.

  9. A patient set-up protocol based on partially blocked cone-beam CT.

    PubMed

    Zhu, Lei; Wang, Jing; Xie, Yaoqin; Starman, Jared; Fahrig, Rebecca; Xing, Lei

    2010-04-01

    Three-dimensional x-ray cone-beam CT (CBCT) is being increasingly used in radiation therapy. Since the whole treatment course typically lasts several weeks, the repetitive x-ray imaging results in large radiation dose delivered on the patient. In the current radiation therapy treatment, CBCT is mainly used for patient set-up, and a rigid transformation of the CBCT data from the planning CT data is also assumed. For an accurate rigid registration, it is not necessary to acquire a full 3D image. In this paper, we propose a patient set-up protocol based on partially blocked CBCT. A sheet of lead strips is inserted between the x-ray source and the scanned patient. From the incomplete projection data, only several axial slices are reconstructed and used in the image registration for patient set-up. Since the radiation is partially blocked, the dose delivered onto the patient is significantly reduced, with an additional benefit of reduced scatter signals. The proposed approach is validated using experiments on two anthropomorphic phantoms. As x-ray beam blocking ratio increases, more dose reduction is achieved, while the patient set-up error also increases. To investigate this tradeoff, two lead sheets with different strip widths are implemented, which correspond to radiation dose reduction of approximately 6 and approximately 11, respectively. We compare the registration results using the partially blocked CBCT with those using the regular CBCT. Both lead sheets achieve high patient set-up accuracies. It is seen that, using the lead sheet with radiation dose reduction by a factor of approximately 11, the patient set-up error is still less than 1mm in translation and less than 0.2 degrees in rotation. The comparison of the reconstructed images also shows that the image quality of the illuminated slices in the partially blocked CBCT is much improved over that in the regular CBCT.

  10. Iterative reconstruction of cone-beam CT data on a cluster

    NASA Astrophysics Data System (ADS)

    Benson, Thomas M.; Gregor, Jens

    2007-02-01

    Three-dimensional iterative reconstruction of large CT data sets poses several challenges in terms of the associated computational and memory requirements. In this paper, we present results obtained by implementing a computational framework for reconstructing axial cone-beam CT data using a cluster of inexpensive dualprocessor PCs. In particular, we discuss our parallelization approach, which uses POSIX threads and message passing (MPI) for local and remote load distribution, as well as the interaction of that load distribution with the implementation of ordered subset based algorithms. We also consider a heuristic data-driven 3D focus of attention algorithm that reduces the amount of data that must be considered for many data sets. Furthermore, we present a modification to the SIRT algorithm that reduces the amount of data that must be communicated between processes. Finally, we introduce a method of separating the work in such a way that some computation can be overlapped with the MPI communication thus further reducing the overall run-time. We summarize the performance results using reconstructions of experimental data.

  11. Dose and image quality for a cone-beam C-arm CT system

    SciTech Connect

    Fahrig, Rebecca; Dixon, Robert; Payne, Thomas; Morin, Richard L.; Ganguly, Arundhuti; Strobel, Norbert

    2006-12-15

    We assess dose and image quality of a state-of-the-art angiographic C-arm system (Axiom Artis dTA, Siemens Medical Solutions, Forchheim, Germany) for three-dimensional neuro-imaging at various dose levels and tube voltages and an associated measurement method. Unlike conventional CT, the beam length covers the entire phantom, hence, the concept of computed tomography dose index (CTDI) is not the metric of choice, and one can revert to conventional dosimetry methods by directly measuring the dose at various points using a small ion chamber. This method allows us to define and compute a new dose metric that is appropriate for a direct comparison with the familiar CTDI{sub W} of conventional CT. A perception study involving the CATPHAN 600 indicates that one can expect to see at least the 9 mm inset with 0.5% nominal contrast at the recommended head-scan dose (60 mGy) when using tube voltages ranging from 70 kVp to 125 kVp. When analyzing the impact of tube voltage on image quality at a fixed dose, we found that lower tube voltages gave improved low contrast detectability for small-diameter objects. The relationships between kVp, image noise, dose, and contrast perception are discussed.

  12. Flat panel detector-based cone beam CT for dynamic imaging: system evaluation

    NASA Astrophysics Data System (ADS)

    Ning, Ruola; Conover, David; Yu, Yong; Zhang, Yan; Cai, Weixing; Yang, Dong; Lu, Xianghua

    2006-03-01

    The purpose of this study is to characterize a newly built flat panel detector (FPD)-based cone beam CT (CBCT) prototype for dynamic imaging. A CBCT prototype has been designed and constructed by completely modifying a GE HiSpeed Advantage (HSA) CT gantry, incorporating a newly acquired large size real-time FPD (Varian PaxScan 4030CB), a new x-ray generator and a dual focal spot angiography x-ray tube that allows the full coverage of the detector. During data acquisition, the x-ray tube and the FPD can be rotated on the gantry over Nx360 degrees due to integrated slip ring technology with the rotation speed of one second/revolution. With a single scan time of up to 40 seconds , multiple sets of reconstructions can be performed for dynamic studies. The upgrade of this system has been completed. The prototype was used for a series of preliminary phantom studies: different sizes of breast phantoms, a Humanoid chest phantom and scatter correction studies. The results of the phantom studies demonstrate that good image quality can be achieved with this newly built prototype.

  13. Deriving Hounsfield units using grey levels in cone beam CT: a clinical application.

    PubMed

    Reeves, T E; Mah, P; McDavid, W D

    2012-09-01

    To present a clinical study demonstrating a method to derive Hounsfield units from grey levels in cone beam CT (CBCT). An acrylic intraoral reference object with aluminium, outer bone equivalent material (cortical bone), inner bone equivalent material (trabecular bone), polymethlymethacrylate and water equivalent material was used. Patients were asked if they would be willing to have an acrylic bite plate with the reference object placed in their mouth during a routine CBCT scan. There were 31 scans taken on the Asahi Alphard 3030 (Belmont Takara, Kyoto, Japan) and 30 scans taken on the Planmeca ProMax 3D (Planmeca, Helsinki, Finland) CBCT. Linear regression between the grey levels of the reference materials and their linear attenuation coefficients was performed for various photon energies. The energy with the highest regression coefficient was chosen as the effective energy. The attenuation coefficients for the five materials at the effective energy were scaled as Hounsfield units using the standard Hounsfield units equation and compared to those derived from the measured grey levels of the materials using the regression equation. In general, there was a satisfactory linear relation between the grey levels and the attenuation coefficients. This made it possible to calculate Hounsfield units from the measured grey levels. Uncertainty in determining effective energies resulted in unrealistic effective energies and significant variability of calculated CT numbers. Linear regression from grey levels directly to Hounsfield units at specified energies resulted in greater consistency. The clinical application of a method for deriving Hounsfield units from grey levels in CBCT was demonstrated.

  14. CT metal artifact reduction method correcting for beam hardening and missing projections

    NASA Astrophysics Data System (ADS)

    Verburg, Joost M.; Seco, Joao

    2012-05-01

    We present and validate a computed tomography (CT) metal artifact reduction method that is effective for a wide spectrum of clinical implant materials. Projections through low-Z implants such as titanium were corrected using a novel physics correction algorithm that reduces beam hardening errors. In the case of high-Z implants (dental fillings, gold, platinum), projections through the implant were considered missing and regularized iterative reconstruction was performed. Both algorithms were combined if multiple implant materials were present. For comparison, a conventional projection interpolation method was implemented. In a blinded and randomized evaluation, ten radiation oncologists ranked the quality of patient scans on which the different methods were applied. For scans that included low-Z implants, the proposed method was ranked as the best method in 90% of the reviews. It was ranked superior to the original reconstruction (p = 0.0008), conventional projection interpolation (p < 0.0001) and regularized limited data reconstruction (p = 0.0002). All reviewers ranked the method first for scans with high-Z implants, and better as compared to the original reconstruction (p < 0.0001) and projection interpolation (p = 0.004). We conclude that effective reduction of CT metal artifacts can be achieved by combining algorithms tailored to specific types of implant materials.

  15. Technical note: cone beam CT imaging for 3D image guided brachytherapy for gynecological HDR brachytherapy.

    PubMed

    Reniers, Brigitte; Verhaegen, Frank

    2011-05-01

    This paper focuses on a novel image guidance technique for gynecological brachytherapy treatment. The present standard technique is orthogonal x-ray imaging to reconstruct the 3D position of the applicator when the availability of CT or MR is limited. Our purpose is to introduce 3D planning in the brachytherapy suite using a cone beam CT (CBCT) scanner dedicated to brachytherapy. This would avoid moving the patient between imaging and treatment procedures which may cause applicator motion. This could be used to replace the x-ray images or to verify the treatment position immediately prior to dose delivery. The sources of CBCT imaging artifacts in the case of brachytherapy were identified and removed where possible. The image quality was further improved by modifying the x-ray tube voltage, modifying the compensator bowtie filter and optimizing technical parameters such as the detector gain or tube current. The image quality was adequate to reconstruct the applicators in the treatment planning system. The position of points A and the localization of the organs at risk (OAR) ICRU points is easily achieved. This allows identification of cases where the rectum had moved with respect to the ICRU point which would require asymmetrical source loading. A better visualization is a first step toward a better sparing of the OAR. Treatment planning for gynecological brachytherapy is aided by CBCT images. CBCT presents advantages over CT: acquisition in the treatment room and in the treatment position due to the larger clearance of the CBCT, thereby reducing problems associated to moving patients between rooms.

  16. Reduction of radiation exposure by lead curtain shielding in dedicated extremity cone beam CT.

    PubMed

    Lee, C-H; Ryu, J H; Lee, Y-H; Yoon, K-H

    2015-06-01

    A dedicated extremity cone beam CT (CBCT) was introduced recently, and is rapidly becoming an attractive modality for extremity imaging. This study aimed to evaluate the effectiveness of a curtain-shaped lead shielding in reducing the exposure of patients to scattered radiation in dedicated extremity CBCT. A dedicated extremity CBCT scanner was used. The lead shielding curtain was 42 × 60 cm with 0.5-mm lead equivalent. Scattered radiation dose from CBCT was measured using thermoluminescence dosimetry chips at 20 points, at different distances and directions from the CT gantry. Two sets of scattered radiation dose measurements were performed before and after installation of curtain-shaped lead shield, and the percentage reduction in dose in air was calculated. Mean radiation exposure dose at measured points was 34.46 ± 48.40 μGy without curtains and 9.67 ± 4.53 μGy with curtains, exhibiting 71.94% reduction (p = 0.000). The use of lead shielding curtains significantly reduced scattered radiation at 0.5, 1.0 and 1.5 m from the CT gantry, with percent reductions of 84.8%, 58.0% and 35.5%, respectively (p = 0.000, 0.000 and 0.002). The percent reduction in the diagonal (+45°, -45°) and vertical forward (0°) directions were 86.3%, 83.1% and 77.7%, respectively, and were statistically significant (p = 0.029, 0.020 and 0.041). Shielding with lead curtains suggests an easy and effective method for reducing patient exposure to radiation in extremity CBCT imaging. Lead shielding curtains are an effective technique to reduce scattered radiation dose in dedicated extremity CBCT, with higher dose reduction closer to the gantry opening.

  17. Directional sinogram interpolation for motion weighted 4D cone-beam CT reconstruction

    NASA Astrophysics Data System (ADS)

    Zhang, Hua; Kruis, Matthijs; Sonke, Jan-Jakob

    2017-03-01

    The image quality of respiratory sorted four-dimensional (4D) cone-beam (CB) computed tomography (CT) is often limited by streak artifacts due to insufficient projections. A motion weighted reconstruction (MWR) method is proposed to decrease streak artifacts and improve image quality. Firstly, respiratory correlated CBCT projections were interpolated by directional sinogram interpolation (DSI) to generate additional CB projections for each phase and subsequently reconstructed. Secondly, local motion was estimated by deformable image registration of the interpolated 4D CBCT. Thirdly, a regular 3D FDK CBCT was reconstructed from the non-interpolated projections. Finally, weights were assigned to each voxel, based on the local motion, and then were used to combine the 3D FDK CBCT and interpolated 4D CBCT to generate the final 4D image. MWR method was compared with regular 4D CBCT scans as well as McKinnon and Bates (MKB) based reconstructions. Comparisons were made in terms of (1) comparing the steepness of an extracted profile from the boundary of the region-of-interest (ROI), (2) contrast-to-noise ratio (CNR) inside certain ROIs, and (3) the root-mean-square-error (RMSE) between the planning CT and CBCT inside a homogeneous moving region. Comparisons were made for both a phantom and four patient scans. In a 4D phantom, RMSE were reduced by 24.7% and 38.7% for MKB and MWR respectively, compared to conventional 4D CBCT. Meanwhile, interpolation induced blur was minimal in static regions for MWR based reconstructions. In regions with considerable respiratory motion, image blur using MWR is less than the MKB and 3D Feldkamp (FDK) methods. In the lung cancer patients, average CNRs of MKB, DSI and MWR improved by a factor 1.7, 2.8 and 3.5 respectively relative to 4D FDK. MWR effectively reduces RMSE in 4D cone-beam CT and improves the image quality in both the static and respiratory moving regions compared to 4D FDK and MKB methods.

  18. Assessment of the effective doses from two dental cone beam CT devices

    PubMed Central

    Schilling, R; Geibel, M-A

    2013-01-01

    Objectives: This study compares the effective dose for different fields of view (FOVs), resolutions and X-ray parameters from two cone beam CT units: the KaVo 3D (three-dimensional) eXam and the KaVo Pan eXam Plus 3D (KaVo Dental, Biberach, Germany). Methods: Measurements were made using thermoluminescent dosemeter chips in a radiation analog dosimetry head and neck phantom. The calculations of effective doses are based on the ICRP 60 and ICRP 103 recommendations of the International Commission on Radiological Protection. Results: Effective doses from the 3D eXam ranged between 32.8 µSv and 169.8 µSv, and for the Pan eXam Plus effective doses ranged between 40.2 µSv and 183.7 µSv; these were measured using ICRP 103 weighting factors in each case. The increase in effective dose between ICRP 60 and ICRP 103 recommendations averaged 157% for all measurements. Conclusions: Effective doses can be reduced significantly with the choice of lower resolutions and mAs settings as well as smaller FOVs to avoid tissues sensitive to radiation being inside the direct beam. Larger FOVs do not necessarily lead to higher effective doses. PMID:23420855

  19. Assessment of the effective doses from two dental cone beam CT devices.

    PubMed

    Schilling, R; Geibel, M-A

    2013-01-01

    This study compares the effective dose for different fields of view (FOVs), resolutions and X-ray parameters from two cone beam CT units: the KaVo 3D (three-dimensional) eXam and the KaVo Pan eXam Plus 3D (KaVo Dental, Biberach, Germany). Measurements were made using thermoluminescent dosemeter chips in a radiation analog dosimetry head and neck phantom. The calculations of effective doses are based on the ICRP 60 and ICRP 103 recommendations of the International Commission on Radiological Protection. Effective doses from the 3D eXam ranged between 32.8 µSv and 169.8 µSv, and for the Pan eXam Plus effective doses ranged between 40.2 µSv and 183.7 µSv; these were measured using ICRP 103 weighting factors in each case. The increase in effective dose between ICRP 60 and ICRP 103 recommendations averaged 157% for all measurements. Effective doses can be reduced significantly with the choice of lower resolutions and mAs settings as well as smaller FOVs to avoid tissues sensitive to radiation being inside the direct beam. Larger FOVs do not necessarily lead to higher effective doses.

  20. Reconstruction algorithm for polychromatic CT imaging: application to beam hardening correction

    NASA Technical Reports Server (NTRS)

    Yan, C. H.; Whalen, R. T.; Beaupre, G. S.; Yen, S. Y.; Napel, S.

    2000-01-01

    This paper presents a new reconstruction algorithm for both single- and dual-energy computed tomography (CT) imaging. By incorporating the polychromatic characteristics of the X-ray beam into the reconstruction process, the algorithm is capable of eliminating beam hardening artifacts. The single energy version of the algorithm assumes that each voxel in the scan field can be expressed as a mixture of two known substances, for example, a mixture of trabecular bone and marrow, or a mixture of fat and flesh. These assumptions are easily satisfied in a quantitative computed tomography (QCT) setting. We have compared our algorithm to three commonly used single-energy correction techniques. Experimental results show that our algorithm is much more robust and accurate. We have also shown that QCT measurements obtained using our algorithm are five times more accurate than that from current QCT systems (using calibration). The dual-energy mode does not require any prior knowledge of the object in the scan field, and can be used to estimate the attenuation coefficient function of unknown materials. We have tested the dual-energy setup to obtain an accurate estimate for the attenuation coefficient function of K2 HPO4 solution.

  1. Differences between panoramic and Cone Beam-CT in the surgical evaluation of lower third molars

    PubMed Central

    Rodriguez y Baena, Ruggero; Beltrami, Riccardo; Tagliabo, Angelo; Rizzo, Silvana

    2017-01-01

    Background The aim of this study was to evaluate the ability to identify the contiguity between the root of the mandibular third molar and the mandibular canal (MC) in panoramic radiographs compared with Cone Beam-CT. Material and Methods Panoramic radiographs of 326 third molars and CBCT radiographs of 86 cases indicated for surgery and considered at risk were evaluated. The following signs were assessed in panoramic radiographs as risk factors: radiolucent band, loss of MC border, change in MC direction, MC narrowing, root narrowing, root deviation, bifid apex, superimposition, and contact between the root third molar and the MC. Results Radiographic signs associated with absence of MC cortical bone are: radiolucent band, loss of MC border, change in MC direction, and superimposition. The number of risk factors was significantly increased with an increasing depth of inclusion. CBCT revealed a significant association between the absence of MC cortical bone and a lingual or interradicular position of the MC. Conclusions In cases in which panoramic radiographs do not exclude contiguity between the MC and tooth, careful assessment the signs and risks on CBCT radiographs is indicated for proper identification of the relationships between anatomic structures. Key words:Panoramic radiography, Cone-Beam computed tomography, third molar, mandibular nerve. PMID:28210446

  2. Development of a Beam Hardening Correction Method for a microCT Scanner Prototype

    SciTech Connect

    Kikushima, J.; Rodriguez-Villafuerte, M.; Martinez-Davalos, A.

    2010-12-07

    The radiographic projections acquired with a microCT were simulated and then corrected for beam hardening effects using the linearized signal to equivalent thickness (LSET) method. This procedure requires a calibration signal for each pixel obtained from a set of images with filters of increasing thickness. The projections are corrected by converting the signal to an equivalent thickness using interpolation over the calibration images. The method was validated using simulated projections of different phantoms. Two calibration sets were simulated using aluminum and water filters of thicknesses ranging from 0 to 5 mm and from 0 to 50 mm, respectively. A simulation of the phantoms' projections using a monoenergetic beam was also obtained to establish the relative intensity on the tomographic images when no cupping artifacts are present. Comparison between corrected and uncorrected tomographic images shows that the LSET method effectively corrects the cupping artifact. Streaking artifacts correction with the LSET method shows better results than with the traditional water correction method. Results are independent of the two calibration materials used.

  3. A Method to Improve Electron Density Measurement of Cone-Beam CT Using Dual Energy Technique

    PubMed Central

    Men, Kuo; Dai, Jian-Rong; Li, Ming-Hui; Chen, Xin-Yuan; Zhang, Ke; Tian, Yuan; Huang, Peng; Xu, Ying-Jie

    2015-01-01

    Purpose. To develop a dual energy imaging method to improve the accuracy of electron density measurement with a cone-beam CT (CBCT) device. Materials and Methods. The imaging system is the XVI CBCT system on Elekta Synergy linac. Projection data were acquired with the high and low energy X-ray, respectively, to set up a basis material decomposition model. Virtual phantom simulation and phantoms experiments were carried out for quantitative evaluation of the method. Phantoms were also scanned twice with the high and low energy X-ray, respectively. The data were decomposed into projections of the two basis material coefficients according to the model set up earlier. The two sets of decomposed projections were used to reconstruct CBCT images of the basis material coefficients. Then, the images of electron densities were calculated with these CBCT images. Results. The difference between the calculated and theoretical values was within 2% and the correlation coefficient of them was about 1.0. The dual energy imaging method obtained more accurate electron density values and reduced the beam hardening artifacts obviously. Conclusion. A novel dual energy CBCT imaging method to calculate the electron densities was developed. It can acquire more accurate values and provide a platform potentially for dose calculation. PMID:26346510

  4. An experimental study on the influence of scatter and beam hardening in x-ray CT for dimensional metrology

    NASA Astrophysics Data System (ADS)

    Lifton, J. J.; Malcolm, A. A.; McBride, J. W.

    2016-01-01

    Scattered radiation and beam hardening introduce artefacts that degrade the quality of data in x-ray computed tomography (CT). It is unclear how these artefacts influence dimensional measurements evaluated from CT data. Understanding and quantifying the influence of these artefacts on dimensional measurements is required to evaluate the uncertainty of CT-based dimensional measurements. In this work the influence of scatter and beam hardening on dimensional measurements is investigated using the beam stop array scatter correction method and spectrum pre-filtration for the measurement of an object with internal and external cylindrical dimensional features. Scatter and beam hardening are found to influence dimensional measurements when evaluated using the ISO50 surface determination method. On the other hand, a gradient-based surface determination method is found to be robust to the influence of artefacts and leads to more accurate dimensional measurements than those evaluated using the ISO50 method. In addition to these observations the GUM method for evaluating standard measurement uncertainties is applied and the standard measurement uncertainty due to scatter and beam hardening is estimated.

  5. High-fidelity artifact correction for cone-beam CT imaging of the brain

    NASA Astrophysics Data System (ADS)

    Sisniega, A.; Zbijewski, W.; Xu, J.; Dang, H.; Stayman, J. W.; Yorkston, J.; Aygun, N.; Koliatsos, V.; Siewerdsen, J. H.

    2015-02-01

    CT is the frontline imaging modality for diagnosis of acute traumatic brain injury (TBI), involving the detection of fresh blood in the brain (contrast of 30-50 HU, detail size down to 1 mm) in a non-contrast-enhanced exam. A dedicated point-of-care imaging system based on cone-beam CT (CBCT) could benefit early detection of TBI and improve direction to appropriate therapy. However, flat-panel detector (FPD) CBCT is challenged by artifacts that degrade contrast resolution and limit application in soft-tissue imaging. We present and evaluate a fairly comprehensive framework for artifact correction to enable soft-tissue brain imaging with FPD CBCT. The framework includes a fast Monte Carlo (MC)-based scatter estimation method complemented by corrections for detector lag, veiling glare, and beam hardening. The fast MC scatter estimation combines GPU acceleration, variance reduction, and simulation with a low number of photon histories and reduced number of projection angles (sparse MC) augmented by kernel de-noising to yield a runtime of ~4 min per scan. Scatter correction is combined with two-pass beam hardening correction. Detector lag correction is based on temporal deconvolution of the measured lag response function. The effects of detector veiling glare are reduced by deconvolution of the glare response function representing the long range tails of the detector point-spread function. The performance of the correction framework is quantified in experiments using a realistic head phantom on a testbench for FPD CBCT. Uncorrected reconstructions were non-diagnostic for soft-tissue imaging tasks in the brain. After processing with the artifact correction framework, image uniformity was substantially improved, and artifacts were reduced to a level that enabled visualization of ~3 mm simulated bleeds throughout the brain. Non-uniformity (cupping) was reduced by a factor of 5, and contrast of simulated bleeds was improved from ~7 to 49.7 HU, in good agreement

  6. A One-Step Cone-Beam CT-Enabled Planning-to-Treatment Model for Palliative Radiotherapy-From Development to Implementation

    SciTech Connect

    Wong, Rebecca K.S.; Letourneau, Daniel; Varma, Anita; Bissonnette, Jean Pierre; Fitzpatrick, David; Grabarz, Daniel; Elder, Christine; Martin, Melanie; Bezjak, Andrea; Panzarella, Tony; Gospodarowicz, Mary; Jaffray, David A.

    2012-11-01

    Purpose: To develop a cone-beam computed tomography (CT)-enabled one-step simulation-to-treatment process for the treatment of bone metastases. Methods and Materials: A three-phase prospective study was conducted. Patients requiring palliative radiotherapy to the spine, mediastinum, or abdomen/pelvis suitable for treatment with simple beam geometry ({<=}2 beams) were accrued. Phase A established the accuracy of cone-beam CT images for the purpose of gross tumor target volume (GTV) definition. Phase B evaluated the feasibility of implementing the cone-beam CT-enabled planning process at the treatment unit. Phase C evaluated the online cone-beam CT-enabled process for the planning and treatment of patients requiring radiotherapy for bone metastases. Results: Eighty-four patients participated in this study. Phase A (n = 9) established the adequacy of cone-beam CT images for target definition. Phase B (n = 45) established the quality of treatment plans to be adequate for clinical implementation for bone metastases. When the process was applied clinically in bone metastases (Phase C), the degree of overlap between planning computed tomography (PCT) and cone-beam CT for GTV and between PCT and cone-beam CT for treatment field was 82% {+-} 11% and 97% {+-} 4%, respectively. The oncologist's decision to accept the plan under a time-pressured environment remained of high quality, with the cone-beam CT-generated treatment plan delivering at least 90% of the prescribed dose to 100% {+-} 0% of the cone-beam CT planning target volume (PTV). With the assumption that the PCT PTV is the gold-standard target, the cone-beam CT-generated treatment plan delivered at least 90% and at least 95% of dose to 98% {+-} 2% and 97% {+-} 5% of the PCT PTV, respectively. The mean time for the online planning and treatment process was 32.7 {+-} 4.0 minutes. Patient satisfaction was high, with a trend for superior satisfaction with the cone-beam CT-enabled process. Conclusions: The cone-beam CT

  7. A one-step cone-beam CT-enabled planning-to-treatment model for palliative radiotherapy-from development to implementation.

    PubMed

    Wong, Rebecca K S; Letourneau, Daniel; Varma, Anita; Bissonnette, Jean Pierre; Fitzpatrick, David; Grabarz, Daniel; Elder, Christine; Martin, Melanie; Bezjak, Andrea; Panzarella, Tony; Gospodarowicz, Mary; Jaffray, David A

    2012-11-01

    To develop a cone-beam computed tomography (CT)-enabled one-step simulation-to-treatment process for the treatment of bone metastases. A three-phase prospective study was conducted. Patients requiring palliative radiotherapy to the spine, mediastinum, or abdomen/pelvis suitable for treatment with simple beam geometry (≤2 beams) were accrued. Phase A established the accuracy of cone-beam CT images for the purpose of gross tumor target volume (GTV) definition. Phase B evaluated the feasibility of implementing the cone-beam CT-enabled planning process at the treatment unit. Phase C evaluated the online cone-beam CT-enabled process for the planning and treatment of patients requiring radiotherapy for bone metastases. Eighty-four patients participated in this study. Phase A (n = 9) established the adequacy of cone-beam CT images for target definition. Phase B (n = 45) established the quality of treatment plans to be adequate for clinical implementation for bone metastases. When the process was applied clinically in bone metastases (Phase C), the degree of overlap between planning computed tomography (PCT) and cone-beam CT for GTV and between PCT and cone-beam CT for treatment field was 82% ± 11% and 97% ± 4%, respectively. The oncologist's decision to accept the plan under a time-pressured environment remained of high quality, with the cone-beam CT-generated treatment plan delivering at least 90% of the prescribed dose to 100% ± 0% of the cone-beam CT planning target volume (PTV). With the assumption that the PCT PTV is the gold-standard target, the cone-beam CT-generated treatment plan delivered at least 90% and at least 95% of dose to 98% ± 2% and 97% ± 5% of the PCT PTV, respectively. The mean time for the online planning and treatment process was 32.7 ± 4.0 minutes. Patient satisfaction was high, with a trend for superior satisfaction with the cone-beam CT-enabled process. The cone-beam CT-enabled palliative treatment process is feasible and is ready for

  8. TU-A-9A-09: Proton Beam X-Ray Fluorescence CT

    SciTech Connect

    Bazalova, M; Ahmad, M; Fahrig, R; Xing, L

    2014-06-15

    Purpose: To evaluate x-ray fluorescence computed tomography induced with proton beams (pXFCT) for imaging of gold contrast agent. Methods: Proton-induced x-ray fluorescence was studied by means of Monte Carlo (MC) simulations using TOPAS, a MC code based on GEANT4. First, proton-induced K-shell and L-shell fluorescence was studied as a function of proton beam energy and 1) depth in water and 2) size of contrast object. Second, pXFCT images of a 2-cm diameter cylindrical phantom with four 5- mm diameter contrast vials and of a 20-cm diameter phantom with 1-cm diameter vials were simulated. Contrast vials were filled with water and water solutions with 1-5% gold per weight. Proton beam energies were varied from 70-250MeV. pXFCT sinograms were generated based on the net number of gold K-shell or L-shell x-rays determined by interpolations from the neighboring 0.5keV energy bins of spectra collected with an idealized 4π detector. pXFCT images were reconstructed with filtered-back projection, and no attenuation correction was applied. Results: Proton induced x-ray fluorescence spectra showed very low background compared to x-ray induced fluorescence. Proton induced L-shell fluorescence had a higher cross-section compared to K-shell fluorescence. Excitation of L-shell fluorescence was most efficient for low-energy protons, i.e. at the Bragg peak. K-shell fluorescence increased with increasing proton beam energy and object size. The 2% and 5% gold contrast vials were accurately reconstructed in K-shell pXFCT images of both the 2-cm and 20-cm diameter phantoms. Small phantom L-shell pXFCT image required attenuation correction and had a higher sensitivity for 70MeV protons compared to 250MeV protons. With attenuation correction, L-shell pXFCT might be a feasible option for imaging of small size (∼2cm) objects. Imaging doses for all simulations were 5-30cGy. Conclusion: Proton induced x-ray fluorescence CT promises to be an alternative quantitative imaging technique to

  9. High-quality four-dimensional cone-beam CT by deforming prior images

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Gu, Xuejun

    2013-01-01

    Due to a limited number of projections at each phase, severe view aliasing artifacts are present in four-dimensional cone beam computed tomography (4D-CBCT) when reconstruction is performed using conventional algorithms. In this work, we aim to obtain high-quality 4D-CBCT of lung cancer patients in radiation therapy by deforming the planning CT. The deformation vector fields (DVF) to deform the planning CT are estimated through matching the forward projection of the deformed prior image and measured on-treatment CBCT projection. The estimation of the DVF is formulated as an unconstrained optimization problem, where the objective function to be minimized is the sum of the squared difference between the forward projection of the deformed planning CT and the measured 4D-CBCT projection. A nonlinear conjugate gradient method is used to solve the DVF. As the number of the variables in the DVF is much greater than the number of measurements, the solution to such a highly ill-posed problem is very sensitive to the initials during the optimization process. To improve the estimation accuracy of DVF, we proposed a new strategy to obtain better initials for the optimization. In this strategy, 4D-CBCT is first reconstructed by total variation minimization. Demons deformable registration is performed to register the planning CT and the 4D-CBCT reconstructed by total variation minimization. The resulted DVF from demons registration is then used as the initial parameters in the optimization process. A 4D nonuniform rotational B-spline-based cardiac-torso (NCAT) phantom and a patient 4D-CBCT are used to evaluate the algorithm. Image quality of 4D-CBCT is substantially improved by using the proposed strategy in both NCAT phantom and patient studies. The proposed method has the potential to improve the temporal resolution of 4D-CBCT. Improved 4D-CBCT can better characterize the motion of lung tumors and will be a valuable tool for image-guided adaptive radiation therapy.

  10. A hybrid reconstruction algorithm for fast and accurate 4D cone-beam CT imaging

    SciTech Connect

    Yan, Hao; Folkerts, Michael; Jiang, Steve B. E-mail: steve.jiang@UTSouthwestern.edu; Jia, Xun E-mail: steve.jiang@UTSouthwestern.edu; Zhen, Xin; Li, Yongbao; Pan, Tinsu; Cervino, Laura

    2014-07-15

    Purpose: 4D cone beam CT (4D-CBCT) has been utilized in radiation therapy to provide 4D image guidance in lung and upper abdomen area. However, clinical application of 4D-CBCT is currently limited due to the long scan time and low image quality. The purpose of this paper is to develop a new 4D-CBCT reconstruction method that restores volumetric images based on the 1-min scan data acquired with a standard 3D-CBCT protocol. Methods: The model optimizes a deformation vector field that deforms a patient-specific planning CT (p-CT), so that the calculated 4D-CBCT projections match measurements. A forward-backward splitting (FBS) method is invented to solve the optimization problem. It splits the original problem into two well-studied subproblems, i.e., image reconstruction and deformable image registration. By iteratively solving the two subproblems, FBS gradually yields correct deformation information, while maintaining high image quality. The whole workflow is implemented on a graphic-processing-unit to improve efficiency. Comprehensive evaluations have been conducted on a moving phantom and three real patient cases regarding the accuracy and quality of the reconstructed images, as well as the algorithm robustness and efficiency. Results: The proposed algorithm reconstructs 4D-CBCT images from highly under-sampled projection data acquired with 1-min scans. Regarding the anatomical structure location accuracy, 0.204 mm average differences and 0.484 mm maximum difference are found for the phantom case, and the maximum differences of 0.3–0.5 mm for patients 1–3 are observed. As for the image quality, intensity errors below 5 and 20 HU compared to the planning CT are achieved for the phantom and the patient cases, respectively. Signal-noise-ratio values are improved by 12.74 and 5.12 times compared to results from FDK algorithm using the 1-min data and 4-min data, respectively. The computation time of the algorithm on a NVIDIA GTX590 card is 1–1.5 min per phase

  11. High-quality four-dimensional cone-beam CT by deforming prior images.

    PubMed

    Wang, Jing; Gu, Xuejun

    2013-01-21

    Due to a limited number of projections at each phase, severe view aliasing artifacts are present in four-dimensional cone beam computed tomography (4D-CBCT) when reconstruction is performed using conventional algorithms. In this work, we aim to obtain high-quality 4D-CBCT of lung cancer patients in radiation therapy by deforming the planning CT. The deformation vector fields (DVF) to deform the planning CT are estimated through matching the forward projection of the deformed prior image and measured on-treatment CBCT projection. The estimation of the DVF is formulated as an unconstrained optimization problem, where the objective function to be minimized is the sum of the squared difference between the forward projection of the deformed planning CT and the measured 4D-CBCT projection. A nonlinear conjugate gradient method is used to solve the DVF. As the number of the variables in the DVF is much greater than the number of measurements, the solution to such a highly ill-posed problem is very sensitive to the initials during the optimization process. To improve the estimation accuracy of DVF, we proposed a new strategy to obtain better initials for the optimization. In this strategy, 4D-CBCT is first reconstructed by total variation minimization. Demons deformable registration is performed to register the planning CT and the 4D-CBCT reconstructed by total variation minimization. The resulted DVF from demons registration is then used as the initial parameters in the optimization process. A 4D nonuniform rotational B-spline-based cardiac-torso (NCAT) phantom and a patient 4D-CBCT are used to evaluate the algorithm. Image quality of 4D-CBCT is substantially improved by using the proposed strategy in both NCAT phantom and patient studies. The proposed method has the potential to improve the temporal resolution of 4D-CBCT. Improved 4D-CBCT can better characterize the motion of lung tumors and will be a valuable tool for image-guided adaptive radiation therapy.

  12. [Impact of planning CT slice thickness on the accuracy of automatic target registration using the on-board cone-beam CT].

    PubMed

    Inoue, Hiroyuki; Tanooka, Masao; Doi, Hiroshi; Miura, Hideharu; Nakagawa, Hideo; Sakai, Toshiyuki; Oda, Masahiko; Yasumasa, Katsumi; Sakamoto, Kiyoshi; Kamikonya, Norihiko; Hirota, Shozo

    2011-01-01

    We have evaluated relationship between planning CT slice thickness and the accuracy of automatic target registration using cone-beam CT (CBCT). Planning CT images were acquired with reconstructed slice thickness of 1, 2, 3, 5, and 10mm for three different phantoms: Penta-Guide phantom, acrylic ball phantom, and pelvic phantom. After correctly placing the phantom at the isocenter using an in-room laser, we purposely displaced it by moving the treatment couch and then obtained CBCT images. Registration between the planning CT and the CBCT was performed using automatic target registration software, and the registration errors were recorded for each planning CT data set with different slice thickness. The respective average and standard deviation of errors for 10 mm slice thickness CT in the lateral, longitudinal, and vertical directions (n=15 data sets) were: 0.7 +/- 0.2mm, 0.8 +/- 0.2mm, and 0.2 +/- 0.2mm for the Penta-Guide phantom; 0.5 +/- 0.4 mm, 0.6 +/- 0.3 mm, and 0.4 +/- 0.3 mm for the acrylic ball phantom; and 0.6 +/- 0.2 mm, 0.9 +/- 0.2 mm, and 0.2 +/- 0.2 mm for the pelvic phantom. We found that the mean registration errors were always less than 1 mm regardless of the slice thickness tested. The results suggest that there is no obvious correlation between the planning CT slice thickness and the registration errors.

  13. Data consistency-driven scatter kernel optimization for x-ray cone-beam CT

    NASA Astrophysics Data System (ADS)

    Kim, Changhwan; Park, Miran; Sung, Younghun; Lee, Jaehak; Choi, Jiyoung; Cho, Seungryong

    2015-08-01

    Accurate and efficient scatter correction is essential for acquisition of high-quality x-ray cone-beam CT (CBCT) images for various applications. This study was conducted to demonstrate the feasibility of using the data consistency condition (DCC) as a criterion for scatter kernel optimization in scatter deconvolution methods in CBCT. As in CBCT, data consistency in the mid-plane is primarily challenged by scatter, we utilized data consistency to confirm the degree of scatter correction and to steer the update in iterative kernel optimization. By means of the parallel-beam DCC via fan-parallel rebinning, we iteratively optimized the scatter kernel parameters, using a particle swarm optimization algorithm for its computational efficiency and excellent convergence. The proposed method was validated by a simulation study using the XCAT numerical phantom and also by experimental studies using the ACS head phantom and the pelvic part of the Rando phantom. The results showed that the proposed method can effectively improve the accuracy of deconvolution-based scatter correction. Quantitative assessments of image quality parameters such as contrast and structure similarity (SSIM) revealed that the optimally selected scatter kernel improves the contrast of scatter-free images by up to 99.5%, 94.4%, and 84.4%, and of the SSIM in an XCAT study, an ACS head phantom study, and a pelvis phantom study by up to 96.7%, 90.5%, and 87.8%, respectively. The proposed method can achieve accurate and efficient scatter correction from a single cone-beam scan without need of any auxiliary hardware or additional experimentation.

  14. Comparison measurements of DQE for two flat panel detectors: fluoroscopic detector vs. cone beam CT detector

    NASA Astrophysics Data System (ADS)

    Betancourt Benítez, Ricardo; Ning, Ruola; Conover, David

    2006-03-01

    The physical performance of two flat panel detectors (FPD) has been evaluated using a standard x-ray beam quality set by IEC, namely RQA5. The FPDs evaluated in this study are based on an amorphous silicon photodiode array that is coupled to a thallium-doped Cesium Iodide scintillator and to a thin film transistor (TFT) array. One detector is the PaxScan 2520 that is designed for fluoro imaging, and has a small dynamic range and a large image lag. The other detector is the PaxScan 4030CB that is designed for cone beam CT, and has a large dynamic range (>16-bit), a reduced image lag and many imaging modes. Varian Medical Systems manufactured both detectors. The linearity of the FPDs was investigated by using an ionization chamber and aluminum filtration in order to obtain the beam quality. Since the FPDs are used in fluoroscopic mode, image lag of the FPD was measured in order to investigate its effect on this study, especially its effect on DQE. The spatial resolution of the FPDs was determined by obtaining the pre-sampling modulation transfer function for each detector. A sharp edge was used in accordance to IEC 62220-1. Next, the Normalized Noise Power Spectrum (NNPS) was calculated for various exposures levels at RQA5 radiation quality. Finally, the DQE of each FPD was obtained with a modified version of the international standard set by IEC 62220-1. The results show that the physical performance in DQE and MTF of the PaxScan 4030CB is superior to that of PaxScan2520.

  15. Influence of electron density spatial distribution and X-ray beam quality during CT simulation on dose calculation accuracy.

    PubMed

    Nobah, Ahmad; Moftah, Belal; Tomic, Nada; Devic, Slobodan

    2011-04-06

    Impact of the various kVp settings used during computed tomography (CT) simulation that provides data for heterogeneity corrected dose distribution calculations in patients undergoing external beam radiotherapy with either high-energy photon or electron beams have been investigated. The change of the Hounsfield Unit (HU) values due to the influence of kVp settings and geometrical distribution of various tissue substitute materials has also been studied. The impact of various kVp settings and electron density (ED) distribution on the accuracy of dose calculation in high-energy photon beams was found to be well within 2%. In the case of dose distributions obtained with a commercially available Monte Carlo dose calculation algorithm for electron beams, differences of more than 10% were observed for different geometrical setups and kVp settings. Dose differences for the electron beams are relatively small at shallow depths but increase with depth around lower isodose values.

  16. SU-E-J-72: Dosimetric Study of Cone-Beam CT-Based Radiation Treatment Planning Using a Patient-Specific Stepwise CT-Density Table

    SciTech Connect

    Chen, S; Le, Q; Mutaf, Y; Yi, B; D’Souza, W

    2015-06-15

    Purpose: To assess dose calculation accuracy of cone-beam CT (CBCT) based treatment plans using a patient-specific stepwise CT-density conversion table in comparison to conventional CT-based treatment plans. Methods: Unlike CT-based treatment planning which use fixed CT-density table, this study used patient-specific CT-density table to minimize the errors in reconstructed mass densities due to the effects of CBCT Hounsfield unit (HU) uncertainties. The patient-specific CT-density table was a stepwise function which maps HUs to only 6 classes of materials with different mass densities: air (0.00121g/cm3), lung (0.26g/cm3), adipose (0.95g/cm3), tissue (1.05 g/cm3), cartilage/bone (1.6g/cm3), and other (3g/cm3). HU thresholds to define different materials were adjusted for each CBCT via best match with the known tissue types in these images. Dose distributions were compared between CT-based plans and CBCT-based plans (IMRT/VMAT) for four types of treatment sites: head and neck (HN), lung, pancreas, and pelvis. For dosimetric comparison, PTV mean dose in both plans were compared. A gamma analysis was also performed to directly compare dosimetry in the two plans. Results: Compared to CT-based plans, the differences for PTV mean dose were 0.1% for pelvis, 1.1% for pancreas, 1.8% for lung, and −2.5% for HN in CBCT-based plans. The gamma passing rate was 99.8% for pelvis, 99.6% for pancreas, and 99.3% for lung with 3%/3mm criteria, and 80.5% for head and neck with 5%/3mm criteria. Different dosimetry accuracy level was observed: 1% for pelvis, 3% for lung and pancreas, and 5% for head and neck. Conclusion: By converting CBCT data to 6 classes of materials for dose calculation, 3% of dose calculation accuracy can be achieved for anatomical sites studied here, except HN which had a 5% accuracy. CBCT-based treatment planning using a patient-specific stepwise CT-density table can facilitate the evaluation of dosimetry changes resulting from variation in patient anatomy.

  17. Comparison of micro-CT and cone beam CT on the feasibility of assessing trabecular structures in mandibular condyle.

    PubMed

    Liang, Xin; Zhang, Zuyan; Gu, Jianping; Wang, Zhihui; Vandenberghe, Bart; Jacobs, Reinhilde; Yang, Jie; Ma, Guowu; Ling, Haibin; Ma, Xuchen

    2017-07-01

    To evaluate the accuracy of CBCT in assessing trabecular structures. Two human mandibles were scanned by micro-CT (Skyscan 1173 high-energy spiral scan micro-CT; Skyscan NV, Kontich, Belgium) and CBCT (3D Accuitomo 170; Morita, Japan). The CBCT images were reconstructed with 0.5 and 1 mm thicknesses. The condylar images were selected for registration. A parallel algorithm for histogram computation was introduced to perform the registration. A mutual information (MI) value was used to evaluate the match between the images obtained from micro-CT and CBCT. In comparison with the micro-CT image for the two samples, the CBCT image with 0.5 mm thickness has a MI value of 0.873 and 0.903 while that with 1.0 mm thickness has a MI value of 0.741 and 0.752. The CBCT images with 0.5 mm thickness were better matched with micro-CT images. CBCT shows comparable accuracy with high-resolution micro-CT in assessing trabecular structures. CBCT can be a feasible tool to evaluate osseous changes of jaw bones.

  18. Low kV settings CT angiography (CTA) with low dose contrast medium volume protocol in the assessment of thoracic and abdominal aorta disease: a feasibility study

    PubMed Central

    Talei Franzesi, C; Fior, D; Bonaffini, P A; Minutolo, O; Sironi, S

    2015-01-01

    Objective: To assess the diagnostic quality of low dose (100 kV) CT angiography (CTA), by using ultra-low contrast medium volume (30 ml), for thoracic and abdominal aorta evaluation. Methods: 67 patients with thoracic or abdominal vascular disease underwent multidetector CT study using a 256 slice scanner, with low dose radiation protocol (automated tube current modulation, 100 kV) and low contrast medium volume (30 ml; 4 ml s−1). Density measurements were performed on ascending, arch, descending thoracic aorta, anonymous branch, abdominal aorta, and renal and common iliac arteries. Radiation dose exposure [dose–length product (DLP)] was calculated. A control group of 35 patients with thoracic or abdominal vascular disease were evaluated with standard CTA protocol (automated tube current modulation, 120 kV; contrast medium, 80 ml). Results: In all patients, we correctly visualized and evaluated main branches of the thoracic and abdominal aorta. No difference in density measurements was achieved between low tube voltage protocol (mean attenuation value of thoracic aorta, 304 HU; abdominal, 343 HU; renal arteries, 331 HU) and control group (mean attenuation value of thoracic aorta, 320 HU; abdominal, 339; renal arteries, 303 HU). Radiation dose exposure in low tube voltage protocol was significantly different between thoracic and abdominal low tube voltage studies (490 and 324 DLP, respectively) and the control group (thoracic DLP, 1032; abdomen, DLP 1078). Conclusion: Low-tube-voltage protocol may provide a diagnostic performance comparable with that of the standard protocol, decreasing radiation dose exposure and contrast material volume amount. Advances in knowledge: Low-tube-voltage-setting protocol combined with ultra-low contrast agent volume (30 ml), by using new multidetector-row CT scanners, represents a feasible diagnostic tool to significantly reduce the radiation dose delivered to patients and to preserve renal function

  19. Hounsfield unit recovery in clinical cone beam CT images of the thorax acquired for image guided radiation therapy.

    PubMed

    Thing, Rune Slot; Bernchou, Uffe; Mainegra-Hing, Ernesto; Hansen, Olfred; Brink, Carsten

    2016-08-07

    A comprehensive artefact correction method for clinical cone beam CT (CBCT) images acquired for image guided radiation therapy (IGRT) on a commercial system is presented. The method is demonstrated to reduce artefacts and recover CT-like Hounsfield units (HU) in reconstructed CBCT images of five lung cancer patients. Projection image based artefact corrections of image lag, detector scatter, body scatter and beam hardening are described and applied to CBCT images of five lung cancer patients. Image quality is evaluated through visual appearance of the reconstructed images, HU-correspondence with the planning CT images, and total volume HU error. Artefacts are reduced and CT-like HUs are recovered in the artefact corrected CBCT images. Visual inspection confirms that artefacts are indeed suppressed by the proposed method, and the HU root mean square difference between reconstructed CBCTs and the reference CT images are reduced by 31% when using the artefact corrections compared to the standard clinical CBCT reconstruction. A versatile artefact correction method for clinical CBCT images acquired for IGRT has been developed. HU values are recovered in the corrected CBCT images. The proposed method relies on post processing of clinical projection images, and does not require patient specific optimisation. It is thus a powerful tool for image quality improvement of large numbers of CBCT images.

  20. Hounsfield unit recovery in clinical cone beam CT images of the thorax acquired for image guided radiation therapy

    NASA Astrophysics Data System (ADS)

    Slot Thing, Rune; Bernchou, Uffe; Mainegra-Hing, Ernesto; Hansen, Olfred; Brink, Carsten

    2016-08-01

    A comprehensive artefact correction method for clinical cone beam CT (CBCT) images acquired for image guided radiation therapy (IGRT) on a commercial system is presented. The method is demonstrated to reduce artefacts and recover CT-like Hounsfield units (HU) in reconstructed CBCT images of five lung cancer patients. Projection image based artefact corrections of image lag, detector scatter, body scatter and beam hardening are described and applied to CBCT images of five lung cancer patients. Image quality is evaluated through visual appearance of the reconstructed images, HU-correspondence with the planning CT images, and total volume HU error. Artefacts are reduced and CT-like HUs are recovered in the artefact corrected CBCT images. Visual inspection confirms that artefacts are indeed suppressed by the proposed method, and the HU root mean square difference between reconstructed CBCTs and the reference CT images are reduced by 31% when using the artefact corrections compared to the standard clinical CBCT reconstruction. A versatile artefact correction method for clinical CBCT images acquired for IGRT has been developed. HU values are recovered in the corrected CBCT images. The proposed method relies on post processing of clinical projection images, and does not require patient specific optimisation. It is thus a powerful tool for image quality improvement of large numbers of CBCT images.

  1. Cone-beam CT breast imaging with a flat panel detector: a simulation study

    NASA Astrophysics Data System (ADS)

    Chen, Lingyun; Shaw, Chris C.; Tu, Shu-Ju; Altunbas, Mustafa C.; Wang, Tianpeng; Lai, Chao-Jen; Liu, Xinming; Kappadath, S. C.

    2005-04-01

    This paper investigates the feasibility of using a flat panel based cone-beam computer tomography (CT) system for 3-D breast imaging with computer simulation and imaging experiments. In our simulation study, 3-D phantoms were analytically modeled to simulate a breast loosely compressed into cylindrical shape with embedded soft tissue masses and calcifications. Attenuation coefficients were estimated to represent various types of breast tissue, soft tissue masses and calcifications to generate realistic image signal and contrast. Projection images were computed to incorporate x-ray attenuation, geometric magnification, x-ray detection, detector blurring, image pixelization and digitization. Based on the two-views mammography comparable dose level on the central axis of the phantom (also the rotation axis), x-ray kVp/filtration, transmittance through the phantom, detected quantum efficiency (DQE), exposure level, and imaging geometry, the photon fluence was estimated and used to estimate the phantom noise level on a pixel-by-pixel basis. This estimated noise level was then used with the random number generator to produce and add a fluctuation component to the noiseless transmitted image signal. The noise carrying projection images were then convolved with a Gaussian-like kernel, computed from measured 1-D line spread function (LSF) to simulated detector blurring. Additional 2-D Gaussian-like kernel is designed to suppress the noise fluctuation that inherently originates from projection images so that the reconstructed image detectability of low contrast masses phantom can be improved. Image reconstruction was performed using the Feldkamp algorithm. All simulations were performed on a 24 PC (2.4 GHz Dual-Xeon CPU) cluster with MPI parallel programming. With 600 mrads mean glandular dose (MGD) at the phantom center, soft tissue masses as small as 1 mm in diameter can be detected in a 10 cm diameter 50% glandular 50% adipose or fatter breast tissue, and 2 mm or larger

  2. Patient dose considerations for routine megavoltage cone-beam CT imaging

    SciTech Connect

    Morin, Olivier; Gillis, Amy; Descovich, Martina; Chen, Josephine; Aubin, Michele; Aubry, Jean-Francois; Chen Hong; Gottschalk, Alexander R.; Xia Ping; Pouliot, Jean

    2007-05-15

    Megavoltage cone-beam CT (MVCBCT), the recent addition to the family of in-room CT imaging systems for image-guided radiation therapy (IGRT), uses a conventional treatment unit equipped with a flat panel detector to obtain a three-dimensional representation of the patient in treatment position. MVCBCT has been used for more than two years in our clinic for anatomy verification and to improve patient alignment prior to dose delivery. The objective of this research is to evaluate the image acquisition dose delivered to patients for MVCBCT and to develop a simple method to reduce the additional dose resulting from routine MVCBCT imaging. Conventional CT scans of phantoms and patients were imported into a commercial treatment planning system (TPS: Phillips, Pinnacle) and an arc treatment mimicking the MVCBCT acquisition process was generated to compute the delivered acquisition dose. To validate the dose obtained from the TPS, a simple water-equivalent cylindrical phantom with spaces for MOSFETs and an ion chamber was used to measure the MVCBCT image acquisition dose. Absolute dose distributions were obtained by simulating MVCBCTs of 9 and 5 monitor units (MU) on pelvis and head and neck patients, respectively. A compensation factor was introduced to generate composite plans of treatment and MVCBCT imaging dose. The article provides a simple equation to compute the compensation factor. The developed imaging compensation method was tested on routinely used clinical plans for prostate and head and neck patients. The quantitative comparison between the calculated dose by the TPS and measurement points on the cylindrical phantom were all within 3%. The dose percentage difference for the ion chamber placed in the center of the phantom was only 0.2%. For a typical MVCBCT, the dose delivered to patients forms a small anterior-posterior gradient ranging from 0.6 to 1.2 cGy per MVCBCT MU. MVCBCT acquisitions in the pelvis and head and neck areas deliver slightly more dose than

  3. Improved image quality of cone beam CT scans for radiotherapy image guidance using fiber-interspaced antiscatter grid

    SciTech Connect

    Stankovic, Uros; Herk, Marcel van; Ploeger, Lennert S.; Sonke, Jan-Jakob

    2014-06-15

    Purpose: Medical linear accelerator mounted cone beam CT (CBCT) scanner provides useful soft tissue contrast for purposes of image guidance in radiotherapy. The presence of extensive scattered radiation has a negative effect on soft tissue visibility and uniformity of CBCT scans. Antiscatter grids (ASG) are used in the field of diagnostic radiography to mitigate the scatter. They usually do increase the contrast of the scan, but simultaneously increase the noise. Therefore, and considering other scatter mitigation mechanisms present in a CBCT scanner, the applicability of ASGs with aluminum interspacing for a wide range of imaging conditions has been inconclusive in previous studies. In recent years, grids using fiber interspacers have appeared, providing grids with higher scatter rejection while maintaining reasonable transmission of primary radiation. The purpose of this study was to evaluate the impact of one such grid on CBCT image quality. Methods: The grid used (Philips Medical Systems) had ratio of 21:1, frequency 36 lp/cm, and nominal selectivity of 11.9. It was mounted on the kV flat panel detector of an Elekta Synergy linear accelerator and tested in a phantom and a clinical study. Due to the flex of the linac and presence of gridline artifacts an angle dependent gain correction algorithm was devised to mitigate resulting artifacts. Scan reconstruction was performed using XVI4.5 augmented with inhouse developed image lag correction and Hounsfield unit calibration. To determine the necessary parameters for Hounsfield unit calibration and software scatter correction parameters, the Catphan 600 (The Phantom Laboratory) phantom was used. Image quality parameters were evaluated using CIRS CBCT Image Quality and Electron Density Phantom (CIRS) in two different geometries: one modeling head and neck and other pelvic region. Phantoms were acquired with and without the grid and reconstructed with and without software correction which was adapted for the different

  4. Radiation dose saving through the use of cone-beam CT in hearing-impaired patients.

    PubMed

    Faccioli, N; Barillari, M; Guariglia, S; Zivelonghi, E; Rizzotti, A; Cerini, R; Mucelli, R Pozzi

    2009-12-01

    Bionic ear implants provide a solution for deafness. Patients treated with these hearing devices are often children who require close follow-up with frequent functional and radiological examinations; in particular, multislice computed tomography (MSCT). Dental volumetric cone-beam CT (CBCT) has been reported as a reliable technique for acquiring images of the temporal bone while delivering low radiation doses and containing costs. The aim of this study was to assess, in terms of radiation dose and image quality, the possibility of using CBCT as an alternative to MSCT in patients with bionic ear implants. One hundred patients (mean age 26 years, range 7-43) with Vibrant SoundBridge implants on the round window underwent follow-up: 85 with CBCT and 15 with MSCT. We measured the average tissue-absorbed doses during both MSCT and CBCT scans. Each scan was focused on the temporal bone with the smallest field of view and a low-dose protocol. In order to estimate image quality, we obtained data about slice thickness, high- and low-contrast resolution, uniformity and noise by using an AAPM CT performance phantom. Although the CBCT images were qualitatively inferior to those of MSCT, they were sufficiently diagnostic to allow evaluation of the position of the implants. The effective dose of MSCT was almost three times higher than that of CBCT. Owing to low radiation dose and sufficient image quality, CBCT could be considered an adequate technique for postoperative imaging and follow-up of patients with bionic ear implants.

  5. Volume-of-change cone-beam CT for image-guided surgery

    NASA Astrophysics Data System (ADS)

    Lee, Junghoon; Webster Stayman, J.; Otake, Yoshito; Schafer, Sebastian; Zbijewski, Wojciech; Khanna, A. Jay; Prince, Jerry L.; Siewerdsen, Jeffrey H.

    2012-08-01

    C-arm cone-beam CT (CBCT) can provide intraoperative 3D imaging capability for surgical guidance, but workflow and radiation dose are the significant barriers to broad utilization. One main reason is that each 3D image acquisition requires a complete scan with a full radiation dose to present a completely new 3D image every time. In this paper, we propose to utilize patient-specific CT or CBCT as prior knowledge to accurately reconstruct the aspects of the region that have changed by the surgical procedure from only a sparse set of x-rays. The proposed methods consist of a 3D-2D registration between the prior volume and a sparse set of intraoperative x-rays, creating digitally reconstructed radiographs (DRRs) from the registered prior volume, computing difference images by subtracting DRRs from the intraoperative x-rays, a penalized likelihood reconstruction of the volume of change (VOC) from the difference images, and finally a fusion of VOC reconstruction with the prior volume to visualize the entire surgical field. When the surgical changes are local and relatively small, the VOC reconstruction involves only a small volume size and a small number of projections, allowing less computation and lower radiation dose than is needed to reconstruct the entire surgical field. We applied this approach to sacroplasty phantom data obtained from a CBCT test bench and vertebroplasty data with a fresh cadaver acquired from a C-arm CBCT system with a flat-panel detector. The VOCs were reconstructed from a varying number of images (10-66 images) and compared to the CBCT ground truth using four different metrics (mean squared error, correlation coefficient, structural similarity index and perceptual difference model). The results show promising reconstruction quality with structural similarity to the ground truth close to 1 even when only 15-20 images were used, allowing dose reduction by the factor of 10-20.

  6. Volume-of-change cone-beam CT for image-guided surgery.

    PubMed

    Lee, Junghoon; Stayman, J Webster; Otake, Yoshito; Schafer, Sebastian; Zbijewski, Wojciech; Khanna, A Jay; Prince, Jerry L; Siewerdsen, Jeffrey H

    2012-08-07

    C-arm cone-beam CT (CBCT) can provide intraoperative 3D imaging capability for surgical guidance, but workflow and radiation dose are the significant barriers to broad utilization. One main reason is that each 3D image acquisition requires a complete scan with a full radiation dose to present a completely new 3D image every time. In this paper, we propose to utilize patient-specific CT or CBCT as prior knowledge to accurately reconstruct the aspects of the region that have changed by the surgical procedure from only a sparse set of x-rays. The proposed methods consist of a 3D-2D registration between the prior volume and a sparse set of intraoperative x-rays, creating digitally reconstructed radiographs (DRRs) from the registered prior volume, computing difference images by subtracting DRRs from the intraoperative x-rays, a penalized likelihood reconstruction of the volume of change (VOC) from the difference images, and finally a fusion of VOC reconstruction with the prior volume to visualize the entire surgical field. When the surgical changes are local and relatively small, the VOC reconstruction involves only a small volume size and a small number of projections, allowing less computation and lower radiation dose than is needed to reconstruct the entire surgical field. We applied this approach to sacroplasty phantom data obtained from a CBCT test bench and vertebroplasty data with a fresh cadaver acquired from a C-arm CBCT system with a flat-panel detector. The VOCs were reconstructed from a varying number of images (10-66 images) and compared to the CBCT ground truth using four different metrics (mean squared error, correlation coefficient, structural similarity index and perceptual difference model). The results show promising reconstruction quality with structural similarity to the ground truth close to 1 even when only 15-20 images were used, allowing dose reduction by the factor of 10-20.

  7. Soft-tissue imaging with C-arm cone-beam CT using statistical reconstruction

    NASA Astrophysics Data System (ADS)

    Wang, Adam S.; Webster Stayman, J.; Otake, Yoshito; Kleinszig, Gerhard; Vogt, Sebastian; Gallia, Gary L.; Khanna, A. Jay; Siewerdsen, Jeffrey H.

    2014-02-01

    The potential for statistical image reconstruction methods such as penalized-likelihood (PL) to improve C-arm cone-beam CT (CBCT) soft-tissue visualization for intraoperative imaging over conventional filtered backprojection (FBP) is assessed in this work by making a fair comparison in relation to soft-tissue performance. A prototype mobile C-arm was used to scan anthropomorphic head and abdomen phantoms as well as a cadaveric torso at doses substantially lower than typical values in diagnostic CT, and the effects of dose reduction via tube current reduction and sparse sampling were also compared. Matched spatial resolution between PL and FBP was determined by the edge spread function of low-contrast (˜40-80 HU) spheres in the phantoms, which were representative of soft-tissue imaging tasks. PL using the non-quadratic Huber penalty was found to substantially reduce noise relative to FBP, especially at lower spatial resolution where PL provides a contrast-to-noise ratio increase up to 1.4-2.2× over FBP at 50% dose reduction across all objects. Comparison of sampling strategies indicates that soft-tissue imaging benefits from fully sampled acquisitions at dose above ˜1.7 mGy and benefits from 50% sparsity at dose below ˜1.0 mGy. Therefore, an appropriate sampling strategy along with the improved low-contrast visualization offered by statistical reconstruction demonstrates the potential for extending intraoperative C-arm CBCT to applications in soft-tissue interventions in neurosurgery as well as thoracic and abdominal surgeries by overcoming conventional tradeoffs in noise, spatial resolution, and dose.

  8. Regularization design for high-quality cone-beam CT of intracranial hemorrhage using statistical reconstruction

    NASA Astrophysics Data System (ADS)

    Dang, H.; Stayman, J. W.; Xu, J.; Sisniega, A.; Zbijewski, W.; Wang, X.; Foos, D. H.; Aygun, N.; Koliatsos, V. E.; Siewerdsen, J. H.

    2016-03-01

    Intracranial hemorrhage (ICH) is associated with pathologies such as hemorrhagic stroke and traumatic brain injury. Multi-detector CT is the current front-line imaging modality for detecting ICH (fresh blood contrast 40-80 HU, down to 1 mm). Flat-panel detector (FPD) cone-beam CT (CBCT) offers a potential alternative with a smaller scanner footprint, greater portability, and lower cost potentially well suited to deployment at the point of care outside standard diagnostic radiology and emergency room settings. Previous studies have suggested reliable detection of ICH down to 3 mm in CBCT using high-fidelity artifact correction and penalized weighted least-squared (PWLS) image reconstruction with a post-artifact-correction noise model. However, ICH reconstructed by traditional image regularization exhibits nonuniform spatial resolution and noise due to interaction between the statistical weights and regularization, which potentially degrades the detectability of ICH. In this work, we propose three regularization methods designed to overcome these challenges. The first two compute spatially varying certainty for uniform spatial resolution and noise, respectively. The third computes spatially varying regularization strength to achieve uniform "detectability," combining both spatial resolution and noise in a manner analogous to a delta-function detection task. Experiments were conducted on a CBCT test-bench, and image quality was evaluated for simulated ICH in different regions of an anthropomorphic head. The first two methods improved the uniformity in spatial resolution and noise compared to traditional regularization. The third exhibited the highest uniformity in detectability among all methods and best overall image quality. The proposed regularization provides a valuable means to achieve uniform image quality in CBCT of ICH and is being incorporated in a CBCT prototype for ICH imaging.

  9. Adaptive planning using megavoltage fan-beam CT for radiation therapy with testicular shielding

    SciTech Connect

    Yadav, Poonam; Kozak, Kevin; Tolakanahalli, Ranjini; Ramasubramanian, V.; Paliwal, Bhudatt R.; Welsh, James S.; Rong, Yi

    2012-07-01

    This study highlights the use of adaptive planning to accommodate testicular shielding in helical tomotherapy for malignancies of the proximal thigh. Two cases of young men with large soft tissue sarcomas of the proximal thigh are presented. After multidisciplinary evaluation, preoperative radiation therapy was recommended. Both patients were referred for sperm banking and lead shields were used to minimize testicular dose during radiation therapy. To minimize imaging artifacts, kilovoltage CT (kVCT) treatment planning was conducted without shielding. Generous hypothetical contours were generated on each 'planning scan' to estimate the location of the lead shield and generate a directionally blocked helical tomotherapy plan. To ensure the accuracy of each plan, megavoltage fan-beam CT (MVCT) scans were obtained at the first treatment and adaptive planning was performed to account for lead shield placement. Two important regions of interest in these cases were femurs and femoral heads. During adaptive planning for the first patient, it was observed that the virtual lead shield contour on kVCT planning images was significantly larger than the actual lead shield used for treatment. However, for the second patient, it was noted that the size of the virtual lead shield contoured on the kVCT image was significantly smaller than the actual shield size. Thus, new adaptive plans based on MVCT images were generated and used for treatment. The planning target volume was underdosed up to 2% and had higher maximum doses without adaptive planning. In conclusion, the treatment of the upper thigh, particularly in young men, presents several clinical challenges, including preservation of gonadal function. In such circumstances, adaptive planning using MVCT can ensure accurate dose delivery even in the presence of high-density testicular shields.

  10. Small field of view cone beam CT temporomandibular joint imaging dosimetry

    PubMed Central

    Lukat, T D; Wong, J C M; Lam, E W N

    2013-01-01

    Objectives: Cone beam CT (CBCT) is generally accepted as the imaging modality of choice for visualisation of the osseous structures of the temporomandibular joint (TMJ). The purpose of this study was to compare the radiation dose of a protocol for CBCT TMJ imaging using a large field of view Hitachi CB MercuRay™ unit (Hitachi Medical Systems, Tokyo, Japan) with an alternative approach that utilizes two CBCT acquisitions of the right and left TMJs using the Kodak 9000® 3D system (Carestream, Rochester, NY). Methods: 25 optically stimulated luminescence dosemeters were placed in various locations of an anthropomorphic RANDO® Man phantom (Alderson Research Laboratories, Stanford, CT). Dosimetric measurements were performed for each technique, and effective doses were calculated using the 2007 International Commission on Radiological Protection tissue weighting factor recommendations for all protocols. Results: The radiation effective dose for the CB MercuRay technique was 223.6 ± 1.1 μSv compared with 9.7 ± 0.1 μSv (child), 13.5 ± 0.9 μSv (adolescent/small adult) and 20.5 ± 1.3 μSv (adult) for the bilateral Kodak acquisitions. Conclusions: Acquisitions of individual right and left TMJ volumes using the Kodak 9000 3D CBCT imaging system resulted in a more than ten-fold reduction in the effective dose compared with the larger single field acquisition with the Hitachi CB MercuRay. This decrease is made even more significant when lower tube potential and tube current settings are used. PMID:24048693

  11. Small field of view cone beam CT temporomandibular joint imaging dosimetry.

    PubMed

    Lukat, T D; Wong, J C M; Lam, E W N

    2013-01-01

    Cone beam CT (CBCT) is generally accepted as the imaging modality of choice for visualisation of the osseous structures of the temporomandibular joint (TMJ). The purpose of this study was to compare the radiation dose of a protocol for CBCT TMJ imaging using a large field of view Hitachi CB MercuRay™ unit (Hitachi Medical Systems, Tokyo, Japan) with an alternative approach that utilizes two CBCT acquisitions of the right and left TMJs using the Kodak 9000(®) 3D system (Carestream, Rochester, NY). 25 optically stimulated luminescence dosemeters were placed in various locations of an anthropomorphic RANDO(®) Man phantom (Alderson Research Laboratories, Stanford, CT). Dosimetric measurements were performed for each technique, and effective doses were calculated using the 2007 International Commission on Radiological Protection tissue weighting factor recommendations for all protocols. The radiation effective dose for the CB MercuRay technique was 223.6 ± 1.1 μSv compared with 9.7 ± 0.1 μSv (child), 13.5 ± 0.9 μSv (adolescent/small adult) and 20.5 ± 1.3 μSv (adult) for the bilateral Kodak acquisitions. Acquisitions of individual right and left TMJ volumes using the Kodak 9000 3D CBCT imaging system resulted in a more than ten-fold reduction in the effective dose compared with the larger single field acquisition with the Hitachi CB MercuRay. This decrease is made even more significant when lower tube potential and tube current settings are used.

  12. Volume-of-Change Cone-Beam CT for Image-Guided Surgery

    PubMed Central

    Lee, Junghoon; Stayman, J. Webster; Otake, Yoshito; Schafer, Sebastian; Zbijewski, Wojciech; Khanna, A. Jay; Prince, Jerry L.; Siewerdsen, Jeffrey H.

    2012-01-01

    C-arm cone-beam CT (CBCT) can provide intraoperative 3D imaging capability for surgical guidance, but workflow and radiation dose are the significant barriers to broad utilization. One main reason is that each 3D image acquisition requires a complete scan with a full radiation dose to present a completely new 3D image every time. In this paper, we propose to utilize patient-specific CT or CBCT as prior knowledge to accurately reconstruct the aspects of the region that have changed by the surgical procedure from only a sparse set of x-rays. The proposed methods consist of a 3D-2D registration between the prior volume and a sparse set of intraoperative x-rays, creating digitally reconstructed radiographs (DRR) from the registered prior volume, computing difference images by subtracting DRRs from the intraoperative x-rays, a penalized likelihood reconstruction of the volume of change (VOC) from the difference images, and finally a fusion of VOC reconstruction with the prior volume to visualize the entire surgical field. When the surgical changes are local and relatively small, the VOC reconstruction involves only a small volume size and a small number of projections, allowing less computation and lower radiation dose than is needed to reconstruct the entire surgical field. We applied this approach to sacroplasty phantom data obtained from a CBCT test bench and vertebroplasty data with a fresh cadaver acquired from a C-arm CBCT system with a flat-panel detector (FPD). The VOCs were reconstructed from varying number of images (10–66 images) and compared to the CBCT ground truth using four different metrics (mean squared error, correlation coefficient, structural similarity index, and perceptual difference model). The results show promising reconstruction quality with structural similarity to the ground truth close to 1 even when only 15–20 images were used, allowing dose reduction by the factor of 10–20. PMID:22801026

  13. Reducing metal artifacts in cone-beam CT images by preprocessing projection data

    SciTech Connect

    Zhang Yongbin; Zhang Lifei; Zhu, X. Ronald; Lee, Andrew K.; Chambers, Mark; Dong Lei . E-mail: ldong@mdanderson.org

    2007-03-01

    Purpose: Computed tomography (CT) streak artifacts caused by metallic implants remain a challenge for the automatic processing of image data. The impact of metal artifacts in the soft-tissue region is magnified in cone-beam CT (CBCT), because the soft-tissue contrast is usually lower in CBCT images. The goal of this study was to develop an effective offline processing technique to minimize the effect. Methods and Materials: The geometry calibration cue of the CBCT system was used to track the position of the metal object in projection views. The three-dimensional (3D) representation of the object can be established from only two user-selected viewing angles. The position of the shadowed region in other views can be tracked by projecting the 3D coordinates of the object. Automatic image segmentation was used followed by a Laplacian diffusion method to replace the pixels inside the metal object with the boundary pixels. The modified projection data were then used to reconstruct a new CBCT image. The procedure was tested in phantoms, prostate cancer patients with implanted gold markers and metal prosthesis, and a head-and-neck patient with dental amalgam in the teeth. Results: Both phantom and patient studies demonstrated that the procedure was able to minimize the metal artifacts. Soft-tissue visibility was improved near or away from the metal object. The processing time was 1-2 s per projection. Conclusion: We have implemented an effective metal artifact-suppressing algorithm to improve the quality of CBCT images.

  14. Flat panel detector-based cone-beam volume CT angiography imaging: system evaluation.

    PubMed

    Ning, R; Chen, B; Yu, R; Conover, D; Tang, X; Ning, Y

    2000-09-01

    Preliminary evaluation of recently developed large-area flat panel detectors (FPDs) indicates that FPDs have some potential advantages: compactness, absence of geometric distortion and veiling glare with the benefits of high resolution, high detective quantum efficiency (DQE), high frame rate and high dynamic range, small image lag (< 1%), and excellent linearity (approximately 1%). The advantages of the new FPD make it a promising candidate for cone-beam volume computed tomography (CT) angiography (CBVCTA) imaging. The purpose of this study is to characterize a prototype FPD-based imaging system for CBVCTA applications. A prototype FPD-based CBVCTA imaging system has been designed and constructed around a modified GE 8800 CT scanner. This system is evaluated for a CBVCTA imaging task in the head and neck using four phantoms and a frozen rat. The system is first characterized in terms of linearity and dynamic range of the detector. Then, the optimal selection of kVps for CBVCTA is determined and the effect of image lag and scatter on the image quality of the CBVCTA system is evaluated. Next, low-contrast resolution and high-contrast spatial resolution are measured. Finally, the example reconstruction images of a frozen rat are presented. The results indicate that the FPD-based CBVCT can achieve 2.75-lp/mm spatial resolution at 0% modulation transfer function (MTF) and provide more than enough low-contrast resolution for intravenous CBVCTA imaging in the head and neck with clinically acceptable entrance exposure level. The results also suggest that to use an FPD for large cone-angle applications, such as body angiography, further investigations are required.

  15. Clinical implementation of intraoperative cone-beam CT in head and neck surgery

    NASA Astrophysics Data System (ADS)

    Daly, M. J.; Chan, H.; Nithiananthan, S.; Qiu, J.; Barker, E.; Bachar, G.; Dixon, B. J.; Irish, J. C.; Siewerdsen, J. H.

    2011-03-01

    A prototype mobile C-arm for cone-beam CT (CBCT) has been translated to a prospective clinical trial in head and neck surgery. The flat-panel CBCT C-arm was developed in collaboration with Siemens Healthcare, and demonstrates both sub-mm spatial resolution and soft-tissue visibility at low radiation dose (e.g., <1/5th of a typical diagnostic head CT). CBCT images are available ~15 seconds after scan completion (~1 min acquisition) and reviewed at bedside using custom 3D visualization software based on the open-source Image-Guided Surgery Toolkit (IGSTK). The CBCT C-arm has been successfully deployed in 15 head and neck cases and streamlined into the surgical environment using human factors engineering methods and expert feedback from surgeons, nurses, and anesthetists. Intraoperative imaging is implemented in a manner that maintains operating field sterility, reduces image artifacts (e.g., carbon fiber OR table) and minimizes radiation exposure. Image reviews conducted with surgical staff indicate bony detail and soft-tissue visualization sufficient for intraoperative guidance, with additional artifact management (e.g., metal, scatter) promising further improvements. Clinical trial deployment suggests a role for intraoperative CBCT in guiding complex head and neck surgical tasks, including planning mandible and maxilla resection margins, guiding subcranial and endonasal approaches to skull base tumours, and verifying maxillofacial reconstruction alignment. Ongoing translational research into complimentary image-guidance subsystems include novel methods for real-time tool tracking, fusion of endoscopic video and CBCT, and deformable registration of preoperative volumes and planning contours with intraoperative CBCT.

  16. Adaptive planning using megavoltage fan-beam CT for radiation therapy with testicular shielding.

    PubMed

    Yadav, Poonam; Kozak, Kevin; Tolakanahalli, Ranjini; Ramasubramanian, V; Paliwal, Bhudatt R; Welsh, James S; Rong, Yi

    2012-01-01

    This study highlights the use of adaptive planning to accommodate testicular shielding in helical tomotherapy for malignancies of the proximal thigh. Two cases of young men with large soft tissue sarcomas of the proximal thigh are presented. After multidisciplinary evaluation, preoperative radiation therapy was recommended. Both patients were referred for sperm banking and lead shields were used to minimize testicular dose during radiation therapy. To minimize imaging artifacts, kilovoltage CT (kVCT) treatment planning was conducted without shielding. Generous hypothetical contours were generated on each "planning scan" to estimate the location of the lead shield and generate a directionally blocked helical tomotherapy plan. To ensure the accuracy of each plan, megavoltage fan-beam CT (MVCT) scans were obtained at the first treatment and adaptive planning was performed to account for lead shield placement. Two important regions of interest in these cases were femurs and femoral heads. During adaptive planning for the first patient, it was observed that the virtual lead shield contour on kVCT planning images was significantly larger than the actual lead shield used for treatment. However, for the second patient, it was noted that the size of the virtual lead shield contoured on the kVCT image was significantly smaller than the actual shield size. Thus, new adaptive plans based on MVCT images were generated and used for treatment. The planning target volume was underdosed up to 2% and had higher maximum doses without adaptive planning. In conclusion, the treatment of the upper thigh, particularly in young men, presents several clinical challenges, including preservation of gonadal function. In such circumstances, adaptive planning using MVCT can ensure accurate dose delivery even in the presence of high-density testicular shields.

  17. High-performance C-arm cone-beam CT guidance of thoracic surgery

    NASA Astrophysics Data System (ADS)

    Schafer, Sebastian; Otake, Yoshito; Uneri, Ali; Mirota, Daniel J.; Nithiananthan, Sajendra; Stayman, J. W.; Zbijewski, Wojciech; Kleinszig, Gerhard; Graumann, Rainer; Sussman, Marc; Siewerdsen, Jeffrey H.

    2012-02-01

    Localizing sub-palpable nodules in minimally invasive video-assisted thoracic surgery (VATS) presents a significant challenge. To overcome inherent problems of preoperative nodule tagging using CT fluoroscopic guidance, an intraoperative C-arm cone-beam CT (CBCT) image-guidance system has been developed for direct localization of subpalpable tumors in the OR, including real-time tracking of surgical tools (including thoracoscope), and video-CBCT registration for augmentation of the thoracoscopic scene. Acquisition protocols for nodule visibility in the inflated and deflated lung were delineated in phantom and animal/cadaver studies. Motion compensated reconstruction was implemented to account for motion induced by the ventilated contralateral lung. Experience in CBCT-guided targeting of simulated lung nodules included phantoms, porcine models, and cadavers. Phantom studies defined low-dose acquisition protocols providing contrast-to-noise ratio sufficient for lung nodule visualization, confirmed in porcine specimens with simulated nodules (3-6mm diameter PE spheres, ~100-150HU contrast, 2.1mGy). Nodule visibility in CBCT of the collapsed lung, with reduced contrast according to air volume retention, was more challenging, but initial studies confirmed visibility using scan protocols at slightly increased dose (~4.6-11.1mGy). Motion compensated reconstruction employing a 4D deformation map in the backprojection process reduced artifacts associated with motion blur. Augmentation of thoracoscopic video with renderings of the target and critical structures (e.g., pulmonary artery) showed geometric accuracy consistent with camera calibration and the tracking system (2.4mm registration error). Initial results suggest a potentially valuable role for CBCT guidance in VATS, improving precision in minimally invasive, lungconserving surgeries, avoid critical structures, obviate the burdens of preoperative localization, and improve patient safety.

  18. Deriving Hounsfield units using grey levels in cone beam CT: a clinical application

    PubMed Central

    Reeves, TE; Mah, P; McDavid, WD

    2012-01-01

    Objective To present a clinical study demonstrating a method to derive Hounsfield units from grey levels in cone beam CT (CBCT). Methods An acrylic intraoral reference object with aluminium, outer bone equivalent material (cortical bone), inner bone equivalent material (trabecular bone), polymethlymethacrylate and water equivalent material was used. Patients were asked if they would be willing to have an acrylic bite plate with the reference object placed in their mouth during a routine CBCT scan. There were 31 scans taken on the Asahi Alphard 3030 (Belmont Takara, Kyoto, Japan) and 30 scans taken on the Planmeca ProMax 3D (Planmeca, Helsinki, Finland) CBCT. Linear regression between the grey levels of the reference materials and their linear attenuation coefficients was performed for various photon energies. The energy with the highest regression coefficient was chosen as the effective energy. The attenuation coefficients for the five materials at the effective energy were scaled as Hounsfield units using the standard Hounsfield units equation and compared to those derived from the measured grey levels of the materials using the regression equation. Results In general, there was a satisfactory linear relation between the grey levels and the attenuation coefficients. This made it possible to calculate Hounsfield units from the measured grey levels. Uncertainty in determining effective energies resulted in unrealistic effective energies and significant variability of calculated CT numbers. Linear regression from grey levels directly to Hounsfield units at specified energies resulted in greater consistency. Conclusions The clinical application of a method for deriving Hounsfield units from grey levels in CBCT was demonstrated. PMID:22752324

  19. Reconstruction-plane-dependent weighted FDK algorithm for cone beam volumetric CT

    NASA Astrophysics Data System (ADS)

    Tang, Xiangyang; Hsieh, Jiang

    2005-04-01

    The original FDK algorithm has been extensively employed in medical and industrial imaging applications. With an increased cone angle, cone beam (CB) artifacts in images reconstructed by the original FDK algorithm deteriorate, since the circular trajectory does not satisfy the so-called data sufficiency condition (DSC). A few "circular plus" trajectories have been proposed in the past to reduce CB artifacts by meeting the DSC. However, the circular trajectory has distinct advantages over other scanning trajectories in practical CT imaging, such as cardiac, vascular and perfusion applications. In addition to looking into the DSC, another insight into the CB artifacts of the original FDK algorithm is the inconsistency between conjugate rays that are 180° apart in view angle. The inconsistence between conjugate rays is pixel dependent, i.e., it varies dramatically over pixels within the image plane to be reconstructed. However, the original FDK algorithm treats all conjugate rays equally, resulting in CB artifacts that can be avoided if appropriate view weighting strategy is exercised. In this paper, a modified FDK algorithm is proposed, along with an experimental evaluation and verification, in which the helical body phantom and a humanoid head phantom scanned by a volumetric CT (64 x 0.625 mm) are utilized. Without extra trajectories supplemental to the circular trajectory, the modified FDK algorithm applies reconstruction-plane-dependent view weighting on projection data before 3D backprojection, which reduces the inconsistency between conjugate rays by suppressing the contribution of one of the conjugate rays with a larger cone angle. Both computer-simulated and real phantom studies show that, up to a moderate cone angle, the CB artifacts can be substantially suppressed by the modified FDK algorithm, while advantages of the original FDK algorithm, such as the filtered backprojection algorithm structure, 1D ramp filtering, and data manipulation efficiency, can be

  20. Low-dose and scatter-free cone-beam CT imaging: a preliminary study

    NASA Astrophysics Data System (ADS)

    Dong, Xue; Jia, Xun; Niu, Tianye; Zhu, Lei

    2012-03-01

    Clinical applications of CBCT imaging are still limited by excessive imaging dose from repeated scans and poor image quality mainly due to scatter contamination. Compressed sensing (CS) reconstruction algorithms have shown promises in recovering faithful signals from low-dose projection data, but do not serve well the needs of accurate CBCT imaging if effective scatter correction is not in place. Scatter can be accurately measured and removed using measurement-based methods. However, in conventional FDK reconstruction, these approaches are considered unpractical since they require multiple scans or moving the beam blocker during the data acquisition to compensate for the inevitable primary loss. In this work, we combine the measurement-based scatter correction and CS-based iterative reconstruction algorithm, such that scatter-free images can be obtained from low-dose data. We lower the CBCT dose by reducing the projection number and inserting lead strips between the x-ray source and the object. The insertion of lead strips also enables scatter measurement on the measured samples inside the strip shadows. CS-based iterative reconstruction is finally carried out to obtain scatter-free and low-dose CBCT images. Simulation studies are designed to optimize the lead strip geometry for a certain dose reduction ratio. After optimization, our approach reduces the CT number error from over 220HU to below 5HU on the Shepp-Logan phantom, with a dose reduction of ~80%. With the same dose reduction and the optimized method parameters, the CT number error is reduced from 242HU to 20HU in the selected region of interest on Catphan©600 phantom.

  1. Technical Note: FreeCT_wFBP: A robust, efficient, open-source implementation of weighted filtered backprojection for helical, fan-beam CT

    PubMed Central

    Hoffman, John; Young, Stefano; Noo, Frédéric

    2016-01-01

    Purpose: With growing interest in quantitative imaging, radiomics, and CAD using CT imaging, the need to explore the impacts of acquisition and reconstruction parameters has grown. This usually requires extensive access to the scanner on which the data were acquired and its workflow is not designed for large-scale reconstruction projects. Therefore, the authors have developed a freely available, open-source software package implementing a common reconstruction method, weighted filtered backprojection (wFBP), for helical fan-beam CT applications. Methods: FreeCT_wFBP is a low-dependency, GPU-based reconstruction program utilizing c for the host code and Nvidia CUDA C for GPU code. The software is capable of reconstructing helical scans acquired with arbitrary pitch-values, and sampling techniques such as flying focal spots and a quarter-detector offset. In this work, the software has been described and evaluated for reconstruction speed, image quality, and accuracy. Speed was evaluated based on acquisitions of the ACR CT accreditation phantom under four different flying focal spot configurations. Image quality was assessed using the same phantom by evaluating CT number accuracy, uniformity, and contrast to noise ratio (CNR). Finally, reconstructed mass-attenuation coefficient accuracy was evaluated using a simulated scan of a FORBILD thorax phantom and comparing reconstructed values to the known phantom values. Results: The average reconstruction time evaluated under all flying focal spot configurations was found to be 17.4 ± 1.0 s for a 512 row × 512 column × 32 slice volume. Reconstructions of the ACR phantom were found to meet all CT Accreditation Program criteria including CT number, CNR, and uniformity tests. Finally, reconstructed mass-attenuation coefficient values of water within the FORBILD thorax phantom agreed with original phantom values to within 0.0001 mm2/g (0.01%). Conclusions: FreeCT_wFBP is a fast, highly configurable reconstruction package for

  2. Technical Note: FreeCT_wFBP: A robust, efficient, open-source implementation of weighted filtered backprojection for helical, fan-beam CT.

    PubMed

    Hoffman, John; Young, Stefano; Noo, Frédéric; McNitt-Gray, Michael

    2016-03-01

    With growing interest in quantitative imaging, radiomics, and CAD using CT imaging, the need to explore the impacts of acquisition and reconstruction parameters has grown. This usually requires extensive access to the scanner on which the data were acquired and its workflow is not designed for large-scale reconstruction projects. Therefore, the authors have developed a freely available, open-source software package implementing a common reconstruction method, weighted filtered backprojection (wFBP), for helical fan-beam CT applications. FreeCT_wFBP is a low-dependency, GPU-based reconstruction program utilizing c for the host code and Nvidia CUDA C for GPU code. The software is capable of reconstructing helical scans acquired with arbitrary pitch-values, and sampling techniques such as flying focal spots and a quarter-detector offset. In this work, the software has been described and evaluated for reconstruction speed, image quality, and accuracy. Speed was evaluated based on acquisitions of the ACR CT accreditation phantom under four different flying focal spot configurations. Image quality was assessed using the same phantom by evaluating CT number accuracy, uniformity, and contrast to noise ratio (CNR). Finally, reconstructed mass-attenuation coefficient accuracy was evaluated using a simulated scan of a FORBILD thorax phantom and comparing reconstructed values to the known phantom values. The average reconstruction time evaluated under all flying focal spot configurations was found to be 17.4 ± 1.0 s for a 512 row × 512 column × 32 slice volume. Reconstructions of the ACR phantom were found to meet all CT Accreditation Program criteria including CT number, CNR, and uniformity tests. Finally, reconstructed mass-attenuation coefficient values of water within the FORBILD thorax phantom agreed with original phantom values to within 0.0001 mm(2)/g (0.01%). FreeCT_wFBP is a fast, highly configurable reconstruction package for third-generation CT available under

  3. Evaluation of On-Board kV Cone Beam Computed Tomography–Based Dose Calculation With Deformable Image Registration Using Hounsfield Unit Modifications

    SciTech Connect

    Onozato, Yusuke; Kadoya, Noriyuki; Fujita, Yukio; Arai, Kazuhiro; Dobashi, Suguru; Takeda, Ken; Kishi, Kazuma; Umezawa, Rei; Matsushita, Haruo; Jingu, Keiichi

    2014-06-01

    Purpose: The purpose of this study was to estimate the accuracy of the dose calculation of On-Board Imager (Varian, Palo Alto, CA) cone beam computed tomography (CBCT) with deformable image registration (DIR), using the multilevel-threshold (MLT) algorithm and histogram matching (HM) algorithm in pelvic radiation therapy. Methods and Materials: One pelvis phantom and 10 patients with prostate cancer treated with intensity modulated radiation therapy were studied. To minimize the effect of organ deformation and different Hounsfield unit values between planning CT (PCT) and CBCT, we modified CBCT (mCBCT) with DIR by using the MLT (mCBCT{sub MLT}) and HM (mCBCT{sub HM}) algorithms. To evaluate the accuracy of the dose calculation, we compared dose differences in dosimetric parameters (mean dose [D{sub mean}], minimum dose [D{sub min}], and maximum dose [D{sub max}]) for planning target volume, rectum, and bladder between PCT (reference) and CBCTs or mCBCTs. Furthermore, we investigated the effect of organ deformation compared with DIR and rigid registration (RR). We determined whether dose differences between PCT and mCBCTs were significantly lower than in CBCT by using Student t test. Results: For patients, the average dose differences in all dosimetric parameters of CBCT with DIR were smaller than those of CBCT with RR (eg, rectum; 0.54% for DIR vs 1.24% for RR). For the mCBCTs with DIR, the average dose differences in all dosimetric parameters were less than 1.0%. Conclusions: We evaluated the accuracy of the dose calculation in CBCT, mCBCT{sub MLT}, and mCBCT{sub HM} with DIR for 10 patients. The results showed that dose differences in D{sub mean}, D{sub min}, and D{sub max} in mCBCTs were within 1%, which were significantly better than those in CBCT, especially for the rectum (P<.05). Our results indicate that the mCBCT{sub MLT} and mCBCT{sub HM} can be useful for improving the dose calculation for adaptive radiation therapy.

  4. Evaluation of on-board kV cone beam computed tomography-based dose calculation with deformable image registration using Hounsfield unit modifications.

    PubMed

    Onozato, Yusuke; Kadoya, Noriyuki; Fujita, Yukio; Arai, Kazuhiro; Dobashi, Suguru; Takeda, Ken; Kishi, Kazuma; Umezawa, Rei; Matsushita, Haruo; Jingu, Keiichi

    2014-06-01

    The purpose of this study was to estimate the accuracy of the dose calculation of On-Board Imager (Varian, Palo Alto, CA) cone beam computed tomography (CBCT) with deformable image registration (DIR), using the multilevel-threshold (MLT) algorithm and histogram matching (HM) algorithm in pelvic radiation therapy. One pelvis phantom and 10 patients with prostate cancer treated with intensity modulated radiation therapy were studied. To minimize the effect of organ deformation and different Hounsfield unit values between planning CT (PCT) and CBCT, we modified CBCT (mCBCT) with DIR by using the MLT (mCBCT(MLT)) and HM (mCBCT(HM)) algorithms. To evaluate the accuracy of the dose calculation, we compared dose differences in dosimetric parameters (mean dose [D(mean)], minimum dose [D(min)], and maximum dose [D(max)]) for planning target volume, rectum, and bladder between PCT (reference) and CBCTs or mCBCTs. Furthermore, we investigated the effect of organ deformation compared with DIR and rigid registration (RR). We determined whether dose differences between PCT and mCBCTs were significantly lower than in CBCT by using Student t test. For patients, the average dose differences in all dosimetric parameters of CBCT with DIR were smaller than those of CBCT with RR (eg, rectum; 0.54% for DIR vs 1.24% for RR). For the mCBCTs with DIR, the average dose differences in all dosimetric parameters were less than 1.0%. We evaluated the accuracy of the dose calculation in CBCT, mCBCT(MLT), and mCBCT(HM) with DIR for 10 patients. The results showed that dose differences in D(mean), D(min), and D(max) in mCBCTs were within 1%, which were significantly better than those in CBCT, especially for the rectum (P<.05). Our results indicate that the mCBCT(MLT) and mCBCT(HM) can be useful for improving the dose calculation for adaptive radiation therapy. Copyright © 2014 Elsevier Inc. All rights reserved.

  5. Task-driven image acquisition and reconstruction in cone-beam CT

    PubMed Central

    Gang, Grace J.; Stayman, J. Webster; Ehtiati, Tina; Siewerdsen, Jeffrey H.

    2015-01-01

    This work introduces a task-driven imaging framework that incorporates a mathematical definition of the imaging task, a model of the imaging system, and a patient-specific anatomical model to prospectively design image acquisition and reconstruction techniques to optimize task performance. The framework is applied to joint optimization of tube current modulation, view-dependent reconstruction kernel, and orbital tilt in cone-beam CT. The system model considers a cone-beam CT system incorporating a flat-panel detector and 3D filtered backprojection and accurately describes the spatially varying noise and resolution over a wide range of imaging parameters and in the presence of a realistic anatomical model. Task-based detectability index (d') is incorporated as the objective function in a task-driven optimization of image acquisition and reconstruction techniques. The orbital tilt was optimized through an exhaustive search across tilt angles ranging ±30°. For each tilt angle, the view-dependent tube current and reconstruction kernel (i.e., the modulation profiles) that maximized detectability were identified via an alternating optimization. The task-driven approach was compared with conventional unmodulated and automatic exposure control (AEC) strategies for a variety of imaging tasks and anthropomorphic phantoms. The task-driven strategy outperformed the unmodulated and AEC cases for all tasks. For example, d' for a sphere detection task in a head phantom was improved by 30% compared to the unmodulated case by using smoother kernels for noisy views and distributing mAs across less noisy views (at fixed total mAs) in a manner that was beneficial to task performance. Similarly for detection of a line-pair pattern, the task-driven approach increased d' by 80% compared to no modulation by means of view-dependent mA and kernel selection that yields modulation transfer function and noise-power spectrum optimal to the task. Optimization of orbital tilt identified the

  6. Task-driven image acquisition and reconstruction in cone-beam CT

    NASA Astrophysics Data System (ADS)

    Gang, Grace J.; Webster Stayman, J.; Ehtiati, Tina; Siewerdsen, Jeffrey H.

    2015-04-01

    This work introduces a task-driven imaging framework that incorporates a mathematical definition of the imaging task, a model of the imaging system, and a patient-specific anatomical model to prospectively design image acquisition and reconstruction techniques to optimize task performance. The framework is applied to joint optimization of tube current modulation, view-dependent reconstruction kernel, and orbital tilt in cone-beam CT. The system model considers a cone-beam CT system incorporating a flat-panel detector and 3D filtered backprojection and accurately describes the spatially varying noise and resolution over a wide range of imaging parameters in the presence of a realistic anatomical model. Task-based detectability index (d‧) is incorporated as the objective function in a task-driven optimization of image acquisition and reconstruction techniques. The orbital tilt was optimized through an exhaustive search across tilt angles ranging ±30°. For each tilt angle, the view-dependent tube current and reconstruction kernel (i.e. the modulation profiles) that maximized detectability were identified via an alternating optimization. The task-driven approach was compared with conventional unmodulated and automatic exposure control (AEC) strategies for a variety of imaging tasks and anthropomorphic phantoms. The task-driven strategy outperformed the unmodulated and AEC cases for all tasks. For example, d‧ for a sphere detection task in a head phantom was improved by 30% compared to the unmodulated case by using smoother kernels for noisy views and distributing mAs across less noisy views (at fixed total mAs) in a manner that was beneficial to task performance. Similarly for detection of a line-pair pattern, the task-driven approach increased d‧ by 80% compared to no modulation by means of view-dependent mA and kernel selection that yields modulation transfer function and noise-power spectrum optimal to the task. Optimization of orbital tilt identified the

  7. Task-driven image acquisition and reconstruction in cone-beam CT.

    PubMed

    Gang, Grace J; Stayman, J Webster; Ehtiati, Tina; Siewerdsen, Jeffrey H

    2015-04-21

    This work introduces a task-driven imaging framework that incorporates a mathematical definition of the imaging task, a model of the imaging system, and a patient-specific anatomical model to prospectively design image acquisition and reconstruction techniques to optimize task performance. The framework is applied to joint optimization of tube current modulation, view-dependent reconstruction kernel, and orbital tilt in cone-beam CT. The system model considers a cone-beam CT system incorporating a flat-panel detector and 3D filtered backprojection and accurately describes the spatially varying noise and resolution over a wide range of imaging parameters in the presence of a realistic anatomical model. Task-based detectability index (d') is incorporated as the objective function in a task-driven optimization of image acquisition and reconstruction techniques. The orbital tilt was optimized through an exhaustive search across tilt angles ranging ± 30°. For each tilt angle, the view-dependent tube current and reconstruction kernel (i.e. the modulation profiles) that maximized detectability were identified via an alternating optimization. The task-driven approach was compared with conventional unmodulated and automatic exposure control (AEC) strategies for a variety of imaging tasks and anthropomorphic phantoms. The task-driven strategy outperformed the unmodulated and AEC cases for all tasks. For example, d' for a sphere detection task in a head phantom was improved by 30% compared to the unmodulated case by using smoother kernels for noisy views and distributing mAs across less noisy views (at fixed total mAs) in a manner that was beneficial to task performance. Similarly for detection of a line-pair pattern, the task-driven approach increased d' by 80% compared to no modulation by means of view-dependent mA and kernel selection that yields modulation transfer function and noise-power spectrum optimal to the task. Optimization of orbital tilt identified the tilt

  8. Stereotactic radiosurgery for intradural spine tumors using cone-beam CT image guidance.

    PubMed

    Monserrate, Andrés; Zussman, Benjamin; Ozpinar, Alp; Niranjan, Ajay; Flickinger, John C; Gerszten, Peter C

    2017-01-01

    OBJECTIVE Cone-beam CT (CBCT) image guidance technology has been widely adopted for spine radiosurgery delivery. There is relatively little experience with spine radiosurgery for intradural tumors using CBCT image guidance. This study prospectively evaluated a series of intradural spine tumors treated with radiosurgery. Patient setup accuracy for spine radiosurgery delivery using CBCT image guidance for intradural spine tumors was determined. METHODS Eighty-two patients with intradural tumors were treated and prospectively evaluated. The positioning deviations of the spine radiosurgery treatments in patients were recorded. Radiosurgery was delivered using a linear accelerator with a beam modulator and CBCT image guidance combined with a robotic couch that allows positioning correction in 3 translational and 3 rotational directions. To measure patient movement, 3 quality assurance CBCTs were performed and recorded in 30 patients: before, halfway, and after the radiosurgery treatment. The positioning data and fused images of planning CT and CBCT from the treatments were analyzed to determine intrafraction patient movements. From each of 3 CBCTs, 3 translational and 3 rotational coordinates were obtained. RESULTS The radiosurgery procedure was successfully completed for all patients. Lesion locations included cervical (22), thoracic (17), lumbar (38), and sacral (5). Tumor histologies included schwannoma (27), neurofibromas (18), meningioma (16), hemangioblastoma (8), and ependymoma (5). The mean prescription dose was 17 Gy (range 12-27 Gy) delivered in 1-3 fractions. At the halfway point of the radiation, the translational variations and standard deviations were 0.4 ± 0.5, 0.5 ± 0.8, and 0.4 ± 0.5 mm in the lateral (x), longitudinal (y), and anteroposterior (z) directions, respectively. Similarly, the variations immediately after treatment were 0.5 ± 0.4, 0.5 ± 0.6, and 0.6 ± 0.5 mm along x, y, and z directions, respectively. The mean rotational angles were 0

  9. Determining superficial dosimetry for the internal canthus from the Monte Carlo simulation of kV photon and MeV electron beams.

    PubMed

    Currie, B E

    2009-06-01

    This paper presents the findings of an investigation into the Monte Carlo simulation of superficial cancer treatments of an internal canthus site using both kilovoltage photons and megavoltage electrons. The EGSnrc system of codes for the Monte Carlo simulation of the transport of electrons and photons through a phantom representative of either a water phantom or treatment site in a patient is utilised. Two clinical treatment units are simulated: the Varian Medical Systems Clinac 2100C accelerator for 6 MeV electron fields and the Pantak Therapax SXT 150 X-ray unit for 100 kVp photon fields. Depth dose, profile and isodose curves for these simulated units are compared against those measured by ion chamber in a PTW Freiburg MP3 water phantom. Good agreement was achieved away from the surface of the phantom between simulated and measured data. Dose distributions are determined for both kV photon and MeV electron fields in the internal canthus site containing lead and tungsten shielding, rapidly sloping surfaces and different density interfaces. There is a relatively high level of deposition of dose in tissue-bone and tissue-cartilage interfaces in the kV photon fields in contrast to the MeV electron fields. This is reflected in the maximum doses in the PTV of the internal canthus field being 12 Gy for kV photons and 4.8 Gy for MeV electrons. From the dose distributions, DVH and dose comparators are used to assess the simulated treatment fields. Any indication as to which modality is preferable to treat the internal canthus requires careful consideration of many different factors, this investigation provides further perspective in being able to assess which modality is appropriate.

  10. A dual modality phantom for cone beam CT and ultrasound image fusion in prostate implant

    SciTech Connect

    Ng, Angela; Beiki-Ardakan, Akbar; Tong, Shidong; Moseley, Douglas; Siewerdsen, Jeffrey; Jaffray, David; Yeung, Ivan W. T.

    2008-05-15

    In transrectal ultrasound (TRUS) guided prostate seed brachytherapy, TRUS provides good delineation of the prostate while x-ray imaging, e.g., C-arm, gives excellent contrast for seed localization. With the recent availability of cone beam CT (CBCT) technology, the combination of the two imaging modalities may provide an ideal system for intraoperative dosimetric feedback during implantation. A dual modality phantom made of acrylic and copper wire was designed to measure the accuracy and precision of image coregistration between a C-arm based CBCT and 3D TRUS. The phantom was scanned with TRUS and CBCT under the same setup condition. Successive parallel transverse ultrasound (US) images were acquired through manual stepping of the US probe across the phantom at an increment of 1 mm over 7.5 cm. The CBCT imaging was done with three reconstructed slice thicknesses (0.4, 0.8, and 1.6 mm) as well as at three different tilt angles (0 deg., 15 deg., 30 deg. ), and the coregistration between CBCT and US images was done using the Variseed system based on four fiducial markers. Fiducial localization error (FLE), fiducial registration error (FRE), and target registration error (TRE) were calculated for all registered image sets. Results showed that FLE were typically less than 0.4 mm, FRE were less than 0.5 mm, and TRE were typically less than 1 mm within the range of operation for prostate implant (i.e., <6 cm to surface of US probe). An analysis of variance test showed no significant difference in TRE for the CBCT-US fusion among the three slice thicknesses (p=0.37). As a comparison, the experiment was repeated with a US-conventional CT scanner combination. No significant difference in TRE was noted between the US-conventional CT fusion and that for all three CBCT image slice thicknesses (p=0.21). CBCT imaging was also performed at three different C-arm tilt angles of 0 deg., 15 deg., and 30 deg. and reconstructed at a slice thickness of 0.8 mm. There is no significant

  11. A dual cone-beam CT system for image guided radiotherapy: Initial performance characterization

    SciTech Connect

    Li Hao; Bowsher, James; Yin Fangfang; Giles, William

    2013-02-15

    Purpose: The purpose of this study is to evaluate the performance of a recently developed benchtop dual cone-beam computed tomography (CBCT) system with two orthogonally placed tube/detector sets. Methods: The benchtop dual CBCT system consists of two orthogonally placed 40 Multiplication-Sign 30 cm flat-panel detectors and two conventional x-ray tubes with two individual high-voltage generators sharing the same rotational axis. The x-ray source to detector distance is 150 cm and x-ray source to rotational axis distance is 100 cm for both subsystems. The objects are scanned through 200 Degree-Sign of rotation. The dual CBCT system utilized 110 Degree-Sign of projection data from one detector and 90 Degree-Sign from the other while the two individual single CBCTs utilized 200 Degree-Sign data from each detector. The system performance was characterized in terms of uniformity, contrast, spatial resolution, noise power spectrum, and CT number linearity. The uniformities, within the axial slice and along the longitudinal direction, and noise power spectrum were assessed by scanning a water bucket; the contrast and CT number linearity were measured using the Catphan phantom; and the spatial resolution was evaluated using a tungsten wire phantom. A skull phantom and a ham were also scanned to provide qualitative evaluation of high- and low-contrast resolution. Each measurement was compared between dual and single CBCT systems. Results: Compared to single CBCT, the dual CBCT presented: (1) a decrease in uniformity by 1.9% in axial view and 1.1% in the longitudinal view, as averaged for four energies (80, 100, 125, and 150 kVp); (2) comparable or slightly better contrast (0{approx}25 HU) for low-contrast objects and comparable contrast for high-contrast objects; (3) comparable spatial resolution; (4) comparable CT number linearity with R{sup 2}{>=} 0.99 for all four tested energies; (5) lower noise power spectrum in magnitude. Dual CBCT images of the skull phantom and the

  12. A model-based scatter artifacts correction for cone beam CT

    SciTech Connect

    Zhao, Wei; Zhu, Jun; Wang, Luyao; Vernekohl, Don; Xing, Lei

    2016-04-15

    Purpose: Due to the increased axial coverage of multislice computed tomography (CT) and the introduction of flat detectors, the size of x-ray illumination fields has grown dramatically, causing an increase in scatter radiation. For CT imaging, scatter is a significant issue that introduces shading artifact, streaks, as well as reduced contrast and Hounsfield Units (HU) accuracy. The purpose of this work is to provide a fast and accurate scatter artifacts correction algorithm for cone beam CT (CBCT) imaging. Methods: The method starts with an estimation of coarse scatter profiles for a set of CBCT data in either image domain or projection domain. A denoising algorithm designed specifically for Poisson signals is then applied to derive the final scatter distribution. Qualitative and quantitative evaluations using thorax and abdomen phantoms with Monte Carlo (MC) simulations, experimental Catphan phantom data, and in vivo human data acquired for a clinical image guided radiation therapy were performed. Scatter correction in both projection domain and image domain was conducted and the influences of segmentation method, mismatched attenuation coefficients, and spectrum model as well as parameter selection were also investigated. Results: Results show that the proposed algorithm can significantly reduce scatter artifacts and recover the correct HU in either projection domain or image domain. For the MC thorax phantom study, four-components segmentation yields the best results, while the results of three-components segmentation are still acceptable. The parameters (iteration number K and weight β) affect the accuracy of the scatter correction and the results get improved as K and β increase. It was found that variations in attenuation coefficient accuracies only slightly impact the performance of the proposed processing. For the Catphan phantom data, the mean value over all pixels in the residual image is reduced from −21.8 to −0.2 HU and 0.7 HU for projection

  13. A model-based scatter artifacts correction for cone beam CT

    PubMed Central

    Zhao, Wei; Vernekohl, Don; Zhu, Jun; Wang, Luyao; Xing, Lei

    2016-01-01

    Purpose: Due to the increased axial coverage of multislice computed tomography (CT) and the introduction of flat detectors, the size of x-ray illumination fields has grown dramatically, causing an increase in scatter radiation. For CT imaging, scatter is a significant issue that introduces shading artifact, streaks, as well as reduced contrast and Hounsfield Units (HU) accuracy. The purpose of this work is to provide a fast and accurate scatter artifacts correction algorithm for cone beam CT (CBCT) imaging. Methods: The method starts with an estimation of coarse scatter profiles for a set of CBCT data in either image domain or projection domain. A denoising algorithm designed specifically for Poisson signals is then applied to derive the final scatter distribution. Qualitative and quantitative evaluations using thorax and abdomen phantoms with Monte Carlo (MC) simulations, experimental Catphan phantom data, and in vivo human data acquired for a clinical image guided radiation therapy were performed. Scatter correction in both projection domain and image domain was conducted and the influences of segmentation method, mismatched attenuation coefficients, and spectrum model as well as parameter selection were also investigated. Results: Results show that the proposed algorithm can significantly reduce scatter artifacts and recover the correct HU in either projection domain or image domain. For the MC thorax phantom study, four-components segmentation yields the best results, while the results of three-components segmentation are still acceptable. The parameters (iteration number K and weight β) affect the accuracy of the scatter correction and the results get improved as K and β increase. It was found that variations in attenuation coefficient accuracies only slightly impact the performance of the proposed processing. For the Catphan phantom data, the mean value over all pixels in the residual image is reduced from −21.8 to −0.2 HU and 0.7 HU for projection

  14. Deformable image registration with local rigidity constraints for cone-beam CT-guided spine surgery

    NASA Astrophysics Data System (ADS)

    Reaungamornrat, S.; Wang, A. S.; Uneri, A.; Otake, Y.; Khanna, A. J.; Siewerdsen, J. H.

    2014-07-01

    Image-guided spine surgery (IGSS) is associated with reduced co-morbidity and improved surgical outcome. However, precise localization of target anatomy and adjacent nerves and vessels relative to planning information (e.g., device trajectories) can be challenged by anatomical deformation. Rigid registration alone fails to account for deformation associated with changes in spine curvature, and conventional deformable registration fails to account for rigidity of the vertebrae, causing unrealistic distortions in the registered image that can confound high-precision surgery. We developed and evaluated a deformable registration method capable of preserving rigidity of bones while resolving the deformation of surrounding soft tissue. The method aligns preoperative CT to intraoperative cone-beam CT (CBCT) using free-form deformation (FFD) with constraints on rigid body motion imposed according to a simple intensity threshold of bone intensities. The constraints enforced three properties of a rigid transformation—namely, constraints on affinity (AC), orthogonality (OC), and properness (PC). The method also incorporated an injectivity constraint (IC) to preserve topology. Physical experiments involving phantoms, an ovine spine, and a human cadaver as well as digital simulations were performed to evaluate the sensitivity to registration parameters, preservation of rigid body morphology, and overall registration accuracy of constrained FFD in comparison to conventional unconstrained FFD (uFFD) and Demons registration. FFD with orthogonality and injectivity constraints (denoted FFD+OC+IC) demonstrated improved performance compared to uFFD and Demons. Affinity and properness constraints offered little or no additional improvement. The FFD+OC+IC method preserved rigid body morphology at near-ideal values of zero dilatation ({ D} = 0.05, compared to 0.39 and 0.56 for uFFD and Demons, respectively) and shear ({ S} = 0.08, compared to 0.36 and 0.44 for uFFD and Demons

  15. Self-calibration of a cone-beam micro-CT system

    SciTech Connect

    Patel, V.; Chityala, R. N.; Hoffmann, K. R.; Ionita, C. N.; Bednarek, D. R.; Rudin, S.

    2009-01-15

    Use of cone-beam computed tomography (CBCT) is becoming more frequent. For proper reconstruction, the geometry of the CBCT systems must be known. While the system can be designed to reduce errors in the geometry, calibration measurements must still be performed and corrections applied. Investigators have proposed techniques using calibration objects for system calibration. In this study, the authors present methods to calibrate a rotary-stage CB micro-CT (CB{mu}CT) system using only the images acquired of the object to be reconstructed, i.e., without the use of calibration objects. Projection images are acquired using a CB{mu}CT system constructed in the authors' laboratories. Dark- and flat-field corrections are performed. Exposure variations are detected and quantified using analysis of image regions with an unobstructed view of the x-ray source. Translations that occur during the acquisition in the horizontal direction are detected, quantified, and corrected based on sinogram analysis. The axis of rotation is determined using registration of antiposed projection images. These techniques were evaluated using data obtained with calibration objects and phantoms. The physical geometric axis of rotation is determined and aligned with the rotational axis (assumed to be the center of the detector plane) used in the reconstruction process. The parameters describing this axis agree to within 0.1 mm and 0.3 deg with those determined using other techniques. Blurring due to residual calibration errors has a point-spread function in the reconstructed planes with a full-width-at-half-maximum of less than 125 {mu}m in a tangential direction and essentially zero in the radial direction for the rotating object. The authors have used this approach on over 100 acquisitions over the past 2 years and have regularly obtained high-quality reconstructions, i.e., without artifacts and no detectable blurring of the reconstructed objects. This self-calibrating approach not only obviates

  16. Deformable Image Registration for Cone-Beam CT Guided Transoral Robotic Base of Tongue Surgery

    PubMed Central

    Reaungamornrat, S.; Liu, W. P.; Wang, A. S.; Otake, Y.; Nithiananthan, S.; Uneri, A.; Schafer, S.; Tryggestad, E.; Richmon, J.; Sorger, J. M.; Siewerdsen, J. H.; Taylor, R. H.

    2013-01-01

    Transoral robotic surgery (TORS) offers a minimally invasive approach to resection of base of tongue tumors. However, precise localization of the surgical target and adjacent critical structures can be challenged by the highly deformed intraoperative setup. We propose a deformable registration method using intraoperative cone-beam CT (CBCT) to accurately align preoperative CT or MR images with the intraoperative scene. The registration method combines a Gaussian mixture (GM) model followed by a variation of the Demons algorithm. First, following segmentation of the volume of interest (i.e., volume of the tongue extending to the hyoid), a GM model is applied to surface point clouds for rigid initialization (GM rigid) followed by nonrigid deformation (GM nonrigid). Second, the registration is refined using the Demons algorithm applied to distance map transforms of the (GM-registered) preoperative image and intraoperative CBCT. Performance was evaluated in repeat cadaver studies (25 image pairs) in terms of target registration error (TRE), entropy correlation coefficient (ECC), and normalized pointwise mutual information (NPMI). Retraction of the tongue in the TORS operative setup induced gross deformation >30 mm. The mean TRE following the GM rigid, GM nonrigid, and Demons steps was 4.6, 2.1, and 1.7 mm, respectively. The respective ECC was 0.57, 0.70, and 0.73 and NPMI was 0.46, 0.57, and 0.60. Registration accuracy was best across the superior aspect of the tongue and in proximity to the hyoid (by virtue of GM registration of surface points on these structures). The Demons step refined registration primarily in deeper portions of the tongue further from the surface and hyoid bone. Since the method does not use image intensities directly, it is suitable to multi-modality registration of preoperative CT or MR with intraoperative CBCT. Extending the 3D image registration to the fusion of image and planning data in stereo-endoscopic video is anticipated to support

  17. Homogeneous and inhomogeneous material effect in gamma index evaluation of IMRT technique based on fan beam and Cone Beam CT patient images

    NASA Astrophysics Data System (ADS)

    Wibowo, W. E.; Waliyyulhaq, M.; Pawiro, S. A.

    2017-05-01

    Patient-specific Quality Assurance (QA) technique in lung case Intensity-Modulated Radiation Therapy (IMRT) is traditionally limited to homogeneous material, although the fact that the planning is carried out with inhomogeneous material present. Moreover, the chest area has many of inhomogeneous material, such as lung, soft tissue, and bone, which inhomogeneous material requires special attention to avoid inaccuracies in dose calculation in the Treatment Planning System (TPS). Recent preliminary studies shown that the role of Cone Beam CT (CBCT) can be used not only to position the patient at the time prior to irradiation but also to serve as planning modality. Our study presented the influence of a homogeneous and inhomogeneous materials using Fan Beam CT and Cone Beam CT modalities in IMRT technique on the Gamma Index (GI) value. We used a variation of the segment and Calculation Grid Resolution (CGR). The results showed the deviation of averaged GI value to be between CGR 0.2 cm and 0.4 cm with homogeneous material ranging from -0.44% to 1.46%. For inhomogeneous material, the value was range from -1.74% to 0.98%. In performing patient-specific IMRT QA techniques for lung cancer, homogeneous material can be implemented in evaluating the gamma index.

  18. Comparison of human and Hotelling observer performance for a fan-beam CT signal detection task

    PubMed Central

    Sanchez, Adrian A.; Sidky, Emil Y.; Reiser, Ingrid; Pan, Xiaochuan

    2013-01-01

    Purpose: A human observer study was performed for a signal detection task for the case of fan-beam x-ray computed tomography. Hotelling observer (HO) performance was calculated for the same detection task without the use of efficient channels. By considering the full image covariance produced by the filtered backprojection (FBP) algorithm and avoiding the use of channels in the computation of HO performance, the authors establish an absolute upper bound on signal detectability. Therefore, this study serves as a baseline for relating human and ideal observer performance in the case of fan-beam CT. Methods: Eight human observers participated in a two-alternative forced choice experiment where the signal of interest was a small simulated ellipsoid in the presence of independent, identically distributed Gaussian detector noise. Theoretical performance of the HO, which is equivalent to the ideal observer in this case (see Sec. 13.2.12 in Barrett and Myers [Foundations of Image Science (Wiley, Hoboken, NJ, 2004)], was also computed and compared to the performance of the human observers. In addition to a reference FBP implementation, two FBP implementations with inherent loss of HO signal detectability (e.g., by apodizing the ramp filter) were also investigated. Each of these latter two implementations takes the form of a discrete-to-discrete linear operator (i.e., a matrix), which has a nontrivial null-space resulting in the loss of detectability. Results: Estimated observer detectability index (\\documentclass[12pt]{minimal}\\begin{document}$\\hat{d}_A$\\end{document}d^A) values for the human observers and SNR values for the HO were obtained. While Hanning filtering in the FBP implementation with a cutoff frequency of 1/4 of the Nyquist frequency reduces HO SNR (due to the reconstruction matrix's nontrivial null-space), this filtering was shown to consistently improve human observer performance. By contrast, increasing the image pixel size was seen to have a comparable

  19. TU-AB-204-00: Advances in Cone-Beam CT and Emerging Applications

    SciTech Connect

    2015-06-15

    This symposium highlights advanced cone-beam CT (CBCT) technologies in four areas of emerging application in diagnostic imaging and image-guided interventions. Each area includes research that extends the spatial, temporal, and/or contrast resolution characteristics of CBCT beyond conventional limits through advances in scanner technology, acquisition protocols, and 3D image reconstruction techniques. Dr. G. Chen (University of Wisconsin) will present on the topic: Advances in C-arm CBCT for Brain Perfusion Imaging. Stroke is a leading cause of death and disability, and a fraction of people having an acute ischemic stroke are suitable candidates for endovascular therapy. Critical factors that affect both the likelihood of successful revascularization and good clinical outcome are: 1) the time between stroke onset and revascularization; and 2) the ability to distinguish patients who have a small volume of irreversibly injured brain (ischemic core) and a large volume of ischemic but salvageable brain (penumbra) from patients with a large ischemic core and little or no penumbra. Therefore, “time is brain” in the care of the stroke patients. C-arm CBCT systems widely available in angiography suites have the potential to generate non-contrast-enhanced CBCT images to exclude the presence of hemorrhage, time-resolved CBCT angiography to evaluate the site of occlusion and collaterals, and CBCT perfusion parametric images to assess the extent of the ischemic core and penumbra, thereby fulfilling the imaging requirements of a “one-stop-shop” in the angiography suite to reduce the time between onset and revascularization therapy. The challenges and opportunities to advance CBCT technology to fully enable the one-stop-shop C-arm CBCT platform for brain imaging will be discussed. Dr. R. Fahrig (Stanford University) will present on the topic: Advances in C-arm CBCT for Cardiac Interventions. With the goal of providing functional information during cardiac interventions

  20. Iterative image-domain ring artifact removal in cone-beam CT

    NASA Astrophysics Data System (ADS)

    Liang, Xiaokun; Zhang, Zhicheng; Niu, Tianye; Yu, Shaode; Wu, Shibin; Li, Zhicheng; Zhang, Huailing; Xie, Yaoqin

    2017-07-01

    Ring artifacts in cone beam computed tomography (CBCT) images are caused by pixel gain variations using flat-panel detectors, and may lead to structured non-uniformities and deterioration of image quality. The purpose of this study is to propose a method of general ring artifact removal in CBCT images. This method is based on the polar coordinate system, where the ring artifacts manifest as stripe artifacts. Using relative total variation, the CBCT images are first smoothed to generate template images with fewer image details and ring artifacts. By subtracting the template images from the CBCT images, residual images with image details and ring artifacts are generated. As the ring artifact manifests as a stripe artifact in a polar coordinate system, the artifact image can be extracted by mean value from the residual image; the image details are generated by subtracting the artifact image from the residual image. Finally, the image details are compensated to the template image to generate the corrected images. The proposed framework is iterated until the differences in the extracted ring artifacts are minimized. We use a 3D Shepp-Logan phantom, Catphan©504 phantom, uniform acrylic cylinder, and images from a head patient to evaluate the proposed method. In the experiments using simulated data, the spatial uniformity is increased by 1.68 times and the structural similarity index is increased from 87.12% to 95.50% using the proposed method. In the experiment using clinical data, our method shows high efficiency in ring artifact removal while preserving the image structure and detail. The iterative approach we propose for ring artifact removal in cone-beam CT is practical and attractive for CBCT guided radiation therapy.

  1. Evaluation of bone changes in the temporomandibular joint using cone beam CT

    PubMed Central

    dos Anjos Pontual, ML; Freire, JSL; Barbosa, JMN; Frazão, MAG; dos Anjos Pontual, A; Fonseca da Silveira, MM

    2012-01-01

    Objective The aim of this study was to assess bone changes and mobility in temporomandibular joints (TMJs) using cone beam CT (CBCT) in a population sample in Recife, PE, Brazil. Methods The TMJ images of patients treated by a radiologist at a private dental radiology service over a period of 1 year were retrieved from the computer database and assessed using a computer with a 21-inch monitor and the iCAT Cone Beam 3D Dental Imaging System Workstation program (Imaging Sciences International, Hatfield, PA). The Pearson χ2 test was used to analyse the differences in percentage of bone changes among the categories of mobility (p ≤ 0.05). The McNemar test was used to compare the presence of bone changes in TMJs on the right and left sides (p ≤ 0.05). Results An adjusted logistic regression model was used to assess the effect of age and gender on the occurrence of bone changes (p ≤ 0.05). Bone changes were present in 227 (71%) patients. Age group and gender showed a statistically significant association with presence of bone changes (p ≤ 0.05). There was no significant difference between the right and left sides (p = 0.556) and in condylar mobility (p = 0.925) with regard to the presence of degenerative bone changes. Conclusions There is a high prevalence of degenerative bone alteration in TMJs, which is more frequent in women and mostly located in the condyle. The prevalence of degenerative bone changes increases with age. There is no correlation between condylar mobility and the presence of degenerative bony changes in TMJs. PMID:22184625

  2. Noise suppression in reconstruction of low-Z target megavoltage cone-beam CT images

    SciTech Connect

    Wang Jing; Robar, James; Guan Huaiqun

    2012-08-15

    Purpose: To improve the image contrast-to-noise (CNR) ratio for low-Z target megavoltage cone-beam CT (MV CBCT) using a statistical projection noise suppression algorithm based on the penalized weighted least-squares (PWLS) criterion. Methods: Projection images of a contrast phantom, a CatPhan{sup Registered-Sign} 600 phantom and a head phantom were acquired by a Varian 2100EX LINAC with a low-Z (Al) target and low energy x-ray beam (2.5 MeV) at a low-dose level and at a high-dose level. The projections were then processed by minimizing the PWLS objective function. The weighted least square (WLS) term models the noise of measured projection and the penalty term enforces the smoothing constraints of the projection image. The variance of projection data was chosen as the weight for the PWLS objective function and it determined the contribution of each measurement. An anisotropic quadratic form penalty that incorporates the gradient information of projection image was used to preserve edges during noise reduction. Low-Z target MV CBCT images were reconstructed by the FDK algorithm after each projection was processed by the PWLS smoothing. Results: Noise in low-Z target MV CBCT images were greatly suppressed after the PWLS projection smoothing, without noticeable sacrifice of the spatial resolution. Depending on the choice of smoothing parameter, the CNR of selected regions of interest in the PWLS processed low-dose low-Z target MV CBCT image can be higher than the corresponding high-dose image.Conclusion: The CNR of low-Z target MV CBCT images was substantially improved by using PWLS projection smoothing. The PWLS projection smoothing algorithm allows the reconstruction of high contrast low-Z target MV CBCT image with a total dose of as low as 2.3 cGy.

  3. Three-dimensional focus of attention for iterative cone-beam micro-CT reconstruction

    NASA Astrophysics Data System (ADS)

    Benson, T. M.; Gregor, J.

    2006-09-01

    Three-dimensional iterative reconstruction of high-resolution, circular orbit cone-beam x-ray CT data is often considered impractical due to the demand for vast amounts of computer cycles and associated memory. In this paper, we show that the computational burden can be reduced by limiting the reconstruction to a small, well-defined portion of the image volume. We first discuss using the support region defined by the set of voxels covered by all of the projection views. We then present a data-driven preprocessing technique called focus of attention that heuristically separates both image and projection data into object and background before reconstruction, thereby further reducing the reconstruction region of interest. We present experimental results for both methods based on mouse data and a parallelized implementation of the SIRT algorithm. The computational savings associated with the support region are substantial. However, the results for focus of attention are even more impressive in that only about one quarter of the computer cycles and memory are needed compared with reconstruction of the entire image volume. The image quality is not compromised by either method.

  4. Clinical Implementation Of Megavoltage Cone Beam CT As Part Of An IGRT Program

    NASA Astrophysics Data System (ADS)

    Gonzalez, Albin; Bauer, Lisa; Kinney, Vicki; Crooks, Cheryl

    2008-03-01

    Knowing where the tumor is at all times during treatment is the next challenge in the field of radiation therapy. This issue has become more important because with treatments such as Intensity Modulated Radiation Therapy (IMRT), healthy tissue is spared by using very tight margins around the tumor. These tight margins leave very small room for patient setup errors. The use of an imaging modality in the treatment room as a way to localize the tumor for patient set up is generally known as "Image Guided Radiation Therapy" or IGRT. This article deals with a form of IGRT known as Megavoltage Cone Beam Computed Tomography (MCBCT) using a Siemens Oncor linear accelerator currently in use at Firelands Regional Medical Center. With MCBCT, we are capable of acquiring CT images right before the treatment of the patient and then use this information to position the patient tumor according to the treatment plan. This article presents the steps followed in order to clinically implement this system, as well as some of the quality assurance tests suggested by the manufacturer and some tests developed in house

  5. Descriptive study of the bifid mandibular canals and retromolar foramina: cone beam CT vs panoramic radiography

    PubMed Central

    Muinelo-Lorenzo, J; Suárez-Quintanilla, J A; Fernández-Alonso, A; Marsillas-Rascado, S

    2014-01-01

    Objectives: To examine the presence and morphologic characteristics of bifid mandibular canals (BMCs) and retromolar foramens (RFs) using cone beam CT (CBCT) and to determine their visualization on panoramic radiographs (PANs). Methods: A sample of 225 CBCT examinations was analysed for the presence of BMCs, as well as length, height, diameter and angle. The diameter of the RF was also determined. Subsequently, corresponding PANs were analysed to determine whether the BMCs and RFs were visible or not. Results: The BMCs were observed on CBCT in 83 out of the 225 patients (36.8%). With respect to gender, statistically significant differences were found in the number of BMCs. There were also significant differences in anatomical characteristics of the types of BMCs. Only 37.8% of the BMCs and 32.5% of the RFs identified on CBCT were also visible on PANs. The diameter had a significant effect on the capability of PANs to visualize BMCs and RFs (B = 0.791, p = 0.035; B = 1.900, p = 0.017, respectively). Conclusions: PANs are unable to sufficiently identify BMCs and RFs. The diameter of these anatomical landmarks represents a relevant factor for visualization on PANs. Pre-operative images using only PANs may lead to underestimation of the presence of BMCs and to surgical complications and anaesthetic failures, which could have been avoided. For true determination of BMCs, a CBCT device should be considered better than a PAN. PMID:24785820

  6. 3D Alternating Direction TV-Based Cone-Beam CT Reconstruction with Efficient GPU Implementation

    PubMed Central

    Cai, Ailong; Zhang, Hanming; Li, Lei; Xi, Xiaoqi; Guan, Min; Li, Jianxin

    2014-01-01

    Iterative image reconstruction (IIR) with sparsity-exploiting methods, such as total variation (TV) minimization, claims potentially large reductions in sampling requirements. However, the computation complexity becomes a heavy burden, especially in 3D reconstruction situations. In order to improve the performance for iterative reconstruction, an efficient IIR algorithm for cone-beam computed tomography (CBCT) with GPU implementation has been proposed in this paper. In the first place, an algorithm based on alternating direction total variation using local linearization and proximity technique is proposed for CBCT reconstruction. The applied proximal technique avoids the horrible pseudoinverse computation of big matrix which makes the proposed algorithm applicable and efficient for CBCT imaging. The iteration for this algorithm is simple but convergent. The simulation and real CT data reconstruction results indicate that the proposed algorithm is both fast and accurate. The GPU implementation shows an excellent acceleration ratio of more than 100 compared with CPU computation without losing numerical accuracy. The runtime for the new 3D algorithm is about 6.8 seconds per loop with the image size of 256 × 256 × 256 and 36 projections of the size of 512 × 512. PMID:25045400

  7. How I Do It: Cone-Beam CT during Transarterial Chemoembolization for Liver Cancer

    PubMed Central

    Tacher, Vania; Radaelli, Alessandro; Lin, MingDe

    2015-01-01

    Cone-beam computed tomography (CBCT) is an imaging technique that provides computed tomographic (CT) images from a rotational scan acquired with a C-arm equipped with a flat panel detector. Utilizing CBCT images during interventional procedures bridges the gap between the world of diagnostic imaging (typically three-dimensional imaging but performed separately from the procedure) and that of interventional radiology (typically two-dimensional imaging). CBCT is capable of providing more information than standard two-dimensional angiography in localizing and/or visualizing liver tumors (“seeing” the tumor) and targeting tumors though precise microcatheter placement in close proximity to the tumors (“reaching” the tumor). It can also be useful in evaluating treatment success at the time of procedure (“assessing” treatment success). CBCT technology is rapidly evolving along with the development of various contrast material injection protocols and multiphasic CBCT techniques. The purpose of this article is to provide a review of the principles of CBCT imaging, including purpose and clinical evidence of the different techniques, and to introduce a decision-making algorithm as a guide for the routine utilization of CBCT during transarterial chemoembolization of liver cancer. © RSNA, 2015 Online supplemental material is available for this article. PMID:25625741

  8. Breast density quantification with cone-beam CT: a post-mortem study.

    PubMed

    Johnson, Travis; Ding, Huanjun; Le, Huy Q; Ducote, Justin L; Molloi, Sabee

    2013-12-07

    Forty post-mortem breasts were imaged with a flat-panel based cone-beam x-ray CT system at 50 kVp. The feasibility of breast density quantification has been investigated using standard histogram thresholding and an automatic segmentation method based on the fuzzy c-means algorithm (FCM). The breasts were chemically decomposed into water, lipid, and protein immediately after image acquisition was completed. The per cent fibroglandular volume (%FGV) from chemical analysis was used as the gold standard for breast density comparison. Both image-based segmentation techniques showed good precision in breast density quantification with high linear coefficients between the right and left breast of each pair. When comparing with the gold standard using %FGV from chemical analysis, Pearson's r-values were estimated to be 0.983 and 0.968 for the FCM clustering and the histogram thresholding techniques, respectively. The standard error of the estimate was also reduced from 3.92% to 2.45% by applying the automatic clustering technique. The results of the postmortem study suggested that breast tissue can be characterized in terms of water, lipid and protein contents with high accuracy by using chemical analysis, which offers a gold standard for breast density studies comparing different techniques. In the investigated image segmentation techniques, the FCM algorithm had high precision and accuracy in breast density quantification. In comparison to conventional histogram thresholding, it was more efficient and reduced inter-observer variation.

  9. Comparative study between conventional and cone beam CT-synthesized half and total skull cephalograms

    PubMed Central

    Liedke, GS; Delamare, EL; Vizzotto, MB; da Silveira, HLD; Prietsch, JR; Dutra, V; da Silveira, HED

    2012-01-01

    Objectives The aim of this study was to compare cephalometric measurements obtained from conventional cephalograms with total and half-skull synthesized cone beam CT (CBCT) cephalograms. Methods Cephalometric analyses of 30 clinically symmetric patients were conducted by a calibrated examiner on conventional and CBCT-synthesized cephalograms (total, right and left). Reproducibility was investigated using the intraclass correlation coefficient (ICC). The Bland–Altman analysis was used to assess the agreement of the measurements from each factor obtained by conventional, total, right and left CBCT-synthesized cephalograms. Results The ICC was above 0.9 for most of the 40 cephalometric factors analysed, revealing similar levels of reproducibility. When the measurements obtained from conventional and CBCT-synthesized cephalograms were compared, the Bland–Altman analysis showed a strong agreement between them. Conclusions Half-skull CBCT-synthesized cephalograms offer the same diagnostic performance and equivalent reproducibility in terms of cephalometric analysis as observed in conventional and total CBCT-synthesized cephalograms. PMID:22301638

  10. Observer Reliability of Three-Dimensional Cephalometric Landmark Identification on Cone-Beam CT

    PubMed Central

    de Oliveira, Ana Emilia F.; Cevidanes, Lucia Helena S.; Phillips, Ceib; Motta, Alexandre; Burke, Brandon; Tyndall, Donald

    2009-01-01

    Objective To evaluate reliability in 3D landmark identification using Cone-Beam CT. Study Design Twelve pre-surgery CBCTs were randomly selected from 159 orthognathic surgery patients. Three observers independently repeated three times the identification of 30 landmarks in the sagittal, coronal, and axial slices. A mixed effects ANOVA model estimated the Intraclass Correlations (ICC) and assessed systematic bias. Results The ICC was >0.9 for 86% of intra-observer assessments and 66% of inter-observer assessments. Only 1% of intra-observer and 3% of inter-observer coefficients were <0.45. The systematic difference among observers was greater in X and Z than in Y dimensions, but the maximum mean difference was quite small. Conclusion Overall, the intra- and inter-observer reliability was excellent. 3D landmark identification using CBCT can offer consistent and reproducible data, if a protocol for operator training and calibration is followed. This is particularly important for landmarks not easily specified in all three planes of space. PMID:18718796

  11. Effect of anatomical backgrounds on detectability in volumetric cone beam CT images

    NASA Astrophysics Data System (ADS)

    Han, Minah; Park, Subok; Baek, Jongduk

    2016-03-01

    As anatomical noise is often a dominating factor affecting signal detection in medical imaging, we investigate the effects of anatomical backgrounds on signal detection in volumetric cone beam CT images. Signal detection performances are compared between transverse and longitudinal planes with either uniform or anatomical backgrounds. Sphere objects with diameters of 1mm, 5mm, 8mm, and 11mm are used as the signals. Three-dimensional (3D) anatomical backgrounds are generated using an anatomical noise power spectrum, 1/fβ, with β=3, equivalent to mammographic background [1]. The mean voxel value of the 3D anatomical backgrounds is used as an attenuation coefficient of the uniform background. Noisy projection data are acquired by the forward projection of the uniform and anatomical 3D backgrounds with/without sphere lesions and by the addition of quantum noise. Then, images are reconstructed by an FDK algorithm [2]. For each signal size, signal detection performances in transverse and longitudinal planes are measured by calculating the task SNR of a channelized Hotelling observer with Laguerre-Gauss channels. In the uniform background case, transverse planes yield higher task SNR values for all sphere diameters but 1mm. In the anatomical background case, longitudinal planes yield higher task SNR values for all signal diameters. The results indicate that it is beneficial to use longitudinal planes to detect spherical signals in anatomical backgrounds.

  12. Investigation on location dependent detectability in cone beam CT images with uniform and anatomical backgrounds

    NASA Astrophysics Data System (ADS)

    Han, Minah; Baek, Jongduk

    2017-03-01

    We investigate location dependent lesion detectability of cone beam computed tomography images for different background types (i.e., uniform and anatomical), image planes (i.e., transverse and longitudinal) and slice thicknesses. Anatomical backgrounds are generated using a power law spectrum of breast anatomy, 1/f3. Spherical object with a 5mm diameter is used as a signal. CT projection data are acquired by the forward projection of uniform and anatomical backgrounds with and without the signal. Then, projection data are reconstructed using the FDK algorithm. Detectability is evaluated by a channelized Hotelling observer with dense difference-of-Gaussian channels. For uniform background, off-centered images yield higher detectability than iso-centered images for the transverse plane, while for the longitudinal plane, detectability of iso-centered and off-centered images are similar. For anatomical background, off-centered images yield higher detectability for the transverse plane, while iso-centered images yield higher detectability for the longitudinal plane, when the slice thickness is smaller than 1.9mm. The optimal slice thickness is 3.8mm for all tasks, and the transverse plane at the off-center (iso-center and off-center) produces the highest detectability for uniform (anatomical) background.

  13. Task-Based Regularization Design for Detection of Intracranial Hemorrhage in Cone-Beam CT

    PubMed Central

    Dang, H.; Stayman, J. W.; Xu, J.; Sisniega, A.; Zbijewski, W.; Wang, X.; Foos, D. H.; Aygun, N.; Koliatsos, V. E.; Siewerdsen, J. H.

    2016-01-01

    Prompt and reliable detection of acute intracranial hemorrhage (ICH) is critical to treatment of a number of neurological disorders. Cone-beam CT (CBCT) systems are potentially suitable for detecting ICH (contrast 40-80 HU, size down to 1 mm) at the point of care but face major challenges in image quality requirements. Statistical reconstruction demonstrates improved noise-resolution tradeoffs in CBCT head imaging, but its capability in improving image quality with respect to the task of ICH detection remains to be fully investigated. Moreover, statistical reconstruction typically exhibits nonuniform spatial resolution and noise characteristics, leading to spatially varying detectability of ICH for a conventional penalty. In this work, we propose a spatially varying penalty design that maximizes detectability of ICH at each location throughout the image. We leverage theoretical analysis of spatial resolution and noise for a penalized weighted least-squares (PWLS) estimator, and employ a task-based imaging performance descriptor in terms of detectability index using a nonprewhitening observer model. Performance prediction was validated using a 3D anthropomorphic head phantom. The proposed penalty achieved superior detectability throughout the head and improved detectability in regions adjacent to the skull base by ~10% compared to a conventional uniform penalty. PWLS reconstruction with the proposed penalty demonstrated excellent visualization of simulated ICH in different regions of the head and provides further support for development of dedicated CBCT head scanning at the point-of-care in the neuro ICU and OR.

  14. 4D cone-beam CT reconstruction using multi-organ meshes for sliding motion modeling

    PubMed Central

    Zhong, Zichun; Gu, Xuejun; Mao, Weihua; Wang, Jing

    2016-01-01

    A simultaneous motion estimation and image reconstruction (SMEIR) strategy was proposed for 4D cone-beam CT (4D-CBCT) reconstruction and showed excellent results in both phantom and lung cancer patient studies. In the original SMEIR algorithm, the deformation vector field (DVF) was defined on voxel grid and estimated by enforcing a global smoothness regularization term on the motion fields. The objective of this work is to improve the computation efficiency and motion estimation accuracy of SMEIR for 4D-CBCT through developing a multi-organ meshing model. Feature-based adaptive meshes were generated to reduce the number of unknowns in the DVF estimation and accurately capture the organ shapes and motion. Additionally, the discontinuity in the motion fields between different organs during respiration was explicitly considered in the multi-organ mesh model. This will help with the accurate visualization and motion estimation of the tumor on the organ boundaries in 4D-CBCT. To further improve the computational efficiency, a GPU-based parallel implementation was designed. The performance of the proposed algorithm was evaluated on a synthetic sliding motion phantom, a 4D NCAT phantom, and four lung cancer patients. The proposed multi-organ mesh based strategy outperformed the conventional Feldkamp–Davis–Kress, iterative total variation minimization, original SMEIR and single meshing method based on both qualitative and quantitative evaluations. PMID:26758496

  15. Measurement of inter and intra fraction organ motion in radiotherapy using cone beam CT projection images

    NASA Astrophysics Data System (ADS)

    Marchant, T. E.; Amer, A. M.; Moore, C. J.

    2008-02-01

    A method is presented for extraction of intra and inter fraction motion of seeds/markers within the patient from cone beam CT (CBCT) projection images. The position of the marker is determined on each projection image and fitted to a function describing the projection of a fixed point onto the imaging panel at different gantry angles. The fitted parameters provide the mean marker position with respect to the isocentre. Differences between the theoretical function and the actual projected marker positions are used to estimate the range of intra fraction motion and the principal motion axis in the transverse plane. The method was validated using CBCT projection images of a static marker at known locations and of a marker moving with known amplitude. The mean difference between actual and measured motion range was less than 1 mm in all directions, although errors of up to 5 mm were observed when large amplitude motion was present in an orthogonal direction. In these cases it was possible to calculate the range of motion magnitudes consistent with the observed marker trajectory. The method was shown to be feasible using clinical CBCT projections of a pancreas cancer patient.

  16. Motion artefacts in cone beam CT: an in vitro study about the effects on the images

    PubMed Central

    Molteni, Roberto; Lorini, Chiara; Taliani, Gian G; Matteuzzi, Benedetta; Mazzoni, Elisa; Colagrande, Stefano

    2016-01-01

    Objective: In cone beam CT (CBCT), imperfect patient immobility, caused by involuntary movements, is one of the most important causes of artefacts and image quality degradation. Various works in literature address this topic, but seldom is the nature of the movement correlated with the type of artefact and the image degradation in a systematic manner, and the correlation analyzed and explained. Methods: All three types of movements that can occur during a scan—nodding, tilting and rolling—were applied to a dry skull, in various manners from abrupt to gradual through the entire scan, at different times and angles, over a wide range of displacements. 84 scans were performed, with different skull movements, and the resulting images examined by two skilled radiologists, rated in a four-point scale and statistically analyzed. A commercial CBCT machine was used, featuring supine patient positioning. Results: Different types of movements induce different artefacts, in different parts of the anatomy. In general, movement of short duration may lead to double contours (bilateral or monolateral depending upon the angle of the scan at which they occur), whereas gradual movements result into blurring. Conclusion: Not all movements cause motion artefacts that equally jeopardize the image. Rolling is the type of movement that most severely affects the image diagnostic value. Advances in knowledge: These findings may help practitioners to identify the causes of motion artefacts and the resulting image degradation, and remediate them, and manufacturers to improve the patient-positioning devices. PMID:26577438

  17. Extra projection data identification method for fast-continuous-rotation industrial cone-beam CT.

    PubMed

    Yang, Min; Duan, Shengling; Duan, Jinghui; Wang, Xiaolong; Li, Xingdong; Meng, Fanyong; Zhang, Jianhai

    2013-01-01

    Fast-continuous-rotation is an effective measure to improve the scanning speed and decrease the radiation dose for cone-beam CT. However, because of acceleration and deceleration of the motor, as well as the response lag of the scanning control terminals to the host PC, uneven-distributed and redundant projections are inevitably created, which seriously decrease the quality of the reconstruction images. In this paper, we first analyzed the aspects of the theoretical sequence chart of the fast-continuous-rotation mode. Then, an optimized sequence chart was proposed by extending the rotation angle span to ensure the effective 2π-span projections were situated in the stable rotation stage. In order to match the rotation angle with the projection image accurately, structure similarity (SSIM) index was used as a control parameter for extraction of the effective projection sequence which was exactly the complete projection data for image reconstruction. The experimental results showed that SSIM based method had a high accuracy of projection view locating and was easy to realize.

  18. Pseudo super-resolution for improved calcification characterization for cone beam breast CT (CBBCT)

    NASA Astrophysics Data System (ADS)

    Liu, Jiangkun; Ning, Ruola; Cai, Weixing

    2010-04-01

    Cone Beam Breast CT imaging (CBBCT) is a promising tool for diagnosis of breast tumors and calcifications. However, as the sizes of calcifications in early stages are very small, it is not easy to distinguish them from background tissues because of the relatively high noise level. Therefore, it is necessary to enhance the visualization of calcifications for accurate detection. In this work, the Papoulis-Gerchberg (PG) method was introduced and modified to improve calcification characterization. PG method is an iterative algorithm of signal extrapolation and has been demonstrated to be very effective in image restoration like super-resolution (SR) and inpainting. The projection images were zoomed by bicubic interpolation method, then the modified PG method were applied to improve the image quality. The reconstruction from processed projection images showed that this approach can effectively improve the image quality by improving the Modulation Transfer Function (MTF) with a limited increase in noise level. As a result, the detectability of calcifications was improved in CBBCT images.

  19. The effect of cone beam CT (CBCT) on therapeutic decision-making in endodontics.

    PubMed

    Mota de Almeida, F J; Knutsson, K; Flygare, L

    2014-01-01

    The aim was to assess to what extent cone beam CT (CBCT) used in accordance with current European Commission guidelines in a normal clinical setting has an impact on therapeutic decisions in a population referred for endodontic problems. The study includes data of consecutively examined patients collected from October 2011 to December 2012. From 2 different endodontic specialist clinics, 57 patients were referred for a CBCT examination using criteria in accordance with current European guidelines. The CBCT examinations were performed using similar equipment and standardized among clinics. After a thorough clinical examination, but before CBCT, the examiner made a preliminary therapy plan which was recorded. After the CBCT examination, the same examiner made a new therapy plan. Therapy plans both before and after the CBCT examination were plotted for 53 patients and 81 teeth. As four patients had incomplete protocols, they were not included in the final analysis. 4% of the patients referred to endodontic clinics during the study period were examined with CBCT. The most frequent reason for referral to CBCT examination was to differentiate pathology from normal anatomy, this was the case in 24 patients (45% of the cases). The primary outcome was therapy plan changes that could be attributed to CBCT examination. There were changes in 28 patients (53%). CBCT has a significant impact on therapeutic decision efficacy in endodontics when used in concordance with the current European Commission guidelines.

  20. The effect of cone beam CT (CBCT) on therapeutic decision-making in endodontics

    PubMed Central

    Knutsson, K; Flygare, L

    2014-01-01

    Objectives: The aim was to assess to what extent cone beam CT (CBCT) used in accordance with current European Commission guidelines in a normal clinical setting has an impact on therapeutic decisions in a population referred for endodontic problems. Methods: The study includes data of consecutively examined patients collected from October 2011 to December 2012. From 2 different endodontic specialist clinics, 57 patients were referred for a CBCT examination using criteria in accordance with current European guidelines. The CBCT examinations were performed using similar equipment and standardized among clinics. After a thorough clinical examination, but before CBCT, the examiner made a preliminary therapy plan which was recorded. After the CBCT examination, the same examiner made a new therapy plan. Therapy plans both before and after the CBCT examination were plotted for 53 patients and 81 teeth. As four patients had incomplete protocols, they were not included in the final analysis. Results: 4% of the patients referred to endodontic clinics during the study period were examined with CBCT. The most frequent reason for referral to CBCT examination was to differentiate pathology from normal anatomy, this was the case in 24 patients (45% of the cases). The primary outcome was therapy plan changes that could be attributed to CBCT examination. There were changes in 28 patients (53%). Conclusions: CBCT has a significant impact on therapeutic decision efficacy in endodontics when used in concordance with the current European Commission guidelines. PMID:24766060

  1. A web-based instruction module for interpretation of craniofacial cone beam CT anatomy.

    PubMed

    Hassan, B A; Jacobs, R; Scarfe, W C; Al-Rawi, W T

    2007-09-01

    To develop a web-based module for learner instruction in the interpretation and recognition of osseous anatomy on craniofacial cone-beam CT (CBCT) images. Volumetric datasets from three CBCT systems were acquired (i-CAT, NewTom 3G and AccuiTomo FPD) for various subjects using equipment-specific scanning protocols. The datasets were processed using multiple software to provide two-dimensional (2D) multiplanar reformatted (MPR) images (e.g. sagittal, coronal and axial) and three-dimensional (3D) visual representations (e.g. maximum intensity projection, minimum intensity projection, ray sum, surface and volume rendering). Distinct didactic modules which illustrate the principles of CBCT systems, guided navigation of the volumetric dataset, and anatomic correlation of 3D models and 2D MPR graphics were developed using a hybrid combination of web authoring and image analysis techniques. Interactive web multimedia instruction was facilitated by the use of dynamic highlighting and labelling, and rendered video illustrations, supplemented with didactic textual material. HTML coding and Java scripting were heavily implemented for the blending of the educational modules. An interactive, multimedia educational tool for visualizing the morphology and interrelationships of osseous craniofacial anatomy, as depicted on CBCT MPR and 3D images, was designed and implemented. The present design of a web-based instruction module may assist radiologists and clinicians in learning how to recognize and interpret the craniofacial anatomy of CBCT based images more efficiently.

  2. [Cone-beam CT study of bone septa during maxillary sinus lift among Changzhou population].

    PubMed

    Chen, Min-zhen; Xie, Yong-fu; Xie, Hui; Wang, Guo-hai; He, Jia-cai

    2016-02-01

    To observe the incidence, location, morphological characteristics of sinus septa among Changzhou population, and to investigate the relationship between maxillary posterior teeth loss and bony septum, and the guiding significance for sinus lift. One hundred and twenty-four subjects were selected, the preoperative cone-beam CT (CBCT) data was analyzed by NNT software, which provided a three-dimensional measurement of the maxillary sinus septa. SPSS 13.0 software package was used for statistical analysis. 33.87%(42/124)subjects had sinus septa, 27.42%(68/248)sinus had septa. 66.18% (45/68) of the septa were located in the middle region, 22.06% (15/68)in the posterior region, 11.76%(8/68) in the anterior region. The occurrence of sinus septa had no relation with gender, age and loss of teeth. The sinus septa can be observed by CBCT for the position, pattern, to predict the difficulty of the surgery, and enhance the success rate.

  3. A motion-compensated cone-beam CT using electrical impedance tomography imaging.

    PubMed

    Pengpan, T; Smith, N D; Qiu, W; Yao, A; Mitchell, C N; Soleimani, M

    2011-01-01

    Cone-beam CT (CBCT) is an imaging technique used in conjunction with radiation therapy. For example CBCT is used to verify the position of lung cancer tumours just prior to radiation treatment. The accuracy of the radiation treatment of thoracic and upper abdominal structures is heavily affected by respiratory movement. Such movement typically blurs the CBCT reconstruction and ideally should be removed. Hence motion-compensated CBCT has recently been researched for correcting image artefacts due to breathing motion. This paper presents a new dual-modality approach where CBCT is aided by using electrical impedance tomography (EIT) for motion compensation. EIT can generate images of contrasts in electrical properties. The main advantage of using EIT is its high temporal resolution. In this paper motion information is extracted from EIT images and incorporated directly in the CBCT reconstruction. In this study synthetic moving data are generated using simulated and experimental phantoms. The paper demonstrates that image blur, created as a result of motion, can be reduced through motion compensation with EIT.

  4. 4D cone-beam CT reconstruction using multi-organ meshes for sliding motion modeling

    NASA Astrophysics Data System (ADS)

    Zhong, Zichun; Gu, Xuejun; Mao, Weihua; Wang, Jing

    2016-02-01

    A simultaneous motion estimation and image reconstruction (SMEIR) strategy was proposed for 4D cone-beam CT (4D-CBCT) reconstruction and showed excellent results in both phantom and lung cancer patient studies. In the original SMEIR algorithm, the deformation vector field (DVF) was defined on voxel grid and estimated by enforcing a global smoothness regularization term on the motion fields. The objective of this work is to improve the computation efficiency and motion estimation accuracy of SMEIR for 4D-CBCT through developing a multi-organ meshing model. Feature-based adaptive meshes were generated to reduce the number of unknowns in the DVF estimation and accurately capture the organ shapes and motion. Additionally, the discontinuity in the motion fields between different organs during respiration was explicitly considered in the multi-organ mesh model. This will help with the accurate visualization and motion estimation of the tumor on the organ boundaries in 4D-CBCT. To further improve the computational efficiency, a GPU-based parallel implementation was designed. The performance of the proposed algorithm was evaluated on a synthetic sliding motion phantom, a 4D NCAT phantom, and four lung cancer patients. The proposed multi-organ mesh based strategy outperformed the conventional Feldkamp-Davis-Kress, iterative total variation minimization, original SMEIR and single meshing method based on both qualitative and quantitative evaluations.

  5. Breast density quantification with cone-beam CT: A post-mortem study

    PubMed Central

    Johnson, Travis; Ding, Huanjun; Le, Huy Q.; Ducote, Justin L.; Molloi, Sabee

    2014-01-01

    Forty post-mortem breasts were imaged with a flat-panel based cone-beam x-ray CT system at 50 kVp. The feasibility of breast density quantification has been investigated using standard histogram thresholding and an automatic segmentation method based on the fuzzy c-means algorithm (FCM). The breasts were chemically decomposed into water, lipid, and protein immediately after image acquisition was completed. The percent fibroglandular volume (%FGV) from chemical analysis was used as the gold standard for breast density comparison. Both image-based segmentation techniques showed good precision in breast density quantification with high linear coefficients between the right and left breast of each pair. When comparing with the gold standard using %FGV from chemical analysis, Pearson’s r-values were estimated to be 0.983 and 0.968 for the FCM clustering and the histogram thresholding techniques, respectively. The standard error of the estimate (SEE) was also reduced from 3.92% to 2.45% by applying the automatic clustering technique. The results of the postmortem study suggested that breast tissue can be characterized in terms of water, lipid and protein contents with high accuracy by using chemical analysis, which offers a gold standard for breast density studies comparing different techniques. In the investigated image segmentation techniques, the FCM algorithm had high precision and accuracy in breast density quantification. In comparison to conventional histogram thresholding, it was more efficient and reduced inter-observer variation. PMID:24254317

  6. Implementation of the FDK algorithm for cone-beam CT on the cell broadband engine architecture

    NASA Astrophysics Data System (ADS)

    Scherl, Holger; Koerner, Mario; Hofmann, Hannes; Eckert, Wieland; Kowarschik, Markus; Hornegger, Joachim

    2007-03-01

    In most of today's commercially available cone-beam CT scanners, the well known FDK method is used for solving the 3D reconstruction task. The computational complexity of this algorithm prohibits its use for many medical applications without hardware acceleration. The brand-new Cell Broadband Engine Architecture (CBEA) with its high level of parallelism is a cost-efficient processor for performing the FDK reconstruction according to the medical requirements. The programming scheme, however, is quite different to any standard personal computer hardware. In this paper, we present an innovative implementation of the most time-consuming parts of the FDK algorithm: filtering and back-projection. We also explain the required transformations to parallelize the algorithm for the CBEA. Our software framework allows to compute the filtering and back-projection in parallel, making it possible to do an on-the-fly-reconstruction. The achieved results demonstrate that a complete FDK reconstruction is computed with the CBEA in less than seven seconds for a standard clinical scenario. Given the fact that scan times are usually much higher, we conclude that reconstruction is finished right after the end of data acquisition. This enables us to present the reconstructed volume to the physician in real-time, immediately after the last projection image has been acquired by the scanning device.

  7. Prevalence of apical periodontitis detected in cone beam CT images of a Brazilian subpopulation

    PubMed Central

    Paes da Silva Ramos Fernandes, LM; Ordinola-Zapata, R; Húngaro Duarte, MA; Alvares Capelozza, AL

    2013-01-01

    Objectives The aim of this study was to determine the prevalence of apical periodontitis (AP) detected in cone beam CT (CBCT) images from a database. Methods CBCT images of 300 Brazilian patients were assessed. AP images were measured in three dimensions. Age, gender, number and location of total teeth in each patient were considered. AP location was considered according to tooth groups. The extent of AP was determined by the largest diameter in any of the three dimensions. Percentages and the χ2 test were used for statistical analysis. Results AP was found in 51.4% of the patients and in 3.4% of the teeth. Higher prevalence of AP was found in 60- to 69-year-olds (73.1%) and in mandibular molars (5.9%) (p < 0.05). Inadequate endodontic treatment presented higher prevalence of AP (78.1%). Conclusions AP can be frequently found in CBCT examinations. The presence of AP has a significant association with patients' age, and tooth type and condition. CBCT databases are useful for cross-sectional studies about AP prevalence in a population. PMID:22752318

  8. Diagnostic value of cone-beam CT in histologically confirmed otosclerosis.

    PubMed

    Liktor, Balázs; Révész, Péter; Csomor, Péter; Gerlinger, Imre; Sziklai, István; Karosi, Tamás

    2014-08-01

    This retrospective case review was performed with the aim to asses the value of cone-beam computed tomography (CBCT) in the preoperative diagnosis of otosclerosis. A total of 32 patients with histologically confirmed stapedial otosclerosis, who underwent unilateral stapedectomies were analyzed. Preoperative temporal bone CBCT scans were performed in all cases. CBCT imaging was characterized by a slice thickness of 0.3 mm and multiplanar image reconstruction. Histopathologic examination of the removed stapes footplates was performed in all cases. Findings of CBCT were categorized according to Marshall's grading system (from grade 0 to grade 3). Histopathologic results were correlated to multiplanar reconstructed CBCT scans, respectively. Histologically active foci of otosclerosis (n = 21) were identified by CBCT in all cases with a sensitivity of 100 %. However, CBCT was unable to detect histologically inactive otosclerosis (n = 11, sensitivity = 0 %). According to CBCT scans, no retrofenestral lesions were found and all positive cases were recruited into the grade 1 group indicating solely fenestral lesions at the anterior pole of stapes footplates. In conclusion, CBCT is a reliable imaging method with considerably lower radiation dose than high-resolution CT (HRCT) in the preoperative diagnosis of otosclerosis. These results indicate that CBCT has high sensitivity and specificity in the detection of hypodense lesions due to histologically active otosclerosis.

  9. Performance of cone-beam CT using a flat-panel imager

    NASA Astrophysics Data System (ADS)

    Endo, Masahiro; Tsunoo, Takanori; Satoh, Kazumasa; Matsusita, Satoshi; Kusakabe, Masahiro; Fukuda, Yasushi

    2001-06-01

    An active matrix flat-panel imager (FPI) is a good candidate for the 2-dimensional detector of cone beam CT (CBCT), because it has a wider dynamic range and less geometrical distortion than video-fluoroscopic system so far employed. However the performance of FPI-based CBCT has not been sufficiently examined yet. The aim of this work is to examine the performance of CBCT using a FPI with several phantoms. An X-ray tube, a phantom and a FPI were aligned on an experimental table. The FPI was PaxScan2520 provided by Varian Medical Systems. It has an active area of approximately 180x240mm and the pixel size is 127 micrometer. CsI is used as a scintillator. The phantom was rotated with 1-degree steps while 360 projection frames (1408x1888 active pixels each frame) were collected. 2x2 pixels were combined into a single pixel to reduce noise. 512x512x512 voxels were reconstructed with the Feldkamp method. The comparison was made between reconstructed images with or without scatter rejecting grid. The uniformity and linearity of reconstruction value was drastically improved with the grid. Scatter rejection using a thin-vane collimator was also examined, and it showed more effective than the grid.

  10. Iterative reconstruction optimisations for high angle cone-beam micro-CT

    NASA Astrophysics Data System (ADS)

    Recur, B.; Fauconneau, M.; Kingston, A.; Myers, G.; Sheppard, A.

    2014-09-01

    We address several acquisition questions that have arisen for the high cone-angle helical-scanning micro-CT facility developed at the Australian National University. These challenges are generally known in medical and industrial cone-beam scanners but can be neglected in these systems. For our large datasets, with more than 20483 voxels, minimising the number of operations (or iterations) is crucial. Large cone-angles enable high signal-to-noise ratio imaging and a large helical pitch to be used. This introduces two challenges: (i) non-uniform resolution throughout the reconstruction, (ii) over-scan beyond the region-of-interest significantly increases re- quired reconstructed volume size. Challenge (i) can be addressed by using a double-helix or lower pitch helix but both solutions slow down iterations. Challenge (ii) can also be improved by using a lower pitch helix but results in more projections slowing down iterations. This may be overcome using less projections per revolution but leads to more iterations required. Here we assume a given total time for acquisition and a given reconstruction technique (SART) and seek to identify the optimal trajectory and number of projections per revolution in order to produce the best tomogram, minimise reconstruction time required, and minimise memory requirements.

  11. Optical CT scanner for in-air readout of gels for external radiation beam 3D dosimetry.

    PubMed

    Ramm, Daniel; Rutten, Thomas P; Shepherd, Justin; Bezak, Eva

    2012-06-21

    Optical CT scanners for a 3D readout of externally irradiated radiosensitive hydrogels currently require the use of a refractive index (RI) matching liquid bath to obtain suitable optical ray paths through the gel sample to the detector. The requirement for a RI matching liquid bath has been negated by the design of a plastic cylindrical gel container that provides parallel beam geometry through the gel sample for the majority of the projection. The design method can be used for various hydrogels. Preliminary test results for the prototype laser beam scanner with ferrous xylenol-orange gel show geometric distortion of 0.2 mm maximum, spatial resolution limited to beam spot size of about 0.4 mm and 0.8% noise (1 SD) for a uniform irradiation. Reconstruction of a star pattern irradiated through the cylinder walls demonstrates the suitability for external beam applications. The extremely simple and cost-effective construction of this optical CT scanner, together with the simplicity of scanning gel samples without RI matching fluid increases the feasibility of using 3D gel dosimetry for clinical external beam dose verifications.

  12. Reconstruction of implanted marker trajectories from cone-beam CT projection images using interdimensional correlation modeling.

    PubMed

    Chung, Hyekyun; Poulsen, Per Rugaard; Keall, Paul J; Cho, Seungryong; Cho, Byungchul

    2016-08-01

    Cone-beam CT (CBCT) is a widely used imaging modality for image-guided radiotherapy. Most vendors provide CBCT systems that are mounted on a linac gantry. Thus, CBCT can be used to estimate the actual 3-dimensional (3D) position of moving respiratory targets in the thoracic/abdominal region using 2D projection images. The authors have developed a method for estimating the 3D trajectory of respiratory-induced target motion from CBCT projection images using interdimensional correlation modeling. Because the superior-inferior (SI) motion of a target can be easily analyzed on projection images of a gantry-mounted CBCT system, the authors investigated the interdimensional correlation of the SI motion with left-right and anterior-posterior (AP) movements while the gantry is rotating. A simple linear model and a state-augmented model were implemented and applied to the interdimensional correlation analysis, and their performance was compared. The parameters of the interdimensional correlation models were determined by least-square estimation of the 2D error between the actual and estimated projected target position. The method was validated using 160 3D tumor trajectories from 46 thoracic/abdominal cancer patients obtained during CyberKnife treatment. The authors' simulations assumed two application scenarios: (1) retrospective estimation for the purpose of moving tumor setup used just after volumetric matching with CBCT; and (2) on-the-fly estimation for the purpose of real-time target position estimation during gating or tracking delivery, either for full-rotation volumetric-modulated arc therapy (VMAT) in 60 s or a stationary six-field intensity-modulated radiation therapy (IMRT) with a beam delivery time of 20 s. For the retrospective CBCT simulations, the mean 3D root-mean-square error (RMSE) for all 4893 trajectory segments was 0.41 mm (simple linear model) and 0.35 mm (state-augmented model). In the on-the-fly simulations, prior projections over more than 60

  13. Cone beam CT--anatomic assessment and legal issues: the new standards of care.

    PubMed

    Curley, Arthur; Hatcher, David C

    2010-01-01

    technology. Multidimensional anatomical reconstruction can be performed through software applications. The ultimate reward of technological imaging advancements is the 3-D representations (digital volume) of anatomy as it exists in nature (anatomic truth). Analysis of the accurate digital volume can provide clinically relevant spatial information or data. Visualization and analysis of 3-D information can benefit a dental practice by providing data that will improve diagnosis, risk assessment, treatment outcome and treatment efficiency, and reduce treatment complications. This article discusses the uses and benefits of 3-D imaging (cone beam CT, CBCT) for diagnosis, treatment planning and the legal issues affecting the standard of care, as well as offering risk management tips and use guidance.

  14. Dose measurements for dental cone-beam CT: a comparison with MSCT and panoramic imaging

    NASA Astrophysics Data System (ADS)

    Deman, P.; Atwal, P.; Duzenli, C.; Thakur, Y.; Ford, N. L.

    2014-06-01

    To date there is a lack of published information on appropriate methods to determine patient doses from dental cone-beam computed tomography (CBCT) equipment. The goal of this study is to apply and extend the methods recommended in the American Association of Physicists in Medicine (AAPM) Report 111 for CBCT equipment to characterize dose and effective dose for a range of dental imaging equipment. A protocol derived from the one proposed by Dixon et al (2010 Technical Report 111, American Association of Physicist in Medicine, MD, USA), was applied to dose measurements of multi-slice CT, dental CBCT (small and large fields of view (FOV)) and a dental panoramic system. The computed tomography dose index protocol was also performed on the MSCT to compare both methods. The dose distributions in a cylindrical polymethyl methacrylate phantom were characterized using a thimble ionization chamber and Gafchromic™ film (beam profiles). Gafchromic™ films were used to measure the dose distribution in an anthropomorphic phantom. A method was proposed to extend dose estimates to planes superior and inferior to the central plane. The dose normalized to 100 mAs measured in the center of the phantom for the large FOV dental CBCT (11.4 mGy/100 mAs) is two times lower than that of MSCT (20.7 mGy/100 mAs) for the same FOV, but approximately 15 times higher than for a panoramic system (0.6 mGy/100 mAs). The effective dose per scan (in clinical conditions) found for the dental CBCT are 167.60 ± 3.62, 61.30 ± 3.88 and 92.86 ± 7.76 mSv for the Kodak 9000 (fixed scan length of 3.7 cm), and the iCAT Next Generation for 6 cm and 13 cm scan lengths respectively. The method to extend the dose estimates from the central slice to superior and inferior slices indicates a good agreement between theory and measurement. The Gafchromic™ films provided useful beam profile data and 2D distributions of dose in phantom.

  15. Accelerated barrier optimization compressed sensing (ABOCS) reconstruction for cone-beam CT: Phantom studies.

    PubMed

    Niu, Tianye; Zhu, Lei

    2012-07-01

    Recent advances in compressed sensing (CS) enable accurate CT image reconstruction from highly undersampled and noisy projection measurements, due to the sparsifiable feature of most CT images using total variation (TV). These novel reconstruction methods have demonstrated advantages in clinical applications where radiation dose reduction is critical, such as onboard cone-beam CT (CBCT) imaging in radiation therapy. The image reconstruction using CS is formulated as either a constrained problem to minimize the TV objective within a small and fixed data fidelity error, or an unconstrained problem to minimize the data fidelity error with TV regularization. However, the conventional solutions to the above two formulations are either computationally inefficient or involved with inconsistent regularization parameter tuning, which significantly limit the clinical use of CS-based iterative reconstruction. In this paper, we propose an optimization algorithm for CS reconstruction which overcomes the above two drawbacks. The data fidelity tolerance of CS reconstruction can be well estimated based on the measured data, as most of the projection errors are from Poisson noise after effective data correction for scatter and beam-hardening effects. We therefore adopt the TV optimization framework with a data fidelity constraint. To accelerate the convergence, we first convert such a constrained optimization using a logarithmic barrier method into a form similar to that of the conventional TV regularization based reconstruction but with an automatically adjusted penalty weight. The problem is then solved efficiently by gradient projection with an adaptive Barzilai-Borwein step-size selection scheme. The proposed algorithm is referred to as accelerated barrier optimization for CS (ABOCS), and evaluated using both digital and physical phantom studies. ABOCS directly estimates the data fidelity tolerance from the raw projection data. Therefore, as demonstrated in both digital Shepp

  16. Accelerated barrier optimization compressed sensing (ABOCS) reconstruction for cone-beam CT: phantom studies.

    PubMed

    Niu, Tianye; Zhu, Lei

    2012-07-01

    Recent advances in compressed sensing (CS) enable accurate CT image reconstruction from highly undersampled and noisy projection measurements, due to the sparsifiable feature of most CT images using total variation (TV). These novel reconstruction methods have demonstrated advantages in clinical applications where radiation dose reduction is critical, such as onboard cone-beam CT (CBCT) imaging in radiation therapy. The image reconstruction using CS is formulated as either a constrained problem to minimize the TV objective within a small and fixed data fidelity error, or an unconstrained problem to minimize the data fidelity error with TV regularization. However, the conventional solutions to the above two formulations are either computationally inefficient or involved with inconsistent regularization parameter tuning, which significantly limit the clinical use of CS-based iterative reconstruction. In this paper, we propose an optimization algorithm for CS reconstruction which overcomes the above two drawbacks. The data fidelity tolerance of CS reconstruction can be well estimated based on the measured data, as most of the projection errors are from Poisson noise after effective data correction for scatter and beam-hardening effects. We therefore adopt the TV optimization framework with a data fidelity constraint. To accelerate the convergence, we first convert such a constrained optimization using a logarithmic barrier method into a form similar to that of the conventional TV regularization based reconstruction but with an automatically adjusted penalty weight. The problem is then solved efficiently by gradient projection with an adaptive Barzilai-Borwein step-size selection scheme. The proposed algorithm is referred to as accelerated barrier optimization for CS (ABOCS), and evaluated using both digital and physical phantom studies. ABOCS directly estimates the data fidelity tolerance from the raw projection data. Therefore, as demonstrated in both digital Shepp

  17. Accelerated barrier optimization compressed sensing (ABOCS) reconstruction for cone-beam CT: Phantom studies

    PubMed Central

    Niu, Tianye; Zhu, Lei

    2012-01-01

    Purpose: Recent advances in compressed sensing (CS) enable accurate CT image reconstruction from highly undersampled and noisy projection measurements, due to the sparsifiable feature of most CT images using total variation (TV). These novel reconstruction methods have demonstrated advantages in clinical applications where radiation dose reduction is critical, such as onboard cone-beam CT (CBCT) imaging in radiation therapy. The image reconstruction using CS is formulated as either a constrained problem to minimize the TV objective within a small and fixed data fidelity error, or an unconstrained problem to minimize the data fidelity error with TV regularization. However, the conventional solutions to the above two formulations are either computationally inefficient or involved with inconsistent regularization parameter tuning, which significantly limit the clinical use of CS-based iterative reconstruction. In this paper, we propose an optimization algorithm for CS reconstruction which overcomes the above two drawbacks. Methods: The data fidelity tolerance of CS reconstruction can be well estimated based on the measured data, as most of the projection errors are from Poisson noise after effective data correction for scatter and beam-hardening effects. We therefore adopt the TV optimization framework with a data fidelity constraint. To accelerate the convergence, we first convert such a constrained optimization using a logarithmic barrier method into a form similar to that of the conventional TV regularization based reconstruction but with an automatically adjusted penalty weight. The problem is then solved efficiently by gradient projection with an adaptive Barzilai–Borwein step-size selection scheme. The proposed algorithm is referred to as accelerated barrier optimization for CS (ABOCS), and evaluated using both digital and physical phantom studies. Results: ABOCS directly estimates the data fidelity tolerance from the raw projection data. Therefore, as

  18. SU-F-I-06: Evaluation of Imaging Dose for Modulation Layer Based Dual Energy Cone-Beam CT

    SciTech Connect

    Ju, Eunbin; Ahn, SoHyun; Cho, Samju; Keum, Ki Chang; Lee, Rena

    2016-06-15

    Purpose: Dual energy cone beam CT system is finding a variety of promising applications in diagnostic CT, both in imaging of endogenous materials and exogenous materials across a range of body sites. Dual energy cone beam CT system to suggest in this study acquire image by rotating 360 degree with half of the X-ray window covered using copper modulation layer. In the region that covered by modulation layer absorb the low energy X-ray by modulation layer. Relative high energy X-ray passes through the layer and contributes to image reconstruction. Dose evaluation should be carried out in order to utilize such an imaging acquirement technology for clinical use. Methods: For evaluating imaging dose of modulation layer based dual energy cone beam CT system, Prototype cone beam CT that configured X-ray tube (D054SB, Toshiba, Japan) and detector (PaxScan 2520V, Varian Medical Systems, Palo Alto, CA) is used. A range of 0.5–2.0 mm thickness of modulation layer is implemented in Monte Carlo simulation (MCNPX, ver. 2.6.0, Los Alamos National Laboratory, USA) with half of X-ray window covered. In-house phantom using in this study that has 3 cylindrical phantoms configured water, Teflon air with PMMA covered for verifying the comparability the various material in human body and is implemented in Monte Carlo simulation. The actual dose with 2.0 mm copper covered half of X-ray window is measured using Gafchromic EBT3 film with 5.0 mm bolus for compared with simulative dose. Results: Dose in phantom reduced 33% by copper modulation layer of 2.0 mm. Scattering dose occurred in modulation layer by Compton scattering effect is 0.04% of overall dose. Conclusion: Modulation layer of that based dual energy cone beam CT has not influence on unnecessary scatter dose. This study was supported by the Radiation Safety Research Programs (1305033) through the Nuclear Safety and Security Commission.

  19. Pelvic Beam-Hardening Artifacts in Dual-Energy CT Image Reconstructions: Occurrence and Impact on Image Quality.

    PubMed

    Winklhofer, Sebastian; Lambert, Jack W; Sun, Yuxin; Wang, Zhen Jane; Sun, Derek S; Yeh, Benjamin M

    2017-01-01

    The purpose of this study was to describe the frequency and appearance of beam-hardening artifacts on rapid-kilovoltage-switching dual-energy CT (DECT) image reconstructions of the pelvis. Monochromatic (70, 52, and 120 keV) and material decomposition CT images (iodine-water and water-iodine) from consecutive pelvic rapid-kilovoltage-switching DECT scans were retrospectively evaluated. We recorded the presence, type (high versus low attenuation), and severity of beam-hardening artifacts (Likert scale from 0, barely seen, to 4, severe), clarity of anatomic delineation (Likert scale from 0, unimpaired, to 4, severely impaired) and SD of CT numbers, iodine and water concentrations, and gray-scale values for artifact-affected regions and corresponding unaffected reference tissue. A pelvic phantom was scanned and evaluated in a similar manner. Wilcoxon signed rank and paired t tests were used to compare results between the image reconstructions. Beam-hardening artifacts were seen in all image reconstructions in all 41 patients (22 men, 19 women; mean age, 57 years; range 22-86 years) who met the inclusion criteria. The median artifact severity score was worse for water-iodine and iodine-water images (score of 3 for each) than for 70-keV (score 1), 52-keV (score 2), and 120-keV (score 1) images (all p < 0.001). The anatomic delineation was worse (p < 0.001) for water-iodine and iodine-water images than for monochromatic images. Higher CT number SD values, material concentrations, and gray-scale values were found for areas affected by artifacts than for reference tissues in all datasets (all p < 0.001). Similar results were seen in the phantom study. Beam-hardening artifacts are prevalent in pelvic rapid-kilovoltage-switching DECT and more severe in material decomposition than monochromatic image reconstructions.

  20. Comprehensive evaluation of ten deformable image registration algorithms for contour propagation between CT and cone-beam CT images in adaptive head & neck radiotherapy

    PubMed Central

    Li, Xin; Zhang, Yuyu; Shi, Yinghua; Wu, Shuyu; Xiao, Yang; Gu, Xuejun; Zhou, Linghong

    2017-01-01

    Deformable image registration (DIR) is a critical technic in adaptive radiotherapy (ART) for propagating contours between planning computerized tomography (CT) images and treatment CT/cone-beam CT (CBCT) images to account for organ deformation for treatment re-planning. To validate the ability and accuracy of DIR algorithms in organ at risk (OAR) contour mapping, ten intensity-based DIR strategies, which were classified into four categories—optical flow-based, demons-based, level-set-based and spline-based—were tested on planning CT and fractional CBCT images acquired from twenty-one head & neck (H&N) cancer patients who underwent 6~7-week intensity-modulated radiation therapy (IMRT). Three similarity metrics, i.e., the Dice similarity coefficient (DSC), the percentage error (PE) and the Hausdorff distance (HD), were employed to measure the agreement between the propagated contours and the physician-delineated ground truths of four OARs, including the vertebra (VTB), the vertebral foramen (VF), the parotid gland (PG) and the submandibular gland (SMG). It was found that the evaluated DIRs in this work did not necessarily outperform rigid registration. DIR performed better for bony structures than soft-tissue organs, and the DIR performance tended to vary for different ROIs with different degrees of deformation as the treatment proceeded. Generally, the optical flow-based DIR performed best, while the demons-based DIR usually ranked last except for a modified demons-based DISC used for CT-CBCT DIR. These experimental results suggest that the choice of a specific DIR algorithm depends on the image modality, anatomic site, magnitude of deformation and application. Therefore, careful examinations and modifications are required before accepting the auto-propagated contours, especially for automatic re-planning ART systems. PMID:28414799

  1. Autotransplantation of an immature premolar, with the aid of cone beam CT and computer-aided prototyping: a case report.

    PubMed

    Keightley, Alexander J; Cross, David L; McKerlie, Robert A; Brocklebank, Laetitia

    2010-04-01

    Autotransplantation of immature teeth has good survival rates, and has benefits over ossointegrated implants in the growing child, but is very technique sensitive. Spiral CT imaging has been previously used in adult patients to enable computer-aided prototyping to produce a surgical template of the donor tooth, further increasing success rates. The case presented describes management of a 9-year-old girl with the combination of hypodontia affecting the upper lateral incisors as well as a severely ectopic maxillary canine. Cone beam CT was used in combination with computer-aided prototyping to produce a surgical template of an immature mandibular second premolar. The surgical template was used to prepare the transplant site before the donor tooth was extracted, greatly reducing the time from extraction to implantation. By 6 months posttransplant the tooth was clinically sound, and continued root development and laying down of dentine was visible radiographically. This paper demonstrates the use of a novel technique to aid the surgical procedure of autotransplantation of immature premolar teeth. The use of autotransplantation in this case allowed the difficult situation of two missing units in the upper left quadrant to be reduced to one unit, while retaining symmetry in the upper arch. Compared to previous studies, the use of cone beam CT to create a 3D prototype reduced radiation dose compared to spiral CT and drastically reduced the extra-oral time of the donor tooth from extraction to transplantation.

  2. Combined MV + kV inverse treatment planning for optimal kV dose incorporation in IGRT

    NASA Astrophysics Data System (ADS)

    Grelewicz, Zachary; Wiersma, Rodney D.

    2014-04-01

    Despite the existence of real-time kV intra-fractional tumor tracking strategies for many years, clinical adoption has been held back by concern over the excess kV imaging dose cost to the patient when imaging in continuous fluoroscopic mode. This work aims to solve this problem by investigating, for the first time, the use of convex optimization tools to optimally integrate this excess kV imaging dose into the MV therapeutic dose in order to make real-time kV tracking clinically feasible. Phase space files modeling both a 6 MV treatment beam and a kV on-board-imaging beam of a commercial LINAC were generated with BEAMnrc, and used to generate dose influence matrices in DOSXYZnrc for ten previously treated lung cancer patients. The dose optimization problem for IMRT, formulated as a quadratic problem, was modified to include additional constraints as required for real-time kV intra-fractional tracking. An interior point optimizer was used to solve the modified optimization problem. It was found that when using large kV imaging apertures during fluoroscopic tracking, combined MV + kV optimization lead to a 0.5%-5.17% reduction in the total number of monitor units assigned to the MV beam due to inclusion of the kV dose over the ten patients. This was accompanied by a reduction of up to 42% of the excess kV dose compared to standard MV IMRT with kV tracking. For all kV field sizes considered, combined MV + kV optimization provided prescription dose to the treatment volume coverage equal to the no-imaging case, yet superior to standard MV IMRT with non-optimized kV fluoroscopic tracking. With combined MV + kV optimization, it is possible to quantify in a patient specific way the dosimetric effect of real-time imaging on the patient. Such information is necessary when substantial kV imaging is performed.

  3. SU-D-206-06: Task-Specific Optimization of Scintillator Thickness for CMOS-Detector Based Cone-Beam Breast CT

    SciTech Connect

    Vedantham, S; Shrestha, S; Shi, L; Vijayaraghavan, G; Karellas, A

    2016-06-15

    Purpose: To optimize the cesium iodide (CsI:Tl) scintillator thickness in a complimentary metal-oxide semiconductor (CMOS)-based detector for use in dedicated cone-beam breast CT. Methods: The imaging task considered was the detection of a microcalcification cluster comprising six 220µm diameter calcium carbonate spheres, arranged in the form of a regular pentagon with 2 mm spacing on its sides and a central calcification, similar to that in ACR-recommended mammography accreditation phantom, at a mean glandular dose of 4.5 mGy. Generalized parallel-cascades based linear systems analysis was used to determine Fourier-domain image quality metrics in reconstructed object space, from which the detectability index inclusive of anatomical noise was determined for a non-prewhitening numerical observer. For 300 projections over 2π, magnification-associated focal-spot blur, Monte Carlo derived x-ray scatter, K-fluorescent emission and reabsorption within CsI:Tl, CsI:Tl quantum efficiency and optical blur, fiberoptic plate transmission efficiency and blur, CMOS quantum efficiency, pixel aperture function and additive noise, and filtered back-projection to isotropic 105µm voxel pitch with bilinear interpolation were modeled. Imaging geometry of a clinical prototype breast CT system, a 60 kV Cu/Al filtered x-ray spectrum from 0.3 mm focal spot incident on a 14 cm diameter semi-ellipsoidal breast were used to determine the detectability index for 300–600 µm thick (75µm increments) CsI:Tl. The CsI:Tl thickness that maximized the detectability index was considered optimal. Results: The limiting resolution (10% modulation transfer function, MTF) progressively decreased with increasing CsI:Tl thickness. The zero-frequency detective quantum efficiency, DQE(0), in projection space increased with increasing CsI:Tl thickness. The maximum detectability index was achieved with 525µm thick CsI:Tl scintillator. Reduced MTF at mid-to-high frequencies for 600µm thick CsI:Tl lowered

  4. Three-dimensional anisotropic adaptive filtering of projection data for noise reduction in cone beam CT.

    PubMed

    Maier, Andreas; Wigstrom, Lars; Hofmann, Hannes G; Hornegger, Joachim; Zhu, Lei; Strobel, Norbert; Fahrig, Rebecca

    2011-11-01

    processing (from 1336 to 150 s). Adaptive anisotropic filtering has the potential to substantially improve image quality and/or reduce the radiation dose required for obtaining 3D image data using cone beam CT.

  5. Deformable image registration for cone-beam CT guided transoral robotic base-of-tongue surgery.

    PubMed

    Reaungamornrat, S; Liu, W P; Wang, A S; Otake, Y; Nithiananthan, S; Uneri, A; Schafer, S; Tryggestad, E; Richmon, J; Sorger, J M; Siewerdsen, J H; Taylor, R H

    2013-07-21

    Transoral robotic surgery (TORS) offers a minimally invasive approach to resection of base-of-tongue tumors. However, precise localization of the surgical target and adjacent critical structures can be challenged by the highly deformed intraoperative setup. We propose a deformable registration method using intraoperative cone-beam computed tomography (CBCT) to accurately align preoperative CT or MR images with the intraoperative scene. The registration method combines a Gaussian mixture (GM) model followed by a variation of the Demons algorithm. First, following segmentation of the volume of interest (i.e. volume of the tongue extending to the hyoid), a GM model is applied to surface point clouds for rigid initialization (GM rigid) followed by nonrigid deformation (GM nonrigid). Second, the registration is refined using the Demons algorithm applied to distance map transforms of the (GM-registered) preoperative image and intraoperative CBCT. Performance was evaluated in repeat cadaver studies (25 image pairs) in terms of target registration error (TRE), entropy correlation coefficient (ECC) and normalized pointwise mutual information (NPMI). Retraction of the tongue in the TORS operative setup induced gross deformation >30 mm. The mean TRE following the GM rigid, GM nonrigid and Demons steps was 4.6, 2.1 and 1.7 mm, respectively. The respective ECC was 0.57, 0.70 and 0.73, and NPMI was 0.46, 0.57 and 0.60. Registration accuracy was best across the superior aspect of the tongue and in proximity to the hyoid (by virtue of GM registration of surface points on these structures). The Demons step refined registration primarily in deeper portions of the tongue further from the surface and hyoid bone. Since the method does not use image intensities directly, it is suitable to multi-modality registration of preoperative CT or MR with intraoperative CBCT. Extending the 3D image registration to the fusion of image and planning data in stereo-endoscopic video is anticipated

  6. Three-dimensional anisotropic adaptive filtering of projection data for noise reduction in cone beam CT

    SciTech Connect

    Maier, Andreas; Wigstroem, Lars; Hofmann, Hannes G.; Hornegger, Joachim; Zhu Lei; Strobel, Norbert; Fahrig, Rebecca

    2011-11-15

    speed-up of the processing (from 1336 to 150 s). Conclusions: Adaptive anisotropic filtering has the potential to substantially improve image quality and/or reduce the radiation dose required for obtaining 3D image data using cone beam CT.

  7. Deformable image registration for cone-beam CT guided transoral robotic base-of-tongue surgery

    NASA Astrophysics Data System (ADS)

    Reaungamornrat, S.; Liu, W. P.; Wang, A. S.; Otake, Y.; Nithiananthan, S.; Uneri, A.; Schafer, S.; Tryggestad, E.; Richmon, J.; Sorger, J. M.; Siewerdsen, J. H.; Taylor, R. H.

    2013-07-01

    Transoral robotic surgery (TORS) offers a minimally invasive approach to resection of base-of-tongue tumors. However, precise localization of the surgical target and adjacent critical structures can be challenged by the highly deformed intraoperative setup. We propose a deformable registration method using intraoperative cone-beam computed tomography (CBCT) to accurately align preoperative CT or MR images with the intraoperative scene. The registration method combines a Gaussian mixture (GM) model followed by a variation of the Demons algorithm. First, following segmentation of the volume of interest (i.e. volume of the tongue extending to the hyoid), a GM model is applied to surface point clouds for rigid initialization (GM rigid) followed by nonrigid deformation (GM nonrigid). Second, the registration is refined using the Demons algorithm applied to distance map transforms of the (GM-registered) preoperative image and intraoperative CBCT. Performance was evaluated in repeat cadaver studies (25 image pairs) in terms of target registration error (TRE), entropy correlation coefficient (ECC) and normalized pointwise mutual information (NPMI). Retraction of the tongue in the TORS operative setup induced gross deformation >30 mm. The mean TRE following the GM rigid, GM nonrigid and Demons steps was 4.6, 2.1 and 1.7 mm, respectively. The respective ECC was 0.57, 0.70 and 0.73, and NPMI was 0.46, 0.57 and 0.60. Registration accuracy was best across the superior aspect of the tongue and in proximity to the hyoid (by virtue of GM registration of surface points on these structures). The Demons step refined registration primarily in deeper portions of the tongue further from the surface and hyoid bone. Since the method does not use image intensities directly, it is suitable to multi-modality registration of preoperative CT or MR with intraoperative CBCT. Extending the 3D image registration to the fusion of image and planning data in stereo-endoscopic video is anticipated to

  8. Three-dimensional anisotropic adaptive filtering of projection data for noise reduction in cone beam CT

    PubMed Central

    Maier, Andreas; Wigström, Lars; Hofmann, Hannes G.; Hornegger, Joachim; Zhu, Lei; Strobel, Norbert; Fahrig, Rebecca

    2011-01-01

    .9-fold speed-up of the processing (from 1336 to 150 s). Conclusions: Adaptive anisotropic filtering has the potential to substantially improve image quality and∕or reduce the radiation dose required for obtaining 3D image data using cone beam CT. PMID:22047354

  9. Effect of beam hardening on transmural myocardial perfusion quantification in myocardial CT imaging

    NASA Astrophysics Data System (ADS)

    Fahmi, Rachid; Eck, Brendan L.; Levi, Jacob; Fares, Anas; Wu, Hao; Vembar, Mani; Dhanantwari, Amar; Bezerra, Hiram G.; Wilson, David L.

    2016-03-01

    The detection of subendocardial ischemia exhibiting an abnormal transmural perfusion gradient (TPG) may help identify ischemic conditions due to micro-vascular dysfunction. We evaluated the effect of beam hardening (BH) artifacts on TPG quantification using myocardial CT perfusion (CTP). We used a prototype spectral detector CT scanner (Philips Healthcare) to acquire dynamic myocardial CTP scans in a porcine ischemia model with partial occlusion of the left anterior descending (LAD) coronary artery guided by pressure wire-derived fractional flow reserve (FFR) measurements. Conventional 120 kVp and 70 keV projection-based mono-energetic images were reconstructed from the same projection data and used to compute myocardial blood flow (MBF) using the Johnson-Wilson model. Under moderate LAD occlusion (FFR~0.7), we used three 5 mm short axis slices and divided the myocardium into three LAD segments and three remote segments. For each slice and each segment, we characterized TPG as the mean "endo-to-epi" transmural flow ratio (TFR). BH-induced hypoenhancement on the ischemic anterior wall at 120 kVp resulted in significantly lower mean TFR value as compared to the 70 keV TFR value (0.29+/-0.01 vs. 0.55+/-0.01 p<1e-05). No significant difference was measured between 120 kVp and 70 keV mean TFR values on segments moderately affected or unaffected by BH. In the entire ischemic LAD territory, 120 kVp mean endocardial flow was significantly reduced as compared to mean epicardial flow (15.80+/-10.98 vs. 40.85+/-23.44 ml/min/100g; p<1e-04). At 70 keV, BH was effectively minimized resulting in mean endocardial MBF of 40.85+/-15.3407 ml/min/100g vs. 74.09+/-5.07 ml/min/100g (p=0.0054) in the epicardium. We also found that BH artifact in the conventional 120 kVp images resulted in falsely reduced MBF measurements even under non-ischemic conditions.

  10. Analytic image reconstruction from partial data for a single-scan cone-beam CT with scatter correction

    SciTech Connect

    Min, Jonghwan; Pua, Rizza; Cho, Seungryong; Kim, Insoo; Han, Bumsoo

    2015-11-15

    Purpose: A beam-blocker composed of multiple strips is a useful gadget for scatter correction and/or for dose reduction in cone-beam CT (CBCT). However, the use of such a beam-blocker would yield cone-beam data that can be challenging for accurate image reconstruction from a single scan in the filtered-backprojection framework. The focus of the work was to develop an analytic image reconstruction method for CBCT that can be directly applied to partially blocked cone-beam data in conjunction with the scatter correction. Methods: The authors developed a rebinned backprojection-filteration (BPF) algorithm for reconstructing images from the partially blocked cone-beam data in a circular scan. The authors also proposed a beam-blocking geometry considering data redundancy such that an efficient scatter estimate can be acquired and sufficient data for BPF image reconstruction can be secured at the same time from a single scan without using any blocker motion. Additionally, scatter correction method and noise reduction scheme have been developed. The authors have performed both simulation and experimental studies to validate the rebinned BPF algorithm for image reconstruction from partially blocked cone-beam data. Quantitative evaluations of the reconstructed image quality were performed in the experimental studies. Results: The simulation study revealed that the developed reconstruction algorithm successfully reconstructs the images from the partial cone-beam data. In the experimental study, the proposed method effectively corrected for the scatter in each projection and reconstructed scatter-corrected images from a single scan. Reduction of cupping artifacts and an enhancement of the image contrast have been demonstrated. The image contrast has increased by a factor of about 2, and the image accuracy in terms of root-mean-square-error with respect to the fan-beam CT image has increased by more than 30%. Conclusions: The authors have successfully demonstrated that the

  11. Analytic image reconstruction from partial data for a single-scan cone-beam CT with scatter correction.

    PubMed

    Min, Jonghwan; Pua, Rizza; Kim, Insoo; Han, Bumsoo; Cho, Seungryong

    2015-11-01

    A beam-blocker composed of multiple strips is a useful gadget for scatter correction and/or for dose reduction in cone-beam CT (CBCT). However, the use of such a beam-blocker would yield cone-beam data that can be challenging for accurate image reconstruction from a single scan in the filtered-backprojection framework. The focus of the work was to develop an analytic image reconstruction method for CBCT that can be directly applied to partially blocked cone-beam data in conjunction with the scatter correction. The authors developed a rebinned backprojection-filteration (BPF) algorithm for reconstructing images from the partially blocked cone-beam data in a circular scan. The authors also proposed a beam-blocking geometry considering data redundancy such that an efficient scatter estimate can be acquired and sufficient data for BPF image reconstruction can be secured at the same time from a single scan without using any blocker motion. Additionally, scatter correction method and noise reduction scheme have been developed. The authors have performed both simulation and experimental studies to validate the rebinned BPF algorithm for image reconstruction from partially blocked cone-beam data. Quantitative evaluations of the reconstructed image quality were performed in the experimental studies. The simulation study revealed that the developed reconstruction algorithm successfully reconstructs the images from the partial cone-beam data. In the experimental study, the proposed method effectively corrected for the scatter in each projection and reconstructed scatter-corrected images from a single scan. Reduction of cupping artifacts and an enhancement of the image contrast have been demonstrated. The image contrast has increased by a factor of about 2, and the image accuracy in terms of root-mean-square-error with respect to the fan-beam CT image has increased by more than 30%. The authors have successfully demonstrated that the proposed scanning method and image

  12. A prototype fan-beam optical CT scanner for 3D dosimetry

    SciTech Connect

    Campbell, Warren G.; Rudko, D. A.; Braam, Nicolas A.; Jirasek, Andrew; Wells, Derek M.

    2013-06-15

    Purpose: The objective of this work is to introduce a prototype fan-beam optical computed tomography scanner for three-dimensional (3D) radiation dosimetry. Methods: Two techniques of fan-beam creation were evaluated: a helium-neon laser (HeNe, {lambda} = 543 nm) with line-generating lens, and a laser diode module (LDM, {lambda} = 635 nm) with line-creating head module. Two physical collimator designs were assessed: a single-slot collimator and a multihole collimator. Optimal collimator depth was determined by observing the signal of a single photodiode with varying collimator depths. A method of extending the dynamic range of the system is presented. Two sample types were used for evaluations: nondosimetric absorbent solutions and irradiated polymer gel dosimeters, each housed in 1 liter cylindrical plastic flasks. Imaging protocol investigations were performed to address ring artefacts and image noise. Two image artefact removal techniques were performed in sinogram space. Collimator efficacy was evaluated by imaging highly opaque samples of scatter-based and absorption-based solutions. A noise-based flask registration technique was developed. Two protocols for gel manufacture were examined. Results: The LDM proved advantageous over the HeNe laser due to its reduced noise. Also, the LDM uses a wavelength more suitable for the PRESAGE{sup TM} dosimeter. Collimator depth of 1.5 cm was found to be an optimal balance between scatter rejection, signal strength, and manufacture ease. The multihole collimator is capable of maintaining accurate scatter-rejection to high levels of opacity with scatter-based solutions (T < 0.015%). Imaging protocol investigations support the need for preirradiation and postirradiation scanning to reduce reflection-based ring artefacts and to accommodate flask imperfections and gel inhomogeneities. Artefact removal techniques in sinogram space eliminate streaking artefacts and reduce ring artefacts of up to {approx}40% in magnitude. The

  13. A prototype fan-beam optical CT scanner for 3D dosimetry.

    PubMed

    Campbell, Warren G; Rudko, D A; Braam, Nicolas A; Wells, Derek M; Jirasek, Andrew

    2013-06-01

    The objective of this work is to introduce a prototype fan-beam optical computed tomography scanner for three-dimensional (3D) radiation dosimetry. Two techniques of fan-beam creation were evaluated: a helium-neon laser (HeNe, λ = 543 nm) with line-generating lens, and a laser diode module (LDM, λ = 635 nm) with line-creating head module. Two physical collimator designs were assessed: a single-slot collimator and a multihole collimator. Optimal collimator depth was determined by observing the signal of a single photodiode with varying collimator depths. A method of extending the dynamic range of the system is presented. Two sample types were used for evaluations: nondosimetric absorbent solutions and irradiated polymer gel dosimeters, each housed in 1 liter cylindrical plastic flasks. Imaging protocol investigations were performed to address ring artefacts and image noise. Two image artefact removal techniques were performed in sinogram space. Collimator efficacy was evaluated by imaging highly opaque samples of scatter-based and absorption-based solutions. A noise-based flask registration technique was developed. Two protocols for gel manufacture were examined. The LDM proved advantageous over the HeNe laser due to its reduced noise. Also, the LDM uses a wavelength more suitable for the PRESAGE(TM) dosimeter. Collimator depth of 1.5 cm was found to be an optimal balance between scatter rejection, signal strength, and manufacture ease. The multihole collimator is capable of maintaining accurate scatter-rejection to high levels of opacity with scatter-based solutions (T < 0.015%). Imaging protocol investigations support the need for preirradiation and postirradiation scanning to reduce reflection-based ring artefacts and to accommodate flask imperfections and gel inhomogeneities. Artefact removal techniques in sinogram space eliminate streaking artefacts and reduce ring artefacts of up to ∼40% in magnitude. The flask registration technique was shown to achieve

  14. A GPU tool for efficient, accurate, and realistic simulation of cone beam CT projections