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Sample records for helical spiral ct

  1. Effect of pitch in multislice spiral/helical CT

    NASA Astrophysics Data System (ADS)

    Wang, Ge; Vannier, Michael W.

    1999-09-01

    To understand the effect of pitch on raw data interpolation in multi-slice spiral/helical CT, and provide guidelines for scanner design and protocol optimization. Multi-slice spiral CT is mainly characterized by the three parameters: the number of detector arrays, the detector collimation, and the table increment per X-ray source rotation. The pitch in multi-slice spiral CT is defined as the ratio of the table increment over the detector collimation. In parallel to the current framework for studying longitudinal image resolution, the central fan- beam rays of direct and opposite directions are considered, assuming a narrow cone-beam angle. Generally speaking, sampling in the Radon domain by the direct and opposite central rays is non-uniform along the longitudinal axis. Using a recently developed methodology for quantifying the sensitivity of signal reconstruction from non-uniformly sampled finite points, the effect of pitch on raw data interpolation is analyzed in multi-slice spiral CT. Unlike single-slice spiral CT, in which image quality deceases monotonically as the pitch increases, the sensitivity of raw data interpolation in multi-slice spiral CT increases in an alternating way as the pitch increases, suggesting that image quality does not decrease monotonically in this case. The most favorable pitch can be found from the sensitivity-pitch plot for any given set of multi-slice spiral CT parameters. An example for four-slice spiral CT is provided. The study on the pitch effect using the sensitivity analysis approach reveals the fundamental characteristics of raw data interpolation in multi-slice spiral CT, and gives insights into interaction between pitch and image quality. These results may be valuable for design of multi-slice spiral CT scanners and imaging protocol optimization in clinical applications.

  2. Spiral CT: vascular applications.

    PubMed

    Rankin, S C

    1998-08-01

    Recent technical advances in CT have renewed interest in the development of CT angiography (CTA). CT angiography is a minimally invasive method of visualising the vascular system and is becoming an alternative to conventional arteriography in some situations. Spiral technology allows a volume of data to be obtained on a single breath-hold with no respiratory misregistration. Fast machines with second or subsecond acquisition times mean the images are obtained while there are high circulating levels of contrast medium giving peak vascular opacification from a peripheral intravenous injection. Accurate timing will ensure either the arterial or venous phase is imaged. Multiple overlapping axial images can be obtained from the data set with no increase in radiation dose to the patient and from these scans computer generated multiplanar and 3D images are obtained which can be viewed from numerous angles. CT angiography can be performed more quickly, less invasively and at reduced cost compared to conventional angiography. PMID:9717621

  3. Design principles for Bernal spirals and helices with tunable pitch

    NASA Astrophysics Data System (ADS)

    Fejer, Szilard N.; Chakrabarti, Dwaipayan; Kusumaatmaja, Halim; Wales, David J.

    2014-07-01

    Using the framework of potential energy landscape theory, we describe two in silico designs for self-assembling helical colloidal superstructures based upon dipolar dumbbells and Janus-type building blocks, respectively. Helical superstructures with controllable pitch length are obtained using external magnetic field driven assembly of asymmetric dumbbells involving screened electrostatic as well as magnetic dipolar interactions. The pitch of the helix is tuned by modulating the Debye screening length over an experimentally accessible range. The second design is based on building blocks composed of rigidly linked spheres with short-range anisotropic interactions, which are predicted to self-assemble into Bernal spirals. These spirals are quite flexible, and longer helices undergo rearrangements via cooperative, hinge-like moves, in agreement with experiment.Using the framework of potential energy landscape theory, we describe two in silico designs for self-assembling helical colloidal superstructures based upon dipolar dumbbells and Janus-type building blocks, respectively. Helical superstructures with controllable pitch length are obtained using external magnetic field driven assembly of asymmetric dumbbells involving screened electrostatic as well as magnetic dipolar interactions. The pitch of the helix is tuned by modulating the Debye screening length over an experimentally accessible range. The second design is based on building blocks composed of rigidly linked spheres with short-range anisotropic interactions, which are predicted to self-assemble into Bernal spirals. These spirals are quite flexible, and longer helices undergo rearrangements via cooperative, hinge-like moves, in agreement with experiment. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00324a

  4. Spiral CT image deblurring for cochlear implantation.

    PubMed

    Wang, G; Vannier, M W; Skinner, M W; Cavalcanti, M G; Harding, G W

    1998-04-01

    Cochlear implantation is the standard treatment for profound hearing loss. Preimplantation and postimplantation spiral computed tomography (CT) is essential in several key clinical and research aspects. The maximum image resolution with commercial spiral CT scanners is insufficient to define clearly anatomical features and implant electrode positions in the inner ear. In this paper, we develop an expectation-maximization (EM)-like iterative deblurring algorithm to achieve spiral CT image super-resolution for cochlear implantation, assuming a spatially invariant linear spiral CT system with a three-dimensional (3-D) separable Gaussian point spread function (PSF). We experimentally validate the 3-D Gaussian blurring model via phantom measurement and profile fitting. The imaging process is further expressed as convolution of an isotropic 3-D Gaussian PSF and a blurred underlying volumetric image. Under practical conditions, an oblique reconstructed section is approximated as convolution of an isotropic two-dimensional (2-D) Gaussian PSF and the corresponding actual cross section. The spiral CT image deblurring algorithm is formulated with sieve and resolution kernels for suppressing noise and edge artifacts. A typical cochlear cross section is used for evaluation, demonstrating a resolution gain up to 30%40% according to the correlation criterion. Physical phantoms, preimplantation and postimplantation patients are reconstructed into volumes of 0.1-mm cubic voxels. The patient images are digitally unwrapped along the central axis of the cochlea and the implanted electrode array respectively, then oblique sections orthogonal to the central axis formed. After deblurring, representation of structural features is substantially improved in all the cases. PMID:9688157

  5. Noncontrast helical CT for ureteral stones.

    PubMed

    Boridy, I C; Nikolaidis, P; Kawashima, A; Sandler, C M; Goldman, S M

    1998-01-01

    Noncontrast helical computed tomography (CT) has recently been found to be superior to excretory urography (IVU) in the evaluation of patients with suspected ureterolithiasis. Noncontrast helical CT does not require the use of intravenous contrast material with its associated cost and risk of adverse reactions and can be completed within 5 min, in most cases. Noncontrast CT often detects extraurinary pathology responsible for the patient's symptoms. CT is also more sensitive than IVU in detecting the calculus, regardless of its size, location, and chemical composition. However, confidently differentiating ureteral calculi from phleboliths along the course of the ureter may, at times, be difficult. The "tissue-rim" sign, a rim of soft tissue attenuation around the suspicious calcification, is helpful in making this distinction. Noncontrast CT does not provide physiological information about renal function and the degree of obstruction. A pilot study has suggested a proportional relationship between the extent of perinephric edema and the degree of obstruction. The cost of the examination and the radiation dose delivered to the patient may be higher with CT. Despite these limitations, noncontrast helical CT has quickly become the imaging study of choice in evaluating patients with acute flank pain. PMID:9542010

  6. Single-slice rebinning method for helical cone-beam CT.

    PubMed

    Noo, F; Defrise, M; Clackdoyle, R

    1999-02-01

    In this paper, we present reconstruction results from helical cone-beam CT data, obtained using a simple and fast algorithm, which we call the CB-SSRB algorithm. This algorithm combines the single-slice rebinning method of PET imaging with the weighting schemes of spiral CT algorithms. The reconstruction is approximate but can be performed using 2D multislice fan-beam filtered backprojection. The quality of the results is surprisingly good, and far exceeds what one might expect, even when the pitch of the helix is large. In particular, with this algorithm comparable quality is obtained using helical cone-beam data with a normalized pitch of 10 to that obtained using standard spiral CT reconstruction with a normalized pitch of 2. PMID:10070801

  7. Windmill artifact in multislice helical CT

    NASA Astrophysics Data System (ADS)

    Silver, Michael D.; Taguchi, Katsuyuki; Hein, Ilmar A.; Chiang, BeShan; Kazama, Masahiro; Mori, Issei

    2003-05-01

    Multi-slice helical CT-systems suffer from windmill artifacts: black/white patterns that spin off of features with high longitudinal gradients. The number of black/white pairs matches the number of slices (detector rows) in the multi-slive detector. The period of spin is the same as the helical pitch. We investigate the cause of the pattern by following the traces of selected voxels through the multi-slive detector array as a function of view position. This forms an "extracted sinogram" which represents the data used to reconstruct the specific voxel. Now we can determine the cause of the artifact by correlating the windmill streak in the image with the extracted data. The investigation shows that inadequate sampling along the longitudinal direction causes the artifact.

  8. Two-phase flow in helical and spiral coils

    NASA Technical Reports Server (NTRS)

    Keshock, Edward G.; Bush, Mia L.; Omrani, Adel; Yan, An

    1995-01-01

    Coiled tube heat exchangers involving two-phase flows are used in a variety of application areas, extending from the aerospace industry to petrochemical, refrigeration land power generation industries. The optimal design in each situation requires a fundamental understanding of the heat, mass and momentum transfer characteristic of the flowing two-phase mixture. However, two-phase flows in lengths of horizontal or vertical straight channels with heat transfer are often quite difficult in themselves to understand sufficiently well to permit accurate system designs. The present study has the following general objectives: (1) Observe two-phase flow patterns of air-water and R-113 working fluids over a range of flow conditions, for helical and spiral coil geometries, of circular and rectangular cross-section; (2) Compare observed flow patterns with predictions of existing flow maps; (3) Study criteria for flow regime transitions for possible modifications of existing flow pattern maps; and (4) Measure associated pressure drops across the coiled test sections over the rage of flow conditions specified.

  9. [Cerebral aneurysms: their 3-dimensional imaging with spiral CT].

    PubMed

    Rieger, J; Hosten, N; Lemke, A J; Langer, R; Lanksch, W R; Felix, R

    1994-03-01

    In this study, the possibility of non-invasive, three-dimensional demonstration of aneurysms of the basal cerebral arteries by means of spiral CT was investigated. The first step was to obtain exact definition of optimal examination parameters. Angio CTs at appropriate levels were performed on 10 subjects and time/density curves of the arterial and venous phases obtained in order to optimise the beginning of the arterial spiral CT series. The second step in this investigation was to examine 7 patients; in 6 of these basal aneurysms had been demonstrated by DSA. By means of multiplanar three-dimensional reconstruction from the data of the spiral CT it was possible to demonstrate 7 aneurysms with a diameter between 5 and 18 mm. Their position and relationship to the bony skull was also shown. PMID:8136472

  10. Spiral bevel and circular arc helical gears: Tooth contact analysis and the effect of misalignment on circular arc helical gears

    NASA Technical Reports Server (NTRS)

    Litvin, F. L.; Tsung, W. T.; Tsay, C. B.; Coy, J. J.; Handschuh, R. F.

    1985-01-01

    A computer aided method for tooth contact analysis was developed and applied. Optimal machine-tool settings for spiral bevel gears are proposed and when applied indicated that kinematic errors can be minimized while maintaining a desirable bearing contact. The effect of misalignment for circular arc helical gears was investigated and the results indicted that directed pinion refinishing can compensate the kinematic errors due to misalignment.

  11. New generation methods for spur, helical, and spiral-bevel gears

    NASA Technical Reports Server (NTRS)

    Litvin, F. L.; Tsung, W.-J.; Coy, J. J.; Handschuh, R. F.; Tsay, C.-B. P.

    1986-01-01

    New methods for generating spur, helical, and spiral-bevel gears are proposed. These methods provide the gears with conjugate gear tooth surfaces, localized bearing contact, and reduced sensitivity to gear misalignment. Computer programs have been developed for simulating gear meshing and bearing contact.

  12. Comparison of fan-beam, cone-beam, and spiral scan reconstruction in x-ray micro-CT

    NASA Astrophysics Data System (ADS)

    Sasov, Alexander

    2001-06-01

    We developed and tested reconstruction software packages for different algorithms: fan-beam, cone-beam (Feldkamp) and spiral (helical) scans. All algorithms were applied to different simulations as well as to the real datasets from the commercial micro-CT instruments. From the results of testing a number of strong and weak points at different approaches was found. Several examples from the different application areas (bone microstructure, industrial applications) show typical reconstruction artifacts with different algorithms.

  13. Helical 4D CT and Comparison with Cine 4D CT

    NASA Astrophysics Data System (ADS)

    Pan, Tinsu

    4D CT was one of the most important developments in radiation oncology in the last decade. Its early development in single slice CT and commercialization in multi-slice CT has radically changed our practice in radiation treatment of lung cancer, and has enabled the stereotactic radiosurgery of early stage lung cancer. In this chapter, we will document the history of 4D CT development, detail the data sufficiency condition governing the 4D CT data collection; present the design of the commercial helical 4D CTs from Philips and Siemens; compare the differences between the helical 4D CT and the GE cine 4D CT in data acquisition, slice thickness, acquisition time and work flow; review the respiratory monitoring devices; and understand the causes of image artifacts in 4D CT.

  14. Primary Cardiac Lymphoma: Helical CT Findings and Radiopathologic Correlation

    SciTech Connect

    Marco de Lucas, Enrique Pagola, Miguel Angel; Fernandez, Fidel; Lastra, Pedro; Delgado, M. Luisa Ruiz; Sadaba, Pablo; Pinto, Jesus; Ballesteros, Ma Angeles; Ortiz, Antonio

    2004-03-15

    Primary tumors of the heart are extremely rare.Clinical manifestations are nondiagnostic and the patients are often misdiagnosed. Magnetic resonance imaging and echocardiography are standard in this diagnostic workup. We report a case of a man with acromegaly, dysphagia, chest pain and weight loss. An invasive cardiac mass was diagnosed by helical-CT. Autopsy demonstrated a B-cell aggressive lymphoma.

  15. A rigid motion correction method for helical computed tomography (CT)

    NASA Astrophysics Data System (ADS)

    Kim, J.-H.; Nuyts, J.; Kyme, A.; Kuncic, Z.; Fulton, R.

    2015-03-01

    We propose a method to compensate for six degree-of-freedom rigid motion in helical CT of the head. The method is demonstrated in simulations and in helical scans performed on a 16-slice CT scanner. Scans of a Hoffman brain phantom were acquired while an optical motion tracking system recorded the motion of the bed and the phantom. Motion correction was performed by restoring projection consistency using data from the motion tracking system, and reconstructing with an iterative fully 3D algorithm. Motion correction accuracy was evaluated by comparing reconstructed images with a stationary reference scan. We also investigated the effects on accuracy of tracker sampling rate, measurement jitter, interpolation of tracker measurements, and the synchronization of motion data and CT projections. After optimization of these aspects, motion corrected images corresponded remarkably closely to images of the stationary phantom with correlation and similarity coefficients both above 0.9. We performed a simulation study using volunteer head motion and found similarly that our method is capable of compensating effectively for realistic human head movements. To the best of our knowledge, this is the first practical demonstration of generalized rigid motion correction in helical CT. Its clinical value, which we have yet to explore, may be significant. For example it could reduce the necessity for repeat scans and resource-intensive anesthetic and sedation procedures in patient groups prone to motion, such as young children. It is not only applicable to dedicated CT imaging, but also to hybrid PET/CT and SPECT/CT, where it could also ensure an accurate CT image for lesion localization and attenuation correction of the functional image data.

  16. Three-dimensional dental imaging by spiral CT

    NASA Astrophysics Data System (ADS)

    Vannier, Michael W.; Hildebolt, Charles F.; Conover, Gary; Knapp, Robert H.; Yokoyama-Crothers, Naoko; Wang, Ge

    1995-05-01

    Three-dimensional image acquisition, display, and analysis of dental structures was performed and validated using spiral computed tomography (SCT) with metal artifact suppression. Isolated extracted teeth, a dry mandible, cadaver mandible, and cadaver head were scanned and reconstructed using a spiral CT scanner (Siemens Somatom PLUS-S) with 1 mm detector collimation, 1-mm table feed, and 0.1 - 1 mm reconstruction interval using specially developed software. Algorithms for metal artifact reduction including extended attenuation range and interpolation of missing projections were applied. Volumetric rendering of voxel sum images was performed to synthesize images comparable to conventional intraoral dental radiographs. Direct comparison of voxel-based synthetic and digitized film images was made. Several isolated, extracted teeth were sectioned with a diamond saw and submitted for histomorphometric analysis to aid in direct comparison with CT slice images obtained by multiplanar reconstruction. Metal artifact reduction was successful in markedly reducing the streaks and star patterns that usually accompany metallic restorations and intraoral appliances. Individual teeth were comparable to CT slice images. Voxel sum images were comparable to dental radiographs; however, for the SCT images, the spatial resolution was higher within the plane of section than it was orthogonal to the plane of section. Serial examinations were obtained by SCT, registered by surface matching, and interval change measured by 3D subtraction. Simulated lesions and restorations were introduced and quantitatively evaluated pre- and post-interventionally to assess imaging method performance.

  17. CEnPiT: Helical cardiac CT reconstruction

    SciTech Connect

    Bontus, Claas; Koken, Peter; Koehler, Thomas; Grass, Michael

    2006-08-15

    Computer tomography (CT) scanners with an increasing number of detector rows offer the potential of shorter scanning times. Nevertheless, the reconstruction problem becomes more challenging, since cone beam artifacts are likely to enter. Here, we consider helical cardiac CT. We analyze how a relationship can be established between exact reconstruction algorithms and the demand to perform a cardiac gating. Utilizing the redundancies requires the consideration of all kinds of Radon planes. For the reconstruction algorithm proposed here, we separate the data into two parts. The first part contains contributions of Radon planes, which are measured with a large number of redundancies. The second part contains the remaining contributions. As it turns out, the second part contributes rather to the low-frequency contents of trans-axial slices. Therefore, we propose to perform a gated back-projection only for the first part, while the second part is back-projected in an ungated way. Data from the complete source trajectory are employed in the reconstruction process in contrary to conventional helical cardiac reconstruction methods. Moreover, all different types of Radon planes are taken into account in the reconstruction, though an ECG-dependent cardiac gating is applied. The reconstruction results, which we present for clinical and simulated data, demonstrate the high potential of CEnPiT for helical cardiac CT with large cone angle systems.

  18. Pediatric organ dose measurements in axial and helical multislice CT

    PubMed Central

    McDermott, Alanna; White, R. Allen; Mc-Nitt-Gray, Mike; Angel, Erin; Cody, Dianna

    2009-01-01

    An anthropomorphic pediatric phantom (5-yr-old equivalent) was used to determine organ doses at specific surface and internal locations resulting from computed tomography (CT) scans. This phantom contains four different tissue-equivalent materials: Soft tissue, bone, brain, and lung. It was imaged on a 64-channel CT scanner with three head protocols (one contiguous axial scan and two helical scans [pitch=0.516 and 0.984]) and four chest protocols (one contiguous axial scan and three helical scans [pitch=0.516, 0.984, and 1.375]). Effective mA s [=(tube current×rotation time)∕pitch] was kept nearly constant at 200 effective mA s for head and 290 effective mA s for chest protocols. Dose measurements were acquired using thermoluminescent dosimeter powder in capsules placed at locations internal to the phantom and on the phantom surface. The organs of interest were the brain, both eyes, thyroid, sternum, both breasts, and both lungs. The organ dose measurements from helical scans were lower than for contiguous axial scans by 0% to 25% even after adjusting for equivalent effective mA s. There was no significant difference (p>0.05) in organ dose values between the 0.516 and 0.984 pitch values for both head and chest scans. The chest organ dose measurements obtained at a pitch of 1.375 were significantly higher than the dose values obtained at the other helical pitches used for chest scans (p<0.05). This difference was attributed to the automatic selection of the large focal spot due to a higher tube current value. These findings suggest that there may be a previously unsuspected radiation dose benefit associated with the use of helical scan mode during computed tomography scanning. PMID:19544765

  19. Pediatric organ dose measurements in axial and helical multislice CT

    SciTech Connect

    McDermott, Alanna; White, R. Allen; Mc-Nitt-Gray, Mike; Angel, Erin; Cody, Dianna

    2009-05-15

    An anthropomorphic pediatric phantom (5-yr-old equivalent) was used to determine organ doses at specific surface and internal locations resulting from computed tomography (CT) scans. This phantom contains four different tissue-equivalent materials: Soft tissue, bone, brain, and lung. It was imaged on a 64-channel CT scanner with three head protocols (one contiguous axial scan and two helical scans [pitch=0.516 and 0.984]) and four chest protocols (one contiguous axial scan and three helical scans [pitch=0.516, 0.984, and 1.375]). Effective mA s [=(tube currentxrotation time)/pitch] was kept nearly constant at 200 effective mA s for head and 290 effective mA s for chest protocols. Dose measurements were acquired using thermoluminescent dosimeter powder in capsules placed at locations internal to the phantom and on the phantom surface. The organs of interest were the brain, both eyes, thyroid, sternum, both breasts, and both lungs. The organ dose measurements from helical scans were lower than for contiguous axial scans by 0% to 25% even after adjusting for equivalent effective mA s. There was no significant difference (p>0.05) in organ dose values between the 0.516 and 0.984 pitch values for both head and chest scans. The chest organ dose measurements obtained at a pitch of 1.375 were significantly higher than the dose values obtained at the other helical pitches used for chest scans (p<0.05). This difference was attributed to the automatic selection of the large focal spot due to a higher tube current value. These findings suggest that there may be a previously unsuspected radiation dose benefit associated with the use of helical scan mode during computed tomography scanning.

  20. Helical cone beam CT with an asymmetrical detector

    SciTech Connect

    Zamyatin, Alexander A.; Taguchi, Katsuyuki; Silver, Michael D.

    2005-10-15

    If a multislice or other area detector is shifted to one side to cover a larger field of view, then the data are truncated on one side. We propose a method to restore the missing data in helical cone-beam acquisitions that uses measured data on the longer side of the asymmetric detector array. The method is based on the idea of complementary rays, which is well known in fan beam geometry; in this paper we extend this concept to the cone-beam case. Different cases of complementary data coverage and dependence on the helical pitch are considered. The proposed method is used in our prototype 16-row CT scanner with an asymmetric detector and a 700 mm field of view. For evaluation we used scanned body phantom data and computer-simulated data. To simulate asymmetric truncation, the full, symmetric datasets were truncated by dropping either 22.5% or 45% from one side of the detector. Reconstructed images from the prototype scanner with the asymmetrical detector show excellent image quality in the extended field of view. The proposed method allows flexible helical pitch selection and can be used with overscan, short-scan, and super-short-scan reconstructions.

  1. 320-Row wide volume CT significantly reduces density heterogeneity observed in the descending aorta: comparisons with 64-row helical CT.

    PubMed

    Yamashiro, Tsuneo; Miyara, Tetsuhiro; Honda, Osamu; Kamiya, Ayano; Tanaka, Yuko; Murayama, Sadayuki

    2014-01-01

    The aim of this study was to compare density heterogeneity on wide volume (WV) scans with that on helical CT scans. 22 subjects underwent chest CT using 320-WV and 64-helical modes. Density heterogeneity of the descending aorta was evaluated quantitatively and qualitatively. At qualitative assessment, the heterogeneity was judged to be smaller on WV scans than on helical scans (p<0.0001). Mean changes in aortic density between two contiguous slices were 1.64 HU (3.40%) on WV scans and 2.29 HU (5.19%) on helical scans (p<0.0001). CT density of thoracic organs is more homogeneous and reliable on WV scans than on helical scans. PMID:24210879

  2. Three-dimensional spiral CT for craniofacial surgical planning and evaluation

    NASA Astrophysics Data System (ADS)

    Cavalcanti, Marcelo G.; Vannier, Michael W.

    1998-06-01

    Purpose: To evaluate measurement accuracy of 3D volumetric medical imaging from Spiral CT for craniofacial surgical planing. Material and methods: The study population consisted of 5 cadaver heads that were imaged on a spiral CT scanner with volumetric technique high-resolution contiguous axial slices 3mm thickness and 2mm/sec table feed, with 120Kvp and 200 mA. The archived CT data were stored on optical disks to allow full retrospective review of any image. The data sets were transferred to a networked computer workstation, to generated 3D volumetric images for subsequent manipulation and analyses. The computer graphics workstation allowed to do measurements, based on conventional craniometric anatomic landmarks, by 2 observers with 2 sessions each. The specimens were then submitted to a dynamic blunt force, in an effort to simulate craniofacial fractures, scanned and measured again. The soft tissues were then partially subsequently removed and the measurements were repeated by electromagnetic digitizer. Statistical analysis was done using analysis of variance. Results: Measurements from 3D spiral CT scans can be precise with high repeatability and sufficient accuracy for surgical planing. Conclusion: 3D computer graphics by spiral CT allowed, in vitro, sufficient precision for assessment of surgical management. Digital volumetric spiral CT imaging is valid quantitatively and qualitatively for craniofacial surgical planning and evaluation.

  3. Study of two-phase flow in helical and spiral coils

    NASA Technical Reports Server (NTRS)

    Keshock, Edward G.; Yan, AN; Omrani, Adel

    1990-01-01

    The principal purposes of the present study were to: (1) observe and develop a fundamental understanding of the flow regimes and their transitions occurring in helical and spiral coils; and (2) obtain pressure drop measurements of such flows, and, if possible, develop a method for predicting pressure drop in these flow geometries. Elaborating upon the above, the general intent is to develop criteria (preferably generalized) for establishing the nature of the flow dynamics (e.g. flow patterns) and the magnitude of the pressure drop in such configurations over a range of flow rates and fluid properties. Additionally, the visualization and identification of flow patterns were a fundamental objective of the study. From a practical standpoint, the conditions under which an annular flow pattern exists is of particular practical importance. In the possible practical applications which would implement these geometries, the working fluids are likely to be refrigerant fluids. In the present study the working fluids were an air-water mixture, and refrigerant 113 (R-113). In order to obtain records of flow patterns and their transitions, video photography was employed extensively. Pressure drop measurements were made using pressure differential transducers connected across pressure taps in lines immediately preceding and following the various test sections.

  4. High-pitch spiral acquisition: a new scan mode for coronary CT angiography.

    PubMed

    Achenbach, Stephan; Marwan, Mohamed; Schepis, Tiziano; Pflederer, Tobias; Bruder, Herbert; Allmendinger, Thomas; Petersilka, Martin; Anders, Katharina; Lell, Michael; Kuettner, Axel; Ropers, Dieter; Daniel, Werner G; Flohr, Thomas

    2009-01-01

    Coronary CT angiography allows high-quality imaging of the coronary arteries when state-of-the-art CT systems are used. However, radiation exposure has been a concern. We describe a new scan mode that uses a very high-pitch spiral acquisition, "Flash Spiral," which has been developed specifically for low-dose imaging with dual-source CT. The scan mode uses a pitch of 3.2 to acquire a spiral CT data set, while covering the entire volume of the heart in one cardiac cycle. Data acquisition is prospectively triggered by the electrocardiogram and starts in late systole to be completed within one cardiac cycle. Images are reconstructed with a temporal resolution that corresponds to one-quarter of the gantry rotation time. Throughout the data set, subsequent images are reconstructed at later time instants in the cardiac cycle. In a patient with a heart rate of 49 beats/min, the Flash Spiral scan mode was used with a first-generation dual-source CT system and allowed artifact-free visualization of the coronary arteries with a radiation exposure of 1.7 mSv for a 12-cm scan range at 120 kVp tube voltage. PMID:19332343

  5. Regularized iterative weighted filtered backprojection for helical cone-beam CT.

    PubMed

    Sunnegårdh, Johan; Danielsson, Per-Erik

    2008-09-01

    Contemporary reconstruction methods employed for clinical helical cone-beam computed tomography (CT) are analytical (noniterative) but mathematically nonexact, i.e., the reconstructed image contains so called cone-beam artifacts, especially for higher cone angles. Besides cone artifacts, these methods also suffer from windmill artifacts: alternating dark and bright regions creating spiral-like patterns occurring in the vicinity of high z-direction derivatives. In this article, the authors examine the possibility to suppress cone and windmill artifacts by means of iterative application of nonexact three-dimensional filtered backprojection, where the analytical part of the reconstruction brings about accelerated convergence. Specifically, they base their investigations on the weighted filtered backprojection method [Stierstorfer et al., Phys. Med. Biol. 49, 2209-2218 (2004)]. Enhancement of high frequencies and amplification of noise is a common but unwanted side effect in many acceleration attempts. They have employed linear regularization to avoid these effects and to improve the convergence properties of the iterative scheme. Artifacts and noise, as well as spatial resolution in terms of modulation transfer functions and slice sensitivity profiles have been measured. The results show that for cone angles up to +/-2.78 degrees, cone artifacts are suppressed and windmill artifacts are alleviated within three iterations. Furthermore, regularization parameters controlling spatial resolution can be tuned so that image quality in terms of spatial resolution and noise is preserved. Simulations with higher number of iterations and long objects (exceeding the measured region) verify that the size of the reconstructible region is not reduced, and that the regularization greatly improves the convergence properties of the iterative scheme. Taking these results into account, and the possibilities to extend the proposed method with more accurate modeling of the acquisition

  6. Pelvic congestion syndrome: demonstration and diagnosis by helical CT.

    PubMed

    Desimpelaere, J H; Seynaeve, P C; Hagers, Y M; Appel, B J; Mortelmans, L L

    1999-01-01

    Pelvic pain is a common gynaecological complaint, sometimes without any obvious etiology. We report a case of pelvic congestion syndrome, an often overlooked cause of pelvic pain, diagnosed by helical computed tomography. This seems to be an effective and noninvasive imaging modality. PMID:9933685

  7. [Fundamental study of helical scanning CT--evaluation of spatial resolution in the longitudinal axis].

    PubMed

    Anno, H; Katada, K; Tsujioka, K; Ida, Y; Ohashi, I; Takeuchi, A; Koga, S

    1992-11-25

    We evaluated spatial resolution in the longitudinal axis with helical scanning CT using a fourth-generation fast CT scanner. We made a phantom by stringing acrylic balls (65 mm phi x 8 and 9 mm phi x 6). The acquired images were processed by MPR and assessed visually to evaluate axis resolution. With the conventional scanning method, the partial volume effect varied with the starting position, but helical scanning was able to reconstruct high-resolution images using continuous raw data. During helical scanning, axis resolution varied depending on the slice width and sliding speed of the couch top. Even if the sliding speed was kept constant at 4 mm/sec, axis resolution was superior with a slice width of 2 mm than with one of 5 mm. PMID:1465334

  8. Spiral CT Quantification of Aorto-Renal Calcification and Its Use in the Detection of Atheromatous Renal Artery Stenosis: A Study in 42 Patients

    SciTech Connect

    Gayard, Pierre; Garcier, Jean-Marc; Boire, Jean-Yves; Ravel, Anne; Perez, Nessim; Privat, Christian; Lucien, Pascal; Viallet, Jean-Francois; Boyer, Louis

    2000-01-15

    Purpose: To investigate whether a correlation exists between aortic and renal arterial calcifications detected with spiral CT and significant angiographic renal artery stenosis (RAS).Methods: Forty-two patients (mean age 67 years, range 37-84 years), of whom 24 were hypertensive, prospectively underwent abdominal helical CT and aortic and renal arteriography. The 3-mm thickness CT scans (pitch = 1) were reconstructed each millimeter. A manual outline of the renal artery including its ostial portion was produced. Calcific hyperdensities were defined as areas of density more than 130 HU. CT data were compared with the presence or absence of RAS on angiography (24 cases); hypertension and age were taken into account (Mann-Whitney U-test).Results: CT detection and quantification appeared to be reliable and reproductible. We did not find any correlation between aortic and renal arterial calcifications and RAS, even for the patients above 65 years, with or without hypertension. There was no correlation either between calcifications and hypertension in patients without RAS. Conclusion: In this population, aortic and renal arterial calcifications have no predictive value for RAS.

  9. [The role and place of helical ct for preporative diagnosis of acute appendicitis].

    PubMed

    Nemsadze, G Sh; Urushadze, O P; Tokhadze, L T; Lomidze, M N; Kipshidze, N N

    2009-09-01

    The goal of our study was to ascertain the role and place of helical CT for preoperative diagnosis of acute appendicitis. Our study relied upon the results of helical CT scans of 60 patients, which were diagnosed probable acute appendicitis based upon clinical signs. Of these 60 patients 49 (81,6%) were female, 11 (18,4%) male. For all patients laboratory studies of blood were made, 31 patients were examined by ultrasonography. Among this group the diagnosis of acute appendicitis was verified by CT scan in 41 patients. In the case of 5 patients the scan was equivocal because of smaller amount of omentum; in this subgroup of 5 patients (5% overall) three were given radiocontrast dye, and two (3,3% overall) were not. In 11 (18,3%) cases the diagnosis of acute appendicitis was not verified, and in three cases the diagnosis was incorrect. According to data of our study and intraoperative data analysis, sensitivity of this method approaches 93% and the specificity - 92%, and overall diagnostic accuracy 93%. Helical CT may be stated as diagnostic method of choice in the diagnosis of acute appendicitis. It is helpful in clinical decision making, and reducing the amount of false appendectomies. PMID:19801721

  10. Megavoltage CT in helical tomotherapy - clinical advantages and limitations of special physical characteristics.

    PubMed

    Sterzing, Florian; Kalz, Jörn; Sroka-Perez, Gabriele; Schubert, Kai; Bischof, Marc; Roder, Falk; Debus, Jürgen; Herfarth, Klaus

    2009-10-01

    Helical tomotherapy is a form of image-guided intensity-modulated radiotherapy that introduces the ring gantry concept into radiation oncology. The system is a combination of a therapeutic linear accelerator and a megavoltage CT-scanner. This work describes the clinical experience with megavoltage CT with 456 patients in more than 11000 fractions. It also provides a review of the current literature of the possibilities and limitations of megavoltage CT. Between July 2006 and October 2008 456 patients were treated with helical tomotherapy and a pretreatment megavoltage CT was performed in 98.1% of the 11821 fractions to perform position control and correction. CT image acquisition was done with 3.5 MV x-rays in the helical tomotherapy machine. MVCT was used for dose recalculations to quantify doses distributions in cases of changing geometry, tumor shrinkage or presence of metal implants. Inverse treatment planning for prostate cancer patients with bilateral hip replacements was performed based upon an MVCT. A mean 3D-correction vector of 7.1mm with a considerable variation was detected and immediately corrected. Mean shifts were lateral 0.9mm (sd 5.0mm), mean longitudinal shift 1.0mm (sd 5.1mm) and mean vertical shift 3.2mm (sd 5.2mm). The MVCT enables imaging of anatomical structures in the presence of dental metal or orthopedic implants. Especially in these cases, dose recomputations can increase the precision of dose calculations. Due to a mean 3d correction vector of more than 7mm and a variation of corrections of more than 5mm daily image-guidance is recommended to achieve a precise dose application. The MVCT shows evident advantages in cases with metal implants but has limitations due to a reduced soft tissue contrast. Compared with megavoltage cone-beam-CT the tomotherapy fan beam CT adds less extra dose fore the patient and has a better soft tissue contrast. PMID:19754210

  11. Cone-angle-dependent generalized weighting scheme for 16-slice helical CT

    NASA Astrophysics Data System (ADS)

    Hsieh, Jiang; Dong, Yanting; Simoni, Piero; Toth, Thomas; Slack, Christopher L.; Grekowicz, Brian; Seidenschnur, George; Shaughnessy, Charlie

    2002-05-01

    Since the recent introduction of multi-slice helical computed tomography (MHCT), new clinical applications have experienced tremendous growth in recent years. MHCT offers improved volume coverage, faster scan speed, more isotropic spatial resolution, and reduced x-ray tube loading. Similar to the single slice helical CT, the projection data collected in MHCT is inherently inconsistent due to the constant table motion. In addition, cone beam effects in MHCT produce additional complexity and image artifacts. Although the cone angle is quite smaller even for the 16-slice configuration, the impact on image artifacts cannot be ignored. Many reconstruction algorithms have been proposed and investigated recently to combat image artifacts associated with the MHCT data acquisition. In this paper, we propose a cone-angle dependent generalized weighting scheme for 16-slice helical CT that allows the production of MHCT images with only 2D backprojection. The cone-angle dependency of the algorithm suppresses image artifacts due to the cone beam effect and the generalized weighting portion enables interpolation be performed with conjugate samples for the 16-slice helical dataset. With the proposed algorithm, image artifacts are significantly reduced.

  12. 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

  13. Correction for human head motion in helical x-ray CT

    NASA Astrophysics Data System (ADS)

    Kim, J.-H.; Sun, T.; Alcheikh, A. R.; Kuncic, Z.; Nuyts, J.; Fulton, R.

    2016-02-01

    Correction for rigid object motion in helical CT can be achieved by reconstructing from a modified source-detector orbit, determined by the object motion during the scan. This ensures that all projections are consistent, but it does not guarantee that the projections are complete in the sense of being sufficient for exact reconstruction. We have previously shown with phantom measurements that motion-corrected helical CT scans can suffer from data-insufficiency, in particular for severe motions and at high pitch. To study whether such data-insufficiency artefacts could also affect the motion-corrected CT images of patients undergoing head CT scans, we used an optical motion tracking system to record the head movements of 10 healthy volunteers while they executed each of the 4 different types of motion (‘no’, slight, moderate and severe) for 60 s. From these data we simulated 354 motion-affected CT scans of a voxelized human head phantom and reconstructed them with and without motion correction. For each simulation, motion-corrected (MC) images were compared with the motion-free reference, by visual inspection and with quantitative similarity metrics. Motion correction improved similarity metrics in all simulations. Of the 270 simulations performed with moderate or less motion, only 2 resulted in visible residual artefacts in the MC images. The maximum range of motion in these simulations would encompass that encountered in the vast majority of clinical scans. With severe motion, residual artefacts were observed in about 60% of the simulations. We also evaluated a new method of mapping local data sufficiency based on the degree to which Tuy’s condition is locally satisfied, and observed that areas with high Tuy values corresponded to the locations of residual artefacts in the MC images. We conclude that our method can provide accurate and artefact-free MC images with most types of head motion likely to be encountered in CT imaging, provided that the motion can

  14. Implementation and evaluation of two helical CT reconstruction algorithms in CIVA

    NASA Astrophysics Data System (ADS)

    Banjak, H.; Costin, M.; Vienne, C.; Kaftandjian, V.

    2016-02-01

    The large majority of industrial CT systems reconstruct the 3D volume by using an acquisition on a circular trajec-tory. However, when inspecting long objects which are highly anisotropic, this scanning geometry creates severe artifacts in the reconstruction. For this reason, the use of an advanced CT scanning method like helical data acquisition is an efficient way to address this aspect known as the long-object problem. Recently, several analytically exact and quasi-exact inversion formulas for helical cone-beam reconstruction have been proposed. Among them, we identified two algorithms of interest for our case. These algorithms are exact and of filtered back-projection structure. In this work we implemented the filtered-backprojection (FBP) and backprojection-filtration (BPF) algorithms of Zou and Pan (2004). For performance evaluation, we present a numerical compari-son of the two selected algorithms with the helical FDK algorithm using both complete (noiseless and noisy) and truncated data generated by CIVA (the simulation platform for non-destructive testing techniques developed at CEA).

  15. Profile of CT scan output dose in axial and helical modes using convolution

    NASA Astrophysics Data System (ADS)

    Anam, C.; Haryanto, F.; Widita, R.; Arif, I.; Dougherty, G.

    2016-03-01

    The profile of the CT scan output dose is crucial for establishing the patient dose profile. The purpose of this study is to investigate the profile of the CT scan output dose in both axial and helical modes using convolution. A single scan output dose profile (SSDP) in the center of a head phantom was measured using a solid-state detector. The multiple scan output dose profile (MSDP) in the axial mode was calculated using convolution between SSDP and delta function, whereas for the helical mode MSDP was calculated using convolution between SSDP and the rectangular function. MSDPs were calculated for a number of scans (5, 10, 15, 20 and 25). The multiple scan average dose (MSAD) for differing numbers of scans was compared to the value of CT dose index (CTDI). Finally, the edge values of MSDP for every scan number were compared to the corresponding MSAD values. MSDPs were successfully generated by using convolution between a SSDP and the appropriate function. We found that CTDI only accurately estimates MSAD when the number of scans was more than 10. We also found that the edge values of the profiles were 42% to 93% lower than that the corresponding MSADs.

  16. Imaging properties of circular and helical interlaced source-detector CT

    NASA Astrophysics Data System (ADS)

    Chen, Yi; Xi, Yan; Zhao, Jun

    2012-10-01

    We study reconstruction methods and imaging properties of the circular and helical interlaced source-detector array (ISDA) computed tomography (CT) system. The system uses carbon nanotube (CNT) based field emission X-ray source arrays and detector arrays. Distributed sources and detectors allow projection data been acquired from different direction by switching on the X-ray sources sequentially, requiring no rotation of gantry or object. Thus the system enables high temporal resolution and eliminates motion artifacts caused by gantry rotation as is common in the conventional CT systems. Interpolation is implemented to patch the absent data in the projection image, and tilted plane Feldkamp type reconstruction algorithm (TPFR) is used to reduce the cone beam artifacts for helical ISDA CT. We analyze the distribution of artifacts in the reconstruction, as well as the influence of the detector array gap and the helix pitch on reconstruction quality. Simulation studies demonstrate that the gap ratio is the key factor on the artifacts due to the gap, and increasing the pitch will reduced gap ratio. Choosing the helix pitch appropriately by getting a balance between cone beam artifacts and gap induced artifacts can get a better reconstruction.

  17. [Small renal cell carcinoma (≤ 4 cm): enhancement patterns on triphasic spiral CT].

    PubMed

    Rebonato, Alberto; Pierotti, Luisa; Barberini, Francesco; Rosi, Giovanni; Macarini, Luca; Scialpi, Michele

    2012-11-01

    The aim of this study was to define enhancement patterns of small renal cell carcinoma (RCC) (≤4 cm) by triphasic spiral CT. In 24 patients with RCC, hypervascularity and hypovascularity were identified in 12 and 12 RO, respectively, in the cortico-medullary phase (CMP). Hypervascular RCC showed increased density in the CMP (170,7±46,3 UH) and a gradual wash-out in the nephrographic phase (NP) (152,5±41 UH) and pielographic phase (PF) (99,2±38 UH). Hypovascular RCC showed increased density in the CMP (52,9±24,7 UH) and a gradual wash-out in NP (64,5±16,9 UH) and PP phases (55,0±17,3 UH). PMID:23096734

  18. Reproducibility of the coronary calcium measurement with different cardiac algorithms using multislice spiral CT

    NASA Astrophysics Data System (ADS)

    Liang, Yun; Krishnamurthi, Ganapathy; Chen, Laigao M.; Meyer, Cristopher A.

    2002-05-01

    Subsecond multi-slice spiral CT has now been recognized with its great potential in cardiac imaging, in particularly for the coronary calcification detection (CCD). Different reconstruction algorithms have been developed in order to optimize the temporal resolution and to improve the measurement accuracy. These algorithms typically incorporate retrospectively gated reconstructions based on a synchronized electrocardiography (ECG) recording. However, these algorithms consist of different approaches in choosing spatial filters, setting ECG delays, and employing the reconstruction geometry (direct fan-beam vs. parallel rebining). These differences are likely to contribute to the intrascanner and interscanner variability in the coronary calcium measurements. This paper investigates in detail about the quantitative effect on calcium detection among different approaches.

  19. Computer-aided diagnosis workstation and database system for chest diagnosis based on multi-helical CT images

    NASA Astrophysics Data System (ADS)

    Satoh, Hitoshi; Niki, Noboru; Mori, Kiyoshi; Eguchi, Kenji; Kaneko, Masahiro; Kakinuma, Ryutarou; Moriyama, Noriyuki; Ohmatsu, Hironobu; Masuda, Hideo; Machida, Suguru; Sasagawa, Michizou

    2006-03-01

    Multi-helical CT scanner advanced remarkably at the speed at which the chest CT images were acquired for mass screening. Mass screening based on multi-helical CT images requires a considerable number of images to be read. It is this time-consuming step that makes the use of helical CT for mass screening impractical at present. To overcome this problem, we have provided diagnostic assistance methods to medical screening specialists by developing a lung cancer screening algorithm that automatically detects suspected lung cancers in helical CT images and a coronary artery calcification screening algorithm that automatically detects suspected coronary artery calcification. We also have developed electronic medical recording system and prototype internet system for the community health in two or more regions by using the Virtual Private Network router and Biometric fingerprint authentication system and Biometric face authentication system for safety of medical information. Based on these diagnostic assistance methods, we have now developed a new computer-aided workstation and database that can display suspected lesions three-dimensionally in a short time. This paper describes basic studies that have been conducted to evaluate this new system. The results of this study indicate that our computer-aided diagnosis workstation and network system can increase diagnostic speed, diagnostic accuracy and safety of medical information.

  20. Novel reconstruction algorithm for multiphasic cardiac imaging using multislice helical CT

    NASA Astrophysics Data System (ADS)

    Cesmeli, Erdogan; Edic, Peter M.; Iatrou, Maria; Pfoh, Armin H.

    2001-06-01

    Cardiac imaging is still a challenge to CT reconstruction algorithms due to the dynamic nature of the heart. We have developed a new reconstruction technique, called the Flexible Algorithm, which achieves high temporal resolution while it is robust to heart-rate variations. The Flexible Algorithm, first, retrospectively tags helical CT views with corresponding cardiac phases obtained from associated EKG. Next, it determines a set of views for each slice, a stack of which covers the entire heart. Subsequently, the algorithm selects an optimum subset of views to achieve the highest temporal resolution for the desired cardiac phase. Finally, it spatiotemporally filters the views in the selected subsets to reconstruct slices. We tested the performance of our algorithm using both a dynamic analytical phantom and clinical data. Preliminary results indicate that the Flexible Algorithm obtains improved spatiotemporal resolution for a large range of heart rates and variations than standard algorithms do. By providing improved image quality at any desired cardiac phase, and robustness to heart rate variations, the Flexible Algorithm enables cardiac applications in CT, including those that benefit from multiphase information.

  1. An unprecedented Ag-pipemidic acid complex with helical structure: Synthesis, structure and interaction with CT-DNA

    NASA Astrophysics Data System (ADS)

    Li, Meng-Ting; Sun, Jing-Wen; Sha, Jing-Quan; Wu, Hong-Bin; Zhang, Er-Lin; Zheng, Tao-Ye

    2013-08-01

    A new Ag-pipemidic acid complex with helical structure has been prepared and structurally characterized by routine technique. Single-crystal X-ray diffraction analysis shows that there are the left- and right-handed helical chains constructed by Ag ions and PPA drugs along the b direction. And two types of helical chains are connected into 2D layer by sharing pseudo-tetra-nuclear clusters, which are stabilized by PPA-1 molecules as scaffolds. UV study of the interaction of the complex with CT-DNA shows that the title complex can bind to the CT-DNA and exhibits the higher binding constant (Kb) than free HPPA drugs. Additionally, its competitive study with ethidium bromide and the relatively high KSV value also indicates that complex can bind to DNA for the intercalative binding sites.

  2. Sinogram restoration for ultra-low-dose x-ray multi-slice helical CT by nonparametric regression

    NASA Astrophysics Data System (ADS)

    Jiang, Lu; Siddiqui, Khan; Zhu, Bin; Tao, Yang; Siegel, Eliot

    2007-03-01

    During the last decade, x-ray computed tomography (CT) has been applied to screen large asymptomatic smoking and nonsmoking populations for early lung cancer detection. Because a larger population will be involved in such screening exams, more and more attention has been paid to studying low-dose, even ultra-low-dose x-ray CT. However, reducing CT radiation exposure will increase noise level in the sinogram, thereby degrading the quality of reconstructed CT images as well as causing more streak artifacts near the apices of the lung. Thus, how to reduce the noise levels and streak artifacts in the low-dose CT images is becoming a meaningful topic. Since multi-slice helical CT has replaced conventional stop-and-shoot CT in many clinical applications, this research mainly focused on the noise reduction issue in multi-slice helical CT. The experiment data were provided by Siemens SOMATOM Sensation 16-Slice helical CT. It included both conventional CT data acquired under 120 kvp voltage and 119 mA current and ultra-low-dose CT data acquired under 120 kvp and 10 mA protocols. All other settings are the same as that of conventional CT. In this paper, a nonparametric smoothing method with thin plate smoothing splines and the roughness penalty was proposed to restore the ultra-low-dose CT raw data. Each projection frame was firstly divided into blocks, and then the 2D data in each block was fitted to a thin-plate smoothing splines' surface via minimizing a roughness-penalized least squares objective function. By doing so, the noise in each ultra-low-dose CT projection was reduced by leveraging the information contained not only within each individual projection profile, but also among nearby profiles. Finally the restored ultra-low-dose projection data were fed into standard filtered back projection (FBP) algorithm to reconstruct CT images. The rebuilt results as well as the comparison between proposed approach and traditional method were given in the results and

  3. A motion-compensated scheme for helical cone-beam reconstruction in cardiac CT angiography

    SciTech Connect

    Stevendaal, U. van; Berg, J. von; Lorenz, C.; Grass, M.

    2008-07-15

    Since coronary heart disease is one of the main causes of death all over the world, cardiac computed tomography (CT) imaging is an application of very high interest in order to verify indications timely. Due to the cardiac motion, electrocardiogram (ECG) gating has to be implemented into the reconstruction of the measured projection data. However, the temporal and spatial resolution is limited due to the mechanical movement of the gantry and due to the fact that a finite angular span of projections has to be acquired for the reconstruction of each voxel. In this article, a motion-compensated reconstruction method for cardiac CT is described, which can be used to increase the signal-to-noise ratio or to suppress motion blurring. Alternatively, it can be translated into an improvement of the temporal and spatial resolution. It can be applied to the entire heart in common and to high contrast objects moving with the heart in particular, such as calcified plaques or devices like stents. The method is based on three subsequent steps: As a first step, the projection data acquired in low pitch helical acquisition mode together with the ECG are reconstructed at multiple phase points. As a second step, the motion-vector field is calculated from the reconstructed images in relation to the image in a reference phase. Finally, a motion-compensated reconstruction is carried out for the reference phase using those projections, which cover the cardiac phases for which the motion-vector field has been determined.

  4. Application of fast radon transform to CT scanners: difficulties and solutions

    NASA Astrophysics Data System (ADS)

    Mitra, Abhishek; Banerjee, Swapna

    2007-03-01

    As a tomographic reconstruction algorithm, the recently proposed "Fast Radon Transform" (FRT) has some computational advantages. To prove its practical importance the technical difficulties associated with its application to fan-beam CT scanners as well as Spiral/Helical CT system are solved here. Some techniques are described to convert the actual fan-beam data or the spiral/helical CT data to parallel-beam data required for the FRT algorithm in order to reconstruct the CT images. Simulation results are presented to validate the complete method.

  5. Effect of CT contrast on volumetric arc therapy planning (RapidArc and helical tomotherapy) for head and neck cancer

    SciTech Connect

    Liu, Alan J.; Vora, Nayana; Suh, Steve; Liu, An; Schultheiss, Timothy E.; Wong, Jeffrey Y.C.

    2015-04-01

    The objectives of the study were to evaluate the effect of intravenous contrast in the dosimetry of helical tomotherapy and RapidArc treatment for head and neck cancer and determine if it is acceptable during the computed tomography (CT) simulation to acquire only CT with contrast for treatment planning of head and neck cancer. Overall, 5 patients with head and neck cancer (4 men and 1 woman) treated on helical tomotherapy were analyzed retrospectively. For each patient, 2 consecutive CT scans were performed. The first CT set was scanned before the contrast injection and secondary study set was scanned 45 seconds after contrast. The 2 CTs were autoregistered using the same Digital Imaging and Communications in Medicine coordinates. Tomotherapy and RapidArc plans were generated on 1 CT data set and subsequently copied to the second CT set. Dose calculation was performed, and dose difference was analyzed to evaluate the influence of intravenous contrast media. The dose matrix used for comparison included mean, minimum and maximum doses of planning target volume (PTV), PTV dose coverage, and V{sub 45} {sub Gy}, V{sub 30} {sub Gy}, and V{sub 20} {sub Gy} organ doses. Treatment planning on contrasted images generally showed a lower dose to both organs and target than plans on noncontrasted images. The doses for the points of interest placed in the organs and target rarely changed more than 2% in any patient. In conclusion, treatment planning using a contrasted image had insignificant effect on the dose to the organs and targets. In our opinion, only CT with contrast needs to be acquired during the CT simulation for head and neck cancer. Dose calculations performed on contrasted images can potentially underestimate the delivery dose slightly. However, the errors of planning on a contrasted image should not affect the result in clinically significant way.

  6. Spiral CT During Selective Accessory Renal Artery Angiography: Assessment of Vascular Territory Before Aortic Stent-Grafting

    SciTech Connect

    Dorffner, Roland; Thurnher, Siegfried; Prokesch, Rupert; Youssefzadeh, Soraya; Hoelzenbein, Thomas; Lammer, Johannes

    1998-03-15

    We evaluated the vascular territory of accessory renal arteries in cases where the vessel might be overlapped by an aortic stent-graft. Spiral CT during selective accessory renal artery angiography was performed in four patients with abdominal aortic aneurysms (including one with a horseshoe kidney). The volume of the vascular territory of each renal artery was measured using a software program provided by the CT unit manufacturer. The supernumerary renal arteries perfused 32%, 37%, 15%, and 16% of the total renal mass, respectively. In two patients, stent-grafts were implanted, which resulted in occlusion of the supernumerary renal artery. The volume of the renal infarction was equal to the volume perfused by the artery as calculated before implantation of the stent-graft.The method proposed is accurate for estimating the size of the expected renal infarction. It might help to determine whether placement of a stent-graft is acceptable.

  7. Effect of lateral target motion on image registration accuracy in CT-guided helical tomotherapy: a phantom study.

    PubMed

    Medwig, J; Gaede, S; Battista, J J; Yartsev, S

    2010-06-01

    Optimisation of imaging modes for kilovoltage CT (kVCT) used for treatment planning and megavoltage CT (MVCT) image guidance used in ungated helical tomotherapy was investigated for laterally moving targets. Computed tomography images of the QUASAR Respiratory Motion Phantom were acquired without target motion and for lateral motion of the target, with 2-cm peak-to-peak amplitude and a period of 4 s. Reference kVCT images were obtained using a 16-slice CT scanner in standard fast helical CT mode, untagged average CT mode and various post-processed 4D-CT modes (0% phase, average and maximum intensity projection). Three sets of MVCT images with different inter-slice spacings of were obtained on a Hi-Art tomotherapy system with the phantom displaced by a known offset position. Eight radiation therapists performed co-registration of MVCT obtained with 2-, 4- and 6-mm slice spacing and kVCT studies independently for all 15 CT imaging combinations. In the investigated case, the untagged average kVCT and 4-mm slice spacing for the MVCT yielded more accurate registration in the transverse plane. The average residual uncertainty of this combination of imaging procedures was 0.61 +/- 0.16 mm in the longitudinal direction, 0.45 +/- 0.14 mm in the anterior-posterior direction and insignificant in the lateral direction. Manual registration of MVCT-kVCT study pairs is necessary to account for a target in significant lateral motion with respect to bony structures. PMID:20598016

  8. Image Quality of 3rd Generation Spiral Cranial Dual-Source CT in Combination with an Advanced Model Iterative Reconstruction Technique: A Prospective Intra-Individual Comparison Study to Standard Sequential Cranial CT Using Identical Radiation Dose

    PubMed Central

    Wenz, Holger; Maros, Máté E.; Meyer, Mathias; Förster, Alex; Haubenreisser, Holger; Kurth, Stefan; Schoenberg, Stefan O.; Flohr, Thomas; Leidecker, Christianne; Groden, Christoph; Scharf, Johann; Henzler, Thomas

    2015-01-01

    Objectives To prospectively intra-individually compare image quality of a 3rd generation Dual-Source-CT (DSCT) spiral cranial CT (cCT) to a sequential 4-slice Multi-Slice-CT (MSCT) while maintaining identical intra-individual radiation dose levels. Methods 35 patients, who had a non-contrast enhanced sequential cCT examination on a 4-slice MDCT within the past 12 months, underwent a spiral cCT scan on a 3rd generation DSCT. CTDIvol identical to initial 4-slice MDCT was applied. Data was reconstructed using filtered backward projection (FBP) and 3rd-generation iterative reconstruction (IR) algorithm at 5 different IR strength levels. Two neuroradiologists independently evaluated subjective image quality using a 4-point Likert-scale and objective image quality was assessed in white matter and nucleus caudatus with signal-to-noise ratios (SNR) being subsequently calculated. Results Subjective image quality of all spiral cCT datasets was rated significantly higher compared to the 4-slice MDCT sequential acquisitions (p<0.05). Mean SNR was significantly higher in all spiral compared to sequential cCT datasets with mean SNR improvement of 61.65% (p*Bonferroni0.05<0.0024). Subjective image quality improved with increasing IR levels. Conclusion Combination of 3rd-generation DSCT spiral cCT with an advanced model IR technique significantly improves subjective and objective image quality compared to a standard sequential cCT acquisition acquired at identical dose levels. PMID:26288186

  9. Noise Reduction for Low-Dose Single-Slice Helical CT Sinograms

    PubMed Central

    Wang, Jing; Li, Tianfang; Lu, Hongbing; Liang, Zhengrong

    2006-01-01

    Helical computed tomography (HCT) has several advantages over conventional step-and-shoot CT for imaging a relatively large object, especially for dynamic studies. However, HCT may increase X-ray exposure significantly. This work aims to reduce the radiation by lowering X-ray tube current (mA) and filtering low-mA (or dose) sinogram noise of HCT. The noise reduction method is based on three observations on HCT: (1) the axial sampling of HCT projections is nearly continuous as detection system rotates; (2) the noise distribution in sinogram space is nearly a Gaussian after system calibration (including logarithmic transform); and (3) the relationship between the calibrated data mean and variance can be expressed as an exponential functional across the field-of-view. Based on the second and third observations, a penalized weighted least-squares (PWLS) solution is an optimal choice, where the weight is given by the mean-variance relationship. The first observation encourages the use of Karhunen-Loève (KL) transform along the axial direction because of the associated correlation. In the KL domain, the eigenvalue of each principal component and the derived data variance provide the signal-to-noise ratio (SNR) information, resulting in a SNR-adaptive noise reduction. The KL-PWLS noise-reduction method was implemented analytically for efficient restoration of large volume HCT sinograms. Simulation studies showed a noticeable improvement, in terms of image quality and defect detectability, of the proposed noise-reduction method over the Ordered-Subsets Expectation-Maximization reconstruction and the conventional low-pass noise filtering with optimal cutoff frequency and/or other filter parameters. PMID:16932806

  10. Age-related differences in image quality of prospectively ECG-triggered axial and helical scans for coronary CT angiography.

    PubMed

    Takase, Makoto; Fujimoto, Shinichiro; Takamura, Kazuhisa; Yamashita, Haruyo; Uno, Kenji; Aoki, Shigeki

    2016-07-01

    We investigated the underlying reasons for the occurrence of misalignment artifacts in prospectively ECG-triggered axial coronary CT angiography scans. In this study we analyzed 56 consecutive patients scanned in axial mode and 66 consecutive patients scanned in helical mode. Predictors for the occurrence of misalignment artifacts were evaluated by multivariable logistic regression analysis for those patients scanned in the axial mode; advanced age was identified as the sole independent predictor (odds ratio: 1.088; 95 % CI: 1.012-1.170; p = 0.0228). In a comparison with the patients scanned in the helical mode, the image quality score for patients aged 65 years or older was significantly higher in helical mode than in axial mode (2.6 ± 0.5 and 2.4 ± 0.7, respectively; p = 0.0313). Misalignment artifacts in the image are more common in the elderly than in younger. Helical mode should be preferred in this older patient population to allow for good diagnostic image quality. PMID:26984733

  11. Lung Motion Model Validation Experiments, Free-Breathing Tissue Densitometry, and Ventilation Mapping using Fast Helical CT Imaging

    NASA Astrophysics Data System (ADS)

    Dou, Hsiang-Tai

    The uncertainties due to respiratory motion present significant challenges to accurate characterization of cancerous tissues both in terms of imaging and treatment. Currently available clinical lung imaging techniques are subject to inferior image quality and incorrect motion estimation, with consequences that can systematically impact the downstream treatment delivery and outcome. The main objective of this thesis is the development of the techniques of fast helical computed tomography (CT) imaging and deformable image registration for the radiotherapy applications in accurate breathing motion modeling, lung tissue density modeling and ventilation imaging. Fast helical CT scanning was performed on 64-slice CT scanner using the shortest available gantry rotation time and largest pitch value such that scanning of the thorax region amounts to just two seconds, which is less than typical breathing cycle in humans. The scanning was conducted under free breathing condition. Any portion of the lung anatomy undergoing such scanning protocol would be irradiated for only a quarter second, effectively removing any motion induced image artifacts. The resulting CT data were pristine volumetric images that record the lung tissue position and density in a fraction of the breathing cycle. Following our developed protocol, multiple fast helical CT scans were acquired to sample the tissue positions in different breathing states. To measure the tissue displacement, deformable image registration was performed that registers the non-reference images to the reference one. In modeling breathing motion, external breathing surrogate signal was recorded synchronously with the CT image slices. This allowed for the tissue-specific displacement to be modeled as parametrization of the recorded breathing signal using the 5D lung motion model. To assess the accuracy of the motion model in describing tissue position change, the model was used to simulate the original high-pitch helical CT scan

  12. Lung Motion Model Validation Experiments, Free-Breathing Tissue Densitometry, and Ventilation Mapping using Fast Helical CT Imaging

    NASA Astrophysics Data System (ADS)

    Dou, Hsiang-Tai

    The uncertainties due to respiratory motion present significant challenges to accurate characterization of cancerous tissues both in terms of imaging and treatment. Currently available clinical lung imaging techniques are subject to inferior image quality and incorrect motion estimation, with consequences that can systematically impact the downstream treatment delivery and outcome. The main objective of this thesis is the development of the techniques of fast helical computed tomography (CT) imaging and deformable image registration for the radiotherapy applications in accurate breathing motion modeling, lung tissue density modeling and ventilation imaging. Fast helical CT scanning was performed on 64-slice CT scanner using the shortest available gantry rotation time and largest pitch value such that scanning of the thorax region amounts to just two seconds, which is less than typical breathing cycle in humans. The scanning was conducted under free breathing condition. Any portion of the lung anatomy undergoing such scanning protocol would be irradiated for only a quarter second, effectively removing any motion induced image artifacts. The resulting CT data were pristine volumetric images that record the lung tissue position and density in a fraction of the breathing cycle. Following our developed protocol, multiple fast helical CT scans were acquired to sample the tissue positions in different breathing states. To measure the tissue displacement, deformable image registration was performed that registers the non-reference images to the reference one. In modeling breathing motion, external breathing surrogate signal was recorded synchronously with the CT image slices. This allowed for the tissue-specific displacement to be modeled as parametrization of the recorded breathing signal using the 5D lung motion model. To assess the accuracy of the motion model in describing tissue position change, the model was used to simulate the original high-pitch helical CT scan

  13. CAD system for the assistance of a comparative reading for lung cancer using retrospective helical CT images

    NASA Astrophysics Data System (ADS)

    Kubo, Mitsuru; Yamamoto, Takuya; Kawata, Yoshiki; Niki, Noboru; Eguchi, Kenji; Ohmatsu, Hironobu; Kakinuma, Ryutaro; Kaneko, Masahiro; Kusumoto, Masahiko; Moriyama, Noriyuki; Mori, Kiyoshi; Nishiyama, Hiroyuki

    2001-07-01

    The objective of our study is to develop a new computer- aided diagnosis (CAD) system to support effectually the comparative reading using serial helical CT images for lung cancer screening without using the film display. The placement of pulmonary shadows between the serial helical CT images is sometimes different to change the size and the shape of lung by inspired air. We analyzed the motion of the pulmonary structure using the serial cases of 17 pairs, which are different in the inspired air. This algorithm consists of the extraction process of region of interest such as the lung, heart and blood vessels region using thresholding and fuzzy c-means method, and the comparison process of each region in serial CT images using template matching. We validated the efficiency of this algorithm by application to image of 60 subjects. The algorithm could compare the slice images correctly in most combinations with respect to physician's point of view. The experimental results of the proposed algorithm indicate that our CAD system without using the film display is useful to increase the efficiency of the mass screening process.

  14. Segmentation of pulmonary nodules in three-dimensional CT images by use of a spiral-scanning technique

    SciTech Connect

    Wang Jiahui; Engelmann, Roger; Li Qiang

    2007-12-15

    Accurate segmentation of pulmonary nodules in computed tomography (CT) is an important and difficult task for computer-aided diagnosis of lung cancer. Therefore, the authors developed a novel automated method for accurate segmentation of nodules in three-dimensional (3D) CT. First, a volume of interest (VOI) was determined at the location of a nodule. To simplify nodule segmentation, the 3D VOI was transformed into a two-dimensional (2D) image by use of a key 'spiral-scanning' technique, in which a number of radial lines originating from the center of the VOI spirally scanned the VOI from the 'north pole' to the 'south pole'. The voxels scanned by the radial lines provided a transformed 2D image. Because the surface of a nodule in the 3D image became a curve in the transformed 2D image, the spiral-scanning technique considerably simplified the segmentation method and enabled reliable segmentation results to be obtained. A dynamic programming technique was employed to delineate the 'optimal' outline of a nodule in the 2D image, which corresponded to the surface of the nodule in the 3D image. The optimal outline was then transformed back into 3D image space to provide the surface of the nodule. An overlap between nodule regions provided by computer and by the radiologists was employed as a performance metric for evaluating the segmentation method. The database included two Lung Imaging Database Consortium (LIDC) data sets that contained 23 and 86 CT scans, respectively, with 23 and 73 nodules that were 3 mm or larger in diameter. For the two data sets, six and four radiologists manually delineated the outlines of the nodules as reference standards in a performance evaluation for nodule segmentation. The segmentation method was trained on the first and was tested on the second LIDC data sets. The mean overlap values were 66% and 64% for the nodules in the first and second LIDC data sets, respectively, which represented a higher performance level than those of two

  15. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion

    PubMed Central

    Tapanila, Leif; Pruitt, Jesse; Pradel, Alan; Wilga, Cheryl D.; Ramsay, Jason B.; Schlader, Robert; Didier, Dominique A.

    2013-01-01

    New CT scans of the spiral-tooth fossil, Helicoprion, resolve a longstanding mystery concerning the form and phylogeny of this ancient cartilaginous fish. We present the first three-dimensional images that show the tooth whorl occupying the entire mandibular arch, and which is supported along the midline of the lower jaw. Several characters of the upper jaw show that it articulated with the neurocranium in two places and that the hyomandibula was not part of the jaw suspension. These features identify Helicoprion as a member of the stem holocephalan group Euchondrocephali. Our reconstruction illustrates novel adaptations, such as lateral cartilage to buttress the tooth whorl, which accommodated the unusual trait of continuous addition and retention of teeth in a predatory chondrichthyan. Helicoprion exemplifies the climax of stem holocephalan diversification and body size in Late Palaeozoic seas, a role dominated today by sharks and rays. PMID:23445952

  16. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion.

    PubMed

    Tapanila, Leif; Pruitt, Jesse; Pradel, Alan; Wilga, Cheryl D; Ramsay, Jason B; Schlader, Robert; Didier, Dominique A

    2013-04-23

    New CT scans of the spiral-tooth fossil, Helicoprion, resolve a longstanding mystery concerning the form and phylogeny of this ancient cartilaginous fish. We present the first three-dimensional images that show the tooth whorl occupying the entire mandibular arch, and which is supported along the midline of the lower jaw. Several characters of the upper jaw show that it articulated with the neurocranium in two places and that the hyomandibula was not part of the jaw suspension. These features identify Helicoprion as a member of the stem holocephalan group Euchondrocephali. Our reconstruction illustrates novel adaptations, such as lateral cartilage to buttress the tooth whorl, which accommodated the unusual trait of continuous addition and retention of teeth in a predatory chondrichthyan. Helicoprion exemplifies the climax of stem holocephalan diversification and body size in Late Palaeozoic seas, a role dominated today by sharks and rays. PMID:23445952

  17. Diffraction of a finite-radius plane wave and a Gaussian beam by a helical axicon and a spiral phase plate

    NASA Astrophysics Data System (ADS)

    Kotlyar, Victor V.; Kovalev, Alexey A.; Skidanov, Roman V.; Moiseev, Oleg Yu.; Soifer, Victor A.

    2007-07-01

    We derive what we believe to be new analytical relations to describe the Fraunhofer diffraction of the finite-radius plane wave by a helical axicon (HA) and a spiral phase plate (SPP). The solutions are deduced in the form of a series of the Bessel functions for the HA and a finite sum of the Bessel functions for the SPP. The solution for the HA changes to that for the SPP if the axicon parameter is set equal to zero. We also derive what we believe to be new analytical relations to describe the Fresnel and Fraunhofer diffraction of the Gaussian beam by a HA are derived. The solutions are deduced in the form of a series of the hypergeometric functions. We have fabricated by photolithography a binary diffractive optical element (a HA with number n=10) able to produce in the focal plane of a spherical lens an optical vortex, which was then used to perform rotation of several polystyrene beads of diameter 5 μm.

  18. Using Helical CT to Predict Stone Fragility in Shock Wave Lithotripsy (SWL)

    SciTech Connect

    Williams, James C. Jr.; Zarse, Chad A.; Jackson, Molly E.; McAteer, James A.; Lingeman, James E.

    2007-04-05

    Great variability exists in the response of urinary stones to SWL, and this is true even for stones composed of the same mineral. Efforts have been made to predict stone fragility to shock waves using computed tomography (CT) patient images, but most work to date has focused on the use of stone CT number (i.e., Hounsfield units). This is an easy number to measure on a patient stone, but its value depends on a number of factors, including the relationship of the size of the stone to me resolution (i.e., the slicewidth) of the CT scan. Studies that have shown a relationship between stone CT number and failure in SWL are reviewed, and all are shown to suffer from error due to stone size, which was not accounted for in the use of Hounsfield unit values. Preliminary data are then presented for a study of calcium oxalate monohydrate (COM) stones, in which stone structure-rather than simple CT number values-is shown to correlate with fragility to shock waves. COM stones that were observed to have structure by micro CT (e.g., voids, apatite regions, unusual shapes) broke to completion in about half the number of shock waves required for COM stones that were observed to be homogeneous in structure by CT. This result suggests another direction for the use of CT in predicting success of SWL: the use of CT to view stone structure, rather than simply measuring stone CT number. Viewing stone structure by CT requires the use of different viewing windows than those typically used for examining patient scans, but much research to date indicates that stone structure can be observed in the clinical setting. Future clinical studies will need to be done to verify the relationship between stone structure observed by CT and stone fragility in SWL.

  19. A three-dimensional-weighted cone beam filtered backprojection (CB-FBP) algorithm for image reconstruction in volumetric CT-helical scanning.

    PubMed

    Tang, Xiangyang; Hsieh, Jiang; Nilsen, Roy A; Dutta, Sandeep; Samsonov, Dmitry; Hagiwara, Akira

    2006-02-21

    Based on the structure of the original helical FDK algorithm, a three-dimensional (3D)-weighted cone beam filtered backprojection (CB-FBP) algorithm is proposed for image reconstruction in volumetric CT under helical source trajectory. In addition to its dependence on view and fan angles, the 3D weighting utilizes the cone angle dependency of a ray to improve reconstruction accuracy. The 3D weighting is ray-dependent and the underlying mechanism is to give a favourable weight to the ray with the smaller cone angle out of a pair of conjugate rays but an unfavourable weight to the ray with the larger cone angle out of the conjugate ray pair. The proposed 3D-weighted helical CB-FBP reconstruction algorithm is implemented in the cone-parallel geometry that can improve noise uniformity and image generation speed significantly. Under the cone-parallel geometry, the filtering is naturally carried out along the tangential direction of the helical source trajectory. By exploring the 3D weighting's dependence on cone angle, the proposed helical 3D-weighted CB-FBP reconstruction algorithm can provide significantly improved reconstruction accuracy at moderate cone angle and high helical pitches. The 3D-weighted CB-FBP algorithm is experimentally evaluated by computer-simulated phantoms and phantoms scanned by a diagnostic volumetric CT system with a detector dimension of 64 x 0.625 mm over various helical pitches. The computer simulation study shows that the 3D weighting enables the proposed algorithm to reach reconstruction accuracy comparable to that of exact CB reconstruction algorithms, such as the Katsevich algorithm, under a moderate cone angle (4 degrees) and various helical pitches. Meanwhile, the experimental evaluation using the phantoms scanned by a volumetric CT system shows that the spatial resolution along the z-direction and noise characteristics of the proposed 3D-weighted helical CB-FBP reconstruction algorithm are maintained very well in comparison to the FDK

  20. A three-dimensional statistical approach to improved image quality for multislice helical CT.

    PubMed

    Thibault, Jean-Baptiste; Sauer, Ken D; Bouman, Charles A; Hsieh, Jiang

    2007-11-01

    Multislice helical computed tomography scanning offers the advantages of faster acquisition and wide organ coverage for routine clinical diagnostic purposes. However, image reconstruction is faced with the challenges of three-dimensional cone-beam geometry, data completeness issues, and low dosage. Of all available reconstruction methods, statistical iterative reconstruction (IR) techniques appear particularly promising since they provide the flexibility of accurate physical noise modeling and geometric system description. In this paper, we present the application of Bayesian iterative algorithms to real 3D multislice helical data to demonstrate significant image quality improvement over conventional techniques. We also introduce a novel prior distribution designed to provide flexibility in its parameters to fine-tune image quality. Specifically, enhanced image resolution and lower noise have been achieved, concurrently with the reduction of helical cone-beam artifacts, as demonstrated by phantom studies. Clinical results also illustrate the capabilities of the algorithm on real patient data. Although computational load remains a significant challenge for practical development, superior image quality combined with advancements in computing technology make IR techniques a legitimate candidate for future clinical applications. PMID:18072519

  1. Evaluation of exposure dose reduction in multislice CT coronary angiography (MS-CTA) with prospective ECG-gated helical scan

    NASA Astrophysics Data System (ADS)

    Ota, Takamasa; Tsuyuki, Masaharu; Okumura, Miwa; Sano, Tomonari; Kondo, Takeshi; Takase, Shinichi

    2008-03-01

    A novel low-dose ECG-gated helical scan method to investigate coronary artery diseases was developed. This method uses a high pitch for scanning (based on the patient's heart rate) and X-rays are generated only during the optimal cardiac phases. The dose reduction was obtained using a two-level approach: 1) To use a 64-slice CT scanner (Aquilion, Toshiba, Otawara, Tochigi, Japan) with a scan speed of 0.35 s/rot. to helically scan the heart at a high pitch based on the patient's heart rate. By changing the pitch from the conventional 0.175 to 0.271 for a heart rate of 60 bpm, the exposure dose was reduced to 65%. 2) To employ tube current gating that predicts the timing of optimal cardiac phases from the previous cardiac cycle and generates X-rays only during the required cardiac phases. The combination of high speed scanning with a high pitch and appropriate X-ray generation only in the cardiac phases from 60% to 90% allows the exposure dose to be reduced to 5.6 mSv for patients with a heart rate lower than 65 bpm. This is a dose reduction of approximately 70% compared to the conventional scanning method recommended by the manufacturer when segmental reconstruction is considered. This low-dose protocol seamlessly allows for wide scan ranges (e.g., aortic dissection) with the benefits of ECG-gated helical scanning: smooth continuity for longitudinal direction and utilization of data from all cardiac cycles.

  2. Impact of the z-flying focal spot on resolution and artifact behavior for a 64-slice spiral CT scanner.

    PubMed

    Kyriakou, Yiannis; Kachelriess, Marc; Knaup, Michael; Krause, Jens U; Kalender, Willi A

    2006-06-01

    The effect of the z-flying focal spot (zFFS) technology was evaluated by simulations and measurements with respect to resolution and artifact behavior for a 64-slice spiral cone-beam computed tomography (CT) scanner. The zFFS alternates between two z-positions of the X-ray focal spot, acquiring two slices per detector row, which results in double sampling in the z-direction. We implemented a modified reconstruction that is able to obtain images as they would be without zFFS. A delta phantom equipped with a thin gold disc was used to measure slice sensitivity profiles (SSP), and a high-contrast bar phantom was used to quantify the resolution in the x/z-plane with and without zFFS. The zFFS decreases the full width at half maximum (FWHM) of the SSPs by a factor of about 1.4. The double z-sampling allows the separation of 0.4 mm bars in the z-direction compared with 0.6 mm in the case without zFFS. The zFFS effectively reduces windmill artifacts in the reconstructed images while maintaining the transverse resolution, even at the largest available pitch value of 1.5. PMID:16541229

  3. SU-E-I-93: Improved Imaging Quality for Multislice Helical CT Via Sparsity Regularized Iterative Image Reconstruction Method Based On Tensor Framelet

    SciTech Connect

    Nam, H; Guo, M; Lee, K; Li, R; Xing, L; Gao, H

    2014-06-01

    Purpose: Inspired by compressive sensing, sparsity regularized iterative reconstruction method has been extensively studied. However, its utility pertinent to multislice helical 4D CT for radiotherapy with respect to imaging quality, dose, and time has not been thoroughly addressed. As the beginning of such an investigation, this work carries out the initial comparison of reconstructed imaging quality between sparsity regularized iterative method and analytic method through static phantom studies using a state-of-art 128-channel multi-slice Siemens helical CT scanner. Methods: In our iterative method, tensor framelet (TF) is chosen as the regularization method for its superior performance from total variation regularization in terms of reduced piecewise-constant artifacts and improved imaging quality that has been demonstrated in our prior work. On the other hand, X-ray transforms and its adjoints are computed on-the-fly through GPU implementation using our previous developed fast parallel algorithms with O(1) complexity per computing thread. For comparison, both FDK (approximate analytic method) and Katsevich algorithm (exact analytic method) are used for multislice helical CT image reconstruction. Results: The phantom experimental data with different imaging doses were acquired using a state-of-art 128-channel multi-slice Siemens helical CT scanner. The reconstructed image quality was compared between TF-based iterative method, FDK and Katsevich algorithm with the quantitative analysis for characterizing signal-to-noise ratio, image contrast, and spatial resolution of high-contrast and low-contrast objects. Conclusion: The experimental results suggest that our tensor framelet regularized iterative reconstruction algorithm improves the helical CT imaging quality from FDK and Katsevich algorithm for static experimental phantom studies that have been performed.

  4. A projection-driven pre-correction technique for iterative reconstruction of helical cone-beam cardiac CT images

    NASA Astrophysics Data System (ADS)

    Do, Synho; Liang, Zhuangli; Karl, William Clem; Brady, Thomas; Pien, Homer

    2008-03-01

    Modern CT systems have advanced at a dramatic rate. Algebraic iterative reconstruction techniques have shown promising and desirable image characteristics, but are seldom used due to their high computational cost for complete reconstruction of large volumetric datasets. In many cases, however, interest in high resolution reconstructions is restricted to smaller regions of interest within the complete volume. In this paper we present an implementation of a simple and practical method to produce iterative reconstructions of reduced-sized ROI from 3D helical tomographic data. We use the observation that the conventional filtered back-projection reconstruction is generally of high quality throughout the entire volume to predict the contributions to ROI-related projections arising from volumes outside the ROI. These predictions are then used to pre-correct the data to produce a tomographic inversion problem of substantially reduced size and memory demands. Our work expands on those of other researchers who have observed similar potential computational gains by exploiting FBP results. We demonstrate our approach using cardiac CT cone-beam imaging, illustrating our results with both ex vivo and in vivo multi-cycle EKG-gated examples.

  5. Fuzzy Clustering Applied to ROI Detection in Helical Thoracic CT Scans with a New Proposal and Variants.

    PubMed

    Castro, Alfonso; Rey, Alberto; Boveda, Carmen; Arcay, Bernardino; Sanjurjo, Pedro

    2016-01-01

    The detection of pulmonary nodules is one of the most studied problems in the field of medical image analysis due to the great difficulty in the early detection of such nodules and their social impact. The traditional approach involves the development of a multistage CAD system capable of informing the radiologist of the presence or absence of nodules. One stage in such systems is the detection of ROI (regions of interest) that may be nodules in order to reduce the space of the problem. This paper evaluates fuzzy clustering algorithms that employ different classification strategies to achieve this goal. After characterising these algorithms, the authors propose a new algorithm and different variations to improve the results obtained initially. Finally it is shown as the most recent developments in fuzzy clustering are able to detect regions that may be nodules in CT studies. The algorithms were evaluated using helical thoracic CT scans obtained from the database of the LIDC (Lung Image Database Consortium). PMID:27517049

  6. Fuzzy Clustering Applied to ROI Detection in Helical Thoracic CT Scans with a New Proposal and Variants

    PubMed Central

    Castro, Alfonso; Boveda, Carmen; Arcay, Bernardino; Sanjurjo, Pedro

    2016-01-01

    The detection of pulmonary nodules is one of the most studied problems in the field of medical image analysis due to the great difficulty in the early detection of such nodules and their social impact. The traditional approach involves the development of a multistage CAD system capable of informing the radiologist of the presence or absence of nodules. One stage in such systems is the detection of ROI (regions of interest) that may be nodules in order to reduce the space of the problem. This paper evaluates fuzzy clustering algorithms that employ different classification strategies to achieve this goal. After characterising these algorithms, the authors propose a new algorithm and different variations to improve the results obtained initially. Finally it is shown as the most recent developments in fuzzy clustering are able to detect regions that may be nodules in CT studies. The algorithms were evaluated using helical thoracic CT scans obtained from the database of the LIDC (Lung Image Database Consortium). PMID:27517049

  7. TH-C-18A-11: Investigating the Minimum Scan Parameters Required to Generate Free-Breathing Fast-Helical CT Scans Without Motion-Artifacts

    SciTech Connect

    Thomas, D; Neylon, J; Dou, T; Jani, S; Lamb, J; Low, D; Tan, J

    2014-06-15

    Purpose: A recently proposed 4D-CT protocol uses deformable registration of free-breathing fast-helical CT scans to generate a breathing motion model. In order to allow accurate registration, free-breathing images are required to be free of doubling-artifacts, which arise when tissue motion is greater than scan speed. This work identifies the minimum scanner parameters required to successfully generate free-breathing fast-helical scans without doubling-artifacts. Methods: 10 patients were imaged under free breathing conditions 25 times in alternating directions with a 64-slice CT scanner using a low dose fast helical protocol. A high temporal resolution (0.1s) 4D-CT was generated using a patient specific motion model and patient breathing waveforms, and used as the input for a scanner simulation. Forward projections were calculated using helical cone-beam geometry (800 projections per rotation) and a GPU accelerated reconstruction algorithm was implemented. Various CT scanner detector widths and rotation times were simulated, and verified using a motion phantom. Doubling-artifacts were quantified in patient images using structural similarity maps to determine the similarity between axial slices. Results: Increasing amounts of doubling-artifacts were observed with increasing rotation times > 0.2s for 16×1mm slice scan geometry. No significant increase in doubling artifacts was observed for 64×1mm slice scan geometry up to 1.0s rotation time although blurring artifacts were observed >0.6s. Using a 16×1mm slice scan geometry, a rotation time of less than 0.3s (53mm/s scan speed) would be required to produce images of similar quality to a 64×1mm slice scan geometry. Conclusion: The current generation of 16 slice CT scanners, which are present in most Radiation Oncology departments, are not capable of generating free-breathing sorting-artifact-free images in the majority of patients. The next generation of CT scanners should be capable of at least 53mm/s scan speed

  8. Helical CT Angiography of Abdominal Aortic Aneurysms Treated with Suprarenal Stent Grafting: A Pictorial Essay

    SciTech Connect

    Sun Zhonghua

    2003-06-15

    The endovascular repair of abdominal aorticaneurysm (AAA) with stent grafts is rapidly becoming an important alternative to open repair. Suprarenal stent grafting, recently modified from conventional infrarenal stent grafting, is a technique for the purpose of treating patients with inappropriate aneurysm necks.Unlike open repair, the success of endoluminal repair cannot be ascertained by means of direct examination and thus relies on imaging results. The use of conventional angiography for arterial imaging has become less dominant, while helical computed tomography angiography(CTA) has become the imaging modality of choice for both preoperative assessment and postoperative followup after treatment with stent graft implants. There is an increasing likelihood that radiologists will become more and more involved in the procedure of aortic stent grafting and in giving the radiological report on these patients treated with stent grafts. It is necessary for radiologists to be familiar with the imaging findings, including common and uncommon appearances following aortic stent grafting. The purpose of this pictorial essay is to describe and present normal and abnormal imaging appearances following aortic stent grafting based on helical CTA.

  9. NOTE: Optimization of megavoltage CT scan registration settings for thoracic cases on helical tomotherapy

    NASA Astrophysics Data System (ADS)

    Woodford, Curtis; Yartsev, Slav; Van Dyk, Jake

    2007-08-01

    This study aims to investigate the settings that provide optimum registration accuracy when registering megavoltage CT (MVCT) studies acquired on tomotherapy with planning kilovoltage CT (kVCT) studies of patients with lung cancer. For each experiment, the systematic difference between the actual and planned positions of the thorax phantom was determined by setting the phantom up at the planning isocenter, generating and registering an MVCT study. The phantom was translated by 5 or 10 mm, MVCT scanned, and registration was performed again. A root-mean-square equation that calculated the residual error of the registration based on the known shift and systematic difference was used to assess the accuracy of the registration process. The phantom study results for 18 combinations of different MVCT/kVCT registration options are presented and compared to clinical registration data from 17 lung cancer patients. MVCT studies acquired with coarse (6 mm), normal (4 mm) and fine (2 mm) slice spacings could all be registered with similar residual errors. No specific combination of resolution and fusion selection technique resulted in a lower residual error. A scan length of 6 cm with any slice spacing registered with the full image fusion selection technique and fine resolution will result in a low residual error most of the time. On average, large corrections made manually by clinicians to the automatic registration values are infrequent. Small manual corrections within the residual error averages of the registration process occur, but their impact on the average patient position is small. Registrations using the full image fusion selection technique and fine resolution of 6 cm MVCT scans with coarse slices have a low residual error, and this strategy can be clinically used for lung cancer patients treated on tomotherapy. Automatic registration values are accurate on average, and a quick verification on a sagittal MVCT slice should be enough to detect registration outliers.

  10. Patient radiation dose in prospectively gated axial CT coronary angiography and retrospectively gated helical technique with a 320-detector row CT scanner

    SciTech Connect

    Seguchi, Shigenobu; Aoyama, Takahiko; Koyama, Shuji; Fujii, Keisuke; Yamauchi-Kawaura, Chiyo

    2010-11-15

    Purpose: The aim of this study was to evaluate radiation dose to patients undergoing computed tomography coronary angiography (CTCA) for prospectively gated axial (PGA) technique and retrospectively gated helical (RGH) technique. Methods: Radiation doses were measured for a 320-detector row CT scanner (Toshiba Aquilion ONE) using small sized silicon-photodiode dosimeters, which were implanted at various tissue and organ positions within an anthropomorphic phantom for a standard Japanese adult male. Output signals from photodiode dosimeters were read out on a personal computer, from which organ and effective doses were computed according to guidelines published in the International Commission on Radiological Protection Publication 103. Results: Organs that received high doses were breast, followed by lung, esophagus, and liver. Breast doses obtained with PGA technique and a phase window width of 16% at a simulated heart rate of 60 beats per minute were 13 mGy compared to 53 mGy with RGH technique using electrocardiographically dependent dose modulation at the same phase window width as that in PGA technique. Effective doses obtained in this case were 4.7 and 20 mSv for the PGA and RGH techniques, respectively. Conversion factors of dose length product to the effective dose in PGA and RGH were 0.022 and 0.025 mSv mGy{sup -1} cm{sup -1} with a scan length of 140 mm. Conclusions: CTCA performed with PGA technique provided a substantial effective dose reduction, i.e., 70%-76%, compared to RGH technique using the dose modulation at the same phase windows as those in PGA technique. Though radiation doses in CTCA with RGH technique were the same level as, or some higher than, those in conventional coronary angiography (CCA), the use of PGA technique reduced organ and effective doses to levels less than CCA except for breast dose.

  11. Dual-source spiral CT with pitch up to 3.2 and 75 ms temporal resolution: Image reconstruction and assessment of image quality

    SciTech Connect

    Flohr, Thomas G.; Leng Shuai; Yu Lifeng; Allmendinger, Thomas; Bruder, Herbert; Petersilka, Martin; Eusemann, Christian D.; Stierstorfer, Karl; Schmidt, Bernhard; McCollough, Cynthia H.

    2009-12-15

    Purpose: To present the theory for image reconstruction of a high-pitch, high-temporal-resolution spiral scan mode for dual-source CT (DSCT) and evaluate its image quality and dose. Methods: With the use of two x-ray sources and two data acquisition systems, spiral CT exams having a nominal temporal resolution per image of up to one-quarter of the gantry rotation time can be acquired using pitch values up to 3.2. The scan field of view (SFOV) for this mode, however, is limited to the SFOV of the second detector as a maximum, depending on the pitch. Spatial and low contrast resolution, image uniformity and noise, CT number accuracy and linearity, and radiation dose were assessed using the ACR CT accreditation phantom, a 30 cm diameter cylindrical water phantom or a 32 cm diameter cylindrical PMMA CTDI phantom. Slice sensitivity profiles (SSPs) were measured for different nominal slice thicknesses, and an anthropomorphic phantom was used to assess image artifacts. Results were compared between single-source scans at pitch=1.0 and dual-source scans at pitch=3.2. In addition, image quality and temporal resolution of an ECG-triggered version of the DSCT high-pitch spiral scan mode were evaluated with a moving coronary artery phantom, and radiation dose was assessed in comparison with other existing cardiac scan techniques. Results: No significant differences in quantitative measures of image quality were found between single-source scans at pitch=1.0 and dual-source scans at pitch=3.2 for spatial and low contrast resolution, CT number accuracy and linearity, SSPs, image uniformity, and noise. The pitch value (1.6{<=}pitch{<=}3.2) had only a minor impact on radiation dose and image noise when the effective tube current time product (mA s/pitch) was kept constant. However, while not severe, artifacts were found to be more prevalent for the dual-source pitch=3.2 scan mode when structures varied markedly along the z axis, particularly for head scans. Images of the moving

  12. The role of the central L- or D-Pro residue on structure and mode of action of a cell-selective alpha-helical IsCT-derived antimicrobial peptide.

    PubMed

    Lim, Shin Saeng; Kim, Yangmee; Park, Yoonkyung; Kim, Jae Il; Park, Il-Seon; Hahm, Kyung-Soo; Shin, Song Yub

    2005-09-01

    IsCT-P (ILKKIWKPIKKLF-NH2) is a novel alpha-helical antimicrobial peptide with bacterial cell selectivity designed from a scorpion-derived peptide IsCT. To investigate the role of L- or D-Pro kink on the structure and the mode of action of a short alpha-helical antimicrobial peptide with bacterial cell selectivity, we synthesized IsCT-p, in which D-Pro is substituted for L-Pro8 of IsCT-P. CD spectra revealed that IsCT-P adopted a typical alpha-helical structure in various membrane-mimicking conditions, whereas IsCT-p showed a random structure. This result indicated that D-Pro in the central position of a short alpha-helical peptide provides more remarkable structural flexibility than L-Pro. Despite its higher antibacterial activity, IsCT-p was much less effective at inducing dye leakage in the negatively charged liposome mimicking bacterial membrane and induced no or little membrane potential depolarization of Staphylococcus aureus. Confocal laser scanning microscopy showed that IsCT-p penetrated the bacterial cell membrane and accumulated in the cytoplasm, whereas IsCT-P remained outside or on the cell membrane. These results suggested that the major target of IsCT-P and IsCT-p is the bacterial membranes and intracellular components, respectively. Collectively, our results demonstrated that the central D-Pro kink in alpha-helical antimicrobial peptides plays an important role in penetrating bacterial membrane as well as bacterial cell selectivity. PMID:16040002

  13. TH-E-17A-02: High-Pitch and Sparse-View Helical 4D CT Via Iterative Image Reconstruction Method Based On Tensor Framelet

    SciTech Connect

    Guo, M; Nam, H; Li, R; Xing, L; Gao, H

    2014-06-15

    Purpose: 4D CT is routinely performed during radiation therapy treatment planning of thoracic and abdominal cancers. Compared with the cine mode, the helical mode is advantageous in temporal resolution. However, a low pitch (∼0.1) for 4D CT imaging is often required instead of the standard pitch (∼1) for static imaging, since standard image reconstruction based on analytic method requires the low-pitch scanning in order to satisfy the data sufficient condition when reconstructing each temporal frame individually. In comparison, the flexible iterative method enables the reconstruction of all temporal frames simultaneously, so that the image similarity among frames can be utilized to possibly perform high-pitch and sparse-view helical 4D CT imaging. The purpose of this work is to investigate such an exciting possibility for faster imaging with lower dose. Methods: A key for highpitch and sparse-view helical 4D CT imaging is the simultaneous reconstruction of all temporal frames using the prior that temporal frames are continuous along the temporal direction. In this work, such a prior is regularized through the sparsity transform based on spatiotemporal tensor framelet (TF) as a multilevel and high-order extension of total variation transform. Moreover, GPU-based fast parallel computing of X-ray transform and its adjoint together with split Bregman method is utilized for solving the 4D image reconstruction problem efficiently and accurately. Results: The simulation studies based on 4D NCAT phantoms were performed with various pitches (i.e., 0.1, 0.2, 0.5, and 1) and sparse views (i.e., 400 views per rotation instead of standard >2000 views per rotation), using 3D iterative individual reconstruction method based on 3D TF and 4D iterative simultaneous reconstruction method based on 4D TF respectively. Conclusion: The proposed TF-based simultaneous 4D image reconstruction method enables high-pitch and sparse-view helical 4D CT with lower dose and faster speed.

  14. A Monte Carlo-based method to estimate radiation dose from spiral CT: from phantom testing to patient-specific models

    NASA Astrophysics Data System (ADS)

    Jarry, G.; DeMarco, J. J.; Beifuss, U.; Cagnon, C. H.; McNitt-Gray, M. F.

    2003-08-01

    The purpose of this work is to develop and test a method to estimate the relative and absolute absorbed radiation dose from axial and spiral CT scans using a Monte Carlo approach. Initial testing was done in phantoms and preliminary results were obtained from a standard mathematical anthropomorphic model (MIRD V) and voxelized patient data. To accomplish this we have modified a general purpose Monte Carlo transport code (MCNP4B) to simulate the CT x-ray source and movement, and then to calculate absorbed radiation dose in desired objects. The movement of the source in either axial or spiral modes was modelled explicitly while the CT system components were modelled using published information about x-ray spectra as well as information provided by the manufacturer. Simulations were performed for single axial scans using the head and body computed tomography dose index (CTDI) polymethylmethacrylate phantoms at both central and peripheral positions for all available beam energies and slice thicknesses. For comparison, corresponding physical measurements of CTDI in phantom were made with an ion chamber. To obtain absolute dose values, simulations and measurements were performed in air at the scanner isocentre for each beam energy. To extend the verification, the CT scanner model was applied to the MIRD V model and compared with published results using similar technical factors. After verification of the model, the generalized source was simulated and applied to voxelized models of patient anatomy. The simulated and measured absolute dose data in phantom agreed to within 2% for the head phantom and within 4% for the body phantom at 120 and 140 kVp; this extends to 8% for the head and 9% for the body phantom across all available beam energies and positions. For the head phantom, the simulated and measured absolute dose data agree to within 2% across all slice thicknesses at 120 kVp. Our results in the MIRD phantom agree within 11% of all the different organ dose values

  15. 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.

  16. Evaluation of Distal Femoral Rotational Alignment with Spiral CT Scan before Total Knee Arthroplasty (A Study in Iranian population)

    PubMed Central

    Jabalameli, Mahmoud; Moradi, Amin; Bagherifard, Abolfazl; Radi, Mehran; Mokhtari, Tahmineh

    2016-01-01

    Background: Evaluating the landmarks for rotation of the distal femur is a challenge for orthopedic surgeons. Although the posterior femoral condyle axis is a good landmark for surgeons, the surgical transepicondylar axis may be a better option with the help of preoperative CT scanning. The purpose of this study was to ascertain relationships among the axes’ guiding distal femur rotational alignment in preoperative CT scans of Iranian patients who were candidates for total knee arthroplasty and the effects of age, gender, and knee alignment on these relationships. Methods: One hundred and eight cases who were admitted to two university hospitals for total knee arthroplasty were included in this study. The rotation of the distal femur was evaluated using single axial CT images through the femoral epicondyle. Four lines were drawn digitally in this view: anatomical and surgical transepicondylar axes, posterior condylar axis and the Whiteside anteroposterior line. The alignment of the extremity was evaluated in the standing alignment view. Then the angles were measured along these lines and their relationship was evaluated. Results: The mean angle between the anatomical transepicondylar axis and posterior condylar axis and between the surgical transepicondylar axis and posterior condylar axis were 5.9 ± 1.6 degrees and 1.6±1.7 degrees respectively. The mean angle between the Whiteside’s anteroposterior line and the line perpendicular to the posterior condylar axis was 3.7±2.1 degrees. Significant differences existed between the two genders in these relationships. No significant correlation between the age of patients and angles of the distal femur was detected. The anatomical surgical transepicondylar axis was in 4.3 degrees external rotation in relation to the surgical transepicondylar axis. Conclusion: Preoperative CT scanning can help accurately determine rotational landmarks of the distal femur. If one of the reference axes cannot be determined, other

  17. Utility of Megavoltage Fan-Beam CT for Treatment Planning in a Head-And-Neck Cancer Patient with Extensive Dental Fillings Undergoing Helical Tomotherapy

    SciTech Connect

    Yang, Claus; Liu Tianxiao; Jennelle, Richard L.; Ryu, Janice K.; Vijayakumar, Srinivasan; Purdy, James A.; Chen, Allen M.

    2010-07-01

    The purpose of this study was to demonstrate the potential utility of megavoltage fan-beam computed tomography (MV-FBCT) for treatment planning in a patient undergoing helical tomotherapy for nasopharyngeal carcinoma in the presence of extensive dental artifact. A 28-year-old female with locally advanced nasopharyngeal carcinoma presented for radiation therapy. Due to the extensiveness of the dental artifact present in the oral cavity kV-CT scan acquired at simulation, which made treatment planning impossible on tomotherapy planning system, MV-FBCT imaging was obtained using the HI-ART tomotherapy treatment machine, with the patient in the treatment position, and this information was registered with her original kV-CT scan for the purposes of structure delineation, dose calculation, and treatment planning. To validate the feasibility of the MV-FBCT-generated treatment plan, an electron density CT phantom (model 465, Gammex Inc., Middleton, WI) was scanned using MV-FBCT to obtain CT number to density table. Additionally, both a 'cheese' phantom (which came with the tomotherapy treatment machine) with 2 inserted ion chambers and a generic phantom called Quasar phantom (Modus Medical Devices Inc., London, ON, Canada) with one inserted chamber were used to confirm dosimetric accuracy. The MV-FBCT could be used to clearly visualize anatomy in the region of the dental artifact and provide sufficient soft-tissue contrast to assist in the delineation of normal tissue structures and fat planes. With the elimination of the dental artifact, the MV-FBCT images allowed more accurate dose calculation by the tomotherapy system. It was confirmed that the phantom material density was determined correctly by the tomotherapy MV-FBCT number to density table. The ion chamber measurements agreed with the calculations from the MV-FBCT generated phantom plan within 2%. MV-FBCT may be useful in radiation treatment planning for nasopharyngeal cancer patients in the setting of extensive

  18. Utility of megavoltage fan-beam CT for treatment planning in a head-and-neck cancer patient with extensive dental fillings undergoing helical tomotherapy.

    PubMed

    Yang, Claus; Liu, Tianxiao; Jennelle, Richard L; Ryu, Janice K; Vijayakumar, Srinivasan; Purdy, James A; Chen, Allen M

    2010-01-01

    The purpose of this study was to demonstrate the potential utility of megavoltage fan-beam computed tomography (MV-FBCT) for treatment planning in a patient undergoing helical tomotherapy for nasopharyngeal carcinoma in the presence of extensive dental artifact. A 28-year-old female with locally advanced nasopharyngeal carcinoma presented for radiation therapy. Due to the extensiveness of the dental artifact present in the oral cavity kV-CT scan acquired at simulation, which made treatment planning impossible on tomotherapy planning system, MV-FBCT imaging was obtained using the HI-ART tomotherapy treatment machine, with the patient in the treatment position, and this information was registered with her original kV-CT scan for the purposes of structure delineation, dose calculation, and treatment planning. To validate the feasibility of the MV-FBCT-generated treatment plan, an electron density CT phantom (model 465, Gammex Inc., Middleton, WI) was scanned using MV-FBCT to obtain CT number to density table. Additionally, both a "cheese" phantom (which came with the tomotherapy treatment machine) with 2 inserted ion chambers and a generic phantom called Quasar phantom (Modus Medical Devices Inc., London, ON, Canada) with one inserted chamber were used to confirm dosimetric accuracy. The MV-FBCT could be used to clearly visualize anatomy in the region of the dental artifact and provide sufficient soft-tissue contrast to assist in the delineation of normal tissue structures and fat planes. With the elimination of the dental artifact, the MV-FBCT images allowed more accurate dose calculation by the tomotherapy system. It was confirmed that the phantom material density was determined correctly by the tomotherapy MV-FBCT number to density table. The ion chamber measurements agreed with the calculations from the MV-FBCT generated phantom plan within 2%. MV-FBCT may be useful in radiation treatment planning for nasopharyngeal cancer patients in the setting of extensive

  19. CT scan

    MedlinePlus

    ... that slides into the center of the CT scanner. Once you are inside the scanner, the machine's x-ray beam rotates around you. Modern spiral scanners can perform the exam without stopping. A computer ...

  20. Spirality: Spiral arm pitch angle measurement

    NASA Astrophysics Data System (ADS)

    Shields, Douglas W.; Boe, Benjamin; Pfountz, Casey; Davis, Benjamin L.; Hartley, Matthew; Pour Imani, Hamed; Slade, Zac; Kennefick, Daniel; Kennefick, Julia

    2015-12-01

    Spirality measures spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Written in MATLAB, the code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined.

  1. Dose calculation software for helical tomotherapy, utilizing patient CT data to calculate an independent three-dimensional dose cube

    SciTech Connect

    Thomas, Simon J.; Eyre, Katie R.; Tudor, G. Samuel J.; Fairfoul, Jamie

    2012-01-15

    Purpose: Treatment plans for the TomoTherapy unit are produced with a planning system that is integral to the unit. The authors have produced an independent dose calculation system, to enable plans to be recalculated in three dimensions, using the patient's CT data. Methods: Software has been written using MATLAB. The DICOM-RT plan object is used to determine the treatment parameters used, including the treatment sinogram. Each projection of the sinogram is segmented and used to calculate dose at multiple calculation points in a three-dimensional grid using tables of measured beam data. A fast ray-trace algorithm is used to determine effective depth for each projection angle at each calculation point. Calculations were performed on a standard desktop personal computer, with a 2.6 GHz Pentium, running Windows XP. Results: The time to perform a calculation, for 3375 points averaged 1 min 23 s for prostate plans and 3 min 40 s for head and neck plans. The mean dose within the 50% isodose was calculated and compared with the predictions of the TomoTherapy planning system. When the modified CT (which includes the TomoTherapy couch) was used, the mean difference for ten prostate patients, was -0.4% (range -0.9% to +0.3%). With the original CT (which included the CT couch), the mean difference was -1.0% (range -1.7% to 0.0%). The number of points agreeing with a gamma 3%/3 mm averaged 99.2% with the modified CT, 96.3% with the original CT. For ten head and neck patients, for the modified and original CT, respectively, the mean difference was +1.1% (range -0.4% to +3.1%) and 1.1% (range -0.4% to +3.0%) with 94.4% and 95.4% passing a gamma 4%/4 mm. The ability of the program to detect a variety of simulated errors has been tested. Conclusions: By using the patient's CT data, the independent dose calculation performs checks that are not performed by a measurement in a cylindrical phantom. This enables it to be used either as an additional check or to replace phantom

  2. CT angiography of neonates and infants: comparison of radiation dose and image quality of target mode prospectively ECG-gated 320-MDCT and ungated helical 64-MDCT.

    PubMed

    Jadhav, Siddharth P; Golriz, Farahnaz; Atweh, Lamya A; Zhang, Wei; Krishnamurthy, Rajesh

    2015-02-01

    OBJECTIVE. The purpose of this study was to evaluate the radiation dose and image quality of target mode prospectively ECG-gated volumetric CT angiography (CTA) performed with a 320-MDCT scanner compared with the radiation dose and image quality of ungated helical CTA performed with a 64-MDCT scanner. MATERIALS AND METHODS. An experience with CTA for cardiovascular indications in neonates and infants 0-6 months old was retrospectively assessed. Radiation doses and quantitative and qualitative image quality scores of 28 CTA examinations performed with a 320-MDCT scanner and volumetric target mode prospective ECG gating plus iterative reconstruction (target mode) were compared with the doses and scores of 28 CTA examinations performed with a 64-MDCT scanner and ungated helical scanning plus filtered back projection reconstruction (ungated mode). All target mode studies were performed during free breathing. Seven ungated CTA examinations (25%) were performed with general endotracheal anesthesia. The findings of 17 preoperative CTA examinations performed in target mode were also compared with surgical reports for evaluation of diagnostic accuracy. RESULTS. All studies performed with target mode technique were diagnostic for the main clinical indication. Effective doses were significantly lower in the target mode group (0.51 ± 0.19 mSv) compared with the ungated mode group (4.8 ± 1.4 mSv) (p < 0.0001). Quantitative analysis revealed no statistically significant difference between the two groups with respect to signal-to-noise ratio (of pulmonary artery and aorta) and contrast-to-noise ratio. Subjective image quality was significantly better with target mode than with ungated mode (p < 0.0001). CONCLUSION. Target mode prospectively ECG-gated volumetric scanning with iterative reconstruction performed with a 320-MDCT scanner has several benefits in cardiovascular imaging of neonates and infants, including low radiation dose, improved image quality, high diagnostic

  3. Automatic registration of megavoltage to kilovoltage CT images in helical tomotherapy: an evaluation of the setup verification process for the special case of a rigid head phantom.

    PubMed

    Boswell, Sarah; Tomé, Wolfgang; Jeraj, Robert; Jaradat, Hazim; Mackie, T Rock

    2006-11-01

    Precise daily target localization is necessary to achieve highly conformal radiation delivery. In helical tomotherapy, setup verification may be accomplished just prior to delivering each fraction by acquiring a megavoltage CT scan of the patient in the treatment position. This daily image set may be manually or automatically registered to the image set on which the treatment plan was calculated, in order to determine any needed adjustments. The system was tested by acquiring 104 MVCT scans of an anthropomorphic head phantom to which translational displacements had been introduced with respect to the planning image set. Registration results were compared against an independent, optically guided positioning system. The total experimental uncertainty was within approximately 1 mm. Although the registration of phantom images is not fully analogous to the registration of patient images, this study confirms that the system is capable of phantom localization with sub-voxel accuracy. In seven registration problems considered, expert human observers were able to perform manual registrations with comparable or inferior accuracy to automatic registration by mutual information. The time to compute an automatic registration is considerably shorter than the time required for manual registration. However, human evaluation of automatic results is necessary in order to identify occasional outliers, and to ensure that the registration is clinically acceptable, especially in the case of deformable patient anatomy. PMID:17153418

  4. Automatic registration of megavoltage to kilovoltage CT images in helical tomotherapy: An evaluation of the setup verification process for the special case of a rigid head phantom

    SciTech Connect

    Boswell, Sarah; Tome, Wolfgang; Jeraj, Robert; Jaradat, Hazim; Mackie, T. Rock

    2006-11-15

    Precise daily target localization is necessary to achieve highly conformal radiation delivery. In helical tomotherapy, setup verification may be accomplished just prior to delivering each fraction by acquiring a megavoltage CT scan of the patient in the treatment position. This daily image set may be manually or automatically registered to the image set on which the treatment plan was calculated, in order to determine any needed adjustments. The system was tested by acquiring 104 MVCT scans of an anthropomorphic head phantom to which translational displacements had been introduced with respect to the planning image set. Registration results were compared against an independent, optically guided positioning system. The total experimental uncertainty was within approximately 1 mm. Although the registration of phantom images is not fully analogous to the registration of patient images, this study confirms that the system is capable of phantom localization with sub-voxel accuracy. In seven registration problems considered, expert human observers were able to perform manual registrations with comparable or inferior accuracy to automatic registration by mutual information. The time to compute an automatic registration is considerably shorter than the time required for manual registration. However, human evaluation of automatic results is necessary in order to identify occasional outliers, and to ensure that the registration is clinically acceptable, especially in the case of deformable patient anatomy.

  5. Multiferroics with spiral spin orders.

    PubMed

    Tokura, Yoshinori; Seki, Shinichiro

    2010-04-12

    Cross correlation between magnetism and electricity in a solid can host magnetoelectric effects, such as magnetic (electric) induction of polarization (magnetization). A key to attain the gigantic magnetoelectric response is to find the efficient magnetism-electricity coupling mechanisms. Among those, recently the emergence of spontaneous (ferroelectric) polarization in the insulating helimagnet or spiral-spin structure was unraveled, as mediated by the spin-exchange and spin-orbit interactions. The sign of the polarization depends on the helicity (spin rotation sense), while the polarization direction itself depends on further details of the mechanism and the underlying lattice symmetry. Here, we describe some prototypical examples of the spiral-spin multiferroics, which enable some unconventional magnetoelectric control such as the magnetic-field-induced change of the polarization direction and magnitude as well as the electric-field-induced change of the spin helicity and magnetic domain. PMID:20496385

  6. Automated detection of pulmonary nodules from whole lung helical CT scans: performance comparison for isolated and attached nodules

    NASA Astrophysics Data System (ADS)

    Enquobahrie, Andinet A.; Reeves, Anthony P.; Yankelevitz, David F.; Henschke, Claudia I.

    2004-05-01

    The objective of this research is to evaluate and compare the performance of our automated detection algorithm on isolated and attached nodules in whole lung CT scans. Isolated nodules are surrounded by the lung parenchyma with no attachment to large solid structures such as the chest wall or mediastinum surface, while attached nodules are adjacent to these structures. The detection algorithm involves three major stages. First, the region of the image space where pulmonary nodules are to be found is identified. This involves segmenting the lung region and generating the pleural surface. In the second stage, which is the hypothesis generation stage, nodule candidate locations are identified and their sizes are estimated. The nodule candidates are successively refined in the third stage a sequence of filters of increasing complexity. The algorithm was tested on a dataset containing 250 low-dose whole lung CT scans with 2.5mm slice thickness. A scan is composed of images covering the whole lung region for a single person. The dataset was partitioned into 200 and 50 scans for training and testing the algorithm. Only solid nodules were considered in this study. Experienced chest radiologists identified a total of 447 solid nodules. 345 and 102 of the nodules were from the training and testing datasets respectively. 126(28.2%) of the nodules in the dataset were attached nodules. The detection performance was then evaluated separately for isolated and attached nodule types considering different size ranges. For nodules 3mm and larger, the algorithm achieved a sensitivity of 97.8% with 2.0 false positives (FPs) per scan and 95.7% with 19.3 FPs per scan for isolated and attached nodules respectively. For nodules 4mm and larger, a sensitivity of 96.6% with 1.5 FP per scan and a 100% sensitivity with 13 FPs per scan were obtained for isolated and attached nodule types respectively. The results show that our algorithm detects isolated and attached nodules with comparable

  7. Frequency spirals

    NASA Astrophysics Data System (ADS)

    Ottino-Löffler, Bertrand; Strogatz, Steven H.

    2016-09-01

    We study the dynamics of coupled phase oscillators on a two-dimensional Kuramoto lattice with periodic boundary conditions. For coupling strengths just below the transition to global phase-locking, we find localized spatiotemporal patterns that we call "frequency spirals." These patterns cannot be seen under time averaging; they become visible only when we examine the spatial variation of the oscillators' instantaneous frequencies, where they manifest themselves as two-armed rotating spirals. In the more familiar phase representation, they appear as wobbly periodic patterns surrounding a phase vortex. Unlike the stationary phase vortices seen in magnetic spin systems, or the rotating spiral waves seen in reaction-diffusion systems, frequency spirals librate: the phases of the oscillators surrounding the central vortex move forward and then backward, executing a periodic motion with zero winding number. We construct the simplest frequency spiral and characterize its properties using analytical and numerical methods. Simulations show that frequency spirals in large lattices behave much like this simple prototype.

  8. A Novel Fast Helical 4D-CT Acquisition Technique to Generate Low-Noise Sorting Artifact–Free Images at User-Selected Breathing Phases

    SciTech Connect

    Thomas, David; Lamb, James; White, Benjamin; Jani, Shyam; Gaudio, Sergio; Lee, Percy; Ruan, Dan; McNitt-Gray, Michael; Low, Daniel

    2014-05-01

    Purpose: To develop a novel 4-dimensional computed tomography (4D-CT) technique that exploits standard fast helical acquisition, a simultaneous breathing surrogate measurement, deformable image registration, and a breathing motion model to remove sorting artifacts. Methods and Materials: Ten patients were imaged under free-breathing conditions 25 successive times in alternating directions with a 64-slice CT scanner using a low-dose fast helical protocol. An abdominal bellows was used as a breathing surrogate. Deformable registration was used to register the first image (defined as the reference image) to the subsequent 24 segmented images. Voxel-specific motion model parameters were determined using a breathing motion model. The tissue locations predicted by the motion model in the 25 images were compared against the deformably registered tissue locations, allowing a model prediction error to be evaluated. A low-noise image was created by averaging the 25 images deformed to the first image geometry, reducing statistical image noise by a factor of 5. The motion model was used to deform the low-noise reference image to any user-selected breathing phase. A voxel-specific correction was applied to correct the Hounsfield units for lung parenchyma density as a function of lung air filling. Results: Images produced using the model at user-selected breathing phases did not suffer from sorting artifacts common to conventional 4D-CT protocols. The mean prediction error across all patients between the breathing motion model predictions and the measured lung tissue positions was determined to be 1.19 ± 0.37 mm. Conclusions: The proposed technique can be used as a clinical 4D-CT technique. It is robust in the presence of irregular breathing and allows the entire imaging dose to contribute to the resulting image quality, providing sorting artifact–free images at a patient dose similar to or less than current 4D-CT techniques.

  9. Bioinspired helical microswimmers based on vascular plants.

    PubMed

    Gao, Wei; Feng, Xiaomiao; Pei, Allen; Kane, Christopher R; Tam, Ryan; Hennessy, Camille; Wang, Joseph

    2014-01-01

    Plant-based bioinspired magnetically propelled helical microswimmers are described. The helical microstructures are derived from spiral water-conducting vessels of different plants, harnessing the intrinsic biological structures of nature. Geometric variables of the spiral vessels, such as the helix diameter and pitch, can be controlled by mechanical stretching for the precise fabrication and consistent performance of helical microswimmers. Xylem vessels of a wide variety of different plants have been evaluated for the consistency and reproducibility of their helical parameters. Sequential deposition of thin Ti and Ni layers directly on the spiral vessels, followed by dicing, leads to an extremely simple and cost-efficient mass-production of functional helical microswimmers. The resulting plant-based magnetic microswimmers display efficient propulsion, with a speed of over 250 μm/s, as well as powerful locomotion in biological media such as human serum. The influence of actuation frequencies on the swimming velocity is investigated. Such use of plant vessels results in significant savings in the processing costs and provides an extremely simple, cost-effective fabrication route for the large-scale production of helical magnetic swimmers. PMID:24283342

  10. Helical equilibrium

    SciTech Connect

    Yoshikawa, S.

    1981-08-01

    A straight, helical plasma equilibrium equation is solved numerically for a plasma with a helical magnetic axis. As is expected, by a suitable choice of the plasma boundary, the vacuum configuration is made line ..integral.. dl/B stable. As the plasma pressure increases, the line ..integral.. dl/B criterion will improve (again as expected). There is apparently no limit on the plasma ..beta.. from the equilibrium consideration. Thus helical-axis stellarator ..beta.. will presumably be limited by MHD stability ..beta.., and not by equilibrium ..beta...

  11. High-pitch spiral CT with 3D reformation: an alternative choice for imaging vascular anomalies with affluent blood flow in the head and neck of infants and children

    PubMed Central

    Li, H-O; Huo, R; Xu, G-Q; Duan, Y-H; Nie, P; Ji, X-P; Cheng, Z-P; Xu, Z-D

    2015-01-01

    Objective: To evaluate the feasibility of high-pitch spiral CT in imaging vascular anomalies (VAs) with affluent blood flow in the head and neck of infants and children. Methods: For patients with suspected VAs and affluent blood flow pre-detected by ultrasound, CT was performed with high-pitch mode, individualized low-dose scan protocol and three-dimensional (3D) reformation. A five-point scale was used for image quality evaluation. Diagnostic accuracy was calculated with clinical diagnosis with/without pathological results as the reference standard. Radiation exposure and single-phase scan time were recorded. Treatment strategies were formulated based on CT images and results and were monitored through follow-up results. Results: 20 lesions were identified in 15 patients (median age of 11 months). The mean score of image quality was 4.13 ± 0.74. 7 patients (7/15, 46.67%) were diagnosed with haemangiomas, 6 patients (6/15, 40%) were diagnosed with venous malformations and 2 patients (2/15, 13.33%) were diagnosed with arteriovenous malformations. The average effective radiation doses of a single phase and of the total procedure were 0.27 ± 0.08 and 0.86 ± 0.21 mSv. The average scanning time of a single phase was 0.46 ± 0.09 s. After treatment, 13 patients (13/15, 86.67%) achieved excellent results, and 2 patients (2/15, 13.33%) showed good results in follow-up visits. Conclusion: High-pitch spiral CT with an individualized low-dose scan protocol and 3D reformation is an effective modality for imaging VAs with affluent blood flow in the head and neck of infants and children when vascular details are needed and ultrasound and MRI could not provide the complete information. Advances in knowledge: This study proposes an alternative modality for imaging VAs with affluent blood flow. PMID:26055504

  12. Helical logic

    NASA Astrophysics Data System (ADS)

    Merkle, Ralph C.; Drexler, K. Eric

    1996-12-01

    Helical logic is a theoretical proposal for a future computing technology using the presence or absence of individual electrons (or holes) to encode 1s and 0s. The electrons are constrained to move along helical paths, driven by a rotating electric field in which the entire circuit is immersed. The electric field remains roughly orthogonal to the major axis of the helix and confines each charge carrier to a fraction of a turn of a single helical loop, moving it like water in an Archimedean screw. Each loop could in principle hold an independent carrier, permitting high information density. One computationally universal logic operation involves two helices, one of which splits into two `descendant' helices. At the point of divergence, differences in the electrostatic potential resulting from the presence or absence of a carrier in the adjacent helix controls the direction taken by a carrier in the splitting helix. The reverse of this sequence can be used to merge two initially distinct helical paths into a single outgoing helical path without forcing a dissipative transition. Because these operations are both logically and thermodynamically reversible, energy dissipation can be reduced to extremely low levels. This is the first proposal known to the authors that combines thermodynamic reversibility with the use of single charge carriers. It is important to note that this proposal permits a single electron to switch another single electron, and does not require that many electrons be used to switch one electron. The energy dissipated per logic operation can very likely be reduced to less than 0957-4484/7/4/004/img5 at a temperature of 1 K and a speed of 10 GHz, though further analysis is required to confirm this. Irreversible operations, when required, can be easily implemented and should have a dissipation approaching the fundamental limit of 0957-4484/7/4/004/img6.

  13. Thoracic spine CT scan

    MedlinePlus

    ... that slides into the center of the CT scanner. Once you are inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam without stopping.) A computer ...

  14. Flexible helical-axis stellarator

    DOEpatents

    Harris, Jeffrey H.; Hender, Timothy C.; Carreras, Benjamin A.; Cantrell, Jack L.; Morris, Robert N.

    1988-01-01

    An 1=1 helical winding which spirals about a conventional planar, circular central conductor of a helical-axis stellarator adds a significant degree of flexibility by making it possible to control the rotational transform profile and shear of the magnetic fields confining the plasma in a helical-axis stellarator. The toroidal central conductor links a plurality of toroidal field coils which are separately disposed to follow a helical path around the central conductor in phase with the helical path of the 1=1 winding. This coil configuration produces bean-shaped magnetic flux surfaces which rotate around the central circular conductor in the same manner as the toroidal field generating coils. The additional 1=1 winding provides flexible control of the magnetic field generated by the central conductor to prevent the formation of low-order resonances in the rotational transform profile which can produce break-up of the equilibrium magnetic surfaces. Further, this additional winding can deepen the magnetic well which together with the flexible control provides increased stability.

  15. Quantum spirals

    NASA Astrophysics Data System (ADS)

    Yoshida, Z.; Mahajan, S. M.

    2016-02-01

    Quantum systems often exhibit fundamental incapability to entertain vortex. The Meissner effect, a complete expulsion of the magnetic field (the electromagnetic vorticity), for instance, is taken to be the defining attribute of the superconducting state. Superfluidity is another, close-parallel example; fluid vorticity can reside only on topological defects with a limited (quantized) amount. Recent developments in the Bose-Einstein condensates produced by particle traps further emphasize this characteristic. We show that the challenge of imparting vorticity to a quantum fluid can be met through a nonlinear mechanism operating in a hot fluid corresponding to a thermally modified Pauli-Schrödinger spinor field. The thermal baroclinic effect is represented by a nonlinear, non-Hermitian Hamiltonian, which, in conjunction with spin vorticity, leads to new interesting quantum states; a spiral solution is explicitly worked out in a simple field-free model.

  16. Spiral tectonics

    NASA Astrophysics Data System (ADS)

    Hassan Asadiyan, Mohammad

    2014-05-01

    Spiral Tectonics (ST) is a new window to global tectonics introduced as alternative model for Plate Tectonics (PT). ST based upon Dahw(rolling) and Tahw(spreading) dynamics. Analogues to electric and magnetic components in the electromagnetic theory we could consider Dahw and Tahw as components of geodynamics, when one component increases the other decreases and vice versa. They are changed to each other during geological history. D-component represents continental crust and T-component represents oceanic crust. D and T are two arm of spiral-cell. T-arm 180 degree lags behind D-arm so named Retard-arm with respect to D or Forward-arm. It seems primary cell injected several billions years ago from Earth's center therefore the Earth's core was built up first then mantel and finally the crust was build up. Crust building initiate from Arabia (Mecca). As the universe extended gravitation wave swirled the earth fractaly along cycloid path from big to small scale. In global scale (order-0) ST collect continents in one side and abandoned Pacific Ocean in the other side. Recent researches also show two mantels upwelling in opposite side of the Earth: one under Africa (tectonic pose) and the other under Pacific Ocean (tectonic tail). In higher order (order-1) ST build up Africa in one side and S.America in the other side therefore left Atlantic Ocean meandered in between. In order-n e.g. Khoor Musa and Bandar-Deylam bay are seen meandered easterly in the Iranian part but Khoor Abdullah and Kuwait bay meandered westerly in the Arabian part, they are distributed symmetrically with respect to axis of Persian Gulf(PG), these two are fractal components of easterly Caspian-wing and westerly Black Sea-wing which split up from Anatoly. Caspian Sea and Black Sea make two legs of Y-like structure, this shape completely fitted with GPS-velocity map which start from PG and split up in the Catastrophic Point(Anatoly). We could consider PG as remnants of Ancient Ocean which spent up

  17. Rational diagnosis of pulmonary embolism (RADIA PE) in symptomatic outpatients with suspected PE: an improved strategy to exclude or diagnose venous thromboembolism by the sequential use of a clinical model, rapid ELISA D-dimer test, perfusion lung scan, ultrasonography, spiral CT, and pulmonary angiography.

    PubMed

    Michiels, J J

    1998-01-01

    A prospective management decision analysis for the exclusion and diagnosis of pulmonary embolism (PE) based on pre-test clinical probability (PCP) estimation for PE, a rapid ELISA D-dimer test, perfusion lungscan (P-scan), CUS, spiral CT, and pulmonary angiography is proposed. The modified PCP model for PE of Wells et al. allows reasonably accurate classification of patients with no, low, moderate, and high probability for PE. The combined rational use of the evidence-based noninvasive imaging techniques P-scan, CUS, and spiral CT with the rapid ELISA D-dimer test and PCP will reduce the need for invasive pulmonary angiography to perhaps 10 to 15% of patients, who initially presented with suspected PE. A Rational Diagnosis of Pulmonary Embolism (RADIA PE) model is proposed for testing in a large multicenter study of patients with suspected PE. PMID:9763360

  18. Helical filaments

    NASA Astrophysics Data System (ADS)

    Barbieri, Nicholas; Hosseinimakarem, Zahra; Lim, Khan; Durand, Magali; Baudelet, Matthieu; Johnson, Eric; Richardson, Martin

    2014-06-01

    The shaping of laser-induced filamenting plasma channels into helical structures by guiding the process with a non-diffracting beam is demonstrated. This was achieved using a Bessel beam superposition to control the phase of an ultrafast laser beam possessing intensities sufficient to induce Kerr effect driven non-linear self-focusing. Several experimental methods were used to characterize the resulting beams and confirm the observed structures are laser air filaments.

  19. Helical differential X-ray phase-contrast computed tomography.

    PubMed

    Fu, Jian; Willner, Marian; Chen, Liyuan; Tan, Renbo; Achterhold, Klaus; Bech, Martin; Herzen, Julia; Kunka, Danays; Mohr, Juergen; Pfeiffer, Franz

    2014-05-01

    We report on the first experimental results of helical differential phase-contrast computed tomography (helical DPC-CT) with a laboratory X-ray tube source and a Talbot-Lau grating interferometer. The results experimentally verify the feasibility of helical data acquisition and reconstruction in phase-contrast imaging, in analogy to its use in clinical CT systems. This allows fast and continuous volumetric scans for long objects with lengths exceeding the dimension of the detector. Since helical CT revolutionized the field of medical CT several years ago, we anticipate that this method will bring the same significant impact on the future medical and industrial applications of X-ray DPC-CT. PMID:24518822

  20. Deceptively Simple Harmonic Motion: A Mass on a Spiral Spring.

    ERIC Educational Resources Information Center

    McDonald, F. Alan

    1980-01-01

    Discusses the oscillatory motion of a mass on a spiral (nonhelical) spring, and calculates the lowest eigenfrequency and the associated effective spring mass for a range of values of the attached mass. Analytic and numerical comparisons are made to the helical spring problem. (HM)

  1. High temporal resolution for multislice helical computed tomography.

    PubMed

    Taguchi, K; Anno, H

    2000-05-01

    Multislice helical computed tomography (CT) substantially reduces scanning time. However, the temporal resolution of individual images is still insufficient for imaging rapidly moving organs such as the heart and adjacent pulmonary vessels. It may, in some cases, be worse than with current single-slice helical CT. The purpose of this study is to describe a novel image reconstruction algorithm to improve temporal resolution in multislice helical CT, and to evaluate its performance against existing algorithms. The proposed image reconstruction algorithm uses helical interpolation followed by data weighting based on the acquisition time. The temporal resolution, the longitudinal (z-axis) spatial resolution, the image noise, and the in-plane image artifacts created by a moving phantom were compared with those from the basic multislice helical reconstruction (helical filter interpolation, HFI) algorithm and the basic single-slice helical reconstruction algorithm (180 degrees linear interpolation, 180LI) using computer simulations. Computer simulation results were verified with CT examinations of the heart and lung vasculature using a 0.5 second multislice scanner. The temporal resolution of HFI algorithm varies from 0.28 and 0.86 s, depending on helical pitch. The proposed method improves the resolution to a constant value of 0.29 s, independent of pitch, allowing moving objects to be imaged with reduced blurring or motion artifacts. The spatial (z) resolution was slightly worse than with the HFI algorithm; the image noise was worse than with the HFI algorithm but was comparable to axial (step-and-shoot) CT. The proposed method provided sharp images of the moving objects, portraying the anatomy accurately. The proposed algorithm for multislice helical CT allowed us to obtain CT images with high temporal resolution. It may improve the image quality of clinical cardiac, lung, and vascular CT imaging. PMID:10841388

  2. [Clinical role of spiral tomodensitometry in pulmonary disorders].

    PubMed

    Scillia, P; Sy, M; Chaminade, L; Gevenois, P A

    1995-04-01

    Spiral CT of the lungs has taken the place of conventional CT in most indications. Until now, some specific indications, concerning the detection of lung nodules, the detection of central pulmonary thromboembolism and the description of the angioarchitecture of pulmonary arteriovenous malformations have been reported. This paper provides an overview of the clinical utility of this new technique. PMID:7601819

  3. Transcatheter Arterial Embolization Therapy for a Hypoplastic Pelvic Kidney with a Single Vaginal Ectopic Ureter to Control Incontinence: The Usefulness of Three-Dimensional CT Angiography Using Multidetector-Row Helical CT

    SciTech Connect

    Kudoh, Kouichi Kadota, Masataka; Nakayama, Yoshiharu; Imuta, Masanori; Yasuda, Tsuyoshi; Yamashita, Yasuyuki; Inadome, Akito; Yoshida, Masaki; Ueda, Shouichi

    2003-09-15

    A girl with continuous urinary incontinence was successfully treated by angiographic embolization of a hypoplastic pelvic kidney with a single unilateral vaginal ectopic opening of the ureter. For this intervention, CT angiography was useful for detecting the corresponding renal artery of the hypoplastic kidney.

  4. Helical localized wave solutions of the scalar wave equation.

    PubMed

    Overfelt, P L

    2001-08-01

    A right-handed helical nonorthogonal coordinate system is used to determine helical localized wave solutions of the homogeneous scalar wave equation. Introducing the characteristic variables in the helical system, i.e., u = zeta - ct and v = zeta + ct, where zeta is the coordinate along the helical axis, we can use the bidirectional traveling plane wave representation and obtain sets of elementary bidirectional helical solutions to the wave equation. Not only are these sets bidirectional, i.e., based on a product of plane waves, but they may also be broken up into right-handed and left-handed solutions. The elementary helical solutions may in turn be used to create general superpositions, both Fourier and bidirectional, from which new solutions to the wave equation may be synthesized. These new solutions, based on the helical bidirectional superposition, are members of the class of localized waves. Examples of these new solutions are a helical fundamental Gaussian focus wave mode, a helical Bessel-Gauss pulse, and a helical acoustic directed energy pulse train. Some of these solutions have the interesting feature that their shape and localization properties depend not only on the wave number governing propagation along the longitudinal axis but also on the normalized helical pitch. PMID:11488494

  5. Improving electricity production in tubular microbial fuel cells through optimizing the anolyte flow with spiral spacers.

    PubMed

    Zhang, Fei; Ge, Zheng; Grimaud, Julien; Hurst, Jim; He, Zhen

    2013-04-01

    The use of spiral spacers to create a helical flow for improving electricity generation in microbial fuel cells (MFCs) was investigated in both laboratory and on-site tests. The lab tests found that the MFC with the spiral spacers produced more electricity than the one without the spiral spacers at different recirculation rates or organic loading rates, likely due to the improved transport/distribution of ions and electron mediators instead of the substrates because the organic removal efficiency was not obviously affected by the presence of the spiral spacers. The energy production in the MFC with the spiral spacers reached 0.071 or 0.073 kWh/kg COD in either vertical or horizontal installment. The examination of the MFCs installed in an aeration tank of a municipal wastewater treatment plant confirmed the advantage of using the spiral spacers. Those results demonstrate that spiral spacers could be an effective approach to improve energy production in MFCs. PMID:23500582

  6. Supracolloidal helices from soft Janus particles by tuning the particle softness

    NASA Astrophysics Data System (ADS)

    Zou, Qing-Zhi; Li, Zhan-Wei; Lu, Zhong-Yuan; Sun, Zhao-Yan

    2016-02-01

    Because of the unique architectures and promising potential applications of biomimetic helical structures in biotechnology and nanotechnology, the design and fabrication of these structures by experimentally realizable anisotropic colloidal particles remain one of the most challenging tasks in materials science. Here we show how soft Janus particles self-assemble into supracolloidal helices with distinctive structural characteristics, including single helices, double helices, and Bernal spirals, by appropriately tuning the particle softness. We further examine the kinetic mechanisms governing the formation of different helical structures by using particle-based dynamics simulations. Our results provide a new way for experimentally fabricating structure-controllable supracolloidal helices solely from the self-assembly of soft Janus particles.Because of the unique architectures and promising potential applications of biomimetic helical structures in biotechnology and nanotechnology, the design and fabrication of these structures by experimentally realizable anisotropic colloidal particles remain one of the most challenging tasks in materials science. Here we show how soft Janus particles self-assemble into supracolloidal helices with distinctive structural characteristics, including single helices, double helices, and Bernal spirals, by appropriately tuning the particle softness. We further examine the kinetic mechanisms governing the formation of different helical structures by using particle-based dynamics simulations. Our results provide a new way for experimentally fabricating structure-controllable supracolloidal helices solely from the self-assembly of soft Janus particles. Electronic supplementary information (ESI) available. See DOI: 10.1039/C5NR07011B

  7. Multiarmed Spirals in Excitable Media

    NASA Astrophysics Data System (ADS)

    Vasiev, Bakthier; Siegert, Florian; Weijer, Cornelis

    1997-03-01

    Numerical studies of the properties of multiarmed spirals show that they can form spontaneously in low excitability media. The maximum number of arms in a multiarmed spiral is proportional to the ratio of the single spiral period to the refractoriness of the medium. Multiarmed spirals are formed due to attraction of single spirals if these spirals rotate in the same direction and their tips are less than one wavelength apart, i.e., a spiral broken not far from its tip can evolve into a 2-armed spiral. We propose this mechanism to be responsible for the formation of multiarmed spirals in mounds of the slime mold Dictyostelium discoideum.

  8. Electromechanics of graphene spirals

    SciTech Connect

    Korhonen, Topi; Koskinen, Pekka

    2014-12-15

    Among the most fascinating nanostructure morphologies are spirals, hybrids of somewhat obscure topology and dimensionality with technologically attractive properties. Here, we investigate mechanical and electromechanical properties of graphene spirals upon elongation by using density-functional tight-binding, continuum elasticity theory, and classical force field molecular dynamics. It turns out that electronic properties are governed by interlayer interactions as opposed to strain effects. The structural behavior is governed by van der Waals interaction: in its absence spirals unfold with equidistant layer spacings, ripple formation at spiral perimeter, and steadily increasing axial force; in its presence, on the contrary, spirals unfold via smooth local peeling, complex geometries, and nearly constant axial force. These electromechanical trends ought to provide useful guidelines not only for additional theoretical investigations but also for forthcoming experiments on graphene spirals.

  9. Spiral Flow Separator

    NASA Technical Reports Server (NTRS)

    Robertson, Glen A.

    1993-01-01

    Proposed liquid-separating device relies on centrifugal force in liquid/liquid or liquid/solid mixture in spiral path. Operates in continuous flow at relatively high rates. Spiral tubes joined in sequence, with outlet tubes connected to joints. Cross-sectional areas of successive spiral tubes decreases by cross-sectional areas of outlet tubes. Centrifugal force pushes denser particles or liquids to outer edge of spiral, where removed from flow. Principle exploited to separate solids from wastewater, oil from fresh or salt water, or contaminants from salt water before evaporation. Also used to extract such valuable materials as precious metals from slurries.

  10. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi

    The magnetic-field characteristics in spiral galaxies are investigated, with emphasis on the Milky Way. The dynamo theory is considered, and axisymmetric spiral (ASS) and bisymmetric spiral (BSS) magnetic fields are analyzed. Toroidal and poloidal magnetic fields are discussed.

  11. Thermal deformation of helical gears

    NASA Astrophysics Data System (ADS)

    Zhang, Yong; Fei, Ye-tai; Liu, Shan-lin

    2010-08-01

    The analytical equation for the thermal field of a helical gear under normal working condition in a stable thermal field is established using mathematical physics, and the thermal deformation of the gear can be computed using this equation. The variations of gear geometric parameters, such as radial dimension, tooth depth, spiral angle, pressure angle, flank clearance and etc., are investigated with respect to the temperature change. According to the analytical and computational results obtained using the equation, the thermal deformation of the gear is strongly dependent on the choice of parameters, which is also confirmed using simulation software (COMSOL Multiphysic software). This is significant for the improvement of the rotation precision and working efficiency of screw gears.

  12. Superluminous Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Ogle, Patrick M.; Lanz, Lauranne; Nader, Cyril; Helou, George

    2016-02-01

    We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity Lr = 8-14L* (4.3-7.5 × 1044 erg s-1). These super spiral galaxies are also giant and massive, with diameter D = 57-134 kpc and stellar mass Mstars = 0.3-3.4 × 1011M⊙. We find 53 super spirals out of a complete sample of 1616 SDSS galaxies with redshift z < 0.3 and Lr > 8L*. The closest example is found at z = 0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and Wide-field Infrared Survey Explorer colors are consistent with normal star-forming spirals on the blue sequence. However, the extreme masses and rapid SFRs of 5-65 M⊙ yr-1 place super spirals in a sparsely populated region of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a diverse range of environments, from isolation to cluster centers. We find four super spiral galaxy systems that are late-stage major mergers—a possible clue to their formation. We suggest that super spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become massive lenticular galaxies after they are cut off from their gas supply and their disks fade.

  13. Spiral model of pitch

    NASA Astrophysics Data System (ADS)

    Miller, James D.

    2003-10-01

    A spiral model of pitch interrelates tone chroma, tone height, equal temperament scales, and a cochlear map. Donkin suggested in 1870 that the pitch of tones could be well represented by an equiangular spiral. More recently, the cylindrical helix has been popular for representing tone chroma and tone height. Here it is shown that tone chroma, tone height, and cochlear position can be conveniently related to tone frequency via a planar spiral. For this ``equal-temperament spiral,'' (ET Spiral) tone chroma is conceived as a circular array with semitones at 30° intervals. The frequency of sound on the cent scale (re 16.351 Hz) is represented by the radius of the spiral defined by r=(1200/2π)θr, where θr is in radians. By these definitions, one revolution represents one octave, 1200 cents, 30° represents a semitone, the radius relates θ to cents in accordance with equal temperament (ET) tuning, and the arclength of the spiral matches the mapping of sound frequency to the basilar membrane. Thus, the ET Spiral gives tone chroma as θ, tone height as the cent scale, and the cochlear map as the arclength. The possible implications and directions for further work are discussed.

  14. Spiral fluid separator

    NASA Technical Reports Server (NTRS)

    Robertson, Glen A. (Inventor)

    1993-01-01

    A fluid separator for separating particulate matter such as contaminates is provided which includes a series of spiral tubes of progressively decreasing cross sectional area connected in series. Each tube has an outlet on the outer curvature of the spiral. As fluid spirals down a tube, centrifugal force acts to force the heavier particulate matter to the outer wall of the tube, where it exits through the outlet. The remaining, and now cleaner, fluid reaches the next tube, which is smaller in cross sectional area, where the process is repeated. The fluid which comes out the final tube is diminished of particulate matter.

  15. Spiral concentrators recover fine coal

    SciTech Connect

    Fiscor, S.

    2005-12-15

    Compound spirals offer better performance in a more efficient configuration. Prep plant operators in the US are increasingly opting to use spiral concentrators. They are easy to install, operate and maintain but their downfall is low capacity. The article describes spirals available from PrepTech/Multotec, Krebs Engineers and Roche MT. It reports on research on spiral concentrator technology. 1 ref., 4 figs.

  16. High assurance SPIRAL

    NASA Astrophysics Data System (ADS)

    Franchetti, Franz; Sandryhaila, Aliaksei; Johnson, Jeremy R.

    2014-06-01

    In this paper we introduce High Assurance SPIRAL to solve the last mile problem for the synthesis of high assurance implementations of controllers for vehicular systems that are executed in today's and future embedded and high performance embedded system processors. High Assurance SPIRAL is a scalable methodology to translate a high level specification of a high assurance controller into a highly resource-efficient, platform-adapted, verified control software implementation for a given platform in a language like C or C++. High Assurance SPIRAL proves that the implementation is equivalent to the specification written in the control engineer's domain language. Our approach scales to problems involving floating-point calculations and provides highly optimized synthesized code. It is possible to estimate the available headroom to enable assurance/performance trade-offs under real-time constraints, and enables the synthesis of multiple implementation variants to make attacks harder. At the core of High Assurance SPIRAL is the Hybrid Control Operator Language (HCOL) that leverages advanced mathematical constructs expressing the controller specification to provide high quality translation capabilities. Combined with a verified/certified compiler, High Assurance SPIRAL provides a comprehensive complete solution to the efficient synthesis of verifiable high assurance controllers. We demonstrate High Assurance SPIRALs capability by co-synthesizing proofs and implementations for attack detection and sensor spoofing algorithms and deploy the code as ROS nodes on the Landshark unmanned ground vehicle and on a Synthetic Car in a real-time simulator.

  17. Spiraling Fermi arcs in Weyl materials

    NASA Astrophysics Data System (ADS)

    Li, Songci; Andreev, Anton

    In Weyl materials the valence and conduction electron bands touch at an even number of isolated points in the Brillouin zone. In the vicinity of these points the electron dispersion is linear and may be described by the massless Dirac equation. This results in nontrivial topology of Berry connection curvature. One of its consequences is the existence of peculiar surface electron states whose Fermi surfaces form arcs connecting projections of the Weyl points onto the surface plane. Band bending near the boundary of the crystal also produces surface states. We show that in Weyl materials band bending near the crystal surface gives rise to spiral structure of energy surfaces of arc states. The corresponding Fermi surface has the shape of a spiral that winds about the projection of the Weyl point onto the surface plane. The direction of the winding is determined by the helicity of the Weyl point and the sign of the band bending potential. For close valleys arc state morphology may be understood in terms of avoided crossing of oppositely winding spirals. This work is supported by the U.S. Department of Energy Office of Science, Basic Energy Sciences under Award Number DE-FG02-07ER46452.

  18. Magnetic stripes and skyrmions with helicity reversals.

    PubMed

    Yu, Xiuzhen; Mostovoy, Maxim; Tokunaga, Yusuke; Zhang, Weizhu; Kimoto, Koji; Matsui, Yoshio; Kaneko, Yoshio; Nagaosa, Naoto; Tokura, Yoshinori

    2012-06-01

    It was recently realized that topological spin textures do not merely have mathematical beauty but can also give rise to unique functionalities of magnetic materials. An example is the skyrmion--a nano-sized bundle of noncoplanar spins--that by virtue of its nontrivial topology acts as a flux of magnetic field on spin-polarized electrons. Lorentz transmission electron microscopy recently emerged as a powerful tool for direct visualization of skyrmions in noncentrosymmetric helimagnets. Topologically, skyrmions are equivalent to magnetic bubbles (cylindrical domains) in ferromagnetic thin films, which were extensively explored in the 1970s for data storage applications. In this study we use Lorentz microscopy to image magnetic domain patterns in the prototypical magnetic oxide-M-type hexaferrite with a hint of scandium. Surprisingly, we find that the magnetic bubbles and stripes in the hexaferrite have a much more complex structure than the skyrmions and spirals in helimagnets, which we associate with the new degree of freedom--helicity (or vector spin chirality) describing the direction of spin rotation across the domain walls. We observe numerous random reversals of helicity in the stripe domain state. Random helicity of cylindrical domain walls coexists with the positional order of magnetic bubbles in a triangular lattice. Most unexpectedly, we observe regular helicity reversals inside skyrmions with an unusual multiple-ring structure. PMID:22615354

  19. Voronoi spiral tilings

    NASA Astrophysics Data System (ADS)

    Yamagishi, Yoshikazu; Sushida, Takamichi; Hizume, Akio

    2015-04-01

    The parameter set of Voronoi spiral tilings gives a dual of van Iterson's bifurcation diagram for phyllotactic spirals. We study the Voronoi tilings for the Bernoulli spiral site sets, as the simplest spirals in the centric representation with similarity symmetry. Their parameter set is composed of a family of real algebraic curves in the complex plane, with the Farey sequence structure. This naturally extends to the parameter set for multiple tilings, i.e., the tilings of the covering spaces of the punctured plane. We show the denseness of the parameters z = reiθ for quadrilateral Voronoi spiral multiple tilings. The techniques of dynamical systems are applied to the group of similarity symmetry. The parastichy numbers and the distortion of the Voronoi regions depend on the rational approximations of θ/2π. We consider the limit set of the shapes of the quadrilateral tiles by taking the limit as r → 1, with θ fixed. If θ/2π is a quadratic irrational number, then the limit set is a finite set of rectangles. In particular, if θ/2π is linearly equivalent to the golden section, then the limit is the square.

  20. Helicity in superfluids

    NASA Astrophysics Data System (ADS)

    Kedia, Hridesh; Kleckner, Dustin; Proment, Davide; Irvine, William T. M.

    Ideal fluid flow conserves a special quantity known as helicity, in addition to energy, momentum and angular momentum. Helicity can be understood as a measure of the knottedness of vortex lines of the flow, providing an important geometric tool to study diverse physical systems such as turbulent fluids and plasmas. Since superfluids flow without resistance just like ideal (Euler) fluids, a natural question arises: Is there an extra conserved quantity akin to helicity in superfluids? We address the question of a ''superfluid helicity'' theoretically and examine its consequences in numerical simulations.

  1. Spiral MR myocardial tagging.

    PubMed

    Ryf, Salome; Kissinger, Kraig V; Spiegel, Marcus A; Börnert, Peter; Manning, Warren J; Boesiger, Peter; Stuber, Matthias

    2004-02-01

    In the present study, complementary spatial modulation of magnetization (CSPAMM) myocardial tagging was extended with an interleaved spiral imaging sequence. The use of a spiral sequence enables the acquisition of grid-tagged images with a tagline distance as low as 4 mm in a single breath-hold. Alternatively, a high temporal resolution of 77 frames per second was obtained with 8-mm grid spacing. Ten healthy adult subjects were studied. With this new approach, high-quality images can be obtained and the tags persist throughout the entire cardiac cycle. PMID:14755646

  2. Imaging study on the optic canal using sixty four-slice spiral computed tomography

    PubMed Central

    Jiang, Peng-Fei; Dai, Xiu-Yu; Lv, Yongbin; Liu, Shaoyi; Mu, Xiao-Yan

    2015-01-01

    Background: Rapid advances in multislice computed tomography (MSCT) technology facilitate accurate clinical imaging. The newly developed 64-slice CT increases temporal and spatial resolution efficiently. Purpose: The purpose of this study is to evaluate the application of 64 slice spiral computed tomography (CT) on the imaging of the normal optics canal. Methods and materials: 100 healthy adults were investigated using 64 slice spiral CT. The optics canal was scanned, reconstructed and examined. Results: Among the four walls of the optic canal, the medial wall is the longest one. The upper wall and outer wall are inferior to the medial wall while the inferior wall is the shortest one. All the data accomplished by the 64 slice CT was consistent with the results of previous reports using other methods. Conclusion: The results suggested that the 64 slice spiral CT could be a valuable and accurate method for measuring the length of optics canal walls. PMID:26885062

  3. Dose management in CT facility

    PubMed Central

    Tsapaki, V; Rehani, M

    2007-01-01

    Computed Tomography (CT) examinations have rapidly increased in number over the last few years due to recent advances such as the spiral, multidetector-row, CT fluoroscopy and Positron Emission Tomography (PET)-CT technology. This has resulted in a large increase in collective radiation dose as reported by many international organisations. It is also stated that frequently, image quality in CT exceeds the level required for confident diagnosis. This inevitably results in patient radiation doses that are higher than actually required, as also stressed by the US Food and Drug Administration (FDA) regarding the CT exposure of paediatric and small adult patients. However, the wide range in exposure parameters reported, as well as the different CT applications reveal the difficulty in standardising CT procedures. The purpose of this paper is to review the basic CT principles, outline the recent technological advances and their impact in patient radiation dose and finally suggest methods of radiation dose optimisation. PMID:21614279

  4. Spiral Waves in Accretion Disks

    NASA Astrophysics Data System (ADS)

    Harlaftis, Emilios

    A review with the most characteristic spiral waves in accretion disks of cataclysmic variables will be presented. Recent work on experiments targeting the detection of spiral waves from time lapse movies of real disks and the study of permanent spiral waves will be discussed. The relevance of spiral waves with other systems such as star-planet X-ray binaries and Algols will be reviewed.

  5. Electric Control of Spin Helicity in a Magnetic Ferroelectric

    SciTech Connect

    Yamasaki, Y.; Goto, T.; Sagayama, H.; Matsuura, M.; Hirota, K.; Arima, T.; Tokura, Y.

    2007-04-06

    Magnetic ferroelectrics or multiferroics, which are currently extensively explored, may provide a good arena to realize a novel magnetoelectric function. Here we demonstrate the genuine electric control of the spiral magnetic structure in one such magnetic ferroelectric, TbMnO{sub 3}. A spin-polarized neutron scattering experiment clearly shows that the spin helicity, clockwise or counterclockwise, is controlled by the direction of spontaneous polarization and hence by the polarity of the small electric field applied on cooling.

  6. Are spiral galaxies heavy smokers

    SciTech Connect

    Davies, J.; Disney, M.; Phillipps, S )

    1990-07-01

    The dustiness of spiral galaxies is discussed. Starburst galaxies and the shortage of truly bright spiral galaxies is cited as evidence that spiral galaxies are far dustier than has been thought. The possibility is considered that the dust may be hiding missing mass.

  7. A Helical Stairway Project

    ERIC Educational Resources Information Center

    Farmer, Tom

    2008-01-01

    We answer a geometric question that was raised by the carpenter in charge of erecting helical stairs in a 10-story hospital. The explanation involves the equations of lines, planes, and helices in three-dimensional space. A brief version of the question is this: If A and B are points on a cylinder and the line segment AB is projected radially onto…

  8. Distortions in protein helices.

    PubMed

    Geetha, V

    1996-08-01

    alpha-helices are the most common secondary structures in observed proteins. However, they are not always found in ideal helical conformation and they often exhibit structural distortions. Quantification of these irregularities become essential in understanding the packing of helices and therefore, their role in the functional characteristics of the protein. The backbone torsions phi, psi are of limited utility in this endeavor, because distorted helices often maintain the backbone geometry. The local compensatory effects are responsible for the preservation of the entire hydrogen bond network of the helical stretch. Earlier descriptions of helical linearity and curvature rest mostly on approximation, thus motivating the search for a better method for understanding and quantifying helical irregularities. We developed a method which involves the rotation and superposition of identical repeating units of the protein by the quaternion method. The set of parameters derived from the rotation-superposition algorithm helps in identifying the bends and kinks which are not necessarily induced by unusual amino acids like proline. The quantification of irregularities of observed helices might lead to a better understanding of their packing interactions. PMID:8842770

  9. Emerging double helical nanostructures

    NASA Astrophysics Data System (ADS)

    Zhao, Meng-Qiang; Zhang, Qiang; Tian, Gui-Li; Wei, Fei

    2014-07-01

    As one of the most important and land-mark structures found in nature, a double helix consists of two congruent single helices with the same axis or a translation along the axis. This double helical structure renders the deoxyribonucleic acid (DNA) the crucial biomolecule in evolution and metabolism. DNA-like double helical nanostructures are probably the most fantastic yet ubiquitous geometry at the nanoscale level, which are expected to exhibit exceptional and even rather different properties due to the unique organization of the two single helices and their synergistic effect. The organization of nanomaterials into double helical structures is an emerging hot topic for nanomaterials science due to their promising exceptional unique properties and applications. This review focuses on the state-of-the-art research progress for the fabrication of double-helical nanostructures based on `bottom-up' and `top-down' strategies. The relevant nanoscale, mesoscale, and macroscopic scale fabrication methods, as well as the properties of the double helical nanostructures are included. Critical perspectives are devoted to the synthesis principles and potential applications in this emerging research area. A multidisciplinary approach from the scope of nanoscience, physics, chemistry, materials, engineering, and other application areas is still required to the well-controlled and large-scale synthesis, mechanism, property, and application exploration of double helical nanostructures.

  10. Spiral wound extraction cartridge

    DOEpatents

    Wisted, Eric E.; Lundquist, Susan H.

    1999-01-01

    A cartridge device for removing an analyte from a fluid comprises a hollow core, a sheet composite comprising a particulate-loaded porous membrane and optionally at least one reinforcing spacer sheet, the particulate being capable of binding the analyte, the sheet composite being formed into a spiral configuration about the core, wherein the sheet composite is wound around itself and wherein the windings of sheet composite are of sufficient tightness so that adjacent layers are essentially free of spaces therebetween, two end caps which are disposed over the core and the lateral ends of the spirally wound sheet composite, and means for securing the end caps to the core, the end caps also being secured to the lateral ends of the spirally wound sheet composite. A method for removing an analyte from a fluid comprises the steps of providing a spirally wound element of the invention and passing the fluid containing the analyte through the element essentially normal to a surface of the sheet composite so as to bind the analyte to the particulate of the particulate-loaded porous membrane, the method optionally including the step of eluting the bound analyte from the sheet composite.

  11. Ubibliotheca The Spiral Library.

    ERIC Educational Resources Information Center

    Ottewell, Guy

    A plan for a library with a storage level in the shape of a flat spiral is presented. The advantages of such a plan include: space saving, easy expansion of the building, an unbroken sequence of shelving, quick access to all books and freedom in the design of the library's other sectors. This plan is especially suited for the research library…

  12. Spiral wound extraction cartridge

    DOEpatents

    Wisted, E.E.; Lundquist, S.H.

    1999-04-27

    A cartridge device for removing an analyte from a fluid comprises a hollow core, a sheet composite comprising a particulate-loaded porous membrane and optionally at least one reinforcing spacer sheet, the particulate being capable of binding the analyte, the sheet composite being formed into a spiral configuration about the core, wherein the sheet composite is wound around itself and wherein the windings of sheet composite are of sufficient tightness so that adjacent layers are essentially free of spaces therebetween, two end caps which are disposed over the core and the lateral ends of the spirally wound sheet composite, and means for securing the end caps to the core, the end caps also being secured to the lateral ends of the spirally wound sheet composite. A method for removing an analyte from a fluid comprises the steps of providing a spirally wound element of the invention and passing the fluid containing the analyte through the element essentially normal to a surface of the sheet composite so as to bind the analyte to the particulate of the particulate-loaded porous membrane, the method optionally including the step of eluting the bound analyte from the sheet composite. 4 figs.

  13. Spiral track oven

    SciTech Connect

    Drobilisch, Sandor

    1998-12-20

    Final report on development of a continuously operating oven system in which the parts are progressing automatically on a spiral track for in-line service installation for the production of electronic and/or other components to be heat cured or dried.

  14. Spiral Galaxies Stripped Bare

    NASA Astrophysics Data System (ADS)

    2010-10-01

    Six spectacular spiral galaxies are seen in a clear new light in images from ESO's Very Large Telescope (VLT) at the Paranal Observatory in Chile. The pictures were taken in infrared light, using the impressive power of the HAWK-I camera, and will help astronomers understand how the remarkable spiral patterns in galaxies form and evolve. HAWK-I [1] is one of the newest and most powerful cameras on ESO's Very Large Telescope (VLT). It is sensitive to infrared light, which means that much of the obscuring dust in the galaxies' spiral arms becomes transparent to its detectors. Compared to the earlier, and still much-used, VLT infrared camera ISAAC, HAWK-I has sixteen times as many pixels to cover a much larger area of sky in one shot and, by using newer technology than ISAAC, it has a greater sensitivity to faint infrared radiation [2]. Because HAWK-I can study galaxies stripped bare of the confusing effects of dust and glowing gas it is ideal for studying the vast numbers of stars that make up spiral arms. The six galaxies are part of a study of spiral structure led by Preben Grosbøl at ESO. These data were acquired to help understand the complex and subtle ways in which the stars in these systems form into such perfect spiral patterns. The first image shows NGC 5247, a spiral galaxy dominated by two huge arms, located 60-70 million light-years away. The galaxy lies face-on towards Earth, thus providing an excellent view of its pinwheel structure. It lies in the zodiacal constellation of Virgo (the Maiden). The galaxy in the second image is Messier 100, also known as NGC 4321, which was discovered in the 18th century. It is a fine example of a "grand design" spiral galaxy - a class of galaxies with very prominent and well-defined spiral arms. About 55 million light-years from Earth, Messier 100 is part of the Virgo Cluster of galaxies and lies in the constellation of Coma Berenices (Berenice's Hair, named after the ancient Egyptian queen Berenice II). The third

  15. Comparison of Conventional Versus Spiral Computed Tomography with Three Dimensional Reconstruction in Chronic Otitis Media with Ossicular Chain Destruction

    PubMed Central

    Naghibi, Saeed; Seifirad, Sirous; Adami Dehkordi, Mahboobeh; Einolghozati, Sasan; Ghaffarian Eidgahi Moghadam, Nafiseh; Akhavan Rezayat, Amir; Seifirad, Soroush

    2016-01-01

    Background: Chronic otitis media (COM) can be treated with tympanoplasty with or without mastoidectomy. In patients who have undergone middle ear surgery, three-dimensional spiral computed tomography (CT) scan plays an important role in optimizing surgical planning. Objectives: This study was performed to compare the findings of three-dimensional reconstructed spiral and conventional CT scan of ossicular chain study in patients with COM. Patients and Methods: Fifty patients enrolled in the study underwent plane and three dimensional CT scan (PHILIPS-MX 8000). Ossicles changes, mastoid cavity, tympanic cavity, and presence of cholesteatoma were evaluated. Results of the two methods were then compared and interpreted by a radiologist, recorded in questionnaires, and analyzed. Logistic regression test and Kappa coefficient of agreement were used for statistical analyses. Results: Sixty two ears with COM were found in physical examination. A significant difference was observed between the findings of the two methods in ossicle erosion (11.3% in conventional CT vs. 37.1% in spiral CT, P = 0.0001), decrease of mastoid air cells (82.3% in conventional CT vs. 93.5% in spiral CT, P = 0.001), and tympanic cavity opacity (12.9% in conventional CT vs. 40.3% in spiral CT, P=0.0001). No significant difference was observed between the findings of the two methods in ossicle destruction (6.5% conventional CT vs. 56.4% in spiral CT, P = 0.125), and presence of cholesteatoma (3.2% in conventional CT vs. 42% in spiral CT, P = 0.172). In this study, spiral CT scan demonstrated ossicle dislocation in 9.6%, decrease of mastoid air cells in 4.8%, and decrease of volume in the tympanic cavity in 1.6%; whereas, none of these findings were reported in the patients' conventional CT scans. Conclusion: Spiral-CT scan is superior to conventional CT in the diagnosis of lesions in COM before operation. It can be used for detailed evaluation of ossicular chain in such patients. PMID:27127583

  16. Spiral waves in Saturn's rings

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.

    1989-01-01

    Spiral density waves and spiral bending waves have been observed at dozens of locations within Saturn's rings. These waves are excited by resonant gravitational perturbations from moons orbiting outside the ring system. Modeling of spiral waves yields the best available estimates for the mass and the thickness of Saturn's ring system. Angular momentum transport due to spiral density waves may cause significant orbital evolution of Saturn's rings and inner moons. Similar angular momentum transfer may occur in other astrophysical systems such as protoplanetary disks, binary star systems with disks and spiral galaxies with satellites.

  17. Structural mechanics and helical geometry of thin elastic composites.

    PubMed

    Wada, Hirofumi

    2016-09-21

    Helices are ubiquitous in nature, and helical shape transition is often observed in residually stressed bodies, such as composites, wherein materials with different mechanical properties are glued firmly together to form a whole body. Inspired by a variety of biological examples, the basic physical mechanism responsible for the emergence of twisting and bending in such thin composite structures has been extensively studied. Here, we propose a simplified analytical model wherein a slender membrane tube undergoes a helical transition driven by the contraction of an elastic ribbon bound to the membrane surface. We analytically predict the curvature and twist of an emergent helix as functions of differential strains and elastic moduli, which are confirmed by our numerical simulations. Our results may help understand shapes observed in different biological systems, such as spiral bacteria, and could be applied to novel designs of soft machines and robots. PMID:27510457

  18. Forming Spirals From Shadows

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-07-01

    What causes the large-scale spiral structures found in some protoplanetary disks? Most models assume theyre created by newly-forming planets, but a new study suggests that planets might have nothing to do with it.Perturbations from Planets?In some transition disks protoplanetary disks with gaps in their inner regions weve directly imaged large-scale spiral arms. Many theories currently attribute the formation of these structures to young planets: either the direct perturbations of a planet embedded in the disk cause the spirals, or theyre indirectly caused by the orbit of a planetary body outside of the arms.Another example of spiral arms detected in a protoplanetary disk, MWC 758. [NASA/ESA/ESO/M. Benisty et al.]But what if you could get spirals without any planets? A team of scientists led by Matas Montesinos (University of Chile) have recently published a study in which they examine what happens to a shadowed protoplanetary disk.Casting Shadows with WarpsIn the teams setup, they envision a protoplanetary disk that is warped: the inner region is slightly tilted relative to the outer region. As the central star casts light out over its protoplanetary disk, this disk warping would cause some regions of the disk to be shaded in a way that isnt axially symmetric with potentially interesting implications.Montesinos and collaborators ran 2D hydrodynamics simulations to determine what happens to the motion of particles within the disk when they pass in and out of the shadowed regions. Since the shadowed regions are significantly colder than the illuminated disk, the pressure in these regions is much lower. Particles are therefore accelerated and decelerated as they pass through these regions, and the lack of axial symmetry causes spiral density waves to form in the disk as a result.Initial profile for the stellar heating rate per unit area for one of the authors simulations. The regions shadowed as a result of the disk warp subtend 0.5 radians each (shown on the left

  19. Fluid mechanics and heat transfer spirally fluted tubing

    NASA Astrophysics Data System (ADS)

    Larue, J. C.; Libby, P. A.; Yampolsky, J. S.

    1981-08-01

    The objective of this program is to develop both a qualitative and a quantitative understanding of the fluid mechanics and heat transfer mechanisms that underlie the measured performance of the spirally fluted tubes under development at General Atomic. The reason for the interest in the spirally fluted tubes is that results to date have indicated three advantages to this tubing concept: The fabrication technique of rolling flutes on strip and subsequently spiralling and simultaneously welding the strip to form tubing results in low fabrication costs, approximately equal to those of commercially welded tubing. The heat transfer coefficient is increased without a concomitant increase of the friction coefficient on the inside of the tube. In single-phase axial flow of water, the helical flutes continuously induce rotation of the flow both within and without the tube as a result of the effect of curvature. An increase in condensation heat transfer on the outside of the tube is achieved. In a vertical orientation with fluid condensing on the outside of the helically fluted tube, the flutes provide a channel for draining the condensed fluid.

  20. Ferroelectricity in spiral magnets.

    PubMed

    Mostovoy, Maxim

    2006-02-17

    It was recently observed that the ferroelectrics showing the strongest sensitivity to an applied magnetic field are spiral magnets. We present a phenomenological theory of inhomogeneous ferroelectric magnets, which describes their thermodynamics and magnetic field behavior, e.g., dielectric susceptibility anomalies at magnetic transitions and sudden flops of electric polarization in an applied magnetic field. We show that electric polarization can also be induced at domain walls and that magnetic vortices carry electric charge. PMID:16606047

  1. Spiral computed tomography phase-space source model in the BEAMnrc/EGSnrc Monte Carlo system: implementation and validation

    NASA Astrophysics Data System (ADS)

    Kim, Sangroh; Yoshizumi, Terry T.; Yin, Fang-Fang; Chetty, Indrin J.

    2013-04-01

    Currently, the BEAMnrc/EGSnrc Monte Carlo (MC) system does not provide a spiral CT source model for the simulation of spiral CT scanning. We developed and validated a spiral CT phase-space source model in the BEAMnrc/EGSnrc system. The spiral phase-space source model was implemented in the DOSXYZnrc user code of the BEAMnrc/EGSnrc system by analyzing the geometry of spiral CT scan—scan range, initial angle, rotational direction, pitch, slice thickness, etc. Table movement was simulated by changing the coordinates of the isocenter as a function of beam angles. Some parameters such as pitch, slice thickness and translation per rotation were also incorporated into the model to make the new phase-space source model, designed specifically for spiral CT scan simulations. The source model was hard-coded by modifying the ‘ISource = 8: Phase-Space Source Incident from Multiple Directions’ in the srcxyznrc.mortran and dosxyznrc.mortran files in the DOSXYZnrc user code. In order to verify the implementation, spiral CT scans were simulated in a CT dose index phantom using the validated x-ray tube model of a commercial CT simulator for both the original multi-direction source (ISOURCE = 8) and the new phase-space source model in the DOSXYZnrc system. Then the acquired 2D and 3D dose distributions were analyzed with respect to the input parameters for various pitch values. In addition, surface-dose profiles were also measured for a patient CT scan protocol using radiochromic film and were compared with the MC simulations. The new phase-space source model was found to simulate the spiral CT scanning in a single simulation run accurately. It also produced the equivalent dose distribution of the ISOURCE = 8 model for the same CT scan parameters. The MC-simulated surface profiles were well matched to the film measurement overall within 10%. The new spiral CT phase-space source model was implemented in the BEAMnrc/EGSnrc system. This work will be beneficial in estimating the

  2. Galaxy Zoo: passive red spirals

    NASA Astrophysics Data System (ADS)

    Masters, Karen L.; Mosleh, Moein; Romer, A. Kathy; Nichol, Robert C.; Bamford, Steven P.; Schawinski, Kevin; Lintott, Chris J.; Andreescu, Dan; Campbell, Heather C.; Crowcroft, Ben; Doyle, Isabelle; Edmondson, Edward M.; Murray, Phil; Raddick, M. Jordan; Slosar, Anže; Szalay, Alexander S.; Vandenberg, Jan

    2010-06-01

    We study the spectroscopic properties and environments of red (or passive) spiral galaxies found by the Galaxy Zoo project. By carefully selecting face-on disc-dominated spirals, we construct a sample of truly passive discs (i.e. they are not dust reddened spirals, nor are they dominated by old stellar populations in a bulge). As such, our red spirals represent an interesting set of possible transition objects between normal blue spiral galaxies and red early types, making up ~6 per cent of late-type spirals. We use optical images and spectra from Sloan Digital Sky Survey to investigate the physical processes which could have turned these objects red without disturbing their morphology. We find red spirals preferentially in intermediate density regimes. However, there are no obvious correlations between red spiral properties and environment suggesting that environment alone is not sufficient to determine whether a galaxy will become a red spiral. Red spirals are a very small fraction of all spirals at low masses (M* < 1010 Msolar), but are a significant fraction of the spiral population at large stellar masses showing that massive galaxies are red independent of morphology. We confirm that as expected, red spirals have older stellar populations and less recent star formation than the main spiral population. While the presence of spiral arms suggests that a major star formation could not have ceased a long ago (not more than a few Gyr), we show that these are also not recent post-starburst objects (having had no significant star formation in the last Gyr), so star formation must have ceased gradually. Intriguingly, red spirals are roughly four times as likely than the normal spiral population to host optically identified Seyfert/low-ionization nuclear emission region (LINER; at a given stellar mass and even accounting for low-luminosity lines hidden by star formation), with most of the difference coming from the objects with LINER-like emission. We also find a

  3. Stellar Populations in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    MacArthur, L. A.; Courteau, S.; Bell, E. F.; Holtzman, J. A.

    2004-12-01

    We investigate optical and near-IR color gradients in a sample of 172 low-inclination galaxies spanning Hubble types S0--Irr. The colors are compared to stellar population synthesis models from which luminosity-weighted average ages and metallicities are determined. We explore the effects of different underlying star formation histories and additional bursts of star formation. Because the observed gradients show radial structure, we measure ``inner'' and ``outer'' disk age and metallicity gradients. Relative trends in age and metallicity and their gradients are explored as a function of Hubble type, rotational velocity, total near-IR galaxy magnitude, central surface brightness, and scale length. We find strong correlations in age and metallicity with Hubble type, rotational velocity, total magnitude, and central surface brightness in the sense that earlier-type, faster rotating, more luminous, and higher surface brightness galaxies are older and more metal-rich, suggesting an early and more rapid star formation history for these galaxies. The increasing trends level off for T ⪉ 4 (Sbc and earlier), V {rot} ⪆ 120 km s-1, MK ⪉ -23 mag, and μ 0 ⪉ 18.5 mag arcsec-2. Outer disk gradients are weaker than the inner gradients as expected for a slower variation of the potential and surface brightness in the outer parts. We find that stronger age gradients are associated with weaker metallicity gradients. Relative trends in gradients with galaxy parameters do not agree with predictions of semi-analytic models of hierarchical galaxy formation, possibly as a result of bar-induced radial flows. However, the observed trends are in agreement with chemo-spectro photometric models of spiral galaxy evolution based on CDM-motivated scaling laws but including none of the hierarchical merging characteristics. This implies a strong dependence of the star formation history of spiral galaxies on the galaxy potential and halo spin parameter. L.A.M. and S.C acknowledge support

  4. Spiral Microstrip Antenna with Resistance

    NASA Technical Reports Server (NTRS)

    Shively, David G. (Inventor)

    1998-01-01

    A spiral microstrip antenna having resistor elements embedded in each of the spiral arms is provided. The antenna is constructed using a conductive back plane as a base. The back plane supports a dielectric slab having a thickness between one-sixteenth and one-quarter of an inch. A square spiral, having either two or four arms, is attached to the dielectric slab. Each arm of the spiral has resistor elements thereby dissipating an excess energy not already emitted through radiation. The entire configuration provides a thin, flat, high gain, wide bandwidth antenna which requires no underlying cavity. The configuration allows the antenna to be mounted conformably on an aircraft surface.

  5. Wafer-scale, three-dimensional helical porous thin films deposited at a glancing angle

    NASA Astrophysics Data System (ADS)

    Huang, Zhifeng; Bai, Fan

    2014-07-01

    Minimization of helices opens a door to impose novel functions derived from the dimensional shrinkage of optical, mechanical and electronic devices. Glancing angle deposition (GLAD) enables one to deposit three-dimensional helical porous thin films (HPTFs) composed of separated spiral micro/nano-columns. GLAD integrates a series of advantageous features, including one-step deposition, wafer-scale production with mono-handedness of spirals, flexible engineering of spiral materials and dimensions, and the adaption to various kinds of substrates. Herein, we briefly review the fabrication of HPTFs by GLAD, specific growth mechanisms, physical properties in structures, mechanics and chiral optics, and the emerging applications in green energy. A prospective outlook is presented to illuminate some promising developments in enantioselection, bio-dynamic analyses, wirelessly-controlled drug delivery and mass production.

  6. Spiral Orbit Tribometer

    NASA Technical Reports Server (NTRS)

    Pepper, Stephen V.; Jones, William R., Jr.; Kingsbury, Edward; Jansen, Mark J.

    2007-01-01

    The spiral orbit tribometer (SOT) bridges the gap between full-scale life testing and typically unrealistic accelerated life testing of ball-bearing lubricants in conjunction with bearing ball and race materials. The SOT operates under realistic conditions and quickly produces results, thereby providing information that can guide the selection of lubricant, ball, and race materials early in a design process. The SOT is based upon a simplified, retainerless thrust bearing comprising one ball between flat races (see figure). The SOT measures lubricant consumption and degradation rates and friction coefficients in boundary lubricated rolling and pivoting contacts. The ball is pressed between the lower and upper races with a controlled force and the lower plate is rotated. The combination of load and rotation causes the ball to move in a nearly circular orbit that is, more precisely, an opening spiral. The spiral s pitch is directly related to the friction coefficient. At the end of the orbit, the ball contacts the guide plate, restoring the orbit to its original radius. The orbit is repeatable throughout the entire test. A force transducer, mounted in-line with the guide plate, measures the force between the ball and the guide plate, which directly relates to the friction coefficient. The SOT, shown in the figure, can operate in under ultra-high vacuum (10(exp -9) Torr) or in a variety of gases at atmospheric pressure. The load force can be adjusted between 45 and 450 N. By varying the load force and ball diameter, mean Hertzian stresses between 0.5 and 5.0 GPa can be obtained. The ball s orbital speed range is between 1 and 100 rpm.

  7. Backwards Spiral Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Astronomers using NASA's Hubble Space Telescope have found a spiral galaxy that may rotate in the opposite direction from what was expected.

    A picture of the oddball galaxy is available at http://heritage.stsci.edu or http://oposite.stsci.edu/pubinfo/pr/2002/03 or http://www.jpl.nasa.gov/images/wfpc . It was taken in May 2001 by Hubble's Wide Field and Planetary Camera 2, designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

    The picture showed which side of galaxy NGC 4622 is closer to Earth; that information helped astronomers determine that the galaxy may be spinning clockwise. The image shows NGC 4622 and its outer pair of winding arms full of new stars, shown in blue.

    Astronomers are puzzled by the clockwise rotation because of the direction the outer spiral arms are pointing. Most spiral galaxies have arms of gas and stars that trail behind as they turn. But this galaxy has two 'leading' outer arms that point toward the direction of the galaxy's clockwise rotation. NGC 4622 also has a 'trailing' inner arm that is wrapped around the galaxy in the opposite direction. Based on galaxy simulations, a team of astronomers had expected that the galaxy was turning counterclockwise.

    NGC 4622 is a rare example of a spiral galaxy with arms pointing in opposite directions. Astronomers suspect this oddity was caused by the interaction of NGC 4622 with another galaxy. Its two outer arms are lopsided, meaning that something disturbed it. The new Hubble image suggests that NGC 4622 consumed a smaller companion galaxy.

    Galaxies, which consist of stars, gas, and dust, rotate very slowly. Our Sun, one of many stars in our Milky Way galaxy, completes a circuit around the Milky Way every 250 million years. NGC 4622 lies 111 million light-years away in the direction of the constellation Centaurus.

    The science team, consisting of Drs. Ron Buta and Gene Byrd from the University of Alabama, Tuscaloosa, and Tarsh Freeman of Bevill State

  8. Rebuilding Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    2005-01-01

    Major Observing Programme Leads to New Theory of Galaxy Formation Summary Most present-day large galaxies are spirals, presenting a disc surrounding a central bulge. Famous examples are our own Milky Way or the Andromeda Galaxy. When and how did these spiral galaxies form? Why do a great majority of them present a massive central bulge? An international team of astronomers [1] presents new convincing answers to these fundamental questions. For this, they rely on an extensive dataset of observations of galaxies taken with several space- and ground-based telescopes. In particular, they used over a two-year period, several instruments on ESO's Very Large Telescope. Among others, their observations reveal that roughly half of the present-day stars were formed in the period between 8,000 million and 4,000 million years ago, mostly in episodic burst of intense star formation occurring in Luminous Infrared Galaxies. From this and other evidence, the astronomers devised an innovative scenario, dubbed the "spiral rebuilding". They claim that most present-day spiral galaxies are the results of one or several merger events. If confirmed, this new scenario could revolutionise the way astronomers think galaxies formed. PR Photo 02a/05: Luminosity - Oxygen Abundance Relation for Galaxies (VLT) PR Photo 02b/05: The Spiral Rebuilding Scenario A fleet of instruments How and when did galaxies form? How and when did stars form in these island universes? These questions are still posing a considerable challenge to present-day astronomers. Front-line observational results obtained with a fleet of ground- and space-based telescopes by an international team of astronomers [1] provide new insights into these fundamental issues. For this, they embarked on an ambitious long-term study at various wavelengths of 195 galaxies with a redshift [2] greater than 0.4, i.e. located more than 4000 million light-years away. These galaxies were studied using ESO's Very Large Telescope, as well as the

  9. Spiral scan long object reconstruction through PI line reconstruction.

    PubMed

    Tam, K C; Hu, J; Sourbelle, K

    2004-06-01

    The response of a point object in a cone beam (CB) spiral scan is analysed. Based on the result, a reconstruction algorithm for long object imaging in spiral scan cone beam CT is developed. A region-of-interest (ROI) of the long object is scanned with a detector smaller than the ROI, and a portion of it can be reconstructed without contamination from overlaying materials. The top and bottom surfaces of the ROI are defined by two sets of PI lines near the two ends of the spiral path. With this novel definition of the top and bottom ROI surfaces and through the use of projective geometry, it is straightforward to partition the cone beam image into regions corresponding to projections of the ROI, the overlaying objects or both. This also simplifies computation at source positions near the spiral ends, and makes it possible to reduce radiation exposure near the spiral ends substantially through simple hardware collimation. Simulation results to validate the algorithm are presented. PMID:15248589

  10. Helical plasma thruster

    NASA Astrophysics Data System (ADS)

    Beklemishev, A. D.

    2015-10-01

    A new scheme of plasma thruster is proposed. It is based on axial acceleration of rotating magnetized plasmas in magnetic field with helical corrugation. The idea is that the propellant ionization zone can be placed into the local magnetic well, so that initially the ions are trapped. The E × B rotation is provided by an applied radial electric field that makes the setup similar to a magnetron discharge. Then, from the rotating plasma viewpoint, the magnetic wells of the helically corrugated field look like axially moving mirror traps. Specific shaping of the corrugation can allow continuous acceleration of trapped plasma ions along the magnetic field by diamagnetic forces. The accelerated propellant is expelled through the expanding field of magnetic nozzle. By features of the acceleration principle, the helical plasma thruster may operate at high energy densities but requires a rather high axial magnetic field, which places it in the same class as the VASIMR® rocket engine.

  11. Helical screw viscometer

    DOEpatents

    Aubert, J.H.; Chapman, R.N.; Kraynik, A.M.

    1983-06-30

    A helical screw viscometer for the measurement of the viscosity of Newtonian and non-Newtonian fluids comprising an elongated cylindrical container closed by end caps defining a circular cylindrical cavity within the container, a cylindrical rotor member having a helical screw or ribbon flight carried by the outer periphery thereof rotatably carried within the cavity whereby the fluid to be measured is confined in the cavity filling the space between the rotor and the container wall. The rotor member is supported by axle members journaled in the end caps, one axle extending through one end cap and connectable to a drive source. A pair of longitudinally spaced ports are provided through the wall of the container in communication with the cavity and a differential pressure meter is connected between the ports for measuring the pressure drop caused by the rotation of the helical screw rotor acting on the confined fluid for computing viscosity.

  12. Helical plasma thruster

    SciTech Connect

    Beklemishev, A. D.

    2015-10-15

    A new scheme of plasma thruster is proposed. It is based on axial acceleration of rotating magnetized plasmas in magnetic field with helical corrugation. The idea is that the propellant ionization zone can be placed into the local magnetic well, so that initially the ions are trapped. The E × B rotation is provided by an applied radial electric field that makes the setup similar to a magnetron discharge. Then, from the rotating plasma viewpoint, the magnetic wells of the helically corrugated field look like axially moving mirror traps. Specific shaping of the corrugation can allow continuous acceleration of trapped plasma ions along the magnetic field by diamagnetic forces. The accelerated propellant is expelled through the expanding field of magnetic nozzle. By features of the acceleration principle, the helical plasma thruster may operate at high energy densities but requires a rather high axial magnetic field, which places it in the same class as the VASIMR{sup ®} rocket engine.

  13. Spiral viscous fingering.

    NASA Astrophysics Data System (ADS)

    Nagatsu, Yuichiro; Hayashi, Atsushi; Kato, Yoshihito; Tada, Yutaka

    2006-11-01

    When a less-viscous fluid displaces a more-viscous fluid in a radial Hele-Shaw cell, viscous fingering pattern is believed to develop in a radial direction. We performed experiments on viscous fingering in a radial Hele-Shaw cell when a polymer solution, a sodium polyacrylate (SPA) solution is used as the more-viscous fluid and the trivalent iron (Fe^3+) solution is as the less-viscous fluid. The experiment was done by varying the concentration of Fe^3+, cFe3+. We have found that viscous fingering pattern develops spirally when cFe3+ is larger than a threshold value, while the pattern develops in a radial direction for small cFe3+. We confirmed from different experiments that an instantaneous chemical reaction takes place between SPA solution and Fe^3+ solution. The chemical reaction produces precipitation and significantly reduces the viscosity of the SPA solution. The quantity of the precipitation is increased with cFe3+. We will make a discussion on the relationship between the formation of spiral viscous fingering and the chemical reaction taking place between the two fluids.

  14. CT Imaging: Basics and New Trends

    NASA Astrophysics Data System (ADS)

    Peyrin, Françoise; Engelke, Klaus

    This chapter presents the principle of X-ray CT and its evolution during the last 40 years. The first section describes the physical basis of X-ray CT, tomographic image reconstruction algorithms, and the source of artifacts in X-ray CT images. The second section is devoted to the evolution of CT technology from the first translation-rotation systems to multi-slice spiral CTs currently used today. The next section addresses specific developments of CT technology and applications, like perfusion CT, quantitative CT, and spectral CT. The fourth section introduces the problem of radiation exposure delivered to the patient and its evaluation. Finally the last section addresses the development in micro- and even nano-CT which is a rapidly evolving area in preclinical imaging and biology.

  15. Experimental investigation of transverse mixing in porous media under helical flow conditions

    NASA Astrophysics Data System (ADS)

    Ye, Yu; Chiogna, Gabriele; Cirpka, Olaf A.; Grathwohl, Peter; Rolle, Massimo

    2016-07-01

    Plume dilution and transverse mixing can be considerably enhanced by helical flow occurring in three-dimensional heterogeneous anisotropic porous media. In this study, we perform tracer experiments in a fully three-dimensional flow-through chamber to investigate the effects of helical flow on plume spiraling and deformation, as well as on its dilution. Porous media were packed in angled stripes of materials with different grain sizes to create blocks with macroscopically anisotropic hydraulic conductivity, which caused helical flows. Steady-state transport experiments were carried out by continuously injecting dye tracers at different inlet ports. High-resolution measurements of concentration and flow rates were performed at 49 outlet ports. These measurements allowed quantifying the spreading and dilution of the solute plumes at the outlet cross section. Direct evidence of plume spiraling and visual proof of helical flow was obtained by freezing and slicing the porous media at different cross sections and observing the dye-tracer distribution. We simulated flow and transport to interpret our experimental observations and investigate the effects of helical flow on mixing-controlled reactive transport. The simulation results were evaluated using metrics of reactive mixing such as the critical dilution index and the length of continuously injected steady-state plumes. The results show considerable reaction enhancement, quantified by the remarkable decrease of reactive plume lengths (up to four times) in helical flows compared to analogous scenarios in uniform flows.

  16. Experimental investigation of transverse mixing in porous media under helical flow conditions.

    PubMed

    Ye, Yu; Chiogna, Gabriele; Cirpka, Olaf A; Grathwohl, Peter; Rolle, Massimo

    2016-07-01

    Plume dilution and transverse mixing can be considerably enhanced by helical flow occurring in three-dimensional heterogeneous anisotropic porous media. In this study, we perform tracer experiments in a fully three-dimensional flow-through chamber to investigate the effects of helical flow on plume spiraling and deformation, as well as on its dilution. Porous media were packed in angled stripes of materials with different grain sizes to create blocks with macroscopically anisotropic hydraulic conductivity, which caused helical flows. Steady-state transport experiments were carried out by continuously injecting dye tracers at different inlet ports. High-resolution measurements of concentration and flow rates were performed at 49 outlet ports. These measurements allowed quantifying the spreading and dilution of the solute plumes at the outlet cross section. Direct evidence of plume spiraling and visual proof of helical flow was obtained by freezing and slicing the porous media at different cross sections and observing the dye-tracer distribution. We simulated flow and transport to interpret our experimental observations and investigate the effects of helical flow on mixing-controlled reactive transport. The simulation results were evaluated using metrics of reactive mixing such as the critical dilution index and the length of continuously injected steady-state plumes. The results show considerable reaction enhancement, quantified by the remarkable decrease of reactive plume lengths (up to four times) in helical flows compared to analogous scenarios in uniform flows. PMID:27575223

  17. Spiral vane bioreactor

    NASA Technical Reports Server (NTRS)

    Morrison, Dennis R. (Inventor)

    1991-01-01

    A spiral vane bioreactor of a perfusion type is described in which a vertical chamber, intended for use in a microgravity condition, has a central rotating filter assembly and has flexible membranes disposed to rotate annularly about the filter assembly. The flexible members have end portions disposed angularly with respect to one another. A fluid replenishment medium is input from a closed loop liquid system to a completely liquid filled chamber containing microcarrier beads, cells and a fluid medium. Output of spent medium is to the closed loop. In the closed loop, the output and input parameters are sensed by sensors. A manifold permits recharging of the nutrients and pH adjustment. Oxygen is supplied and carbon dioxide and bubbles are removed and the system is monitored and controlled by a microprocessor.

  18. Arsia Mons Spiral Cloud

    NASA Technical Reports Server (NTRS)

    2002-01-01

    One of the benefits of the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) Extended Mission is the opportunity to observe how the planet's weather changes during a second full martian year. This picture of Arsia Mons was taken June 19, 2001; southern spring equinox occurred the same day. Arsia Mons is a volcano nearly large enough to cover the state of New Mexico. On this particular day (the first day of Spring), the MOC wide angle cameras documented an unusual spiral-shaped cloud within the 110 km (68 mi) diameter caldera--the summit crater--of the giant volcano. Because the cloud is bright both in the red and blue images acquired by the wide angle cameras, it probably consisted mostly of fine dust grains. The cloud's spin may have been induced by winds off the inner slopes of the volcano's caldera walls resulting from the temperature differences between the walls and the caldera floor, or by a vortex as winds blew up and over the caldera. Similar spiral clouds were seen inside the caldera for several days; we don't know if this was a single cloud that persisted throughout that time or one that regenerated each afternoon. Sunlight illuminates this scene from the left/upper left.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  19. Rejuvenation of spiral bulges

    NASA Astrophysics Data System (ADS)

    Thomas, Daniel; Davies, Roger L.

    2006-02-01

    indistinguishable as far as their stellar populations are concerned. These results favour an inside-out formation scenario and indicate that the discs in spiral galaxies of Hubble types Sbc and earlier cannot have a significant influence on the evolution of the stellar populations in the bulge component. The phenomenon of pseudo-bulge formation must be restricted to spirals of types later than Sbc.

  20. Sinonasal Angiomatous Polyp: Evaluation With 2-Phase Helical Computed Tomography

    PubMed Central

    Ding, Changwei; Wang, Qiushi; Guo, Qiyong; Wang, Zhenhai; Lu, Xiaomei; Zhang, Jun

    2015-01-01

    Abstract Sinonasal angiomatous polyp (SAP) is a rare benign nontumorous lesion and previously considered lack of characteristic computed tomography (CT) findings. This study aimed to evaluate 2-phase helical CT for characterization of SAP. Twelve patients with pathologically confirmed SAP underwent 2-phase helical CT preoperatively. After injection of 80 mL contrast material at a rate of 3 mL/s, early and delayed phases were obtained with delays of 30 and 120 s, respectively. The degree and pattern of enhancement were visually analyzed. The attenuation changes were also analyzed quantitatively by measuring CT values and compared with those of the internal maxillary artery (IMA). All 12 cases showed vessel-like marked heterogeneous enhancement at both early and delayed phases. An irregular linear, nodular, and patchy enhancement pattern was found at the early phase, and enlarged and fused together, that is, progressive enhancement pattern was found at the delayed phase. There was no significant difference between the CT values of SAP and those of the IMA at the plain, arterial phase, and delayed phase (53 ± 6 Hounsfield units [HU] vs 56 ± 7 HU, 187 ± 56 HU vs 209 ± 71 HU, and 143 ± 22 HU vs 139 ± 19 HU, respectively, P = 0.361, 0.429, and 0.613, respectively). Vessel-like marked heterogeneous enhancement was a characteristic CT feature of SAP, and progressive enhancement on 2-phase helical CT could further convince the diagnosis. PMID:26200632

  1. Helically linked mirror arrangement

    SciTech Connect

    Ranjan, P.

    1986-08-01

    A scheme is described for helical linking of mirror sections, which endeavors to combine the better features of toroidal and mirror devices by eliminating the longitudinal loss of mirror machines, having moderately high average ..beta.. and steady state operation. This scheme is aimed at a device, with closed magnetic surfaces having rotational transform for equilibrium, one or more axisymmetric straight sections for reduced radial loss, a simple geometrical axis for the links and an overall positive magnetic well depth for stability. We start by describing several other attempts at linking of mirror sections, made both in the past and the present. Then a description of our helically linked mirror scheme is given. This example has three identical straight sections connected by three sections having helical geometric axes. A theoretical analysis of the magnetic field and single-particle orbits in them leads to the conclusion that most of the passing particles would be confined in the device and they would have orbits independent of pitch angle under certain conditions. Numerical results are presented, which agree well with the theoretical results as far as passing particle orbits are concerned.

  2. Three-dimensional spirals of atomic layered MoS2.

    PubMed

    Zhang, Liming; Liu, Kaihui; Wong, Andrew Barnabas; Kim, Jonghwan; Hong, Xiaoping; Liu, Chong; Cao, Ting; Louie, Steven G; Wang, Feng; Yang, Peidong

    2014-11-12

    Atomically thin two-dimensional (2D) layered materials, including graphene, boron nitride, and transition metal dichalcogenides (TMDs), can exhibit novel phenomena distinct from their bulk counterparts and hold great promise for novel electronic and optoelectronic applications. Controlled growth of such 2D materials with different thickness, composition, and symmetry are of central importance to realize their potential. In particular, the ability to control the symmetry of TMD layers is highly desirable because breaking the inversion symmetry can lead to intriguing valley physics, nonlinear optical properties, and piezoelectric responses. Here we report the first chemical vapor deposition (CVD) growth of spirals of layered MoS2 with atomically thin helical periodicity, which exhibits a chiral structure and breaks the three-dimensional (3D) inversion symmetry explicitly. The spirals composed of tens of connected MoS2 layers with decreasing areas: each basal plane has a triangular shape and shrinks gradually to the summit when spiraling up. All the layers in the spiral assume an AA lattice stacking, which is in contrast to the centrosymmetric AB stacking in natural MoS2 crystals. We show that the noncentrosymmetric MoS2 spiral leads to a strong bulk second-order optical nonlinearity. In addition, we found that the growth of spirals involves a dislocation mechanism, which can be generally applicable to other 2D TMD materials. PMID:25343743

  3. Spiral Shock and Feathering Instability in Spiral Arms

    NASA Astrophysics Data System (ADS)

    Lee, Wing-Kit

    2013-11-01

    A theoretical framework is developed to understand the feathering substructures along spiral arms by considering the perturbational gas response to a spiral shock. Feathers are density fluctuations that jut out from the spiral arm to the interarm region at large pitch angles. In a localized asymptotic approximation, related to the shearing sheet except that the inhomogeneities occur in space rather than in time, we derive the linearized perturbation equations for a razor-thin disk with turbulent interstellar gas, frozen-in magnetic field, and gaseous self-gravity. In the addition to the formulation, we investigate how individual normal modes of the system depend on seven dimensionless quantities that characterize the underlying time-independent axisymmetric state plus its steady, nonlinear, two-armed spiral-shock response to a hypothesized background density wave supported by the disk stars of the galaxy. In a particular case using galactic parameters at the inner part of M51 galaxy, we show that the normal mode with the maximum growth rate has the wavelength along the spiral arm that matches the observation of spacing of the feathers at around 500 pc. We also demonstrate that the self-gravity is an important parameter governing the feathering instability.

  4. Economical beneficiation of fine coal by using Reichert spiral and its application to Turkish coals

    SciTech Connect

    Atesok, G.; Oenal, G.; Altas, A.; Arslan, F.

    1993-12-31

    In this study, the possibility of applying Reichert spiral to Turkish coals is discussed. In the first part of the study, nine coal samples, six of them are lignite and one bituminous coal, collected from seven different locations of Turkey, have been studied. Their {open_quotes}Density Histograms{close_quotes} and {open_quotes}Optimum Separation Densities{close_quotes} were investigated. In the second part of the study, pilot scale experiments were carried out with Mark 10 type of Reichert spiral with six helical turns, on the coal samples taken from Zonguldak, the only bituminous coal area in Turkey, and the characteristic Turkish lignite. The results of the pilot scale experiments were compared to that of the known properties of the Reichert spiral.

  5. Helical x-ray differential phase contrast computed tomography

    NASA Astrophysics Data System (ADS)

    Qi, Zhihua; Thériault-Lauzier, Pascal; Bevins, Nicholas; Zambelli, Joseph; Li, Ke; Chen, Guang-Hong

    2011-03-01

    Helical computed tomography revolutionized the field of x-ray computed tomography two decades ago. The simultaneous translation of an image object with a standard computed tomography acquisition allows for fast volumetric scan for long image objects. X-ray phase sensitive imaging methods have been studied over the past few decades to provide new contrast mechanisms for imaging an object. A Talbot-Lau grating interferometer based differential phase contrast imaging method has recently demonstrated its potential for implementation in clinical and industrial applications. In this work, the principles of helical computed tomography are extended to differential phase contrast imaging to produce volumetric reconstructions based on fan-beam data. The method demonstrates the potential for helical differential phase contrast CT to scan long objects with relatively small detector coverage in the axial direction.

  6. Hydrodynamic interactions between rotating helices.

    PubMed

    Kim, MunJu; Powers, Thomas R

    2004-06-01

    Escherichia coli bacteria use rotating helical flagella to swim. At this scale, viscous effects dominate inertia, and there are significant hydrodynamic interactions between nearby helices. These interactions cause the flagella to bundle during the "runs" of bacterial chemotaxis. Here we use slender-body theory to solve for the flow fields generated by rigid helices rotated by stationary motors. We determine how the hydrodynamic forces and torques depend on phase and phase difference, show that rigid helices driven at constant torque do not synchronize, and solve for the flows. We also use symmetry arguments based on kinematic reversibility to show that for two rigid helices rotating with zero phase difference, there is no time-averaged attractive or repulsive force between the helices. PMID:15244620

  7. Implementation of an effective KL domain penalized weighted least-squares sinogram restoration for low-dose CT colonography

    NASA Astrophysics Data System (ADS)

    Fan, Yi; Wang, Jing; Lu, Hongbing; Liang, Zhengrong

    2009-02-01

    Currently available spiral/helical computed tomography (HCT) technologies have demonstrated the potential for CTbased virtual colonoscopy or CT-colonography (CTC). However, a major limitation for this clinical application is associated with the risk of high radiation exposure, especially for its use for screening purpose at a large population. In this work, we presented an improved Karhunen-Loeve (KL) domain penalized weighted least-squares (PWLS) strategy which considers the data correlation among the nearby angular views and nearby axial slices simultaneously so that a fully three-dimensional (3D) restoration problem can be reduced to a 1D operation and therefore an analytical calculation is feasible for highest computing efficiency. The KL-PWLS strategy was implemented and tested on computer simulated sinograms which mimic low-dose CT scans at different noise levels characterized by 50, 40, 30, 20 and 10 mAs respectively. The reconstructed images by the presented strategy demonstrated the potential of ultra low-dose CT at as low as 10 mAs for VC application. Further evaluation by receiver operating characteristic study is needed and is under progress.

  8. Conservation of helicity in superfluids

    NASA Astrophysics Data System (ADS)

    Kedia, Hridesh; Kleckner, Dustin; Proment, Davide; Irvine, William T. M.

    2015-03-01

    Helicity arises as a special conserved quantity in ideal fluids, in addition to energy, momentum and angular momentum. As a measure of the knottedness of vortex lines, Helicity provides an important tool for studying a wide variety of physical systems such as plasmas and turbulent fluids. Superfluids flow without resistance just like ideal (Euler) fluids, making it natural to ask whether their knottedness is similarly preserved. We address the conservation of helicity in superfluids theoretically and examine its consequences in numerical simulations.

  9. Image reconstruction and image quality evaluation for a 64-slice CT scanner with z-flying focal spot.

    PubMed

    Flohr, T G; Stierstorfer, K; Ulzheimer, S; Bruder, H; Primak, A N; McCollough, C H

    2005-08-01

    We present a theoretical overview and a performance evaluation of a novel z-sampling technique for multidetector row CT (MDCT), relying on a periodic motion of the focal spot in the longitudinal direction (z-flying focal spot) to double the number of simultaneously acquired slices. The z-flying focal spot technique has been implemented in a recently introduced MDCT scanner. Using 32 x 0.6 mm collimation, this scanner acquires 64 overlapping 0.6 mm slices per rotation in its spiral (helical) mode of operation, with the goal of improved longitudinal resolution and reduction of spiral artifacts. The longitudinal sampling distance at isocenter is 0.3 mm. We discuss in detail the impact of the z-flying focal spot technique on image reconstruction. We present measurements of spiral slice sensitivity profiles (SSPs) and of longitudinal resolution, both in the isocenter and off-center. We evaluate the pitch dependence of the image noise measured in a centered 20 cm water phantom. To investigate spiral image quality we present images of an anthropomorphic thorax phantom and patient scans. The full width at half maximum (FWHM) of the spiral SSPs shows only minor variations as a function of the pitch, measured values differ by less than 0.15 mm from the nominal values 0.6, 0.75, 1, 1.5, and 2 mm. The measured FWHM of the smallest slice ranges between 0.66 and 0.68 mm at isocenter, except for pitch 0.55 (0.72 mm). In a centered z-resolution phantom, bar patterns up to 15 lp/cm can be visualized independent of the pitch, corresponding to 0.33 mm longitudinal resolution. 100 mm off-center, bar patterns up to 14 lp/cm are visible, corresponding to an object size of 0.36 mm that can be resolved in the z direction. Image noise for constant effective mAs is almost independent of the pitch. Measured values show a variation of less than 7% as a function of the pitch, which demonstrates correct utilization of the applied radiation dose at any pitch. The product of image noise and

  10. Image reconstruction and image quality evaluation for a 64-slice CT scanner with z-flying focal spot

    SciTech Connect

    Flohr, T.G.; Stierstorfer, K.; Ulzheimer, S.; Bruder, H.; Primak, A.N.; McCollough, C.H.

    2005-08-15

    We present a theoretical overview and a performance evaluation of a novel z-sampling technique for multidetector row CT (MDCT), relying on a periodic motion of the focal spot in the longitudinal direction (z-flying focal spot) to double the number of simultaneously acquired slices. The z-flying focal spot technique has been implemented in a recently introduced MDCT scanner. Using 32x0.6 mm collimation, this scanner acquires 64 overlapping 0.6 mm slices per rotation in its spiral (helical) mode of operation, with the goal of improved longitudinal resolution and reduction of spiral artifacts. The longitudinal sampling distance at isocenter is 0.3 mm. We discuss in detail the impact of the z-flying focal spot technique on image reconstruction. We present measurements of spiral slice sensitivity profiles (SSPs) and of longitudinal resolution, both in the isocenter and off-center. We evaluate the pitch dependence of the image noise measured in a centered 20 cm water phantom. To investigate spiral image quality we present images of an anthropomorphic thorax phantom and patient scans. The full width at half maximum (FWHM) of the spiral SSPs shows only minor variations as a function of the pitch, measured values differ by less than 0.15 mm from the nominal values 0.6, 0.75, 1, 1.5, and 2 mm. The measured FWHM of the smallest slice ranges between 0.66 and 0.68 mm at isocenter, except for pitch 0.55 (0.72 mm). In a centered z-resolution phantom, bar patterns up to 15 lp/cm can be visualized independent of the pitch, corresponding to 0.33 mm longitudinal resolution. 100 mm off-center, bar patterns up to 14 lp/cm are visible, corresponding to an object size of 0.36 mm that can be resolved in the z direction. Image noise for constant effective mAs is almost independent of the pitch. Measured values show a variation of less than 7% as a function of the pitch, which demonstrates correct utilization of the applied radiation dose at any pitch. The product of image noise and square

  11. Spiral Surface Growth without Desorption

    NASA Astrophysics Data System (ADS)

    Karma, Alain; Plapp, Mathis

    1998-11-01

    Spiral surface growth is well understood in the limit where the step motion is controlled by the local supersaturation of adatoms near the spiral ridge. In epitaxial thin-film growth, however, spirals can form in a step-flow regime where desorption of adatoms is negligible and the ridge dynamics is governed by the nonlocal diffusion field of adatoms on the whole surface. We investigate this limit numerically using a phase-field formulation of the Burton-Cabrera-Frank model, as well as analytically. Quantitative predictions, which differ strikingly from those of the local limit, are made for the selected step spacing as a function of the deposition flux, as well as for the dependence of the relaxation time to steady-state growth on the screw dislocation density.

  12. [Rational CT diagnosis before operations on the paranasal sinuses].

    PubMed

    Koitschev, A; Baumann, I; Remy, C T; Dammann, F

    2002-03-01

    Movement or metal artefacts as well as the relatively high radiation exposure of both the axial and the coronal scan are disadvantages of computed tomography. A single spiral CT scan with a secondary reformation replacing the second CT scan might solve these problems. The goal of this project was to compare the diagnostic value of primary spiral CT scans of paranasal sinuses with secondary reformations. These were evaluated by ENT surgeons as well as radiologists. We performed axial and coronal spiral-CT's of paranasal sinuses in 80 patients. The secondary coronal and axial reformations were calculated with 2 mm image sections. Although a reduced resolution was observed in the secondary reformations, this did not compromise the detection of important anatomical features. Image deterioration due to artifacts was significantly reduced. PMID:11975076

  13. Helical tomotherapy quality assurance.

    PubMed

    Balog, John; Soisson, Emilie

    2008-01-01

    Helical tomotherapy uses a dynamic delivery in which the gantry, treatment couch, and multileaf collimator leaves are all in motion during treatment. This results in highly conformal radiotherapy, but the complexity of the delivery is partially hidden from the end-user because of the extensive integration and automation of the tomotherapy control systems. This presents a challenge to the medical physicist who is expected to be both a system user and an expert, capable of verifying relevant aspects of treatment delivery. A related issue is that a clinical tomotherapy planning system arrives at a customer's site already commissioned by the manufacturer, not by the clinical physicist. The clinical physicist and the manufacturer's representative verify the commissioning at the customer site before acceptance. Theoretically, treatment could begin immediately after acceptance. However, the clinical physicist is responsible for the safe and proper use of the machine. In addition, the therapists and radiation oncologists need to understand the important machine characteristics before treatment can proceed. Typically, treatment begins about 2 weeks after acceptance. This report presents an overview of the tomotherapy system. Helical tomotherapy has unique dosimetry characteristics, and some of those features are emphasized. The integrated treatment planning, delivery, and patient-plan quality assurance process is described. A quality assurance protocol is proposed, with an emphasis on what a clinical medical physicist could and should check. Additionally, aspects of a tomotherapy quality assurance program that could be checked automatically and remotely because of its inherent imaging system and integrated database are discussed. PMID:18406907

  14. Helical Tomotherapy Quality Assurance

    SciTech Connect

    Balog, John Soisson, Emilie

    2008-05-01

    Helical tomotherapy uses a dynamic delivery in which the gantry, treatment couch, and multileaf collimator leaves are all in motion during treatment. This results in highly conformal radiotherapy, but the complexity of the delivery is partially hidden from the end-user because of the extensive integration and automation of the tomotherapy control systems. This presents a challenge to the medical physicist who is expected to be both a system user and an expert, capable of verifying relevant aspects of treatment delivery. A related issue is that a clinical tomotherapy planning system arrives at a customer's site already commissioned by the manufacturer, not by the clinical physicist. The clinical physicist and the manufacturer's representative verify the commissioning at the customer site before acceptance. Theoretically, treatment could begin immediately after acceptance. However, the clinical physicist is responsible for the safe and proper use of the machine. In addition, the therapists and radiation oncologists need to understand the important machine characteristics before treatment can proceed. Typically, treatment begins about 2 weeks after acceptance. This report presents an overview of the tomotherapy system. Helical tomotherapy has unique dosimetry characteristics, and some of those features are emphasized. The integrated treatment planning, delivery, and patient-plan quality assurance process is described. A quality assurance protocol is proposed, with an emphasis on what a clinical medical physicist could and should check. Additionally, aspects of a tomotherapy quality assurance program that could be checked automatically and remotely because of its inherent imaging system and integrated database are discussed.

  15. The effect of z overscanning on patient effective dose from multidetector helical computed tomography examinations

    SciTech Connect

    Tzedakis, A.; Damilakis, J.; Perisinakis, K.; Stratakis, J.; Gourtsoyiannis, N.

    2005-06-15

    z overscanning in multidetector (MD) helical CT scanning is prerequisite for the interpolation of acquired data required during image reconstruction and refers to the exposure of tissues beyond the boundaries of the volume to be imaged. The aim of the present study was to evaluate the effect of z overscanning on the patient effective dose from helical MD CT examinations. The Monte Carlo N-particle radiation transport code was employed in the current study to simulate CT exposure. The validity of the Monte Carlo simulation was verified by (a) a comparison of calculated and measured standard computed tomography dose index (CTDI) dosimetric data, and (b) a comparison of calculated and measured dose profiles along the z axis. CTDI was measured using a pencil ionization chamber and head and body CT phantoms. Dose profiles along the z axis were obtained using thermoluminescence dosimeters. A commercially available mathematical anthropomorphic phantom was used for the estimation of effective doses from four standard CT examinations, i.e., head and neck, chest, abdomen and pelvis, and trunk studies. Data for both axial and helical modes of operation were obtained. In the helical mode, z overscanning was taken into account. The calculated effective dose from a CT exposure was normalized to CTDI{sub freeinair}. The percentage differences in the normalized effective dose between contiguous axial and helical scans with pitch=1, may reach 13.1%, 35.8%, 29.0%, and 21.5%, for head and neck, chest, abdomen and pelvis, and trunk studies, respectively. Given that the same kilovoltage and tube load per rotation were used in both axial and helical scans, the above differences may be attributed to z overscanning. For helical scans with pitch=1, broader beam collimation is associated with increased z overscanning and consequently higher normalized effective dose value, when other scanning parameters are held constant. For a given beam collimation, the selection of a higher value of

  16. Spirals in the Mandelbrot set I

    NASA Astrophysics Data System (ADS)

    Stephenson, John

    1994-04-01

    An explicit function is constructed to permit easy calculation of the asymptotic structure of the various spirals and branches around the main cardioid in the Mandelbrot set. Details of its application to “exterior” spirals are presented.

  17. Efficient Algorithm for Rectangular Spiral Search

    NASA Technical Reports Server (NTRS)

    Brugarolas, Paul; Breckenridge, William

    2008-01-01

    An algorithm generates grid coordinates for a computationally efficient spiral search pattern covering an uncertain rectangular area spanned by a coordinate grid. The algorithm does not require that the grid be fixed; the algorithm can search indefinitely, expanding the grid and spiral, as needed, until the target of the search is found. The algorithm also does not require memory of coordinates of previous points on the spiral to generate the current point on the spiral.

  18. Magnetic design constraints of helical solenoids

    SciTech Connect

    Lopes, M. L.; Krave, S. T.; Tompkins, J. C.; Yonehara, K.; Flanagan, G.; Kahn, S. A.; Melconian, K.

    2015-01-30

    Helical solenoids have been proposed as an option for a Helical Cooling Channel for muons in a proposed Muon Collider. Helical solenoids can provide the required three main field components: solenoidal, helical dipole, and a helical gradient. In general terms, the last two are a function of many geometric parameters: coil aperture, coil radial and longitudinal dimensions, helix period and orbit radius. In this paper, we present design studies of a Helical Solenoid, addressing the geometric tunability limits and auxiliary correction system.

  19. Helicity patterns on the Sun

    NASA Astrophysics Data System (ADS)

    Pevtsov, A.

    Solar magnetic fields exhibit hemispheric preference for negative (pos- itive) helicity in northern (southern) hemisphere. The hemispheric he- licity rule, however, is not very strong, - the patterns of opposite sign helicity were observed on different spatial scales in each hemisphere. For instance, many individual sunspots exhibit patches of opposite he- licity inside the single polarity field. There are also helicity patterns on scales larger than the size of typical active region. Such patterns were observed in distribution of active regions with abnormal (for a give hemisphere) helicity, in large-scale photospheric magnetic fields and coronal flux systems. We will review the observations of large-scale pat- terns of helicity in solar atmosphere and their possible relationship with (sub-)photospheric processes. The emphasis will be on large-scale pho- tospheric magnetic field and solar corona.

  20. Monte Carlo calculation of helical tomotherapy dose delivery

    SciTech Connect

    Zhao Yingli; Mackenzie, M.; Kirkby, C.; Fallone, B. G.

    2008-08-15

    Helical tomotherapy delivers intensity modulated radiation therapy using a binary multileaf collimator (MLC) to modulate a fan beam of radiation. This delivery occurs while the linac gantry and treatment couch are both in constant motion, so the beam describes, from a patient/phantom perspective, a spiral or helix of dose. The planning system models this continuous delivery as a large number (51) of discrete gantry positions per rotation, and given the small jaw/fan width setting typically used (1 or 2.5 cm) and the number of overlapping rotations used to cover the target (pitch often <0.5), the treatment planning system (TPS) potentially employs a very large number of static beam directions and leaf opening configurations to model the modulated fields. All dose calculations performed by the system employ a convolution/superposition model. In this work the authors perform a full Monte Carlo (MC) dose calculation of tomotherapy deliveries to phantom computed tomography (CT) data sets to verify the TPS calculations. All MC calculations are performed with the EGSnrc-based MC simulation codes, BEAMnrc and DOSXYZnrc. Simulations are performed by taking the sinogram (leaf opening versus time) of the treatment plan and decomposing it into 51 different projections per rotation, as does the TPS, each of which is segmented further into multiple MLC opening configurations, each with different weights that correspond to leaf opening times. Then the projection is simulated by the summing of all of the opening configurations, and the overall rotational treatment is simulated by the summing of all of the projection simulations. Commissioning of the source model was verified by comparing measured and simulated values for the percent depth dose and beam profiles shapes for various jaw settings. The accuracy of the MLC leaf width and tongue and groove spacing were verified by comparing measured and simulated values for the MLC leakage and a picket fence pattern. The validated source

  1. Probing an Interfacial Surface in the Cyanide Dihydratase from Bacillus pumilus, A Spiral Forming Nitrilase

    PubMed Central

    Park, Jason M.; Mulelu, Andani; Sewell, B. Trevor; Benedik, Michael J.

    2016-01-01

    Nitrilases are of significant interest both due to their potential for industrial production of valuable products as well as degradation of hazardous nitrile-containing wastes. All known functional members of the nitrilase superfamily have an underlying dimer structure. The true nitrilases expand upon this basic dimer and form large spiral or helical homo-oligomers. The formation of this larger structure is linked to both the activity and substrate specificity of these nitrilases. The sequences of the spiral nitrilases differ from the non-spiral forming homologs by the presence of two insertion regions. Homology modeling suggests that these regions are responsible for associating the nitrilase dimers into the oligomer. Here we used cysteine scanning across these two regions, in the spiral forming nitrilase cyanide dihydratase from Bacillus pumilus (CynD), to identify residues altering the oligomeric state or activity of the nitrilase. Several mutations were found to cause changes to the size of the oligomer as well as reduction in activity. Additionally one mutation, R67C, caused a partial defect in oligomerization with the accumulation of smaller oligomer variants. These results support the hypothesis that these insertion regions contribute to the unique quaternary structure of the spiral microbial nitrilases. PMID:26779137

  2. The Advanced Helical Generator

    SciTech Connect

    Reisman, D B; Javedani, J B; Ellsworth, G F; Kuklo, R M; Goerz, D A; White, A D; Tallerico, L J; Gidding, D A; Murphy, M J; Chase, J B

    2009-10-26

    A high explosive pulsed power (HEPP) generator called the Advanced Helical Generator (AHG) has been designed, built, and successfully tested. The AHG incorporates design principles of voltage and current management to obtain a high current and energy gain. Its design was facilitated by the use of modern modeling tools as well as high precision manufacture. The result was a first-shot success. The AHG delivered 16 Mega-Amperes of current and 11 Mega-Joules of energy to a quasi-static 80 nH inductive load. A current gain of 154 times was obtained with a peak exponential rise time of 20 {micro}s. We will describe in detail the design and testing of the AHG.

  3. Spiral Galactic Formation and Evolution

    NASA Astrophysics Data System (ADS)

    Brekke, Stewart

    2009-05-01

    Before the period of galactic formation the uiverse consisted of a vast number of pre-formed systems consisting of two or more pre-galactic arms, the arms orbiting each other. As the orbits of the arms decayed the sides of the fore-sections of the arms tangentially collided and joined and thereby forming multi-armed spiral galaxies which began to rotate.The rotation resulted from the conversion of the orbital motion of the individual arms when joined into faster rotational motion of the newly formed galaxy. The spiral arms were maintained by the centripital force of the rapidly rotational motion of the galaxy system. As the rotational motion of the galaxy slowed down the arms of the spiral galaxy collapsed towards the body of the galaxy due to lessening of centripetal force on the arms and elliptical galaxies were formed and with further lessening of galactic rotational motion galactic disks were formed. One can see in galaxies M51, M100, NGC2336 and NGC4939 the galactic arms came from external orbit, not disks or instabilities in support of this theory. Also in support of this theory of galactic evolution is that spiral galaxies rotate faster than ellipticals or disks.

  4. VIBRATORY SPIRAL BLANCHER-COOLER

    EPA Science Inventory

    The objective of the demonstration project was to test the commercial feasibility of the vibratory spiral blancher-cooler, a newly designed steam blancher and air cooler that previous small scale tests showed could reduce the wasteload and energy consumption of preparing vegetabl...

  5. The enigma of auroral spirals

    NASA Astrophysics Data System (ADS)

    Haerendel, G.

    One of the most spectacular forms that the aurora borealis can assume is the large-scale spiral Spirals are dominantly observed along the poleward boundary of the auroral oval during active periods Two concepts have been pursued in explaining their origin and in particular the counterclockwise sense of rotation of the luminous structures when viewed along the magnetic field direction An essentially magnetostatic theory following Hallinan 1976 attributes the spiral pattern to the twisting of field-lines caused by a centrally located upward field-aligned current According to Oguti 1981 and followers a clockwise rotation of the plasma flow produces the anticlockwise structure There are observations seemingly confirming or contradicting either theory In this paper it is argued that both concepts are insufficient in that only parts of the underlying physics are considered Besides field-aligned currents and plasma flow one has to take into at least two further aspects The ionospheric conductivity modified by particle precipitation has an impact on the magnetospheric plasma dynamics Furthermore auroral arcs are not fixed entities subject to distortions by plasma flows or twisted field-lines but sites of transient releases of energy We suggest that auroral spirals are ports of entry or exit of plasma into or out of the auroral oval This way it can be understood why a clockwise plasma flow can create an anticlockwise luminous pattern

  6. Spiral tendency in blind flying

    NASA Technical Reports Server (NTRS)

    Carroll, Thomas; Mcavoy, William H

    1929-01-01

    The flight path followed by an airplane which was being flown by a blindfolded pilot was observed and recorded. When the pilot attempted to make a straight-away flight there was a tendency to deviate from the straight path and to take up a spiral one.

  7. Communication: from rods to helices: evidence of a screw-like nematic phase.

    PubMed

    Kolli, Hima Bindu; Frezza, Elisa; Cinacchi, Giorgio; Ferrarini, Alberta; Giacometti, Achille; Hudson, Toby S

    2014-02-28

    Evidence of a special chiral nematic phase is provided using numerical simulation and Onsager theory for systems of hard helical particles. This phase appears at the high density end of the nematic phase, when helices are well aligned, and is characterized by the C2 symmetry axes of the helices spiraling around the nematic director with periodicity equal to the particle pitch. This coupling between translational and rotational degrees of freedom allows a more efficient packing and hence an increase of translational entropy. Suitable order parameters and correlation functions are introduced to identify this screw-like phase, whose main features are then studied as a function of radius and pitch of the helical particles. Our study highlights the physical mechanism underlying a similar ordering observed in colloidal helical flagella [E. Barry, Z. Hensel, Z. Dogic, M. Shribak, and R. Oldenbourg, Phys. Rev. Lett. 96, 018305 (2006)] and raises the question of whether it could be observed in other helical particle systems, such as DNA, at sufficiently high densities. PMID:24588140

  8. CT -- Body

    MedlinePlus

    ... News Physician Resources Professions Site Index A-Z Computed Tomography (CT) - Body Computed tomography (CT) of the body uses special x-ray ... Body? What is CT Scanning of the Body? Computed tomography, more commonly known as a CT or CAT ...

  9. Multiple helical configuration and quantity threshold of graphene nanoribbons inside a single-walled carbon nanotube

    PubMed Central

    Li, Yifan; Chen, Wei; Ren, Hongru; Zhou, Xuyan; Li, Hui

    2015-01-01

    Molecular dynamics simulation has been carried out to explore the configuration and quantity threshold of multiple graphene nanoribbons (GNRs) in single-walled carbon nanotube (SWCNT). The simulation results showed that several GNRs tangled together to form a perfect spiral structure to maximize the π-π stacking area when filling inside SWCNT. The formation of multiple helical configuration is influenced by the combined effect of structure stability, initial arrangement and tube space, meanwhile its forming time is related to helical angle. The simulated threshold of GNRs in SWCNT decreases with GNR width but increases with SWCNT diameter, and two formulas have come up in this study to estimate the quantity threshold for GNRs. It has been found that multilayered graphite is hard to be stripped in SWCNT because the special helical configuration with incompletely separated GNRs is metastable. This work provides a possibility to control the configuration of GNR@SWCNT. PMID:26374276

  10. Multiple helical configuration and quantity threshold of graphene nanoribbons inside a single-walled carbon nanotube.

    PubMed

    Li, Yifan; Chen, Wei; Ren, Hongru; Zhou, Xuyan; Li, Hui

    2015-01-01

    Molecular dynamics simulation has been carried out to explore the configuration and quantity threshold of multiple graphene nanoribbons (GNRs) in single-walled carbon nanotube (SWCNT). The simulation results showed that several GNRs tangled together to form a perfect spiral structure to maximize the π-π stacking area when filling inside SWCNT. The formation of multiple helical configuration is influenced by the combined effect of structure stability, initial arrangement and tube space, meanwhile its forming time is related to helical angle. The simulated threshold of GNRs in SWCNT decreases with GNR width but increases with SWCNT diameter, and two formulas have come up in this study to estimate the quantity threshold for GNRs. It has been found that multilayered graphite is hard to be stripped in SWCNT because the special helical configuration with incompletely separated GNRs is metastable. This work provides a possibility to control the configuration of GNR@SWCNT. PMID:26374276

  11. CT Angiography after 20 Years

    PubMed Central

    Rubin, Geoffrey D.; Leipsic, Jonathon; Schoepf, U. Joseph; Fleischmann, Dominik; Napel, Sandy

    2015-01-01

    Through a marriage of spiral computed tomography (CT) and graphical volumetric image processing, CT angiography was born 20 years ago. Fueled by a series of technical innovations in CT and image processing, over the next 5–15 years, CT angiography toppled conventional angiography, the undisputed diagnostic reference standard for vascular disease for the prior 70 years, as the preferred modality for the diagnosis and characterization of most cardiovascular abnormalities. This review recounts the evolution of CT angiography from its development and early challenges to a maturing modality that has provided unique insights into cardiovascular disease characterization and management. Selected clinical challenges, which include acute aortic syndromes, peripheral vascular disease, aortic stent-graft and transcatheter aortic valve assessment, and coronary artery disease, are presented as contrasting examples of how CT angiography is changing our approach to cardiovascular disease diagnosis and management. Finally, the recently introduced capabilities for multispectral imaging, tissue perfusion imaging, and radiation dose reduction through iterative reconstruction are explored with consideration toward the continued refinement and advancement of CT angiography. PMID:24848958

  12. Power spiral conveyor section and method

    SciTech Connect

    Justice, J.C.; Delli-Gatti, F. Jr.

    1992-02-11

    This patent describes a method of mining a mine having a mine mouth, using a mining head with a spiral conveyor including a spiral conveyor screw rotatable with a shaft about an axis of rotation. It comprises: inserting the mining head in the mine through the mine mouth, and advancing the head into the mine mouth; continuously conveying mined material from the mine toward the mine mouth using the spiral conveyor; adding incremental lengths to the spiral conveyor screw as the distance from the mining head to the mouth increases; periodically providing power assists for effecting powered rotating of the spiral conveyor about its axis of rotation along the length of the spiral conveyor about its axis of rotation along the length of the spiral conveyor in the mine as the incremental lengths are added.

  13. Antialiasing backprojection for helical MDCT.

    PubMed

    Mori, I

    2008-03-01

    Helical CTs are well known to suffer from aliasing artifacts because of their finite longitudinal sampling pitch. The artifact pattern is typically strong streaks from bone edges in clinical images. Especially in the case of multidetector row CT, the artifact resulting from longitudinal aliasing is often called a windmill artifact because the visible streaks form a windmill pattern when the object is of a particular shape. The scan must be performed using a very thin slice thickness, i.e., fine sampling in the longitudinal direction, with a longer scan time to mitigate this aliasing artifact. Some elaborate longitudinal interpolation methods to remediate longitudinal aliasing have been proposed, but they have not been successful in practice despite their theoretical importance. A periodic swing of the focal spot in the longitudinal direction, a so-called z-flying focal spot, was introduced recently to achieve finer sampling. Although it is a useful technique, some important deficiencies exist: It is sufficiently effective only near the isocenter and is difficult to apply to a scan using a thick slice thickness, even though longitudinal aliasing is more serious at the thicker scan. In this paper, the author addresses the nature of interlaced (or unequally spaced) sampling and derives a new principle of data treatment that can suppress the aliased spectra selectively. According to this principle, the common practice of image reconstruction, which backprojects data along the original sampling ray path, is never the best choice. The author proposes a new scheme of backprojection, which involves the longitudinal shift of projection data. A proper choice of longitudinal shift for backprojection provides effective and selective suppression of aliased spectra, with retention of the original frequency spectrum depending on the level of focus swing. With this shifted backprojection, the swing of focus can be made much smaller than for a conventional z-flying focal spot. The

  14. Fabrication of Spiral Micro Coil Lines for Electromagnetic Actuators

    NASA Astrophysics Data System (ADS)

    Setomoto, Masaru; Matsumoto, Yoshifumi; Yamashita, Shuhei; Noda, Daiji; Hattori, Tadashi

    With the recent progress in downsizing and the sophistication of various industrial products, the need for more compact actuators is increasing. Actuators account for the larger percentage of volume and weight of a product compared with other parts and devices. We have proposed fabrication process of spiral micro coils that employs X-ray lithography. This process will be effective for fabricating coils of a high aspect ratio lines. Reducing the size of coil lines and increasing their aspect ratio are expected to reduce the size and increase the output of actuators. Using this process, we formed spiral coil lines that can be used in electromagnetic actuators. X-ray lithography was used to form a high aspect ratio helical structure on the surface of an acrylic resin pipe. As a measure to suppress void generation, which is one of the shortcomings of electroplating processes, the sputtering apparatus and plating equipment were improved, a pretreatment process was additionally provided, and the actual electroplating method was improved. As a result, a void-free metallic deposit could be formed on a thin coil line. At the final step of this research study, we etched the coil line to determine optimal etching conditions.

  15. Twist Helicity in Classical Vortices

    NASA Astrophysics Data System (ADS)

    Scheeler, Martin W.; Kedia, Hridesh; Kleckner, Dustin; Irvine, William T. M.

    2015-11-01

    Recent experimental work has demonstrated that a partial measure of fluid Helicity (the sum of linking and writhing of vortex tubes) is conserved even as those vortices undergo topology changing reconnections. Measuring the total Helicity, however, requires additional information about how the vortex lines are locally twisted inside the vortex core. To bridge this gap, we have developed a novel technique for experimentally measuring twist Helicity. Using this method, we are able to measure the production and eventual decay of twist for a variety of vortex evolutions. Remarkably, we observe twist dynamics capable of conserving total Helicity even in the presence of rapidly changing writhe. This work was supported by the NSF MRSEC shared facilities at the University of Chicago (DMR-0820054) and an NSF CAREER award (DMR-1351506). W.T.M.I. further acknowledges support from the A.P. Sloan Foundation and the Packard Foundation.

  16. Helicity multiplexed broadband metasurface holograms

    PubMed Central

    Wen, Dandan; Yue, Fuyong; Li, Guixin; Zheng, Guoxing; Chan, Kinlong; Chen, Shumei; Chen, Ming; Li, King Fai; Wong, Polis Wing Han; Cheah, Kok Wai; Yue Bun Pun, Edwin; Zhang, Shuang; Chen, Xianzhong

    2015-01-01

    Metasurfaces are engineered interfaces that contain a thin layer of plasmonic or dielectric nanostructures capable of manipulating light in a desirable manner. Advances in metasurfaces have led to various practical applications ranging from lensing to holography. Metasurface holograms that can be switched by the polarization state of incident light have been demonstrated for achieving polarization multiplexed functionalities. However, practical application of these devices has been limited by their capability for achieving high efficiency and high image quality. Here we experimentally demonstrate a helicity multiplexed metasurface hologram with high efficiency and good image fidelity over a broad range of frequencies. The metasurface hologram features the combination of two sets of hologram patterns operating with opposite incident helicities. Two symmetrically distributed off-axis images are interchangeable by controlling the helicity of the input light. The demonstrated helicity multiplexed metasurface hologram with its high performance opens avenues for future applications with functionality switchable optical devices. PMID:26354497

  17. Helicity multiplexed broadband metasurface holograms.

    PubMed

    Wen, Dandan; Yue, Fuyong; Li, Guixin; Zheng, Guoxing; Chan, Kinlong; Chen, Shumei; Chen, Ming; Li, King Fai; Wong, Polis Wing Han; Cheah, Kok Wai; Pun, Edwin Yue Bun; Zhang, Shuang; Chen, Xianzhong

    2015-01-01

    Metasurfaces are engineered interfaces that contain a thin layer of plasmonic or dielectric nanostructures capable of manipulating light in a desirable manner. Advances in metasurfaces have led to various practical applications ranging from lensing to holography. Metasurface holograms that can be switched by the polarization state of incident light have been demonstrated for achieving polarization multiplexed functionalities. However, practical application of these devices has been limited by their capability for achieving high efficiency and high image quality. Here we experimentally demonstrate a helicity multiplexed metasurface hologram with high efficiency and good image fidelity over a broad range of frequencies. The metasurface hologram features the combination of two sets of hologram patterns operating with opposite incident helicities. Two symmetrically distributed off-axis images are interchangeable by controlling the helicity of the input light. The demonstrated helicity multiplexed metasurface hologram with its high performance opens avenues for future applications with functionality switchable optical devices. PMID:26354497

  18. M51's spiral structure

    NASA Technical Reports Server (NTRS)

    Howard, S.; Byrd, Gene G.

    1990-01-01

    The M51 system (NGC 5194/5195) provides an excellent problem both in spiral structure and in galaxy interactions. The authors present an analytic study of a computer experiment on the excitation mechanisms for M51's spiral arms and whether or not a halo is important for these mechanisms. This work extends previous numerical studies of the M51 system by including self-gravitation in a two component disk: gas and stars, and a dark halo. The analytic study provides two new observational constraints: the time (approx. 70 to 84 million years ago) and position angle of perigalacticon (300 degrees). By using these constraints and a simple conic approximation, the search for the companion's possible orbit is greatly simplified. This requires fewer N-body simulations than a fully self-gravitating orbit search.

  19. Planet Masses from Disk Spirals

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-12-01

    Young, forming planets can generate immense spiral structures within their protoplanetary disks. A recent study has shown that observations of these spiral structures may allow astronomers to measure the mass of the planets that create them.Spirals From WavesSnapshots of the surface density of a protoplanetary disk in a 2D simulation, 3D simulation, and synthesized scattered-light image. Click for a closer look! [Fung Dong, 2015]Recent studies have shown that a single planet, if it is massive enough, can excite multiple density waves within a protoplanetary disk as it orbits. These density waves can then interfere to produce a multiple-armed spiral structure in the disk inside of the planets orbit a structure which can potentially be observed in scattered-light images of the disk.But what do these arms look like, and what factors determine their structure? In a recently published study, Jeffrey Fung and Ruobing Dong, two researchers at the University of California at Berkeley, have modeled the spiral arms in an effort to answer these questions.Arms Provide AnswersA useful parameter for describing the structure is the azimuthal separation (sep) between the primary and secondary spiral arms. If you draw a circle within the disk and measure the angle between the two points where the primary and secondary arms cross it, thats sep.Azimuthal separation of the primary and secondary spiral arms, as a function of the planet-to-star mass ratio q. The different curves represent different disk aspect ratios. [Fung Dong, 2015]The authors find thatsep stays roughly constant for different radii, but its strongly dependent on the planets mass: for larger planets, sep increases. They discover that sep scales as a power of the planet mass for companions between Neptune mass and 16 Jupiter masses, orbiting around a solar-mass star. For larger, brown-dwarf-size companions, sep is a constant 180.If this new theory is confirmed, it could have very interesting implications for

  20. Spiralling dynamics near heteroclinic networks

    NASA Astrophysics Data System (ADS)

    Rodrigues, Alexandre A. P.; Labouriau, Isabel S.

    2014-02-01

    There are few explicit examples in the literature of vector fields exhibiting complex dynamics that may be proved analytically. We construct explicitly a two parameter family of vector fields on the three-dimensional sphere S, whose flow has a spiralling attractor containing the following: two hyperbolic equilibria, heteroclinic trajectories connecting them transversely and a non-trivial hyperbolic, invariant and transitive set. The spiralling set unfolds a heteroclinic network between two symmetric saddle-foci and contains a sequence of topological horseshoes semiconjugate to full shifts over an alphabet with more and more symbols, coexisting with Newhouse phenomena. The vector field is the restriction to S of a polynomial vector field in R. In this article, we also identify global bifurcations that induce chaotic dynamics of different types.

  1. THE SPIRAL GALAXY M100

    NASA Technical Reports Server (NTRS)

    2002-01-01

    An image of the grand design of spiral galaxy M100 obtained with NASA's Hubble Space Telescope resolves individual stars within the majestic spiral arms. (These stars typically appeared blurred together when viewed with ground-based telescopes.) Hubble has the ability to resolve individual stars in other galaxies and measure accurately the light from very faint stars. This makes space telescope invaluable for identifying a rare class of pulsating stars, called Cepheid Variable stars embedded within M100's spiral arms. Cepheids are reliable cosmic distance mileposts. The interval it takes for the Cepheid to complete one pulsation is a direct indication of the stars's intrinsic brightness. This value can be used to make a precise measurement of the galaxy's distance, which turns out to be 56 million light-years. M100 (100th object in the Messier catalog of non-stellar objects) is a majestic face-on spiral galaxy. It is a rotating system of gas and stars, similar to our own galaxy, the Milky Way. Hubble routinely can view M100 with a level of clarity and sensitivity previously possible only for the very few nearby galaxies that compose our 'Local Group.'' M100 is a member of the huge Virgo cluster of an estimated 2,500 galaxies. The galaxy can be seen by amateur astronomers as a faint, pinwheel-shaped object in the spring constellation Coma Berenices. Technical Information: The Hubble Space Telescope image was taken on December 31, 1993 with the Wide Field Planetary Camera 2 (WFPC 2). This color picture is a composite of several images taken in different colors of light. Blue corresponds to regions containing hot newborn stars. The Wide Field and Planetary Camera 2 was developed by the Jet Propulsion Laboratory (JPL) and managed by the Goddard Space Flight Center for NASA's Office of Space Science. Credit: J. Trauger, JPL and NASA

  2. Saved by a Spiral Notebook

    ERIC Educational Resources Information Center

    Taylor, Kristan

    2005-01-01

    In this article, the author shares how she used journal exercises to unify her classroom. Students used cheap spiral notebooks and followed a few very basic rules: (1) Start out by writing for 5 minutes, increasing to 15 or more; (2) Read the entry to the class only if you want to; and (3) Use the given topic or write whatever is on your mind.…

  3. Employing helicity amplitudes for resummation

    NASA Astrophysics Data System (ADS)

    Moult, Ian; Stewart, Iain W.; Tackmann, Frank J.; Waalewijn, Wouter J.

    2016-05-01

    Many state-of-the-art QCD calculations for multileg processes use helicity amplitudes as their fundamental ingredients. We construct a simple and easy-to-use helicity operator basis in soft-collinear effective theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are directly given in terms of color-ordered helicity amplitudes. Using this basis allows one to seamlessly combine fixed-order helicity amplitudes at any order they are known with a resummation of higher-order logarithmic corrections. In particular, the virtual loop amplitudes can be employed in factorization theorems to make predictions for exclusive jet cross sections without the use of numerical subtraction schemes to handle real-virtual infrared cancellations. We also discuss matching onto SCET in renormalization schemes with helicities in 4- and d -dimensions. To demonstrate that our helicity operator basis is easy to use, we provide an explicit construction of the operator basis, as well as results for the hard matching coefficients, for p p →H +0 , 1, 2 jets, p p →W /Z /γ +0 , 1, 2 jets, and p p →2 , 3 jets. These operator bases are completely crossing symmetric, so the results can easily be applied to processes with e+e- and e-p collisions.

  4. 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.

  5. Spiral inertial waves emitted from geophysical vortices

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Özgökmen, Tamay M.

    2016-03-01

    By numerically simulating an initially unstable geophysical vortex, we discover for the first time a special kind of inertial waves, which are emitted in a spiral manner from the vortices; we refer to these waves as spiral inertial waves (SIWs). SIWs appear at small Rossby numbers (0.01 ≤ Ro ≤ 1) according to our parameter sweep experiments; the amplitude, wavelength and frequency of SIWs are sensitive to Rossby numbers. We extend the Lighthill-Ford radiation into inertial waves, and propose an indicator for the emission of inertial waves; this indicator may be adopted into general circulation models to parameterize inertial waves. Additionally, in our tracer releasing experiments, SIWs organize tracers into spirals, and modify the tracer's local rate of change by advecting tracers vertically. Further, the spirals of SIWs resembles some spiral features observed in the ocean and atmosphere, such as spiral ocean eddies and spiral hurricane rainbands; thus, SIWs may offer another mechanism to form spiral eddies and rainbands. Since no density anomaly is required to generate the spirals of SIWs, we infer that the density anomaly, hence the baroclinic or frontal instability, is unlikely to be the key factor in the formation of these spiral features.

  6. Transient spirals as superposed instabilities

    SciTech Connect

    Sellwood, J. A.; Carlberg, R. G. E-mail: carlberg@astro.utoronto.ca

    2014-04-20

    We present evidence that recurrent spiral activity, long manifested in simulations of disk galaxies, results from the superposition of a few transient spiral modes. Each mode lasts between 5 and 10 rotations at its corotation radius where its amplitude is greatest. The scattering of stars as each wave decays takes place over narrow ranges of angular momentum, causing abrupt changes to the impedance of the disk to subsequent traveling waves. Partial reflections of waves at these newly created features allows new standing-wave instabilities to appear that saturate and decay in their turn, scattering particles at new locations, creating a recurring cycle. The spiral activity causes the general level of random motion to rise, gradually decreasing the ability of the disk to support further activity unless the disk contains a dissipative gas component from which stars form on near-circular orbits. We also show that this interpretation is consistent with the behavior reported in other recent simulations with low-mass disks.

  7. Monte Carlo simulation of helical tomotherapy with PENELOPE

    NASA Astrophysics Data System (ADS)

    Sterpin, E.; Salvat, F.; Cravens, R.; Ruchala, K.; Olivera, G. H.; Vynckier, S.

    2008-04-01

    Helical tomotherapy (HT) delivers intensity-modulated radiation therapy (IMRT) using the simultaneous movement of the couch, the gantry and the binary multileaf collimator (MLC), a procedure that differs from conventional dynamic or step-and-shoot IMRT. A Monte Carlo (MC) simulation of HT in the helical mode therefore requires a new approach. Using validated phase-space files (PSFs) obtained through the MC simulation of the static mode with PENELOPE, an analytical model of the binary MLC, called the 'transfer function' (TF), was first devised to perform the transport of particles through the MLC much faster than time-consuming MC simulation and with no significant loss of accuracy. Second, a new tool, called TomoPen, was designed to simulate the helical mode by rotating and translating the initial coordinates and directions of the particles in the PSF according to the instantaneous position of the machine, transporting the particles through the MLC (in the instantaneous configuration defined by the sinogram), and computing the dose distribution in the CT structure using PENELOPE. Good agreement with measurements and with the treatment planning system of tomotherapy was obtained, with deviations generally well within 2%/1 mm, for the simulation of the helical mode for two commissioning procedures and a clinical plan calculated and measured in homogeneous conditions.

  8. Collective excitations in itinerant spiral magnets

    SciTech Connect

    Kampf, A.P.

    1996-01-01

    We investigate the coupled charge and spin collective excitations in the spiral phases of the two-dimensional Hubbard model using a generalized random-phase approximation. Already for small doping the spin-wave excitations are strongly renormalized due to low-energy particle-hole excitations. Besides the three Goldstone modes of the spiral state the dynamical susceptibility reveals an extra zero mode for low doping and strong coupling values signaling an intrinsic instability of the homogeneous spiral state. In addition, near-zero modes are found in the vicinity of the spiral pitch wave number for out-of-plane spin fluctuations. Their origin is found to be the near degeneracy with staggered noncoplanar spiral states which, however, are not the lowest energy Hartree-Fock solutions among the homogeneous spiral states. {copyright} {ital 1996 The American Physical Society.}

  9. CT Scans

    MedlinePlus

    ... cross-sectional pictures of your body. Doctors use CT scans to look for Broken bones Cancers Blood clots Signs of heart disease Internal bleeding During a CT scan, you lie still on a table. The table ...

  10. In-Orbit Construction with a Helical Seam Pipe Mill

    NASA Astrophysics Data System (ADS)

    Gilhooley, N.

    The challenges of building large structures in space, and in particular a torus habitat, require novel processes. One potential method is to manufacture helical seam (also called spiral) pipe in orbit using a pipe mill. These machines turn rolls of steel or alloy into fully formed, welded and inspected pipe, pressure vessels and silos of various diameters. Pipe mills are highly automated and efficient in a factory environment and are increasingly being used for in-situ repair. By constructing in-orbit (on-orbit assembly) the launch vehicle can supply full payloads of compact, robust rolls of material; and the installation design is less restricted by fairing constraints and modular limitations. The use of a pipe mill is discussed as a possible construction method, for comparison an example design envelope is shown and further pipe mill products are considered.

  11. Recent manufacturing advances for spiral bevel gears

    NASA Technical Reports Server (NTRS)

    Handschuh, Robert F.; Bill, Robert C.

    1991-01-01

    The U.S. Army Aviation Systems Command (AVSCOM), through the Propulsion Directorate at NASA LRC, has recently sponsored projects to advance the manufacturing process for spiral bevel gears. This type of gear is a critical component in rotary-wing propulsion systems. Two successfully completed contracted projects are described. The first project addresses the automated inspection of spiral bevel gears through the use of coordinate measuring machines. The second project entails the computer-numerical-control (CNC) conversion of a spiral bevel gear grinding machine that is used for all aerospace spiral bevel gears. The results of these projects are described with regard to the savings effected in manufacturing time.

  12. Recent manufacturing advances for spiral bevel gears

    NASA Technical Reports Server (NTRS)

    Handschuh, Robert F.; Bill, Robert C.

    1991-01-01

    The U.S. Army Aviation Systems Command (AVSCOM), through the Propulsion Directorate at NASA Lewis Research Center, has recently sponsored projects to advance the manufacturing process for spiral bevel gears. This type of gear is a critical component in rotary-wing propulsion systems. Two successfully completed contracted projects are described. The first project addresses the automated inspection of spiral bevel gears through the use of coordinate measuring machines. The second project entails the computer-numerical-control (CNC) conversion of a spiral bevel gear grinding machine that is used for all aerospace spiral bevel gears. The results of these projects are described with regard to the savings effected in manufacturing time.

  13. Optical fiber antenna generating spiral beam shapes

    SciTech Connect

    Sarkar Pal, S.; Mondal, S. K. Kumar, R.; Akula, A.; Ghosh, R.; Bhatnagar, R.; Kumbhakar, D.

    2014-01-20

    A simple method is proposed here to generate vortex beam and spiral intensity patterns from a Gaussian source. It uses a special type of optical fiber antenna of aperture ∼80 nm having naturally grown surface curvature along its length. The antenna converts linearly polarized Gaussian beam into a beam with spiral intensity patterns. The experimentally obtained spiral patterns with single and double spiral arms manifest the orbital angular momentum, l = ±1, 2, carried by the output beam. Such beam can be very useful for optical tweezer, metal machining, and similar applications.

  14. Disk's Spiral Arms Point to Possible Planets

    NASA Video Gallery

    Simulations of young stellar systems suggest that planets embedded in a circumstellar disk can produce many distinctive structures, including rings, gaps and spiral arms. This video compares comput...

  15. Translational Symmetry-Breaking for Spiral Waves

    NASA Astrophysics Data System (ADS)

    LeBlanc, V. G.; Wulff, C.

    2000-10-01

    Spiral waves are observed in numerous physical situations, ranging from Belousov-Zhabotinsky (BZ) chemical reactions, to cardiac tissue, to slime-mold aggregates. Mathematical models with Euclidean symmetry have recently been developed to describe the dynamic behavior (for example, meandering) of spiral waves in excitable media. However, no physical experiment is ever infinite in spatial extent, so the Euclidean symmetry is only approximate. Experiments on spiral waves show that inhomogeneities can anchor spirals and that boundary effects (for example, boundary drifting) become very important when the size of the spiral core is comparable to the size of the reacting medium. Spiral anchoring and boundary drifting cannot be explained by the Euclidean model alone. In this paper, we investigate the effects on spiral wave dynamics of breaking the translation symmetry while keeping the rotation symmetry. This is accomplished by introducing a small perturbation in the five-dimensional center bundle equations (describing Hopf bifurcation from one-armed spiral waves) which is SO(2)-equivariant but not equivariant under translations. We then study the effects of this perturbation on rigid spiral rotation, on quasi-periodic meandering and on drifting.

  16. Selective control for helical microswimmers

    NASA Astrophysics Data System (ADS)

    Katsamba, Panayiota; Lauga, Eric

    2015-11-01

    One of the greatest aspirations for artificial microswimmers is their application in non-invasive medicine. For any practical use, adequate mechanisms enabling control of multiple artificial swimmers is of paramount importance. Here we propose a multi-helical, freely-jointed motor as a novel selective control mechanism. We show that the nonlinear step-out behavior of a magnetized helix driven by a rotating magnetic field can be exploited, when used in conjunction with other helices, to obtain a velocity profile that is non-negligible only within a chosen interval of operating frequencies. Specifically, the force balance between the competing opposite-handed helices is tuned to give no net motion at low frequencies while in the middle frequency range, the swimming velocity increases monotonically with the driving frequency if two opposite helices are used, thereby allowing speed adjustment by varying the driving frequency. We illustrate this idea in detail on a two-helix system, and demonstrate how to generalize to N helices, both numerically and theoretically. We finish by explaining how to solve the inverse problem and design an artificial swimmer with an arbitrarily-complex velocity vs. frequency relationship.

  17. Helicity Injected Torus Program Overview

    NASA Astrophysics Data System (ADS)

    Redd, A. J.; Jarboe, T. R.; Aboulhosn, R. Z.; Akcay, C.; Hamp, W. T.; Marklin, G.; Nelson, B. A.; O'Neill, R. G.; Raman, R.; Sieck, P. E.; Smith, R. J.; Sutphin, G. L.; Wrobel, J. S.; Mueller, D.; Roquemore, L.

    2006-10-01

    The Helicity Injected Torus with Steady Inductive Helicity Injection (HIT--SI) spheromak experiment [Sieck, Nucl. Fusion v.46, p.254 (2006)] addresses critical issues for spheromaks, including current drive, high-beta operation, confinement quality and efficient steady-state operation. HIT--SI has a ``bow-tie'' shaped axisymmetric confinement region (major radius R=0.33 m, axial extent of 0.57 m) and two half-torus helicity injectors, one mounted on each end of the flux conserver. HIT--SI has produced spheromaks with up to 30 kA of toroidal current, using less than 4 MW of applied power, demonstrating that Steady Inductive Helicity Injection can generate and sustain discharges with modest power requirements. Fast camera images of HIT--SI discharges indicate a toroidally rotating n=1 structure, driven by the helicity injectors. The direction of the toroidal current is determined by the direction of rotation of the driven n=1. Measured surface and internal magnetic fields in HIT--SI discharges are consistent with that of the true 3D Taylor state, including the injectors. Recent HIT--SI physics studies, diagnostic improvements and machine upgrades will also be summarized.

  18. Exact helical reconstruction using native cone-beam geometries

    NASA Astrophysics Data System (ADS)

    Noo, Frédéric; Pack, Jed; Heuscher, Dominic

    2003-12-01

    This paper is about helical cone-beam reconstruction using the exact filtered backprojection formula recently suggested by Katsevich (2002a Phys. Med. Biol. 47 2583-97). We investigate how to efficiently and accurately implement Katsevich's formula for direct reconstruction from helical cone-beam data measured in two native geometries. The first geometry is the curved detector geometry of third-generation multi-slice CT scanners, and the second geometry is the flat detector geometry of C-arms systems and of most industrial cone-beam CT scanners. For each of these two geometries, we determine processing steps to be applied to the measured data such that the final outcome is an implementation of the Katsevich formula. These steps are first described using continuous-form equations, disregarding the finite detector resolution and the source position sampling. Next, techniques are presented for implementation of these steps with finite data sampling. The performance of these techniques is illustrated for the curved detector geometry of third-generation CT scanners, with 32, 64 and 128 detector rows. In each case, resolution and noise measurements are given along with reconstructions of the FORBILD thorax phantom.

  19. Behavior of a particle-laden flow in a spiral channel

    NASA Astrophysics Data System (ADS)

    Lee, Sungyon; Stokes, Yvonne; Bertozzi, Andrea L.

    2014-04-01

    Spiral gravity separators are devices used in mineral processing to separate particles based on their specific gravity or size. The spiral geometry allows for the simultaneous application of gravitational and centripetal forces on the particles, which leads to segregation of particles. However, this segregation mechanism is not fundamentally understood, and the spiral separator literature does not tell a cohesive story either experimentally or theoretically. While experimental results vary depending on the specific spiral separator used, present theoretical works neglect the significant coupling between the particle dynamics and the flow field. Using work on gravity-driven monodisperse slurries on an incline that empirically accounts for this coupling, we consider a monodisperse particle slurry of small depth flowing down a rectangular channel that is helically wound around a vertical axis. We use a thin-film approximation to derive an equilibrium profile for the particle concentration and fluid depth and find that, in the steady state limit, the particles concentrate towards the vertical axis of the helix, leaving a region of clear fluid.

  20. How Does Carbon Nanoring Deform to Spiral Induced by Carbon Nanotube?

    PubMed Central

    Chen, Wei; Li, Hui

    2014-01-01

    Molecular dynamics (MD) simulations have been performed on the interaction between carbon nanoring (CNR) and single-wall carbon nanotube (SWCNT). The results show that, the CNR can spontaneously insert into the hollow interior of the SWCNTs to form a DNA-like double-helix, or collapse to a linked double graphitic nanoribbon and wrap in a helical manner around a tube. Further analyses of energy components show that this unique phenomenon is the result of the Van der Waals interaction. The spiral configuration of the CNR takes the least amount of energy and achieves the maximum occupancy. The sizes of CNR and SWCNT should meet the required conditions to guarantee the spiral form in the insertion and wrapping processes. Two CNRs can also be encapsulated in the SWCNT to form a helix at the same time. Furthermore, we also studied the encapsulation process of CNRs modified with –OH and –H functional groups. PMID:24463737

  1. Helical instability of a rotating viscous liquid jet

    NASA Astrophysics Data System (ADS)

    Kubitschek, J. P.; Weidman, P. D.

    2007-11-01

    Vertical rotating viscous liquid jet experiments show a clear preference for helical instabilities that evolve from initially planar disturbances at large rotation rates for fixed fluid properties. The laboratory setup for the experiments described herein was chosen as the nearest earth-based equivalent to a uniformly rotating viscous liquid column in the absence of gravity. In the ideal situation with stress-free boundaries, the preferred modes of linear temporal instability are theoretically known over the entire physical domain spanned by the Hocking parameter L =γ/ρa3Ω2 and the rotational Reynolds number Re =a2Ω/ν, where a is the column radius, Ω is its uniform angular velocity, and ρ, ν, and γ are, respectively, the fluid density, kinematic viscosity, and surface tension. The theoretical results show that instability in L-Re parameter space is dominated by three mode types: The axisymmetric mode, the n ≥2 planar modes, and the first n =1 spiral mode. Experiments reveal that, in the L-Re region for which the uniformly rotating liquid column is dominated by planar modes of instability, the rotating liquid jet spontaneously gives rise to planar disturbances of mode n ≥2 that rapidly evolve into helical instabilities. However, these observed instabilities are not the spiral normal modes that exist for n ≥1 as posited in linear stability theory. In spite of obvious fundamental differences between the rotating liquid jet and the uniformly rotating liquid column, some remarkable similarities associated with initial growth rates, angular frequencies, and mode transitions between the two systems are found.

  2. Magnetic fields in nearby spirals

    NASA Astrophysics Data System (ADS)

    Sun, Xiaohui; Lenc, Emil

    2013-10-01

    Magnetic fields play an important role in star formation process and dynamic evolution of galaxies. Previous studies of magnetic fields relied on narrow band polarisation observations and difficult to disentangle magnetised structures along line of sight. Thanks to the broad bandwidth and multi-channels of CABB we are now able to recover the 3D structures of magnetic fields using RM synthesis and QU-fitting. We propose to observe two nearby spirals M83 and NGC 4945 to build clear pictures of their magnetic fields.

  3. Emergency Physicians Think in Spirals

    PubMed Central

    Renouf, Tia; Whalen, Desmond; Pollard, Megan

    2015-01-01

    As adult learners, junior clerks on core rotations in emergency medicine (EM) are expected to “own” their patients and follow them from presentation to disposition in the Emergency Department (ED). Traditionally, we teach clerks to present an exhaustive linear list of symptoms and signs to their preceptors. This does not apply well to the fast-paced ED setting. Mnemonics have been developed to teach clerks how to present succinctly and cohesively. To address the need for continual patient reassessment throughout the patient’s journey in the ED, we propose a complimentary approach called SPIRAL. PMID:26719824

  4. HUBBLE REVEALS 'BACKWARDS' SPIRAL GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Astronomers have found a spiral galaxy that may be spinning to the beat of a different cosmic drummer. To the surprise of astronomers, the galaxy, called NGC 4622, appears to be rotating in the opposite direction to what they expected. Pictures by NASA's Hubble Space Telescope helped astronomers determine that the galaxy may be spinning clockwise by showing which side of the galaxy is closer to Earth. A Hubble telescope photo of the oddball galaxy is this month's Hubble Heritage offering. The image shows NGC 4622 and its outer pair of winding arms full of new stars [shown in blue]. Astronomers are puzzled by the clockwise rotation because of the direction the outer spiral arms are pointing. Most spiral galaxies have arms of gas and stars that trail behind as they turn. But this galaxy has two 'leading' outer arms that point toward the direction of the galaxy's clockwise rotation. To add to the conundrum, NGC 4622 also has a 'trailing' inner arm that is wrapped around the galaxy in the opposite direction it is rotating. Based on galaxy simulations, a team of astronomers had expected that the galaxy was turning counterclockwise. NGC 4622 is a rare example of a spiral galaxy with arms pointing in opposite directions. What caused this galaxy to behave differently from most galaxies? Astronomers suspect that NGC 4622 interacted with another galaxy. Its two outer arms are lopsided, meaning that something disturbed it. The new Hubble image suggests that NGC 4622 consumed a small companion galaxy. The galaxy's core provides new evidence for a merger between NGC 4622 and a smaller galaxy. This information could be the key to understanding the unusual leading arms. Galaxies, which consist of stars, gas, and dust, rotate very slowly. Our Sun, one of many stars in our Milky Way Galaxy, completes a circuit around the Milky Way every 250 million years. NGC 4622 resides 111 million light-years away in the constellation Centaurus. The pictures were taken in May 2001 with Hubble

  5. Generalized helicity and Beltrami fields

    SciTech Connect

    Buniy, Roman V.; Kephart, Thomas W.

    2014-05-15

    We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy–momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang–Mills action functional 1/4 ∫{sub Ω}trF{sub μν}F{sup μν}d{sup 4}x subject to the local constraint ε{sup μναβ}trF{sub μν}F{sub αβ}=0 satisfies the covariant non-abelian Beltrami equation. -- Highlights: •We introduce the covariant non-abelian helicity and Beltrami equation. •The Yang–Mills action and instanton term constraint lead to the Beltrami equation. •Solutions of the Beltrami equation conserve helicity.

  6. Rational design of helical architectures

    PubMed Central

    Chakrabarti, Dwaipayan; Fejer, Szilard N.; Wales, David J.

    2009-01-01

    Nature has mastered the art of creating complex structures through self-assembly of simpler building blocks. Adapting such a bottom-up view provides a potential route to the fabrication of novel materials. However, this approach suffers from the lack of a sufficiently detailed understanding of the noncovalent forces that hold the self-assembled structures together. Here we demonstrate that nature can indeed guide us, as we explore routes to helicity with achiral building blocks driven by the interplay between two competing length scales for the interactions, as in DNA. By characterizing global minima for clusters, we illustrate several realizations of helical architecture, the simplest one involving ellipsoids of revolution as building blocks. In particular, we show that axially symmetric soft discoids can self-assemble into helical columnar arrangements. Understanding the molecular origin of such spatial organisation has important implications for the rational design of materials with useful optoelectronic applications.

  7. 20 percent lower lung cancer mortality with low-dose CT vs chest X-ray

    Cancer.gov

    Scientists have found a 20 percent reduction in deaths from lung cancer among current or former heavy smokers who were screened with low-dose helical computed tomography (CT) versus those screened by chest X-ray.

  8. Helical axis stellarator equilibrium model

    SciTech Connect

    Koniges, A.E.; Johnson, J.L.

    1985-02-01

    An asymptotic model is developed to study MHD equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two-dimensional generalized partial differential equation of the Grad-Shafranov type. A stellarator-expansion free-boundary equilibrium code is modified to solve the helical-axis equations. The expansion model is used to predict the equilibrium properties of Asperators NP-3 and NP-4. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift.

  9. Brownian motion of helical flagella.

    PubMed

    Hoshikawa, H; Saito, N

    1979-07-01

    We develops a theory of the Brownian motion of a rigid helical object such as bacterial flagella. The statistical properties of the random forces acting on the helical object are discussed and the coefficients of the correlations of the random forces are determined. The averages , and are also calculated where z and theta are the position along and angle around the helix axis respectively. Although the theory is limited to short time interval, direct comparison with experiment is possible by using the recently developed cinematography technique. PMID:16997210

  10. OPE for all helicity amplitudes

    NASA Astrophysics Data System (ADS)

    Basso, Benjamin; Caetano, João; Córdova, Lucía; Sever, Amit; Vieira, Pedro

    2015-08-01

    We extend the Operator Product Expansion (OPE) for scattering amplitudes in planar SYM to account for all possible helicities of the external states. This is done by constructing a simple map between helicity configurations and so-called charged pentagon transitions. These OPE building blocks are generalizations of the bosonic pentagons entering MHV amplitudes and they can be bootstrapped at finite coupling from the integrable dynamics of the color flux tube. A byproduct of our map is a simple realization of parity in the super Wilson loop picture.

  11. Artifacts in CT: recognition and avoidance.

    PubMed

    Barrett, Julia F; Keat, Nicholas

    2004-01-01

    Artifacts can seriously degrade the quality of computed tomographic (CT) images, sometimes to the point of making them diagnostically unusable. To optimize image quality, it is necessary to understand why artifacts occur and how they can be prevented or suppressed. CT artifacts originate from a range of sources. Physics-based artifacts result from the physical processes involved in the acquisition of CT data. Patient-based artifacts are caused by such factors as patient movement or the presence of metallic materials in or on the patient. Scanner-based artifacts result from imperfections in scanner function. Helical and multisection technique artifacts are produced by the image reconstruction process. Design features incorporated into modern CT scanners minimize some types of artifacts, and some can be partially corrected by the scanner software. However, in many instances, careful patient positioning and optimum selection of scanning parameters are the most important factors in avoiding CT artifacts. PMID:15537976

  12. Slow bars in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Fridman, A. M.; Khoruzhii, O. V.

    2000-11-01

    Here we put forward some arguments in favour of the existence of slow bars. More then a half of spiral galaxies have in their central regions a bar - a structure in the form of triaxial ellipsoid. Historically two models of the bar were developed - those of the so called ``slow'' and ``fast'' bars. In both cases the bar is in some resonance with the galactic disc region near the bar ends - it is the corotation resonance for a fast bar and the inner Lindblad resonance for a slow bar. For the same angular velocity the fast bar would be larger then the slow bar. Alternatively, for the same size the fast bar would have much higher angular velocity, that being the reason for the terminology used. Up till now, the direct measurement of angular velocity of a bar has been an open problem. This is why all arguments on the nature of bar observed in some particular galaxy are inevitably indirect. Despite the fact that the model of slow bars was developed slightly earlier, the main part of attention was focused on the fast bars. Presently many researchers believe in the existence of the fast bars in real galaxies, while discussions on the existence of the slow bars continue so far. In this Letter we demonstrate that the bar detected in the grand design spiral galaxy NGC 157 is the slow bar.

  13. 29 CFR 1917.121 - Spiral stairways.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 7 2010-07-01 2010-07-01 false Spiral stairways. 1917.121 Section 1917.121 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR (CONTINUED) MARINE TERMINALS Terminal Facilities § 1917.121 Spiral stairways. (a) Definition....

  14. Generation and characterization of spirally polarized fields

    NASA Astrophysics Data System (ADS)

    Ramírez-Sánchez, V.; Piquero, G.; Santarsiero, M.

    2009-08-01

    Recently introduced global parameters for describing the polarization of a beam are used to characterize spirally polarized fields, which include as particular cases azimuthally and radially polarized fields. Theoretical predictions about such global parameters are experimentally confirmed by generating beams with spirally polarized transverse patterns, by means of two different procedures.

  15. Twokink excitation in a spiral magnetic structure

    NASA Astrophysics Data System (ADS)

    Kiselev, V. V.; Raskovalov, A. A.

    2016-01-01

    Twokink excitations in the spiral structures of magnets and multiferroics are found and analyzed within the framework for the sine-Gordon model. It is shown that the movement and interaction of the kinks is accompanied by macroscopic translations of the spiral structure. The ways of observing and exciting kinks in the external magnetic field are discussed.

  16. The smallest fullerene without a spiral

    NASA Astrophysics Data System (ADS)

    Brinkmann, Gunnar; Goedgebeur, Jan; McKay, Brendan D.

    2012-01-01

    In this note, we give the result of a computer search for the smallest fullerene that does not allow a face spiral code as used by Manolopoulos and Fowler and adopted in IUPAC recommendations for fullerene nomenclature. The search enumerated all the small fullerenes on up to 400 vertices and the conclusion is that the smallest fullerene without a face spiral has 380 vertices.

  17. 29 CFR 1917.121 - Spiral stairways.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 7 2011-07-01 2011-07-01 false Spiral stairways. 1917.121 Section 1917.121 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR (CONTINUED) MARINE TERMINALS Terminal Facilities § 1917.121 Spiral stairways. (a) Definition....

  18. Spiral density waves in M81. I. Stellar spiral density waves

    SciTech Connect

    Feng, Chien-Chang; Lin, Lien-Hsuan; Wang, Hsiang-Hsu; Taam, Ronald E.

    2014-04-20

    Aside from the grand-design stellar spirals appearing in the disk of M81, a pair of stellar spiral arms situated well inside the bright bulge of M81 has been recently discovered by Kendall et al. The seemingly unrelated pairs of spirals pose a challenge to the theory of spiral density waves. To address this problem, we have constructed a three-component model for M81, including the contributions from a stellar disk, a bulge, and a dark matter halo subject to observational constraints. Given this basic state for M81, a modal approach is applied to search for the discrete unstable spiral modes that may provide an understanding for the existence of both spiral arms. It is found that the apparently separated inner and outer spirals can be interpreted as a single trailing spiral mode. In particular, these spirals share the same pattern speed 25.5 km s{sup –1} kpc{sup –1} with a corotation radius of 9.03 kpc. In addition to the good agreement between the calculated and the observed spiral pattern, the variation of the spiral amplitude can also be naturally reproduced.

  19. The transport of relative canonical helicity

    SciTech Connect

    You, S.

    2012-09-15

    The evolution of relative canonical helicity is examined in the two-fluid magnetohydrodynamic formalism. Canonical helicity is defined here as the helicity of the plasma species' canonical momentum. The species' canonical helicity are coupled together and can be converted from one into the other while the total gauge-invariant relative canonical helicity remains globally invariant. The conversion is driven by enthalpy differences at a surface common to ion and electron canonical flux tubes. The model provides an explanation for why the threshold for bifurcation in counter-helicity merging depends on the size parameter. The size parameter determines whether magnetic helicity annihilation channels enthalpy into the magnetic flux tube or into the vorticity flow tube components of the canonical flux tube. The transport of relative canonical helicity constrains the interaction between plasma flows and magnetic fields, and provides a more general framework for driving flows and currents from enthalpy or inductive boundary conditions.

  20. Helical instability of a rotating viscous liquid jet

    NASA Astrophysics Data System (ADS)

    Kubitschek, J. P.; Weidman, P. D.

    2007-11-01

    Experimental results are presented for a rotating viscous liquid jet showing a clear preference for helical instabilities that evolve from initially planar disturbances at large rotation rates. In the ideal case of a uniformly rotating viscous liquid column with stress-free boundaries in the absence of gravity, the preferred modes of linear temporal instability are theoretically known over the entire physical domain. The relevant physical parameters are L=γ/ρa^3φ^2 and Re = a^2φ/ν, where a is the column radius, φ the uniform angular velocity and ρ, ν, and γ are fluid density, kinematic viscosity and surface tension, respectively. The theoretical results suggest that instability in different regions of L-Re parameter space is dominated by three modes: the axisymmetric mode, n>= 2 planar modes, and the first n = 1 spiral mode. For the rotating viscous liquid jet, experiments reveal that planar disturbances of the same mode numbers (n>= 2) spontaneously arise in the same regions of parameter space predicted by uniformly rotating viscous liquid column theory. However, these planar disturbances do not persist, but instead rapidly evolve into helical instabilities. Although fundamental differences exist between the rotating liquid jet and the uniformly rotating liquid column, some remarkable similarities associated with initial growth rates, disturbances frequencies, and mode transitions between the two systems are found.

  1. Electrodynamics of planar Archimedean spiral resonator

    NASA Astrophysics Data System (ADS)

    Maleeva, N.; Averkin, A.; Abramov, N. N.; Fistul, M. V.; Karpov, A.; Zhuravel, A. P.; Ustinov, A. V.

    2015-07-01

    We present a theoretical and experimental study of electrodynamics of a planar spiral superconducting resonator of a finite length. The resonator is made in the form of a monofilar Archimedean spiral. By making use of a general model of inhomogeneous alternating current flowing along the resonator and specific boundary conditions on the surface of the strip, we obtain analytically the frequencies fn of resonances which can be excited in such system. We also calculate corresponding inhomogeneous RF current distributions ψ n ( r ) , where r is the coordinate across a spiral. We show that the resonant frequencies and current distributions are well described by simple relationships f n = f 1 n and ψ n ( r ) ≃ sin [ π n ( r / R e ) 2 ] , where n = 1 , 2... and Re is the external radius of the spiral. Our analysis of electrodynamic properties of spiral resonators' is in good agreement with direct numerical simulations and measurements made using specifically designed magnetic probe and laser scanning microscope.

  2. Bifurcations and Dynamics of Spiral Waves

    NASA Astrophysics Data System (ADS)

    Sandstede, B.; Scheel, A.; Wulff, P. C.

    1999-08-01

    . In this article, it is shown that the dynamics near meandering spiral waves or other patterns is determined by a finite-dimensional vector field that has a certain skew-product structure over the group SE SE(N) . This generalizes our earlier work on center-manifold theory near rigidly rotating spiral waves to meandering spirals. In particular, for meandering spirals, it is much more sophisticated to extract the aforementioned skew-product structure since spatio-temporal rather than only spatial symmetries have to be accounted for. Another difficulty is that the action of the Euclidean symmetry group on the underlying function space is not differentiable, and in fact may be discontinuous. Using this center-manifold reduction, Hopf bifurcations and periodic forcing of spiral waves are then investigated. The results explain the transitions to patterns with two or more temporal frequencies that have been observed in various experiments and numerical simulations.

  3. Conservation of magnetic helicity during plasma relaxation

    SciTech Connect

    Ji, H.; Prager, S.C.; Sarff, J.S.

    1994-07-01

    Decay of the total magnetic helicity during the sawtooth relaxation in the MST Reversed-Field Pinch is much larger than the MHD prediction. However, the helicity decay (3--4%) is smaller than the magnetic energy decay (7--9%), modestly supportive of the helicity conservation hypothesis in Taylor`s relaxation theory. Enhanced fluctuation-induced helicity transport during the relaxation is observed.

  4. Head CT scan

    MedlinePlus

    Brain CT; Cranial CT; CT scan - skull; CT scan - head; CT scan - orbits; CT scan - sinuses; Computed tomography - cranial ... or other growth (mass) Cerebral atrophy (loss of brain tissue) ... with the hearing nerve Stroke or transient ischemic attack (TIA)

  5. Rare helical spheroidal fossils from the Doushantuo Lagerstätte: Ediacaran animal embryos come of age?

    NASA Astrophysics Data System (ADS)

    Xiao, Shuhai; Hagadorn, James W.; Zhou, Chuanming; Yuan, Xunlai

    2007-02-01

    A small quantity of helically coiled spheroidal fossils has been recovered from acid digestion of phosphorite samples from the Ediacaran Doushantuo Formation, South China. These fossils consist of an internal body enclosed in a sculptured envelope that is very similar to that of Doushantuo animal eggs and blastula embryos such as Megasphaera ornata. A hallmark of these fossils is a three-dimensional spiral structure, which always consists of three clockwise coils, and occurs on both the envelope and the internal body. The spiral structure consists of a spiral tunnel or canal flanked by two raised levees, and it is punctured by a series of holes. Some specimens show evidence of uncoiling, invagination along the spiral structure, or bipectinate furrowing on the band between canals. A possible ontogenetic link between these helical spheroidal fossils and Megasphaera ornata is suggested by similar size, similar envelope sculptures, and co-occurrence. We tentatively interpret these fossils as postblastula embryos related to Megasphaera ornata. Thus, they may represent the most advanced embryonic fossils so far known from the Ediacaran, although their adult morphologies and phylogenetic affinity remain unknown.

  6. Helicity Generation by Heat Pulses

    NASA Astrophysics Data System (ADS)

    Stenzel, R. L.; Urrutia, J. M.

    1996-11-01

    In a large laboratory plasma (ne ~= 10^12 cm-3, k Te ~= 2 eV, B0 ~= 30 G, 1 m ⊥ B_0, 2.5 m allel B_0), the electrons are heated locally by a short intense current pulse (100 A, 0.2 μs) using a magnetic loop antenna or a biased electrode. The heat transport along the field establishes a flux tube with strong radial and weak axial temperature gradients. The time scale of temperature relaxation (Δ t ~= 50 μs) is much longer than that of the transient whistler wave pulse excited by the initial current pulse (Δ t < 2 μs). The temperature gradients drive linked field-aligned and diamagnetic currents which, due to their linkage, exhibit helicity and form a flux rope with J × B ~= 0.(R. L. Stenzel and J. M. Urrutia, Phys. Rev. Lett. 76), 1469 (1996). Alternatively, the helicity generation can be understood by the twisting of magnetic field lines which, in the parameter regime of electron MHD, are frozen into the electron fluid. The electron heating at one end of the flux tube causes a nonuniform diamagnetic rotation, hence the helicity. The heat transport by helical convection and conduction is investigated. The slowly time-varying magnetic field may excite Alfvénic perturbations.

  7. Note: Helical nanobelt force sensors

    SciTech Connect

    Hwang, G.; Hashimoto, H.

    2012-12-15

    We present the fabrication and characterization of helical nanobelt force sensors. These self-sensing force sensors are based on the giant piezoresistivity of helical nanobelts. The three-dimensional helical nanobelts are self-formed from 27 nm-thick n-type InGaAs/GaAs bilayers using rolled-up techniques, and assembled onto electrodes on a micropipette using nanorobotic manipulations. The helical nanobelt force sensors can be calibrated using a calibrated atomic force microscope cantilever system under scanning electron microscope. Thanks to their giant piezoresistance coefficient (515 Multiplication-Sign 10{sup -10} Pa{sup -1}), low stiffness (0.03125 N/m), large-displacement capability ({approx}10 {mu}m), and good fatigue resistance, they are well suited to function as stand-alone, compact ({approx}20 {mu}m without the plug-in support), light ({approx}5 g including the plug-in support), versatile and large range ({approx}{mu}N) and high resolution ({approx}nN) force sensors.

  8. Note: helical nanobelt force sensors.

    PubMed

    Hwang, G; Hashimoto, H

    2012-12-01

    We present the fabrication and characterization of helical nanobelt force sensors. These self-sensing force sensors are based on the giant piezoresistivity of helical nanobelts. The three-dimensional helical nanobelts are self-formed from 27 nm-thick n-type InGaAs/GaAs bilayers using rolled-up techniques, and assembled onto electrodes on a micropipette using nanorobotic manipulations. The helical nanobelt force sensors can be calibrated using a calibrated atomic force microscope cantilever system under scanning electron microscope. Thanks to their giant piezoresistance coefficient (515 × 10(-10) Pa(-1)), low stiffness (0.03125 N/m), large-displacement capability (~10 μm), and good fatigue resistance, they are well suited to function as stand-alone, compact (~20 μm without the plug-in support), light (~5 g including the plug-in support), versatile and large range (~μN) and high resolution (~nN) force sensors. PMID:23278031

  9. Note: Helical nanobelt force sensors

    NASA Astrophysics Data System (ADS)

    Hwang, G.; Hashimoto, H.

    2012-12-01

    We present the fabrication and characterization of helical nanobelt force sensors. These self-sensing force sensors are based on the giant piezoresistivity of helical nanobelts. The three-dimensional helical nanobelts are self-formed from 27 nm-thick n-type InGaAs/GaAs bilayers using rolled-up techniques, and assembled onto electrodes on a micropipette using nanorobotic manipulations. The helical nanobelt force sensors can be calibrated using a calibrated atomic force microscope cantilever system under scanning electron microscope. Thanks to their giant piezoresistance coefficient (515 × 10-10 Pa-1), low stiffness (0.03125 N/m), large-displacement capability (˜10 μm), and good fatigue resistance, they are well suited to function as stand-alone, compact (˜20 μm without the plug-in support), light (˜5 g including the plug-in support), versatile and large range (˜μN) and high resolution (˜nN) force sensors.

  10. Numerical Simulation of Magnetic Flux Compression in Helical-Cone Magnetoexplosive Generators

    NASA Astrophysics Data System (ADS)

    Deryugin, Yu. N.; Korolev, P. V.; Kargin, V. I.; Pikar, A. S.; Popkov, N. F.; Ryaslov, E. A.

    2004-11-01

    We present the results of calculations of the physical processes of magnetic flux compression in a magnetocumulative generator with a large diameter spiral. The generator considered is a modification of the one developed for the multimegajoule energy source and intended for the PIRIT-EMG stationary electrophysical facility, pumping a pulsed energy of 80 MJ. The development of the magnetocumulative generator required calculating its output parameters and optimizing the generator dimensions, choosing the form and calculating the shape and thickness, insulation type and electric strength of the spiral wire. The authors developed a program package to simulate the helical-cone generator operation and numerically investigate the physical processes occurring at magnetic flux compression. To calculate the liner scatter dynamics, Eulerian equations were solved for counter-running sliding detonation waves. The system of equations is integrated using a finite-difference method for 2-D stationary grids adapting to the peculiarities of the flow. The liner collision with spiral coils as well as the destruction of the insulation is considered in 2-D through a model of nonviscous gas without heat conductivity. The magnetic flux compression is calculated using the analytical solutions of dynamic tasks and a 1-D non-linear diffusion of the magnetic field in conductors. Moreover, using a sufficiently simple algorithm, we managed to account for the basic losses of the magnetic flux related to diffusion, cuts-off at section and wire joints, and the losses related to spiral and liner misalignment.