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1

Quantitative phase imaging via Fourier ptychographic microscopy.  

PubMed

Fourier ptychographic microscopy (FPM) is a recently developed imaging modality that uses angularly varying illumination to extend a system's performance beyond the limit defined by its optical components. The FPM technique applies a novel phase-retrieval procedure to achieve resolution enhancement and complex image recovery. In this Letter, we compare FPM data to theoretical prediction and phase-shifting digital holography measurement to show that its acquired phase maps are quantitative and artifact-free. We additionally explore the relationship between the achievable spatial and optical thickness resolution offered by a reconstructed FPM phase image. We conclude by demonstrating enhanced visualization and the collection of otherwise unobservable sample information using FPM's quantitative phase. PMID:24322147

Ou, Xiaoze; Horstmeyer, Roarke; Yang, Changhuei; Zheng, Guoan

2013-11-15

2

Quantitative phase imaging via Fourier ptychographic microscopy  

PubMed Central

Fourier ptychographic microscopy (FPM) is a recently developed imaging modality that uses angularly varying illumination to extend a system’s performance beyond the limit defined by its optical components. The FPM technique applies a novel phase-retrieval procedure to achieve resolution enhancement and complex image recovery. In this Letter, we compare FPM data to theoretical prediction and phase-shifting digital holography measurement to show that its acquired phase maps are quantitative and artifact-free. We additionally explore the relationship between the achievable spatial and optical thickness resolution offered by a reconstructed FPM phase image. We conclude by demonstrating enhanced visualization and the collection of otherwise unobservable sample information using FPM’s quantitative phase. PMID:24322147

Ou, Xiaoze; Horstmeyer, Roarke; Yang, Changhuei; Zheng, Guoan

2014-01-01

3

Quantitative phase imaging of live cells using fast Fourier phase microscopy  

Microsoft Academic Search

Using the decomposition of an image field in two spatial components that can be controllably shifted in phase with respect to each other, a new quantitative-phase microscope has been developed. The new instrument, referred to as the fast Fourier phase microscope (f-FPM), provides a factor of 100 higher acquisition rate compared with our previously reported Fourier phase microscope. The resulting

Niyom Lue; Wonshik Choi; Gabriel Popescu; Takahiro Ikeda; Ramachandra R. Dasari; Kamran Badizadegan; Michael S. Feld

2007-01-01

4

Single-channel color image encryption using phase retrieve algorithm in fractional Fourier domain  

NASA Astrophysics Data System (ADS)

A single-channel color image encryption is proposed based on a phase retrieve algorithm and a two-coupled logistic map. Firstly, a gray scale image is constituted with three channels of the color image, and then permuted by a sequence of chaotic pairs generated by the two-coupled logistic map. Secondly, the permutation image is decomposed into three new components, where each component is encoded into a phase-only function in the fractional Fourier domain with a phase retrieve algorithm that is proposed based on the iterative fractional Fourier transform. Finally, an interim image is formed by the combination of these phase-only functions and encrypted into the final gray scale ciphertext with stationary white noise distribution by using chaotic diffusion, which has camouflage property to some extent. In the process of encryption and decryption, chaotic permutation and diffusion makes the resultant image nonlinear and disorder both in spatial domain and frequency domain, and the proposed phase iterative algorithm has faster convergent speed. Additionally, the encryption scheme enlarges the key space of the cryptosystem. Simulation results and security analysis verify the feasibility and effectiveness of this method.

Sui, Liansheng; Xin, Meiting; Tian, Ailing; Jin, Haiyan

2013-12-01

5

Fractional Fourier domain optical image hiding using phase retrieval algorithm based on iterative nonlinear double random phase encoding.  

PubMed

We present a novel image hiding method based on phase retrieval algorithm under the framework of nonlinear double random phase encoding in fractional Fourier domain. Two phase-only masks (POMs) are efficiently determined by using the phase retrieval algorithm, in which two cascaded phase-truncated fractional Fourier transforms (FrFTs) are involved. No undesired information disclosure, post-processing of the POMs or digital inverse computation appears in our proposed method. In order to achieve the reduction in key transmission, a modified image hiding method based on the modified phase retrieval algorithm and logistic map is further proposed in this paper, in which the fractional orders and the parameters with respect to the logistic map are regarded as encryption keys. Numerical results have demonstrated the feasibility and effectiveness of the proposed algorithms. PMID:25321769

Wang, Xiaogang; Chen, Wen; Chen, Xudong

2014-09-22

6

Fourier plane imaging microscopy  

NASA Astrophysics Data System (ADS)

We show how the image of an unresolved photonic crystal can be reconstructed using a single Fourier plane (FP) image obtained with a second camera that was added to a traditional compound microscope. We discuss how Fourier plane imaging microscopy is an application of a remarkable property of the obtained FP images: they contain more information about the photonic crystals than the images recorded by the camera commonly placed at the real plane of the microscope. We argue that the experimental results support the hypothesis that surface waves, contributing to enhanced resolution abilities, were optically excited in the studied photonic crystals.

Dominguez, Daniel; Alharbi, Nouf; Alhusain, Mdhaoui; Bernussi, Ayrton A.; Peralta, Luis Grave de

2014-09-01

7

Fourier plane imaging microscopy  

SciTech Connect

We show how the image of an unresolved photonic crystal can be reconstructed using a single Fourier plane (FP) image obtained with a second camera that was added to a traditional compound microscope. We discuss how Fourier plane imaging microscopy is an application of a remarkable property of the obtained FP images: they contain more information about the photonic crystals than the images recorded by the camera commonly placed at the real plane of the microscope. We argue that the experimental results support the hypothesis that surface waves, contributing to enhanced resolution abilities, were optically excited in the studied photonic crystals.

Dominguez, Daniel, E-mail: daniel.dominguez@ttu.edu; Peralta, Luis Grave de [Department of Physics, Texas Tech University, Lubbock, Texas 79409 (United States); Nano Tech Center, Texas Tech University, Lubbock, Texas 79409 (United States); Alharbi, Nouf; Alhusain, Mdhaoui [Department of Physics, Texas Tech University, Lubbock, Texas 79409 (United States); Bernussi, Ayrton A. [Nano Tech Center, Texas Tech University, Lubbock, Texas 79409 (United States); Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas 79409 (United States)

2014-09-14

8

Fourier plane image amplifier  

DOEpatents

A solid state laser is frequency tripled to 0.3 .mu.m. A small portion of the laser is split off and generates a Stokes seed in a low power oscillator. The low power output passes through a mask with the appropriate hole pattern. Meanwhile, the bulk of the laser output is focused into a larger stimulated Brillouin scattering (SBS) amplifier. The low power beam is directed through the same cell in the opposite direction. The majority of the amplification takes place at the focus which is the fourier transform plane of the mask image. The small holes occupy large area at the focus and thus are preferentially amplified. The amplified output is now imaged onto the multichip module where the holes are drilled. Because of the fourier plane amplifier, only .about.1/10th the power of a competitive system is needed. This concept allows less expensive masks to be used in the process and requires much less laser power.

Hackel, Lloyd A. (Livermore, CA); Hermann, Mark R. (San Ramon, CA); Dane, C. Brent (Livermore, CA); Tiszauer, Detlev H. (Tracy, CA)

1995-01-01

9

Fourier plane image amplifier  

DOEpatents

A solid state laser is frequency tripled to 0.3 {micro}m. A small portion of the laser is split off and generates a Stokes seed in a low power oscillator. The low power output passes through a mask with the appropriate hole pattern. Meanwhile, the bulk of the laser output is focused into a larger stimulated Brillouin scattering (SBS) amplifier. The low power beam is directed through the same cell in the opposite direction. The majority of the amplification takes place at the focus which is the fourier transform plane of the mask image. The small holes occupy large area at the focus and thus are preferentially amplified. The amplified output is now imaged onto the multichip module where the holes are drilled. Because of the fourier plane amplifier, only about 1/10th the power of a competitive system is needed. This concept allows less expensive masks to be used in the process and requires much less laser power. 1 fig.

Hackel, L.A.; Hermann, M.R.; Dane, C.B.; Tiszauer, D.H.

1995-12-12

10

Imaging Fourier Transform Spectrometer  

SciTech Connect

The operating principles of an Imaging Fourier Transform Spectrometer (IFTS) are discussed. The advantages and disadvantages of such instruments with respect to alternative imaging spectrometers are discussed. The primary advantages of the IFTS are the capacity to acquire more than an order of magnitude more spectral channels than alternative systems with more than an order of magnitude greater etendue than for alternative systems. The primary disadvantage of IFTS, or FTS in general, is the sensitivity to temporal fluctuations, either random or periodic. Data from the IRIFTS (ir IFTS) prototype instrument, sensitive in the infrared, are presented having a spectral sensitivity of 0.01 absorbance units, a spectral resolution of 6 cm{sup {minus}1} over the range 0 to 7899 cm{sup {minus}1}, and a spatial resolution of 2.5 mr.

Bennett, C.L.; Carter, M.R.; Fields, D.J.; Hernandez, J.

1993-04-14

11

Electro-optic imaging Fourier transform spectrometer  

NASA Technical Reports Server (NTRS)

An Electro-Optic Imaging Fourier Transform Spectrometer (EOIFTS) for Hyperspectral Imaging is described. The EOIFTS includes an input polarizer, an output polarizer, and a plurality of birefringent phase elements. The relative orientations of the polarizers and birefringent phase elements can be changed mechanically or via a controller, using ferroelectric liquid crystals, to substantially measure the spectral Fourier components of light propagating through the EIOFTS. When achromatic switches are used as an integral part of the birefringent phase elements, the EIOFTS becomes suitable for broadband applications, with over 1 micron infrared bandwidth.

Chao, Tien-Hsin (Inventor); Znod, Hanying (Inventor)

2009-01-01

12

Fourier phasing with phase-uncertain mask  

NASA Astrophysics Data System (ADS)

Fourier phasing is the problem of retrieving Fourier phase information from Fourier intensity data. The standard Fourier phase retrieval (without a mask) is known to have many solutions which cause the standard phasing algorithms to stagnate and produce wrong or inaccurate solutions. In this paper Fourier phase retrieval is carried out with the introduction of a randomly fabricated mask in measurement and reconstruction. Highly probable uniqueness of solution, up to a global phase, was previously proved with exact knowledge of the mask. Here the uniqueness result is extended to the case where only rough information about the mask’s phases is assumed. The exponential probability bound for uniqueness is given in terms of the uncertainty-to-diversity ratio of the unknown mask. New phasing algorithms alternating between the object update and the mask update are systematically tested and demonstrated to have the capability of recovering both the object and the mask (within the object support) simultaneously, consistent with the uniqueness result. Phasing with a phase-uncertain mask is shown to be robust with respect to the correlation in the mask as well as the Gaussian and Poisson noises.

Fannjiang, Albert; Liao, Wenjing

2013-12-01

13

Double image encryption based on iterative fractional Fourier transform  

Microsoft Academic Search

We present an image encryption algorithm to simultaneously encrypt two images into a single one as the amplitudes of fractional Fourier transform with different orders. From the encrypted image we can get two original images independently by fractional Fourier transforms with two different fractional orders. This algorithm can be independent of additional random phases as the encryption\\/decryption keys. Numerical results

Zhengjun Liu; Shutian Liu

2007-01-01

14

Electro-optic Imaging Fourier Transform Spectrometer  

NASA Technical Reports Server (NTRS)

JPL is developing an innovative compact, low mass, Electro-Optic Imaging Fourier Transform Spectrometer (E-0IFTS) for hyperspectral imaging applications. The spectral region of this spectrometer will be 1 - 2.5 pm (1000 -4000 cm-') to allow high-resolution, high-speed hyperspectral imaging applications [l-51. One application will be theremote sensing of the measurement of a large number of different atmospheric gases simultaneously in the sameairmass. Due to the use of a combination of birefiingent phase retarders and multiple achromatic phase switches toachieve phase delay, this spectrometer is capable of hyperspectral measurements similar to that of the conventionalFourier transform spectrometer but without any moving parts. In this paper, the principle of operations, systemarchitecture and recent experimental progress will be presen.

Chao, Tien-Hsin

2005-01-01

15

Electro-optic Imaging Fourier Transform Spectrometer  

NASA Technical Reports Server (NTRS)

JPL is developing an innovative compact, low mass, Electro-Optic Imaging Fourier Transform Spectrometer (E-O IFTS) for hyperspectral imaging applications. The spectral region of this spectrometer will be 1 - 2.5 micron (1000-4000/cm) to allow high-resolution, high-speed hyperspectral imaging applications. One application will be the remote sensing of the measurement of a large number of different atmospheric gases simultaneously in the same airmass. Due to the use of a combination of birefringent phase retarders and multiple achromatic phase switches to achieve phase delay, this spectrometer is capable of hyperspectral measurements similar to that of the conventional Fourier transform spectrometer but without any moving parts. In this paper, the principle of operations, system architecture and recent experimental progress will be presented.

Chao, Tien-Hsin

2005-01-01

16

Optical image-hiding method with false information disclosure based on the interference principle and partial-phase-truncation in the fractional Fourier domain  

NASA Astrophysics Data System (ADS)

An image-hiding method based on the optical interference principle and partial-phase-truncation in the fractional Fourier domain is proposed. The primary image is converted into three phase-only masks (POMs) using an analytical algorithm involved partial-phase-truncation and a fast random pixel exchange process. A procedure of a fake silhouette for a decryption key is suggested to reinforce the encryption and give a hint of the position of the key. The fractional orders of FrFT effectively enhance the security of the system. In the decryption process, the POM with false information and the other two POMs are, respectively, placed in the input and fractional Fourier planes to recover the primary image. There are no unintended information disclosures and iterative computations involved in the proposed method. Simulation results are presented to verify the validity of the proposed approach.

Dai, Chaoqing; Wang, Xiaogang; Zhou, Guoquan; Chen, Junlang

2014-05-01

17

Fourier phase microscopy with white light.  

PubMed

Laser-based Fourier phase microscopy (FPM) works on the principle of decomposition of an image field in two spatial components that can be controllably shifted in phase with respect to each other. However, due to the coherent illumination, the contrast in phase images is degraded by speckles. In this paper we present FPM with spatially coherent white light (wFPM), which offers high spatial phase sensitivity due to the low temporal coherence and high temporal phase stability due to common path geometry. Further, by using a fast spatial light modulator (SLM) and a fast scientific-grade complementary metal oxide semiconductor (sCMOS) camera, we report imaging at a maximum rate of 12.5 quantitative phase frames per second with 5.5 mega pixels image size. We illustrate the utility of wFPM as a contrast enhancement as well as dynamic phase measurement method by imaging section of benign colonic glands and red blood cell membrane fluctuation. PMID:24010005

Bhaduri, Basanta; Tangella, Krishnarao; Popescu, Gabriel

2013-01-01

18

Fourier phase microscopy with white light  

PubMed Central

Laser-based Fourier phase microscopy (FPM) works on the principle of decomposition of an image field in two spatial components that can be controllably shifted in phase with respect to each other. However, due to the coherent illumination, the contrast in phase images is degraded by speckles. In this paper we present FPM with spatially coherent white light (wFPM), which offers high spatial phase sensitivity due to the low temporal coherence and high temporal phase stability due to common path geometry. Further, by using a fast spatial light modulator (SLM) and a fast scientific-grade complementary metal oxide semiconductor (sCMOS) camera, we report imaging at a maximum rate of 12.5 quantitative phase frames per second with 5.5 mega pixels image size. We illustrate the utility of wFPM as a contrast enhancement as well as dynamic phase measurement method by imaging section of benign colonic glands and red blood cell membrane fluctuation. PMID:24010005

Bhaduri, Basanta; Tangella, Krishnarao; Popescu, Gabriel

2013-01-01

19

Color image projection based on Fourier holograms.  

PubMed

A method of color image projection is experimentally validated. It assumes a simultaneous illumination of a spatial light modulator (SLM) with three laser beams converging in a common point on a projection screen. The beams are masked with amplitude filters so that each one illuminates one third of the area of the SLM. A Fourier hologram of a chosen color component of an input image is calculated, and its phase pattern is addressed on a corresponding part of the SLM area. A full-color flat image is formed on the screen as a result of color mixing. Additional techniques of image optimization are applied: time-integral speckle averaging and an off-axis shift of a zero-order peak. Static and animated experimental results of such a color holographic projection with a good image quality are presented. PMID:20410975

Makowski, Michal; Ducin, Izabela; Sypek, Maciej; Siemion, Agnieszka; Siemion, Andrzej; Suszek, Jaroslaw; Kolodziejczyk, Andrzej

2010-04-15

20

Fourier transform based scalable image quality measure.  

PubMed

We present a new image quality assessment (IQA) algorithm based on the phase and magnitude of the 2D (twodimensional) Discrete Fourier Transform (DFT). The basic idea is to compare the phase and magnitude of the reference and distorted images to compute the quality score. However, it is well known that the Human Visual Systems (HVSs) sensitivity to different frequency components is not the same. We accommodate this fact via a simple yet effective strategy of nonuniform binning of the frequency components. This process also leads to reduced space representation of the image thereby enabling the reduced-reference (RR) prospects of the proposed scheme. We employ linear regression to integrate the effects of the changes in phase and magnitude. In this way, the required weights are determined via proper training and hence more convincing and effective. Lastly, using the fact that phase usually conveys more information than magnitude, we use only the phase for RR quality assessment. This provides the crucial advantage of further reduction in the required amount of reference image information. The proposed method is therefore further scalable for RR scenarios. We report extensive experimental results using a total of 9 publicly available databases: 7 image (with a total of 3832 distorted images with diverse distortions) and 2 video databases (totally 228 distorted videos). These show that the proposed method is overall better than several of the existing fullreference (FR) algorithms and two RR algorithms. Additionally, there is a graceful degradation in prediction performance as the amount of reference image information is reduced thereby confirming its scalability prospects. To enable comparisons and future study, a Matlab implementation of the proposed algorithm is available at http://www.ntu.edu.sg/home/wslin/reduced_phase.rar. PMID:22562758

Narwaria, Manish; Lin, Weisi; McLoughlin, Ian; Emmanuel, Sabu; Chia, Liang-Tien

2012-08-01

21

Medical image processing with optical Fourier techniques  

Microsoft Academic Search

Medical image processing is demonstrated by using Fourier techniques. Two optical Fourier systems are designed: the first one is a real-time optical processor with spatial filters and the second one is a self-adaptive optical processor with nonlinear optical films of the biomaterial Bacteriorhodopsin. Medical images including mammograms and Pap smears are investigated by using our optical systems. The desired components

Pengfei Wu

2003-01-01

22

Rotational-translational fourier imaging system  

NASA Technical Reports Server (NTRS)

This invention has the ability to create Fourier-based images with only two grid pairs. The two grid pairs are manipulated in a manner that allows (1) a first grid pair to provide multiple real components of the Fourier-based image and (2) a second grid pair to provide multiple imaginary components of the Fourier-based image. The novelty of this invention resides in the use of only two grid pairs to provide the same imaging information that has been traditionally collected with multiple grid pairs.

Campbell, Jonathan W. (Inventor)

2004-01-01

23

Single-pixel imaging by means of Fourier spectrum acquisition.  

PubMed

Single-pixel imaging techniques enable to capture a scene without a direct line of sight to the object, but high-quality imaging has been proven challenging especially in the presence of noisy environmental illumination. Here we present a single-pixel imaging technique that can achieve high-quality images by acquiring their Fourier spectrum. We use phase-shifting sinusoid structured illumination for the spectrum acquisition. Applying inverse Fourier transform to the obtained spectrum yields the desired image. The proposed technique is capable of capturing a scene without a direct view of it. Thus, it enables a feasible placement of detectors, only if the detectors can collect the light signals from the scene. The technique is also a compressive sampling like approach, so it can reconstruct an image from sub-Nyquist measurements. We experimentally obtain clear images by utilizing a detector not placed in direct view of the imaged scene even with noise introduced by environmental illuminations. PMID:25649009

Zhang, Zibang; Ma, Xiao; Zhong, Jingang

2015-01-01

24

Livermore Imaging Fourier Transform Infrared Spectrometer (LIFTIRS)  

SciTech Connect

Lawrence Livermore National Laboratory is currently operating a hyperspectral imager, the Livermore Imaging Fourier Transform Infrared Spectrometer (LIFTIRS). This instrument is capable of operating throughout the infrared spectrum from 3 to 12.5 {mu}m with controllable spectral resolution. In this presentation we report on it`s operating characteristics, current capabilities, data throughput and calibration issues.

Carter, M.R.; Bennett, C.L.; Fields, D.J.; Lee, F.D.

1995-05-10

25

Coherent electromagnetic field imaging through Fourier transform heterodyne  

SciTech Connect

The authors present a detection process capable of directly imaging the transverse amplitude, phase, and if desired, Doppler shift of coherent electromagnetic fields. Based on coherent detection principles governing conventional heterodyned RADAR/LIDAR systems, Fourier Transform Heterodyne (FTH) incorporates transverse spatial encoding of the local oscillator for image capture. Appropriate selection of spatial encoding functions, or basis set, allows image retrieval by way of classic Fourier manipulations. Of practical interest: (1) imaging is accomplished on a single element detector requiring no additional scanning or moving components, and (2) a wide variety of appropriate spatial encoding functions exist that may be adaptively configured in real-time for applications requiring optimal detection. In this paper, they introduce the underlying principles governing FTH imaging, followed by demonstration of concept via a simple experimental setup based on a HeNe laser and a 69 element spatial phase modulator.

Cooke, B.J.; Laubscher, B.E.; Olivas, N.L.; Goeller, R.M.; Cafferty, M.; Briles, S.D. [Los Alamos National Lab., NM (United States); Galbraith, A.E. [Los Alamos National Lab., NM (United States)]|[Univ. of Arizona, Tucson, AZ (United States). Electrical and Computer Engineering Dept.; Grubler, A.C. [Los Alamos National Lab., NM (United States)]|[Naval Academy, Annapolis, MD (United States)

1998-12-31

26

Direct phase retrieval in double blind Fourier holography.  

PubMed

Phase measurement is a long-standing challenge in a wide range of applications, from X-ray imaging to astrophysics and spectroscopy. While in some scenarios the phase is resolved by an interferometric measurement, in others it is reconstructed via numerical optimization, based on some a-priori knowledge about the signal. The latter commonly use iterative algorithms, and thus have to deal with their convergence, stagnation, and robustness to noise. Here we combine these two approaches and present a new scheme, termed double blind Fourier holography, providing an efficient solution to the phase problem in two dimensions, by solving a system of linear equations. We present and experimentally demonstrate our approach for the case of lens-less imaging. PMID:25401527

Raz, Oren; Leshem, Ben; Miao, Jianwei; Nadler, Boaz; Oron, Dan; Dudovich, Nirit

2014-10-20

27

Fourier transform digital holographic adaptive optics imaging system  

PubMed Central

A Fourier transform digital holographic adaptive optics imaging system and its basic principles are proposed. The CCD is put at the exact Fourier transform plane of the pupil of the eye lens. The spherical curvature introduced by the optics except the eye lens itself is eliminated. The CCD is also at image plane of the target. The point-spread function of the system is directly recorded, making it easier to determine the correct guide-star hologram. Also, the light signal will be stronger at the CCD, especially for phase-aberration sensing. Numerical propagation is avoided. The sensor aperture has nothing to do with the resolution and the possibility of using low coherence or incoherent illumination is opened. The system becomes more efficient and flexible. Although it is intended for ophthalmic use, it also shows potential application in microscopy. The robustness and feasibility of this compact system are demonstrated by simulations and experiments using scattering objects. PMID:23262541

Liu, Changgeng; Yu, Xiao; Kim, Myung K.

2013-01-01

28

Quantitative phase microscopy through differential interference imaging  

Microsoft Academic Search

An extension of Nomarski differential interference contrast microscopy enables isotropic linear phase imaging through the combination of phase shifting, two directions of shear and Fourier-space integration using a modified spiral phase transform. We apply this method to simulated and experimentally acquired images of partially absorptive test objects. A direct comparison of the computationally determined phase to the true object phase

Sharon V. King; Ariel Libertun; Rafael Piestun; Carol J. Cogswell; Chrysanthe Preza

2008-01-01

29

Target Image Enhancement in Radar Imaging Using Fractional Fourier Transform  

NASA Astrophysics Data System (ADS)

This paper presents a new Range-Doppler Algorithm based on Fractional Fourier Transform (RDA-FrFT) to obtain High-Resolution (HR) images for targets in radar imaging. The performance of the proposed RDA-FrFT is compared with the classical RDA algorithm, which is based on the Fast Fourier Transform (FFT). A closed-form expression for the range and azimuth compression of the proposed RDA-FrFT is mathematically derived and analyzed from the HR Synthetic Aperture Radar (SAR) imaging point of view. The proposed RDA-FrFT takes its advantage of the property of the FrFT to resolve chirp signals with high precision. Results show that the proposed RDA-FrFT gives low Peak Side-Lobe (PSL) and Integrated Side-Lobe (ISL) levels in range and azimuth directions for detected targets. HR images are obtained using the proposed RDA-FrFT algorithm.

El-Mashed, M. G.; Dessouky, M. I.; El-Kordy, M.; Zahran, O.; Abd El-Samie, F. E.

2012-03-01

30

Single beam Fourier transform digital holographic quantitative phase microscopy  

SciTech Connect

Quantitative phase contrast microscopy reveals thickness or height information of a biological or technical micro-object under investigation. The information obtained from this process provides a means to study their dynamics. Digital holographic (DH) microscopy is one of the most used, state of the art single-shot quantitative techniques for three dimensional imaging of living cells. Conventional off axis DH microscopy directly provides phase contrast images of the objects. However, this process requires two separate beams and their ratio adjustment for high contrast interference fringes. Also the use of two separate beams may make the system more vulnerable to vibrations. Single beam techniques can overcome these hurdles while remaining compact as well. Here, we describe the development of a single beam DH microscope providing whole field imaging of micro-objects. A hologram of the magnified object projected on to a diffuser co-located with a pinhole is recorded with the use of a commercially available diode laser and an arrayed sensor. A Fourier transform of the recorded hologram directly yields the complex amplitude at the image plane. The method proposed was investigated using various phase objects. It was also used to image the dynamics of human red blood cells in which sub-micrometer level thickness variation were measurable.

Anand, A., E-mail: arun-nair-in@yahoo.com; Chhaniwal, V. K.; Mahajan, S.; Trivedi, V. [Optics Laboratory, Applied Physics Department, Faculty of Technology and Engineering, M.S. University of Baroda, Vadodara 390001 (India)] [Optics Laboratory, Applied Physics Department, Faculty of Technology and Engineering, M.S. University of Baroda, Vadodara 390001 (India); Faridian, A.; Pedrini, G.; Osten, W. [Institut für Technische Optik, Universität Stuttgart, Pfaffenwaldring 9, 70569 Stuttgart (Germany)] [Institut für Technische Optik, Universität Stuttgart, Pfaffenwaldring 9, 70569 Stuttgart (Germany); Dubey, S. K. [Siemens Technology and Services Pvt. Ltd, Corporate Technology—Research and Technology Centre, Bangalore 560100 (India)] [Siemens Technology and Services Pvt. Ltd, Corporate Technology—Research and Technology Centre, Bangalore 560100 (India); Javidi, B. [Department of Electrical and Computer Engineering, U-4157, University of Connecticut, Storrs, Connecticut 06269-2157 (United States)] [Department of Electrical and Computer Engineering, U-4157, University of Connecticut, Storrs, Connecticut 06269-2157 (United States)

2014-03-10

31

Single beam Fourier transform digital holographic quantitative phase microscopy  

NASA Astrophysics Data System (ADS)

Quantitative phase contrast microscopy reveals thickness or height information of a biological or technical micro-object under investigation. The information obtained from this process provides a means to study their dynamics. Digital holographic (DH) microscopy is one of the most used, state of the art single-shot quantitative techniques for three dimensional imaging of living cells. Conventional off axis DH microscopy directly provides phase contrast images of the objects. However, this process requires two separate beams and their ratio adjustment for high contrast interference fringes. Also the use of two separate beams may make the system more vulnerable to vibrations. Single beam techniques can overcome these hurdles while remaining compact as well. Here, we describe the development of a single beam DH microscope providing whole field imaging of micro-objects. A hologram of the magnified object projected on to a diffuser co-located with a pinhole is recorded with the use of a commercially available diode laser and an arrayed sensor. A Fourier transform of the recorded hologram directly yields the complex amplitude at the image plane. The method proposed was investigated using various phase objects. It was also used to image the dynamics of human red blood cells in which sub-micrometer level thickness variation were measurable.

Anand, A.; Faridian, A.; Chhaniwal, V. K.; Mahajan, S.; Trivedi, V.; Dubey, S. K.; Pedrini, G.; Osten, W.; Javidi, B.

2014-03-01

32

Wide Field Imaging: Fourier and Fresnel  

NASA Astrophysics Data System (ADS)

Wide field imaging with low frequency synthesis arrays is limited by a number of troublesome effects. First amongst these is the ``non-coplanar baselines'' distortion whereby the integral relationship between sky brightness and measured visibility function is not a simple Fourier transform. A piece wise approximation to the integrals can be used and forms the basis of the facet approaches used for the last 15 years. These approaches are difficult to program and perform relatively poorly. We have developed a novel, high performance algorithm based upon convolution of the visibility samples with a Fresnel kernel. We interpret the Fresnel kernel as being required to propagate the electric field to a common reference plane. The role of Fresnel diffraction in radio inteferometry seems to have been unrecognized previously.

Cornwell, T. J.; Golap, K.; Bhatnagar, S.

2005-12-01

33

Theoretical for astigmatism Fourier transform-based imaging processor  

NASA Astrophysics Data System (ADS)

We propose a new step imaging method based on astigmatism Fourier transform for synthetic-aperture ladar imaging processor, which is mainly used in optical imaging processing system of synthetic-aperture imaging ladar. The time-domain data is translated into spatial coordinate expression suitable for space optical conversion. The Fourier transform is realized by astigmatism principle. It can simultaneously achieve radar goals focusing both on distance and azimuth. Processor scale is effectively reduced. The process of target echo confocal imaging data is simplified. The requirements of ladar imaging processing system are reduced. It has a great advantage in the synthetic-aperture imaging ladar target echo confocal imaging data processing.

Hou, Peipei; Sun, Jianfeng; Zhi, Ya'nan; Liu, Liren

2014-09-01

34

Interference imaging with a spatial spiral phase filter  

Microsoft Academic Search

Established phase contrast methods in microscopy use the phase-shifted zeroth order Fourier component of an image-carrying light wave as a reference wave for interferometric superposition with the remaining part of the image wave. Our method consists of a spatial Fourier filtering of the image wave with a spiral phase element which leads to an edge enhancement of both amplitude and

Severin Fürhapter; Alexander Jesacher; Stefan Bernet; Monika Ritsch-Marte

2005-01-01

35

Fourier Phase Domain Steganography: Phase Bin Encoding Via Interpolation  

NASA Astrophysics Data System (ADS)

In recent years there has been an increased interest in audio steganography and watermarking. This is due primarily to two reasons. First, an acute need to improve our national security capabilities in light of terrorist and criminal activity has driven new ideas and experimentation. Secondly, the explosive proliferation of digital media has forced the music industry to rethink how they will protect their intellectual property. Various techniques have been implemented but the phase domain remains a fertile ground for improvement due to the relative robustness to many types of distortion and immunity to the Human Auditory System. A new method for embedding data in the phase domain of the Discrete Fourier Transform of an audio signal is proposed. Focus is given to robustness and low perceptibility, while maintaining a relatively high capacity rate of up to 172 bits/s.

Rivas, Edward

2007-04-01

36

Operation of a deformable mirror device as a Fourier plane phase modulating filter  

NASA Technical Reports Server (NTRS)

The operation of a deformable mirror device (DMD) as a Fourier plane phase modulating filter is described. An analysis of the optical characteristics of the DMD elements as phase modulators is summarized. Analytical and experimental results indicating the existence of a quasi-phase-only operational mode are presented. These results are used to specify the mirror deflection required to implement a binary phase-only image correlation operation. An optical correlator system is implemented using the DMD Fourier plane filter and experimental results from this system are compared with computer simulations of the correlator operation.

Florence, James M.; Giles, Michael K.; Smith, Jeffery Z.

1988-01-01

37

Calibration of the Geostationary Imaging Fourier Transform Spectrometer (GIFTS)  

NASA Technical Reports Server (NTRS)

The NASA New Millennium Program's Geostationary Imaging Fourier Transform Spectrometer (GIFTS) requires highly accurate radiometric and spectral calibration in order to carry out its mission to provide water vapor, wind, temperature, and trace gas profiling from geostationary orbit. A calibration concept has been developed for the GIFTS Phase A instrument design. The in-flight calibration is performed using views of two on-board blackbody sources along with cold space. A radiometric calibration uncertainty analysis has been developed and used to show that the expected performance for GIFTS exceeds its top level requirement to measure brightness temperature to better than 1 K. For the Phase A GIFTS design, the spectral calibration is established by the highly stable diode laser used as the reference for interferogram sampling, and verified with comparisons to atmospheric calculations.

Best, F. A.; Revercomb, H. E.; Bingham, G. E.; Knuteson, R. O.; Tobin, D. C.; LaPorte, D. D.; Smith, W. L.

2001-01-01

38

TRAITEMENT D'IMAGES TRANSFORME DE FOURIER  

E-print Network

(-jx) #1; 2 #12; TRANSFORM�E DE FOURIER CONVOLUTION 1D -FONCTIONS CONTINUES- (f # g)(x) = Z +# -# f(t)g SPECTRE . Signal sinusoïdal de fréquence f0 # f(x) = c cos(2#f0x) (c est l'amplitude du signal et T = 1/f0 FOURIER (4) Série de Fourier de l'onde carrée 1D f(x) = A0 2 + # X n=1 An cos(2#nf0x) + # X n=1 Bn sin(2

Mignotte, Max

39

Improving imaging resolution of shaking targets by Fourier-transform ghost diffraction  

NASA Astrophysics Data System (ADS)

For conventional imaging, shaking of the imaging system or the target leads to the degradation of imaging resolution. The influence of the target's shaking to Fourier-transform ghost diffraction (FGD) is investigated and phase-retrieval method is used to recover the target's imaging. The analytical results, which are backed up by numerical simulation and experiments, demonstrate that the quiver of target has no effect on the resolution of FGD and high-resolution imaging can be always achieved by phase-retrieval method from FGD patterns. This approach can be applied in high-precision imaging systems, to overcome the influence of the system's shaking to imaging resolution.

Zhang, Cong; Gong, Wenlin; Han, Shensheng

2013-01-01

40

Fourier domain OCT imaging of American cockroach nervous system  

NASA Astrophysics Data System (ADS)

In this pilot study we demonstrate results of structural Fourier domain OCT imaging of the nervous system of Periplaneta americana L. (American cockroach). The purpose of this research is to develop an OCT apparatus enabling structural imaging of insect neural system. Secondary purpose of the presented research is to develop methods of the sample preparation and handling during the OCT imaging experiments. We have performed imaging in the abdominal nerve cord excised from the American cockroach. For this purpose we have developed a Fourier domain / spectral OCT system operating at 820 nm wavelength range.

Wyszkowska, Joanna; Gorczynska, Iwona; Ruminski, Daniel; Karnowski, Karol; Kowalczyk, Andrzej; Stankiewicz, Maria; Wojtkowski, Maciej

2012-01-01

41

Radial Hilbert Transform in terms of the Fourier Transform applied to Image Encryption  

NASA Astrophysics Data System (ADS)

In the present investigation, a mathematical algorithm under Matlab platform using Radial Hilbert Transform and Random Phase Mask for encrypting digital images is implemented. The algorithm is based on the use of the conventional Fourier transform and two random phase masks, which provide security and robustness to the system implemented. Random phase masks used during encryption and decryption are the keys to improve security and make the system immune to attacks by program generation phase masks.

Morales, Y.; Díaz, L.; Torres, C.

2015-01-01

42

Quantized phase optimization of two-dimensional Fourier kinoforms by a genetic algorithm  

NASA Astrophysics Data System (ADS)

We have developed a phase optimization method of a quantized kinoform by a genetic algorithm. Because the genetic algorithm inherently deals with discrete values, the quantized phase of the kinoform can be easily estimated. The two-dimensional Fourier kinoform can utilize effectively the periodicity of the discrete Fourier transform in the genetic algorithm. This condition enables us to perform the crossover process that is one of the processes in genetic algorithm without a spatial bandwidth of the kinoform. The optimization has been performed successfully in computer simulation. The optically reconstructed image agrees well with the theoretical one.

Yoshikawa, N.; Itoh, M.; Yatagai, T.

1995-04-01

43

Fractional Fourier transform in temporal ghost imaging with classical light  

SciTech Connect

We investigate temporal, second-order classical ghost imaging with long, incoherent, scalar plane-wave pulses. We prove that in rather general conditions, the intensity correlation function at the output of the setup is given by the fractional Fourier transform of the temporal object. In special cases, the correlation function is shown to reduce to the ordinary Fourier transform and the temporal image of the object. Effects influencing the visibility and the resolution are considered. This work extends certain known results on spatial ghost imaging into the time domain and could find applications in temporal tomography of pulses.

Setaelae, Tero [Department of Applied Physics, Aalto University, P.O. Box 13500, FI-00076 Aalto (Finland); Shirai, Tomohiro [Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, 1-2-1 Namiki, Tsukuba 305-8564 (Japan); Friberg, Ari T. [Department of Applied Physics, Aalto University, P.O. Box 13500, FI-00076 Aalto (Finland); Department of Physics and Mathematics, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu (Finland)

2010-10-15

44

Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS): Imaging and Tracking Capability  

NASA Technical Reports Server (NTRS)

The geosynchronous-imaging Fourier transform spectrometer (GIFTS) engineering demonstration unit (EDU) is an imaging infrared spectrometer designed for atmospheric soundings. It measures the infrared spectrum in two spectral bands (14.6 to 8.8 microns, 6.0 to 4.4 microns) using two 128 128 detector arrays with a spectral resolution of 0.57/cm with a scan duration of approx. 11 seconds. From a geosynchronous orbit, the instrument will have the capability of taking successive measurements of such data to scan desired regions of the globe, from which atmospheric status, cloud parameters, wind field profiles, and other derived products can be retrieved. The GIFTS EDU provides a flexible and accurate testbed for the new challenges of the emerging hyperspectral era. The EDU ground-based measurement experiment, held in Logan, Utah during September 2006, demonstrated its extensive capabilities and potential for geosynchronous and other applications (e.g., Earth observing environmental measurements). This paper addresses the experiment objectives and overall performance of the sensor system with a focus on the GIFTS EDU imaging capability and proof of the GIFTS measurement concept.

Zhou, D. K.; Larar, A. M.; Liu, Xu; Reisse, R. A.; Smith, W. L.; Revercomb, H. E.; Bingham, G. E.; Zollinger, L. J.; Tansock, J. J.; Huppi, Ronald J.

2007-01-01

45

Electro-Optical Imaging Fourier-Transform Spectrometer  

NASA Technical Reports Server (NTRS)

An electro-optical (E-O) imaging Fourier-transform spectrometer (IFTS), now under development, is a prototype of improved imaging spectrometers to be used for hyperspectral imaging, especially in the infrared spectral region. Unlike both imaging and non-imaging traditional Fourier-transform spectrometers, the E-O IFTS does not contain any moving parts. Elimination of the moving parts and the associated actuator mechanisms and supporting structures would increase reliability while enabling reductions in size and mass, relative to traditional Fourier-transform spectrometers that offer equivalent capabilities. Elimination of moving parts would also eliminate the vibrations caused by the motions of those parts. Figure 1 schematically depicts a traditional Fourier-transform spectrometer, wherein a critical time delay is varied by translating one the mirrors of a Michelson interferometer. The time-dependent optical output is a periodic representation of the input spectrum. Data characterizing the input spectrum are generated through fast-Fourier-transform (FFT) post-processing of the output in conjunction with the varying time delay.

Chao, Tien-Hsin; Zhou, Hanying

2006-01-01

46

Study of phase transition by far infrared fourier spectroscopy  

Microsoft Academic Search

A far-infrared Fourier spectrometer which utilizes the Martin-Puplet interferometer has been newly constructed, and shown to be useful particularly for the measurements of low-frequency spectra, which are important for the study of dynamics of phase transition. Transmission spectra of quartz and Li2Ge7O15 crystals are shown as examples.

Akikatsu Sawada; Mitsuo Wada; Yoshihiro Ishibashi

1983-01-01

47

Note: Phase sensitive detection of photoluminescence with Fourier transform spectroscopy.  

PubMed

Although known for more than twenty years, there is limited information in the literature regarding the experimental parameters of lock-in based phase sensitive emission detection in conjunction with Fourier spectrometers. For this technique - also known as double modulation spectroscopy - we present a guideline for parameter optimization by measuring the photoluminescence of InSb:Te at cryogenic temperatures. PMID:22300001

Ullrich, B; Brown, G J

2012-01-01

48

Image encryption based on the multiple-parameter discrete fractional Fourier transform and chaos function  

NASA Astrophysics Data System (ADS)

In recent years, the chaos-based cryptographic algorithms have suggested some new and efficient ways to develop secure image encryption techniques. In this paper, we propose a new approach for image encryption based on the multiple-parameter discrete fractional Fourier transform and chaotic logistic maps in order to meet the requirements of the secure image transmission. In the proposed image encryption scheme, the image is encrypted by juxtaposition of sections of the image in the multiple-parameter discrete fractional Fourier domains and the alignment of sections is determined by chaotic logistic maps. This method does not require the use of phase keys. The new method has been compared with several existing methods and shows comparable or superior robustness to blind decryption.

Lang, Jun; Tao, Ran; Wang, Yue

2010-05-01

49

Visible-NIR imaging optics for a Fourier transform spectrometer  

NASA Astrophysics Data System (ADS)

We present details of optical design, opto-mechanical design and testing of a visible-NIR imaging optical system for a Fourier transform spectrometer dedicated to astronomical application at the Mont Mégantic Observatory (Observatoire du Mont Mégantic, OMM, located south Québec city, Canada). Design considerations as well as testing and experimental results are presented.

Thibault, Simon; Reecht, Jérôme; Lavigne, Jean-François; Desnoyers, Nichola

2004-10-01

50

Linear phase imaging using differential interference contrast microscopy  

Microsoft Academic Search

Summary We propose an extension to Nomarski differential interference contrast microscopy that enables isotropic linear phase imag- ing. The method combines phase shifting, two directions of shear and Fourier-space integration using a modified spiral phase transform. We simulated the method using a phantom object with spatially varying amplitude and phase. Simulated results show good agreement between the final phase image

M. R. Arnison; K. G. Larkin; C. J. R. Sheppard; N. I. Smith; C. J. Cogswell

2004-01-01

51

Fourier-ring descriptor to characterize rare circulating cells from images generated using immunofluorescence microscopy.  

PubMed

We address the problem of subclassification of rare circulating cells using data driven feature selection from images of candidate circulating tumor cells from patients diagnosed with breast, prostate, or lung cancer. We determine a set of low level features which can differentiate among candidate cell types. We have implemented an image representation based on concentric Fourier rings (FRDs) which allow us to exploit size variations and morphological differences among cells while being rotationally invariant. We discuss potential clinical use in the context of treatment monitoring for cancer patients with metastatic disease. PMID:25456146

Emerson, Tegan; Kirby, Michael; Bethel, Kelly; Kolatkar, Anand; Luttgen, Madelyn; O'Hara, Stephen; Newton, Paul; Kuhn, Peter

2014-10-23

52

Reconstruction of multispectral image cubes from multiple-telescope array Fourier transform imaging spectrometer  

E-print Network

] demonstrated this technique with a two-aperture telescope and a scene of point sources. However, the spatialReconstruction of multispectral image cubes from multiple- telescope array Fourier transform@optics.rochester.edu Abstract: Multiple-telescope arrays can function as Fourier transform imaging spectrometers, using

Fienup, James R.

53

Pansharpening of multispectral images using filtering in Fourier domain  

NASA Astrophysics Data System (ADS)

In this study, there is examined filtering based pansharpening methods which means of using several 2D FIR filters in Fourier domain which implies that the filters are applied after taking 2D Discrete Fourier Transform of both multispectral and panchromatic image and after the pansharpening process in Fourier domain, the resulting pansharpened image is obtained with an inverse 2D DFT. In addition, these methods are compared with commonly used fusion methods which are combined as modulation based and component substitution based methods. The algorithms are applied to SPOT 6 co-registered image couples that were acquired simultaneously. Couples are chosen for three different regions which are a city image (Gebze/Turkey), a forest image (Istanbul/Turkey) and an agriculture field image (Sanliurfa/Turkey) in order to analyse the methods in different regional characteristics. These methods are compared by the fusion quality assessments that have common acceptance in community. The results of these quality assessments shows the filtering based methods had the best scores among the traditional methods.

Akoguz, Alper; Kurt, Burak; Pinar, Sedef K.

2014-10-01

54

Atmospheric convective velocities and the Fourier phase spectrum  

NASA Technical Reports Server (NTRS)

The relationship between convective velocity and the Fourier phase spectrum of the cross correlation is developed. By examining the convective velocity as a function of frequency, one may determine if Taylor's conversion from time statistics to space statistics is valid. It is felt that the high shear regions of the atmospheric boundary layer need to be explored to determine the validity of the use of Taylor's hypothesis for this region.

Cliff, W. C.

1974-01-01

55

Method for suppressing the mirror image in Fourier-domain optical coherence tomography.  

PubMed

A method, novel to our knowledge, for effective mirror image suppression in Fourier-domain optical coherence tomography based on a phase shift between neighboring A-mode scans is demonstrated. By realizing that the phase shifts of the real and mirror images are mutually reversed and assuming that the real image intensities of the two successive A-mode scans are the same, we can solve a set of two coupled equations to obtain the real image signals. The images based on the scanning of a high-resolution spectral-domain optical coherence tomography system are processed to show effective mirror image suppression results. Compared with a similar method of broad application, our approach has the advantages of shorter process time and higher flexibility in selecting the concerned image portions for processing. PMID:21808348

Wu, Chiung-Ting; Chi, Ting-Ta; Lee, Cheng-Kuang; Kiang, Yean-Woei; Yang, Chih-Chung; Chiang, Chun-Pin

2011-08-01

56

Astronomical imaging Fourier spectroscopy at far-infrared wavelengths  

E-print Network

The principles and practice of astronomical imaging Fourier transform spectroscopy (FTS) at far-infrared wavelengths are described. The Mach-Zehnder interferometer design has been widely adopted for current and future imaging FTS instruments; we compare this design with two other common interferometer formats. Examples of three instruments based on the Mach-Zehnder design are presented. The techniques for retrieving astrophysical parameters from the measured spectra are discussed using calibration data obtained with the Herschel SPIRE instrument. The paper concludes with an example of imaging spectroscopy obtained with the SPIRE FTS instrument.

Naylor, David A; van der Wiel, Matthijs H D; Makiwa, Gibion

2013-01-01

57

Infrared small target enhancement via phase spectrum of Quaternion Fourier Transform  

NASA Astrophysics Data System (ADS)

Small target enhancement is one of the crucial stages in infrared small target detection. In this paper, we propose a new method using phase spectrum of Quaternion Fourier Transform to enhance small targets while suppressing backgrounds for infrared images. This is inspired by the property that regularly Gaussian-like shape small targets could be considered as attractively salient signal in infrared images and the location information of such signal is implicitly contained in the phase spectrum from frequency domain. Formally, in the proposed method, we adopt the phase spectrum of Quaternion Fourier Transform instead of using traditional Fourier Transform to enhance the targets since the quaternion provides at most four data channels than only one for the latter, which could be helpful to broad types of background clutters by adding more information. For the construction of the quaternion, we present a second-order directional derivative filter via facet model to compute four second order directional derivative maps from four directions respectively as the four data channels. This filter is used to suppress noises and distinguish the targets and backgrounds into separably different textures so that it would boost the robustness of small target enhancement. In experiments, some typical infrared images with various scenes are tested to validate the effectiveness of the proposed method. The results demonstrate that our method actually has good performance and outperforms several state-of-the-art methods, which can be further used for infrared small target detection and tracking.

Qi, Shengxiang; Ma, Jie; Li, Hang; Zhang, Shuiping; Tian, Jinwen

2014-01-01

58

Dealiased spectral images from aliased Fizeau Fourier transform spectroscopy measurements.  

PubMed

Fizeau Fourier transform imaging spectroscopy (FTIS) is a technique for collecting both spatial and spectral information about an object with a Fizeau imaging interferometer and postprocessing. The technique possesses unconventional imaging properties due to the fact that the system transfer functions, including the imaging and spectral postprocessing operations, are given by cross correlations between subapertures of the optical system, in comparison with the conventional optical transfer function, which is given by the autocorrelation of the entire aperture of the system. The unconventional imaging properties of Fizeau FTIS can be exploited to form spatially dealiased spectral images from undersampled intensity measurements (obtain superresolution relative to the detector pixel spacing). We demonstrate this dealiasing technique through computer simulations and discuss the associated design and operational trade-offs. PMID:17164844

Thurman, Samuel T; Fienup, James R

2007-01-01

59

Asymmetric multiple-image encryption based on coupled logistic maps in fractional Fourier transform domain  

NASA Astrophysics Data System (ADS)

A multiple-image encryption scheme is proposed based on the asymmetric technique, in which the encryption keys are not identical to the decryption ones. First, each plain image is scrambled based on a sequence of chaotic pairs generated with a system of two symmetrically coupled identical logistic maps. Then, the phase-only function of each scrambled image is retrieved with an iterative phase retrieval process in the fractional Fourier transform domain. Second, all phase-only functions are modulated into an interim, which is encrypted into the ciphertext with stationary white noise distribution by using the fractional Fourier transform and chaotic diffusion. In the encryption process, three random phase functions are used as encryption keys to retrieve the phase-only functions of plain images. Simultaneously, three decryption keys are generated in the encryption process, which make the proposed encryption scheme has high security against various attacks, such as chosen plaintext attack. The peak signal-to-noise is used to evaluate the quality of the decrypted image, which shows that the encryption capacity of the proposed scheme is enhanced considerably. Numerical simulations demonstrate the validity and efficiency of the proposed method.

Sui, Liansheng; Duan, Kuaikuai; Liang, Junli; Zhang, Zhiqiang; Meng, Haining

2014-11-01

60

Nonlinear effects of phase blurring on Fourier transform holograms  

SciTech Connect

Liquid-crystal light valves can have intensity-dependent resolution. We find for a nematic liquid-crystal light valve that this effect is well modeled as a phase that has been blurred by a linear space-invariant filter. The phase point-spread function is measured and is used in simulations to demonstrate that it introduces intermodulation products to the diffraction patterns of computer-generated Fourier transform holograms. Also, the influence of phase blurring on a pseudorandom-encoding algorithm is evaluated in closed form. This analysis applied to a spot array generator design indicates that nonlinear effects are negligible only if the diameter of the point-spread function is a small fraction of the pixel spacing. (c) 2000 Optical Society of America.

Duelli, Markus [The ElectroOptics Research Institute, University of Louisville, Louisville, Kentucky 40292 (United States); Ge, Li [The ElectroOptics Research Institute, University of Louisville, Louisville, Kentucky 40292 (United States); Cohn, Robert W. [The ElectroOptics Research Institute, University of Louisville, Louisville, Kentucky 40292 (United States)

2000-09-01

61

UNIQUENESS RESULTS FOR THE PHASE RETRIEVAL PROBLEM OF FRACTIONAL FOURIER TRANSFORMS OF VARIABLE ORDER  

E-print Network

problem for the fractional Fourier transform (FrFT) of variable order. This problem occurs naturally and phrases. Phase retrieval; Pauli problem; Fractional Fourier transform; entire function of finite order. 1UNIQUENESS RESULTS FOR THE PHASE RETRIEVAL PROBLEM OF FRACTIONAL FOURIER TRANSFORMS OF VARIABLE

Paris-Sud XI, Université de

62

Binary-Phase Fourier Gratings for Nonuniform Array Generation  

NASA Technical Reports Server (NTRS)

We describe a design method for a binary-phase Fourier grating that generates an array of spots with nonuniform, user-defined intensities symmetric about the zeroth order. Like the Dammann fanout grating approach, the binary-phase Fourier grating uses only two phase levels in its grating surface profile to generate the final spot array. Unlike the Dammann fanout grating approach, this method allows for the generation of nonuniform, user-defined intensities within the final fanout pattern. Restrictions governing the specification and realization of the array's individual spot intensities are discussed. Design methods used to realize the grating employ both simulated annealing and nonlinear optimization approaches to locate optimal solutions to the grating design problem. The end-use application driving this development operates in the near- to mid-infrared spectrum - allowing for higher resolution in grating specification and fabrication with respect to wavelength than may be available in visible spectrum applications. Fabrication of a grating generating a user-defined nine spot pattern is accomplished in GaAs for the near-infrared. Characterization of the grating is provided through the measurement of individual spot intensities, array uniformity, and overall efficiency. Final measurements are compared to calculated values with a discussion of the results.

Keys, Andrew S.; Crow, Robert W.; Ashley, Paul R.

2003-01-01

63

Fizeau Fourier transform imaging spectroscopy: missing data reconstruction.  

PubMed

Fizeau Fourier transform imaging spectroscopy yields both spatial and spectral information about an object. Spectral information, however, is not obtained for a finite area of low spatial frequencies. A nonlinear reconstruction algorithm based on a gray-world approximation is presented. Reconstruction results from simulated data agree well with ideal Michelson interferometer-based spectral imagery. This result implies that segmented-aperture telescopes and multiple telescope arrays designed for conventional imaging can be used to gather useful spectral data through Fizeau FTIS without the need for additional hardware. PMID:18545367

Thurman, Samuel T; Fienup, James R

2008-04-28

64

A phase space model of Fourier ptychographic microscopy  

PubMed Central

A new computational imaging technique, termed Fourier ptychographic microscopy (FPM), uses a sequence of low-resolution images captured under varied illumination to iteratively converge upon a high-resolution complex sample estimate. Here, we propose a mathematical model of FPM that explicitly connects its operation to conventional ptychography, a common procedure applied to electron and X-ray diffractive imaging. Our mathematical framework demonstrates that under ideal illumination conditions, conventional ptychography and FPM both produce datasets that are mathematically linked by a linear transformation. We hope this finding encourages the future cross-pollination of ideas between two otherwise unconnected experimental imaging procedures. In addition, the coherence state of the illumination source used by each imaging platform is critical to successful operation, yet currently not well understood. We apply our mathematical framework to demonstrate that partial coherence uniquely alters both conventional ptychography’s and FPM’s captured data, but up to a certain threshold can still lead to accurate resolution-enhanced imaging through appropriate computational post-processing. We verify this theoretical finding through simulation and experiment. PMID:24514995

Horstmeyer, Roarke; Yang, Changhuei

2014-01-01

65

Fourier transform method for imaging atmospheric Cherenkov telescopes  

NASA Astrophysics Data System (ADS)

We propose Fourier transform (hereafter FT) method for processing the images of extensive air showers (EAS) detected by imaging atmospheric Cherenkov telescopes (IACT) used in the very high energy (VHE) gamma-ray astronomy. The method uses a special type of discrete Fourier transforms (DFT) based on orbit functions of compact Lie groups, and the use of continuous extension of the inverse transform to approximate the discrete images by continuous EAS brightness distribution functions. Here we present the FT-method for SU(3) group which provides a practicable technique for realization of the DFT approach for functions sampled on hexagonal symmetry grids implemented in the current IACT cameras. We note that the proposed FT-method can also be implemented for the rectangular grids using the DFT on SU(2) × SU(2) group. To show the viability of the FT-method, here we apply it to Monte-Carlo simulated bank of TeV proton and gamma-ray EAS images only for the case of a stand-alone telescope and use a simple single-parameter (ALPHA) analysis. Comparing between the FT-method and the currently used ‘standard’ method for signal enhancement shows that a straightforward use of FT technique within standard parameterization scheme allows a better and systematic enhancement of the gamma-ray signal. The relative difference between these two methods becomes more profound especially for ‘photon poor’ images, for which the standard method significantly deteriorates. It suggests that the effective EAS detection thresholds could be reduced with implementation of the FT technique for IACTs. This prediction is further supported by a significant noise suppression capability of the method after using simple ‘low-pass’ filters in the image frequency domain. This new approach allows very deep ‘tail’ (and ‘height’) image cuts, differentiation of images, provides frequency spectra, etc., which could be used for development of new effective parameters for the EAS image processing.

Atoyan, A.; Patera, J.; Sahakian, V.; Akhperjanian, A.

2005-02-01

66

Multiple images encryption based on Fourier transform hologram  

NASA Astrophysics Data System (ADS)

A new optical encryption method is proposed in this paper to achieve multiple images encryption. We introduce reference waves with different incident angles and random amplitude masks into a Fourier transform hologram configuration to encrypt multiple images. In the encryption procedure, different random amplitude masks (RAMs) which are placed into the reference arm vertically admit the multiplexing capability. When decrypting one of the original images, reference wave with the same incident angle as encrypting the target image is used to illuminate the encrypted hologram with the insertion of random amplitude mask whose transmissivity is reciprocal of that of the encrypting random amplitude mask in the reference arm. We also simulate and analyze the influence of partly wrong decrypting key on the decrypted results. Numerical simulation proves that the proposed encryption method is valid and of high security level.

Lin, Chao; Shen, Xueju; Tang, Rui; Zou, Xiao

2012-03-01

67

Ghost imaging of phase objects with classical incoherent light  

SciTech Connect

We describe an optical setup for performing spatial Fourier filtering in ghost imaging with classical incoherent light. This is achieved by a modification of the conventional geometry for lensless ghost imaging. It is shown on the basis of classical coherence theory that with this technique one can realize what we call phase-contrast ghost imaging to visualize pure phase objects.

Shirai, Tomohiro [Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, 1-2-1 Namiki, Tsukuba 305-8564 (Japan); Setaelae, Tero [Department of Applied Physics, Aalto University, P.O. Box 13500, FI-00076 Aalto (Finland); Friberg, Ari T. [Department of Applied Physics, Aalto University, P.O. Box 13500, FI-00076 Aalto (Finland); Department of Physics and Mathematics, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu (Finland); Department of Microelectronics and Applied Physics, Royal Institute of Technology, Electrum 229, SE-164 40 Kista (Sweden)

2011-10-15

68

Geometric phase analysis based on the windowed Fourier transform for the deformation field measurement  

NASA Astrophysics Data System (ADS)

The geometric phase analysis (GPA), an important image-based deformation measurement method, has been used at both micro- and nano-scale. However, when a deformed image has apparent distortion, non-ignorable error in the obtained deformation field could occur by using this method. In this paper, the geometric phase analysis based on the windowed Fourier transform (WFT) is proposed to solve the above-mentioned issue, defined as the WFT-GPA method. In WFT-GPA, instead of the Fourier transform (FT), the WFT is utilized to extract the phase field block by block, and therefore more accurate local phase information can be acquired. The simulation tests, which include detailed discussion of influence factors for measurement accuracy such as window size and image noise, are conducted with digital deformed grids. The results verify that the WFT-GPA method not only keeps all advantages of traditional GPA method, but also owns a better accuracy for deformation measurement. Finally, the WFT-GPA method is applied to measure the machining distortion incurred in soft ultraviolet nanoimprint lithography (UV-NIL) process. The successful measurement shows the feasibility of this method and offers a full-field way for characterizing the replication quality of UV-NIL process.

Dai, Xianglu; Xie, Huimin; Wang, Qinghua

2014-06-01

69

Imaging Organ of Corti Vibration Using Fourier-Domain OCT  

NASA Astrophysics Data System (ADS)

Measuring the sound stimulated vibration from various structures in the organ of Corti is important in understanding how the small vibrations are amplified and detected. In this study we examine the feasibility of using phase-sensitive Fourier domain optical coherence tomography (PSFD-OCT) to measure vibration of the cellular structures of the organ of Corti. PSFD-OCT is a low coherence interferrometry system where the interferrogram is detected as a function of wavelength. The phase of the Fourier transformation of the detected spectra contains path deference (between the sample arm and the reference arm) information of the interferometer. In PSFD-OCT this phase is measured as a function of time and thus any time dependent change in the path difference between the sample arm and the reference arm can be detected. In the experiment, we used an in vitro preparation of the guinea pig cochlea and made a surgical opening at the apical end to access the organ of Corti. By applying tones with different frequencies via the intact middle ear, we recorded the structural vibration inside the organ of Corti. Vibration amplitude and phase of different substructures were mapped on a cross-section view of the organ of Corti. Although the measurements were made at the apical turn of the cochlea, it will be possible to make vibration measurement from various turns of the cochlea. The noise floor of the system was 0.3 nm, calibrated using a piezo stack as a calibrator.

Choudhury, Niloy; Chen, Fangyi; Fridberger, Anders; Zha, Dingjun; Jacques, Steven L.; Wang, Ruikang K.; Nuttall, Alfred L.

2011-11-01

70

A watermark strategy for quantum images based on quantum fourier transform  

NASA Astrophysics Data System (ADS)

We present a robust watermark strategy for quantum images. The watermark image is embedded into the fourier coefficients of the quantum carrier image, which will not affect the carrier image's visual effect. Before being embedded into the carrier image, the watermark image is preprocessed to be seemingly meaningless using quantum circuit, which further ensures the security of the watermark image. The properties of fourier transform ensure that the watermark embedded in the carrier image resists the unavoidable noise and cropping.

Zhang, Wei-Wei; Gao, Fei; Liu, Bin; Wen, Qiao-Yan; Chen, Hui

2013-02-01

71

Stages: Sub-Fourier Dynamic Shim Updating Using Nonlinear Magnetic Field Phase Preparation  

PubMed Central

Heterogeneity of the static magnetic field in magnetic resonance imaging may cause image artifacts and degradation in image quality. The field heterogeneity can be reduced by dynamically adjusting shim fields or dynamic shim updating (DSU), in which magnetic field homogeneity is optimized for each tomographic slice to improve image quality. A limitation of this approach is that a new magnetic field can be applied only once for each slice, otherwise image quality would improve somewhere to its detriment elsewhere in the slice. The motivation of this work is to overcome this limitation and develop a technique using nonlinear magnetic fields to dynamically shim the static magnetic field within a single Fourier-encoded volume or slice, called sub-Fourier dynamic shim updating. However, the nonlinear magnetic fields are not used as shim fields; instead, they impart a strong spatial dependence to the acquired MR signal by nonlinear phase preparation, which may be exploited to locally improve magnetic field homogeneity during acquisition. A theoretical description of the method is detailed, simulations and a proof-of-principle experiment are performed using a magnet coil with a known field geometry. The method is shown to remove artifacts associated with magnetic field homogeneity in balanced steady-state free precession (bSSFP) pulse sequences. We anticipate that this method will be useful to improve the quality of magnetic resonance images by removing deleterious artifacts associated with a heterogeneous static magnetic field. PMID:23440677

Cocosco, Chris A; Gallichan, Daniel; Schultz, Gerrit; Weber, Hans; Welz, Anna; Hennig, Jürgen; Zaitsev, Maxim

2014-01-01

72

Universal and efficient compressed sensing by spread spectrum and application to realistic Fourier imaging techniques  

NASA Astrophysics Data System (ADS)

We advocate a compressed sensing strategy that consists of multiplying the signal of interest by a wide bandwidth modulation before projection onto randomly selected vectors of an orthonormal basis. First, in a digital setting with random modulation, considering a whole class of sensing bases including the Fourier basis, we prove that the technique is universal in the sense that the required number of measurements for accurate recovery is optimal and independent of the sparsity basis. This universality stems from a drastic decrease of coherence between the sparsity and the sensing bases, which for a Fourier sensing basis relates to a spread of the original signal spectrum by the modulation (hence the name "spread spectrum"). The approach is also efficient as sensing matrices with fast matrix multiplication algorithms can be used, in particular in the case of Fourier measurements. Second, these results are confirmed by a numerical analysis of the phase transition of the ?1-minimization problem. Finally, we show that the spread spectrum technique remains effective in an analog setting with chirp modulation for application to realistic Fourier imaging. We illustrate these findings in the context of radio interferometry and magnetic resonance imaging.

Puy, Gilles; Vandergheynst, Pierre; Gribonval, Rémi; Wiaux, Yves

2012-12-01

73

Registration of Translated and Rotated Images Using Finite Fourier Transforms  

Microsoft Academic Search

A well-known method for image registration is based on a conventional correlation between phase-only, or whitened, versions of the two images to be realigned. The method, covering rigid translational movements, is characterized by an outstanding robustness against correlated noise and disturbances, such as those encountered with nonuniform, time varying illumination. This correspondence discusses an extension of the method to cover

E. De Castro; C. Morandi

1987-01-01

74

Phase closure and object reconstruction algorithm for Fourier telescopy applied to fast-moving targets  

NASA Astrophysics Data System (ADS)

Fourier Telescopy (FT) is an active imaging method which interferes spatially diverse, frequency-encoded laser beams on a distant target, and records a time history of the reflected intensity measured by a single photodetector on a large receiver. FT has been studied extensively for imaging Geostationary objects, using high-energy pulsed lasers to project triplets of laser beams, by gradually stepping over time through the multitude of u,v-plane baselines required for accurate object reconstruction. Phase closure among the received triplets plays a key role in canceling out random atmospheric phase errors between laser beams. A new method has been devised to apply FT to rapidly moving targets, such as LEO space objects. In order to implement the thousands of baselines in a short engagement time, approximately 20 continuous-wave laser beams are simultaneously broadcast, and the baseline configurations are rapidly changed through a dynamic optical element. In order to eliminate unknown atmospheric errors, a new type of global phase closure has been developed, which allows image reconstruction from the time history of measured total reflected intensity, originating from the complex 20-beam interference patterns. In this paper, we summarize the new FT LEO method, and give a detailed derivation of the phase closure and image reconstruction algorithms that will lead to ultra-high resolution images of fast-moving space objects.

Spivey, Brett; Stapp, James; Sandler, David

2006-08-01

75

Comparison of kinoform synthesis methods for image reconstruction in Fourier plane  

NASA Astrophysics Data System (ADS)

Kinoform is synthesized phase diffractive optical element which allows to reconstruct image by its illumination with plane wave. Kinoforms are used in image processing systems. For tasks of kinoform synthesis iterative methods had become wide-spread because of relatively small error of resulting intensity distribution. There are articles in which two or three iterative methods are compared but they use only one or several test images. The goal of this work is to compare iterative methods by using many test images of different types. Images were reconstructed in Fourier plane from synthesized kinoforms displayed on phase-only LCOS SLM. Quality of reconstructed images and computational resources of the methods were analyzed. For kinoform synthesis four methods were implemented in programming environment: Gerchberg-Saxton algorithm (GS), Fienup algorithm (F), adaptive-additive algorithm (AA) and Gerchberg-Saxton algorithm with weight coefficients (GSW). To compare these methods 50 test images with different characteristics were used: binary and grayscale, contour and non-contour. Resolution of images varied from 64×64 to 1024×1024. Occupancy of images ranged from 0.008 to 0.89. Quantity of phase levels of synthesized kinoforms was 256 which is equal to number of phase levels of SLM LCOS HoloEye PLUTO VIS. Under numerical testing it was found that the best quality of reconstructed images provides the AA method. The GS, F and GSW methods showed worse results but roughly similar between each other. Execution time of single iteration of the analyzed methods is minimal for the GS method. The F method provides maximum execution time. Synthesized kinoforms were optically reconstructed using phase-only LCOS SLM HoloEye PLUTO VIS. Results of optical reconstruction were compared to the numerical ones. The AA method showed slightly better results than other methods especially in case of gray-scale images.

Cheremkhin, Pavel A.; Evtikhiev, Nikolay N.; Krasnov, Vitaly V.; Porshneva, Liudmila A.; Rodin, Vladislav G.; Starikov, Sergey N.

2014-05-01

76

The data processing pipeline for the Herschel/SPIRE Imaging Fourier Transform Spectrometer  

E-print Network

The data processing pipeline for the Herschel/SPIRE Imaging Fourier Transform Spectrometer Trevor R the data processing pipeline to generate calibrated data products from the Spectral and Photometric Imaging Receiver (SPIRE) imaging Fourier Transform Spectrometer. The pipeline processes telemetry from SPIRE point

Naylor, David A.

77

Reconstruction of piecewise homogeneous images from partial knowledge of their Fourier Transform  

NASA Astrophysics Data System (ADS)

Fourier synthesis (FS) inverse problem consists in reconstructing a multi-variable function from the measured data which correspond to partial and uncertain knowledge of its Fourier Transform (FT). By partial knowledge we mean either partial support and/or the knowledge of only the module and by uncertain we mean both uncertainty of the model and noisy data. This inverse problem arises in many applications such as : optical imaging, radio astronomy, magnetic resonance imaging (MRI) and diffraction scattering (ultrasounds or microwave imaging). Most classical methods of inversion are based on interpolation of the data and fast inverse FT. But when the data do not fill uniformly the Fourier domain or when the phase of the signal is lacking as in optical interferometry, the results obtained by such methods are not satisfactory, because these inverse problems are ill-posed. The Bayesian estimation approach, via an appropriate modeling of the unknown functions gives the possibility of compensating the lack of information in the data, thus giving satisfactory results. In this paper we study the case where the observations are a part of the FT modulus of objects which are composed of a few number of homogeneous materials. To model such objects we use a Hierarchical Hidden Markov Modeling (HMM) and propose a Bayesian inversion method using appropriate Markov Chain Monte Carlo (MCMC) algorithms.

Féron, Olivier; Chama, Zouaoui; Mohammad-Djafari, Ali

2004-11-01

78

Optical phase retrieval by phase-space tomography and fractional-order Fourier transforms  

Microsoft Academic Search

Phase-space tomography is experimentally demonstrated for the determination of the spatially varying amplitude and phase of a quasi-monochromatic optical f ield by measurements of intensity only. Both fully and partially coherent sources are characterized. The method, which makes use of the fractional-order Fourier transform, also yields the Wigner distribution of the f ield and works in one or two dimensions.

D. F. McAlister; M. Beck; L. Clarke; A. Mayer; M. G. Raymer

1995-01-01

79

ULTRASOUND PULSE-ECHO IMAGING USING THE SPLIT-STEP FOURIER PROPAGATOR  

SciTech Connect

Ultrasonic reflection imaging has the potential to produce higher image resolution than transmission tomography, but imaging resolution and quality still need to be further improved for early cancer detection and diagnosis. We present an ultrasound reflection image reconstruction method using the split-step Fourier propagator. It is based on recursive inward continuation of ultrasonic wavefields in the frequency-space and frequency-wavenumber domains. The inward continuation within each extrapolation interval consists of two steps. In the first step, a phase-shift term is applied to the data in the frequency-wavenumber domain for propagation in a reference medium. The second step consists of applying another phase-shift term to data in the frequency-space domain to approximately compensate for ultrasonic scattering effects of heterogeneities within the breast. We use synthetic ultrasound pulse-echo data recorded around a ring for heterogeneous, computer-generated numerical breast phantoms to study the imaging capability of the method. The phantoms are derived from an experimental breast phantom and a sound-speed tomography image of an in-vivo ultrasound breast data collected usi ng a ring array. The heterogeneous sound-speed models used for pulse-echo imaging are obtained using a computationally efficient, first-arrival-time (time-of-flight) transmission tomography method. Our studies demonstrate that reflection image reconstruction using the split-step Fourier propagator with heterogeneous sound-speed models significantly improves image quality and resolution. We also numerically verify the spatial sampling criterion of wavefields for a ring transducer array.

HUANG, LIANJIE [Los Alamos National Laboratory; QUAN, YOULI [Los Alamos National Laboratory

2007-01-31

80

Continued Development of a Planetary Imaging Fourier Transform Spectrometer (PIFTS)  

NASA Technical Reports Server (NTRS)

This report describes continued efforts to evaluate a breadboard of a Planetary Imaging Fourier Transform Spectrometer (PIFTS). The PIFTS breadboard was developed under prior PIDDP funding. That effort is described in the final report for NASA Grant NAG5-6248 and in two conference papers (Sromovsky et al. 2000; Revercomb et al. 2000). The PIFTS breadboard was designed for near-IR (1-5.2 micrometer imaging of planetary targets with spectral resolving powers of several hundred to several thousand, using an InSb detector array providing at least 64x64 pixels imaging detail. The major focus of the development effort was to combine existing technologies to produce a small and low power design compatible with a very low mass flyable instrument. The objective of this grant (NAG5-10729) was further characterization of the breadboard performance, including intercomparisons with the highly accurate non-imaging Advanced Emitted Radiance Interferometer (AERI) (Revercomb et al. 1994; Best et al. 1997).

Sromovsky, L. A.

2002-01-01

81

Amplitude and phase fourier correlation of ``twin'' GC-spectra of fatty acids from sheep dairy  

NASA Astrophysics Data System (ADS)

Authors present the discrimination performances of amplitude and phase-only Fourier correlation over the "twin" typed GC-spectra of sheep milk and ripened cheese. Therefore, in order to assess the most robust Fourier correlation method for the "twin" GC-spectra discrimination, the correlation matrix is built up over 17 analyzed GC-spectra in both amplitude and phase domains.

Teusdea, Alin C.; Gabor, Gianina; Hilma, Elena

2012-08-01

82

Challenge for spectroscopic tomography of biomembrane using imaging type two-dimensional Fourier spectroscopy  

NASA Astrophysics Data System (ADS)

We propose an image-producing Fourier spectroscopic technology that enables two-dimensional spectroscopic images to be obtained within the focusing plane alone. This technology incorporates auto-correlational phase-shift interferometry that uses only object light generated by the bright points that optically make up the object. We are currently involved in studies of non-invasive technologies used to measure blood components such as glucose and lipids, which are measured for use in daily living. Previous studies have investigated non-invasive technologies that measure blood glucose levels by utilizing near-infrared light that permeates the skin well. It has been confirmed that subtle changes in the concentration of a glucose solution, a sample used to measure the glucose level, can be measured by analyzing the spectroscopic characteristics of near-infrared light; however, when applied to a biomembrane, technology such as this is incapable of precisely measuring the glucose level because light diffusion within the skin disturbs the measurement. Our proposed technology enables two-dimensional spectroscopy to a limited depth below the skin covered by the measurement. Specifically, our technology concentrates only on the vascular territory near the skin surface, which is only minimally affected by light diffusion, as discussed previously; the spectroscopic characteristics of this territory are obtained and the glucose level can be measured with good sensitivity. In this paper we propose an image-producing Fourier spectroscopy method that is used as the measuring technology in producing a three-dimensional spectroscopic image.

Qi, Wei; Ishimaru, Ichiro

2010-02-01

83

Spatial Phase Imaging  

NASA Technical Reports Server (NTRS)

Frequently, scientists grow crystals by dissolving a protein in a specific liquid solution, and then allowing that solution to evaporate. The methods used next have been, variously, invasive (adding a dye that is absorbed by the protein), destructive (crushing protein/salt-crystal mixtures and observing differences between the crushing of salt and protein), or costly and time-consuming (X-ray crystallography). In contrast to these methods, a new technology for monitoring protein growth, developed in part through NASA Small Business Innovation Research (SBIR) funding from Marshall Space Flight Center, is noninvasive, nondestructive, rapid, and more cost effective than X-ray analysis. The partner for this SBIR, Photon-X, Inc., of Huntsville, Alabama, developed spatial phase imaging technology that can monitor crystal growth in real time and in an automated mode. Spatial phase imaging scans for flaws quickly and produces a 3-D structured image of a crystal, showing volumetric growth analysis for future automated growth.

2006-01-01

84

Fourier-Doppler Imaging of Line Profile Variations in ? Ophiuchi  

NASA Astrophysics Data System (ADS)

We present, for the first time, the Fourier-Doppler Imaging (FDI) analysis of periodic line profile variations in a ? Oph-type star. For this purpose we obtained, in the period from 1996 May 3 to May 5, a total of 242 high-resolution, high signal-to-noise ratio spectra of the Be star ? Oph itself. Using the FDI technique, we examine the variations in both time and wavelength and complement it with time series analysis. This kind of analysis is valid for both the nonradial pulsator model and the rotation modulation model, but we discuss the results in terms of the former model, considering it the more likely explanation for the observed line profile variability. Two distinct groups of modes are detected: medium (4<=l~|m|<=8) and high-degree modes (which could be associated with 13<=l~|m|<=17). It is shown that the high-frequency oscillations were strongly confined to an equatorial belt narrower than 20° and that the line profile variability was caused predominantly by sectoral modes, although tesseral modes |m|=l-1 are not excluded in taking into account the effect of fast rotation. We discuss the modal nature of the waves with respect to the characteristic oscillation periods in the corotating frame and the high amplitude of the projected rotational velocity variations (~20 km s-1).

Jankov, S.; Janot-Pacheco, E.; Leister, N. V.

2000-09-01

85

Rotational-translational fourier imaging system requiring only one grid pair  

NASA Technical Reports Server (NTRS)

The sky contains many active sources that emit X-rays, gamma rays, and neutrons. Unfortunately hard X-rays, gamma rays, and neutrons cannot be imaged by conventional optics. This obstacle led to the development of Fourier imaging systems. In early approaches, multiple grid pairs were necessary in order to create rudimentary Fourier imaging systems. At least one set of grid pairs was required to provide multiple real components of a Fourier derived image, and another set was required to provide multiple imaginary components of the image. It has long been recognized that the expense associated with the physical production of the numerous grid pairs required for Fourier imaging was a drawback. Herein one grid pair (two grids), with accompanying rotation and translation, can be used if one grid has one more slit than the other grid, and if the detector is modified.

Campbell, Jonathan W. (Inventor)

2006-01-01

86

Vector power multiple-parameter fractional Fourier transform of image encryption algorithm  

NASA Astrophysics Data System (ADS)

In this paper, we propose a multiple-parameter fractional Fourier transform with its transform order being a real vector, based on which a high-security image encryption scheme is also given. This novel fractional Fourier transform has removed the restriction on the dimension of transform order and highly enhances the security of image encryption scheme proposed in this paper without increasing the computational complexity and hardware cost. The numerical results verify the efficacy and security of this image encryption method. The vector power multi-parameter fractional Fourier transform is a generalized form of the classical fractional Fourier transform with all the previous fractional Fourier transform as its special cases and has theoretical significance in information processing and information security.

Ran, Qiwen; Zhao, Tieyu; Yuan, Lin; Wang, Jian; Xu, Lei

2014-11-01

87

Derivative method for phase retrieval in off-axis quantitative phase imaging.  

PubMed

We present a method for phase retrieval in off-axis interferometric systems. By numerically calculating the transverse 1st and 2nd order derivatives of the interferogram, we show that one can directly retrieve the quantitative phase image, without the need for Fourier or Hilbert transformations. Because of this, the method is significantly faster than the current approaches. We illustrate our method using biological specimen data from three different off-axis quantitative phase imaging techniques. PMID:22660056

Bhaduri, Basanta; Popescu, Gabriel

2012-06-01

88

Design and application of the snapshot hyperspectral imaging Fourier transform (SHIFT) spectropolarimeter for fluorescence imaging  

NASA Astrophysics Data System (ADS)

We present a novel and inexpensive Stokes imaging spectropolarimeter based on the Snapshot Hyperspectral Imaging Fourier Transform (SHIFT) spectrometer. A rotating quarter wave plate and stationary linear polarizer placed in front of the SHIFT spectrometer enables us to reconstruct an object's spectra and Stokes parameters in the visible spectrum. Measurements are stored in the form of four-dimensional (4D) Stokes datacubes containing the object's spatial, spectral, and polarization information. We discuss calibration methods, review design considerations, and present preliminary results from proof-of-concept experiments.

Chan, Victoria C.; Kudenov, Michael; Liang, Chen; Zhou, Pixuan; Dereniak, Eustace

2014-03-01

89

Complete fourier direct magnetic resonance imaging (CFD-MRI) for diffusion MRI  

PubMed Central

The foundation for an accurate and unifying Fourier-based theory of diffusion weighted magnetic resonance imaging (DW–MRI) is constructed by carefully re-examining the first principles of DW–MRI signal formation and deriving its mathematical model from scratch. The derivations are specifically obtained for DW–MRI signal by including all of its elements (e.g., imaging gradients) using complex values. Particle methods are utilized in contrast to conventional partial differential equations approach. The signal is shown to be the Fourier transform of the joint distribution of number of the magnetic moments (at a given location at the initial time) and magnetic moment displacement integrals. In effect, the k-space is augmented by three more dimensions, corresponding to the frequency variables dual to displacement integral vectors. The joint distribution function is recovered by applying the Fourier transform to the complete high-dimensional data set. In the process, to obtain a physically meaningful real valued distribution function, phase corrections are applied for the re-establishment of Hermitian symmetry in the signal. Consequently, the method is fully unconstrained and directly presents the distribution of displacement integrals without any assumptions such as symmetry or Markovian property. The joint distribution function is visualized with isosurfaces, which describe the displacement integrals, overlaid on the distribution map of the number of magnetic moments with low mobility. The model provides an accurate description of the molecular motion measurements via DW–MRI. The improvement of the characterization of tissue microstructure leads to a better localization, detection and assessment of biological properties such as white matter integrity. The results are demonstrated on the experimental data obtained from an ex vivo baboon brain. PMID:23596401

Özcan, Alpay

2013-01-01

90

Time-average Fourier telescopy: a scheme for high-resolution imaging through horizontal-path turbulence.  

PubMed

The problem of high-resolution imaging through long horizontal-path ground-level turbulence has gone unsolved since it was first addressed many decades ago. In this paper I describe a method that shows promise for diffraction-limited imaging through ground-level turbulence with large (meters) apertures and at large (kilometers) distances. The key lies in collecting image data in the spatial frequency domain via the method of Fourier telescopy and taking suitable time averages of the magnitude and phase of the Fourier telescopy signal. The method requires active illumination of the target with laser light, and the time averages required will likely be over many tens of seconds if not tens of minutes or more. The scheme will thus not be suitable for time-varying scenes. The basic scheme is described, and principle challenges briefly discussed. PMID:22307125

Rhodes, William T

2012-02-01

91

Single-Grid-Pair Fourier Telescope for Imaging in Hard-X Rays and gamma Rays  

NASA Technical Reports Server (NTRS)

This instrument, a proposed Fourier telescope for imaging in hard-x rays and gamma rays, would contain only one pair of grids made of an appropriate radiation-absorpting/ scattering material, in contradistinction to multiple pairs of such as grids in prior Fourier x- and gamma-ray telescopes. This instrument would also include a relatively coarse gridlike image detector appropriate to the radiant flux to be imaged. Notwithstanding the smaller number of grids and the relative coarseness of the imaging detector, the images produced by the proposed instrument would be of higher quality.

Campbell, Jonathan

2008-01-01

92

Synthetic quadrature phase detector/demodulator for Fourier transform spectrometers.  

PubMed

A method is developed to demodulate (velocity correct) Fourier transform spectrometer data that are taken with an analog to digital converter that digitizes equally spaced in time. This method makes it possible to use simple low-cost, high-resolution audio digitizers to record high-quality data without the need for an event timer or quadrature laser hardware and makes it possible to use a metrology laser of any wavelength. The reduced parts count and simple implementation make it an attractive alternative in space-based applications when compared to previous methods such as the Brault algorithm. PMID:19104542

Campbell, Joel

2008-12-20

93

Quantitative phase imaging with single shot digital holography  

NASA Astrophysics Data System (ADS)

We demonstrate quantitative phase imaging using single shot digital holography for a calibrated spiral phase object. A single frame of near on-axis digital hologram of a spiral phase plate is recorded and the complex object field in the hologram plane is retrieved using a constrained optimization approach. Experimental results show the feasibility of a quantitative phase imaging technique which has superior performance to conventional Fourier filtering methods. Single shot capability suggests that this method is suitable for holographic imaging of dynamic objects such as live biological cells.

Samsheerali, P. T.; Khare, Kedar; Joseph, Joby

2014-05-01

94

Midwave infrared imaging Fourier transform spectrometry of combustion plumes  

NASA Astrophysics Data System (ADS)

A midwave infrared (MWIR) imaging Fourier transform spectrometer (IFTS) was used to successfully capture and analyze hyperspectral imagery of combustion plumes. Jet engine exhaust data from a small turbojet engine burning diesel fuel at a low rate of 300 cm3/min was collected at 1 cm -1 resolution from a side-plume vantage point on a 200x64 pixel window at a range of 11.2 meters. Spectral features of H2O, CO, and CO2 were present, and showed spatial variability within the plume structure. An array of thermocouple probes was positioned within the plume to aid in temperature analysis. A single-temperature plume model was implemented to obtain spatially-varying temperatures and plume concentrations. Model-fitted temperatures of 811 +/- 1.5 K and 543 +/- 1.6 K were obtained from plume regions in close proximity to thermocouple probes measuring temperatures of 719 K and 522 K, respectively. Industrial smokestack plume data from a coal-burning stack collected at 0.25 cm-1 resolution at a range of 600 meters featured strong emission from NO, CO, CO2, SO 2, and HCl in the spectral region 1800-3000 cm-1. A simplified radiative transfer model was employed to derive temperature and concentrations for clustered regions of the 128x64 pixel scene, with corresponding statistical error bounds. The hottest region (closest to stack centerline) was 401 +/- 0.36 K, compared to an in-stack measurement of 406 K, and model-derived concentration values of NO, CO2, and SO2 were 140 +/- 1 ppmV, 110,400 +/- 950 ppmV, and 382 +/- 4 ppmV compared to in-stack measurements of 120 ppmV (NOx), 94,000 ppmV, and 382 ppmV, respectively. In-stack measurements of CO and HCl were not provided by the stack operator, but model-derived values of 19 +/- 0.2 ppmV and 111 +/- 1 ppmV are reported near stack centerline. A deployment to Dugway Proving Grounds, UT to collect hyperspectral imagery of chemical and biological threat agent simulants resulted in weak spectral signatures from several species. Plume detection of methyl salicilate was achieved from both a stack release and explosive detonation, although spectral identification was not accomplished due to weak signal strength.

Bradley, Kenneth C.

95

Discovering ordered phases of block copolymers: new results from a generic Fourier-space approach.  

PubMed

A generic Fourier-space approach to solve the self-consistent field theory of block copolymers is developed. This approach is based on the fact that, for any computational box with periodic boundary conditions, all spatially varying functions are spanned by the Fourier series determined by the size and shape of the box. The method reproduces all known diblock copolymer phases. The application of this method to a model "frustrated" triblock copolymer leads to a phase diagram with a number of new phases. Furthermore, the capability of the method to reproduce experimentally observed structures is demonstrated using the knitting pattern of triblock copolymers. PMID:18764231

Guo, Zuojun; Zhang, Guojie; Qiu, Feng; Zhang, Hongdong; Yang, Yuliang; Shi, An-Chang

2008-07-11

96

Analysis and improvement of the watermark strategy for quantum images based on quantum Fourier transform  

NASA Astrophysics Data System (ADS)

We investigate the quantum watermark strategy for quantum images based on quantum Fourier transform proposed by Zhang et al.(Quantum Inf Process 12(2):793-803, 2013). It is aimed to embed the watermark image into the Fourier coefficients of the quantum carrier image without affecting the carrier image's visual effect. However, in our opinion the protocol is not clearly described and several steps are ambiguous. Moreover, we argue that the watermarking algorithm claimed by the authors is incorrect. At last, a possible improvement strategy is presented.

Yang, Yu-Guang; Jia, Xin; Xu, Peng; Tian, Ju

2013-08-01

97

Limitations in Imaging Common Conjunctival and Corneal Pathologies with Fourier-Domain Optical Coherence Tomography  

PubMed Central

Purpose: To describe the limitations of Fourier-domain optical coherence tomography (OCT) in imaging common conjunctival and corneal pathology. Materials and Methods: Retrospective, single-center case series of 40 patients with conjunctival and cornea pathology. Results: Fourier-domain OCT imaged laser in situ keratomileusis (LASIK) flaps in detail, including its relation to other corneal structures and abnormalities. Similarly, in infectious or degenerative corneal disorders, Fourier-domain OCT successfully showed the extent of infiltration or material deposition, which appeared as hyper-reflective areas. In cases with pterygium, the underlying cornea could not be imaged. All cases of common conjunctival pathologies, such as nevus or pinguecula, were successfully imaged in detail. Nevi, scleritis, pterygium, pinguecula, and subconjunctival hemorrhage were hyper-reflective lesions, while cysts and lymphangiectasia were hyporeflective. The details of the underlying sclera were not uniformly imaged in conjunctival pathologies. Fourier-domain OCT imaged the trabeculectomy bleb in detail, whereas the details of structures of the anterior chamber angle were not routinely visualized in all cases. Conclusions: Light scatter through vascularized, densely inflamed, or thick lesions limits the imaging capabilities of Fourier-domain anterior segment OCT. PMID:25100905

Demirci, Hakan; Steen, Daniel W.

2014-01-01

98

Experimental geometry for simultaneous beam characterization and sample imaging allowing for pink beam Fourier transform holography or coherent diffractive imaging  

SciTech Connect

One consequence of the self-amplified stimulated emission process used to generate x rays in free electron lasers (FELs) is the intrinsic shot-to-shot variance in the wavelength and temporal coherence. In order to optimize the results from diffractive imaging experiments at FEL sources, it will be advantageous to acquire a means of collecting coherence and spectral information simultaneously with the diffraction pattern from the sample we wish to study. We present a holographic mask geometry, including a grating structure, which can be used to extract both temporal and spatial coherence information alongside the sample scatter from each individual FEL shot and also allows for the real space reconstruction of the sample using either Fourier transform holography or iterative phase retrieval.

Flewett, Samuel; Eisebitt, Stefan

2011-02-20

99

A surface acoustic wave device for obtaining direct electronic Fourier transforms of images  

Microsoft Academic Search

A one-dimensional acoustic surface wave direct electronic Fourier transform (DEFT) camera was fabricated and evaluated. This device employs the elastophotoconductance mechanism (the interaction of a surface acoustic wave with a photo-conductive CdS polycrystalline film), creating electrical signals proportional to a spatial Fourier transform of the image incident on it. In this device, the surface acoustic wave is generated by a

N. T. Yang

1974-01-01

100

Polar factorization of Fourier phase operators in the coherent-state basis  

SciTech Connect

Coherent-state expectation values of Fourier-phase-operator products (of arbitrary order) are shown to exhibit polar factorization, and to be identical for the Susskind-Glogower and the Pegg-Barnett quantum phase operators. Concurrently, it follows that {ital q} deformation only directly affects the radial part (the Higgs modes) and not the phase part (the Nambu-Goldstone modes) of these expectation values. {copyright} {ital 1996 The American Physical Society.}

Kimler, W.C. IV; Nelson, C.A. [Department of Physics, State University of New York at Binghamton, Binghamton, New York 13902-6016 (United States)] [Department of Physics, State University of New York at Binghamton, Binghamton, New York 13902-6016 (United States)

1996-10-01

101

Alpha-rooting method of color image enhancement by discrete quaternion Fourier transform  

NASA Astrophysics Data System (ADS)

This paper presents a novel method for color image enhancement based on the discrete quaternion Fourier transform. We choose the quaternion Fourier transform, because it well-suited for color image processing applications, it processes all 3 color components (R,G,B) simultaneously, it capture the inherent correlation between the components, it does not generate color artifacts or blending , finally it does not need an additional color restoration process. Also we introduce a new CEME measure to evaluate the quality of the enhanced color images. Preliminary results show that the ?-rooting based on the quaternion Fourier transform enhancement method out-performs other enhancement methods such as the Fourier transform based ?-rooting algorithm and the Multi scale Retinex. On top, the new method not only provides true color fidelity for poor quality images but also averages the color components to gray value for balancing colors. It can be used to enhance edge information and sharp features in images, as well as for enhancing even low contrast images. The proposed algorithms are simple to apply and design, which makes them very practical in image enhancement.

Grigoryan, Artyom M.; Agaian, Sos S.

2014-02-01

102

Uniqueness results for the phase retrieval problem of fractional Fourier transforms of variable order  

E-print Network

In this paper, we investigate the uniqueness of the phase retrieval problem for the fractional Fourier transform (FrFT) of variable order. This problem occurs naturally in optics and quantum physics. More precisely, we show that if $u$ and $v$ are such that fractional Fourier transforms of order $\\alpha$ have same modulus $|F_\\alpha u|=|F_\\alpha v|$ for some set $\\tau$ of $\\alpha$'s, then $v$ is equal to $u$ up to a constant phase factor. The set $\\tau$ depends on some extra assumptions either on $u$ or on both $u$ and $v$. Cases considered here are $u$, $v$ of compact support, pulse trains, Hermite functions or linear combinations of translates and dilates of Gaussians. In this last case, the set $\\tau$ may even be reduced to a single point (i.e. one fractional Fourier transform may suffice for uniqueness in the problem).

Philippe Jaming

2010-09-17

103

Fourier Magnetic Imaging with Nanoscale Resolution and Compressed Sensing Speed-up using Electronic Spins in Diamond  

E-print Network

Optically-detected magnetic resonance using Nitrogen Vacancy (NV) color centres in diamond is a leading modality for nanoscale magnetic field imaging, as it provides single electron spin sensitivity, three-dimensional resolution better than 1 nm, and applicability to a wide range of physical and biological samples under ambient conditions. To date, however, NV-diamond magnetic imaging has been performed using real space techniques, which are either limited by optical diffraction to 250 nm resolution or require slow, point-by-point scanning for nanoscale resolution, e.g., using an atomic force microscope, magnetic tip, or super-resolution optical imaging. Here we introduce an alternative technique of Fourier magnetic imaging using NV-diamond. In analogy with conventional magnetic resonance imaging (MRI), we employ pulsed magnetic field gradients to phase-encode spatial information on NV electronic spins in wavenumber or k-space followed by a fast Fourier transform to yield real-space images with nanoscale resolution, wide field-of-view (FOV), and compressed sensing speed-up.

K. Arai; C. Belthangady; H. Zhang; N. Bar-Gill; S. J. DeVience; P. Cappellaro; A. Yacoby; R. L. Walsworth

2014-09-09

104

Two-Dimensional Photoacoustic Imaging by Use of FourierTransform Image Reconstruction and a Detector with an Anisotropic Response  

Microsoft Academic Search

Theoretical and experimental aspects of two-dimensional 2D biomedical photoacoustic imaging have been investigated. A 2D Fourier-transform-based reconstruction algorithm that is significantly faster and produces fewer artifacts than simple radial backprojection methods is described. The image- reconstruction time for a 208 482 pixel image is 1 s. For the practical implementation of 2D photoacoustic imaging, a rectangular detector geometry was used

Kornel P. Kostli; Paul C. Beard

2003-01-01

105

Three-dimensional retinal imaging with ultrahigh resolution Fourier\\/spectral domain optical coherence tomography  

Microsoft Academic Search

Ultrahigh resolution OCT using broadband light sources achieves improved axial image resolutions of ~2-3 um compared to standard 10 um resolution OCT used in current commercial instruments. High-speed OCT using Fourier\\/spectral domain detection enables dramatic increases in imaging speeds. 3D OCT retinal imaging is performed in human subjects using high-speed, ultrahigh resolution OCT, and the concept of an OCT fundus

Vivek J. Srinivasan; Maciej Wojtkowski; Tony Ko; Mariana Carvalho; James Fujimoto; Jay Duker; Joel Schumann; Andrzej Kowalczyk

2005-01-01

106

Fabrication and Testing of Binary-Phase Fourier Gratings for Nonuniform Array Generation  

NASA Technical Reports Server (NTRS)

This effort describes the fabrication and testing of binary-phase Fourier gratings designed to generate an incoherent array of output source points with nonuniform user-defined intensities, symmetric about the zeroth order. Like Dammann fanout gratings, these binary-phase Fourier gratings employ only two phase levels to generate a defined output array. Unlike Dammann fanout gratings, these gratings generate an array of nonuniform, user-defined intensities when projected into the far-field regime. The paper describes the process of design, fabrication, and testing for two different version of the binary-phase grating; one designed for a 12 micron wavelength, referred to as the Long-Wavelength Infrared (LWIR) grating, and one designed for a 5 micron wavelength, referred to as the Mid-Wavelength Infrared Grating (MWIR).

Keys, Andrew S.; Crow, Robert W.; Ashley, Paul R.; Nelson, Tom R., Jr.; Parker, Jack H.; Beecher, Elizabeth A.

2004-01-01

107

Improvement of quality of optical reconstruction of digital Fourier holograms displayed on phase-only SLM by its digital preprocessing  

NASA Astrophysics Data System (ADS)

Digital holography is popular tool for research and practical applications in various fields of science and technology. Most widespread method of optical reconstruction implements digital hologram display on spatial light modulators (SLM). Optical reconstruction of digital holograms is used for remote display of static and dynamic 2D and 3D scenes, in optical information processing, metrology, interferometry, microscopy, etc. Holograms recorded with digital cameras are amplitude type. Therefore quality of its optical reconstruction with phase SLM is worse compared to amplitude SLM. However application of phase SLM can provide higher diffraction efficiency. To improve quality of optical reconstruction with phase SLM, method of SLM phase modulation depth reduction at digital hologram display is proposed. To our knowledge, this method was applied only in analog holography. Also two other methods of quality improvement are considered: hologram to kinoform conversion and holograms multiplexing. Numerical experiments on modelling of digital Fourier holograms recording and their optical reconstruction by phase SLM were performed. Method of SLM phase modulation depth reduction at digital holograms display was proposed and tested. SLM phase modulation depth ranged from 0 to 2?. Quantity of hologram phase levels equal to 256 corresponds to 2? phase modulation depth. To keep SLM settings while changing phase modulation depth hologram phase distribution was renormalized instead. Dependencies of reconstruction quality on hologram phase modulation depth were obtained. Best quality is achieved at 0.27?÷0.31? phase modulation depth. To reduce speckle noise, hologram multiplexing can be applied. Modeling of multiplex holograms optical reconstruction was conducted. Speckle noise reduction was achieved. For improvement of digital hologram optical reconstruction quality and diffraction efficiency hologram to kinoform conversion can be used. Firstly numerically reconstructed image of object was obtained. Then this image was used for kinoform synthesis. Diffraction efficiency was increased by 6.4 times in comparison with hologram reconstruction.

Cheremkhin, Pavel A.; Evtikhiev, Nikolay N.; Krasnov, Vitaly V.; Porshneva, Liudmila A.; Rodin, Vladislav G.; Starikov, Sergey N.

2014-10-01

108

Terahertz holography for imaging amplitude and phase objects.  

PubMed

A non-monochromatic THz Quantum Cascade Laser and an uncooled micro-bolometer array detector with VGA resolution are used in a beam-splitter free holographic set-up to measure amplitude and phase objects in transmission. Phase maps of the diffraction pattern are retrieved using the Fourier transform carrier fringe method; while a Fresnel-Kirchhoff back propagation algorithm is used to reconstruct the complex object image. A lateral resolution of 280 µm and a relative phase sensitivity of about 0.5 rad are estimated from reconstructed images of a metallic Siemens star and a polypropylene test structure, respectively. Simulations corroborate the experimental results. PMID:24977861

Hack, Erwin; Zolliker, Peter

2014-06-30

109

Nonlinear optical Fourier filtering technique for medical image processing  

E-print Network

spatial frequen- cies corresponding to soft dense breast tissue and displaying only high spatial modulators SLM , mirrors, and a diode laser, portable systems can be fabricated for medical image processing

Rao, D.V.G.L.N.

110

Spectral multiplexing and coherent-state decomposition in Fourier ptychographic imaging.  

PubMed

Information multiplexing is important for biomedical imaging and chemical sensing. In this paper, we report a microscopy imaging technique, termed state-multiplexed Fourier ptychography (FP), for information multiplexing and coherent-state decomposition. Similar to a typical Fourier ptychographic setting, we use an array of light sources to illuminate the sample from different incident angles and acquire corresponding low-resolution images using a monochromatic camera. In the reported technique, however, multiple light sources are lit up simultaneously for information multiplexing, and the acquired images thus represent incoherent summations of the sample transmission profiles corresponding to different coherent states. We show that, by using the state-multiplexed FP recovery routine, we can decompose the incoherent mixture of the FP acquisitions to recover a high-resolution sample image. We also show that, color-multiplexed imaging can be performed by simultaneously turning on R/G/B LEDs for data acquisition. The reported technique may provide a solution for handling the partially coherent effect of light sources used in Fourier ptychographic imaging platforms. It can also be used to replace spectral filter, gratings or other optical components for spectral multiplexing and demultiplexing. With the availability of cost-effective broadband LEDs, the reported technique may open up exciting opportunities for computational multispectral imaging. PMID:24940538

Dong, Siyuan; Shiradkar, Radhika; Nanda, Pariksheet; Zheng, Guoan

2014-06-01

111

Spectral multiplexing and coherent-state decomposition in Fourier ptychographic imaging  

PubMed Central

Information multiplexing is important for biomedical imaging and chemical sensing. In this paper, we report a microscopy imaging technique, termed state-multiplexed Fourier ptychography (FP), for information multiplexing and coherent-state decomposition. Similar to a typical Fourier ptychographic setting, we use an array of light sources to illuminate the sample from different incident angles and acquire corresponding low-resolution images using a monochromatic camera. In the reported technique, however, multiple light sources are lit up simultaneously for information multiplexing, and the acquired images thus represent incoherent summations of the sample transmission profiles corresponding to different coherent states. We show that, by using the state-multiplexed FP recovery routine, we can decompose the incoherent mixture of the FP acquisitions to recover a high-resolution sample image. We also show that, color-multiplexed imaging can be performed by simultaneously turning on R/G/B LEDs for data acquisition. The reported technique may provide a solution for handling the partially coherent effect of light sources used in Fourier ptychographic imaging platforms. It can also be used to replace spectral filter, gratings or other optical components for spectral multiplexing and demultiplexing. With the availability of cost-effective broadband LEDs, the reported technique may open up exciting opportunities for computational multispectral imaging. PMID:24940538

Dong, Siyuan; Shiradkar, Radhika; Nanda, Pariksheet; Zheng, Guoan

2014-01-01

112

NONCONVEX COMPRESSIVE SENSING AND RECONSTRUCTION OF GRADIENT-SPARSE IMAGES: RANDOM VS. TOMOGRAPHIC FOURIER SAMPLING  

E-print Network

approaches, in terms of the number of samples necessary for exact recovery, algorithmic performance-valued but nonlinear function | x|. The assumption that x at least be well-approximated by an image with sparse) on the number of random Fourier samples was shown in [1] to suffice with high probability for exact recovery

Kurien, Susan

113

Full-range Fourier domain optical coherence tomography imaging probe with a magnetic-driven resonant fiber cantilever  

NASA Astrophysics Data System (ADS)

In this work, we developed a full-range Fourier domain optical coherence tomography (FD-OCT) imaging probe with a magnetic-driven resonant fiber cantilever. A galvanometer-driven reference mirror provides a linear phase modulation to each M-scan/B-scan frame to enable complex conjugate-free, full-range FD-OCT imaging. A fiber cantilever inside the probe is driven by a low-voltage miniature magnetic transducer. The fiber cantilever scans at its resonant frequency synchronized to the phase modulation induced by the reference mirror. Using a CCD line-scan camera-based spectrometer, we demonstrated real-time full-range FD-OCT at 34 frame/s (1024 pixel lateral × 2048 pixel axial).

Zhang, Kang; Huang, Yong; Kang, Jin U.

2011-11-01

114

Polarization contrast imaging of biological tissues by polarization-sensitive Fourier-domain optical coherence tomography  

Microsoft Academic Search

Jones matrix imaging of biological samples by a polarization-sensitive Fourier-domain optical coherence tomography has been demonstrated using a two-dimensional CCD camera to obtain two spectra corresponding to the orthogonal polarization components simultaneously. The measurement results of a quarter-wave plate are compared between the two incident polarization sets, H-V linear and R-L circular polarization. Jones matrix imaging of the bovine tendon

Shuichi Makita; Yoshiaki Yasuno; Takashi Endo; Masahide Itoh; Toyohiko Yatagai

2006-01-01

115

Image Stability Requirements For a Geostationary Imaging Fourier Transform Spectrometer (GIFTS)  

NASA Technical Reports Server (NTRS)

A Geostationary Imaging Fourier Transform Spectrometer (GIFTS) has been selected for the NASA New Millennium Program (NMP) Earth Observing-3 (EO-3) mission. Our paper will discuss one of the key GIFTS measurement requirements, Field of View (FOV) stability, and its impact on required system performance. The GIFTS NMP mission is designed to demonstrate new and emerging sensor and data processing technologies with the goal of making revolutionary improvements in meteorological observational capability and forecasting accuracy. The GIFTS payload is a versatile imaging FTS with programmable spectral resolution and spatial scene selection that allows radiometric accuracy and atmospheric sounding precision to be traded in near real time for area coverage. The GIFTS sensor combines high sensitivity with a massively parallel spatial data collection scheme to allow high spatial resolution measurement of the Earth's atmosphere and rapid broad area coverage. An objective of the GIFTS mission is to demonstrate the advantages of high spatial resolution (4 km ground sample distance - gsd) on temperature and water vapor retrieval by allowing sampling in broken cloud regions. This small gsd, combined with the relatively long scan time required (approximately 10 s) to collect high resolution spectra from geostationary (GEO) orbit, may require extremely good pointing control. This paper discusses the analysis of this requirement.

Bingham, G. E.; Cantwell, G.; Robinson, R. C.; Revercomb, H. E.; Smith, W. L.

2001-01-01

116

Single-channel color image encryption based on iterative fractional Fourier transform and chaos  

NASA Astrophysics Data System (ADS)

A single-channel color image encryption is proposed based on iterative fractional Fourier transform and two-coupled logistic map. Firstly, a gray scale image is constituted with three channels of the color image, and permuted by a sequence of chaotic pairs which is generated by two-coupled logistic map. Firstly, the permutation image is decomposed into three components again. Secondly, the first two components are encrypted into a single one based on iterative fractional Fourier transform. Similarly, the interim image and third component are encrypted into the final gray scale ciphertext with stationary white noise distribution, which has camouflage property to some extent. In the process of encryption and description, chaotic permutation makes the resulting image nonlinear and disorder both in spatial domain and frequency domain, and the proposed iterative fractional Fourier transform algorithm has faster convergent speed. Additionally, the encryption scheme enlarges the key space of the cryptosystem. Simulation results and security analysis verify the feasibility and effectiveness of this method.

Sui, Liansheng; Gao, Bo

2013-06-01

117

Extracting and compensating dispersion mismatch in ultrahigh-resolution Fourier domain OCT imaging of the retina.  

PubMed

We present a numerical approach to extract the dispersion mismatch in ultrahigh-resolution Fourier domain optical coherence tomography (OCT) imaging of the retina. The method draws upon an analogy with a Shack-Hartmann wavefront sensor. By exploiting mathematical similarities between the expressions for aberration in optical imaging and dispersion mismatch in spectral / Fourier domain OCT, Shack-Hartmann principles can be extended from the two-dimensional paraxial wavevector space (or the x-y plane in the spatial domain) to the one-dimensional wavenumber space (or the z-axis in the spatial domain). For OCT imaging of the retina, different retinal layers, such as the retinal nerve fiber layer (RNFL), the photoreceptor inner and outer segment junction (IS/OS), or all the retinal layers near the retinal pigment epithelium (RPE) can be used as point source beacons in the axial direction, analogous to point source beacons used in conventional two-dimensional Shack-Hartman wavefront sensors for aberration characterization. Subtleties regarding speckle phenomena in optical imaging, which affect the Shack-Hartmann wavefront sensor used in adaptive optics, also occur analogously in this application. Using this approach and carefully suppressing speckle, the dispersion mismatch in spectral / Fourier domain OCT retinal imaging can be successfully extracted numerically and used for numerical dispersion compensation to generate sharper, ultrahigh-resolution OCT images. PMID:23187353

Choi, WooJhon; Baumann, Bernhard; Swanson, Eric A; Fujimoto, James G

2012-11-01

118

Extracting and compensating dispersion mismatch in ultrahigh-resolution Fourier domain OCT imaging of the retina  

PubMed Central

We present a numerical approach to extract the dispersion mismatch in ultrahigh-resolution Fourier domain optical coherence tomography (OCT) imaging of the retina. The method draws upon an analogy with a Shack-Hartmann wavefront sensor. By exploiting mathematical similarities between the expressions for aberration in optical imaging and dispersion mismatch in spectral / Fourier domain OCT, Shack-Hartmann principles can be extended from the two-dimensional paraxial wavevector space (or the x-y plane in the spatial domain) to the one-dimensional wavenumber space (or the z-axis in the spatial domain). For OCT imaging of the retina, different retinal layers, such as the retinal nerve fiber layer (RNFL), the photoreceptor inner and outer segment junction (IS/OS), or all the retinal layers near the retinal pigment epithelium (RPE) can be used as point source beacons in the axial direction, analogous to point source beacons used in conventional two-dimensional Shack-Hartman wavefront sensors for aberration characterization. Subtleties regarding speckle phenomena in optical imaging, which affect the Shack-Hartmann wavefront sensor used in adaptive optics, also occur analogously in this application. Using this approach and carefully suppressing speckle, the dispersion mismatch in spectral / Fourier domain OCT retinal imaging can be successfully extracted numerically and used for numerical dispersion compensation to generate sharper, ultrahigh-resolution OCT images. PMID:23187353

Choi, WooJhon; Baumann, Bernhard; Swanson, Eric A.; Fujimoto, James G.

2012-01-01

119

Phase-image-based content-addressable holographic data storage  

NASA Astrophysics Data System (ADS)

We propose and demonstrate the use of phase images for content-addressable holographic data storage. Use of binary phase-based data pages with 0 and ? phase changes, produces uniform spectral distribution at the Fourier plane. The absence of strong DC component at the Fourier plane and more intensity of higher order spatial frequencies facilitate better recording of higher spatial frequencies, and improves the discrimination capability of the content-addressable memory. This improves the results of the associative recall in a holographic memory system, and can give low number of false hits even for small search arguments. The phase-modulated pixels also provide an opportunity of subtraction among data pixels leading to better discrimination between similar data pages.

John, Renu; Joseph, Joby; Singh, Kehar

2004-03-01

120

Fourier-domain beamforming: the path to compressed ultrasound imaging.  

PubMed

Sonography techniques use multiple transducer elements for tissue visualization. Signals received at each element are sampled before digital beamforming. The sampling rates required to perform high-resolution digital beamforming are significantly higher than the Nyquist rate of the signal and result in considerable amount of data that must be stored and processed. A recently developed technique, compressed beamforming, based on the finite rate of innovation model, compressed sensing (CS), and Xampling ideas, allows a reduction in the number of samples needed to reconstruct an image comprised of strong reflectors. A drawback of this method is its inability to treat speckle, which is of significant importance in medical imaging. Here, we build on previous work and extend it to a general concept of beamforming in frequency. This allows exploitation of the low bandwidth of the ultrasound signal and bypassing of the oversampling dictated by digital implementation of beamforming in time. By using beamforming in frequency, the same image quality is obtained from far fewer samples. We next present a CS technique that allows for further rate reduction, using only a portion of the beamformed signal's bandwidth. We demonstrate our methods on in vivo cardiac data and show that reductions up to 1/28 of the standard beamforming rates are possible. Finally, we present an implementation on an ultrasound machine using sub-Nyquist sampling and processing. Our results prove that the concept of sub-Nyquist processing is feasible for medical ultrasound, leading to the potential of considerable reduction in future ultrasound machines' size, power consumption, and cost. PMID:25073133

Chernyakova, Tanya; Eldar, Yonina

2014-08-01

121

Evaluation of shape variability of stallion sperm heads by means of image analysis and Fourier descriptors.  

PubMed

This study quantified and evaluated the variability of sperm head shape for 10 different stallions. Sperm head shape characteristics including sperm head length to width ratio, position of the center of gravity, curvature, and degree of roundness were assessed and analysed from images using elliptic Fourier descriptors and inverse Fourier transformation. The first four principal components accounted for 88.46-92.33% of the total variance and provided a good summary of the overall data. In the case of the ejaculate with defective sperm heads the components accounted for 97.35-98.21% of variation. The study was able to quantitatively confirm that head length to width ratio, which contributed 48.63-53.48% and 71.30-73.34% to the total variance for normal and defective sperm, respectively, was the predominant determining parameter of sperm head shape. There were no statistical significant relationships between Fourier descriptors and values of sperm concentration and/or motility. PMID:20047805

Severa, L; Máchal, L; Svábová, L; Mamica, O

2010-05-01

122

Instrumental phase-based method for Fourier transform spectrometer measurements processing.  

PubMed

Phase correction is a critical procedure for most space-borne Fourier transform spectrometers (FTSs) whose accuracy (owing to often poor signal-to-noise ratio, SNR) can be jeopardized from many uncontrollable environmental conditions. This work considers the phase correction in an FTS working under significant temperature change during the measurement and affected by mechanical disturbances. The implemented method is based on the identification of an instrumental phase that is dependent on the interferometer temperature and on the extraction of a linear phase component through a least-squares approach. The use of an instrumental phase parameterized with the interferometer temperature eases the determination of the linear phase that can be extracted using only a narrow spectral region selected to be immune from disturbances. The procedure, in this way, is made robust against phase errors arising from instrumental effects, a key feature to reduce the disturbances through spectra averaging. The method was specifically developed for the Mars IR Mapper spectrometer, that was designed for operation onboard a rover on the Mars surface; the validation was performed using ground and in-flight measurements of the Fourier transform IR spectrometer planetary Fourier spectrometer, onboard the MarsExpress mission. The symmetrization has been exploited also for the spectra calibration, highlighting the issues deriving from the cases of relevant beamsplitter emission. The applicability of this procedure to other instruments is conditional to the presence in the spectra of at least one spectral region with a large SNR along with a negligible (or known) beamsplitter emission. For the PFS instrument, the processing of data with relevant beamsplitter emission has been performed exploiting the absorption carbon dioxide bands present in Martian spectra. PMID:21509063

Saggin, Bortolino; Scaccabarozzi, Diego; Tarabini, Marco

2011-04-20

123

Characterizing and tracking individual colloidal particles using Fourier-Bessel image decomposition.  

PubMed

We use Fourier-Bessel Image Decomposition (FBID) of microscopy images to investigate the size, refractive index and 3-dimensional position of individual colloidal microspheres. With measurements of monodisperse polystyrene and poly(methyl methacrylate) particles we achieve a resolution of 1% in size and 0.2% in refractive index for a single image which is sufficient for accurate in situ characterization of polydisperse colloids. Also the binding of avidin molecules to individual biotinylated polystyrene particles is resolved. Finally, the FBID method offers a straightforward approach to 3-dimensional out-of-focus tracking. Here, the z-position of a freely diffusing particle is calculated by applying the statistics of Brownian motion to its set of Fourier-Bessel coefficients. PMID:25322038

Strubbe, Filip; Vandewiele, Stijn; Schreuer, Caspar; Beunis, Filip; Drobchak, Oksana; Brans, Toon; Neyts, Kristiaan

2014-10-01

124

Quantitative ultrasonic phased array imaging  

NASA Astrophysics Data System (ADS)

When imaging with ultrasonic phased arrays, what do we actually image? What quantitative information is contained in the image? Ad-hoc delay-and-sum methods such as the synthetic aperture focusing technique (SAFT) and the total focusing method (TFM) fail to answer these questions. We have shown that a new quantitative approach allows the formation of flaw images by explicitly inverting the Thompson-Gray measurement model. To examine the above questions, we have set up a software simulation test bed that considers a 2-D scalar scattering problem of a cylindrical inclusion with the method of separation of variables. It is shown that in SAFT types of imaging the only part of the flaw properly imaged is the front surface specular response of the flaw. Other responses (back surface reflections, creeping waves, etc.) are improperly imaged and form artifacts in the image. In the case of TFM-like imaging the quantity being properly imaged is an angular integration of the front surface reflectivity. The other, improperly imaged responses are also averaged, leading to a reduction in some of the artifacts present. Our results have strong implications for flaw sizing and flaw characterization with delay-and-sum images.

Engle, Brady J.; Schmerr, Lester W., Jr.; Sedov, Alexander

2014-02-01

125

Digital watermarking algorithm research of color images based on quaternion Fourier transform  

NASA Astrophysics Data System (ADS)

A watermarking algorithm of color images based on the quaternion Fourier Transform (QFFT) and improved quantization index algorithm (QIM) is proposed in this paper. The original image is transformed by QFFT, the watermark image is processed by compression and quantization coding, and then the processed watermark image is embedded into the components of the transformed original image. It achieves embedding and blind extraction of the watermark image. The experimental results show that the watermarking algorithm based on the improved QIM algorithm with distortion compensation achieves a good tradeoff between invisibility and robustness, and better robustness for the attacks of Gaussian noises, salt and pepper noises, JPEG compression, cropping, filtering and image enhancement than the traditional QIM algorithm.

An, Mali; Wang, Weijiang; Zhao, Zhen

2013-10-01

126

Phase shifts in the Fourier spectra of phase gratings and phase grids: an application for one-shot phase-shifting interferometry.  

PubMed

Among several techniques, phase shifting interferometry can be implemented with a grating used as a beam divider to attain several interference patterns around each diffraction order. Because each pattern has to show a different phase-shift, a suitable shifting technique must be employed. Phase gratings are attractive to perform the former task due to their higher diffraction efficiencies. But as is very well known, the Fourier coefficients of only-phase gratings are integer order Bessel functions of the first kind. The values of these real-valued functions oscillate around zero, so they can adopt negative values, thereby introducing phase shifts of pi at certain diffraction orders. Because this almost trivial fact seems to have been overlooked in the literature regarding its practical implications, in this communication such phase shifts are stressed in the description of interference patterns obtained with grating interferometers. These patterns are obtained by placing two windows in the object plane of a 4f system with a sinusoidal grating/grid in the Fourier plane. It is shown that the corresponding experimental observations of the fringe modulation, as well as the corresponding phase measurements, are all in agreement with the proposed description. A one-shot phase shifting interferometer is finally proposed taking into account these properties after proper incorporation of modulation of polarization. PMID:19582027

Toto-Arellano, Noel-Ivan; Rodriguez-Zurita, Gustavo; Meneses-Fabian, Cruz; Vazquez-Castillo, Jose F

2008-11-10

127

Definition and application of a fourier domain texture measure: applications to histological image segmentation.  

PubMed

A texture measure is defined for the purpose of two-dimensional histological image classification, based upon a novel exploitation of the modulus of the Fourier transform. Its implementation in the form of an algorithm is presented and discussed, and employed to classify a set of histological images. The results, which were obtained by the analysis and classification of different mammalian tissue types, compare favourably with established texture recognition techniques. Furthermore, the results suggest that the method has a comparable performance to other techniques at reduced storage and time costs for images of a high grey level resolution. PMID:8665799

Gibson, D; Gaydecki, P A

1995-11-01

128

Accurate determination of the diffusion coefficient of proteins by fourier analysis with whole column imaging detection.  

PubMed

Analysis in the frequency domain is considered a powerful tool to elicit precise information from spectroscopic signals. In this study, the Fourier transformation technique is employed to determine the diffusion coefficient (D) of a number of proteins in the frequency domain. Analytical approaches are investigated for determination of D from both experimental and data treatment viewpoints. The diffusion process is modeled to calculate diffusion coefficients based on the Fourier transformation solution to Fick's law equation, and its results are compared to time domain results. The simulations characterize optimum spatial and temporal conditions and demonstrate the noise tolerance of the method. The proposed model is validated by its application for the electropherograms from the diffusion path of a set of proteins. Real-time dynamic scanning is conducted to monitor dispersion by employing whole column imaging detection technology in combination with capillary isoelectric focusing (CIEF) and the imaging plug flow (iPF) experiment. These experimental techniques provide different peak shapes, which are utilized to demonstrate the Fourier transformation ability in extracting diffusion coefficients out of irregular shape signals. Experimental results confirmed that the Fourier transformation procedure substantially enhanced the accuracy of the determined values compared to those obtained in the time domain. PMID:25607375

Zarabadi, Atefeh S; Pawliszyn, Janusz

2015-02-17

129

Mid-infrared imaging Fourier transform spectrometry for high power fiber laser irradiated fiberglass composites  

NASA Astrophysics Data System (ADS)

New measurement techniques to study continuous wave (CW) laser-material interactions are emerging with the ability to monitor the evolving, spatial distribution of the state of the surface-gas boundary layer. A qualitative analysis of gas phase combustion plumes above the surface of laser irradiated fiberglass composites is developed from fast framing hyperspectral imagery observations. An imaging Fourier Transform Spectrometer (IFTS) operating in the mid-infrared (MWIR) with high framing rate has recently been developed at the Air Force Institute of Technology (AFIT) in collaboration with Telops Inc. A 320 x 256 indium antimonide (InSb) focal plane array with spectral response from 1.5 - 5.5 ?m is mated with a Michelson interferometer to achieve spectral resolutions as high as 0.25 cm-1. The very fast 16- tap InSb array frames at 1.9 kHz for the full 320 x 256 frame size. The single pixel field of view of 0.3 mrad provides a spatial resolution of 1 mm at the minimum focal distance of 3 m. Painted and unpainted fiberglass composites are irradiated with a 1064 nm CW Nd:YAG laser for 60 s at 100 W in air at atmospheric pressure. Selective emission in the region of 2100 - 3200 cm-1 is readily evident and is used to develop a time-dependent spatial map of both temperature and plume constituents. The time evolution of gas phase combustion products such as CO and CO2 molecules are monitored, with a spectral resolution of 2 cm-1. High-speed imagery is obtained using a low-pass filter for the interferograms, illustrating significant turbulent behavior during laser irradiation. Spatial brightness temperature maps exceed 600 K. Spatial variation in the ratio of [CO2]/[CO] indicates an interplay between heterogeneous and homogeneous kinetics.

Acosta, R. I.; Gross, K. C.; Perram, G. P.

2012-03-01

130

Identification of Earthquake Induced Damage Areas Using Fourier Transform and SPOT HRVIR Pan Images  

PubMed Central

A devastating earthquake with a magnitude of Mw 7.4 occurred on the North Anatolian Fault Zone (NAFZ) of Turkey on August 17, 1999 at 00:01:39 UTC (3:01 a.m. local time). The aim of this study is to propose a new approach to automatically identify earthquake induced damage areas which can provide valuable information to support emergency response and recovery assessment procedures. This research was conducted in the Adapazari inner city, covering a 3 × 3 km area, where 11,373 buildings collapsed as a result of the earthquake. SPOT high resolution visible infrared (HRVIR) Pan images obtained before (25 June 1999) and after (4 October 1999) the earthquake were used in the study. Five steps were employed to conduct the research and these are: (i) geometric and radiometric correction of satellite images, (ii) Fast Fourier Transform (FFT) of pre- and post-earthquake images and filtering the images in frequency domain, (iii) generating difference image using Inverse Fast Fourier Transform (IFFT) pre- and post- earthquake images, (iv) application of level slicing to difference image to identify the earthquake-induced damages, (v) accuracy assessment of the method using ground truth obtained from a 1/5,000 scale damage map. The total accuracy obtained in the research is 80.19 %, illustrating that the proposed method can be successfully used to automatically identify earthquake-induced damage areas. PMID:22573966

Sertel, Elif

2009-01-01

131

Identification of Earthquake Induced Damage Areas Using Fourier Transform and SPOT HRVIR Pan Images.  

PubMed

A devastating earthquake with a magnitude of Mw 7.4 occurred on the North Anatolian Fault Zone (NAFZ) of Turkey on August 17, 1999 at 00:01:39 UTC (3:01 a.m. local time). The aim of this study is to propose a new approach to automatically identify earthquake induced damage areas which can provide valuable information to support emergency response and recovery assessment procedures. This research was conducted in the Adapazari inner city, covering a 3 × 3 km area, where 11,373 buildings collapsed as a result of the earthquake. SPOT high resolution visible infrared (HRVIR) Pan images obtained before (25 June 1999) and after (4 October 1999) the earthquake were used in the study. Five steps were employed to conduct the research and these are: (i) geometric and radiometric correction of satellite images, (ii) Fast Fourier Transform (FFT) of pre- and post-earthquake images and filtering the images in frequency domain, (iii) generating difference image using Inverse Fast Fourier Transform (IFFT) pre- and post- earthquake images, (iv) application of level slicing to difference image to identify the earthquake-induced damages, (v) accuracy assessment of the method using ground truth obtained from a 1/5,000 scale damage map. The total accuracy obtained in the research is 80.19 %, illustrating that the proposed method can be successfully used to automatically identify earthquake-induced damage areas. PMID:22573966

Sertel, Elif

2009-01-01

132

Determination of the unit size of the corneal endothelial cell mosaic from Fourier component image analysis.  

PubMed

Scanning electron micrographs were taken of the central region of the corneal endothelium of cows (Holstein). The cells were outlined and an image overlay generated of approximately 100 cells. Via a Windows-based scanning system, the overlay was subjected to a two-dimensional Fourier transform on a Unix-based system. A custom algorithm was developed (IRIS) to sequentially analyse the Fourier transform pattern. The transform and resultant harmonics spectrum were compared to those obtained from artificial cell mosaics generated from uniform sized symmetrical hexagons. The position, width, and height of the 1st harmonic component of the frequency distribution appears to be derived from average cell-cell border distances across the image. The radial position of the 1st harmonic is inversely related to the unit cell size in the mosaic, i.e. the dominant cell size. The application of such techniques to cell mosaic analyses is discussed. PMID:9149445

Doughty, M J; Spiteri, M; Dilts, D M

1997-04-01

133

Approximate Fourier phase information in the phase retrieval problem: what it gives and how to use it.  

PubMed

This work evaluates the importance of approximate Fourier phase information in the phase retrieval problem. The main discovery is that a rough phase estimate (up to ?/2 rad) allows development of very efficient algorithms whose reconstruction time is an order of magnitude faster than that of the current method of choice--the hybrid input-output (HIO) algorithm. Moreover, a heuristic explanation is provided of why continuous optimization methods like gradient descent or Newton-type algorithms fail when applied to the phase retrieval problem and how the approximate phase information can remedy this situation. Numerical simulations are presented to demonstrate the validity of our analysis and success of our reconstruction method even in cases where the HIO algorithm fails, namely, complex-valued signals without tight support information. PMID:21979518

Osherovich, Eliyahu; Zibulevsky, Michael; Yavneh, Irad

2011-10-01

134

PHASE CORRELATION METHOD FOR THE ALIGNMENT OF TOTAL SOLAR ECLIPSE IMAGES  

SciTech Connect

A modified phase correlation method, based on Fourier transform, which enables the alignment of solar coronal images taken during the total solar eclipses, is presented. The method enables the measurement of translation, rotation, and scaling factor between two images. With the application of this technique, pairs of images with different exposure times, different brightness scale, such as linear for CCD and nonlinear for images taken with photographic film, and even images from different emission lines can be aligned with sub-pixel precision.

Druckmueller, M., E-mail: druckmuller@fme.vutbr.c [Institute of Mathematics, Faculty of Mechanical Engineering, Brno University of Technology, 616 69 Brno (Czech Republic)

2009-12-01

135

Mapping agroecological zones and time lag in vegetation growth by means of Fourier analysis of time series of NDVI images  

NASA Technical Reports Server (NTRS)

Examples are presented of applications of a fast Fourier transform algorithm to analyze time series of images of Normalized Difference Vegetation Index values. The results obtained for a case study on Zambia indicated that differences in vegetation development among map units of an existing agroclimatic map were not significant, while reliable differences were observed among the map units obtained using the Fourier analysis.

Menenti, M.; Azzali, S.; Verhoef, W.; Van Swol, R.

1993-01-01

136

X-ray Phase Imaging Microscopy with Two-Dimensional Knife-Edge Filters  

NASA Astrophysics Data System (ADS)

A novel scheme of X-ray differential phase imaging was implemented with an array source and a two-dimensional Foucault knife-edge (2DFK). A pinhole array lens was employed to manipulate the X-ray beam on the Fourier space. An emerging biaxial scanning procedure was also demonstrated with the periodic 2DFK. The differential phase images (DPIs) of the midrib in a leaf of a rose bush were visualized to verify the phase imaging of biological specimens by the proposed method. It also has features of depicting multiple-stack phase images, and rendering morphological DPIs, because it acquires pure phase information.

Choi, Jaeho; Park, Yong-Sung

2012-04-01

137

Depth resolved hyperspectral imaging spectrometer based on structured light illumination and Fourier transform interferometry  

PubMed Central

A depth resolved hyperspectral imaging spectrometer can provide depth resolved imaging both in the spatial and the spectral domain. Images acquired through a standard imaging Fourier transform spectrometer do not have the depth-resolution. By post processing the spectral cubes (x, y, ?) obtained through a Sagnac interferometer under uniform illumination and structured illumination, spectrally resolved images with depth resolution can be recovered using structured light illumination algorithms such as the HiLo method. The proposed scheme is validated with in vitro specimens including fluorescent solution and fluorescent beads with known spectra. The system is further demonstrated in quantifying spectra from 3D resolved features in biological specimens. The system has demonstrated depth resolution of 1.8 ?m and spectral resolution of 7 nm respectively. PMID:25360367

Choi, Heejin; Wadduwage, Dushan; Matsudaira, Paul T.; So, Peter T.C.

2014-01-01

138

Perfusion and ventilation filters for Fourier-decomposition MR lung imaging.  

PubMed

MR imaging without the use of contrast agents has recently been used for creating perfusion and ventilation functional lung images. The technique incorporates frequency- or wavelet-domain filters to separate the MR signal components. This paper presents a new, subject-adaptive algorithm for perfusion and ventilation filters design. The proposed algorithm uses a lung signal model for separation of the signal components in the frequency domain. Non-stationary lung signals are handled by a short time Fourier transform. This method was applied to sets of 192 and 90 co-registered non-contrast MR lung images measured for five healthy subjects at the rate of 3,33 images per second, using different slice thicknesses. In each case, the resulted perfusion and ventilation images showed a smaller amount of mutual information, when compared to those obtained using the known lowpass/highpass filter approach. PMID:25466452

Wujcicki, Artur; Corteville, Dominique; Materka, Andrzej; Schad, Lothar R

2014-11-20

139

Investigation of a phase-only correlation technique for anatomical alignment of portal images in radiation therapy  

Microsoft Academic Search

A new image registration algorithm based on phase-only correlation is applied to portal images in radiation therapy to detect translational shift. The phase-only correlation shows a sharp peak in the correlation distribution as compared to the broad peak computed from conventional correlation using fast Fourier transform. In this paper, the algorithm of phase- only correlation is described and its applicability

J. Wang; L. E. Reinstein; J. Hanley; A. G. Meek

1996-01-01

140

Acceleration of integral imaging based incoherent Fourier hologram capture using graphic processing unit.  

PubMed

Speed enhancement of integral imaging based incoherent Fourier hologram capture using a graphic processing unit is reported. Integral imaging based method enables exact hologram capture of real-existing three-dimensional objects under regular incoherent illumination. In our implementation, we apply parallel computation scheme using the graphic processing unit, accelerating the processing speed. Using enhanced speed of hologram capture, we also implement a pseudo real-time hologram capture and optical reconstruction system. The overall operation speed is measured to be 1 frame per second. PMID:23188339

Jeong, Kyeong-Min; Kim, Hee-Seung; Hong, Sung-In; Lee, Sung-Keun; Jo, Na-Young; Kim, Yong-Soo; Lim, Hong-Gi; Park, Jae-Hyeung

2012-10-01

141

Multicomponent FM demodulation of speech based on the short-time Fourier transform (STFT) phase  

NASA Astrophysics Data System (ADS)

Speech is a signal which is produced as a combination of frication and a quasi periodic train of glottal pulses excites the vocal tract and causes it to resonate. Information is encoded on the signal as the vocal tract changes configuration, resulting in a rapid change of the resonant frequencies. We develop methods, based on differentiation of the short time Fourier transform (STFT) phase, which effectively demodulates the speech signal and produces accurate, high resolution time-frequency estimates of both the resonances and the signal excitation. The method effectively condenses the STFT surface along curves representing the instantaneous frequencies of the vocal tract resonances and the channel group delay function.

Nelson, Douglas J.

2001-03-01

142

MightySat II.1 Fourier-transform hyperspectral imager payload performance  

NASA Astrophysics Data System (ADS)

Using a new microsat called MightySat II as a platform, Kestrel Corporation is designing and building the first Fourier transform hyperspectral imager (FTHSI) to be operated from a spacecraft. This payload will also be the first to fly on the Phillips Laboratory MightySat II spacecraft series, a new, innovative approach, to affordable space testing of high risk, high payoff technologies. Performance enhancements offered by the Fourier transform approach have shown it to be one of the more promising spaceborne hyperspectral concepts. Simulations of the payload's performance have shown that the instrument is capable of separating a wide range of subtle spectral differences. Variations in the return from the Georges Bank and shoals are discernible and various types of coastal grasses (sea oats and spartina) can be isolated against a sand background.

Otten, Leonard J.; Sellar, R. Glenn; Rafert, J. Bruce

1995-12-01

143

Multi-wavelength phase imaging interference microscopy  

Microsoft Academic Search

Multi-wavelength phase imaging interferography is a technique that combines phase-shifting interferometry with multi-wavelength phase unwrapping. It can be used to obtain phase profile of an object without 2pi ambiguities inherent to single wavelength phase images. In this technique, a Michelson-type interferometer is illuminated by an LED and the reference mirror is dithered for obtaining interference images at four phase quadratures,

Nilanthi Warnasooriya; Myung K. Kim

2006-01-01

144

The New Physical Optics Notebook: Tutorials in Fourier Optics.  

ERIC Educational Resources Information Center

This is a textbook of Fourier optics for the classroom or self-study. Major topics included in the 38 chapters are: Huygens' principle and Fourier transforms; image formation; optical coherence theory; coherent imaging; image analysis; coherent noise; interferometry; holography; communication theory techniques; analog optical computing; phase

Reynolds, George O.; And Others

145

Higher-dimensional phase imaging  

Microsoft Academic Search

Traditional full-field interferometric techniques (speckle, moiré, holography etc) provide 2-D phase images, which encode the surface deformation state of the object under test. Over the past 15 years, the use of additional spatial or temporal dimensions has been investigated by a number of research groups. Early examples include the measurement of 3-D surface profiles by temporally-varying projected fringe patterns, and

Jonathan M. Huntley

2010-01-01

146

Higher-dimensional phase imaging  

Microsoft Academic Search

Traditional full-field interferometric techniques (speckle, moire´, holography etc) provide 2-D phase images, which encode the surface deformation state of the object under test. Over the past 15 years, the use of additional spatial or temporal dimensions has been investigated by a number of research groups. Early examples include the measurement of 3-D surface profiles by temporally-varying projected fringe patterns, and

Jonathan M. Huntley

2010-01-01

147

Higher-dimensional phase imaging  

NASA Astrophysics Data System (ADS)

Traditional full-field interferometric techniques (speckle, moiré, holography etc) provide 2-D phase images, which encode the surface deformation state of the object under test. Over the past 15 years, the use of additional spatial or temporal dimensions has been investigated by a number of research groups. Early examples include the measurement of 3-D surface profiles by temporally-varying projected fringe patterns, and dynamic speckle interferometry. More recently (the past 5 years) a family of related techniques (Wavelength Scanning Interferometry, Phase Contrast Spectral Optical Coherence Tomography (OCT), and Tilt Scanning Interferometry) has emerged that provides the volume deformation state of the object. The techniques can be thought of as a marriage between the phase sensing capabilities of Phase Shifting Interferometry and the depth-sensing capabilities of OCT. Finally, in the past 12 months a technique called Hyperspectral Interferometry has been proposed in which absolute optical path distributions are obtained in a single shot through the spectral decomposition of a white light interferogram, and for which the additional dimension therefore corresponds to the illumination wavenumber. An overview of these developments, and the related issue of robust phase unwrapping of noisy 3-D wrapped phase volumes, is presented in this paper.

Huntley, Jonathan M.

2010-04-01

148

An image reconstruction method from Fourier data with uncertainties on the spatial frequencies  

NASA Astrophysics Data System (ADS)

In this paper the reconstruction of a two-dimensional image from a nonuniform sampling of its Fourier transform is considered, in the presence of uncertainties on the frequencies corresponding to the measured data. The problem therefore becomes a blind deconvolution, in which the unknowns are both the image to be reconstructed and the exact frequencies. The availability of information on the image and the frequencies allows to reformulate the problem as a constrained minimization of the least squares functional. A regularized solution of this optimization problem is achieved by early stopping an alternating minimization scheme. In particular, a gradient projection method is employed at each step to compute an inexact solution of the minimization subproblems. The resulting algorithm is applied on some numerical examples arising in a real-world astronomical application.

Cornelio, Anastasia; Bonettini, Silvia; Prato, Marco

2013-10-01

149

Breast cancer detection from MR images through an auto-probing discrete Fourier transform system.  

PubMed

A computer-aided detection auto-probing (CADAP) system is presented for detecting breast lesions using dynamic contrast enhanced magnetic resonance imaging, through a spatial-based discrete Fourier transform. The stand-alone CADAP system reduces noise, refines region of interest (ROI) automatically, and detects the breast lesion with minimal false positive detection. The lesions are then classified and colourised according to their characteristics, whether benign, suspicious or malignant. To enhance the visualisation, the entire analysed ROI is constructed into a 3-D image, so that the user can diagnose based on multiple views on the ROI. The proposed method has been applied to 101 sets of digital images, and the results compared with the biopsy results done by radiologists. The proposed scheme is able to identify breast cancer regions accurately and efficiently. PMID:24736203

Sim, K S; Chia, F K; Nia, M E; Tso, C P; Chong, A K; Abbas, Siti Fathimah; Chong, S S

2014-06-01

150

Analysis of stacking faults in gallium nitride by Fourier transform of high-resolution images  

NASA Astrophysics Data System (ADS)

We present results of studying stacking faults (SFs) in gallium nitride (GaN) with the aid of Fourier transform of high-resolution transmission electron microscopy (HRTEM) images. Using this method, it is possible both to determine the SF type and to directly measure the corresponding displacement vector. This allowed us to explain the peculiarities of the contrast of HRTEM of structures with high SF density (above 106 cm-1). It is established that the displacement vector component in the (0001) plane in these structures can significantly differ from the expected value of that is typical of single SFs.

Kirilenko, D. A.; Sitnikova, A. A.; Kremleva, A. V.; Mynbaeva, M. G.; Nikolaev, V. I.

2014-12-01

151

Utilization of a liquid crystal spatial light modulator in a gray scale detour phase method for Fourier holograms.  

PubMed

This paper introduces a new modification for the well-known binary detour phase method, which is largely used to represent Fourier holograms; the modification utilizes gray scale level control provided by a liquid crystal spatial light modulator to improve the traditional binary detour phase. Results are shown by both simulation and experiment. PMID:23142903

Makey, Ghaith; El-Daher, Moustafa Sayem; Al-Shufi, Kanj

2012-11-10

152

Functional imaging of hemodynamic stimulus response in the rat retina with ultrahigh-speed spectral / Fourier domain OCT  

NASA Astrophysics Data System (ADS)

Measuring retinal hemodynamics in response to flicker stimulus is important for investigating pathophysiology in small animal models of diabetic retinopathy, because a reduction in the hyperemic response is thought to be one of the earliest changes in diabetic retinopathy. In this study, we investigated functional imaging of retinal hemodynamics in response to flicker stimulus in the rat retina using an ultrahigh speed spectral / Fourier domain OCT system at 840nm with an axial scan rate of 244kHz. At 244kHz the nominal axial velocity range that could be measured without phase wrapping was +/-37.7mm/s. Pulsatile total retinal arterial blood flow as a function of time was measured using an en face Doppler approach where a 200?m × 200?m area centered at the central retinal artery was repeatedly raster scanned at a volume acquisition rate of 55Hz. Three-dimensional capillary imaging was performed using speckle decorrelation which has minimal angle dependency compared to other angiography techniques based on OCT phase information. During OCT imaging, a flicker stimulus could be applied to the retina synchronously by inserting a dichroic mirror in the imaging interface. An acute transient increase in total retinal blood flow could be detected. At the capillary level, an increase in the degree of speckle decorrelation in capillary OCT angiography images could also be observed, which indicates an increase in the velocity of blood at the capillary level. This method promises to be useful for the investigation of small animal models of ocular diseases.

Choi, WooJhon; Baumann, Bernhard; Clermont, Allen C.; Feener, Edward P.; Boas, David A.; Fujimoto, James G.

2013-03-01

153

Fourier Monte Carlo simulation of crystalline membranes in the flat phase  

NASA Astrophysics Data System (ADS)

Stimulated by the recent interest in graphene, the elastic behavior of crystalline membranes continues to be under debate. In their flat phase, one observes scaling of the correlation functions of in-plane and out-of-plane deformations u(x) and f(x) at long wavelengths with respect to a given reference plane governed by a single universal exponent ?. The purpose of the present article is to explain the ideas and techniques underlying our Fourier Monte Carlo simulation approach to the numerical determination of ? in much greater detail than was possible in a recent letter that is currently under review. Our simulations are based on an effective Hamiltonian first derived by Nelson and Peliti formulated exclusively in terms of the Fourier amplitudes tilde f(q) of the field f(x), and we calculate the out-of-plane correlation function langle|tilde f(q)|2rangle = tilde G(q) and their related mean squared displacement langle(?f)2rangle. The key to the progress reported in this work is the observation that on tuning the Monte Carlo acceptance rates separately for each wave vector, we are able to eliminate critical slowing down and thus achieve unprecedented statistical accuracy. A finite size scaling analysis for langle(?f)2rangle gives ? = 0.795(10). In the alternative approach, where we study the scaling of tilde G(q), we observe an unexpected anisotropic finite size effect at small wave vectors which hampers a similarly accurate numerical analysis.

Tröster, Andreas

2013-08-01

154

Fourier transform infared spectroscopic imaging for the identification of concealed drug residue particles and fingerprints  

NASA Astrophysics Data System (ADS)

Conventional FTIR spectroscopy and microscopy has been widely used in forensic science. New opportunities exist to obtain rapid chemical images and to enhance the sensitivity of detection of trace materials using attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy coupled with a focal-plane array (FPA) detector. In this work, the sensitivity of ATR-FTIR spectroscopic imaging using three different kinds of ATR crystals (Ge coupled with an infrared microscope, ZnSe and diamond) and resulting in three different optical arrangements for the detection of model drug particles is discussed. Model systems of ibuprofen and paracetamol particles having a size below 32 micrometers have been prepared by sieving. The sensitivity level in the three different approaches has been compared and it has been found that both micro and macro-ATR imaging methods have proven to be a promising techniques for the identification of concealed drug particles. To demonstrate the power and applicability of FTIR chemical imaging to forensic research, various examples are discussed. This includes investigation of the changes of chemical nature of latent fingerprint residue under controlled conditions of humidity and temperature studied by ATR-FTIR imaging. This study demonstrates the potential of spectroscopic imaging for visualizing the chemical changes of fingerprints.

Ricci, Camilla; Chan, K. L. Andrew; Kazarian, Sergei G.

2006-09-01

155

Slit Function Measurement of An Imaging Spectrograph Using Fourier Transform Techniques  

NASA Technical Reports Server (NTRS)

Knowledge of a spectrograph slit function is necessary to interpret the unresolved lines in an observed spectrum. A theoretical slit function can be calculated from the sizes of the entrance slit, the detector aperture when it functions as an exit slit, the dispersion characteristic of the disperser, and the point spread function of the spectrograph. A measured slit function is preferred to the theoretical one for the correct interpretation of the spectral data. In a scanning spectrometer with a single exit slit, the slit function is easily measured. In a fixed grating/or disperser spectrograph, illuminating the entrance slit with a near monochromatic light from a pre-monochrmator or a tunable laser and varying the wavelength of the incident light can measure the slit function. Even though the latter technique had been used successfully for the slit function measurements, it had been very laborious and it would be prohibitive to an imaging spectrograph or a multi-object spectrograph that has a large field of view. We explore an alternative technique that is manageable for the measurements. In the proposed technique, the imaging spectrograph is used as a detector of a Fourier transform spectrometer. This method can be applied not only to an IR spectrograph but also has a potential to a visible/UV spectrograph including a wedge filter spectrograph. This technique will require a blackbody source of known temperature and a bolometer to characterize the interferometer part of the Fourier Transform spectrometer. This pa?er will describe the alternative slit function measurement technique using a Fourier transform spectrometer.

Park, Hongwoo; Swimyard, Bruce; Jakobsen, Peter; Moseley, Harvey; Greenhouse, Matthew

2004-01-01

156

Extended Field of View Soft X-Ray Fourier Transform Holography: Toward Imaging Ultrafast Evolution in a Single Shot  

SciTech Connect

Panoramic full-field imaging is demonstrated by applying spatial multiplexing to Fourier transform holography. Multiple object and reference waves extend the effective field of view for lensless imaging without compromising the spatial resolution. In this way, local regions of interest distributed throughout a sample can be simultaneously imaged with high spatial resolution. A method is proposed for capturing multiple ultrafast images of a sample with a single x-ray pulse.

Schlotter, W.F.; /Stanford U., Appl. Phys. Dept. /SLAC, SSRL; Luening, J.; /Paris, Lab Chim. Quantique /SOLEIL, Saint-Aubin /BESSY, Berlin; Rick, R.; Chen, K.; /Stanford U., Appl. Phys. Dept. /SLAC, SSRL; Scherz, A.; /SLAC, SSRL; Eisebitt, S.; Guenther, C.M.; Eberhardt, W.; /BESSY, Berlin; Hellwig, O.; /Hitachi Global Stor. Tech., San Jose; Stohr, J.; /SLAC, SSRL

2009-04-29

157

Hybrid-dual-fourier tomographic algorithm for a fast three-dimensionial optical image reconstruction in turbid media  

NASA Technical Reports Server (NTRS)

A reconstruction technique for reducing computation burden in the 3D image processes, wherein the reconstruction procedure comprises an inverse and a forward model. The inverse model uses a hybrid dual Fourier algorithm that combines a 2D Fourier inversion with a 1D matrix inversion to thereby provide high-speed inverse computations. The inverse algorithm uses a hybrid transfer to provide fast Fourier inversion for data of multiple sources and multiple detectors. The forward model is based on an analytical cumulant solution of a radiative transfer equation. The accurate analytical form of the solution to the radiative transfer equation provides an efficient formalism for fast computation of the forward model.

Alfano, Robert R. (Inventor); Cai, Wei (Inventor)

2007-01-01

158

A Novel Gradient Projection Approach for Fourier-Based Image Restoration  

SciTech Connect

This work deals with the ill-posed inverse problem of reconstructing a two-dimensional image of an unknown object starting from sparse and nonuniform measurements of its Fourier Transform. In particular, if we consider a priori information about the target image (e.g., the nonnegativity of the pixels), this inverse problem can be reformulated as a constrained optimization problem, in which the stationary points of the objective function can be viewed as the solutions of a deconvolution problem with a suitable kernel. We propose a fast and effective gradient-projection iterative algorithm to provide regularized solutions of such a deconvolution problem by early stopping the iterations. Preliminary results on a real-world application in astronomy are presented.

Bonettini, S. [Dipartimento di Matematica, Universita di Ferrara, Via Saragat 1, 44122 Ferrara (Italy); Prato, M. [Dipartimento di Matematica, Universita di Modena e Reggio Emilia, Via Campi 213/b, 41125 Modena (Italy); CNR-SPIN, Via Dodecaneso 33, 16146 Genova (Italy)

2010-09-30

159

566 IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. 26, NO. 4, APRIL 2007 Weighted Fourier Series Representation and  

E-print Network

Imaging and Behavior, University of Wisconsin, Madison, WI 53706 USA (e-mail: mchung@stat.wisc. edu). K. M, Alan C. Evans, and Richard J. Davidson Abstract--We present a novel weighted Fourier series (WFS- versity of Massachusetts, Darthmouth, MA 02747 USA. A. C. Evans is with the McConnell Brain Imaging Centre

Wisconsin at Madison, University of

160

Measurement of the mid-infrared Fourier spectroscopic imaging of whole human face by portable apparatus (size: 50*50 mm, weight: 200 g)  

NASA Astrophysics Data System (ADS)

In the daily living space, measurement of the biological-substance distributions such as sebum can be realized by the proposed method of imaging-type 2-dimensional Fourier spectroscopy. This method has the strong robustness for mechanical vibrations. So, the spectrometer (size: 50*50mm, weight: 200g) can be produced without anti-vibration mechanism. Moreover, the phase shifter is a core part of the spectrometer, and it is constructed by the low-price bimorph type actuator which is depending on the vibration control of the piezoceramic in proposed method. It is appropriate as the actuator of the phase shifter from the evaluation results of the actuator straightness and position accuracy in the midinfrared region. As we know, the Fourier spectroscopy has a high light utilization efficiency. Therefore, the low price microbolometer can be used as the imaging sensor. So, the low-price (10,000 U.S. dollars), compact and high portability spectrometer can be produced. Furthermore, the much higher position accuracy in the short wavelength region is requested as we know, the phase shift correction method has been proposed. In this paper, high performance evaluations of the portable spectroscopy apparatus have been discussed by using the CO2 laser spectroscopy results in the midinfrared region. Then, the phase shift correction method was explained. At the end, we demonstrated the feasibility of the mid-infrared imaging of whole human faces without active illuminations.

Qi, Wei; Suzuki, Yo; Fujiwara, Masaru; Saito, Tsubasa; Suzuki, Satoru; Abeygunawardhana, Pradeep K.; Wada, Kenji; Nishiyama, Akira; Ishimaru, Ichiro

2014-11-01

161

Multilevel image encryption by binary phase XOR operations  

Microsoft Academic Search

We propose a multilevel image encryption by using binary phase exclusive-OR(XOR) operations and image dividing technique. The multilevel image can be divided to binary images that have same gray levels. We convert each binary image to binary phase image by phase encoding and encrypt these images with binary random phase images by binary phase XOR operation. We make encrypted gray

Chang-Mok Shin; Dong-Hoan Seo; Kyu-Bo Cho; Ha-Woon Lee; Soo-Joong Kim

2003-01-01

162

Modeling the viscoplastic micromechanical response of two-phase materials using fast Fourier transforms  

SciTech Connect

A viscoplastic approach using the Fast Fourier Transform (FFT) method for obtaining local mechanical response is utilized to study microstructure-property relationships in composite materials. Specifically, three-dimensional, two-phase digital materials containing isotropically coarsened particles surrounded by a matrix phase, generated through a Kinetic Monte Carlo Potts model for Ostwald ripening, are used as instantiations in order to calculate the stress and strain rate fields under uniaxial tension. The effects of the morphology of the matrix phase, the volume fraction and the contiguity of particles, and the polycrystallinity of matrix phase, on the stress and strain rate fields under uniaxial tension are examined. It is found that the first moments of the stress and strain rate fields have a different dependence on the particle volume fraction and the particle contiguity from their second moments. The average stresses and average strain rates of both phases and of the overall composite have rather simple relationships with the particle volume fraction whereas their standard deviations vary strongly, especially when the particle volume fraction is high, and the contiguity of particles has a noticeable effect on the mechanical response. It is also found that the shape of stress distribution in the BCC hard particle phase evolves as the volume fraction of particles in the composite varies, such that it agrees with the stress field in the BCC polycrystal as the volume of particles approaches unity. Finally, it is observed that the stress and strain rate fields in the microstructures with a polycrystalline matrix are less sensitive to changes in volume fraction and contiguity of particles.

Lebensohn, Ricardo A [Los Alamos National Laboratory; Lee, Sukbin [CMU; Rollett, Anthony D [CMU

2009-01-01

163

Real-time three-dimensional Fourier-domain optical coherence tomography video image guided microsurgeries  

PubMed Central

Abstract. The authors describe the development of an ultrafast three-dimensional (3D) optical coherence tomography (OCT) imaging system that provides real-time intraoperative video images of the surgical site to assist surgeons during microsurgical procedures. This system is based on a full-range complex conjugate free Fourier-domain OCT (FD-OCT). The system was built in a CPU-GPU heterogeneous computing architecture capable of video OCT image processing. The system displays at a maximum speed of 10??volume/s for an image volume size of 160×80×1024 (X×Y×Z) pixels. We have used this system to visualize and guide two prototypical microsurgical maneuvers: microvascular anastomosis of the rat femoral artery and ultramicrovascular isolation of the retinal arterioles of the bovine retina. Our preliminary experiments using 3D-OCT-guided microvascular anastomosis showed optimal visualization of the rat femoral artery (diameter<0.8??mm), instruments, and suture material. Real-time intraoperative guidance helped facilitate precise suture placement due to optimized views of the vessel wall during anastomosis. Using the bovine retina as a model system, we have performed “ultra microvascular” feasibility studies by guiding handheld surgical micro-instruments to isolate retinal arterioles (diameter?0.1??mm). Isolation of the microvessels was confirmed by successfully passing a suture beneath the vessel in the 3D imaging environment. PMID:23224164

Kang, Jin U.; Huang, Yong; Zhang, Kang; Ibrahim, Zuhaib; Cha, Jaepyeong; Lee, W. P. Andrew; Brandacher, Gerald; Gehlbach, Peter L.

2012-01-01

164

Attenuated total reflectance Fourier-transform infrared spectroscopic imaging for breast histopathology.  

PubMed

Histopathology forms the gold standard for the diagnosis of breast cancer. Fourier Transform Infrared (FT-IR) spectroscopic imaging has been proposed to be a potentially powerful adjunct to current histopathological techniques. Most studies using FT-IR imaging for breast tissue analysis have been in the transmission or transmission-reflection mode, in which the wavelength and optics limit the data to a relatively coarse spatial resolution (typically, coarser than 5 ?m × 5 ?m per pixel). This resolution is insufficient to examine many histologic structures. Attenuated Total Reflectance (ATR) FT-IR imaging incorporating a Germanium optic can allow for a four-fold increase in spatial resolution due to the material's high refractive index in the mid-IR. Here, we employ ATR FT-IR imaging towards examining cellular and tissue structures that constitute and important component of breast cancer diagnosis. In particular, we resolve and chemically characterize endothelial cells, myoepithelial cells and terminal ductal lobular units. Further extending the ability of IR imaging to examine sub-cellular structures, we report the extraction of intact chromosomes from a breast cancer cells and their spatially localized analysis as a novel approach to understand changes associated with the molecular structure of DNA in breast cancer. PMID:22773893

Walsh, Michael J; Kajdacsy-Balla, Andre; Holton, Sarah E; Bhargava, Rohit

2012-05-01

165

Real-time three-dimensional Fourier-domain optical coherence tomography video image guided microsurgeries  

NASA Astrophysics Data System (ADS)

The authors describe the development of an ultrafast three-dimensional (3D) optical coherence tomography (OCT) imaging system that provides real-time intraoperative video images of the surgical site to assist surgeons during microsurgical procedures. This system is based on a full-range complex conjugate free Fourier-domain OCT (FD-OCT). The system was built in a CPU-GPU heterogeneous computing architecture capable of video OCT image processing. The system displays at a maximum speed of 10 volume/s for an image volume size of 160×80×1024 (X×Y×Z) pixels. We have used this system to visualize and guide two prototypical microsurgical maneuvers: microvascular anastomosis of the rat femoral artery and ultramicrovascular isolation of the retinal arterioles of the bovine retina. Our preliminary experiments using 3D-OCT-guided microvascular anastomosis showed optimal visualization of the rat femoral artery (diameter<0.8 mm), instruments, and suture material. Real-time intraoperative guidance helped facilitate precise suture placement due to optimized views of the vessel wall during anastomosis. Using the bovine retina as a model system, we have performed "ultra microvascular" feasibility studies by guiding handheld surgical micro-instruments to isolate retinal arterioles (diameter˜0.1 mm). Isolation of the microvessels was confirmed by successfully passing a suture beneath the vessel in the 3D imaging environment.

Kang, Jin U.; Huang, Yong; Zhang, Kang; Ibrahim, Zuhaib; Cha, Jaepyeong; Lee, W. P. Andrew; Brandacher, Gerald; Gehlbach, Peter L.

2012-08-01

166

Real-time three-dimensional Fourier-domain optical coherence tomography video image guided microsurgeries.  

PubMed

The authors describe the development of an ultrafast three-dimensional (3D) optical coherence tomography (OCT) imaging system that provides real-time intraoperative video images of the surgical site to assist surgeons during microsurgical procedures. This system is based on a full-range complex conjugate free Fourier-domain OCT (FD-OCT). The system was built in a CPU-GPU heterogeneous computing architecture capable of video OCT image processing. The system displays at a maximum speed of 10 volume/s for an image volume size of 160 × 80 × 1024(X × Y × Z) pixels. We have used this system to visualize and guide two prototypical microsurgical maneuvers: microvascular anastomosis of the rat femoral artery and ultramicrovascular isolation of the retinal arterioles of the bovine retina. Our preliminary experiments using 3D-OCT-guided microvascular anastomosis showed optimal visualization of the rat femoral artery (diameter<0.8 mm), instruments, and suture material. Real-time intraoperative guidance helped facilitate precise suture placement due to optimized views of the vessel wall during anastomosis. Using the bovine retina as a model system, we have performed "ultra microvascular" feasibility studies by guiding handheld surgical micro-instruments to isolate retinal arterioles (diameter ~0.1 mm). Isolation of the microvessels was confirmed by successfully passing a suture beneath the vessel in the 3D imaging environment. PMID:23224164

Kang, Jin U; Huang, Yong; Zhang, Kang; Ibrahim, Zuhaib; Cha, Jaepyeong; Lee, W P Andrew; Brandacher, Gerald; Gehlbach, Peter L

2012-08-01

167

Ultra-Rapid Categorization of Fourier-Spectrum Equalized Natural Images: Macaques and Humans Perform Similarly  

PubMed Central

Background Comparative studies of cognitive processes find similarities between humans and apes but also monkeys. Even high-level processes, like the ability to categorize classes of object from any natural scene under ultra-rapid time constraints, seem to be present in rhesus macaque monkeys (despite a smaller brain and the lack of language and a cultural background). An interesting and still open question concerns the degree to which the same images are treated with the same efficacy by humans and monkeys when a low level cue, the spatial frequency content, is controlled. Methodology/Principal Findings We used a set of natural images equalized in Fourier spectrum and asked whether it is still possible to categorize them as containing an animal and at what speed. One rhesus macaque monkey performed a forced-choice saccadic task with a good accuracy (67.5% and 76% for new and familiar images respectively) although performance was lower than with non-equalized images. Importantly, the minimum reaction time was still very fast (100 ms). We compared the performances of human subjects with the same setup and the same set of (new) images. Overall mean performance of humans was also lower than with original images (64% correct) but the minimum reaction time was still short (140 ms). Conclusion Performances on individual images (% correct but not reaction times) for both humans and the monkey were significantly correlated suggesting that both species use similar features to perform the task. A similar advantage for full-face images was seen for both species. The results also suggest that local low spatial frequency information could be important, a finding that fits the theory that fast categorization relies on a rapid feedforward magnocellular signal. PMID:21326600

Girard, Pascal; Koenig-Robert, Roger

2011-01-01

168

MEMS-Based Handheld Fourier Domain Doppler Optical Coherence Tomography for Intraoperative Microvascular Anastomosis Imaging  

PubMed Central

Purpose To demonstrate the feasibility of a miniature handheld optical coherence tomography (OCT) imager for real time intraoperative vascular patency evaluation in the setting of super-microsurgical vessel anastomosis. Methods A novel handheld imager Fourier domain Doppler optical coherence tomography based on a 1.3-µm central wavelength swept source for extravascular imaging was developed. The imager was minimized through the adoption of a 2.4-mm diameter microelectromechanical systems (MEMS) scanning mirror, additionally a 12.7-mm diameter lens system was designed and combined with the MEMS mirror to achieve a small form factor that optimize functionality as a handheld extravascular OCT imager. To evaluate in-vivo applicability, super-microsurgical vessel anastomosis was performed in a mouse femoral vessel cut and repair model employing conventional interrupted suture technique as well as a novel non-suture cuff technique. Vascular anastomosis patency after clinically successful repair was evaluated using the novel handheld OCT imager. Results With an adjustable lateral image field of view up to 1.5 mm by 1.5 mm, high-resolution simultaneous structural and flow imaging of the blood vessels were successfully acquired for BALB/C mouse after orthotopic hind limb transplantation using a non-suture cuff technique and BALB/C mouse after femoral artery anastomosis using a suture technique. We experimentally quantify the axial and lateral resolution of the OCT to be 12.6 µm in air and 17.5 µm respectively. The OCT has a sensitivity of 84 dB and sensitivity roll-off of 5.7 dB/mm over an imaging range of 5 mm. Imaging with a frame rate of 36 Hz for an image size of 1000(lateral)×512(axial) pixels using a 50,000 A-lines per second swept source was achieved. Quantitative vessel lumen patency, lumen narrowing and thrombosis analysis were performed based on acquired structure and Doppler images. Conclusions A miniature handheld OCT imager that can be used for intraoperative evaluation of microvascular anastomosis was successfully demonstrated. PMID:25474742

Huang, Yong; Furtmüller, Georg J.; Tong, Dedi; Zhu, Shan; Lee, W. P. Andrew; Brandacher, Gerald; Kang, Jin U.

2014-01-01

169

A Fourier-based compressed sensing technique for accelerated CT image reconstruction using first-order methods  

NASA Astrophysics Data System (ADS)

As a solution to iterative CT image reconstruction, first-order methods are prominent for the large-scale capability and the fast convergence rate {O}(1/k^2). In practice, the CT system matrix with a large condition number may lead to slow convergence speed despite the theoretically promising upper bound. The aim of this study is to develop a Fourier-based scaling technique to enhance the convergence speed of first-order methods applied to CT image reconstruction. Instead of working in the projection domain, we transform the projection data and construct a data fidelity model in Fourier space. Inspired by the filtered backprojection formalism, the data are appropriately weighted in Fourier space. We formulate an optimization problem based on weighted least-squares in the Fourier space and total-variation (TV) regularization in image space for parallel-beam, fan-beam and cone-beam CT geometry. To achieve the maximum computational speed, the optimization problem is solved using a fast iterative shrinkage-thresholding algorithm with backtracking line search and GPU implementation of projection/backprojection. The performance of the proposed algorithm is demonstrated through a series of digital simulation and experimental phantom studies. The results are compared with the existing TV regularized techniques based on statistics-based weighted least-squares as well as basic algebraic reconstruction technique. The proposed Fourier-based compressed sensing (CS) method significantly improves both the image quality and the convergence rate compared to the existing CS techniques.

Choi, Kihwan; Li, Ruijiang; Nam, Haewon; Xing, Lei

2014-06-01

170

INTERFACE OF A REVERSE-PHASE HIGH-PERFORMANCE LIQUID CHROMATOGRAPH WITH A DIFFUSE REFLECTANCE FOURIER TRANSFORM INFRARED SPECTROMETER  

EPA Science Inventory

An approach to the interface of a reverse-phase high-performance liquid chromatograph and a Fourier transform infrared spectrometer has been developed in which the solutes eluting from the column are continuously extracted into dichloromethane. The application of both flow cell a...

171

Compressive sensing imaging with optical Fourier frequency spectrum coding and optical wavelet transform  

NASA Astrophysics Data System (ADS)

In traditional signal sampling process, Shannon - Nyquist (Shoon-Nyquist) sampling theorem is a fundamental principle that must be followed, in that the sampling frequency must be at least twice the highest frequency of the sampled signal. However, with the increasing of data acquisition capabilities of sensing systems, acquisition of high-resolution images will inevitably lead to a flood of sampling data according to Shoon-Nyquist sampling theorem, which increases the cost of data transport and storage, and also the demand for the resolution of the detector. Donoho and Candes proposed the compressed sensing theory which is considered as a revolutionary breakthrough in that it breaks Shoon-Nyquist sampling frequency requirements. For compressible or sparse signals, signal sampling can be implemented with the sampling frequency that is less than that of Shoon-Nyquist sampling theorem, and the signal is also compressed meanwhile. This paper studied compressive coding imaging based on optical wavelet transform coupled with the frequency spectrum coding. The imaging quality can be enhanced by introducing optical wavelet transform for pre-treatment of the target image before the compression coding on the frequency spectrum plane. Simulation results show that higher quality images can be obtained with the pre-treatment of optical wavelet transform than that of purely optical Fourier transform without any increasing of the transmitted data. With the proposed method, we have conducted the numerical simulations. The results show that the proposed compression sampling method can achieve the real-time compression sampling of the images without distortion, and a compression ratio of 4:1 can be obtained.

Han, Jiyu; Xu, Feng; Wang, Chinhua

2013-08-01

172

New scientific results with SpIOMM: a testbed for CFHT's imaging Fourier transform spectrometer SITELLE  

NASA Astrophysics Data System (ADS)

We present new data obtained with SpIOMM, the imaging Fourier transform spectrometer attached to the 1.6-m telescope of the Observatoire du Mont-Megantic in Québec. Recent technical and data reduction improvements have significantly increased SpIOMM's capabilities to observe fainter objects or weaker nebular lines, as well as continuum sources and absorption lines, and to increase its modulation efficiency in the near ultraviolet. To illustrate these improvements, we present data on the supernova remnant Cas A, planetary nebulae M27 and M97, the Wolf-Rayet ring nebula M1-67, spiral galaxies M63 and NGC 3344, as well as the interacting pair of galaxies Arp 84.

Drissen, L.; Alarie, A.; Martin, T.; Lagrois, D.; Rousseau-Nepton, L.; Bilodeau, A.; Robert, C.; Joncas, G.; Iglesias-Páramo, J.

2012-09-01

173

Fourier Interferometry as Applied to Microspectrofluorometry and Fluorescence Imaging of Living Cells  

NASA Astrophysics Data System (ADS)

Excitation-emission fluorescence spectroscopy and imaging are applied to studies of cellular metabolism and at the convergence of cellular differentiation, detoxification, transformation, and senescence. Metabolic activity, intracellular redox levels, and compartmentation are probed by coenzyme [NAD(P)H] transients and monochlorobimane for glutathione dehydrogenase. Gene expression or its failure in lysosomal disorders is identified with fluorogenic probes. The "multiorganelle detoxification complex" is visualized and investigated with cytotoxic agents. A kind of photoactivated "accelerated cellular senescence" is recognized by accumulation of Schiff bases. Conventional and novel mitochondrial probes are used to localize these organelles in Saccharomyces cerevisiae as a model for future studies in mammalian cells and to detect in these very cells the organelle interactions resulting from the action of mitochondria-toxic drugs. The potential of these studies for biotechnology and instrumentation relying on fibers and integrated optics is considerably enhanced by Fourier interferometry.

Kohen, E.; Hirschberg, J. G.; Kohen, C.; Schachtschabel, D. O.; Stanikun Aite, R.; Monti, M.

174

Digital holography forquantitative phase-contrast imaging  

Microsoft Academic Search

We present a new application of digital holography for phase-contrast imaging and optical metrology. This holographic imaging technique uses a CCD camera for recording of a digital Fresnel off-axis hologram and a numerical method for hologram reconstruction. The method simultaneously provides an amplitude-contrast image and a quantitative phase-contrast image. An application to surface profilometry is presented and shows excellent agreement

Etienne Cuche; Frédéric Bevilacqua; Christian Depeursinge

1999-01-01

175

Mathematical Investigation of Gamma Ray and Neutron Absorption Grid Patterns for Homeland Defense Related Fourier Imaging Systems  

NASA Technical Reports Server (NTRS)

Terrorist suitcase nuclear devices typically using converted Soviet tactical nuclear warheads contain several kilograms of plutonium. This quantity of plutonium emits a significant number of gamma rays and neutrons as it undergoes radioactive decay. These gamma rays and neutrons normally penetrate ordinary matter to a significant distance. Unfortunately this penetrating quality of the radiation makes imaging with classical optics impractical. However, this radiation signature emitted by the nuclear source may be sufficient to be imaged from low-flying aerial platforms carrying Fourier imaging systems. The Fourier imaging system uses a pair of co-aligned absorption grids to measure a selected range of spatial frequencies from an object. These grids typically measure the spatial frequency in only one direction at a time. A grid pair that looks in all directions simultaneously would be an improvement over existing technology. A number of grid pairs governed by various parameters were investigated to solve this problem. By examining numerous configurations, it became apparent that an appropriate spiral pattern could be made to work. A set of equations was found to describe a grid pattern that produces straight fringes. Straight fringes represent a Fourier transform of a point source at infinity. An inverse Fourier transform of this fringe pattern would provide an accurate image (location and intensity) of a point source.

Boccio, Dona

2003-01-01

176

Investigation of Moiré Pattern-based Phase Retrieval Approach for Differential Phase-contrast Cone Beam CT Imaging Using a Hospital-grade Tube  

PubMed Central

The phase stepping algorithm is commonly used for phase retrieval in grating-based differential phase-contrast (DPC) imaging, which requires multiple intensity images to compute one DPC image. It is not efficient for data acquisition, especially in the case of dynamic imaging using either DPC imaging or DPC-based come beam CT (DPC-CBCT) imaging. A Fourier transform-based approach has been developed for fringe pattern analysis in optics, and it was recently implemented into a synchrotron-based DPC tomography system. In this research, this approach is further developed for a bench-top DPC-CBCT imaging system with a hospital-grade x-ray tube. The key idea is to separate carrier fringes and object information in Fourier domain of the interferogram and to reconstruct the differentiated phase information using the object information. Only one interferogram is required for phase retrieval at a cost of spatial resolution. The fringes of moiré patterns are used as the carrier fringes, and a phantom is scanned to evaluate the approach. Various interferograms with different carrier fringe frequencies are investigated and the reconstruction image quality is evaluated in terms of contrast, noise and sharpness. The results indicated that the DPC images can be effectively retrieved using the Fourier transform-based approach and the reconstructed phase coefficient showed better contrast compared to that of attenuation-based contrast. The spatial resolution is acceptable in the phantom studies although it is not as good as the results of phase-stepping approach. The Fourier transform-based phase retrieval approach is able to greatly simplify data acquisition, to improve the temporal resolution and to make it possible for dynamic DPC-CBCT imaging. It is promising for perfusion imaging where spatial resolution is not a concern. PMID:23378889

Cai, Weixing; Ning, Ruola; Yu, Yang; Liu, Jiangkun; Conover, David

2012-01-01

177

Investigation of Moiré pattern-based phase retrieval approach for differential phase-contrast cone beam CT imaging using a hospital-grade tube  

NASA Astrophysics Data System (ADS)

The phase stepping algorithm is commonly used for phase retrieval in grating-based differential phase-contrast (DPC) imaging, which requires multiple intensity images to compute one DPC image. It is not efficient for data acquisition, especially in the case of dynamic imaging using either DPC imaging or DPC-based come beam CT (DPC-CBCT) imaging. A Fourier transform-based approach has been developed for fringe pattern analysis in optics, and it was recently implemented into a synchrotron-based DPC tomography system. In this research, this approach is further developed for a bench-top DPC-CBCT imaging system with a hospital-grade x-ray tube. The key idea is to separate carrier fringes and object information in Fourier domain of the interferogram and to reconstruct the differentiated phase information using the object information. Only one interferogram is required for phase retrieval at a cost of spatial resolution. The fringes of moiré patterns are used as the carrier fringes, and a phantom is scanned to evaluate the approach. Various interferograms with different carrier fringe frequencies are investigated and the reconstruction image quality is evaluated in terms of contrast, noise and sharpness. The results indicated that the DPC images can be effectively retrieved using the Fourier transform-based approach and the reconstructed phase coefficient showed better contrast compared to that of attenuation-based contrast. The spatial resolution is acceptable in the phantom studies although it is not as good as the results of phase-stepping approach. The Fourier transform-based phase retrieval approach is able to greatly simplify data acquisition, to improve the temporal resolution and to make it possible for dynamic DPC-CBCT imaging. It is promising for perfusion imaging where spatial resolution is not a concern.

Cai, Weixing; Ning, Ruola; Yu, Yang; Liu, Jiangkun; Conover, David

2012-03-01

178

Research on methods of spectral calibration and radiometric calibration of the windowing Fourier transform imaging spectrometer  

NASA Astrophysics Data System (ADS)

Spectral calibration and radiometric calibration is an important part in the data processing of the windowing Fourier transform imaging spectrometer, it can ensure that the spectral curve output from spectrometer are more closely to target spectrum. The main idea of spectral calibration is using a monochromatic source whose wavelength is known, in the same way, radiometric calibration can be achieved by using radiation source whose radiation characteristic is known. In this paper, we propose a set of methods of spectral calibration and radiometric calibration. In order to carry out spectral calibration, we use monocharomator to scan several sample points near the position of every spectral channel of imaging spectrometer, and then we employ Gaussian fitting function to determine the central wavelength and bandwidth of every spectral channel. In order to carry out radiometric calibration, we employ panchromatic light source and integrating sphere, at the position of every spectral channel of imaging spectrometer, we measure the response ability of spectrometer to radiation. The calibration accuracy is carefully analyzed. Experimental results show that calibration accuracy meet the given requirements.

Zhang, Lei; Gao, Jiao Bo; Zhao, Yu Jie; Luo, Yan Ling; Xiao, Xiang Guo; Zhang, Fang

2013-08-01

179

Multi-resolution Graph Fourier Transform for Compression of Piecewise Smooth Images.  

PubMed

Piecewise smooth (PWS) images (e.g., depth maps or animation images) contain unique signal characteristics such as sharp object boundaries and slowly-varying interior surfaces. Leveraging on recent advances in graph signal processing, in this paper we propose to compress PWS images using suitable Graph Fourier Transforms (GFT) to minimize the total signal representation cost of each pixel block, considering both the sparsity of the signal's transform coefficients and the compactness of transform description. Unlike fixed transforms such as the Discrete Cosine Transform (DCT), we can adapt GFT to a particular class of pixel blocks. In particular, we select one among a defined search space of GFTs to minimize total representation cost via our proposed algorithms, leveraging on graph optimization techniques such as spectral clustering and minimum graph cuts. Further, for practical implementation of GFT we introduce two techniques to reduce computation complexity. First, at the encoder we low-pass filter and down-sample a high-resolution (HR) pixel block to obtain a low-resolution (LR) one, so that a LR-GFT can be employed. At the decoder, up-sampling and interpolation are performed adaptively along HR boundaries coded using arithmetic edge coding (AEC), so that sharp object boundaries can be well preserved. Second, instead of computing GFT from a graph in real-time via eigen-decomposition, the most popular LR-GFTs are pre-computed and stored in a table for lookup during encoding and decoding. Using depth maps and computer-graphics images as examples of PWS images, experimental results show that our proposed multi-resolution (MR)-GFT scheme outperforms H.264 intra by 6:8 dB on average in PSNR at the same bit rate. PMID:25494508

Hu, Wei; Cheung, Gene; Ortega, Antonio; Au, Oscar

2014-12-01

180

Quantitative-phase-contrast imaging of a two-level surface described as a 2D linear filtering process.  

PubMed

The paper deals with quantitative phase imaging of two-height-level surface reliefs. The imaging is considered to be a linear system and, consequently, the Fourier transform of the image is the product of the Fourier transform of a 2D function characterizing the surface and a specific 2D coherent transfer function. The Fourier transform of functions specifying periodic surface reliefs is factorized into two functions similar to lattice and structure amplitudes in crystal structure analysis. The approach to the imaging process described in the paper enables us to examine the dependence of the phase image on the surface geometry. Theoretical results are verified experimentally by means of a digital holographic microscope. PMID:20940953

Lovicar, Lud?k; Komrska, Ji?í; Chmelík, Radim

2010-09-27

181

Determination of grain size distribution function using two-dimensional Fourier transforms of tone pulse encoded images  

NASA Technical Reports Server (NTRS)

Microstructural images may be tone pulse encoded and subsequently Fourier transformed to determine the two-dimensional density of frequency components. A theory is developed relating the density of frequency components to the density of length components. The density of length components corresponds directly to the actual grain size distribution function from which the mean grain shape, size, and orientation can be obtained.

Generazio, E. R.

1986-01-01

182

Determination of grain-size distribution function using two-dimensional Fourier transforms of tone-pulse-encoded images  

NASA Technical Reports Server (NTRS)

Microstructural images may be tone pulse encoded and subsequently Fourier transformed to determine the two-dimensional density of frequency components. A theory is developed relating the density of frequency components to the density of length components. The density of length components corresponds directly to the actual grain-size distribution function from which the mean grain shape, size, and orientation can be obtained.

Generazio, E. R.

1988-01-01

183

Development of imaging Fourier-transform spectroscopy for the characterization of turbulent jet flames  

NASA Astrophysics Data System (ADS)

Recent advances in computational models to simulate turbulent, reactive flow fields have outpaced the ability to collect highly constraining data---throughout the entire flow field---for validating and improving such models. In particular, the ability to quantify in three dimensions both the mean scalar fields (i.e. temperature & species concentrations) and their respective fluctuation statistics via hyperspectral imaging would be a game-changing advancement in combustion diagnostics, with high impact in both validation and improvement efforts for computational combustion models. This research effort establishes imaging Fourier- transform spectrometry (IFTS) as a valuable tool (which complements laser diagnostics) for the study of turbulent combustion. Specifically, this effort (1) demonstrates that IFTS can be used to quantitatively measure spatially resolved spectra from a canonical turbulent flame; (2) establishes the utility of quantile spectra in first-ever quantitative comparisons between measured and modeled turbulent radiation interaction (TRI); (3) develops a simple onion-peeling-like spectral inversion methodology suitable for estimating radial scalar distributions in axisymmetric, optically-thick flames; (4) builds understanding of quantile spectra and demonstrates proof of concept for their use in estimating scalar fluctuation statistics.

Harley, Jacob L.

184

Design and performance of a compact miniature static Fourier transform imaging spectropolarimeter  

NASA Astrophysics Data System (ADS)

We propose a compact, miniature static Fourier transform imaging spectropolarimeter (SFTISP). The spectropolarimeter is formed by cascading two high order crystal retarders and a Wollaston birefringent interferometer. Compared with previous instruments, the most significant advantage of the described model is that without any internal moving parts, electrically controllable or micro-components, the entire wavelength-dependent state of polarization (SOP) is acquired simultaneously along a one-dimensional spatial image by a single snapshot. Also, we show that in this configuration we can benefit from the advantages of the element: compact, robust and high throughput of the Wollaston birefringent interferometer. The theory of the birefringent SFTISP is provided, followed by details of its specific embodiment. A simulation and an experimental demonstration of the sensor are also presented. The core optics of the breadboard sensor is as small as 8×? 3.5 cm3 in size. The operation spectral range is from 450 nm to 850 nm. The experiment results were shown to yield accuracy better than 3% over most of the operation spectral band.

Li, Jie; Zhu, Jing-ping; Wu, Hai-ying; Hou, Xun

2011-08-01

185

A Fourier-based method for the restoration of chopped and nodded images  

NASA Astrophysics Data System (ADS)

In a series of previous papers we have proposed and validated an iterative method, known as the projected Landweber method, for the restoration of astronomical images taken in chopping and nodding mode. While the method generally provides good results, it may also generate artifacts related to the huge non-uniqueness of the solution of the restoration problem. If the image satisfies additional boundary conditions, the non-uniqueness can be reduced, or even entirely removed. In this paper we investigate the case of periodic boundary conditions, which apply, in particular, to the case of a target area surrounded by a suitable region of empty sky. Periodic boundary conditions do not entirely remove the non-uniqueness of the solution, but allow using Fourier-based techniques. We introduce a new iterative method which can be considered as a relaxed and projected version of the van Cittert method. We formally demonstrate why this method does not produce the artifacts generated by the one we previously proposed, and we present numerical simulations confirming this result. We illustrate the convergence properties of the algorithm in the case of both compact and extended sources. Finally, we briefly discuss the potential and the limitations of the proposed technique.

Bertero, M.; Boccacci, P.; Custo, A.; De Mol, C.; Robberto, M.

2003-08-01

186

Design considerations for the development of a space qualification Short Wavelength Imaging Fourier Transform Spectrometer (SWIFTS)  

SciTech Connect

This document is the final report on work performed at Sandia National Laboratories during FY 1992 and 1993 for a Laboratory Directed Research and Development (LDRD) program to look at problems associated with the design and long term operation of a short wavelength imaging Fourier Transform (FT) spectrometer for use in space. In attempts to answer two fundamental questions: is a FT spectrometer with a resolution of 1 cm{sup {minus}1} covering the silicon detector wavelength range of 0.4 to 1.1 microns feasible in a long life space instrument and, if so, is it the best method of obtaining the desired information? Emphasis has been on identifying methods which minimize reliance on precision mechanical alignment and precise velocity control. An important consideration has also been to develop methods which will be compatible with a variety of self-scanning solid state imaging devices. A breadboard instrument was constructed using cube corner retroreflectors and a laser diode position reference. Some preliminary results are reported. This work is primarily intended to act as an aid to engineers at Sandia who wish to pursue the fabrication of a flight qualified instrument. The theoretical parts are intended to be somewhat tutorial in nature to aid the engineer who is not familiar with FT spectroscopy.

Abbink, R.E.

1997-06-01

187

Quantitative amplitude and phase contrast imaging in a scanning transmission X-ray microscope  

Microsoft Academic Search

Phase contrast in X-ray imaging provides lower radiation dose, and dramatically higher contrast at multi-keV photon energies when compared with absorption contrast. We describe here the use of a segmented detector in a scanning transmission X-ray microscope to collect partially coherent bright field images. We have adapted a Fourier filter reconstruction technique developed by McCallum, Landauer and Rodenburg to retrieve

Benjamin Hornberger; Michael Feser; Chris Jacobsen

2007-01-01

188

Symmetric Phase-Only Filtering in Particle-Image Velocimetry  

NASA Technical Reports Server (NTRS)

Symmetrical phase-only filtering (SPOF) can be exploited to obtain substantial improvements in the results of data processing in particle-image velocimetry (PIV). In comparison with traditional PIV data processing, SPOF PIV data processing yields narrower and larger amplitude correlation peaks, thereby providing more-accurate velocity estimates. The higher signal-to-noise ratios associated with the higher amplitude correlation peaks afford greater robustness and reliability of processing. SPOF also affords superior performance in the presence of surface flare light and/or background light. SPOF algorithms can readily be incorporated into pre-existing algorithms used to process digitized image data in PIV, without significantly increasing processing times. A summary of PIV and traditional PIV data processing is prerequisite to a meaningful description of SPOF PIV processing. In PIV, a pulsed laser is used to illuminate a substantially planar region of a flowing fluid in which particles are entrained. An electronic camera records digital images of the particles at two instants of time. The components of velocity of the fluid in the illuminated plane can be obtained by determining the displacements of particles between the two illumination pulses. The objective in PIV data processing is to compute the particle displacements from the digital image data. In traditional PIV data processing, to which the present innovation applies, the two images are divided into a grid of subregions and the displacements determined from cross-correlations between the corresponding sub-regions in the first and second images. The cross-correlation process begins with the calculation of the Fourier transforms (or fast Fourier transforms) of the subregion portions of the images. The Fourier transforms from the corresponding subregions are multiplied, and this product is inverse Fourier transformed, yielding the cross-correlation intensity distribution. The average displacement of the particles across a subregion results in a displacement of the correlation peak from the center of the correlation plane. The velocity is then computed from the displacement of the correlation peak and the time between the recording of the two images. The process as described thus far is performed for all the subregions. The resulting set of velocities in grid cells amounts to a velocity vector map of the flow field recorded on the image plane. In traditional PIV processing, surface flare light and bright background light give rise to a large, broad correlation peak, at the center of the correlation plane, that can overwhelm the true particle- displacement correlation peak. This has made it necessary to resort to tedious image-masking and background-subtraction procedures to recover the relatively small amplitude particle-displacement correlation peak. SPOF is a variant of phase-only filtering (POF), which, in turn, is a variant of matched spatial filtering (MSF). In MSF, one projects a first image (denoted the input image) onto a second image (denoted the filter) as part of a computation to determine how much and what part of the filter is present in the input image. MSF is equivalent to cross-correlation. In POF, the frequency-domain content of the MSF filter is modified to produce a unitamplitude (phase-only) object. POF is implemented by normalizing the Fourier transform of the filter by its magnitude. The advantage of POFs is that they yield correlation peaks that are sharper and have higher signal-to-noise ratios than those obtained through traditional MSF. In the SPOF, these benefits of POF can be extended to PIV data processing. The SPOF yields even better performance than the POF approach, which is uniquely applicable to PIV type image data. In SPOF as now applied to PIV data processing, a subregion of the first image is treated as the input image and the corresponding subregion of the second image is treated as the filter. The Fourier transforms from both the firs and second- image subregions are normalized by the square roots of their respective magnitudes.

Wemet, Mark P.

2008-01-01

189

Flexible Retrospective Phase Stepping in X-Ray Scatter Correction and Phase Contrast Imaging Using Structured Illumination  

PubMed Central

The development of phase contrast methods for diagnostic x-ray imaging is inspired by the potential of seeing the internal structures of the human body without the need to deposit any harmful radiation. An efficient class of x-ray phase contrast imaging and scatter correction methods share the idea of using structured illumination in the form of a periodic fringe pattern created with gratings or grids. They measure the scatter and distortion of the x-ray wavefront through the attenuation and deformation of the fringe pattern via a phase stepping process. Phase stepping describes image acquisition at regular phase intervals by shifting a grating in uniform steps. However, in practical conditions the actual phase intervals can vary from step to step and also spatially. Particularly with the advent of electromagnetic phase stepping without physical movement of a grating, the phase intervals are dependent upon the focal plane of interest. We describe a demodulation algorithm for phase stepping at arbitrary and position-dependent (APD) phase intervals without assuming a priori knowledge of the phase steps. The algorithm retrospectively determines the spatial distribution of the phase intervals by a Fourier transform method. With this ability, grating-based x-ray imaging becomes more adaptable and robust for broader applications. PMID:24205177

Wen, Han; Miao, Houxun; Bennett, Eric E.; Adamo, Nick M.; Chen, Lei

2013-01-01

190

Characterizing and overcoming spectral artifacts in imaging Fourier-transform spectroscopy of turbulent exhaust plumes  

NASA Astrophysics Data System (ADS)

The midwave and shortwave infrared regions of the electromagnetic spectrum contain rich information enabling the characterization of hot, rapid events such as explosions, engine plumes, flares and other combustion events. High-speed sensors are required to analyze the content of such rapidly evolving targets. Cameras with high frame rates and non-imaging spectrometers with high data rates are typically used; however the information from these two types of instruments must be later fused to enable characterization of the transient targets. Imaging spectrometers have recently become commercially available for general scientific use, thus enabling simultaneous capture of both spatial and spectral information without co-registration issues. However, their use against rapidly-varying sources has traditionally been considered problematic, for even at moderate spatial and spectral resolutions the time to acquire a single spectrum can be long compared to the timescales associated with combustion events. This paper demonstrates that imaging Fourier-transform spectroscopy (IFTS) can successfully characterize the turbulent combustion exhaust from a turbojet engine. A Telops Hyper-Cam IFTS collected hyperspectral video from a Turbine Technologies SR-30 turbojet engine with a spectral resolution of ?? = 1/cm-1 on a 200×64 pixel sub-window at a rate of 0.3 Hz. Scene-change artifacts (SCAs) are present in the spectra; however, the stochastic fluctuations in source intensity translate into high-frequency "noise." Temporal averaging affords a significant reduction of the noise associated with SCAs. Emission from CO and CO2 are clearly recognized in the averaged spectra, and information about their temperature and relative concentrations is evident.

Moore, Elizabeth A.; Gross, Kevin C.; Bowen, Spencer J.; Perram, Glen P.; Chamberland, Martin; Farley, Vincent; Gagnon, Jean-Philippe; Lagueux, Philippe; Villemaire, André

2009-05-01

191

Fourier transform infrared spectroscopic imaging identifies early biochemical markers of tissue damage  

NASA Astrophysics Data System (ADS)

Fourier Transform Infrared (FT-IR) spectroscopic imaging can allow for the rapid imaging of tissue biochemistry in a label-free and non-perturbing fashion. With the rapid adoption of new minimally invasive surgery (MIS) technologies over the last 20 years, adequate skill to safely and effectively use these technologies may not be achieved and risk of undue physical pressure being placed on tissues is a concern. Previous work has demonstrated that a number of histological stains can detect tissue damage, however, this process requires the initiation and progression of a signaling cascade that results in the epitope of interest being expressed. We proposed to identify the early biochemical markers associated with physical tissue damage from applied forces, thus not requiring transcriptional and translational protein synthesis as traditional immunohistochemistry does. To demonstrate that FT-IR can measure biochemical changes in tissues that have undergone physical force, we took ex-vivo lamb's liver that had been freshly excised and applied varying levels of physical pressure (0kPa to 30kPa). Tissues were then formalin-fixed, paraffin-embedded, and sectioned on to glass for H and E staining to identify damage and on to an IR slide for FT-IR imaging. Regions of interest containing hepatocytes were identified and average FT-IR spectra were extracted from the damaged and undamaged livers. FT-IR spectra showed clear biochemical changes associated with tissue damage. In addition, chemical changes could be observed proceeding histological changes observed when using conventional staining approaches.

Varma, Vishal K.; Ohlander, Samuel; Nguyen, Peter; Vendryes, Christopher; Parthiban, Sujeeth; Hamilton, Blake; Wallis, M. Chad; Kajdacsy-Balla, Andre; Hannaford, Blake; Lendvay, Thomas; Hotaling, James M.; Walsh, Michael J.

2014-03-01

192

Quantitative phase contrast imaging using common-path in-line digital holography  

NASA Astrophysics Data System (ADS)

We propose a method to carry out quantitative phase contrast imaging using in-line digital holography. The phase shifting digital holography is implemented in a common-path in-line configuration with the help of diffraction from a phase grating displayed on a spatial light modulator. The phase shifted interferograms are recorded by shifting the grating within a selected area corresponding to the dc spot in the Fourier transform plane. The feasibility of method is verified by using a multimode fiber as phase object. The method addresses a number of challenges faced by existing methods and dispenses the need for special optics.

P. T., Samsheerali; Das, Bhargab; Joseph, Joby

2012-03-01

193

Null test fourier domain alignment technique for phase-shifting point diffraction interferometer  

DOEpatents

Alignment technique for calibrating a phase-shifting point diffraction interferometer involves three independent steps where the first two steps independently align the image points and pinholes in rotation and separation to a fixed reference coordinate system, e.g, CCD. Once the two sub-elements have been properly aligned to the reference in two parameters (separation and orientation), the third step is to align the two sub-element coordinate systems to each other in the two remaining parameters (x,y) using standard methods of locating the pinholes relative to some easy to find reference point.

Naulleau, Patrick (5239 Miles Ave., Apt. A, Oakland, CA 94618); Goldberg, Kenneth Alan (1622 Oxford St., #5t, Berkeley, CA 94709)

2000-01-01

194

Imaging of the three-dimensional alveolar structure and the alveolar mechanics of a ventilated and perfused isolated rabbit lung with Fourier domain optical coherence tomography  

NASA Astrophysics Data System (ADS)

In this feasibility study, Fourier domain optical coherence tomography (FDOCT) is used for visualizing the 3-D structure of fixated lung parenchyma and to capture real-time cross sectional images of the subpleural alveolar mechanics in a ventilated and perfused isolated rabbit lung. The compact and modular setup of the FDOCT system allows us to image the first 500 µm of subpleural lung parenchyma with a 3-D resolution of 16×16×8 µm (in air). During mechanical ventilation, real-time cross sectional FDOCT images visualize the inflation and deflation of alveoli and alveolar sacks (acini) in successive images of end-inspiratory and end-expiratory phase. The FDOCT imaging shows the relation of local alveolar mechanics to the setting of tidal volume (VT), peak airway pressure, and positive end-expiratory pressure (PEEP). Application of PEEP leads to persistent recruitment of alveoli and acini in the end-expiratory phase, compared to ventilation without PEEP where alveolar collapse and reinflation are observed. The imaging of alveolar mechanics by FDOCT will help to determine the amount of mechanical stress put on the alveolar walls during tidal ventilation, which is a key factor in understanding the development of ventilator induced lung injury (VILI).

Popp, Alexander; Wendel, Martina; Knels, Lilla; Koch, T.; Koch, Edmund

2006-01-01

195

Fourier transform infrared spectroscopic imaging of cardiac tissue to detect collagen deposition after myocardial infarction  

NASA Astrophysics Data System (ADS)

Myocardial infarction often leads to an increase in deposition of fibrillar collagen. Detection and characterization of this cardiac fibrosis is of great interest to investigators and clinicians. Motivated by the significant limitations of conventional staining techniques to visualize collagen deposition in cardiac tissue sections, we have developed a Fourier transform infrared imaging spectroscopy (FT-IRIS) methodology for collagen assessment. The infrared absorbance band centered at 1338 cm-1, which arises from collagen amino acid side chain vibrations, was used to map collagen deposition across heart tissue sections of a rat model of myocardial infarction, and was compared to conventional staining techniques. Comparison of the size of the collagen scar in heart tissue sections as measured with this methodology and that of trichrome staining showed a strong correlation (R=0.93). A Pearson correlation model between local intensity values in FT-IRIS and immuno-histochemical staining of collagen type I also showed a strong correlation (R=0.86). We demonstrate that FT-IRIS methodology can be utilized to visualize cardiac collagen deposition. In addition, given that vibrational spectroscopic data on proteins reflect molecular features, it also has the potential to provide additional information about the molecular structure of cardiac extracellular matrix proteins and their alterations.

Cheheltani, Rabee; Rosano, Jenna M.; Wang, Bin; Sabri, Abdel Karim; Pleshko, Nancy; Kiani, Mohammad F.

2012-05-01

196

Fourier Transform Infrared Imaging Analysis of Cancellous Bone in Alendronate- and Raloxifene-Treated Osteopenic Sheep  

PubMed Central

Fourier transform infrared imaging spectroscopy (FTIRI)-assessed bone composition parameters (mineral content, collagen maturity, crystal size and perfection, and carbonate content) describe bone quality and correlate to bone fracture risk. The challenge with studying bone quality in patients treated with antiresorptive drugs such as bisphosphonates (e.g., alendronate) and selective estrogen receptor modulators (SERMs) (e.g. raloxifene) is being able to test bone mechanical performance and material properties pre- and posttreatment. The purpose of this study was to evaluate the FTIRI changes in a large animal model of osteoporosis (female sheep with dietary induced metabolic acidosis; MA). Previous studies have investigated the relationship between bone material properties and bone strength in humans and smaller animals and have shown that changes in compositional properties influence fracture risk. Here we characterize the MA model at 6 and 12 months, demonstrate the loss of bone and changes in compositional properties, and show that 6 months of treatment with both antiresorptives ameliorate the bone loss as assessed by bone mineral density and FTIRI. This preliminary data suggest that the MA sheep model allows investigation of whether drug treatments preserve bone properties that exist at the time of treatment or if they induce further beneficial changes. PMID:21597262

Calton, Ericka F.; MacLeay, Jennifer; Boskey, Adele L.

2011-01-01

197

Genetic Algorithm Phase Retrieval for the Systematic Image-Based Optical Alignment Testbed  

NASA Technical Reports Server (NTRS)

Phase retrieval requires calculation of the real-valued phase of the pupil fimction from the image intensity distribution and characteristics of an optical system. Genetic 'algorithms were used to solve two one-dimensional phase retrieval problem. A GA successfully estimated the coefficients of a polynomial expansion of the phase when the number of coefficients was correctly specified. A GA also successfully estimated the multiple p h e s of a segmented optical system analogous to the seven-mirror Systematic Image-Based Optical Alignment (SIBOA) testbed located at NASA s Marshall Space Flight Center. The SIBOA testbed was developed to investigate phase retrieval techniques. Tiphilt and piston motions of the mirrors accomplish phase corrections. A constant phase over each mirror can be achieved by an independent tip/tilt correction: the phase Conection term can then be factored out of the Discrete Fourier Tranform (DFT), greatly reducing computations.

Taylor, Jaime; Rakoczy, John; Steincamp, James

2003-01-01

198

Optical flow estimation using Fourier Mellin Transform  

Microsoft Academic Search

In this paper, we propose a novel method of computing the optical flow using the Fourier Mellin Transform (FMT). Each image in a sequence is divided into a regular grid of patches and the optical flow is estimated by calculating the phase correlation of each pair of co-sited patches using the FMT. By applying the FMT in calculating the phase

Huy Tho Ho; Roland Goecke

2008-01-01

199

A new phase difference measurement algorithm for extreme frequency signals based on discrete time Fourier transform with negative frequency contribution  

NASA Astrophysics Data System (ADS)

For the ultralow frequency signals or adjacent Nyquist frequency signals, which widely exist in vibration engineering domain, the traditional discrete time Fourier transform (DTFT) algorithms show poor performance for phase difference measurement. To improve the accuracy of phase difference measurement for these extreme frequency signals, the phase difference measurement error of DTFT algorithm is analyzed, which indicates that the negative frequency contribution is the main cause of the bias. By considering the negative frequency contribution, a new phase difference measurement algorithm for extreme frequency signals is proposed based on DTFT, and the new formulas for phase difference calculation with different windows are derived in detail. The new algorithm has stronger inhibition of spectrum leakage and has a higher accuracy than traditional DTFT algorithms. Simulation and experimental results show that the proposed algorithm has better performance than the other DTFT algorithms.

Shen, Ting'ao; Tu, Yaqing; Li, Ming; Zhang, Haitao

2015-01-01

200

Imaging of weak phase objects with a Zernike phase plate  

E-print Network

Analysis of the imaging of some simple distributions of object phase by a phase plate of Zernike type shows that sharp transitions in the object phase are well transmitted. The low-frequency components of the complete object function are attenuated by the plate. The behaviour can be characterised by a cut-on parameter defined as the product of the cut-on frequency of the plate and a characteristic dimension of the object. When this parameter exceeds a value of the order of unity, a sharp boundary in the object is imaged by a Zernike plate as a dark lining inside the boundary with a white outline or halo outside the boundary, in agreement with reported observations. The maximum diameter of objects that can be imaged accurately is inversely proportional to the diameter of the hole for beam transmission in the phase plate.

Edgcombe, C J

2013-01-01

201

Imaging of weak phase objects by a Zernike phase plate.  

PubMed

Analysis of the imaging of some simple distributions of object phase by a phase plate of Zernike type shows that sharp transitions in the object phase are well transmitted. The low-frequency components of the complete object function are attenuated by the plate. The behaviour can be characterised by a cut-on parameter defined as the product of the cut-on frequency of the plate and a characteristic dimension of the object. When this parameter exceeds a value of the order of unity, a sharp boundary in the object is imaged by a Zernike plate as a dark lining inside the boundary with a white outline or halo outside the boundary, in agreement with reported observations. The maximum diameter of objects that can be imaged accurately is inversely proportional to the diameter of the hole for beam transmission in the phase plate. PMID:24184389

Edgcombe, C J

2014-01-01

202

Nonlinear Ultrasonic Phased Array Imaging  

NASA Astrophysics Data System (ADS)

This Letter reports a technique for the imaging of acoustic nonlinearity. By contrasting the energy of the diffuse field produced through the focusing of an ultrasonic array by delayed parallel element transmission with that produced by postprocessing of sequential transmission data, acoustic nonlinearity local to the focal point is measured. Spatially isolated wave distortion is inferred without requiring interrogation of the wave at the inspection point, thereby allowing nonlinear imaging through depth.

Potter, J. N.; Croxford, A. J.; Wilcox, P. D.

2014-10-01

203

Removing Background Phase Variations in Susceptibility Weighted Imaging Using a Fast, Forward-Field Calculation  

PubMed Central

Purpose To estimate magnetic field variations induced from air-tissue interface geometry and remove their effects from susceptibility weighted imaging (SWI) data. Materials and Methods A Fourier-transform-based field estimation method is used to calculate the field deviation arising from air-tissue interface geometry. This is accomplished by, first, manually drawing or automatically detecting the sinuses, the mastoid cavity and the head geometry. The difference in susceptibility, ??, between brain tissue and air-spaces is then calculated using a residual-phase minimization approach. SWI data are corrected by subtracting the predicted phase from the original phase image. Resultant phase images are then used to perform the SWI post-processing. Results Significant improvement in the post-processed SWI data is demonstrated, most notably in the frontal and midbrain regions and to a lesser extent at the boundary of the brain. Specifically, there is much less dropout of signal after phase correction near air-tissue interfaces making it possible to see vessels and structures that were often incorrectly removed by the conventional SWI post-processing. Conclusion The Fourier-transform-based field estimation method is a powerful 3D background phase removal method for improving SW images, providing clearer images of the fore-brain and the mid-brain regions. PMID:19306433

Neelavalli, Jaladhar; Cheng, Yu-Chung N.; Jiang, Jing; Haacke, E. Mark

2009-01-01

204

Quantitative x-ray phase imaging at the nanoscale by multilayer Laue lenses  

PubMed Central

For scanning x-ray microscopy, many attempts have been made to image the phase contrast based on a concept of the beam being deflected by a specimen, the so-called differential phase contrast imaging (DPC). Despite the successful demonstration in a number of representative cases at moderate spatial resolutions, these methods suffer from various limitations that preclude applications of DPC for ultra-high spatial resolution imaging, where the emerging wave field from the focusing optic tends to be significantly more complicated. In this work, we propose a highly robust and generic approach based on a Fourier-shift fitting process and demonstrate quantitative phase imaging of a solid oxide fuel cell (SOFC) anode by multilayer Laue lenses (MLLs). The high sensitivity of the phase to structural and compositional variations makes our technique extremely powerful in correlating the electrode performance with its buried nanoscale interfacial structures that may be invisible to the absorption and fluorescence contrasts. PMID:23419650

Yan, Hanfei; Chu, Yong S.; Maser, Jörg; Nazaretski, Evgeny; Kim, Jungdae; Kang, Hyon Chol; Lombardo, Jeffrey J.; Chiu, Wilson K. S.

2013-01-01

205

Rugged high-speed rotary imaging Fourier transform spectrometer for industrial use  

NASA Astrophysics Data System (ADS)

A new rugged rotary Fourier Transform Spectrometer (FTS) has been developed. It can be used for environmental remote sensing and monitoring of chemical processes. Both single pixel and mosaic imaging configurations have been built and tested. The continuous rotary scan of the 'Turbo FT' allows operation without the laser reference of a conventional FTS, and it has been demonstrated to deliver 30 to 360 spectral scans per second and 1 cm-1 resolution, with excellent lineshape. A new 'space frame' version of the interferometer, with excellent mechanical and thermal stability, was field tested in both airborne and ground systems during the year 2000, with good results. The interferometer for this instrument is palm sized, and weighs 20 oz. It is totally sealed from the environment, and can be mounted, with its drive electronics, into a temperature stabilized enclosure for outside remote sensing applications For industrial applications, it can be used on-line or off-line, in conjunction with fiber optics, to measure and/or control multiple process lines. With the appropriate optics and detector set, the wavelength range can be adjusted from 1.0 to 25.0 micrometers. The resolution is variable from 1 to 8 cm-1. Various processors, data acquisition boards, and software have been used in the development, including the Labview package from National Instruments. Custom software for acquisition, display, and storage is being developed in summer 2001. The data acquisition system can be tailored for the speed and number of pixels required for the application. The current commercially available hardware being used can support up to 16 pixels at up to 100 scans per second.

Wadsworth, Winthrop; Dybwad, Jens-Peter

2002-02-01

206

Resampling algorithm for the Spatial Infrared Imaging Telescope (SPIRIT III) Fourier transform spectrometer  

NASA Astrophysics Data System (ADS)

The Spatial Infrared Imaging Telescope (SPIRIT III) is the primary sensor aboard the Midcourse Space Experiment (MSX), which was launched 24 April 1996. SPIRIT III included a Fourier transform spectrometer that collected terrestrial and celestial background phenomenology data for the Ballistic Missile Defense Organization (BMDO). This spectrometer used a helium-neon reference laser to measure the optical path difference (OPD) in the spectrometer and to command the analog-to-digital conversion of the infrared detector signals, thereby ensuring the data were sampled at precise increments of OPD. Spectrometer data must be sampled at accurate increments of OPD to optimize the spectral resolution and spectral position of the transformed spectra. Unfortunately, a failure in the power supply preregulator at the MSX spacecraft/SPIRIT III interface early in the mission forced the spectrometer to be operated without the reference laser until a failure investigation was completed. During this time data were collected in a backup mode that used an electronic clock to sample the data. These data were sampled evenly in time, and because the scan velocity varied, at nonuniform increments of OPD. The scan velocity profile depended on scan direction and scan length, and varied over time, greatly degrading the spectral resolution and spectral and radiometric accuracy of the measurements. The Convert software used to process the SPIRIT III data was modified to resample the clock-sampled data at even increments of OPD, using scan velocity profiles determined from ground and on-orbit data, greatly improving the quality of the clock-sampled data. This paper presents the resampling algorithm, the characterization of the scan velocity profiles, and the results of applying the resampling algorithm to on-orbit data.

Sargent, Steven D.; Greenman, Mark E.; Hansen, Scott M.

1998-11-01

207

Spatial-phase code-division multiple-access system with multiplexed Fourier holography switching for reconfigurable optical interconnection.  

PubMed

A new, to our knowledge, space-variant optical interconnection system based on a spatial-phase code-division multiple-access technique with multiplexed Fourier holography is described. In this technique a signal beam is spread over wide spatial frequencies by an M-sequence pseudorandom phase code. At a receiver side a selected signal beam is properly decoded, and at the same time its spatial pattern is shaped with a Fourier hologram, which is recorded by light that is encoded with the same M-sequence phase mask as the desired signal beam and by light whose spatial beam pattern is shaped to a signal routing pattern. Using the multiplexed holography, we can simultaneously route multisignal flows into individually specified receiver elements. The routing pattern can also be varied by means of switching the encoding phase code or replacing the hologram. We demonstrated a proof-of-principle experiment with a doubly multiplexed hologram that enables simultaneous routing of two signal beams. Using a numerical model, we showed that the proposed scheme can manage more than 250 routing patterns for one signal flow with one multiplexed hologram at a signal-to-noise ratio of ~5. PMID:18345134

Takasago, K; Takekawa, M; Shirakawa, A; Kannari, F

2000-05-10

208

Synchronous Phase-Resolving Flash Range Imaging  

NASA Technical Reports Server (NTRS)

An apparatus, now undergoing development, for range imaging based on measurement of the round-trip phase delay of a pulsed laser beam is described. The apparatus would operate in a staring mode. A pulsed laser would illuminate a target. Laser light reflected from the target would be imaged on a verylarge- scale integrated (VLSI)-circuit image detector, each pixel of which would contain a photodetector and a phase-measuring circuit. The round-trip travel time for the reflected laser light incident on each pixel, and thus the distance to the portion of the target imaged in that pixel, would be measured in terms of the phase difference between (1) the photodetector output pulse and (2) a local-oscillator signal that would have a frequency between 10 and 20 MHz and that would be synchronized with the laser-pulse-triggering signal.

Pain, Bedabrata; Hancock, Bruce

2007-01-01

209

From regular text to artistic writing and artworks: Fourier statistics of images with low and high aesthetic appeal  

PubMed Central

The spatial characteristics of letters and their influence on readability and letter identification have been intensely studied during the last decades. There have been few studies, however, on statistical image properties that reflect more global aspects of text, for example properties that may relate to its aesthetic appeal. It has been shown that natural scenes and a large variety of visual artworks possess a scale-invariant Fourier power spectrum that falls off linearly with increasing frequency in log-log plots. We asked whether images of text share this property. As expected, the Fourier spectrum of images of regular typed or handwritten text is highly anisotropic, i.e., the spectral image properties in vertical, horizontal, and oblique orientations differ. Moreover, the spatial frequency spectra of text images are not scale-invariant in any direction. The decline is shallower in the low-frequency part of the spectrum for text than for aesthetic artworks, whereas, in the high-frequency part, it is steeper. These results indicate that, in general, images of regular text contain less global structure (low spatial frequencies) relative to fine detail (high spatial frequencies) than images of aesthetics artworks. Moreover, we studied images of text with artistic claim (ornate print and calligraphy) and ornamental art. For some measures, these images assume average values intermediate between regular text and aesthetic artworks. Finally, to answer the question of whether the statistical properties measured by us are universal amongst humans or are subject to intercultural differences, we compared images from three different cultural backgrounds (Western, East Asian, and Arabic). Results for different categories (regular text, aesthetic writing, ornamental art, and fine art) were similar across cultures. PMID:23554592

Melmer, Tamara; Amirshahi, Seyed A.; Koch, Michael; Denzler, Joachim; Redies, Christoph

2013-01-01

210

Gas-phase Fourier Transform Far-Infrared Spectroscopy of Astrophycical Species  

Microsoft Academic Search

In the next future, space-based and ground-based missions will produced high spatial and spectral resolution data of the Universe. Consequently, laboratory measurements are necessary to complete the spectroscopic knowledge of important molecules. We have measured emission and absorption spectra of several species by Fourier transform spectroscopy in the range 60 - 600 cm-1 (2 - 20 THz) at Doppler-limited resolution.

O. Pirali; M. Vervloet

2003-01-01

211

Image Display and Manipulation System (IDAMS) program documentation, Appendixes A-D. [including routines, convolution filtering, image expansion, and fast Fourier transformation  

NASA Technical Reports Server (NTRS)

The IDAMS Processor is a package of task routines and support software that performs convolution filtering, image expansion, fast Fourier transformation, and other operations on a digital image tape. A unique task control card for that program, together with any necessary parameter cards, selects each processing technique to be applied to the input image. A variable number of tasks can be selected for execution by including the proper task and parameter cards in the input deck. An executive maintains control of the run; it initiates execution of each task in turn and handles any necessary error processing.

Cecil, R. W.; White, R. A.; Szczur, M. R.

1972-01-01

212

Computer-generated phase-modulated full parallax holographic stereograms without conjugate images  

NASA Astrophysics Data System (ADS)

A pure phase-modulated computer-generated hologram (CGH) method is presented to generate a full parallax holographic stereogram. The holographic stereogram plane is divided into several two-dimensional holographic elements (hogels). The spectra of the hogels are rendered from multiview full parallax images of three-dimensional (3-D) objects. The phase-modulated hogel is calculated by iterative Fourier transform algorithms to improve diffraction efficiency and eliminate conjugate images. A gray calibration technique is introduced to generate the accurate intensity modulation of pure phase hogels. The holographic stereogram that we proposed is reconstructed by an optical system based on a phase only spatial light modulator. The experimental results demonstrate that our proposed method can successfully reconstruct parallax images of 3-D objects.

Pei, Chuang; Yan, Xingpeng; Jiang, Xiaoyu

2014-10-01

213

Two-dimensional gratings-based phase-contrast imaging using a conventional x-ray tube.  

PubMed

A Talbot-Lau interferometer using two-dimensional gratings and a conventional x-ray tube has been used to investigate a phase-contrast imaging technique that is sensitive to phase gradients in two orthogonal directions. Fourier analysis of Moiré fringe patterns was introduced to obtain differential phase images and scattering images from a single exposure. Two-dimensional structures of plastic phantoms and characteristic features of soft tissue were clearly obtained at 17.5 keV. The phase-stepping technique was also examined to investigate the spatial resolution of different phase retrieval methods. In the presented setup we found that the choice of phase retrieval method made little difference in image blur, and a large effective source size was found to give a high intensity in the image plane. PMID:21931387

Sato, Genta; Kondoh, Takeshi; Itoh, Hidenosuke; Handa, Soichiro; Yamaguchi, Kimiaki; Nakamura, Takashi; Nagai, Kentaro; Ouchi, Chidane; Teshima, Takayuki; Setomoto, Yutaka; Den, Toru

2011-09-15

214

Phase unwrapping problems in ISAR images  

NASA Astrophysics Data System (ADS)

The problem of the phase unwrapping in the ISAR (Interoferometric Synthetic Aperture Radar) images is studied. This problem is tricky when the image is noisy and when the local gradient is high (like in mountainous areas). A theoretical approach is chosen and work in a continuous space is carried out. A formal analogy with a problem of magnetostatics is proposed, and, using simple physics tools, an expression of the unwrapped phase is obtained. Unfortunately this result is not fully transposable to a discrete space (real case). However, implementations which would improve the performance of the existing algorithms are discussed.

Veran, Jean-Pierre

1992-12-01

215

Bilateral filtering of magnetic resonance phase images.  

PubMed

High-pass filtering is required for the removal of background field inhomogeneities in magnetic resonance phase images. This high-pass filtering smooths across boundaries between areas with large differences in phase. The most prominent boundary is the surface of the brain where areas with large phase values inside the brain are located close to areas outside the brain where the phase is, on average, zero. Cortical areas, which are of great interest in brain MRI, are therefore often degraded by high-pass filtering. Here, we propose the use of the bilateral filter for the high-pass filtering step. The bilateral filter is essentially a Gaussian filter that stops smoothing at boundaries. We show that the bilateral filter improves image quality at the brain's surface, without sacrificing contrast within the brain. PMID:21664782

McPhee, Kelly C; Denk, Christian; Al-Rekabi, Zeinab; Rauscher, Alexander

2011-09-01

216

A Synthetic Quadrature Phase Detector/Demodulator for Fourier Transform Transform Spectrometers  

NASA Technical Reports Server (NTRS)

A method is developed to demodulate (velocity correct) Fourier transform spectrometer (FTS) data that is taken with an analog to digital converter that digitizes equally spaced in time. This method makes it possible to use simple low cost, high resolution audio digitizers to record high quality data without the need for an event timer or quadrature laser hardware, and makes it possible to use a metrology laser of any wavelength. The reduced parts count and simplicity implementation makes it an attractive alternative in space based applications when compared to previous methods such as the Brault algorithm.

Campbell, Joel

2008-01-01

217

Imaging IR spectrometer, phase 2  

NASA Technical Reports Server (NTRS)

The development is examined of a prototype multi-channel infrared imaging spectrometer. The design, construction and preliminary performance is described. This instrument is intended for use with JPL Table Mountain telescope as well as the 88 inch UH telescope on Mauna Kea. The instrument is capable of sampling simultaneously the spectral region of 0.9 to 2.6 um at an average spectral resolution of 1 percent using a cooled (77 K) optical bench, a concave holographic grating and a special order sorting filter to allow the acquisition of the full spectral range on a 128 x 128 HgCdTe infrared detector array. The field of view of the spectrometer is 0.5 arcsec/pixel in mapping mode and designed to be 5 arcsec/pixel in spot mode. The innovative optical design has resulted in a small, transportable spectrometer, capable of remote operation. Commercial applications of this spectrometer design include remote sensing from both space and aircraft platforms as well as groundbased astronomical observations.

Gradie, Jonathan; Lewis, Ralph; Lundeen, Thomas; Wang, Shu-I

1990-01-01

218

Quadriwave lateral shearing interferometry for quantitative phase microscopy: coupling phase imaging and fluorescence imaging  

NASA Astrophysics Data System (ADS)

Phase imaging with a high-resolution wavefront sensor is a useful setup for biological imaging. Our setup is based on a quadriwave lateral shearing interferometer mounted on a commercial non-modified transmission white-light microscope. That allows us to make simultaneous measurement in both quantitative transmission phase and fluorescence imaging. We propose here to study co-localization between phase and fluorescence on african green monkey kidney COS7 cells. Phase permits an enhanced visualization of the whole cell and intracellular components while the fluorescence allows a complete identification of each component. Post treatments on phase-shift images are proposed and become very interesting for enhanced visualization of small details such as vesicles or mitochondrias.

Bon, Pierre; Savatier, Julien; Wattellier, Benoit; Marguet, Didier; Monneret, Serge

2011-03-01

219

Level 0 to 1 processing of the imaging Fourier transform spectrometer GLORIA: generation of radiometrically and spectrally calibrated spectra  

NASA Astrophysics Data System (ADS)

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an imaging Fourier transform spectrometer that is capable of operating on various high-altitude research aircraft. It measures the atmospheric emission in the thermal infrared spectral region in limb and nadir geometry. GLORIA consists of a classical Michelson interferometer combined with an infrared camera. The infrared detector has a usable area of 128 × 128 pixels, measuring up to 16 384 interferograms simultaneously. Imaging Fourier transform spectrometers impose a number of challenges with respect to instrument calibration and algorithm development. The optical setup with extremely high optical throughput requires the development of new methods and algorithms for spectral and radiometric calibration. Due to the vast amount of data there is a high demand for scientifically intelligent optimisation of the data processing. This paper outlines the characterisation and processing steps required for the generation of radiometrically and spectrally calibrated spectra. Methods for performance optimisation of the processing algorithm are presented. The performance of the data processing and the quality of the calibrated spectra are demonstrated for measurements collected during the first deployments of GLORIA on aircraft.

Kleinert, A.; Friedl-Vallon, F.; Guggenmoser, T.; Höpfner, M.; Neubert, T.; Ribalda, R.; Sha, M. K.; Ungermann, J.; Blank, J.; Ebersoldt, A.; Kretschmer, E.; Latzko, T.; Oelhaf, H.; Olschewski, F.; Preusse, P.

2014-12-01

220

Phase-Scrambler Plate Spreads Point Image  

NASA Technical Reports Server (NTRS)

Array of small prisms retrofit to imaging lens. Phase-scrambler plate essentially planar array of small prisms partitioning aperture of lens into many subapertures, and prism at each subaperture designed to divert relatively large diffraction spot formed by that subaperture to different, specific point on focal plane.

Edwards, Oliver J.; Arild, Tor

1992-01-01

221

Digitizing Images for Curriculum 21: Phase II.  

ERIC Educational Resources Information Center

Although visual databases exist for the study of art, architecture, geography, health care, and other areas, readily accessible sources of quality images are not available for engineering faculty interested in developing multimedia modules or for student projects. Presented here is a brief review of Phase I of the Engineering Visual Database…

Walker, Alice D.

222

Ultrahigh-speed imaging of the rat retina using ultrahigh-resolution spectral/Fourier domain OCT  

NASA Astrophysics Data System (ADS)

We performed OCT imaging of the rat retina at 70,000 axial scans per second with ~3 ?m axial resolution. Three-dimensional OCT (3D-OCT) data sets of the rat retina were acquired. The high speed and high density data sets enable improved en face visualization by reducing eye motion artifacts and improve Doppler OCT measurements. Minimal motion artifacts were visible and the OCT fundus images offer more precise registration of individual OCT images to retinal fundus features. Projection OCT fundus images show features such as the nerve fiber layer, retinal capillary networks and choroidal vasculature. Doppler OCT images and quantitative measurements show pulsatility in retinal blood vessels. Doppler OCT provides noninvasive in vivo quantitative measurements of retinal blood flow properties and may benefit studies of diseases such as glaucoma and diabetic retinopathy. Ultrahigh speed imaging using ultrahigh resolution spectral / Fourier domain OCT promises to enable novel protocols for measuring small animal retinal structure and retinal blood flow. This non-invasive imaging technology is a promising tool for monitoring disease progression in rat and mouse models to assess ocular disease pathogenesis and response to treatment.

Liu, Jonathan J.; Potsaid, Benjamin; Chen, Yueli; Gorczynska, Iwona; Srinivasan, Vivek J.; Duker, Jay S.; Fujimoto, James G.

2010-02-01

223

Color image hiding based on the phase retrieval technique and Arnold transform.  

PubMed

A new (to our knowledge) method is proposed in this paper for color image hiding and extracting using the phase retrieval algorithm in the fractional Fourier transform (FRFT) domain and Arnold transform (ART). Based on a cascaded phase iterative FRFT algorithm, the three channels (R, G, and B) of the secret color image permuted by ART are encrypted. Then the encoded information is embedded in the blue channel (B channel) of the enlarged color host image. Using the security enhanced encryption method, not only the random phase mask and the wavelength but also the transform parameters of ART and FRFT are provided as additional keys for decryption. It is shown that the security of information hiding will be enhanced. Computer simulations are performed to show the hiding capacity of the proposed system. Numerical results are presented to verify the validity and efficiency of the proposed method. PMID:21556114

Shi, Xiaoyan; Zhao, Daomu

2011-05-10

224

3-D Image Registration Using Fast Fourier Transform, with Potential Applications to Geoinformatics and Bioinformatics  

E-print Network

.g., in protein docking) and geoin- formatics (e.g., in earth modeling). Keywords: Image Registration, 3- D Images and Bioinformatics Roberto Araiza Matthew G. Averill G. Randy Keller Scott A. Starks NASA Pan-American Center images. Registration of 3-D images is an important prob- lem in areas such as bioinformatics (e

Texas at Austin, University of

225

3D Image Registration Using Fast Fourier Transform, with Potential Applications to Geoinformatics and Bioinformatics  

E-print Network

.g., in protein docking) and geoin­ formatics (e.g., in earth modeling). Keywords: Image Registration, 3­ D Images and Bioinformatics Roberto Araiza Matthew G. Averill G. Randy Keller Scott A. Starks NASA Pan­American Center images. Registration of 3­D images is an important prob­ lem in areas such as bioinformatics (e

Ward, Karen

226

Cardiac phase detection in intravascular ultrasound images  

NASA Astrophysics Data System (ADS)

Image gating is related to image modalities that involve quasi-periodic moving organs. Therefore, during intravascular ultrasound (IVUS) examination, there is cardiac movement interference. In this paper, we aim to obtain IVUS gated images based on the images themselves. This would allow the reconstruction of 3D coronaries with temporal accuracy for any cardiac phase, which is an advantage over the ECG-gated acquisition that shows a single one. It is also important for retrospective studies, as in existing IVUS databases there are no additional reference signals (ECG). From the images, we calculated signals based on average intensity (AI), and, from consecutive frames, average intensity difference (AID), cross-correlation coefficient (CC) and mutual information (MI). The process includes a wavelet-based filter step and ascendant zero-cross detection in order to obtain the phase information. Firstly, we tested 90 simulated sequences with 1025 frames each. Our method was able to achieve more than 95.0% of true positives and less than 2.3% of false positives ratio, for all signals. Afterwards, we tested in a real examination, with 897 frames and ECG as gold-standard. We achieved 97.4% of true positives (CC and MI), and 2.5% of false positives. For future works, methodology should be tested in wider range of IVUS examinations.

Matsumoto, Monica M. S.; Lemos, Pedro Alves; Yoneyama, Takashi; Furuie, Sergio Shiguemi

2008-03-01

227

Method of spectral subtraction of gas-phase Fourier transform infrared (FT-IR) spectra by minimizing the spectrum length.  

PubMed

A new method of spectral subtraction for gas-phase Fourier transform infrared (FT-IR) spectra was developed for long-path gas measurements. The method is based on minimization of the length of the spectrum that results from subtracting the spectrum of an individual component of a gas mixture (water, CO(2), etc.) from the experimental spectrum of the mixture. For this purpose a subtraction coefficient (k(min)) is found for which the length of the resulting spectrum is minimized. A mathematical simulation with two Lorentzian absorption bands was conducted and the limits of application for the proposed method were determined. Two experimental examples demonstrate that a successful result could be achieved in the case when the subtrahend spectrum contains a number of narrow absorption bands (such as the spectrum of water vapor). PMID:21819781

Kozlov, Denis; Besov, Alexey

2011-08-01

228

Wave-front reconstruction from shear phase maps by use of the discrete Fourier transform.  

PubMed

Fast wave-front reconstruction methods are becoming increasingly important, for example, in large astronomical adaptive optics systems and high spatial resolution shear interferometry, where pseudoinverse matrix methods scale poorly with problem size. Wave-front reconstruction from difference measurements can be achieved by use of fast implementations of the discrete Fourier transform (DFT), obtaining performance comparable with that of the pseudoinverse in terms of the noise propagation coefficient. Existing methods that are based on the use of the DFT give exact results (in the absence of noise) only for the particular case in which the shear is a divisor of the number of samples to be reconstructed. We present two alternate solutions for the more general case when the shear is any integer. In the first solution the dimensions of the problem are enlarged, and in the second the problem is subdivided into a set of smaller problems with shear amplitude equal to one. We also show that the retrieved solutions have minimum norm and calculate the noise propagation coefficient for both methods. The proposed algorithms are implemented and timed against pseudoinverse multiplication. The results show a speed increase by a factor of 50 over the pseudoinverse multiplication for a grid with N = 3 x 10(3) samples. PMID:15008490

Dubra, Alfredo; Paterson, Carl; Dainty, Christopher

2004-02-10

229

Automated Processing of Shoeprint Images Based on the Fourier Transform for Use in Forensic Science  

Microsoft Academic Search

The development of a system for automatically sorting a database of shoeprint images based on the outsole pattern in response to a reference shoeprint image is presented. The database images are sorted so that those from the same pattern group as the reference shoeprint are likely to be at the start of the list. A database of 476 complete shoeprint

Philip De Chazal; John Flynn; Richard B. Reilly

2005-01-01

230

[Research of dual-photoelastic-modulator-based beat frequency modulation and Fourier-Bessel transform imaging spectrometer].  

PubMed

As the existing photoelastic-modulator(PEM) modulating frequency in the tens of kHz to hundreds of kHz between, leading to frequency of modulated interference signal is higher, so ordinary array detector cannot effectively caprure interference signal..A new beat frequency modulation method based on dual-photoelastic-modulator (Dual-PEM) and Fourier-Bessel transform is proposed as an key component of dual-photoelastic-modulator-based imaging spectrometer (Dual-PEM-IS) combined with charge coupled device (CCD). The dual-PEM are operated as an electro-optic circular retardance modulator, Operating the PEMs at slightly different resonant frequencies w1 and w2 respectively, generates a differential signal at a much lower heterodyne frequency that modulates the incident light. This method not only retains the advantages of the existing PEM, but also the frequency of modulated photocurrent decreased by 2-3 orders of magnitude (10-500 Hz) and can be detected by common array detector, and the incident light spectra can be obtained by Fourier-Bessel transform of low frequency component in the modulated signal. The method makes the PEM has the dual capability of imaging and spectral measurement. The basic principle is introduced, the basic equations is derived, and the feasibility is verified through the corresponding numerical simulation and experiment. This method has' potential applications in imaging spectrometer technology, and analysis of the effect of deviation of the optical path difference. This work provides the necessary theoretical basis for remote sensing of new Dual-PEM-IS and for engineering implementation of spectra inversion. PMID:24822442

Wang, Zhi-Bin; Zhang, Rui; Wang, Yao-Li; Huang, Yan-Fei; Chen, You-Hua; Wang, Li-Fu; Yang, Qiang

2014-02-01

231

Phase error suppression by low-pass filtering for synthetic aperture imaging ladar  

NASA Astrophysics Data System (ADS)

Compared to synthetic aperture radar (SAR), synthetic aperture imaging ladar (SAIL) is more sensitive to the phase errors induced by atmospheric turbulence, undesirable line-of-sight translation-vibration and waveform phase error, because the light wavelength is about 3-6 orders of magnitude less than that of the radio frequency. This phase errors will deteriorate the imaging results. In this paper, an algorithm based on low-pass filtering to suppress the phase error is proposed. In this algorithm, the azimuth quadratic phase history with phase error is compensated, then the fast Fourier transform (FFT) is performed in azimuth direction, after the low-pass filtering, the inverse FFT is performed, then the image is reconstructed simultaneously in the range and azimuth direction by the two-dimensional (2D) FFT. The highfrequency phase error can be effectively eliminated hence the imaging results can be optimized by this algorithm. The mathematical analysis by virtue of data-collection equation of side-looking SAIL is presented. The theoretical modeling results are also given. In addition, based on this algorithm, a principle scheme of optical processor is proposed. The verified experiment is performed employing the data obtained from a SAIL demonstrator.

Sun, Zhiwei; Hou, Peipei; Zhi, Ya'nan; Sun, Jianfeng; Zhou, Yu; Xu, Qian; Lu, Zhiyong; Liu, Liren

2014-09-01

232

Turbulence Mitigation in Phase-Conjugated Two-Photon Imaging  

E-print Network

It is shown that the use of phase conjugation in one arm of a correlated two-photon imaging apparatus allows undistorted ghost imaging through a region with randomly-varying phase shifts. The images are formed from correlated pairs of photons in such a way that turbulence-induced phase shifts gained by the photons during passage through the medium cancel pairwise.

David S. Simon; Alexander V. Sergienko

2011-06-26

233

Scanning hard x-ray differential phase contrast imaging with a double wedge absorber  

SciTech Connect

Two-directional differential phase contrast images were measured using an x-ray microbeam and a double wedge absorber. The wedge absorber converts the displacement of an x-ray beam that is refracted by an object into change of x-ray intensity. The double wedge absorber made it possible to detect values of two-directional refraction angle with {mu}rad sensitivity simultaneously. By Fourier integration of two-directional phase gradients calculated from the refraction angle instead of line integration of one-directional phase gradients, we obtained a quantitative phase map without artifacts even when only a part of the boundaries of the object were in the field of view. One of the characteristics of this technique is flexibility in a sensitivity of the phase gradient. By changing of shape or material of the wedge absorber, it is comparatively easy to control the detection limit of the refraction angle.

Mukaide, Taihei; Takada, Kazuhiro; Watanabe, Masatoshi; Noma, Takashi [Materials Technology Development Center, Canon Inc., 30-2, Shimomaruko 3-chome, Ohta-ku, Tokyo 146-8501 (Japan); Iida, Atsuo [Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization, 1-1, Oho Tsukuba, Ibaraki 305-0801 (Japan)

2009-03-15

234

Understanding and overcoming scene-change artifacts in imaging Fourier-transform spectroscopy of turbulent jet engine exhaust  

NASA Astrophysics Data System (ADS)

Jet engine exhaust radiates strongly in the midwave infrared due to line emission from combustion byproducts such as CO2, CO, and H2O. Imaging Fourier-transform spectrometers (IFTS) have the potential to measure spatial variations in plume temperature and density. However, the turbulent flow yields rapid, stochastic fluctuations in radiance during interferometric measurements which corrupt corresponding spectra. A novel, statistics-based method of interpreting a time-sequence of interferograms collected from a stochastic blackbody source is presented which enables good estimation of the underlying temperature distribution. It is shown that the median (and various other quantiles) interferograms afford unbiased spectral estimates of temperature upon Fourier transformation, in contrast to temperature estimates based on spectra obtained from mean interferograms. This method is then applied to IFTS data (200×64 pixels at 1cm-1 resolution) of a turbulent exhaust plume from a small turbojet engine. Spatial maps of brightness temperature and estimates of turbulence-induced temperature distribution are presented.

Tremblay, Pierre; Gross, Kevin C.; Farley, Vincent; Chamberland, Martin; Villemaire, André; Perram, Glen P.

2009-08-01

235

Fourier Series Approximation  

NSDL National Science Digital Library

This site includes a Java applet that displays Fourier series approximations and corresponding magnitude and phase spectra of a periodic continuous-time signal. Select from provided signals, or draw a signal with the mouse.

2012-08-14

236

Far-infrared Fourier transform emission spectroscopy in the gas phase  

Microsoft Academic Search

We report in this Letter several techniques that we have developed for emission spectroscopy in the far-infrared spectral region (30–500cm?1) using a high resolution interferometer. The thermal emission of gas phase polycyclic aromatic hydrocarbons has been recorded from a furnace while the spectra of lighter molecules and radicals, such as H2O, OH, NH3, NH2 and HCN, were obtained from a

O. Pirali; M. Vervloet

2006-01-01

237

Classification of Carpiodes Using Fourier Descriptors: A Content Based Image Retrieval Approach  

Microsoft Academic Search

Taxonomic classification has always been important to the study of any biological system. Many biological species will go unclassified and become lost forever at the current rate of classification. The current state of computer technology makes image storage and retrieval possible on a global level. As a result, computer-aided taxonomy is now possible. Content based image retrieval techniques utilize visual

Patrick Trahan

2009-01-01

238

High-Spatial- and High-Temporal-Resolution Dynamic Contrast-enhanced MR Breast Imaging with Sweep Imaging with Fourier Transformation: A Pilot Study.  

PubMed

Purpose To report the results of sweep imaging with Fourier transformation (SWIFT) magnetic resonance (MR) imaging for diagnostic breast imaging. Materials and Methods Informed consent was obtained from all participants under one of two institutional review board-approved, HIPAA-compliant protocols. Twelve female patients (age range, 19-54 years; mean age, 41.2 years) and eight normal control subjects (age range, 22-56 years; mean age, 43.2 years) enrolled and completed the study from January 28, 2011, to March 5, 2013. Patients had previous lesions that were Breast Imaging Reporting and Data System 4 and 5 based on mammography and/or ultrasonographic imaging. Contrast-enhanced SWIFT imaging was completed by using a 4-T research MR imaging system. Noncontrast studies were completed in the normal control subjects. One of two sized single-breast SWIFT-compatible transceiver coils was used for nine patients and five controls. Three patients and five control subjects used a SWIFT-compatible dual breast coil. Temporal resolution was 5.9-7.5 seconds. Spatial resolution was 1.00 mm isotropic, with later examinations at 0.67 mm isotropic, and dual breast at 1.00 mm or 0.75 mm isotropic resolution. Results Two nonblinded breast radiologists reported SWIFT image findings of normal breast tissue, benign fibroadenomas (six of six lesions), and malignant lesions (10 of 12 lesions) concordant with other imaging modalities and pathologic reports. Two lesions in two patients were not visualized because of coil field of view. The images yielded by SWIFT showed the presence and extent of known breast lesions. Conclusion The SWIFT technique could become an important addition to breast imaging modalities because it provides high spatial resolution at all points during the dynamic contrast-enhanced examination. © RSNA, 2014. PMID:25247405

Corum, Curtis A; Benson, John C; Idiyatullin, Djaudat; Snyder, Angela L; Snyder, Carl J; Hutter, Diane; Everson, Lenore I; Eberly, Lynn E; Nelson, Michael T; Garwood, Michael

2015-02-01

239

In Vivo 3D Meibography of the Human Eyelid Using Real Time Imaging Fourier-Domain OCT.  

PubMed

Recently, we reported obtaining tomograms of meibomian glands from healthy volunteers using commercial anterior segment optical coherence tomography (AS-OCT), which is widely employed in clinics for examination of the anterior segment. However, we could not create 3D images of the meibomian glands, because the commercial OCT does not have a 3D reconstruction function. In this study we report the creation of 3D images of the meibomian glands by reconstructing the tomograms of these glands using high speed Fourier-Domain OCT (FD-OCT) developed in our laboratory. This research was jointly undertaken at the Department of Ophthalmology, Seoul St. Mary's Hospital (Seoul, Korea) and the Advanced Photonics Research Institute of Gwangju Institute of Science and Technology (Gwangju, Korea) with two healthy volunteers and seven patients with meibomian gland dysfunction. A real time imaging FD-OCT system based on a high-speed wavelength swept laser was developed that had a spectral bandwidth of 100 nm at the 1310 nm center wavelength. The axial resolution was 5 µm and the lateral resolution was 13 µm in air. Using this device, the meibomian glands of nine subjects were examined. A series of tomograms from the upper eyelid measuring 5 mm (from left to right, B-scan) × 2 mm (from upper part to lower part, C-scan) were collected. Three-D images of the meibomian glands were then reconstructed using 3D "data visualization, analysis, and modeling software". Established infrared meibography was also performed for comparison. The 3D images of healthy subjects clearly showed the meibomian glands, which looked similar to bunches of grapes. These results were consistent with previous infrared meibography results. The meibomian glands were parallel to each other, and the saccular acini were clearly visible. Here we report the successful production of 3D images of human meibomian glands by reconstructing tomograms of these glands with high speed FD-OCT. PMID:23805297

Hwang, Ho Sik; Shin, Jun Geun; Lee, Byeong Ha; Eom, Tae Joong; Joo, Choun-Ki

2013-01-01

240

In Vivo 3D Meibography of the Human Eyelid Using Real Time Imaging Fourier-Domain OCT  

PubMed Central

Recently, we reported obtaining tomograms of meibomian glands from healthy volunteers using commercial anterior segment optical coherence tomography (AS-OCT), which is widely employed in clinics for examination of the anterior segment. However, we could not create 3D images of the meibomian glands, because the commercial OCT does not have a 3D reconstruction function. In this study we report the creation of 3D images of the meibomian glands by reconstructing the tomograms of these glands using high speed Fourier-Domain OCT (FD-OCT) developed in our laboratory. This research was jointly undertaken at the Department of Ophthalmology, Seoul St. Mary's Hospital (Seoul, Korea) and the Advanced Photonics Research Institute of Gwangju Institute of Science and Technology (Gwangju, Korea) with two healthy volunteers and seven patients with meibomian gland dysfunction. A real time imaging FD-OCT system based on a high-speed wavelength swept laser was developed that had a spectral bandwidth of 100 nm at the 1310 nm center wavelength. The axial resolution was 5 µm and the lateral resolution was 13 µm in air. Using this device, the meibomian glands of nine subjects were examined. A series of tomograms from the upper eyelid measuring 5 mm (from left to right, B-scan) × 2 mm (from upper part to lower part, C-scan) were collected. Three-D images of the meibomian glands were then reconstructed using 3D “data visualization, analysis, and modeling software”. Established infrared meibography was also performed for comparison. The 3D images of healthy subjects clearly showed the meibomian glands, which looked similar to bunches of grapes. These results were consistent with previous infrared meibography results. The meibomian glands were parallel to each other, and the saccular acini were clearly visible. Here we report the successful production of 3D images of human meibomian glands by reconstructing tomograms of these glands with high speed FD-OCT. PMID:23805297

Hwang, Ho Sik; Shin, Jun Geun; Lee, Byeong Ha; Eom, Tae Joong; Joo, Choun-Ki

2013-01-01

241

Proteoglycan concentrations in healthy and diseased articular cartilage by Fourier transform infrared imaging and principal component regression.  

PubMed

Fourier transform infrared imaging (FTIRI) combining with principal component regression (PCR) analysis were used to determine the reduction of proteoglycan (PG) in articular cartilage after the transection of the anterior cruciate ligament (ACL). A number of canine knee cartilage sections were harvested from the meniscus-covered and meniscus-uncovered medial tibial locations from the control joints, the ACL joints at three time points after the surgery, and their contralateral joints. The PG loss in the ACL cartilage was related positively to the durations after the surgery. The PG loss in the contralateral knees was less than that of the ACL knees. The PG loss in the meniscus-covered cartilage was less than that of the meniscus-uncovered tissue in both ACL and contralateral knees. The quantitative mapping of PG loss could monitor the disease progression and repair processes in arthritis. PMID:25000570

Yin, Jianhua; Xia, Yang

2014-12-10

242

Genetic algorithms applied to Fourier-descriptor-based geometric models for anatomical object recognition in medical images  

NASA Astrophysics Data System (ADS)

In this work we encode the shape complexity of a search object using 3D Fourier descriptors (FDs) and allow genetic algorithms (GAs) to optimize the object's shape and position. Using magnetic resonance image (MRI) data, we perform an approximate segmentation on one lateral ventricle in the brain and use the FDs from this as seeding values for the GAs to search for the left and right lateral ventricles in subsequent 3D data sets. We show that the method is capable of coping with normal biological variation. We compare a GA-guided segmentation with an interactive region growing method and find an agreement of not less than 80 plus or minus 6% in voxel classification with a corresponding average edge placement error of 2.2 plus or minus 0.4 mm. Finally we examine how the optimization can be speeded up by a distributed parallel implementation.

Delibasis, Kostas; Undrill, Peter E.; Cameron, George G.

1996-04-01

243

Fourier transform-infrared studies of thin HâSOâ\\/HâO films: Formation, water uptake, and solid-liquid phase changes  

Microsoft Academic Search

Fourier transform-infrared (FTIR) spectroscopy was used to examine films representative of stratospheric sulfuric acid aerosols. Thin films of sulfuric acid were formed in situ by the condensed phase reaction of SOâ with HâO. FTIR spectra show that the sulfuric acid films absorb water while cooling in the presence of water vapor. Using stratospheric water pressures, the most dilute solutions observed

Ann M. Middlebrook; Laura T. Iraci; Laurie S. Mcneill; Birgit G. Koehler; Margaret A. Wilson; Ole W. Saastad; Margaret A. Tolbert; David R. Hanson

1993-01-01

244

Multicontrast x-ray computed tomography imaging using Talbot-Lau interferometry without phase stepping  

PubMed Central

Purpose: The purpose of this work is to demonstrate that multicontrast computed tomography (CT) imaging can be performed using a Talbot-Lau interferometer without phase stepping, thus allowing for an acquisition scheme like that used for standard absorption CT. Methods: Rather than using phase stepping to extract refraction, small-angle scattering (SAS), and absorption signals, the two gratings of a Talbot-Lau interferometer were rotated slightly to generate a moiré pattern on the detector. A Fourier analysis of the moiré pattern was performed to obtain separate projection images of each of the three contrast signals, all from the same single-shot of x-ray exposure. After the signals were extracted from the detector data for all view angles, image reconstruction was performed to obtain absorption, refraction, and SAS CT images. A physical phantom was scanned to validate the proposed data acquisition method. The results were compared with a phantom scan using the standard phase stepping approach. Results: The reconstruction of each contrast mechanism produced the expected results. Signal levels and contrasts match those obtained using the phase stepping technique. Conclusions: Absorption, refraction, and SAS CT imaging can be achieved using the Talbot-Lau interferometer without the additional overhead of long scan time and phase stepping. PMID:22225312

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

2012-01-01

245

Multicontrast x-ray computed tomography imaging using Talbot-Lau interferometry without phase stepping  

SciTech Connect

Purpose: The purpose of this work is to demonstrate that multicontrast computed tomography (CT) imaging can be performed using a Talbot-Lau interferometer without phase stepping, thus allowing for an acquisition scheme like that used for standard absorption CT. Methods: Rather than using phase stepping to extract refraction, small-angle scattering (SAS), and absorption signals, the two gratings of a Talbot-Lau interferometer were rotated slightly to generate a moire pattern on the detector. A Fourier analysis of the moire pattern was performed to obtain separate projection images of each of the three contrast signals, all from the same single-shot of x-ray exposure. After the signals were extracted from the detector data for all view angles, image reconstruction was performed to obtain absorption, refraction, and SAS CT images. A physical phantom was scanned to validate the proposed data acquisition method. The results were compared with a phantom scan using the standard phase stepping approach. Results: The reconstruction of each contrast mechanism produced the expected results. Signal levels and contrasts match those obtained using the phase stepping technique. Conclusions: Absorption, refraction, and SAS CT imaging can be achieved using the Talbot-Lau interferometer without the additional overhead of long scan time and phase stepping.

Bevins, Nicholas; Zambelli, Joseph; Li Ke; Qi Zhihua; Chen Guanghong [Department of Medical Physics, University of Wisconsin-Madison, 1111 Highland Avenue, Madison, Wisconsin 53705 (United States); Department of Medical Physics, University of Wisconsin-Madison, 1111 Highland Avenue, Madison, Wisconsin 53705 (United States) and Department of Radiology, University of Wisconsin-Madison, 600 Highland Avenue, Madison, Wisconsin 53792 (United States)

2012-01-15

246

PHASED ARRAY FEED CALIBRATION, BEAMFORMING, AND IMAGING  

SciTech Connect

Phased array feeds (PAFs) for reflector antennas offer the potential for increased reflector field of view and faster survey speeds. To address some of the development challenges that remain for scientifically useful PAFs, including calibration and beamforming algorithms, sensitivity optimization, and demonstration of wide field of view imaging, we report experimental results from a 19 element room temperature L-band PAF mounted on the Green Bank 20 Meter Telescope. Formed beams achieved an aperture efficiency of 69% and a system noise temperature of 66 K. Radio camera images of several sky regions are presented. We investigate the noise performance and sensitivity of the system as a function of elevation angle with statistically optimal beamforming and demonstrate cancelation of radio frequency interference sources with adaptive spatial filtering.

Landon, Jonathan; Elmer, Michael; Waldron, Jacob; Jones, David; Stemmons, Alan; Jeffs, Brian D.; Warnick, Karl F. [Department of Electrical and Computer Engineering, Brigham Young University, 459 Clyde Building, Provo, UT 84602 (United States); Richard Fisher, J. [National Radio Astronomy Observatory, Charlottesville, VA (United States); Norrod, Roger D. [National Radio Astronomy Observatory, Green Bank, WV (United States)

2010-03-15

247

Phased Array Feed Calibration, Beamforming and Imaging  

E-print Network

Phased array feeds (PAFs) for reflector antennas offer the potential for increased reflector field of view and faster survey speeds. To address some of the development challenges that remain for scientifically useful PAFs, including calibration and beamforming algorithms, sensitivity optimization, and demonstration of wide field of view imaging, we report experimental results from a 19 element room temperature L-band PAF mounted on the Green Bank 20-Meter Telescope. Formed beams achieved an aperture efficiency of 69% and system noise temperature of 66 K. Radio camera images of several sky regions are presented. We investigate the noise performance and sensitivity of the system as a function of elevation angle with statistically optimal beamforming and demonstrate cancelation of radio frequency interference sources with adaptive spatial filtering.

Landon, Jonathan; Waldron, Jacob; Jones, David; Stemmons, Alan; Jeffs, Brian D; Warnick, Karl F; Fisher, J Richard; Norrod, Roger D

2009-01-01

248

Encrypted imaging based on algebraic implementation of double random phase encoding.  

PubMed

The security of important information captured by sensors and cameras is currently a growing concern as information theft via techniques such as side-channel attacks become increasingly more prevalent. Double random phase encoding (DRPE) is an optical encryption method based on optical Fourier transform that is currently being used to implement secure coherent optical systems. In this paper, we propose a new DRPE implementation for incoherent optical systems based on integral photography that can be applied to "encrypted imaging (EI)" to optically encrypt an image before it is captured by an image sensor. Because the proposed incoherent DRPE is constituted from conventional DRPE by rewriting the optical encryption via discretization and Euler's formula, its security level is the same as that of conventional DRPE. The results of an experiment in which we encrypted a plaintext image optically and then decrypted it numerically demonstrate that our proposed incoherent optical security system is feasible. PMID:24922013

Nakano, Kazuya; Takeda, Masafumi; Suzuki, Hiroyuki; Yamaguchi, Masahiro

2014-05-10

249

Ground-Based Measurement Experiment and First Results with Geosynchronous-Imaging Fourier Transform Spectrometer Engineering Demonstration Unit  

NASA Technical Reports Server (NTRS)

The geosynchronous-imaging Fourier transform spectrometer (GIFTS) engineering demonstration unit (EDU) is an imaging infrared spectrometer designed for atmospheric soundings. It measures the infrared spectrum in two spectral bands (14.6 to 8.8 microns, 6.0 to 4.4 microns) using two 128 x 128 detector arrays with a spectral resolution of 0.57 cm(exp -1) with a scan duration of approximately 11 seconds. From a geosynchronous orbit, the instrument will have the capability of taking successive measurements of such data to scan desired regions of the globe, from which atmospheric status, cloud parameters, wind field profiles, and other derived products can be retrieved. The GIFTS EDU provides a flexible and accurate testbed for the new challenges of the emerging hyperspectral era. The EDU ground-based measurement experiment, held in Logan, Utah during September 2006, demonstrated its extensive capabilities and potential for geosynchronous and other applications (e.g., Earth observing environmental measurements). This paper addresses the experiment objectives and overall performance of the sensor system with a focus on the GIFTS EDU imaging capability and proof of the GIFTS measurement concept.

Zhou, Daniel K.; Smith, William L.; Bingham, Gail E.; Huppi, Ronald J.; Revercomb, Henry E.; Zollinger, Lori J.; Larar, Allen M.; Liu, Xu; Tansock, Joseph J.; Reisse, Robert A.; Hooker, Ronald

2007-01-01

250

Testing results and current status of FTS-2, an imaging Fourier transform spectrometer for SCUBA-2  

E-print Network

-Zehnder imaging spectrometer, built for use with the SCUBA-2 camera on the James Clerk Maxwell Telescope (JCMT (FTS) which has been built for use with the SCUBA-2 camera1 on the James Clerk Maxwell Telescope (JCMT

Naylor, David A.

251

Parallel imaging acceleration of spiral Fourier velocity encoded MRI using SPIRiT  

E-print Network

, followed by a non-Cartesian inverse *This work was supported by the Brazilian National Council for Tech used image domain SPIRiT, because the data was acquired in a non-Cartesian fashion (spiral trajectory

Carvalho, João Luiz

252

Analysis of hyper-spectral data derived from an imaging Fourier transform: A statistical perspective  

SciTech Connect

Fourier transform spectrometers (FTS) using optical sensors are increasingly being used in various branches of science. Typically, a FTS generates a three-dimensional data cube with two spatial dimensions and one frequency/wavelength dimension. The number of frequency dimensions in such data cubes is generally very large, often in the hundreds, making data analytical procedures extremely complex. In the present report, the problem is viewed from a statistical perspective. A set of procedures based on the high degree of inter-channel correlation structure often present in such hyper-spectral data, has been identified and applied to an example data set of dimension 100 x 128 x 128 comprising 128 spectral bands. It is shown that in this case, the special eigen-structure of the correlation matrix has allowed the authors to extract just a few linear combinations of the channels (the significant principal vectors) that effectively contain almost all of the spectral information contained in the data set analyzed. This in turn, enables them to segment the objects in the given spatial frame using, in a parsimonious yet highly effective way, most of the information contained in the data set.

Sengupta, S.K.; Clark, G.A.; Fields, D.J.

1996-01-10

253

Demonstration of Imaging Fourier Transform Spectrometer (FTS) Performance for Planetary and Geostationary Earth Observing  

NASA Technical Reports Server (NTRS)

The combination of massively parallel spatial sampling and accurate spectral radiometry offered by imaging FTS makes it extremely attractive for earth and planetary remote sensing. We constructed a breadboard instrument to help assess the potential for planetary applications of small imaging FTS instruments in the 1 - 5 micrometer range. The results also support definition of the NASA Geostationary Imaging FTS (GIFTS) instrument that will make key meteorological and climate observations from geostationary earth orbit. The Planetary Imaging FTS (PIFTS) breadboard is based on a custom miniaturized Bomen interferometer that uses corner cube reflectors, a wishbone pivoting voice-coil delay scan mechanism, and a laser diode metrology system. The interferometer optical output is measured by a commercial infrared camera procured from Santa Barbara Focalplane. It uses an InSb 128x128 detector array that covers the entire FOV of the instrument when coupled with a 25 mm focal length commercial camera lens. With appropriate lenses and cold filters the instrument can be used from the visible to 5 micrometers. The delay scan is continuous, but slow, covering the maximum range of +/- 0.4 cm in 37.56 sec at a rate of 500 image frames per second. Image exposures are timed to be centered around predicted zero crossings. The design allows for prediction algorithms that account for the most recent fringe rate so that timing jitter produced by scan speed variations can be minimized. Response to a fixed source is linear with exposure time nearly to the point of saturation. Linearity with respect to input variations was demonstrated to within 0.16% using a 3-point blackbody calibration. Imaging of external complex scenes was carried out at low and high spectral resolution. These require full complex calibration to remove background contributions that vary dramatically over the instrument FOV. Testing is continuing to demonstrate the precise radiometric accuracy and noise characteristics.

Revercomb, Henry E.; Sromovsky, Lawrence A.; Fry, Patrick M.; Best, Fred A.; LaPorte, Daniel D.

2001-01-01

254

Phase-contrast imaging of thin biomaterials.  

PubMed

The necessity of information about the inner microscopical features of low absorbing materials is one of the most important goals in the structural research field. So far, non destructive analysis have been performed using contact radiography giving the scope for great advances in the production and application of new materials. However, the nature of interaction, namely X-ray absorption, limited the observations only to materials having sufficient heavy elements content. The adoption of a different X-ray interaction with matter which involves refractive properties of materials is at the basis of phase-contrast imaging. The novel method allows the use of high X-ray energies, for a deeper penetration and a lower released dose, without losing any information on the nature of the sample. A demonstration study, performed at the third generation European Synchrotron Radiation Facility (ESRF)-Grenoble, to show the potential of the new technique applied to biomaterials characterization is presented here. The test samples are a commercial matrix barrier (GUIDOR) intended to aid the healing process after periodontal surgery and a hydroxyapatite thin slab originally deposited by plasma spray technique on a TA6V alloy substrate. Phase-contrast images showed significant advantages revealing features that have negligible absorption contrast. The technique can be successfully used for the characterization of biomaterials. PMID:11374450

Baruchel, J; Lodini, A; Romanzetti, S; Rustichelli, F; Scrivani, A

2001-06-01

255

Simple merging technique for improving resolution in qualitative single image phase contrast tomography.  

PubMed

For dynamic samples and/or for simple ease-of-use experiments, single-image phase contrast tomography is a very effective method for the 3D visualization of materials which would otherwise be indiscernible in attenuation based x-ray imaging. With binary samples (e.g. air-material) and monochromatic wavefields a transport-of-intensity (TIE)-based phase retrieval algorithm is known to retrieve accurate quantitative maps of the phase distribution. For mixed material samples and/or white beam radiation the algorithm can still produce useful qualitative tomographic reconstructions with significantly improved area contrast. The stability of the algorithm comes with a recognized associated loss of spatial resolution due to its essential behaviour as a low-pass filter. One possible answer to this is an image fusion technique that merges the slices reconstructed from raw phase contrast images and those after phase retrieval, where the improved contrast may be acquired without the associated loss of high-frequency information. We present this technique as a simple few-parameter Fourier method, which is easily tunable and highly compatible with current reconstruction steps. PMID:25401876

Irvine, S; Mokso, R; Modregger, P; Wang, Z; Marone, F; Stampanoni, M

2014-11-01

256

LED-based multi-wavelength phase imaging interference microscopy  

Microsoft Academic Search

LED-based multi-wavelength phase imaging interference microscopy combines phase-shifting interferometry with multi-wavelength optical phase unwrapping. This technique consists of a Michelson-type interferometer illuminated with a LED. The reference mirror is dithered for obtaining interference images at four phase quadratures, which are then combined to calculate the phase of the object surface. The 2pi ambiguities are removed by repeating the experiment using

N. Warnasooriya; M. K. Kim

2007-01-01

257

Quantitative cell imaging using single beam phase retrieval method  

Microsoft Academic Search

Quantitative three-dimensional imaging of cells can provide important information about their morphology as well as their dynamics, which will be useful in studying their behavior under various conditions. There are several microscopic techniques to image unstained, semi-transparent specimens, by converting the phase information into intensity information. But most of the quantitative phase contrast imaging techniques is realized either by using

Arun Anand; Vani Chhaniwal; Bahram Javidi

2011-01-01

258

Investigating the biochemical progression of liver disease through fibrosis, cirrhosis, dysplasia, and hepatocellular carcinoma using Fourier transform infrared spectroscopic imaging  

NASA Astrophysics Data System (ADS)

Hepatocellular carcinoma (HCC) is the most common form of primary hepatic carcinoma. HCC ranks the fourth most prevalent malignant tumor and the third leading cause of cancer related death in the world. Hepatocellular carcinoma develops in the context of chronic liver disease and its evolution is characterized by progression through intermediate stages to advanced disease and possibly even death. The primary sequence of hepatocarcinogenesis includes the development of cirrhosis, followed by dysplasia, and hepatocellular carcinoma.1 We addressed the utility of Fourier Transform Infrared (FT-IR) spectroscopic imaging, both as a diagnostic tool of the different stages of the disease and to gain insight into the biochemical process associated with disease progression. Tissue microarrays were obtained from the University of Illinois at Chicago tissue bank consisting of liver explants from 12 transplant patients. Tissue core biopsies were obtained from each explant targeting regions of normal, liver cell dysplasia including large cell change and small cell change, and hepatocellular carcinoma. We obtained FT-IR images of these tissues using a modified FT-IR system with high definition capabilities. Firstly, a supervised spectral classifier was built to discriminate between normal and cancerous hepatocytes. Secondly, an expanded classifier was built to discriminate small cell and large cell changes in liver disease. With the emerging advances in FT-IR instrumentation and computation there is a strong drive to develop this technology as a powerful adjunct to current histopathology approaches to improve disease diagnosis and prognosis.

Sreedhar, Hari; Pant, Mamta; Ronquillo, Nemencio R.; Davidson, Bennett; Nguyen, Peter; Chennuri, Rohini; Choi, Jacqueline; Herrera, Joaquin A.; Hinojosa, Ana C.; Jin, Ming; Kajdacsy-Balla, Andre; Guzman, Grace; Walsh, Michael J.

2014-03-01

259

Vacuum compatible sample positioning device for matrix assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry imaging  

SciTech Connect

The high mass accuracy and resolving power of Fourier transform ion cyclotron resonance mass spectrometers (FT-ICR MS) make them ideal mass detectors for mass spectrometry imaging (MSI), promising to provide unmatched molecular resolution capabilities. The intrinsic low tolerance of FT-ICR MS to RF interference, however, along with typically vertical positioning of the sample, and MSI acquisition speed requirements present numerous engineering challenges in creating robotics capable of achieving the spatial resolution to match. This work discusses a two-dimensional positioning stage designed to address these issues. The stage is capable of operating in {approx}1 x 10{sup -8} mbar vacuum. The range of motion is set to 100 mm x 100 mm to accommodate large samples, while the positioning accuracy is demonstrated to be less than 0.4 micron in both directions under vertical load over the entire range. This device was integrated into three different matrix assisted laser desorption/ionization (MALDI) FT-ICR instruments and showed no detectable RF noise. The ''oversampling'' MALDI-MSI experiments, under which the sample is completely ablated at each position, followed by the target movement of the distance smaller than the laser beam, conducted on the custom-built 7T FT-ICR MS demonstrate the stability and positional accuracy of the stage robotics which delivers high spatial resolution mass spectral images at a fraction of the laser spot diameter.

Aizikov, Konstantin; Lin, Tzu-Yung [Cardiovascular Proteomics Center, Boston University School of Medicine, 670 Albany Street, Room 504 Boston, Massachusetts 02118 (United States); Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215 (United States); Smith, Donald F.; Heeren, Ron M. A. [FOM Institute for Atomic and Molecular Physics (AMOLF), Science Park 104, 1098 XG Amsterdam (Netherlands); Chargin, David A.; Ivanov, Sergei [Fraunhofer CMI, Boston, Massachusetts 02215 (United States); O'Connor, Peter B. [Cardiovascular Proteomics Center, Boston University School of Medicine, 670 Albany Street, Room 504 Boston, Massachusetts 02118 (United States); Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215 (United States); Department of Chemistry, University of Warwick, Coventry CV4 7AL (United Kingdom)

2011-05-15

260

Fourier Transform Infrared Imaging Showing Reduced Unsaturated Lipid Content in the Hippocampus of a mouse Model of Alzheimer's Disease  

SciTech Connect

Polyunsaturated fatty acids are essential to brain functions such as membrane fluidity, signal transduction, and cell survival. It is also thought that low levels of unsaturated lipid in the brain may contribute to Alzheimer's disease (AD) risk or severity. However, it is not known how accumulation of unsaturated lipids is affected in different regions of the hippocampus, which is a central target of AD plaque pathology, during aging. In this study, we used Fourier transform infrared imaging (FTIRI) to visualize the unsaturated lipid content in specific regions of the hippocampus in the PSAPP mouse model of AD as a function of plaque formation. Specifically, the unsaturated lipid content was imaged using the olefinic {double_bond}CH stretching mode at 3012 cm{sup -1}. The axonal, dendritic, and somatic layers of the hippocampus were examined in the mice at 13, 24, 40, and 56 weeks old. Results showed that lipid unsaturation in the axonal layer was significantly increased with normal aging in control (CNT) mice (p < 0.01) but remained low and relatively constant in PSAPP mice. Thus, these findings indicate that unsaturated lipid content is reduced in hippocampal white matter during amyloid pathogenesis and that maintaining unsaturated lipid content early in the disease may be critical in avoiding progression of the disease.

Leskovjan, A.C.; Kretlow, A.; Miller, L.M.

2010-04-01

261

Lossless data compression studies for the geostationary imaging Fourier transform spectrometer (GIFTS) with the bias-adjusted reordering preprocessing  

NASA Astrophysics Data System (ADS)

The NASA Geostationary Imaging Fourier Transform Spectrometer (GIFTS) represents a revolutionary step in remote sensing of Earth's atmosphere that will demonstrate the technology and measurement concepts for future NOAA geostationary operational environmental satellites (GOES). GIFTS consists of a 128 x 128 large focal plane array (LFPA) imaging FTS with the spectral coverage from 685 to 1130 cm -1 and 1650 to 2250 cm -1. GIFTS was selected for flight demonstration on NASA's New Millennium Program (NMP) Earth Observing 3 (EO-3) Satellite Mission. GIFTS provides full disk global coverage obtained within an hour at moderate spectral resolutions (e.g. 1.2 cm -1) as well as regional sounding of atmospheric temperature and absorbing gas profiles at high spectral resolution (e.g. 0.6 cm -1). Given the unprecedented data volume produced by GIFTS, lossless data compression is critical for the overall success of the GIFTS experiment where the data is to be disseminated to the user community in real-time and archived for scientific studies and climate assessment. In this paper we will study lossless compression of GIFTS data that has been collected as part of the calibration or Ground Based Tests that were conducted in 2006. Standard compression methods JPEG-2000, JPEG-LS, and CCSDS IDC 9/7M & 5/3 are investigated for compression benchmarks. The bias-adjusted reordering (BAR) preprocessing scheme is also investigated to improve their performance on GIFTS data compression.

Huang, Bormin; Wei, Shih-Chieh; Huang, Allen H.-L.; Smuga-Otto, Maciek; Knuteson, Robert; Revercomb, Henry E.; Smith, William L., Sr.

2007-09-01

262

Phase Retrieval Using a Genetic Algorithm on the Systematic Image-Based Optical Alignment Testbed  

NASA Technical Reports Server (NTRS)

NASA s Marshall Space Flight Center s Systematic Image-Based Optical Alignment (SIBOA) Testbed was developed to test phase retrieval algorithms and hardware techniques. Individuals working with the facility developed the idea of implementing phase retrieval by breaking the determination of the tip/tilt of each mirror apart from the piston motion (or translation) of each mirror. Presented in this report is an algorithm that determines the optimal phase correction associated only with the piston motion of the mirrors. A description of the Phase Retrieval problem is first presented. The Systematic Image-Based Optical Alignment (SIBOA) Testbeb is then described. A Discrete Fourier Transform (DFT) is necessary to transfer the incoming wavefront (or estimate of phase error) into the spatial frequency domain to compare it with the image. A method for reducing the DFT to seven scalar/matrix multiplications is presented. A genetic algorithm is then used to search for the phase error. The results of this new algorithm on a test problem are presented.

Taylor, Jaime R.

2003-01-01

263

Structured illumination quantitative phase microscopy for enhanced resolution amplitude and phase imaging  

PubMed Central

Structured illumination microscopy (SIM) is an established microscopy technique typically used to image samples at resolutions beyond the diffraction limit. Until now, however, achieving sub-diffraction resolution has predominantly been limited to intensity-based imaging modalities. Here, we introduce an analogue to conventional SIM that allows sub-diffraction resolution, quantitative phase-contrast imaging of optically transparent objects. We demonstrate sub-diffraction resolution amplitude and quantitative-phase imaging of phantom targets and enhanced resolution quantitative-phase imaging of cells. We report a phase accuracy to within 5% and phase noise of 0.06 rad. PMID:24156044

Chowdhury, Shwetadwip; Izatt, Joseph

2013-01-01

264

Fourier Program  

NSDL National Science Digital Library

The Fourier program displays the Fourier transform of a user-defined complex spatial function of position. The default spatial function is a complex Gaussian. Additional parameters can be specified using the Display | Switch GUI menu item. Fourier is an Open Source Physics program written for the teaching of mathematical methods in the sciences. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the math_fourier.jar file will run the program if Java is installed. Other mathematical methods programs are also available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Math.

Christian, Wolfgang

2008-05-14

265

X-ray phase imaging with a paper analyzer  

SciTech Connect

We present a simple x-ray phase imaging method that utilizes the sample-induced distortion of a high contrast random intensity pattern to quantitatively retrieve the two-dimensional phase map at the exit surface of a coherently illuminated sample. This reference pattern is created by placing a sheet of sandpaper in the x-ray beam, with the sample-induced distortion observed after propagation to the detector, a meter downstream. Correlation analysis comparing a single ''sample and sandpaper'' image to a reference ''sandpaper only'' image produces two sensitive differential phase contrast images, giving the sample phase gradient in vertical and horizontal directions. These images are then integrated to recover the projected phase depth of the sample. The simple experimental set-up, retention of flux, and the need for only a single sample image per reconstruction suggest that this method is of value in imaging a range of dynamic processes at both synchrotron and laboratory x-ray sources.

Morgan, Kaye S.; Paganin, David M. [School of Physics, Monash University, Victoria 3800 (Australia); Siu, Karen K. W. [Monash Biomedical Imaging, Monash University, Victoria 3800 (Australia); Australian Synchrotron, Victoria 3168 (Australia)

2012-03-19

266

Real-time measurement of alveolar size and population using phase contrast x-ray imaging  

PubMed Central

Herein a propagation-based phase contrast x-ray imaging technique for measuring particle size and number is presented. This is achieved with an algorithm that utilizes the Fourier space signature of the speckle pattern associated with the images of particles. We validate this algorithm using soda-lime glass particles, demonstrating its effectiveness on random and non-randomly packed particles. This technique is then applied to characterise lung alveoli, which are difficult to measure dynamically in vivo with current imaging modalities due to inadequate temporal resolution and/or depth of penetration and field-of-view. We obtain an important result in that our algorithm is able to measure changes in alveolar size on the micron scale during ventilation and shows the presence of alveolar recruitment/de-recruitment in newborn rabbit kittens. This technique will be useful for ventilation management and lung diagnostic procedures. PMID:25426328

Leong, Andrew F.T.; Buckley, Genevieve A.; Paganin, David M.; Hooper, Stuart B.; Wallace, Megan J.; Kitchen, Marcus J.

2014-01-01

267

Application of a Fourier-transform infrared imaging system to deciphering obliterated writings for forensic purposes  

NASA Astrophysics Data System (ADS)

A new method of deciphering obliterated writing is proposed in this paper. Inks with a peak at 1620 cm-1 were used for writing characters on paper, and information protection stamps were then used to obliterate them. Conventional detection methods consisting of visible and near-infrared spectroscopic photography and fluorescent photography of wavelength between 0.4-1.0 ?m were compared with a novel method using infrared spectroscopic imaging with a 16-element mercury cadmium telluride array detector. The samples of obliterated writing could not be detected by the conventional methods, but could by the new method. Therefore, this new method is very useful for deciphering obliterated writing.

Sugawara, Shigeru

2014-05-01

268

Digital holography for quantitative phase-contrast imaging.  

PubMed

We present a new application of digital holography for phase-contrast imaging and optical metrology. This holographic imaging technique uses a CCD camera for recording of a digital Fresnel off-axis hologram and a numerical method for hologram reconstruction. The method simultaneously provides an amplitude-contrast image and a quantitative phase-contrast image. An application to surface profilometry is presented and shows excellent agreement with contact-stylus probe measurements. PMID:18071483

Cuche, E; Bevilacqua, F; Depeursinge, C

1999-03-01

269

Accurate quantitative phase imaging through telecentric digital holographic microscopy  

NASA Astrophysics Data System (ADS)

The use of non-telecentric imaging systems in quantitative phase digital holographic microscopy introduces strong inaccuracies. We show that even negligible errors in the radius and center of curvature of the remaining quadratic phase factor introduce big errors in the numerical phase measurements. The errors depend on the position of the object in the field-of-view. However, when a telecentric imaging system is utilized for the recording of the holograms, the hybrid imaging method shows shift-invariant behavior, and therefore accurate quantitative phase imaging can be performed.

Doblas, Ana; Sánchez-Ortiga, Emilio; Martínez-Corral, Manuel; Saavedra, Genaro; Garcia-Sucerquia, Jorge

2014-06-01

270

Fourier analysis of a gated blood-pool study during atrial flutter  

SciTech Connect

First-harmonic Fourier analysis of a gated blood-pool study is based on the assumption that the cardiac chambers contract once per cardiac cycle. In atrial arrhythmias this condition may not exist for the atria. We recently studied a patient with atrial flutter and 2:1 artioventricular conduction. There were predictable alterations in the first-harmonic Fourier phase and amplitude images. The observed changes from first-harmonic Fourier analysis were: (a) very low atrial amplitude values, and (b) absence of identifiable atrial regions on the phase image.

Makler, P.T. Jr.; McCarthy, D.M.; London, J.W.; Sandler, M.S.; Alavi, A.

1983-08-01

271

Automation and Control of an Imaging Internal Laser Desorption Fourier Transform Mass Spectrometer (I2LD-FTMS)  

SciTech Connect

This paper describes the automation of an imaging internal source laser desorption Fourier transform mass spectrometer (I2LD-FTMS). The I2LD-FTMS consists of a laser-scanning device [Scott and Tremblay, Rev. Sci. Instrum. 2002, 73, 1108–1116] that has been integrated with a laboratory-built FTMS using a commercial data acquisition system (ThermoFinnigan FT/MS, Bremen, Germany). A new user interface has been developed in National Instrument's (Austin, Texas) graphical programming language LabVIEW to control the motors of the laser positioning system and the commercial FTMS data acquisition system. A feature of the FTMS software that allows the user to write macros in a scripting language is used creatively to our advantage in creating a mechanism to control the FTMS from outside its graphical user interface. The new user interface also allows the user to configure target locations. Automation of the data analysis along with data display using commercial graphing software is also described.

McJunkin, Timothy R; Tranter, Troy Joseph; Scott, Jill Rennee

2002-06-01

272

Performance of the Imaging Fourier Transform Spectrometer with Photoconductive Detector Arrays: An Application for the AKARI Far-Infrared Instrument  

E-print Network

We have developed an imaging Fourier transform spectrometer (FTS) for space-based far-infrared astronomical observations. The FTS employs a newly developed photoconductive detector arrays with a capacitive trans-impedance amplifier, which makes the FTS a completely unique instrument. The FTS was installed as a function of the far-infrared instrument (FIS: Far-Infrared Surveyor) on the Japanese astronomical satellite, AKARI, which was launched on February 21, 2006 (UT) from the Uchinoura Space Center. The FIS-FTS had been operated for more than one year before liquid helium ran out on August 26, 2007. The FIS-FTS was operated nearly six hundreds times, which corresponds to more than one hundred hours of astronomical observations and almost the same amount of time for calibrations. As expected from laboratory measurements, the FIS-FTS performed well and has produced a large set of astronomical data for valuable objects. Meanwhile, it becomes clear that the detector transient effect is a considerable factor for FTSs with photoconductive detectors. In this paper, the instrumentation of the FIS-FTS and interesting phenomena related to FTS using photoconductive detectors are described, and future applications of this kind of FTS system are discussed.

Mitsunobu Kawada; Hidenori Takahashi; Noriko Murakami; Hiroshi Matsuo; Yoko Okada; Akiko Yasuda; Shuji Matsuura; Mai Shirahata; Yasuo Doi; Hidehiro Kaneda; Takafumi Ootsubo; Takao Nakagawa; Hiroshi Shibai

2008-11-18

273

Quantitative evaluation of phase processing approaches in susceptibility weighted imaging  

NASA Astrophysics Data System (ADS)

Susceptibility weighted imaging (SWI) takes advantage of the local variation in susceptibility between different tissues to enable highly detailed visualization of the cerebral venous system and sensitive detection of intracranial hemorrhages. Thus, it has been increasingly used in magnetic resonance imaging studies of traumatic brain injury as well as other intracranial pathologies. In SWI, magnitude information is combined with phase information to enhance the susceptibility induced image contrast. Because of global susceptibility variations across the image, the rate of phase accumulation varies widely across the image resulting in phase wrapping artifacts that interfere with the local assessment of phase variation. Homodyne filtering is a common approach to eliminate this global phase variation. However, filter size requires careful selection in order to preserve image contrast and avoid errors resulting from residual phase wraps. An alternative approach is to apply phase unwrapping prior to high pass filtering. A suitable phase unwrapping algorithm guarantees no residual phase wraps but additional computational steps are required. In this work, we quantitatively evaluate these two phase processing approaches on both simulated and real data using different filters and cutoff frequencies. Our analysis leads to an improved understanding of the relationship between phase wraps, susceptibility effects, and acquisition parameters. Although homodyne filtering approaches are faster and more straightforward, phase unwrapping approaches perform more accurately in a wider variety of acquisition scenarios.

Li, Ningzhi; Wang, Wen-Tung; Sati, Pascal; Pham, Dzung L.; Butman, John A.

2012-03-01

274

Radiometric Modeling and Calibration of the Geostationary Imaging Fourier Transform Spectrometer (GIFTS)Ground Based Measurement Experiment  

NASA Technical Reports Server (NTRS)

The ultimate remote sensing benefits of the high resolution Infrared radiance spectrometers will be realized with their geostationary satellite implementation in the form of imaging spectrometers. This will enable dynamic features of the atmosphere s thermodynamic fields and pollutant and greenhouse gas constituents to be observed for revolutionary improvements in weather forecasts and more accurate air quality and climate predictions. As an important step toward realizing this application objective, the Geostationary Imaging Fourier Transform Spectrometer (GIFTS) Engineering Demonstration Unit (EDU) was successfully developed under the NASA New Millennium Program, 2000-2006. The GIFTS-EDU instrument employs three focal plane arrays (FPAs), which gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral bands. The GIFTS calibration is achieved using internal blackbody calibration references at ambient (260 K) and hot (286 K) temperatures. In this paper, we introduce a refined calibration technique that utilizes Principle Component (PC) analysis to compensate for instrument distortions and artifacts, therefore, enhancing the absolute calibration accuracy. This method is applied to data collected during the GIFTS Ground Based Measurement (GBM) experiment, together with simultaneous observations by the accurately calibrated AERI (Atmospheric Emitted Radiance Interferometer), both simultaneously zenith viewing the sky through the same external scene mirror at ten-minute intervals throughout a cloudless day at Logan Utah on September 13, 2006. The accurately calibrated GIFTS radiances are produced using the first four PC scores in the GIFTS-AERI regression model. Temperature and moisture profiles retrieved from the PC-calibrated GIFTS radiances are verified against radiosonde measurements collected throughout the GIFTS sky measurement period. Using the GIFTS GBM calibration model, we compute the calibrated radiances from data collected during the moon tracking and viewing experiment events. From which, we derive the lunar surface temperature and emissivity associated with the moon viewing measurements.

Tian, Jialin; Smith, William L.; Gazarik, Michael J.

2008-01-01

275

Measurement of retinal blood flow in the rat by combining Doppler Fourier-domain optical coherence tomography with fundus imaging.  

PubMed

A wide variety of ocular diseases are associated with abnormalities in ocular circulation. As such, there is considerable interest in techniques for quantifying retinal blood flow, among which Doppler optical coherence tomography (OCT) may be the most promising. We present an approach to measure retinal blood flow in the rat using a new optical system that combines the measurement of blood flow velocities via Doppler Fourier-domain optical coherence tomography and the measurement of vessel diameters using a fundus camera-based technique. Relying on fundus images for extraction of retinal vessel diameters instead of OCT images improves the reliability of the technique. The system was operated with an 841-nm superluminescent diode and a charge-coupled device camera that could be operated at a line rate of 20 kHz. We show that the system is capable of quantifying the response of 100% oxygen breathing on the retinal blood flow. In six rats, we observed a decrease in retinal vessel diameters of 13.2% and a decrease in retinal blood velocity of 42.6%, leading to a decrease in retinal blood flow of 56.7%. Furthermore, in four rats, the response of retinal blood flow during stimulation with diffuse flicker light was assessed. Retinal vessel diameter and blood velocity increased by 3.4% and 28.1%, respectively, leading to a relative increase in blood flow of 36.2%. The presented technique shows much promise to quantify early changes in retinal blood flow during provocation with various stimuli in rodent models of ocular diseases in rats. PMID:25321400

Werkmeister, René M; Vietauer, Martin; Knopf, Corinna; Fürnsinn, Clemens; Leitgeb, Rainer A; Reitsamer, Herbert; Gröschl, Martin; Garhöfer, Gerhard; Vilser, Walthard; Schmetterer, Leopold

2014-10-01

276

Computational phase imaging based on intensity transport  

E-print Network

Light is a wave, having both an amplitude and a phase. However, optical frequencies are too high to allow direct detection of phase; thus, our eyes and cameras see only real values - intensity. Phase carries important ...

Waller, Laura A. (Laura Ann)

2010-01-01

277

ATMOSPHERIC PHASE NOISE AND APERTURE SYNTHESIS IMAGING AT MILLIMETER WAVELENGTHS  

E-print Network

wavelength aperture synthesis images is limited by atmospheric turbulence. Observing techniques and dataATMOSPHERIC PHASE NOISE AND APERTURE SYNTHESIS IMAGING AT MILLIMETER WAVELENGTHS M. C. H. Wright on short baselines and in turbulent weather. The rms phase at a 1 km baseline is 1 mm, with a variation

Militzer, Burkhard

278

An ultrafast phase modulator for 3D imaging  

Microsoft Academic Search

In this paper we explore potential applications of a new transparent Electro-Optic Ceramic in 3D imaging as a fast phase shifter and demonstrate its performance in a newly developed Low Coherence Polarization Interference Microscopy (LCPIM). The new phase modulator is fast, convenient and inexpensive. It makes the 3D imaging system that employs it mechanically efficient and compact. The LCPIM proposed

Janice Y. Cheng; Qiushui Chen

2006-01-01

279

Image quality and dose efficiency of high energy phase sensitive x-ray imaging: Phantom studies  

PubMed Central

The goal of this preliminary study was to perform an image quality comparison of high energy phase sensitive imaging with low energy conventional imaging at similar radiation doses. The comparison was performed with the following phantoms: American College of Radiology (ACR), contrast-detail (CD), acrylic edge and tissue-equivalent. Visual comparison of the phantom images indicated comparable or improved image quality for all phantoms. Quantitative comparisons were performed through ACR and CD observer studies, both of which indicated higher image quality in the high energy phase sensitive images. The results of this study demonstrate the ability of high energy phase sensitive imaging to overcome existing challenges with the clinical implementation of phase contrast imaging and improve the image quality for a similar radiation dose as compared to conventional imaging near typical mammography energies. In addition, the results illustrate the capability of phase sensitive imaging to sustain the image quality improvement at high x-ray energies and for – breast – simulating phantoms, both of which indicate the potential to benefit fields such as mammography. Future studies will continue to investigate the potential for dose reduction and image quality improvement provided by high energy phase sensitive contrast imaging. PMID:24865208

Wong, Molly Donovan; Wu, Xizeng; Liu, Hong

2014-01-01

280

Magnetic field induced differential neutron phase contrast imaging  

SciTech Connect

Besides the attenuation of a neutron beam penetrating an object, induced phase changes have been utilized to provide contrast in neutron and x-ray imaging. In analogy to differential phase contrast imaging of bulk samples, the refraction of neutrons by magnetic fields yields image contrast. Here, it will be reported how double crystal setups can provide quantitative tomographic images of magnetic fields. The use of magnetic air prisms adequate to split the neutron spin states enables a distinction of field induced phase shifts and these introduced by interaction with matter.

Strobl, M.; Treimer, W.; Walter, P.; Keil, S.; Manke, I. [Department of Physical Chemistry, Ruprecht Karls University Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany and Hahn-Meitner Institute Berlin, SF1, Glienickerstr. 100, 14109 Berlin (Germany); Hahn-Meitner Institute Berlin, Glienickerstr. 100, 14109 Berlin, Germany and University of Applied Sciences (TFH) Berlin, Luxemburger Str. 10, 13353 Berlin (Germany); Hahn-Meitner Institute Berlin, Glienickerstr. 100, 14109 Berlin (Germany)

2007-12-17

281

Phase contrast portal imaging for image-guided microbeam radiation therapy  

NASA Astrophysics Data System (ADS)

High-dose synchrotron microbeam radiation therapy is a unique treatment technique used to destroy tumors without severely affecting circumjacent healthy tissue. We applied a phase contrast technique to portal imaging in preclinical microbeam radiation therapy experiments. Phase contrast portal imaging is expected to enable us to obtain higherresolution X-ray images at therapeutic X-ray energies compared to conventional portal imaging. Frontal view images of a mouse head sample were acquired in propagation-based phase contrast imaging. The phase contrast images depicted edge-enhanced fine structures of the parietal bones surrounding the cerebrum. The phase contrast technique is expected to be effective in bony-landmark-based verification for image-guided radiation therapy.

Umetani, Keiji; Kondoh, Takeshi

2014-03-01

282

Fourier Theory  

NSDL National Science Digital Library

This module, developed by the Maricopa Advanced Technology Education Center (MATEC) project called Work-Ready Electronics, presents the basis and applications of Fourier theory. On this site, visitors will find five sections: Frequency Domain View of Electronic Signals, the Frequency Domain, The Fourier Theory: A Technician Level Explanation, Bandwidth, and Applications of Fourier Theory. Each section is followed by a Knowledge Probe assessment which asks questions about the material that was just covered. The Learning Resource section of the site contains laboratory activities and questions for practice and research as well as links to further information on Fourier theory. There is also a glossary of terms from all aspects of electronics, and a handy notebook tool with allows visitors to jot down notes and thoughts as they work through the activities.

2008-08-15

283

Signal demodulation of Fourier telescopy based on spectrum correction  

NASA Astrophysics Data System (ADS)

Fourier telescopy is an active unconventional imaging technique. Three or more beams from different spatially separated transmitters are pointed at a distant and faint object. The spatial Fourier spectrum of the object is carried on the reflected temporally modulated signals. The image of the target can be reconstructed from the back signals by demodulation and phase closure algorithm. The conventional demodulation processing is calculating spectrum directly by inverse Fourier transform of the signal. However spectrum estimated by inverse Fourier transform has non-negligible errors caused by frequency shift error of the Acoustic-optical modulator, the noise and the relative motion between beams and the target. An improved demodulation method based on spectrum correction of FT is proposed. The method corrects the amplitude and the phase on the demodulated frequency of the signal by which better reconstructed image can be obtained. In this paper, the effect of the frequency shift error in Fourier telescopy demodulation is investigated. The degradation of the reconstructed image is simulated. We summarize the new demodulation method based on spectrum correction and give the simulated comparison between the conventional demodulation and the developed method. The result confirms the effectiveness of the improved demodulation method.

Li, Yang; Xiangli, Bin; Zhang, Wenxi; Nie, Yunfeng

2013-09-01

284

Broadband Phase Retrieval for Image-Based Wavefront Sensing  

NASA Technical Reports Server (NTRS)

A focus-diverse phase-retrieval algorithm has been shown to perform adequately for the purpose of image-based wavefront sensing when (1) broadband light (typically spanning the visible spectrum) is used in forming the images by use of an optical system under test and (2) the assumption of monochromaticity is applied to the broadband image data. Heretofore, it had been assumed that in order to obtain adequate performance, it is necessary to use narrowband or monochromatic light. Some background information, including definitions of terms and a brief description of pertinent aspects of image-based phase retrieval, is prerequisite to a meaningful summary of the present development. Phase retrieval is a general term used in optics to denote estimation of optical imperfections or aberrations of an optical system under test. The term image-based wavefront sensing refers to a general class of algorithms that recover optical phase information, and phase-retrieval algorithms constitute a subset of this class. In phase retrieval, one utilizes the measured response of the optical system under test to produce a phase estimate. The optical response of the system is defined as the image of a point-source object, which could be a star or a laboratory point source. The phase-retrieval problem is characterized as image-based in the sense that a charge-coupled-device camera, preferably of scientific imaging quality, is used to collect image data where the optical system would normally form an image. In a variant of phase retrieval, denoted phase-diverse phase retrieval [which can include focus-diverse phase retrieval (in which various defocus planes are used)], an additional known aberration (or an equivalent diversity function) is superimposed as an aid in estimating unknown aberrations by use of an image-based wavefront-sensing algorithm. Image-based phase-retrieval differs from such other wavefront-sensing methods, such as interferometry, shearing interferometry, curvature wavefront sensing, and Shack-Hartmann sensing, all of which entail disadvantages in comparison with image-based methods. The main disadvantages of these non-image based methods are complexity of test equipment and the need for a wavefront reference.

Dean, Bruce H.

2007-01-01

285

Image region duplication detection based on circular window expansion and phase correlation.  

PubMed

Region duplication forgery is one of the tampering techniques that are frequently used, where a part of an image is copied and pasted into another part of the same image. In this paper, a phase correlation method based on polar expansion and adaptive band limitation is proposed for region duplication forgery detection. Our method starts by calculating the Fourier transform of the polar expansion on overlapping windows pair, and then an adaptive band limitation procedure is implemented to obtain a correlation matrix in which the peak is effectively enhanced. After estimating the rotation angle of the forgery region, a searching algorithm in the sense of seed filling is executed to display the whole duplicated region. Experimental results show that the proposed approach can detect duplicated region with high accuracy and robustness to rotation, illumination adjustment, blur and JPEG compression while rotation angle is estimated precisely for further calculation. PMID:22658742

Shao, Hong; Yu, Tianshu; Xu, Mengjia; Cui, Wencheng

2012-10-10

286

Phase contrast imaging of small transparent objects using digital shearography  

NASA Astrophysics Data System (ADS)

Phase contrast imaging of small transparent objects having complex shape is difficult to achieve using theoretical modeling. Present communication reports investigations undertaken towards testing applicability of Digital Shearography for phase contrast imaging of small object. The experimental arrangement is simple and primarily uses a pair of gratings. The result of experimental investigation reveals that the technique can be successfully used for mapping the phase of transparent objects.

Dhanotia, Jitendra; Prakash, Shashi

2014-10-01

287

Transport of intensity phase imaging in a volume holographic microscope.  

PubMed

We demonstrate a method for single-shot quantitative phase imaging based on the transport of intensity equation (TIE) in a volume holographic microscope (VHM). The VHM system uses a multiplexed volume hologram to laterally separate images from different focal planes. This axial intensity information is then used to solve the TIE and recover object phase quantitatively. Further, we show improved phase recovery by using five multiplexed gratings in one hologram. PMID:20808383

Waller, Laura; Luo, Yuan; Yang, Se Young; Barbastathis, George

2010-09-01

288

Quantitative phase imaging microscopy with multi-wavelength optical phase unwrapping  

Microsoft Academic Search

This dissertation presents a quantitative phase imaging microscopy technique that combines phase-shifting interferometry with multi-wavelength optical phase unwrapping. The technique consists of a Michelson-type interferometer illuminated with any of three types of light sources; light emitting diodes, laser diodes and a ring dye laser. Interference images are obtained by using a 4-frame phase shifting method, and are combined to calculate

Nilanthi Warnasooriya

2008-01-01

289

X-ray phase contrast imaging and noise evaluation using a single phase grating interferometer.  

PubMed

In this paper we present some quantitative measurements of X-ray phase contrast images and noise evaluation obtained with a recent grating based X-ray phase contrast interferometer. This device is built using a single phase grating and a large broadband X-ray source. It was calibrated using a reference sample and finally used to perform measurements of a biological fossil: a mosquito trapped in amber. As phase images, noise was evaluated from the measured interferograms. PMID:23938580

Rizzi, J; Mercère, P; Idir, M; Silva, P Da; Vincent, G; Primot, Jérôme

2013-07-15

290

Effect of coherence loss in differential phase contrast imaging  

NASA Astrophysics Data System (ADS)

Coherence property of x-rays is critical in the grating-based differential phase contrast (DPC) imaging because it is the physical foundation that makes any form of phase contrast imaging possible. Loss of coherence is an important experimental issue, which results in increased image noise and reduced object contrast in DPC images and DPC cone beam CT (DPC-CBCT) reconstructions. In this study, experimental results are investigated to characterize the visibility loss (a measurement of coherence loss) in several different applications, including different-sized phantom imaging, specimen imaging and small animal imaging. Key measurements include coherence loss (relative intensity changes in the area of interest in phase-stepping images), contrast and noise level in retrieved DPC images, and contrast and noise level in reconstructed DPC-CBCT images. The influence of size and composition of imaged object (uniform object, bones, skin hairs, tissues, and etc) will be quantified. The same investigation is also applied for moiré pattern-based DPC-CBCT imaging with the same exposure dose. A theoretical model is established to relate coherence loss, noise level in phase stepping images (or moiré images), and the contrast and noise in the retrieved DPC images. Experiment results show that uniform objects lead to a small coherence loss even when the attenuation is higher, while objects with large amount of small structures result in huge coherence loss even when the attenuation is small. The theoretical model predicts the noise level in retrieved DPC images, and it also suggests a minimum dose required for DPC imaging to compensate for coherence loss.

Cai, Weixing; Ning, Ruola; Liu, Jiangkun

2014-03-01

291

Phase contrast without phase plates and phase rings--optical solutions for improved imaging of phase structures.  

PubMed

Using the optical methods described, phase specimens can be observed with a modified light microscope in enhanced clarity, purified from typical artifacts which are apparent in standard phase contrast illumination. In particular, haloing and shade-off are absent, lateral and vertical resolution are maximized and the image quality remains constant even in problematic preparations which cannot be well examined in normal phase contrast, such as specimens beyond a critical thickness or covered by obliquely situated cover slips. The background brightness and thus the range of contrast can be continuously modulated and specimens can be illuminated in concentric-peripheral, axial or paraxial light. Additional contrast effects can be achieved by spectral color separation. Normal glass or mirror lenses can be used; they do not need to be fitted with a phase plate or a phase ring. The methods described should be of general interest for all disciplines using phase microscopy. PMID:23913620

Piper, Timm; Piper, Jörg

2013-10-01

292

Figure 2. Initial images (a) were reconstructed from data acquired with reduction factor R=4 by 4-coil phase array (Nc=4); (b) is the resulting  

E-print Network

obtained on a 1.5T GE SIGNA (GE Medical Systems, Milwaukee, WI) system using 4- coil phased arrays. Typical-coil phase array (Nc=4); (b) is the resulting image (50 iterations of the proposed method with n=1.5Ln is the number of coil elements; si(r), Si(k) are i-th coil sensitivity profile and its Fourier transform (i=1

Utah, University of

293

Nonlinear Fourier correlation  

NASA Astrophysics Data System (ADS)

Fourier correlators perform space-invariant linear filtering on all input points, so they can identify and locate patterns in parallel. Each output point is a weighted sum of components of the Fourier transform of the input, so the discriminants used are inherently linear. As most practical problems are not linearly discriminable, that causes a problem. This paper describes a quite general solution involving nonlinear combining of nonlinearly processed outputs from multiple Fourier masks. The design of the masks and nonlinearities allows very powerful nonlinear discrimination that preserves the space-invariant feature that makes Fourier correlators attractive. Given a set of target-class images, henceforth referred to as the training set or trainers, the algorithm developed herein computes an ordered set of classifier filters - Generalized Matched Filters (GMFs) threshold values. An unlabeled image is applied to the classifier filter set, hereafter referred to as super-generalized matched filter (SGMF). If the peak response of any of the classifier filters (GMFs) to the unlabeled test image exceeds the threshold level the decision is made in favor of labeling the image as target-class otherwise it is labeled non-target- class.

Heidary, Kaveh; Caulfield, H. John

2009-04-01

294

Lensless Coherent Imaging with Shaped Illumination and Phase-Retrieval Image Reconstruction  

E-print Network

on the illumination system. For imaging through atmospheric turbulence with adaptive optics, a great burden is placed on the receiving optics, wavefront sensor, and deformable mirror. For imaging through atmospheric turbulence usingLensless Coherent Imaging with Shaped Illumination and Phase-Retrieval Image Reconstruction James R

Fienup, James R.

295

Fast volumetric phase-gradient imaging in thick samples  

PubMed Central

Oblique back-illumination microscopy (OBM) provides high resolution, sub-surface phase-gradient images from arbitrarily thick samples. We present an image formation theory for OBM and demonstrate that OBM lends itself to volumetric imaging because of its capacity for optical sectioning. In particular, OBM can provide extended depth of field (EDOF) images from single exposures, by rapidly scanning the focal plane with an electrically tunable lens. These EDOF images can be further enhanced by deconvolution. We corroborate our theory with experimental volumetric images obtained from transparent bead samples and mouse cortical brain slices. PMID:24515075

David Giese, J.; Ford, Tim N.; Mertz, Jerome

2014-01-01

296

a One-Dimensional Phased Array Acoustic Imaging System.  

NASA Astrophysics Data System (ADS)

An acoustic phased array imaging system is a device that uses high frequency sound waves to image the acoustic reflectivity or opacity of objects in an acoustically transparent medium. Its operation is similar to that of phased array radar in that a phase front is synthesized by controlling the phase of the energy radiated from each element of an array of radiators. The resulting beam is electronically translated across the field of view thereby producing a scan of the image field. The acoustic phased array systems described in this dissertation differ from most phased array radar systems in that they were designed to image objects in the near field of the array aperture. The first system could control the phase in increments of 3.14 radians. Unfortunately, this system was unusable due to a very high background level in its focal plane response. Analysis of this effect showed that this background was a direct result of the large phase increment. A computer program was written to look at the effects of reducing the size of this phase step. The computer generated results differed enough from those predicted by the phased array theories to warrant a theoretical investigation. The resulting analyses are presented along with those that predict the effects due to element to element crosstalk, missing elements, and amplitude and phase errors in the radiated acoustic field. The second phased array system was designed using the results of these analyses. A detailed description of the design concepts are presented along with the construction details of this, the multi-phase imaging, system. The focal plane responses of this device are shown to verify the predicted effects the phase increment size.

Bates, Kenneth Norris

1982-03-01

297

Shot noise perturbations in digital holographic microscopy phase images  

NASA Astrophysics Data System (ADS)

In digital holographic microscopy, shot noise is an intrinsic part of the recording process with a digital camera. We present a study based on simulations describing how shot noise influences the quality of the reconstructed phase images under different beams intensities configurations. A model for image quality estimation based on the decision statistical theory proposed by Wagner and Brown (R.F. Wagner and D.G. Brown, "Unified SNR Analysis of Medical Imaging-Systems," Phys. Med. Biol. 30, 489-518 (1985)) will be presented. A simulation will depict the variations of the reconstructed phase images SNR for different distributions of the total intensity between the reference and the object beam.

Charrière, Florian; Montfort, Frederic; Cuche, Etienne; Depeursinge, Christian D.

2006-05-01

298

Real-time pipelined heterogeneous system for windowed Fourier filtering and quality guided phase unwrapping algorithm using Graphic Processing Unit  

Microsoft Academic Search

Phase unwrapping refers to the reconstruction process of a continuous phase distribution from a wrapped phase map in optical interferometers, fringe projection systems and synthetic aperture radars. Usually, phase unwrapping (PU) is challenging due to speckle noise, atmosphere interference, and long discontinuities. Two dimensional phase unwrapping algorithms have been developed for several decades including the classic path-following PU algorithm and

Wenjing Gao; Qian Kemao

2010-01-01

299

Characterization of skin abnormalities in a mouse model of osteogenesis imperfecta using high resolution magnetic resonance imaging and Fourier transform infrared imaging spectroscopy.  

PubMed

Evaluation of the skin phenotype in osteogenesis imperfecta (OI) typically involves biochemical measurements, such as histologic or biochemical assessment of the collagen produced from biopsy-derived dermal fibroblasts. As an alternative, the current study utilized non-invasive magnetic resonance imaging (MRI) microscopy and optical spectroscopy to define biophysical characteristics of skin in an animal model of OI. MRI of skin harvested from control, homozygous oim/oim and heterozygous oim/+ mice demonstrated several differences in anatomic and biophysical properties. Fourier transform infrared imaging spectroscopy (FT-IRIS) was used to interpret observed MRI signal characteristics in terms of chemical composition. Differences between wild-type and OI mouse skin included the appearance of a collagen-depleted lower dermal layer containing prominent hair follicles in the oim/oim mice, accounting for 55% of skin thickness in these. The MRI magnetization transfer rate was lower by 50% in this layer as compared to the upper dermis, consistent with lower collagen content. The MRI transverse relaxation time, T2, was greater by 30% in the dermis of the oim/oim mice compared to controls, consistent with a more highly hydrated collagen network. Similarly, an FT-IRIS-defined measure of collagen integrity was 30% lower in the oim/oim mice. We conclude that characterization of phenotypic differences between the skin of OI and wild-type mice by MRI and FT-IRIS is feasible, and that these techniques provide powerful complementary approaches for the analysis of the skin phenotype in animal models of disease. PMID:21845737

Canuto, H C; Fishbein, K W; Huang, A; Doty, S B; Herbert, R A; Peckham, J; Pleshko, N; Spencer, R G

2012-01-01

300

ECT imaging of three-phase fluidized bed based on three-phase capacitance model  

Microsoft Academic Search

In this work, the electrical capacitance tomography (ECT) with neural network multi-criteria optimization image reconstruction technique (NN-MOIRT), early developed by the authors, is applied to imaging bubble column and three-phase fluidized bed systems in the real time manner. Air, norpar (paraffin) and glass-beads are used as the gas, liquid, and solid phases, respectively. A three-phase capacitance model coupled with a

W Warsito; L.-S Fan

2003-01-01

301

Algorithms for extracting true phase from rotationally-diverse and phase-shifted DIC images  

Microsoft Academic Search

In this paper, we report on the status of our current algorithms and extensions for improved algorithms for extracting phase from images acquired with differential-interference-contrast (DIC) microscopy. Our algorithms are based on two different approaches for the computation of a specimen's phase function or optical path length (OPL) distribution from DIC images. The first approach uses an iterative phase-estimation method

Chrysanthe Preza; Sharon V. King; Carol J. Cogswell

2006-01-01

302

Geometric phase analysis of lattice images from algal cellulose microfibrils  

Microsoft Academic Search

A geometric phase analysis has been applied to high-resolution transmission electron microscopy images from algal cellulose microcrystals. The pictures were decomposed into images containing selectively the amplitude or phase information associated to selected Bragg reflections. Compared with I? (monoclinic)-rich cellulose microfibrils, I?(triclinic)-rich microfibrils were found to be more heterogeneous when viewed along the H-bonding sheets. As a microfibril twist and

Tomoya Imai; Jean-Luc Putaux; Junji Sugiyama

2003-01-01

303

Phase contrast enhanced x-ray imaging of ICF capsules  

Microsoft Academic Search

We experimentally demonstrate phase-contrast enhanced x-ray imaging of deuterium-tritium (D-T) fuel layers inside of a copper-doped beryllium ablator using a point-projection x-ray microscope. Solid D-T layers with a RMS roughness of 2 mum have been made inside of a Be capsule. Computational modeling demonstrates that a rough surface can be accurately characterized using phase-contrast enhanced x-ray imaging. This characterization method

Bernard Kozioziemski; James Sater; John Moody; Jeffrey Koch; Anton Barty; Harry Martz; Thomas Bernat; James Pipes; John Burmann; Russell Jones; R. Derrill Rikard; William Brown

2004-01-01

304

Data Fusion of Lockin-Thermography Phase Images  

Microsoft Academic Search

Lockin-thermography is a valuable tool in non-destructive testing of materials because it provides reliable and easy-to-interpret phase images. This paper presents a way to combine phase images obtained at different lockin-frequencies by using scatter plots. Not only features like defects can be extracted out of the raw data, but also thermal wave parameters like reflection coefficients. The extracted features can

C. Spiessberger; A. Gleiter; G. Busse

305

Advanced phase correction approach to obtain radiometric calibrated spectra of the optically well-balanced balloonborne Fourier transform spectrometer MIPAS-B2  

NASA Astrophysics Data System (ADS)

The balloon borne IR-Fourier transform spectrometer (FTS) MIPAS-B2 has been designed for a low self-emission from each of the instrument ports leading to low noise signals and a radiometrically balanced interferometer. The radiometric accuracy depends strongly on the quality of the phase correction of interferograms and of the calibration measurements and algorithms. It could be observed that the classically derived phases of the complex spectra are in correlation with line structures in the spectrum and cause disturbed calibrated spectra. These phase functions cannot be explained by the instrumental phase due to the beamsplitter nor by sampling shifts but by the emission of the beamsplitter itself. The determination of the instrumental phase function requires to invent an unconventional technique. According to the low radiance received from the stratosphere noise has also to be taken into account, especially in case of single non- coadded spectra. Therefore an advanced statistical method was investigated to derive the phase of the interferogram by minimizing the correlation of the real and imaginary part of the spectrum as well as the variance of the imaginary part (the beamsplitter spectrum). The complete processing and calibration scheme of the FTS-emission sounder will be presented focusing on a detailed description of phase behavior due to the beamsplitter emission and of the correction process.

Trieschmann, Olaf; Friedl-Vallon, Felix; Lengel, Anton; Oelhaf, Hermann; Wetzel, Gerald; Fischer, Herbert

1999-10-01

306

Phase Sensitive X-Ray Imaging: Towards its Interdisciplinary Applications  

NASA Astrophysics Data System (ADS)

X-ray phase imaging including phase tomography has been attracting increasing attention during the past few decades. The advantage of X-ray phase imaging is that an extremely high sensitivity is achieved for weakly absorbing materials, such as biological soft tissues, which generate a poor contrast by conventional schemes. Especially for such living samples, where the reduction of the applied dose is of paramount interest, phase sensitive measurements schemes have an inherent potential for a significant dose reduction combined with an image quality enhancement. Several methods have been invented for x-ray phase contrast imaging that either use an approach based on interferometry, diffraction or wave-field propagation. Some of these techniques have a potential for commercial applications, such as in medicine, non-destructive testing, security and inspection. The scope of this manuscript thus deals with one particular such technique that measures the diffraction caused by the specimen by means of a grating interferometer. Examples of measurements are shown that depict the potential of phase contrast imaging for future commercial applications, such as in medical imaging, non-destructive testing and inspection for quality control. The current state of the technology is briefly reviewed as well as its shortcomings to be overcome with regard to the applications.

Kottler, C.; Revol, V.; Kaufmann, R.; Urban, C.; Knop, K.; Sennhauser, U.; Jerjen, I.; Lüthi, T.; Cardot, F.; Niedermann, P.; Morel, J.-P.; Maake, C.; Walt, H.; Knop, E.; Blanc, N.

2010-04-01

307

Imaging through turbulence with a quadrature-phase optical interferometer  

Microsoft Academic Search

We present an improved technique for imaging through turbulence at visible wavelengths using a rotation shearing pupil-plane interferometer, intended for astronomical and terrestrial imaging applications. While previous astronomical rotation shearing interferometers have made only visibility modulus measurements, this interferometer makes four simultaneous measurements on each interferometric baseline, with phase differences of 2 between each measurement, allowing complex visibility measurements (modulus

Brian Kern; Paul E. Dimotakis; Chris Martin; Daniel B. Lang; Rachel N. Thessin

2005-01-01

308

Motionless phase stepping in X-ray phase contrast imaging with a compact source  

PubMed Central

X-ray phase contrast imaging offers a way to visualize the internal structures of an object without the need to deposit significant radiation, and thereby alleviate the main concern in X-ray diagnostic imaging procedures today. Grating-based differential phase contrast imaging techniques are compatible with compact X-ray sources, which is a key requirement for the majority of clinical X-ray modalities. However, these methods are substantially limited by the need for mechanical phase stepping. We describe an electromagnetic phase-stepping method that eliminates mechanical motion, thus removing the constraints in speed, accuracy, and flexibility. The method is broadly applicable to both projection and tomography imaging modes. The transition from mechanical to electromagnetic scanning should greatly facilitate the translation of X-ray phase contrast techniques into mainstream applications. PMID:24218599

Miao, Houxun; Chen, Lei; Bennett, Eric E.; Adamo, Nick M.; Gomella, Andrew A.; DeLuca, Alexa M.; Patel, Ajay; Morgan, Nicole Y.; Wen, Han

2013-01-01

309

Triple-phase bone image abnormalities in Lyme arthritis  

SciTech Connect

Arthritis is a frequent manifestation of Lyme disease. Limited triple-phase Tc-99m MDP bone imaging of the wrists and hands with delayed whole-body images was performed in a patient with Lyme arthritis. This demonstrated abnormal joint uptake in the wrists and hands in all three phases, with increased activity seen in other affected joints on delayed whole-body images. These findings are nonspecific and have been previously described in a variety of rheumatologic conditions, but not in Lyme disease. Lyme disease should be considered in the differential diagnosis of articular and periarticular bone scan abnormalities.

Brown, S.J.; Dadparvar, S.; Slizofski, W.J.; Glab, L.B.; Burger, M. (Hahnemann Univ. Hospital, Philadelphia, PA (USA))

1989-10-01

310

Range estimation from two-dimensional images using phase modulation  

Microsoft Academic Search

A new approach for estimating the depth of both diffuse and specular surfaces is presented. The method uses the 1D local spatial phase of a 2D image of the object acquired using structured-light illumination. The induced phase modulation of the structured-light pattern is used as a depth cue. For diffuse surfaces, the local phase is used directly to estimate the

Xiaoyu Zhang; Richard J. Mammone

1994-01-01

311

Quantitative phase imaging using a partitioned detection aperture.  

PubMed

We present a technique to quantitatively image the phase of thin quasi-transparent samples using extended source incoherent illumination and off-axis detection apertures. Our technique is achromatic and polarization independent, requires no active elements, and can be readily adapted to standard bright-field microscopes. We demonstrate our technique by quantitatively reconstructing the phase of cheek cells and a microlens. The light efficient, single-shot nature of our technique enables phase imaging at frame rates that are camera limited. PMID:23027279

Parthasarathy, Ashwin B; Chu, Kengyeh K; Ford, Tim N; Mertz, Jerome

2012-10-01

312

Phase-shifting technique for improving the imaging capacity of sparse-aperture optical interferometers.  

PubMed

We describe the principle of a multiaperture interferometer that uses a phase-shifting technique and is suitable for quick snapshot imaging of astrophysical objects at extreme angular resolution through Fourier inversion. A few advantages of the proposed design are highlighted, among which are radiometric efficiency, field of view equivalent to those of Fizeau interferometers, and a preliminary calibration procedure allowing characterization of instrumental errors. For large telescope numbers, the proposed design also results in considerable simplification of the optical and mechanical design. Numerical simulations suggest that it should be possible to couple hundreds of telescopes on a single 4K × 4K detector array, using only conventional optical components or emerging technologies. PMID:21772409

Hénault, François

2011-07-20

313

Phase Preserving Dynamic Range Compression of Aeromagnetic Images  

NASA Astrophysics Data System (ADS)

Geoscientific images with a high dynamic range, such as aeromagnetic images, are difficult to present in a manner that facilitates interpretation. The data values may range over 20000 nanoteslas or more but a computer monitor is typically designed to present input data constrained to 8 bit values. Standard photographic high dynamic range tonemapping algorithms may be unsuitable, or inapplicable to such data because they are have been developed on the basis of statistics of natural images, feature types found in natural images, and models of the human visual system. These algorithms may also require image segmentation and/or decomposition of the image into base and detail layers but these operations may have no meaning for geoscientific images. For geological and geophysical data high dynamic range images are often dealt with via histogram equalization. The problem with this approach is that the contrast stretch or compression applied to data values depends on how frequently the data values occur in the image and not on the magnitude of any data features themselves. This can lead to inappropriate distortions in the output. Other approaches include use of the Automatic Gain Control algorithm developed by Rajagopalan, or the tilt derivative. A difficulty with these approaches is that the signal can be over-normalized and perception of the overall variations in the signal can be lost. To overcome these problems a method is presented that compresses the dynamic range of an image while preserving local features. It makes no assumptions about the formation of the image, the feature types it contains, or its range of values. Thus, unlike algorithms designed for photographic images, this algorithm can be applied to a wide range of scientific images. The method is based on extracting local phase and amplitude values across the image using monogenic filters. The dynamic range of the image can then be reduced by applying a range reducing function to the amplitude values, for example taking the logarithm, and then reconstructing the image using the original phase values. An important attribute of this approach is that the local phase information is preserved, this is important for the human visual system in interpreting the image. The result is an image that retains the fidelity of its features within a greatly reduced dynamic range. An additional advantage of the method is that the range of spatial frequencies that are used to reconstruct the image can be chosen via high-pass filtering to control the scale of analysis. A relatively low cutoff frequency allows large overall trends in the data to be observed. As the spatial cutoff frequency is progressively increased the analysis becomes more localized and the relative magnitudes of features become more equal.

Kovesi, Peter

2014-05-01

314

Automatic evaluation of nickel alloy secondary phases from SEM images.  

PubMed

Quantitative metallography is a technique to determine and correlate the microstructures of materials with their properties and behavior. Generic commercial image processing and analysis software packages have been used to quantify material phases from metallographic images. However, these all-purpose solutions also have some drawbacks, particularly when applied to segmentation of material phases. To overcome such limitations, this work presents a new solution to automatically segment and quantify material phases from SEM metallographic images. The solution is based on a neuronal network and in this work was used to identify the secondary phase precipitated in the gamma matrix of a Nickel base alloy. The results obtained by the new solution were validated by visual inspection and compared with the ones obtained by a commonly used commercial software. The conclusion is that the new solution is precise, reliable and more accurate and faster than the commercial software. PMID:21181708

de Albuquerque, Victor Hugo C; Silva, Cleiton Carvalho; Menezes, Thiago Ivo de S; Farias, Jesualdo Pereira; Tavares, João Manuel R S

2011-01-01

315

The Asymmetric Pupil Fourier Wavefront Sensor  

E-print Network

This paper introduces a novel wavefront sensing approach that relies on the Fourier analysis of a single conventional direct image. In the high Strehl ratio regime, the relation between the phase measured in the Fourier plane and the wavefront errors in the pupil can be linearized, as was shown in a previous work that introduced the notion of generalized closure-phase, or kernel-phase. The technique, to be usable as presented requires two conditions to be met: (1) the wavefront errors must be kept small (of the order of one radian or less) and (2) the pupil must include some asymmetry, that can be introduced with a mask, for the problem to become solvable. Simulations show that this asymmetric pupil Fourier wavefront sensing or APF-WFS technique can improve the Strehl ratio from 50 to over 90 % in just a few iterations, with excellent photon noise sensitivity properties, suggesting that on-sky close loop APF-WFS is possible with an extreme adaptive optics system.

Martinache, Frantz

2013-01-01

316

Self-imaging of transparent objects and structures in focusing of spatially phase-modulated laser radiation into a weakly absorbing medium  

SciTech Connect

Self-imaging of transparent objects and structures in focusing of a spatially phase-modulated laser beam into an extended weakly absorbing medium is described. The laser power level that is necessary for effective imaging corresponds to the illuminating beam power when thermal self-defocusing starts evolving in the medium. The effect can be described in terms of the ideology of Zernike's classical phase-contrast method. Edge enhancement in visualised images of transparent objects is experimentally demonstrated. Self-imaging of a microscopic object in the form of transparent letters and long-lived refractive-index fluctuations in liquid glycerol is shown. Due to the adaptivity of the process under consideration, unlike the classical case, self-imaging occurs also in the situations where a beam is displaced (undergoes random walk) as a whole in the Fourier plane, for example, in the presence of thermal flows. (image processing)

Bubis, E L [Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod (Russian Federation)

2011-06-30

317

Phase-Based Road Detection in Multi-Source Images  

SciTech Connect

The problem of robust automatic road detection in remotely sensed images is complicated by the fact that the sensor, spatial resolution, acquisition conditions, road width, road orientation and road material composition can all vary. A novel technique for detecting road pixels in multi-source remotely sensed images based on the phase (i.e., orientation or directional) information in edge pixels is described. A very dense map of edges extracted from the image is separated into channels, each containing edge pixels whose phases lie within a different range of orientations. The edge map associated with each channel is de-cluttered. A map of road pixels is formed by re-combining the de-cluttered channels into a composite edge image which is itself then separately de-cluttered. Road detection results are provided for DigitalGlobe and TerraServerUSA images. Road representations suitable for various applications are then discussed.

Sengupta, S K; Lopez, A S; Brase, J M; Paglieroni, D W

2004-06-16

318

Fourier Preprocessing for Hand Print Character Recognition  

Microsoft Academic Search

A pattern-recognition method, making use of Fourier transformations to extract features which are significant for a pattern, is described. The ordinary Fourier coefficients are difficult to use as input to categorizers because they contain factors dependent upon size and rotation as well as an arbitrary phase angle. From these Fourier coefficients, however, other more useful features can easily be derived.

G. H. Granlund

1972-01-01

319

Perceived Blur in Naturally Contoured Images Depends on Phase  

PubMed Central

Perceived blur is an important measure of image quality and clinical visual function. The magnitude of image blur varies across space and time under natural viewing conditions owing to changes in pupil size and accommodation. Blur is frequently studied in the laboratory with a variety of digital filters, without comparing how the choice of filter affects blur perception. We examine the perception of image blur in synthetic images composed of contours whose orientation and curvature spatial properties matched those of natural images but whose blur could be directly controlled. The images were blurred by manipulating the slope of the amplitude spectrum, Gaussian low-pass filtering or filtering with a Sinc function, which, unlike slope or Gaussian filtering, introduces periodic phase reversals similar to those in optically blurred images. For slope-filtered images, blur discrimination thresholds for over-sharpened images were extremely high and perceived blur could not be matched with either Gaussian or Sinc filtered images, suggesting that directly manipulating image slope does not simulate the perception of blur. For Gaussian- and Sinc-blurred images, blur discrimination thresholds were dipper-shaped and were well-fit with a simple variance discrimination model and with a contrast detection threshold model, but the latter required different contrast sensitivity functions for different types of blur. Blur matches between Gaussian- and Sinc-blurred images were used to test several models of blur perception and were in good agreement with models based on luminance slope, but not with spatial frequency based models. Collectively, these results show that the relative phases of image components, in addition to their relative amplitudes, determines perceived blur. PMID:21833246

Murray, Stephanie; Bex, Peter J.

2010-01-01

320

Super resolution imaging with an ELT: Kernel-phase interferometry  

NASA Astrophysics Data System (ADS)

Kernel-phase is a recently developed paradigm that tackles the classical problem of image deconvolution, based on an interferometric point of view of image formation. Kernel-phase inherits and borrows from the notion of closure-phase, especially as it is used in the context of non-redundant Fizeau interferometry, but extends its application to pupils of arbitrary shape, for diffraction limited images. The additional calibration brought by kernel-phase boosts the resolution of conventional images and enables the detection of otherwise hidden faint features at the resolution limit and beyond, a regime often refered to as super-resolution, which for a 30-meter telescope in the near IR, this translates into a resolving power smaller than 10 mas. Kernel-phase analysis of archival space and ground based AO data leads to new discoveries and/or improved relative astrometry and photometry. The paper presents the current status of the technique and some of its recent developments and applications that lead to recommendations for super-resolution imaging with ELTs.

Martinache, Frantz

2013-12-01

321

Robustness of phase retrieval methods in x-ray phase contrast imaging: A comparison  

SciTech Connect

Purpose: The robustness of the phase retrieval methods is of critical importance for limiting and reducing radiation doses involved in x-ray phase contrast imaging. This work is to compare the robustness of two phase retrieval methods by analyzing the phase maps retrieved from the experimental images of a phantom. Methods: Two phase retrieval methods were compared. One method is based on the transport of intensity equation (TIE) for phase contrast projections, and the TIE-based method is the most commonly used method for phase retrieval in the literature. The other is the recently developed attenuation-partition based (AP-based) phase retrieval method. The authors applied these two methods to experimental projection images of an air-bubble wrap phantom for retrieving the phase map of the bubble wrap. The retrieved phase maps obtained by using the two methods are compared. Results: In the wrap's phase map retrieved by using the TIE-based method, no bubble is recognizable, hence, this method failed completely for phase retrieval from these bubble wrap images. Even with the help of the Tikhonov regularization, the bubbles are still hardly visible and buried in the cluttered background in the retrieved phase map. The retrieved phase values with this method are grossly erroneous. In contrast, in the wrap's phase map retrieved by using the AP-based method, the bubbles are clearly recovered. The retrieved phase values with the AP-based method are reasonably close to the estimate based on the thickness-based measurement. The authors traced these stark performance differences of the two methods to their different techniques employed to deal with the singularity problem involved in the phase retrievals. Conclusions: This comparison shows that the conventional TIE-based phase retrieval method, regardless if Tikhonov regularization is used or not, is unstable against the noise in the wrap's projection images, while the AP-based phase retrieval method is shown in these experiments to be superior to the TIE-based method for the robustness in performing the phase retrieval.

Yan, Aimin; Wu, Xizeng; Liu, Hong [Department of Radiology, University of Alabama at Birmingham, Birmingham, Alabama 35233 (United States); Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma 73019 (United States)

2011-09-15

322

A community detection approach to image segmentation and its phases  

NASA Astrophysics Data System (ADS)

In this talk, I will discuss ``unsupervised'' image segmentation that relies on phase diagram structure of the community detection method. Specifically, we apply a replica-inference-based community detection method. ``Community detection'' describes the general problem of partitioning a complex system involving many elements into optimally decoupled communities of such elements. In our image segmentation analysis, we invoke a multi-resolution community detection variant to ascertain the overall structure of the image at different resolutions. Information based measures (e.g., the normalized mutual information) are used to determine the significant structures at which ``replicas'' of the systems are strongly correlated. We report on the ``easy'', ``hard'', and ``unsolvable'' phases of the corresponding Potts model at both zero and finite temperatures. The optimal image segmentations are obtained by choosing parameters at the easy phase of the Potts model. The determination of the phase diagram in the analysis of the image segmentation is proved to be highly efficient. We demonstrate in a detailed study of various test cases that our method is fast and accurate and to be especially suited to the detection of camouflaged images.

Hu, Dandan; Ronhovde, Peter; Nussinov, Zohar

2012-02-01

323

Phase transfer function based method to alleviate image artifacts in wavefront coding imaging system  

NASA Astrophysics Data System (ADS)

Wavefront coding technique can extend the depth of filed (DOF) of the incoherent imaging system. Several rectangular separable phase masks (such as cubic type, exponential type, logarithmic type, sinusoidal type, rational type, et al) have been proposed and discussed, because they can extend the DOF up to ten times of the DOF of ordinary imaging system. But according to the research on them, researchers have pointed out that the images are damaged by the artifacts, which usually come from the non-linear phase transfer function (PTF) differences between the PTF used in the image restoration filter and the PTF related to real imaging condition. In order to alleviate the image artifacts in imaging systems with wavefront coding, an optimization model based on the PTF was proposed to make the PTF invariance with the defocus. Thereafter, an image restoration filter based on the average PTF in the designed depth of field was introduced along with the PTF-based optimization. The combination of the optimization and the image restoration proposed can alleviate the artifacts, which was confirmed by the imaging simulation of spoke target. The cubic phase mask (CPM) and exponential phase mask (EPM) were discussed as example.

Mo, Xutao; Wang, Jinjiang

2013-09-01

324

Motion-compensated hand-held common-path Fourier-domain optical coherence tomography probe for image-guided intervention  

PubMed Central

A motion-compensated, hand-held, common-path, Fourier-domain optical coherence tomography imaging probe has been developed for image-guided intervention during microsurgery. A hand-held prototype instrument was achieved by integrating an imaging fiber probe inside a stainless steel needle and attached to the ceramic shaft of a piezoelectric motor housed in an aluminum handle. The fiber probe obtains A-scan images. The distance information was extracted from the A-scans to track the sample surface distance and a fixed distance was maintained by a feedback motor control which effectively compensated hand tremor and target movements in the axial direction. Real-time data acquisition, processing, motion compensation, and image visualization and saving were implemented on a custom CPU-GPU hybrid architecture. We performed 10× zero padding to the raw spectrum to obtain 0.16 µm position accuracy with a compensation rate of 460 Hz. The root-mean-square error of hand-held distance variation from target position was measured to be 2.93 µm. We used a cross-correlation maximization-based shift correction algorithm for topology correction. To validate the system, we performed free-hand OCT M-scan imaging using various samples. PMID:23243562

Huang, Yong; Liu, Xuan; Song, Cheol; Kang, Jin U.

2012-01-01

325

An analysis of the influence of the color rendition of images reconstructed from full-color computer-generated Fourier-transform holograms  

NASA Astrophysics Data System (ADS)

The color rendition of an image reconstructed from a color computer-generated Fourier hologram (CCGFH) is both a basic and an important issue in the field of holography. In this study, CCGFHs are encoded with the Burch encoding algorithm and then loaded onto a spatial light modulator for optical reconstruction. The influence of the color rendition of the reconstructed images has been analyzed primarily through experiments. The experimental results show that the individual element size used in encoding the CCGFH is inversely proportional to both the size and the central location of the reconstructed images, whereas the wavelength of the monochromatic light used in optical reconstruction is proportional. Some parameters related to the spectrum, such as different transmittances, half-widths of the three primary color filters and different sensitivity levels to the three primary colors of the complementary metal-oxide-semiconductor (CMOS), affect the color rendition of the reconstructed image. A method for correcting color aberration in reconstructed images is proposed. Using this method, the influence of the wavelength can be corrected by stretching the reconstructed image to an appropriate size and the influence of the spectrum can be corrected by equalizing the spectral sensitivity levels of the CMOS. The color rendition of the reconstruction is improved significantly using the method. The proof-of-principle experiments demonstrate that the method is effective and feasible.

Sun, Ping; Wei, Yiwen; Wang, Zhong; Luo, Yuhan

2014-03-01

326

Optical image encryption in phase space  

NASA Astrophysics Data System (ADS)

In the field of optical information security, the research of double random phase encoding is becoming deeper with each passing day, however the encryption system is linear, and the dependencies between plaintext and ciphertext is not complicated, with leaving a great hidden danger to the security of the encryption system. In this paper, we encrypted the higher dimensional Wigner distribution function of low dimensional plaintext by using the bilinear property of Wigner distribution function. Computer simulation results show that this method can not only enlarge the key space, but also break through the linear characteristic of the traditional optical encryption technology. So it can significantly improve the safety of the encryption system.

Liu, Jun; Xu, Xiaobin; Situ, Guohai; Wu, Quanying

2014-11-01

327

Fourier Series Applet  

NSDL National Science Digital Library

This java applet simulates fourier approximations of sine, triangle, sawtooth and square waves, as well as noise, along with their phase terms and harmonics. The number of terms is adjustable, and the function can be played(in Windows), with adjustable frequency. The function can be resampled, quantized, rectified and full rectified. The applet can also simulate distortion. The page includes extensive instructions for the applet and source code.

Falstad, Paul

2004-07-13

328

Rotating vortex imaging implemented by a quantized spiral phase modulation  

NASA Astrophysics Data System (ADS)

We demonstrate both theoretically and experimentally that a spiral mask with a finite number of discrete phase levels allows a defocusing induced rotation of the point spread function in the vortex imaging. Two experimental configurations based on a spiral phase modulation of light and a spiral filtering of the spatial spectrum are studied in a unified theoretical treatment. The rotating point spread functions are analyzed in detail for imaging realized by the vortex lens and the 4-f system used in the spiral phase contrast microscopy. The theoretical results are verified by experiments using a spatial light modulator. The method is applicable to a precise focusing and optical imaging allowing depth estimation from diffracted rotation. Apart from implementation simplicity, the main advantages of the method are high energy efficiency, a possibility to operate with either complex amplitude or spatial spectrum of light and variability allowing a simple control of number of lobes of the point spread function.

Baránek, M.; Bouchal, Z.

2013-03-01

329

Single-shot phase imaging with a coded aperture.  

PubMed

We present a method of quantitatively acquiring a large complex field, containing not only amplitude information but also phase information, based on single-shot phase imaging with a coded aperture (SPICA). In SPICA, the propagating field from an object illuminated by partially coherent visible light is sieved by a coded mask, and the sieved field propagates to an image sensor, where it is captured. The sieved field is recovered from the single captured intensity image via a phase retrieval algorithm with an amplitude support constraint using the mask pattern, and then the object's complex field is reconstructed from the recovered sieved field by an algorithm employing a sparsity constraint based on compressive sensing. The system model and the theoretical bounds of SPICA are derived. We also verified the concept with numerical demonstrations. PMID:25490495

Horisaki, Ryoichi; Ogura, Yusuke; Aino, Masahiko; Tanida, Jun

2014-11-15

330

Application of Phase Correction to Improve the Interpretation of Crude Oil Spectra Obtained Using 7 T Fourier Transform Ion Cyclotron Resonance Mass Spectrometry  

NASA Astrophysics Data System (ADS)

In this study, a phase-correction technique was applied to the study of crude oil spectra obtained using a 7 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). 7 T FT-ICR MS had not been widely used for oil analysis due to the lower resolving power compared with high field FT-ICR MS. For low field instruments, usage of data that has not been phase-corrected results in an inability to resolve critical mass splits of C3 and SH4 (3.4 mDa), and 13C and CH (4.5 mDa). This results in incorrect assignments of molecular formulae, and discontinuous double bond equivalents (DBE) and carbon number distributions of S1, S2, and hydrocarbon classes are obtained. Application of phase correction to the same data, however, improves the reliability of assignments and produces continuous DBE and carbon number distributions. Therefore, this study clearly demonstrates that phase correction improves data analysis and the reliability of assignments of molecular formulae in crude oil anlayses.

Cho, Yunju; Qi, Yulin; O'Connor, Peter B.; Barrow, Mark P.; Kim, Sunghwan

2014-01-01

331

2-D phase contrast imaging of turbulence structure on LHD  

Microsoft Academic Search

CO2 laser-based phase contrast imaging (PCI) equipped with a 6 by 8 element two-dimensional (2-D) array of photoconductors is used on the large helical device (LHD) for studying plasma density microfluctuations. Observing 2-D structures of turbulence and strong magnetic shear along the viewing line on LHD permit conversion of a 2-D-PCI image to a 2-D picture of the radial distribution

Leonid N. Vyacheslavov; K. Tanaka; A. L. Sanin; K. Kawahata; C. Michael; T. Akiyama

2005-01-01

332

Characterization using Phase-Contrast Enhanced X-Ray Imaging  

Microsoft Academic Search

Summary form only given. We demonstrate phase-contrast enhanced X-ray imaging (PCXI) for characterization of the solid deuterium-tritium surface inside of beryllium shells. This novel method of X-ray imaging takes advantage of the small refraction and diffraction of the X-rays at boundaries between materials. PCXI is more sensitive to small density changes in low atomic number materials than traditional absorption radiography.

B. Kozioziemski; J. D. Moody; J. D. Sater; H. E. Martz; A. Barty; D. S. Montgomery

2005-01-01

333

Application of phase stepping imaging polarimetry technique in ophthalmology  

NASA Astrophysics Data System (ADS)

The cornea is the outermost segment of the eyeball. Due to it's lamellar structure the cornea indicates the optical anisotropy and effect of birefringence. We have applied phase stepping imaging polarimetry to measure birefringence of the human cornea in vivo and in vitro. Investigation of the corneal birefringence could be useful for examining the inner corneal structure, its lamellar arrangement and in medical diagnosing of corneal pathologies. There are also some potential applications of this method in transplantation of human corneas and refractive surgery procedures. The phase stepping imaging polarimetry technique used here, allows calculating azimuth angle, phase retardation and transmission coefficient of the sample. The method uses simple setup, sample at rest, and enables fast and accurate acquisition of data. The theory of the method is included. Experimental results of azimuth angle and phase retardation distribution for human cornea in vivo and in vitro are also presented.

Jaronski, Jaroslaw W.; Kasprzak, Henryk T.

1999-08-01

334

Self-imaging of transparent objects and structures in focusing of spatially phase-modulated laser radiation into a weakly absorbing medium  

NASA Astrophysics Data System (ADS)

Self-imaging of transparent objects and structures in focusing of a spatially phase-modulated laser beam into an extended weakly absorbing medium is described. The laser power level that is necessary for effective imaging corresponds to the illuminating beam power when thermal self-defocusing starts evolving in the medium. The effect can be described in terms of the ideology of Zernike's classical phase-contrast method. Edge enhancement in visualised images of transparent objects is experimentally demonstrated. Self-imaging of a microscopic object in the form of transparent letters and long-lived refractive-index fluctuations in liquid glycerol is shown. Due to the adaptivity of the process under consideration, unlike the classical case, self-imaging occurs also in the situations where a beam is displaced (undergoes random walk) as a whole in the Fourier plane, for example, in the presence of thermal flows.

Bubis, E. L.

2011-06-01

335

Dynamic quantitative phase imaging for biological objects using a pixelated phase mask  

PubMed Central

This paper describes research in developing a dynamic quantitative phase imaging microscope providing instantaneous measurements of dynamic motions within and among live cells without labels or contrast agents. It utilizes a pixelated phase mask enabling simultaneous measurement of multiple interference patterns derived using the polarization properties of light to track dynamic motions and morphological changes. Optical path difference (OPD) and optical thickness (OT) data are obtained from phase images. Two different processing routines are presented to remove background surface shape to enable quantification of changes in cell position and volume over time. Data from a number of different moving biological organisms and cell cultures are presented. PMID:23162725

Creath, Katherine; Goldstein, Goldie

2012-01-01

336

Full-phase image encryption by two-step phase-shifting interferometry  

NASA Astrophysics Data System (ADS)

We have proposed a full-phase image encryption method based on double random-phase encoding in Fresnel domain and pixel random permutation (PRP) technique with the use of two-step phase-shifting interferometry (PSI) we reported recently, and verified the effectiveness of this method and its robustness against occlusion and noise attacks by a series of numerical simulations. Comparing with other similar methods, this approach can decrease the number of the interferograms to be delivered from at least three needed in ordinary PSI to only two, give much better performance of image reconstruction than amplitude-based encryption, and provide much higher security level. This method is usable for both the gray-level images and binary images, and usually the latter will lead to better results.

Meng, Xiangfeng; Cai, Luzhong; Xu, Xianfeng; Yang, Xiulun; Shen, Xiaoxia; Dong, Guoyan; Zhang, Hao

2008-07-01

337

Phase-shifting digital holography in image reconstruction  

Microsoft Academic Search

A phase-shifting digital holography scheme developed to investigate internal defects in artworks is described. Phase-shifting\\u000a is utilized to obtain a clear reconstructed object wave from a rough surface texture. A reverse-transform algorithm is employed\\u000a to reconstruct the object wave on its original position of unknown distance or the imaging position from the object wave information\\u000a on the holographic plane. To

Ying-jie Yu; Wen-jing Zhou; Orphanos Yannis; Tornari Vivi

2006-01-01

338

Image quality evaluation with a new phase rotation beamformer  

Microsoft Academic Search

Over the last few decades, dynamic focusing based on digital receive beamforming (DRBF) has led to significant improvements in image quality. However, it is computationally very demanding due to its requirement for multiple lowpass filters (e.g., a complex filter for each receive channel in quadrature demodulation-based phase rotation beamform- ers (QD-PRBF)). We recently developed a novel phase rotation beamformer with

Anup Agarwal; Fabio Kurt Schneider; Yang Mo Yoo; Yongmin Kim

2008-01-01

339

DIPSI: the diffraction image phase sensing instrument for APE  

NASA Astrophysics Data System (ADS)

Large segmented mirrors require efficient co-phasing techniques in order to avoid the image degradation due to segments misalignment. For this purpose in the last few years new co-phasing techniques have been developed in collaboration with several European institutes. The Active Phasing Experiment (APE) will be a technical instrument aimed at testing different phasing techniques for an Extremely Large Telescope (ELT). A mirror composed of 61 hexagonal segments will be conjugated to the primary mirror of the VLT (Very Large Telescope). Each segment can be moved in piston, tip and tilt. Three new types of co-phasing sensors dedicated to the measurement of segmentation errors will be tested, evaluated and compared: ZEUS (Zernike Unit for Segment phasing) developed by LAM and IAC, PYPS (PYramid Phase Sensor) developed by INAF/ARCETRI, and DIPSI (Diffraction Image Phase Sensing Instrument) developed by IAC, GRANTECAN and LAM. This experiment will first run in the laboratory with point-like polychromatic sources and a turbulence generator. In a second step, it will be mounted at the Nasmyth platform focus of a VLT unit telescope. This paper describes the scientific concept of DIPSI, its optomechanical design, the signal analysis to retrieve segment piston and tip-tilt, the multiwavelength algorithm to increase the capture range, and the multiple segmentation case, including both simulation and laboratory tests results.

Montoya-Martínez, Luzma; Reyes, Marcos; Schumacher, Achim; Hernández, Elvio

2006-06-01

340

Sparse phase-stepping in two-dimensional x-ray phase contrast imaging.  

PubMed

We have developed a sparse phase-stepping (SPS) method for x-ray Talbot-Lau interferometry, which first constructs a SPS intensity pattern of fewer images than the conventional phase-stepping (PS) method and then fills the data gap with neighboring pixels for phase retrieval. The SPS method is highly beneficial in practice since the fundamental difference in spatial resolution between the SPS and PS methods becomes negligible due to the blur caused by an interferometer. The concept of the SPS method has been proved by the experiment using a small effective source size. Furthermore, the experiment using a large effective source size has verified that in practical situations the SPS method can reduce the required number of images for phase retrieval and still offer the retrieved images with as high a spatial resolution as the PS method. PMID:24787585

Kondoh, Takeshi; Date, Takashi; Yamaguchi, Kimiaki; Nagai, Kentaro; Sato, Genta; Handa, Soichiro; Den, Toru; Itoh, Hidenosuke; Nakamura, Takashi

2014-04-20

341

Whole-cell phase contrast imaging at the nanoscale using Fresnel Coherent Diffractive Imaging Tomography  

NASA Astrophysics Data System (ADS)

X-ray tomography can provide structural information of whole cells in close to their native state. Radiation-induced damage, however, imposes a practical limit to image resolution, and as such, a choice between damage, image contrast, and image resolution must be made. New coherent diffractive imaging techniques, such Fresnel Coherent Diffractive Imaging (FCDI), allows quantitative phase information with exceptional dose efficiency, high contrast, and nano-scale resolution. Here we present three-dimensional quantitative images of a whole eukaryotic cell by FCDI at a spatial resolution below 70 nm with sufficient phase contrast to distinguish major cellular components. From our data, we estimate that the minimum dose required for a similar resolution is close to that predicted by the Rose criterion, considerably below accepted estimates of the maximum dose a frozen-hydrated cell can tolerate. Based on the dose efficiency, contrast, and resolution achieved, we expect this technique will find immediate applications in tomographic cellular characterisation.

Jones, Michael W. M.; van Riessen, Grant A.; Abbey, Brian; Putkunz, Corey T.; Junker, Mark D.; Balaur, Eugeniu; Vine, David J.; McNulty, Ian; Chen, Bo; Arhatari, Benedicta D.; Frankland, Sarah; Nugent, Keith A.; Tilley, Leann; Peele, Andrew G.

2013-07-01

342

Advanced phase-contrast imaging using a grating interferometer.  

PubMed

Phase-sensitive X-ray imaging methods can provide substantially increased contrast over conventional absorption-based imaging, and therefore new and otherwise inaccessible information. Differential phase-contrast (DPC) imaging, which uses a grating interferometer and a phase-stepping technique, has been integrated into TOMCAT, a beamline dedicated to tomographic microscopy and coherent radiology experiments at the Swiss Light Source. Developments have been made focusing on the fast acquisition and post-processing of data to enable a high-throughput of samples, with obvious advantages, also through increasing the efficiency of the detecting system, of helping to reduce radiation dose imparted to the sample. A novel aquarium design allows a vertical rotation axis below the sample with measurements performed in aqueous environment. Optimization of the data acquisition procedure enables a full phase volume (1024 x 1024 pixels x 1000 projections x 9 phase steps, i.e. 9000 projections in total) to be acquired in 20 min (with a pixel size of 7.4 microm), and the subsequent post-processing has been integrated into the beamline pipeline for sinogram generation. Local DPC tomography allows one to focus with higher magnification on a particular region of interest of a sample without the presence of local tomography reconstruction artifacts. Furthermore, 'widefield' imaging is shown for DPC scans for the first time, enabling the field of view of the imaging system to be doubled for samples that are larger than the magnification allows. A case study is illustrated focusing on the visualization of soft tissue features, and particularly the substantia nigra of a rat brain. Darkfield images, based on local X-ray scattering, can also be extracted from a grating-based DPC scan: an example of the advantages of darkfield contrast is shown and the potential of darkfield X-ray tomography is discussed. PMID:19535872

McDonald, Samuel Alan; Marone, Federica; Hintermüller, Christoph; Mikuljan, Gordan; David, Christian; Pfeiffer, Franz; Stampanoni, Marco

2009-07-01

343

Programs for high-speed Fourier, Mellin and Fourier-Bessel transforms  

NASA Technical Reports Server (NTRS)

Several FORTRAN program modules for performing one-dimensional and two-dimensional discrete Fourier transforms, Mellin, and Fourier-Bessel transforms are described along with programs that realize the algebra of high speed Fourier transforms on a computer. The programs can perform numerical harmonic analysis of functions, synthesize complex optical filters on a computer, and model holographic image processing methods.

Ikhabisimov, D. K.; Debabov, A. S.; Kolosov, B. I.; Usikov, D. A.

1979-01-01

344

Correction of phase-error for phase-resolved k-clocked optical frequency domain imaging  

NASA Astrophysics Data System (ADS)

Phase-resolved optical frequency domain imaging (OFDI) has emerged as a promising technique for blood flow measurement in human tissues. Phase stability is essential for this technique to achieve high accuracy in flow velocity measurement. In OFDI systems that use k-clocking for the data acquisition, phase-error occurs due to jitter in the data acquisition electronics. We presented a statistical analysis of jitter represented as point shifts of the k-clocked spectrum. We demonstrated a real-time phase-error correction algorithm for phase-resolved OFDI. A 50 KHz wavelength-swept laser (Axsun Technologies) based balanced-detection OFDI system was developed centered at 1310 nm. To evaluate the performance of this algorithm, a stationary gold mirror was employed as sample for phase analysis. Furthermore, we implemented this algorithm for imaging of human skin. Good-quality skin structure and Doppler image can be observed in real-time after phase-error correction. The results show that the algorithm can effectively correct the jitter-induced phase error in OFDI system.

Mo, Jianhua; Li, Jianan; de Boer, Johannes F.

2012-01-01

345

Differential phase contrast X-ray imaging system and components  

DOEpatents

A differential phase contrast X-ray imaging system includes an X-ray illumination system, a beam splitter arranged in an optical path of the X-ray illumination system, and a detection system arranged in an optical path to detect X-rays after passing through the beam splitter.

Stutman, Daniel; Finkenthal, Michael

2014-07-01

346

Clinical study in phase- contrast mammography: image-quality analysis.  

PubMed

The first clinical study of phase-contrast mammography (PCM) with synchrotron radiation was carried out at the Synchrotron Radiation for Medical Physics beamline of the Elettra synchrotron radiation facility in Trieste (Italy) in 2006-2009. The study involved 71 patients with unresolved breast abnormalities after conventional digital mammography and ultrasonography exams carried out at the Radiology Department of Trieste University Hospital. These cases were referred for mammography at the synchrotron radiation facility, with images acquired using a propagation-based phase-contrast imaging technique. To investigate the contribution of phase-contrast effects to the image quality, two experienced radiologists specialized in mammography assessed the visibility of breast abnormalities and of breast glandular structures. The images acquired at the hospital and at the synchrotron radiation facility were compared and graded according to a relative seven-grade visual scoring system. The statistical analysis highlighted that PCM with synchrotron radiation depicts normal structures and abnormal findings with higher image quality with respect to conventional digital mammography. PMID:24470410

Longo, Renata; Tonutti, Maura; Rigon, Luigi; Arfelli, Fulvia; Dreossi, Diego; Quai, Elisa; Zanconati, Fabrizio; Castelli, Edoardo; Tromba, Giuliana; Cova, Maria A

2014-03-01

347

Dynamic Studies of Lung Fluid Clearance with Phase Contrast Imaging  

SciTech Connect

Clearance of liquid from the airways at birth is a poorly understood process, partly due to the difficulties of observing and measuring the distribution of air within the lung. Imaging dynamic processes within the lung in vivo with high contrast and spatial resolution is therefore a major challenge. However, phase contrast X-ray imaging is able to exploit inhaled air as a contrast agent, rendering the lungs of small animals visible due to the large changes in the refractive index at air/tissue interfaces. In concert with the high spatial resolution afforded by X-ray imaging systems (<100 {mu}m), propagation-based phase contrast imaging is ideal for studying lung development. To this end we have utilized intense, monochromatic synchrotron radiation, together with a fast readout CCD camera, to study fluid clearance from the lungs of rabbit pups at birth. Local rates of fluid clearance have been measured from the dynamic sequences using a single image phase retrieval algorithm.

Kitchen, Marcus J.; Williams, Ivan; Irvine, Sarah C.; Morgan, Michael J.; Paganin, David M. [School of Physics, Monash University, Victoria 3800 (Australia); Lewis, Rob A.; Pavlov, Konstantin [Monash Centre for Synchrotron Science, Monash University, Victoria 3800 (Australia); Hooper, Stuart B.; Wallace, Megan J. [Department of Physiology, Monash University, Victoria 3800 (Australia); Siu, Karen K. W. [School of Physics, Monash University, Victoria 3800 (Australia); Department of Medical Imaging and Radiation Science, Monash University, Victoria 3800 (Australia); Yagi, Naoto; Uesugi, Kentaro [SPring-8/JASRI, Mikazuki, Hyogo 679-5198 (Japan)

2007-01-19

348

Phase classification by mean shift clustering of multispectral materials images.  

PubMed

A mean-shift clustering (MSC) algorithm is introduced as a valuable alternative to perform materials phase classification from multispectral images. As opposed to other multivariate statistical techniques, such as factor analysis or principal component analysis (PCA), clustering techniques directly assign a class label to each pixel, so that their outputs are phase segmented images, i.e., there is no need for an additional segmentation algorithm. On the other hand, as compared to other clustering procedures and classification methods, such as segmentation by thresholding of multiple spectral components, MSC has the advantages of not requiring previous knowledge of the number of data clusters and not assuming any shape for these clusters, i.e., neither the number nor the composition of the phases must be previously known. This makes MSC a particularly useful tool for exploratory research, assisting phase identification of unknown samples. Visualization and interpretation of the results are also simplified, since the information content of the output image does not depend on the particular choice of the content of the color channels.We applied MSC to the analysis of two sets of X-ray maps acquired in scanning electron microscopes equipped with energy-dispersive detection systems. Our results indicate that MSC is capable of detecting additional phases, not clearly identified through PCA or multiple thresholding, with a very low empirical reject rate. PMID:23800390

Martins, Diego Schmaedech; Josa, Victor M Galván; Castellano, Gustavo; da Costa, José A T Borges

2013-10-01

349

Partially coherent phase imaging with simultaneous source recovery  

PubMed Central

We propose a new method for phase retrieval that uses partially coherent illumination created by any arbitrary source shape in Köhler geometry. Using a stack of defocused intensity images, we recover not only the phase and amplitude of the sample, but also an estimate of the unknown source shape, which describes the spatial coherence of the illumination. Our algorithm uses a Kalman filtering approach which is fast, accurate and robust to noise. The method is experimentally simple and flexible, so should find use in optical, electron, X-ray and other phase imaging systems which employ partially coherent light. We provide an experimental demonstration in an optical microscope with various condenser apertures. PMID:25657890

Jingshan, Zhong; Tian, Lei; Dauwels, Justin; Waller, Laura

2014-01-01

350

Implications of a new phase function for autonomous underwater imaging  

NASA Astrophysics Data System (ADS)

Autonomous underwater vehicles do not have sufficient communications bandwidth over long ranges to send back real time images even for monitoring purposes. Autonomous imaging from underwater vehicles will therefore, require realtime imaging system performance prediction in order to ensure that the vehicle can position itself at a range that will allow it to take an image of the scene or target of interest at the required resolution and contrast level. Ideally the inherent optical properties of the surrounding waters should be measured onboard. This may not be feasible or only a restricted set may be measurable. In order to improve the prediction of the imaging performance, a physics-based analytic phase function that could effectively exploit any a priori or in-situ measured parameters would be extremely helpful. Such a new physics-based analytic phase function has been derived and tested against exact scattering codes. Among other features it is sufficiently precise to allow an accurate determination of the backscatter ratio based on an estimate of the mean index of refraction. The new formulation shows clearly why the backscatter ratio, which is the dominant factor in determining imaging range, is insensitive to the inverse power of the size distribution and almost entirely controlled by the mean index of refraction. This new formulation also has a direct application to improve inverse radiative transfer equation (RTE) modeling for estimating inherent optical properties (total absorption and total backscattering) from measured apparent optical properties (ocean color).

Fournier, G. R.; Sanjuan-Calzado, V.; Trees, C.

2014-05-01

351

Peripheral Artery Wall Imaging Using Contrast-Enhanced, Susceptibility Weighted Phase Imaging  

PubMed Central

Purpose To demonstrate improved delineation of peripheral artery wall in susceptibility weighted imaging (SWI) phase images by utilizing gadolinium contrast agent. Materials and methods Superficial femoral arteries were imaged using high resolution SWI in 11 healthy volunteers before, and after injection of gadopentetate dimeglumine. Two post-contrast scans started 1 min and 11 mins after injection respectively. Eight out of the 11 volunteers also underwent double-inversion-recovery (DIR) turbo-spin-echo (TSE) scans. The same resolution and matrix size were used between SWI and TSE studies, and TSE locations were matched to SWI images. Arterial lumen-wall phase difference and phase contrast-to-noise ratio (CNR) were measured and compared between pre- and post-contrast SWI measurements. The lumen and wall areas measured on both TSE and matching SWI images were respectively analyzed for agreement. Another 2 volunteers participated in a double-echo gradient-echo study. Results were compared to SWI. Results By injecting gadolinium contrast agent, phase difference changed by 54.5% and ?1.6%, and phase CNR changed by 85.7% and 27.0%, for the 1st and 2nd post-contrast scans respectively. Morphological measurements showed insignificant difference between TSE and SWIs based on paired t-tests; good agreements in Bland-Altman plots were achieved. The double-echo gradient-echo study had similar phase measurements as SWI. Conclusion Contrast-enhanced phase imaging improves artery wall delineation in SWI of peripheral artery wall. Contrast-enhanced SWI is a promising vessel wall imaging technique. PMID:22261774

Liu, Qi; Fan, Zhaoyang; Yang, Qi; Li, Debiao

2011-01-01

352

Absorption-Mode Fourier Transform Mass Spectrometry: the Effects of Apodization and Phasing on Modified Protein Spectra  

PubMed Central

The method of phasing broadband FT-ICR spectra allows plotting the spectra in the absorption-mode; this new approach significantly improves the quality of the data at no extra cost. Herein, an internal calibration method for calculating the phase function has been developed, and successfully applied to the top-down spectra of modified proteins, where the peak intensities vary by >100×. The result shows that the use of absorption-mode spectra allows more peaks to be discerned within the recorded data, and this can reveal much greater information about the protein and modifications under investigation. In addition, noise and harmonic peaks can be assigned immediately in the absorption-mode. PMID:23568027

Qi, Yulin; Li, Huilin; Wills, Rebecca H.; Perez-Hurtado, Pilar; Yu, Xiang; Kilgour, David. P. A.; Barrow, Mark P.; Lin, Cheng; O’Connor, Peter B.

2014-01-01

353

Fourier transform spectral imaging microscopy (FT-SIM) and scanning Raman microscopy for the detection of indoor common contaminants on the surface of dental implants.  

PubMed

Endosteal dental implants are used routinely with high success rates to rehabilitate the integrity of the dentition. However if implant surfaces become contaminated by foreign material, osseointegration may not occur and the dental implant will fail because of the lack of mechanical stability. Detection and characterization of dental implant surface contaminants is a difficult task. In this article we investigate the application of several spectral microscopy methods to detect airborne contaminants on dental implant surfaces. We found that Fourier Transform Spectral Imaging Microscopy (FT-SIM) and scanning Raman microscopy provided the most useful information. Some implants possess weak and homogeneous auto-fluorescence and are best analyzed using FT-SIM methods, while others are Raman inactive and can be analyzed using scanning Raman microscopy. PMID:25618702

Lutin, Anna; Bulatov, Valery; Jadwat, Yusuf; Wood, Neil H; Feller, Liviu; Schechter, Israel

2015-03-01

354

Fourier X-ray Scattering Radiography Yields Bone Structural Information  

PubMed Central

Purpose: To characterize certain aspects of the microscopic structures of cortical and trabecular bone by using Fourier x-ray scattering imaging. Materials and Methods: Protocols approved by the National Institutes of Health Animal Care and Use Committee were used to examine ex vivo the hind limb of a rat and the toe of a pig. The Fourier x-ray scattering imaging technique involves the use of a grid mask to modulate the cone beam and Fourier spectral filters to isolate the harmonic images. The technique yields attenuation, scattering, and phase-contrast (PC) images from a single exposure. In the rat tibia cortical bone, the scattering signals from two orthogonal grid orientations were compared by using Wilcoxon signed rank tests. In the pig toe, the heterogeneity of scattering and PC signals was compared between trabecular and compact bone regions of uniform attenuation by using F tests. Results: In cortical bone, the scattering signal was significantly higher (P < 10?15) when the grid was parallel to the periosteal surface. Trabecular bone, as compared with cortical bone, appeared highly heterogeneous on the scattering (P < 10?34) and PC (P < 10?27) images. Conclusion: The ordered alignment of the mineralized collagen fibrils in compact bone was reflected in the anisotropic scattering signal in this bone. In trabecular bone, the porosity of the mineralized matrix accounted for the granular pattern seen on the scattering and PC images. © RSNA, 2009 PMID:19403849

Wen, Han; Bennett, Eric E.; Hegedus, Monica M.; Rapacchi, Stanislas

2009-01-01

355

Fourier methods for biosequence analysis.  

PubMed Central

Novel methods are discussed for using fast Fourier transforms for DNA or protein sequence comparison. These methods are also intended as a contribution to the more general computer science problem of text search. These methods extend the capabilities of previous FFT methods and show that these methods are capable of considerable refinement. In particular, novel methods are given which (1) enable the detection of clusters of matching letters, (2) facilitate the insertion of gaps to enhance sequence similarity, and (3) accommodate to varying densities of letters in the input sequences. These methods use Fourier analysis in two distinct ways. (1) Fast Fourier transforms are used to facilitate rapid computation. (2) Fourier expansions are used to form an 'image' of the sequence comparison. PMID:2243777

Benson, D C

1990-01-01

356

Phase Closure Image Reconstruction for Future VLTI Instrumentation  

E-print Network

Classically, optical and near-infrared interferometry have relied on closure phase techniques to produce images. Such techniques allow us to achieve modest dynamic ranges. In order to test the feasibility of next generation optical interferometers in the context of the VLTI-spectro-imager (VSI), we have embarked on a study of image reconstruction and analysis. Our main aim was to test the influence of the number of telescopes, observing nights and distribution of the visibility points on the quality of the reconstructed images. Our results show that observations using six Auxiliary Telescopes (ATs) during one complete night yield the best results in general and is critical in most science cases; the number of telescopes is the determining factor in the image reconstruction outcome. In terms of imaging capabilities, an optical, six telescope VLTI-type configuration and ~200 meter baseline will achieve 4 mas spatial resolution, which is comparable to ALMA and almost 50 times better than JWST will achieve at 2.2 microns. Our results show that such an instrument will be capable of imaging, with unprecedented detail, a plethora of sources, ranging from complex stellar surfaces to microlensing events.

Mercedes E. Filho; Stephanie Renard; Paulo Garcia; Gilles Duvert; Gaspard Duchene; Eric Thiebaut; John Young; Olivier Absil; Jean-Phillipe Berger; Thomas Beckert; Sebastian Hoenig; Dieter Schertl; Gerd Weigelt; Leonardo Testi; Eric Tatuli; Virginie Borkowski; Michael de Becker; Jean Surdej; Bernard Aringer; Joseph Hron; Thomas Lebzelter; Andrea Chiavassa; Romano Corradi; Tim Harries

2008-10-02

357

Adaptive minimum variance beamforming combined with phase coherence imaging for ultrasound imaging  

NASA Astrophysics Data System (ADS)

Delay-and-sum (DAS) beamformer is extensively used in ultrasound imaging. However, the DAS beamformed signals have wide main lobe widths and high side lobe levels, which result in images with limited resolution and low contrast. Recently, a new signal processing method named phase coherence imaging (PCI) for side and grating lobes suppression was proposed. It was based on a statistical analysis of the phase dispersion in the received signals. The contrast could be significantly enhanced. For spatial resolution improvement, adaptive minimum variance (MV)-based beamformer presented in the ultrasound imaging literatures shows great potentials by minimizing off-axis signals, while keeping on-axis ones. In this paper, MV beamforming combined with PCI is introduced to effectively increase the imaging resolution and contrast simultaneously and outperform both MV and PCI beamformers. Two phase coherence factors, the phase coherence factor (PCF) and the sign coherence factor (SCF), are computed based on the measurement of the phase diversity of the received aperture data, and then used to weight the MV beamformed channel sum output. Simulations with point and cyst phantoms using FIELD II demonstrate the expected performance of the proposed beamforming method.

Xu, Mengling; Chen, Yimin; Ding, Mingyue; Ming, Yuchi

2012-03-01

358

Measurement of drug and macromolecule diffusion across atherosclerotic rabbit aorta ex vivo by attenuated total reflection-Fourier transform infrared imaging  

NASA Astrophysics Data System (ADS)

Diffusion of two model drugs-benzyl nicotinate and ibuprofen-and the plasma macromolecule albumin across atherosclerotic rabbit aorta was studied ex vivo by attenuated total reflection-Fourier transform infrared (ATR-FTIR) imaging. Solutions of these molecules were applied to the endothelial surface of histological sections of the aortic wall that were sandwiched between two impermeable surfaces. An array of spectra, each corresponding to a specific location in the section, was obtained at various times during solute diffusion into the wall and revealed the distribution of the solutes within the tissue. Benzyl nicotinate in Ringer's solution showed higher affinity for atherosclerotic plaque than for apparently healthy tissue. Transmural concentration profiles for albumin demonstrated its permeation across the section and were consistent with a relatively low distribution volume for the macromolecule in the middle of the wall. The ability of albumin to act as a drug carrier for ibuprofen, otherwise undetected within the tissue, was demonstrated by multivariate subtraction image analysis. In conclusion, ATR-FTIR imaging can be used to study transport processes in tissue samples with high spatial and temporal resolution and without the need to label the solutes under study.

Palombo, Francesca; Danoux, Charlène B.; Weinberg, Peter D.; Kazarian, Sergei G.

2009-07-01

359

Direct observation of bulk and surface chemical morphologies of Ginkgo biloba leaves by Fourier transform mid- and near-infrared microspectroscopic imaging.  

PubMed

Fourier transform infrared microspectroscopy is a powerful tool to obtain knowledge about the spatial and/or temporal distributions of the chemical compositions of plants for better understanding of their biological properties. However, the chemical morphologies of plant leaves in the plane of the blade are barely studied, because sections in this plane for mid-infrared transmission measurements are difficult to obtain. Besides, native compositions may be changed by chemical reagents used when plant samples are microtomed. To improve methods for direct infrared microspectroscopic imaging of plant leaves in the plane of the blade, the bulk and surface chemical morphologies of nonmicrotomed Ginkgo biloba leaves were characterized by near-infrared transmission and mid-infrared attenuated total reflection microspectroscopic imaging. A new self-modeling curve resolution procedure was proposed to extract the spectral and concentration information of pure compounds. Primary and secondary metabolites of secretory cavities, veins, and mesophylls of Ginkgo biloba leaf blades were analyzed, and the distributions of cuticle, protein, calcium oxalate, cellulose, and ginkgolic acids on the adaxial surface were determined. By the integration of multiple infrared microspectroscopic imaging and chemometrics methods, it is possible to analyze nonmicrotomed leaves and other plant samples directly to understand their native chemical morphologies in detail. PMID:24091737

Chen, Jianbo; Sun, Suqin; Zhou, Qun

2013-11-01

360

Structural and functional imaging of the human and small animal eyes using ultrahigh speed Fourier domain optical coherence tomography  

E-print Network

Optical coherence tomography (OCT) is a non-invasive optical imaging technique that allows the three-dimensional structure of biological tissue to be visualized with micrometer resolution. In ophthalmology OCT has the ...

Choi, Woo Jhon

2014-01-01

361

Parallel phase-sensitive three-dimensional imaging camera  

DOEpatents

An apparatus is disclosed for generating a three-dimensional (3-D) image of a scene illuminated by a pulsed light source (e.g. a laser or light-emitting diode). The apparatus, referred to as a phase-sensitive 3-D imaging camera utilizes a two-dimensional (2-D) array of photodetectors to receive light that is reflected or scattered from the scene and processes an electrical output signal from each photodetector in the 2-D array in parallel using multiple modulators, each having inputs of the photodetector output signal and a reference signal, with the reference signal provided to each modulator having a different phase delay. The output from each modulator is provided to a computational unit which can be used to generate intensity and range information for use in generating a 3-D image of the scene. The 3-D camera is capable of generating a 3-D image using a single pulse of light, or alternately can be used to generate subsequent 3-D images with each additional pulse of light.

Smithpeter, Colin L. (Albuquerque, NM); Hoover, Eddie R. (Sandia Park, NM); Pain, Bedabrata (Los Angeles, CA); Hancock, Bruce R. (Altadena, CA); Nellums, Robert O. (Albuquerque, NM)

2007-09-25

362

Image fusion scheme for differential phase contrast mammography  

NASA Astrophysics Data System (ADS)

Latest progresses in breast imaging using differential phase contrast technique pose the question how to fuse multiple information (yielded by the absorption, differential phase, and scattering signals) into a single, but more informative image for clinical diagnosis and evaluation. In this work, we propose an image fusion scheme based on the multiple-resolution (MR) framework. The three signals are first transformed into multiple bands presenting information at different frequency and then a two-step processing follows: section 3.2 an intra-band processing enhances the local signal-to-noise ratio using a novel noise estimation method and context modeling; section 3.3 an inter-band processing weights each band by considering their characteristics and contributions, as well as suppressing the global noise level. The fused image, which looks similar to conventional mammogram but with significantly enhanced detail features, is then reconstructed by inverse transform. This fused image is compatible with clinical settings and enables the radiologists to use their years of diagnosis experiences in mammography.

Wang, Z.; Clavijo, C. A.; Roessl, E.; van Stevendaal, U.; Koehler, T.; Hauser, N.; Stampanoni, M.

2013-07-01

363

A grating-based single-shot x-ray phase contrast and diffraction method for in vivo imaging  

PubMed Central

Purpose: The purpose of this study is to develop a single-shot version of the grating-based phase contrast x-ray imaging method and demonstrate its capability of in vivo animal imaging. Here, the authors describe the principle and experimental results. They show the source of artifacts in the phase contrast signal and optimal designs that minimize them. They also discuss its current limitations and ways to overcome them. Methods: A single lead grid was inserted midway between an x-ray tube and an x-ray camera in the planar radiography setting. The grid acted as a transmission grating and cast periodic dark fringes on the camera. The camera had sufficient spatial resolution to resolve the fringes. Refraction and diffraction in the imaged object manifested as position shifts and amplitude attenuation of the fringes, respectively. In order to quantify these changes precisely without imposing a fixed geometric relationship between the camera pixel array and the fringes, a spatial harmonic method in the Fourier domain was developed. The level of the differential phase (refraction) contrast as a function of hardware specifications and device geometry was derived and used to guide the optimal placement of the grid and object. Both ex vivo and in vivo images of rodent extremities were collected to demonstrate the capability of the method. The exposure time using a 50 W tube was 28 s. Results: Differential phase contrast images of glass beads acquired at various grid and object positions confirmed theoretical predictions of how phase contrast and extraneous artifacts vary with the device geometry. In anesthetized rats, a single exposure yielded artifact-free images of absorption, differential phase contrast, and diffraction. Differential phase contrast was strongest at bone-soft tissue interfaces, while diffraction was strongest in bone. Conclusions: The spatial harmonic method allowed us to obtain absorption, differential phase contrast, and diffraction images, all from a single raw image and is feasible in live animals. Because the sensitivity of the method scales with the density of the gratings, custom microfabricated gratings should be superior to off-the-shelf lead grids. PMID:21158316

Bennett, Eric E.; Kopace, Rael; Stein, Ashley F.; Wen, Han

2010-01-01

364

Optimization of grating-based phase-contrast imaging setup  

NASA Astrophysics Data System (ADS)

Phase contrast imaging (PCI) technology has emerged over the last decade as a novel imaging technique capable of probing phase characteristics of an object as complimentary information to conventional absorption properties. In this work, we identified and provided a rationale for optimization of key parameters that determine the performance of a Talbot-Lau PCI system. The study used the Fresnel wave propagation theory and system geometry to predict optimal grating alignment conditions necessary for producing maximum-phase contrast. The moiré fringe pattern frequency and angular orientation produced in the X-ray detector plane were studied as functions of the gratings' axial rotation. The effect of axial displacement between source-to-phase (L) and phase-to-absorption (d) gratings, on system contrast, was discussed in detail. The L-d regions of highest contrast were identified, and the dependence of contrast on the energy of the X-ray spectrum was also studied. The predictions made in this study were tested experimentally and showed excellent agreement. The results indicated that the PCI system performance is highly sensitive to alignment. The rationale and recommendations made should serve as guidance in design, development, and optimization of Talbot-Lau PCI systems.

Baturin, Pavlo; Shafer, Mark

2014-03-01

365

Images of the Moon: Predicting Phases and Features  

NSDL National Science Digital Library

This is an activity about investigating students' preconceptions of the Moon's appearance and its phases. Learners will first draw an image of how they think the Moon looks and then discuss as a group why the drawn pictures may vary. Then, learners will analyze a series of lunar phase photos, sorting them in the order they believe to be correct based on their experiences and ideas. This is Activity A-1 of Universe at Your Fingertips 2.0: A Collection of Activities and Resources for Teaching Astronomy DVD-ROM, which is available for purchase.

366

Process control of apple winemaking by low-resolution gas-phase Fourier-transform infrared spectroscopy.  

PubMed

Four apple wine fermentation processes have been observed by means of direct-inlet gas-phase FTIR spectroscopy. The apple juice concentrates were each fermented by two species of Saccharomyces cerevisiae starters, and the experiment was repeated. The development of the concentrations of 1-propanol, 4-methylpyridine, acetaldehyde, acetic acid, and ethyl acetate was monitored. Two different sampling methods were used--static headspace and direct injection of the must. The performance of the FTIR method is limited by the high ethanol concentration. It can be mathematically proven that the amount of sample can be selected so that any distortion due to ethanol is minimized. Headspace GC-MS was used for preliminary compound identification. PMID:11760067

Ahro, M; Hakala, M; Kauppinen, J; Kallio, H

2001-10-01

367

Fourier analysis of the imaging characteristics of a CMOS active pixel detector for mammography by using a linearization method  

NASA Astrophysics Data System (ADS)

Active pixel design using the complementary metal-oxide-semiconductor (CMOS) process is a compelling solution for use in X-ray imaging detectors because of its excellent electronic noise characteristics. We have investigated the imaging performance of a CMOS active pixel photodiode array coupled to a granular phosphor through a fiber-optic faceplate for mammographic applications. The imaging performance included the modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). Because we observed a nonlinear detector response at low exposures, we used the linearization method for the analysis of the DQE. The linearization method uses the images obtained at detector input, which are converted from those obtained at detector output by using the inverse of the detector response. Compared to the conventional method, the linearization method provided almost the same MTF and a slightly lower normalized NPS. However, the difference between the DQE results obtained by using the two methods was significant. We claim that the conventional DQE analysis of a detector having a nonlinear response characteristic can yield wrong results. Under the standard mammographic imaging condition, we obtained a DQE performance that was competitive with the performances of conventional flat-panel mammography detectors. We believe that the CMOS detector investigated in this study can be successfully used for mammography.

Han, Jong Chul; Yun, Seungman; Youn, Hanbean; Kam, Soohwa; Cho, Seungryong; Achterkirchen, Thorsten G.; Kim, Ho Kyung

2014-09-01

368

Quantitative confocal phase imaging by synthetic optical holography.  

PubMed

We demonstrate quantitative phase mapping in confocal optical microscopy by applying synthetic optical holography (SOH), a recently introduced method for technically simple and fast phase imaging in scanning optical microscopy. SOH is implemented in a confocal microscope by simply adding a linearly moving reference mirror to the microscope setup, which generates a synthetic reference wave analogous to the plane reference wave of wide-field off-axis holography. We demonstrate that SOH confocal microscopy allows for non-contact surface profiling with sub-nanometer depth resolution. As an application for biological imaging, we apply SOH confocal microscopy to map the surface profile of an onion cell, revealing nanoscale-height features on the cell surface. PMID:24977617

Schnell, M; Perez-Roldan, M J; Carney, P S; Hillenbrand, R

2014-06-16

369

Quantitative phase imaging using a deep UV LED source.  

PubMed

We propose a method for high resolution phase imaging of biological and non-biological samples using an incoherent deep ultraviolet (DUV) LED source. The diffraction pattern of the object wave is recorded at different axial planes and the phase is retrieved by propagation of the angular spectrum. To maintain enough light intensity, we avoided using a pinhole or spectral filter for increasing the coherence of the DUV LED source. This makes the setup very simple and cost effective. The short wavelength (285 nm) of the DUV light, tuned to the absorption peak of the biological samples, allows simultaneously high resolution and high contrast images. The experimental results are presented to verify this principle. PMID:24978513

Singh, Alok Kumar; Faridian, Ahmad; Gao, Peng; Pedrini, Giancarlo; Osten, Wolfgang

2014-06-15

370

Automatic detection of ridges in lunar images using phase symmetry and phase congruency  

NASA Astrophysics Data System (ADS)

Lunar surface exploration is increasing rapidly. These exploring satellites provide a large number of high resolution images containing topographical information. The topographical information in lunar surface are craters, ridges, mountains and grabens. Extracting this topographical information manually is time-consuming. Hence, an automatic feature extraction is favored. This paper presents a novel approach using image processing techniques to automatically detect ridges in lunar images. The approaches adopted for this development includes phase symmetry, phase congruency and morphological operations to automatically detect significant ridges. The phase symmetry extracts symmetry features with discontinuities, phase congruency extracts features lying in low contrast regions and morphological operations such as thinning and pruning are used to obtain significant ridges. The proposed novel approach experiments on a test set of different regions. These different region images are obtained from different sensors (LROC, Selene and Clementine) having different spatial resolution and illumination variation. The results obtained are compared with the plan curvature method; and they are evaluated based on true and false detection of ridge pixels. Irrespective of illumination variation and spatial resolution, the proposed approach provides better results than the plan curvature method and its detection rate is approximately 92%.

Micheal, Anto A.; Vani, K.; Sanjeevi, S.

2014-12-01

371

PHASE IMAGING WITH AN X-RAY TALBOT INTERFEROMETER  

Microsoft Academic Search

X-ray Talbot interferometry (XTI) is described as a novel phase-sensitive X-ray imaging method. XTI uses two transmission gratings, and therefore in principle it functions with cone-beam X-rays of a broad energy band width, allowing its instrumentation with a compact X-ray source. Because an amplitude transmission grating is needed, X-ray lithography and electrochemical gold plating were employed to fabricate a high-aspect-ratio

Atsushi Momose; Wataru Yashiro; Yoshihiro Takeda; Yoshio Suzuki; Tadashi Hattorid

372

Quantitative phase imaging with scanning holographic microscopy: an experimental assesment  

PubMed Central

This paper demonstrates experimentally how quantitative phase information can be obtained in scanning holographic microscopy. Scanning holography can operate in both coherent and incoherent modes, simultaneously if desired, with different detector geometries. A spatially integrating detector provides an incoherent hologram of the object's intensity distribution (absorption and/or fluorescence, for example), while a point detector in a conjugate plane of the pupil provides a coherent hologram of the object's complex amplitude, from which a quantitative measure of its phase distribution can be extracted. The possibility of capturing simultaneously holograms of three-dimensional specimens, leading to three-dimensional reconstructions with absorption contrast, reflectance contrast, fluorescence contrast, as was previously demonstrated, and quantitative phase contrast, as shown here for the first time, opens up new avenues for multimodal imaging in biological studies. PMID:17132171

Indebetouw, Guy; Tada, Yoshitaka; Leacock, John

2006-01-01

373

Effect of ingested tungsten oxide (WOx) nanofibers on digestive gland tissue of Porcellio scaber (Isopoda, Crustacea): fourier transform infrared (FTIR) imaging.  

PubMed

Tungsten nanofibers are recognized as biologically potent. We study deviations in molecular composition between normal and digestive gland tissue of WOx nanofibers (nano-WOx) fed invertebrate Porcellio scaber (Iosopda, Crustacea) and revealed mechanisms of nano-WOx effect in vivo. Fourier Transform Infrared (FTIR) imaging performed on digestive gland epithelium was supplemented by toxicity and cytotoxicity analyses as well as scanning electron microscopy (SEM) of the surface of the epithelium. The difference in the spectra of the Nano-WOx treated and control cells showed up in the central region of the cells and were related to lipid peroxidation, and structural changes of nucleic acids. The conventional toxicity parameters failed to show toxic effects of nano-WOx, whereas the cytotoxicity biomarkers and SEM investigation of digestive gland epithelium indicated sporadic effects of nanofibers. Since toxicological and cytological measurements did not highlight severe effects, the biochemical alterations evidenced by FTIR imaging have been explained as the result of cell protection (acclimation) mechanisms to unfavorable conditions and indication of a nonhomeostatic state, which can lead to toxic effects. PMID:23952740

Novak, Sara; Drobne, Damjana; Vaccari, Lisa; Kiskinova, Maya; Ferraris, Paolo; Birarda, Giovanni; Remškar, Maja; Ho?evar, Matej

2013-10-01

374

Packed capillary reversed-phase liquid chromatography with high-performance electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry for proteomics.  

PubMed

In this study, high-efficiency packed capillary reversed-phase liquid chromatography (RPLC) coupled on-line with high-performance Fourier transform ion cyclotron resonance (FTICR) mass spectrometry has been investigated for the characterization of complex cellular proteolytic digests. Long capillary columns (80-cm) packed with small (3-micron) C18 bonded particles provided a total peak capacity of approximately 1000 for cellular proteolytic polypeptides when interfaced with an ESI-FTICR mass spectrometer under composition gradient conditions at a pressure of 10,000 psi. Large quantities of cellular proteolytic digests (e.g., 500 micrograms) could be loaded onto packed capillaries of 150-micron inner diameter without a significant loss of separation efficiency. Precolumns with suitable inner diameters were found useful for improving the elution reproducibility without a significant loss of separation quality. Porous particle packed capillaries were found to provide better results than those containing nonporous particles because of their higher sample capacity. Two-dimensional analyses from the combination of packed capillary RPLC with high-resolution FTICR yield a combined capacity for separations of > 1 million polypeptide components and simultaneously provided information for the identification of the separated components based upon the accurate mass tag concept previously described. PMID:11338590

Shen, Y; Zhao, R; Belov, M E; Conrads, T P; Anderson, G A; Tang, K; Pasa-Toli?, L; Veenstra, T D; Lipton, M S; Udseth, H R; Smith, R D

2001-04-15

375

Quadrature Phase Interferometry: a phase-sensitive rotation shearing interferometer for diffraction-limited imaging  

NASA Astrophysics Data System (ADS)

We have developed a new technique of rotation shearing interferometry, for diffraction-limited imaging through turbulence at visible wavelengths from single ground-based telescopes. While previous rotation shearing interferometers have been used in astronomical observations, none has successfully measured visibility phase in the presence of turbulent aberrations. Our technique, called Quadrature Phase Interferometery (QPI), simultaneously obtains four interferograms, each of which observes the same interferometric baselines with differing instrumental phase contributions. These instrumental phase contributions allow full determination of the complex visibility (modulus and phase) from a single exposure, over all baselines up to the telescope diameter. Turbulent phase aberrations can be averaged out of successive exposures to obtain diffraction-limited images. The expected limiting magnitudes of this technique are comparable to those of other passive techniques such as speckle interferometry or non-redundant masking. The QPI has been tested in the laboratory and at Palomar Observatory, with encouraging results. The design principles and results will be discussed. This work was supported by the National Science Foundation and the Air Force Office of Scientific Research.

Kern, B.; Dimotakis, P. E.; Martin, C.; Lang, D. B.; Thessin, R. N.

2004-12-01

376

Phase error correction for synthetic-aperture phased-array imaging systems  

NASA Astrophysics Data System (ADS)

If one replaces the ordinary single receiver of a synthetic- aperture radar (SAR) with a linear array of receivers underneath the wings of an aircraft, one obtains a 3D signal history (to spatial dimensions plus the frequency dimension) that allows the computation of a 3D image (angle-angle- range) of a scene. Because of the limited extent of the wingspan, the cross-track resolution is limited, driving one to use high frequencies, such as 94 GHz, having a wavelength of 3.2 mm. At such short wavelengths, the motion of the wings during the synthetic-aperture integration time will cause large phase errors that will severely blur the image. This paper describes an approach to measuring and correcting these and other phase errors. The approach involves having three transmitters, each at a slightly different monotone frequency. Relative to the first receiver, the second is displaced along the direction of the array of receivers and the third is displaced perpendicular to that direction. The array of receivers can separate the three corresponding signals reflected form the ground from one another. We will show mathematical analysis that allows us to determine the phase errors at each receiver form these three signals. It is required either that the three transmitters experience the same phase errors (so they should be rigidly mounted together) or that the phase errors at the three transmitters are measured. No measurement of phase errors on the receivers is required.

Fienup, James R.

2000-11-01

377

Experience with 800 x 800 virtual phase and 500 x 500 three-phase CCD imagers  

NASA Technical Reports Server (NTRS)

A description of the Galileo/Institute for Astronomy charge-coupled device (CCD) imaging system and its initial operation has been presented previously. Originally designed to operate a 500 x 500 backside illuminated three-phase CCD, the system has been modified to allow use of either the 500 x 500 sensor or the TI 800 x 800 virtual phase CCD. The modifications for the operation of the virtual phase CCD and current system performance with each type of sensor are discussed. A description is given of the implementation of various techniques discovered at the Jet Propulsion Laboratory that improve imager performance. These techniques include tri-level clocking of the virtual phase CCD to eliminate spurious charge generation in the serial register, the use of ultraviolet light flood with the backside thinned 500 x 500 three-phase device to dramatically improve the quantum efficiency in the blue, and the practical elimination of deferred charge in the three-phase device. Results of astronomical observations with each sensor are presented.

Hlivak, R. J.; Henry, J. P.; Pilcher, C. B.

1984-01-01

378

Acoustic imaging by second harmonic of phase-conjugate wave in inhomogeneous medium  

NASA Astrophysics Data System (ADS)

Application of the supercritical magnetoelastic wave phase conjugation to harmonic imaging in acoustic C-scan microscopy is demonstrated. Second-harmonic generation by phase-conjugate wave is used for improvement of resolution of an imaging system. Possibility to compensate phase aberrations introduced in harmonic image by inhomogeneity of propagation medium is shown experimentally and explained theoretically.

Pyl'nov, Yu.; Pernod, P.; Preobrazhensky, V.

2001-01-01

379

Radio astronomy image enhancement in the presence of phase errors using genetic algorithms  

Microsoft Academic Search

Modern radio astronomy interferometric telescopes use Earth rotation aperture synthesis imaging techniques. New projects for radio telescopes include hundreds and thousands of elements and presume multibeam and snapshot imaging. Each element, or base station, in its turn is a phase-array antenna. Phase instabilities due to instrumentation and atmospheric phase variations can ruin the synthesized image. There is a need to

Peter Fridman

2001-01-01

380

Phase-unwrapping algorithm for images with high noise content based on a local histogram  

NASA Astrophysics Data System (ADS)

We present a robust algorithm of phase unwrapping that was designed for use on phase images with high noise content. We proceed with the algorithm by first identifying regions with continuous phase values placed between fringe boundaries in an image and then phase shifting the regions with respect to one another by multiples of 2pi to unwrap the phase. Image pixels are segmented between interfringe and fringe boundary areas by use of a local histogram of a wrapped phase. The algorithm has been used successfully to unwrap phase images generated in a three-dimensional shape measurement for noninvasive quantification of human skin structure in dermatology, cosmetology, and plastic surgery.

Meneses, Jaime; Gharbi, Tijani; Humbert, Philippe

2005-03-01

381

Image sharpness assessment based on local phase coherence.  

PubMed

Sharpness is an important determinant in visual assessment of image quality. The human visual system is able to effortlessly detect blur and evaluate sharpness of visual images, but the underlying mechanism is not fully understood. Existing blur/sharpness evaluation algorithms are mostly based on edge width, local gradient, or energy reduction of global/local high frequency content. Here we understand the subject from a different perspective, where sharpness is identified as strong local phase coherence (LPC) near distinctive image features evaluated in the complex wavelet transform domain. Previous LPC computation is restricted to be applied to complex coefficients spread in three consecutive dyadic scales in the scale-space. Here we propose a flexible framework that allows for LPC computation in arbitrary fractional scales. We then develop a new sharpness assessment algorithm without referencing the original image. We use four subject-rated publicly available image databases to test the proposed algorithm, which demonstrates competitive performance when compared with state-of-the-art algorithms. PMID:23481852

Hassen, Rania; Wang, Zhou; Salama, Magdy M A

2013-07-01

382

Noninvasive Imaging of the Foveal Avascular Zone with High-Speed, Phase-Variance Optical Coherence Tomography  

PubMed Central

Purpose. To demonstrate the application of phase-variance optical coherence tomography (pvOCT) for contrast agent–free in vivo imaging of volumetric retinal microcirculation in the human foveal region and for extraction of foveal avascular zone dimensions. Methods. A custom-built, high-speed Fourier-domain OCT retinal imaging system was used to image retinas of two healthy subjects and eight diabetic patients. Through the acquisition of multiple B-scans for each scan location, phase differences between consecutive scans were extracted and used for phase-variance contrast, identifying motion signals from within blood vessels and capillaries. The en face projection view of the inner retinal layers segmented out from volumetric pvOCT data sets allowed visualization of a perfusion network with the foveal avascular zone (FAZ). In addition, the authors presented 2D retinal perfusion maps with pseudo color-coded depth positions of capillaries. Results. Retinal vascular imaging with pvOCT provides accurate measurements of the FAZ area and its morphology and a volumetric perfusion map of microcapillaries. In this study using two images from each fundus fluorescein angiography (FA) and pvOCT, the measured average areas of the FAZ from two healthy subjects were below 0.22 mm2, and each of eight diabetic patients had an enlarged FAZ area, larger than 0.22 mm2. Moreover, the FAZ areas demonstrated a significant correlation (r = 0.91) between measurements from FA and pvOCT. Conclusions. The high-speed pvOCT allows contrast agent–free visualization of capillary networks in the human foveal region that is analogous to fundus FA imaging. This could allow for noninvasive diagnosis and progression monitoring of diabetic retinopathy in clinical settings. PMID:22125275

Fingler, Jeff; Zawadzki, Robert J.; Park, Susanna S.; Morse, Lawrence S.; Schwartz, Daniel M.; Fraser, Scott E.; Werner, John S.

2012-01-01

383

Fourier–Bessel rotational invariant eigenimages  

PubMed Central

We present an efficient and accurate algorithm for principal component analysis (PCA) of a large set of two-dimensional images and, for each image, the set of its uniform rotations in the plane and its reflection. The algorithm starts by expanding each image, originally given on a Cartesian grid, in the Fourier–Bessel basis for the disk. Because the images are essentially band limited in the Fourier domain, we use a sampling criterion to truncate the Fourier–Bessel expansion such that the maximum amount of information is preserved without the effect of aliasing. The constructed covariance matrix is invariant to rotation and reflection and has a special block diagonal structure. PCA is efficiently done for each block separately. This Fourier–Bessel-based PCA detects more meaningful eigenimages and has improved denoising capability compared to traditional PCA for a finite number of noisy images. PMID:23695317

Zhao, Zhizhen; Singer, Amit

2013-01-01

384

Relation between substructure position of phase objects in optical axial direction and phase information in quantitative phase imaging  

NASA Astrophysics Data System (ADS)

Substructure position of biological cells and tissues owns much more information about the state and evolution of these cells and tissues. Comparing with the substructure position of these biological objects at the plane perpendicular to the optical axial, the substructure position of these objects in optical axial direction is hard to be measured by the general quantitative phase imaging (QPI). Here, based on the split-step beam propagation theory, we numerically investigate the relation between substructure position of phase objects in optical axial direction and phase information in QPI. Five groups of two-sphere model with the internal sphere at different positions in optical axial direction are studied. The results show that the position of the internal sphere in optical axial direction does not change the general morphology of the phase map, but it leads to some differences near the boundary of the internal sphere. Further, we get the relation between the maximum positive phase deviation and the position of the internal sphere in optical axial direction. Such a relation will provide the theoretical basis for the analysis of experimental results in phase imaging.

Jin, Weifeng; Wang, Yawei; Ren, Naifei; Bu, Min; Shang, Xuefu; Xu, Yuanyuan; Wu, Hui

2014-02-01

385

Fourier transform channeled spectropolarimetry in the MWIR  

E-print Network

forms of spectroscopic measurement, such as a diffraction grating spectrometer, in the MWIR. Luo, et al, "Polarization acquisition using a commercial Fourier transform spectrometer in the MWIR. Chapman et al, "Data processing pipeline for a time-sampled imaging Fourier transform spectrometer

Dereniak, Eustace L.

386

Mouse blood vessel imaging by in-line x-ray phase-contrast imaging  

NASA Astrophysics Data System (ADS)

It is virtually impossible to observe blood vessels by conventional x-ray imaging techniques without using contrast agents. In addition, such x-ray systems are typically incapable of detecting vessels with diameters less than 200 µm. Here we show that vessels as small as 30 µm could be detected using in-line phase-contrast x-ray imaging without the use of contrast agents. Image quality was greatly improved by replacing resident blood with physiological saline. Furthermore, an entire branch of the portal vein from the main axial portal vein to the eighth generation of branching could be captured in a single phase-contrast image. Prior to our work, detection of 30 µm diameter blood vessels could only be achieved using x-ray interferometry, which requires sophisticated x-ray optics. Our results thus demonstrate that in-line phase-contrast x-ray imaging, using physiological saline as a contrast agent, provides an alternative to the interferometric method that can be much more easily implemented and also offers the advantage of a larger field of view. A possible application of this methodology is in animal tumor models, where it can be used to observe tumor angiogenesis and the treatment effects of antineoplastic agents.

Zhang, Xi; Liu, Xiao-Song; Yang, Xin-Rong; Chen, Shao-Liang; Zhu, Pei-Ping; Yuan, Qing-Xi

2008-10-01

387

Restoration of weak phase-contrast images recorded with a high degree of defocus: the "twin image" problem associated with CTF correction.  

PubMed

Relatively large values of objective-lens defocus must normally be used to produce detectable levels of image contrast for unstained biological specimens, which are generally weak phase objects. As a result, a subsequent restoration operation must be used to correct for oscillations in the contrast transfer function (CTF) at higher resolution. Currently used methods of CTF correction assume the ideal case in which Friedel mates in the scattered wave have contributed pairs of Fourier components that overlap with one another in the image plane. This "ideal" situation may be only poorly satisfied, or not satisfied at all, as the particle size gets smaller, the defocus value gets larger, and the resolution gets higher. We have therefore investigated whether currently used methods of CTF correction are also effective in restoring the single-sideband image information that becomes displaced (delocalized) by half (or more) the diameter of a particle of finite size. Computer simulations are used to show that restoration either by "phase flipping" or by multiplying by the CTF recovers only about half of the delocalized information. The other half of the delocalized information goes into a doubly defocused "twin" image of the type produced during optical reconstruction of an in-line hologram. Restoration with a Wiener filter is effective in recovering the delocalized information only when the signal-to-noise ratio (S/N) is orders of magnitude higher than that which exists in low-dose images of biological specimens, in which case the Wiener filter approaches division by the CTF (i.e. the formal inverse). For realistic values of the S/N, however, the "twin image" problem seen with a Wiener filter is very similar to that seen when either phase flipping or multiplying by the CTF is used for restoration. The results of these simulations suggest that CTF correction is a poor alternative to using a Zernike-type phase plate when imaging biological specimens, in which case the images can be recorded in a close-to-focus condition, and delocalization of high-resolution information is thus minimized. PMID:18508199

Downing, Kenneth H; Glaeser, Robert M

2008-08-01

388

Molecular events in deliquescence and efflorescence phase transitions of sodium nitrate particles studied by Fourier transform infrared attenuated total reflection spectroscopy  

NASA Astrophysics Data System (ADS)

The NaNO3 droplets with sizes of 1-5?m generated from a nebulizer were deposited on a ZnSe substrate in a Fourier transform infrared attenuated total reflection (FTIR-ATR) chamber. After solidification of the droplets with dry N2 gas passing through the chamber, the solid NaNO3 particles were monitored by in situ FTIR-ATR spectra in cycles of deliquescence and efflorescence processes with varying relative humidities (RHs). With an increase in the RH, a dominant peak at ˜3539cm-1, together with three relatively weak peaks at ˜3400, ˜3272, and ˜3167cm-1, in the O-H stretching band of water was resolved by the high signal-to-noise ratio FTIR-ATR spectra. The dominant peak and the three relatively weak peaks were contributed by the water monomers and the aggregated water molecules adsorbed on the surfaces of solid NaNO3 particles, respectively. When the RH approached ˜72%, slightly lower than the deliquescence RH (74.5%), the band component at ˜3400cm-1 became the main peak, indicating that the water monomers and the aggregated water molecules aggregated to form a thin water layer on the surfaces of solid NaNO3 particles. A splitting of the ?3-NO3- band at 1363 and 1390cm-1 at the RH of ˜72%, instead of the single ?3-NO3- band at 1357cm-1 for the initial solid NaNO3, was observed. We suggested that this reflected a phase transition from the initial solid to a metastable solid phase of NaNO3. The metastable solid phase deliquesced completely in the region from ˜87% to ˜96% RH according to the fact that the ?3-NO3- band showed two overlapping peaks at 1348 and 1405cm-1 similar to those of bulk NaNO3 solutions. In the efflorescence process of the NaNO3 droplets, the ?1-NO3- band presented a continuous blueshift from 1049cm-1 at ˜77% RH to 1055cm-1 at ˜36% RH, indicating the formation of contact ion pairs between Na + and NO3-. Moreover, in the RH range from ˜53% down to ˜26%, two peaks at 836 and 829cm-1 were observed in the ?2-NO3- band region, demonstrating the coexistence of NaNO3 solid particles and droplets.

Lu, Pei-Dong; Wang, Feng; Zhao, Li-Jun; Li, Wen-Xue; Li, Xiao-Hong; Dong, Jin-Ling; Zhang, Yun-Hong; Lu, Gao-Qing

2008-09-01

389

Dose and detectability improvements with high energy phase sensitive x-ray imaging in comparison to low energy conventional imaging  

PubMed Central

The objective of this study was to demonstrate the potential benefits of using high energy x-rays for phase sensitive breast imaging through a comparison with conventional mammography imaging. We compared images of a contrast-detail (CD) phantom acquired on a prototype phase sensitive x-ray imaging system with images acquired on a commercial flat panel digital mammography unit. The phase contrast images were acquired using a micro-focus x-ray source with a 50 ?m focal spot at 120 kVp and 4.5 mAs, with a magnification factor of 2.46 and a 50 ?m pixel pitch. A phase attenuation duality (PAD)-based phase retrieval algorithm that requires only a single phase contrast image was applied. Conventional digital mammography images were acquired at 27 kVp, 131 mAs and 28 kVp, 54 mAs. For the same radiation dose, both the observer study and SNR/FOM comparisons indicated a large improvement by the phase retrieved image as compared to the clinical system for the larger disk sizes, but the improvement was not enough to detect the smallest disks. Compared to the double dose image acquired with the clinical system, the observer study also indicated that the phase retrieved image provided improved detection capabilities for all disk sizes except the smallest disks. Thus the SNR improvement provided by phase contrast imaging is not yet enough to offset the noise reduction provided by the clinical system at the doubled dose level. However, the potential demonstrated by this study for high energy phase sensitive x-ray imaging to improve lesion detection and reduce radiation dose in mammography warrants further investigation of this technique. PMID:24732108

Wong, Molly Donovan; Yan, Aimin; Ghani, Muhammad; Li, Yuhua; Fajardo, Laurie; Wu, Xizeng; Liu, Hong

2014-01-01

390

X-ray phase imaging: from synchrotron to hospital  

PubMed Central

With the aim of clinical applications of X-ray phase imaging based on Talbot–Lau-type grating interferometry to joint diseases and breast cancer, machines employing a conventional X-ray generator have been developed and installed in hospitals. The machine operation especially for diagnosing rheumatoid arthritis is described, which relies on the fact that cartilage in finger joints can be depicted with a dose of several milligray. The palm of a volunteer observed with 19?s exposure (total scan time: 32?s) is reported with a depicted cartilage feature in joints. This machine is now dedicated for clinical research with patients. PMID:24470409

Momose, Atsushi; Yashiro, Wataru; Kido, Kazuhiro; Kiyohara, Junko; Makifuchi, Chiho; Ito, Tsukasa; Nagatsuka, Sumiya; Honda, Chika; Noda, Daiji; Hattori, Tadashi; Endo, Tokiko; Nagashima, Masabumi; Tanaka, Junji

2014-01-01

391

Spatiotemporal characterization of a fibrin clot using quantitative phase imaging.  

PubMed

Studying the dynamics of fibrin clot formation and its morphology is an important problem in biology and has significant impact for several scientific and clinical applications. We present a label-free technique based on quantitative phase imaging to address this problem. Using quantitative phase information, we characterized fibrin polymerization in real-time and present a mathematical model describing the transition from liquid to gel state. By exploiting the inherent optical sectioning capability of our instrument, we measured the three-dimensional structure of the fibrin clot. From this data, we evaluated the fractal nature of the fibrin network and extracted the fractal dimension. Our non-invasive and speckle-free approach analyzes the clotting process without the need for external contrast agents. PMID:25386701

Gannavarpu, Rajshekhar; Bhaduri, Basanta; Tangella, Krishnarao; Popescu, Gabriel

2014-01-01

392

3D Cardiac microvessels embolization imaging based on X-ray phase contrast imaging  

PubMed Central

Background The treatment of microcirculatory impairment will have great impact if it can be applied to myocardial infarction (MI) patients. The problem is how to study these tiny structures and microphenomenon in heart. Methods We investigated the visualization of cardiac microvessels embolization by the mean of X-ray phase contrast imaging (XPCI), which is a recently emerged imaging technique. Using the information of X-ray phase shift, it is sensitive to weak absorbing materials. Two MI SD rats were used as the microvessel embolization samples. MI was surgically induced by ligating left anterior descending artery. Imaging was performed 24 hours post-infarct, with barium sulfate as contrast agent. Results The coronary arteries were visualized with smooth walls and clear edges. The ligated vessels, with the diameter of about three hundred microns, can be clearly distinguished and there were no distal blood flow downstream from these branches. The results indicate that phase contrast imaging can directly demonstrate the distribution of microvessels, and estimate the area of MI. The infarct location was in good agreement with pathological analyses of the models. Conclusions The advantage of our method is directly observing and evaluating microvessel embolization which simplifies the procedure of diagnoses. Moreover, it is helpful for predicting the prognosis in MI and judging if angiogenesis happens. PMID:24886327

2014-01-01

393

Efficient phase contrast imaging in STEM using a pixelated detector. Part 1: Experimental demonstration at atomic resolution.  

PubMed

We demonstrate a method to achieve high efficiency phase contrast imaging in aberration corrected scanning transmission electron microscopy (STEM) with a pixelated detector. The pixelated detector is used to record the Ronchigram as a function of probe position which is then analyzed with ptychography. Ptychography has previously been used to provide super-resolution beyond the diffraction limit of the optics, alongside numerically correcting for spherical aberration. Here we rely on a hardware aberration corrector to eliminate aberrations, but use the pixelated detector data set to utilize the largest possible volume of Fourier space to create high efficiency phase contrast images. The use of ptychography to diagnose the effects of chromatic aberration is also demonstrated. Finally, the four dimensional dataset is used to compare different bright field detector configurations from the same scan for a sample of bilayer graphene. Our method of high efficiency ptychography produces the clearest images, while annular bright field produces almost no contrast for an in-focus aberration-corrected probe. PMID:25458189

Pennycook, Timothy J; Lupini, Andrew R; Yang, Hao; Murfitt, Matthew F; Jones, Lewys; Nellist, Peter D

2014-10-15

394

Application of a linear time-invariant model in the Fourier domain to perform statistical analysis of functional magnetic resonance images  

NASA Astrophysics Data System (ADS)

A linear time invariant model is applied to functional fMRI blood flow data. This model assumes that the fMRI stochastic output sequence can be determined by a constant plus a linear filter (hemodynamic response function) of several fixed deterministic inputs and an error term, assumed stationary with zero mean and error spectrum. An on-off finger tapping experiment was performed where the subject repetitively tapped their fingers for 30 seconds and remained still for 30 seconds. Thirty three disjoint frequency bands, 3 wave numbers wide were chosen to analyze the data. At each band an F- statistical image was constructed to test ((alpha) equals .05/33) whether power from the input signal induced a response in the output signal. Activation was seen at frequency .0154 Hz close to the frequency for maximum power of the input signal, .0167 Hz in the contralateral motor strip and motor cortex. In conclusion, (1) No assumptions are made about the filter. (2) Several different deterministic inputs may be applied. (3) Problems with temporal correlation are avoided by performing the statistics in the Fourier domain. (4) Testing can be performed for differences in the hemodynamic transfer function at different spatial locations under different experimental conditions.

Rio, Daniel E.; Rawlings, Robert R.; Hommer, Daniel

2000-04-01

395

Level 2 processing for the imaging Fourier transform spectrometer GLORIA: derivation and validation of temperature and trace gas volume mixing ratios from calibrated dynamics mode spectra  

NASA Astrophysics Data System (ADS)

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an airborne infrared limb-imager combining a two-dimensional infrared detector with a Fourier transform spectrometer. It was operated aboard the new German Gulfstream G550 research aircraft HALO during the Transport And Composition in the upper Troposphere/lowermost Stratosphere (TACTS) and Earth System Model Validation (ESMVAL) campaigns in summer 2012. This paper describes the retrieval of temperature and trace gas (H2O, O3, HNO3) volume mixing ratios from GLORIA dynamics mode spectra. 26 integrated spectral windows are employed in a joint fit to retrieve seven targets using consecutively a fast and an accurate tabulated radiative transfer model. Typical diagnostic quantities are provided including effects of uncertainties in the calibration and horizontal resolution along the line-of-sight. Simultaneous in-situ observations by the BAsic HALO Measurement And Sensor System (BAHAMAS), the Fast In-Situ Stratospheric Hygrometer (FISH), FAIRO, and the Atmospheric chemical Ionization Mass Spectrometer (AIMS) allow a validation of retrieved values for three flights in the upper troposphere/lowermost stratosphere region spanning polar and sub-tropical latitudes. A high correlation is achieved between the remote sensing and the in-situ trace gas data, and discrepancies can to a large fraction be attributed to differences in the probed air masses caused by different sampling characteristics of the instruments. This 1-D processing of GLORIA dynamics mode spectra provides the basis for future tomographic inversions from circular and linear flight paths to better understand selected dynamical processes of the upper troposphere and lowermost stratosphere.

Ungermann, J.; Blank, J.; Dick, M.; Ebersoldt, A.; Friedl-Vallon, F.; Giez, A.; Guggenmoser, T.; Höpfner, M.; Jurkat, T.; Kaufmann, M.; Kaufmann, S.; Kleinert, A.; Krämer, M.; Latzko, T.; Oelhaf, H.; Olchewski, F.; Preusse, P.; Rolf, C.; Schillings, J.; Suminska-Ebersoldt, O.; Tan, V.; Thomas, N.; Voigt, C.; Zahn, A.; Zöger, M.; Riese, M.

2014-12-01

396

Detection and imaging of the moving target using frequency space-time adaptive processing and fractional Fourier transform  

NASA Astrophysics Data System (ADS)

As for multi-channel SAR, the spectrum of the clutter is spatially-temporally coupled, and the echo of the moving target is chirp signal. A novel method based on STAP and FrFT is proposed in this paper, which is used for moving target detection and parameter estimation. Two steps are used for fast target detection : the coarse detection in low range resolution and parameter estimation for the specific data where the moving target appears. This paper discusses the principle of frequency STAP for clutter suppression firstly, and subsequently infers that the signal after clutter suppression is chirp signal. Then FrFT is introduced to estimate the parameters of the output signal, which can be used to estimate the parameters of the moving target. Finally, the process of the proposed method is introduced. Matching function is constructed to compensate the phase deviation caused by movement and focus the moving target. The effectiveness of the proposed method is validated by the simulation.

Wu, Jian; Jiang, Yongmei; Kuang, Gangyao

2014-10-01

397

Fractional order Fourier transform and Fourier optics  

Microsoft Academic Search

The electromagnetic field transfer from a spherical emitter to a spherical receiver is expressed through a fractional order Fourier transform. Given an emitter and a receiver, the order of the fractional transform is calculated as a function of their distance and their radii of curvature. The continuity of fractional Fourier transforms with respect to their orders corresponds to the continuity

Pierre Pellat-Finet; Georges Bonnet

1994-01-01

398

Real time blood testing using quantitative phase imaging.  

PubMed

We demonstrate a real-time blood testing system that can provide remote diagnosis with minimal human intervention in economically challenged areas. Our instrument combines novel advances in label-free optical imaging with parallel computing. Specifically, we use quantitative phase imaging for extracting red blood cell morphology with nanoscale sensitivity and NVIDIA's CUDA programming language to perform real time cellular-level analysis. While the blood smear is translated through focus, our system is able to segment and analyze all the cells in the one megapixel field of view, at a rate of 40 frames/s. The variety of diagnostic parameters measured from each cell (e.g., surface area, sphericity, and minimum cylindrical diameter) are currently not available with current state of the art clinical instruments. In addition, we show that our instrument correctly recovers the red blood cell volume distribution, as evidenced by the excellent agreement with the cell counter results obtained on normal patients and those with microcytic and macrocytic anemia. The final data outputted by our instrument represent arrays of numbers associated with these morphological parameters and not images. Thus, the memory necessary to store these data is of the order of kilobytes, which allows for their remote transmission via, for example, the cellular network. We envision that such a system will dramatically increase access for blood testing and furthermore, may pave the way to digital hematology. PMID:23405194

Pham, Hoa V; Bhaduri, Basanta; Tangella, Krishnarao; Best-Popescu, Catherine; Popescu, Gabriel

2013-01-01

399

Real Time Blood Testing Using Quantitative Phase Imaging  

PubMed Central

We demonstrate a real-time blood testing system that can provide remote diagnosis with minimal human intervention in economically challenged areas. Our instrument combines novel advances in label-free optical imaging with parallel computing. Specifically, we use quantitative phase imaging for extracting red blood cell morphology with nanoscale sensitivity and NVIDIA’s CUDA programming language to perform real time cellular-level analysis. While the blood smear is translated through focus, our system is able to segment and analyze all the cells in the one megapixel field of view, at a rate of 40 frames/s. The variety of diagnostic parameters measured from each cell (e.g., surface area, sphericity, and minimum cylindrical diameter) are currently not available with current state of the art clinical instruments. In addition, we show that our instrument correctly recovers the red blood cell volume distribution, as evidenced by the excellent agreement with the cell counter results obtained on normal patients and those with microcytic and macrocytic anemia. The final data outputted by our instrument represent arrays of numbers associated with these morphological parameters and not images. Thus, the memory necessary to store these data is of the order of kilobytes, which allows for their remote transmission via, for example, the cellular network. We envision that such a system will dramatically increase access for blood testing and furthermore, may pave the way to digital hematology. PMID:23405194

Pham, Hoa V.; Bhaduri, Basanta; Tangella, Krishnarao; Best-Popescu, Catherine; Popescu, Gabriel

2013-01-01

400

Matrix phased array (MPA) imaging technology for resistance spot welds  

NASA Astrophysics Data System (ADS)

A three-dimensional MPA probe has been incorporated with a high speed phased array electronic board to visualize nugget images of resistance spot welds. The primary application area of this battery operated portable MPA ultrasonic imaging system is in the automotive industry which a conventional destructive testing process is commonly adopted to check the quality of resistance spot welds in auto bodies. Considering an average of five-thousand spot welds in a medium size passenger vehicle, the amount of time and effort given to popping the welds and measuring nugget size are immeasurable in addition to the millions of dollars' worth of scrap metals recycled per plant per year. This wasteful labor intensive destructive testing process has become less reliable as auto body sheet metal has transitioned from thick and heavy mild steels to thin and light high strength steels. Consequently, the necessity of developing a non-destructive inspection methodology has become inevitable. In this paper, the fundamental aspects of the current 3-D probe design, data acquisition algorithms, and weld nugget imaging process are discussed.

Na, Jeong K.; Gleeson, Sean T.

2014-02-01

401

Matrix phased array (MPA) imaging technology for resistance spot welds  

SciTech Connect

A three-dimensional MPA probe has been incorporated with a high speed phased array electronic board to visualize nugget images of resistance spot welds. The primary application area of this battery operated portable MPA ultrasonic imaging system is in the automotive industry which a conventional destructive testing process is commonly adopted to check the quality of resistance spot welds in auto bodies. Considering an average of five-thousand spot welds in a medium size passenger vehicle, the amount of time and effort given to popping the welds and measuring nugget size are immeasurable in addition to the millions of dollars' worth of scrap metals recycled per plant per year. This wasteful labor intensive destructive testing process has become less reliable as auto body sheet metal has transitioned from thick and heavy mild steels to thin and light high strength steels. Consequently, the necessity of developing a non-destructive inspection methodology has become inevitable. In this paper, the fundamental aspects of the current 3-D probe design, data acquisition algorithms, and weld nugget imaging process are discussed.

Na, Jeong K.; Gleeson, Sean T. [Edison Welding Institute, 1250 Arthur E. Adams Drive, Columbus, OH 43221 (United States)

2014-02-18

402

Simultaneous acquisition of the real and imaginary components in Fourier domain optical coherence tomography using harmonic detection  

Microsoft Academic Search

Fourier domain optical coherence tomography (FD-OCT) is an interferometric imaging technique that allows imaging to depths of a few mm in scattering biological tissues with high resolution of the order of 1-10 mum. However, the usefulness of FD-OCT is limited by background and autocorrelation interference terms that reduce the sensitivity and by phase ambiguity that halves the useful imaging depth

Andrei B. Vakhtin; Daniel J. Kane; Kristen A. Peterson

2006-01-01

403

Optimization of phase contrast imaging using hard x rays  

SciTech Connect

X ray radiography and tomography are important tools in medicine as well as in life science and materials science. Not long ago an approach called in-line holography based on simple propagation became possible using partially coherent synchrotron beams like the ones available at the European Synchrotron Radiation Facility (ESRF). Theoretical and experimental work by Cloetens et al. [Appl. Phys. Lett 75, 2912 (1999)] have shown that quantitative retrieval of the optical phase, from a set of radiographs taken at different sample-to-detector distances, is feasible. Mathematically speaking we are dealing with a direct method based on linearization in order to solve an inverse nonlinear problem. The phase retrieval can be combined with classical tomography in order to obtain a three-dimensional representation of the object's electron density (holotomography). In order to optimize the image contrast for the numerical phase retrieval process, we have carried out calculations resulting in an optimized choice of value and number of the sample-to-detector distances as well as of the photon energy. These results were then confirmed by experiments on the ESRF long beamline ID19.

Zabler, S.; Cloetens, P.; Guigay, J.-P.; Baruchel, J.; Schlenker, M. [European Synchrotron Radiation Facility, ESRF Grenoble (France); Laboratoire Louis Neel, CNRS-UJF-INPG, Grenoble (France)

2005-07-15

404

Imaging the cell membrane with surface plasmon resonance phase microscopy  

NASA Astrophysics Data System (ADS)

Molecular interactions occurring on or near cell membrane surfaces are expected to have different properties from those occurring in bulk solutions. In order to analyze molecular interactions between the cell membrane with biomolecules having no additional fluorescence labeling, a microscope based on the integration of surface plasmon resonance (SPR) and common-path phase-shift interferometry (PSI) techniques is developed and used to study the cell adhesion and migration on the biosurfaces. The surface plasmons are excited by light via the attenuated total reflection method. The common-path PSI technique has features of long-term stability, even when subjected to external disturbances. Hence, the developed SPR phase microscope meets the requirements of real-time kinetic imaging. The proposed common-path SPR-PSI microscope demonstrates a detection limit of 2x10 -7 refractive index unit and a long-term phase stability of 2.5x10 -4 ? root mean square over four hours. The developed microscope is successfully applied to the real-time observation the live cell membranes with thrombomodulin proteins.

He, R.-Y.; Su, Y.-D.; Chang, G.-L.; Chen, S.-J.

2006-08-01

405

X-ray Bragg magnifier microscope as a linear shift invariant imaging system: image formation and phase retrieval.  

PubMed

We present the theoretical description of the image formation with the in-line germanium Bragg Magnifier Microscope (BMM) and the first successful phase retrieval of X-ray holograms recorded with this imaging system. The conditions under which the BMM acts as a linear shift invariant system are theoretically explained and supported by the experiment. Such an approach simplifies the mathematical treatment of the image formation and reconstruction as complicated propagation of the wavefront onto inclined planes can be avoided. Quantitative phase retrieval is demonstrated using a test sample and a proof of concept phase imaging of a spider leg is also presented. PMID:25321529

Vagovi?, P; Svéda, L; Cecilia, A; Hamann, E; Pelliccia, D; Gimenez, E N; Korytár, D; Pavlov, K M; Zápražný, Z; Zuber, M; Koenig, T; Olbinado, M; Yashiro, W; Momose, A; Fiederle, M; Baumbach, T

2014-09-01

406

Structure and Thermotropic phase Behavior of Fluorinated Phospholipid Bilayers: A combined Attenuated Total Reflection FTIR Spectroscopy and Imaging Ellipsometry Study  

PubMed Central

Lipid bilayers consisting of lipids with terminally perfluoroalkylated chains have remarkable properties. They exhibit increased stability and phase-separated nanoscale patterns in mixtures with nonfluorinated lipids. In order to understand the bilayer properties that are responsible for this behavior, we have analyzed the structure of solid-supported bilayers composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and of a DPPC analogue with 6 terminal perfluorinated methylene units (F6-DPPC). Polarized attenuated total reflection Fourier-transform infrared spectroscopy indicates that for F6-DPPC, the tilt of the lipid acyl chains to the bilayer normal is increased to 39° as compared to 21° for native DPPC, for both lipids in the gel phase. This substantial increase of the tilt angle is responsible for a decrease of the bilayer thickness from 5.4 nm for DPPC to 4.5 nm for F6-DPPC, as revealed by temperature-controlled imaging ellipsometry on microstructured lipid bilayers and solution atomic force microscopy. During the main phase transition from the gel to the fluid phase, both the relative bilayer thickness change and the relative area change are substantially smaller for F6-DPPC than for DPPC. In light of these structural and thermotropic data, we propose a model in which the higher acyl-chain tilt angle in F6-DPPC is the result of a conformational rearrangement to minimize unfavorable fluorocarbon–hydrocarbon interactions in the center of the bilayer due to chain staggering. PMID:18563929

Schuy, Steffen; Faiss, Simon; Yoder, Nicholas C.; Kalsani, Venkateshwarlu; Kumar, Krishna; Janshoff, Andreas; Vogel, Reiner

2008-01-01

407

Imaging voltage-dependent cell motions with heterodyne MachZehnder phase microscopy  

E-print Network

are typically limited in speed. In this paper we describe a quanti- tative interferometric microscope in which image include variable spatial filtering [11­13], variable defocusing [14,15], or stepped phase shifting and may limit certain spatial frequencies of the phase image. Defo- cusing and phase-shifting techniques

Seung, Sebastian

408

Fourier Transform Infrared Imaging Microspectroscopy and Tissue-Level Mechanical Testing Reveal Intraspecies Variation in Mouse Bone Mineral and Matrix Composition  

PubMed Central

Fracture susceptibility is heritable and dependent upon bone morphology and quality. However, studies of bone quality are typically overshadowed by emphasis on bone geometry and bone mineral density. Given that differences in mineral and matrix composition exist in a variety of species, we hypothesized that genetic variation in bone quality and tissue-level mechanical properties would also exist within species. Sixteen-week-old female A/J, C57BL/6J (B6), and C3H/HeJ (C3H) inbred mouse femora were analyzed using Fourier transform infrared imaging and tissue-level mechanical testing for variation in mineral composition, mineral maturity, collagen cross-link ratio, and tissue-level mechanical properties. A/J femora had an increased mineral-to-matrix ratio compared to B6. The C3H mineral-to-matrix ratio was intermediate of A/J and B6. C3H femora had reduced acid phosphate and carbonate levels and an increased collagen cross-link ratio compared to A/J and B6. Modulus values paralleled mineral-to-matrix values, with A/J femora being the most stiff, B6 being the least stiff, and C3H having intermediate stiffness. In addition, work-to-failure varied among the strains, with the highly mineralized and brittle A/J femora performing the least amount of work-to-failure. Inbred mice are therefore able to differentially modulate the composition of their bone mineral and the maturity of their bone matrix in conjunction with tissue-level mechanical properties. These results suggest that specific combinations of bone quality and morphological traits are genetically regulated such that mechanically functional bones can be constructed in different ways. PMID:18855037

Courtland, Hayden-William; Nasser, Philip; Goldstone, Andrew B.; Spevak, Lyudmila; Boskey, Adele L.; Jepsen, Karl J.

2009-01-01

409

Tunable elastomer-based virtually imaged phased array.  

PubMed

Virtually imaged phased arrays (VIPAs) offer a high potential for wafer-level integration and superior optical properties compared to conventional gratings. We introduce an elastomer-based tunable VIPA enabling fine tuning of the dispersion characteristics. It consists of a poly-dimethylsiloxane (PDMS) layer sandwiched between silver bottom and top coatings, which form the VIPA's high reflective and semi-transparent mirror, respectively. The latter also acts as an electrode for Joule heating, such that the optical PDMS resonator cavity tuning is carried out via a combination of thermal expansion and the thermo-optic effect. Analogous to the free spectral range (FSR), based on a VIPA specific dispersion law, we introduce a new characteristic VIPA performance measure, namely the free angular range (FAR). We report a tuning span of one FAR achieved by a 7.2K temperature increase of a 170?m PDMS VIPA. Both resonance quality and tunability are analyzed in numerical simulations and experiments. PMID:23481792

Metz, Philipp; Block, Hendrik; Behnke, Christopher; Krantz, Matthias; Gerken, Martina; Adam, Jost

2013-02-11

410

A quantitative, non-interferometric X-ray phase contrast imaging technique  

PubMed Central

We present a quantitative, non-interferometric, X-ray differential phase contrast imaging technique based on the edge illumination principle. We derive a novel phase retrieval algorithm which requires only two images to be acquired and verify the technique experimentally using synchrotron radiation. The technique is useful for planar imaging but is expected to be important for quantitative phase tomography also. The properties and limitations of the technique are studied in detail. PMID:23388958

Munro, Peter R.T.; Rigon, Luigi; Ignatyev, Konstantin; Lopez, Frances C.M.; Dreossi, Diego; Speller, Robert D.; Olivo, Alessandro

2013-01-01

411

Interparticle Interactions and Direct Imaging of Colloidal Phases Assembled from Microsphere-Nanoparticle  

E-print Network

Interparticle Interactions and Direct Imaging of Colloidal Phases Assembled from Microsphere the interparticle interactions, phase behavior, and structure of microsphere-nanoparticle mixtures that possess high microsphere interactions in suspension, yielding new insight into the origin of the experimentally observed

Weeks, Eric R.

412

Grating-based x-ray phase-contrast imaging at PETRA III  

NASA Astrophysics Data System (ADS)

Conventional absorption-based imaging often lacks in good contrast at special applications like visualization of soft tissue or weak absorbing material in general. To overcome this limitation, several new X-ray phase-contrast imaging methods have been developed at synchrotron radiation facilities. Our aim was to establish the possibility of different phase-contrast imaging modalities at the Imaging Beamline (IBL, P05) and the High Energy Material Science beamline (HEMS, P07) at Petra III (DESY, Germany). Here we present the instrumentation and the status of the currently successfully established phase-contrast imaging techniques. First results from measurements of biomedical samples will be presented as demonstration.

Hipp, A.; Beckmann, F.; Lytaev, P.; Greving, I.; Lottermoser, L.; Dose, T.; Kirchhof, R.; Burmester, H.; Schreyer, A.; Herzen, J.

2014-09-01

413

Detection of unstained living neurospheres from phase contrast images with very large illumination variations.  

PubMed

Live imaging of neural stem cells and progenitors is important to follow the biology of these cells. Non-invasive imaging techniques, such as phase contrast microscopy, are preferred as neural stem cells are very sensitive to photoxic damage cause by excitation of fluorescent molecules. However, large illumination variations and weak foreground/background contrast make phase contrast images challenging for image processing. In the current work, we propose a new method to segment neurospheres imaged under phase contrast microscopy by employing high dynamic range imaging and advanced level-set method. The use of high dynamic range imaging enhances the fused image by expressing cell signatures from various exposure captures. We apply advanced level-set method in cell segmentation to improve the detection rate over simple methods such as thresholding. Validation experiments in the analysis of 21 images containing over 400 cells have demonstrated accuracy improvements over existing techniques. PMID:22255744

Xiong, Wei; Chia, Shue-Ching; Lim, Joo-Hwee; Shvetha, Sankaran; Ahmed, Sohail

2011-01-01

414

Experimental verification of improvement of phase shifting moiré interferometry using wavelet-based image processing  

Microsoft Academic Search

Phase shifting interferometry is combined with wavelet-based image processing techniques to extract precise phase information for applications of moireinterferometry. Specifically, a diffraction grating identical to the specimen grating is used to introduce the additional phase shifts needed to implement phase shifting moireinterferometry. The phase map is calculated with the four-step phase shifting algorithm with 90-deg relative shifts between adjacent frames.

Heng Liu; Alexander N. Cartwright; Cemal Basaran

2004-01-01

415

A Fourier approach to cloud motion estimation  

NASA Technical Reports Server (NTRS)

A Fourier phase-difference technique for cloud motion estimation from pairs of pictures is described, and results obtained using this technique are compared with the results of a Fourier-domain cross-correlation scheme. The phase-difference technique makes use of the phase of the cross-spectral density and allows motion estimates to be made for individual spatial frequencies, which are related to cloud pattern dimensions. When objects being tracked do not change their shape, size, and orientation to more than a limited degree, both techniques are effective. The phase difference technique is relatively sensitive to the presence of mixtures of motions, changes in cloud shape, and edge effects; in these circumstances, the cross-correlation scheme is preferable. It is suggested that the Fourier transform phase difference estimation methods can be applied in problems such as landmark matching.

Arking, A.; Lo, R. C.; Rosenfeld, A.

1978-01-01

416

Limitations imposed by specimen phase gradients on the design of grating based x-ray phase contrast imaging systems  

SciTech Connect

X-ray phase contrast imaging is a very promising technique that may lead to significant advancements in a variety of fields, perhaps most notably, medical imaging. The radiation physics group at University College London is currently developing an x-ray phase contrast imaging technique that works with laboratory x-ray sources. This system essentially measures the degree to which photons are refracted by regions of an imaged object. The amount of refraction that may be expected to be encountered in practice impacts strongly upon the design of the imaging system. In this paper, we derive an approximate expression between the properties of archetypal imaged objects encountered in practice and the resulting distribution of refracted photons. This is used to derive constraints governing the design of the system.

Munro, Peter R. T.; Ignatyev, Konstantin; Speller, Robert D.; Olivo, Alessandro

2010-07-10

417

The History of the Fourier Tachometer  

NASA Astrophysics Data System (ADS)

Following a suggestion by one of us (T. Brown) we developed in 1978 at the Sacramento Peak Observatory the first version of what we called a Fourier Tachometer which measured the phase of a single frequency component of the Fourier transform of the solar spectrum associated with a specific solar spectrum line (Beckers & Brown 1978). This phase is a direct measure of the wavelength of that Line, its Doppler shift and by using polarization optics, its Zeeman splitting. This first version based on a Michelson interferometer (FT I) was later (Evans 1081) greatly improved by J.W. Evans by using a Solid Polarizing Interferometer (version FT II). The latest version stands out by its ability to: (i) get wavelength measurements over a large 2D field-of-view without the cumbersome use of a high-resolution spectrograph, (ii) have a wide angular field-of-view and étendue, (iii) be mechanically stable and use much real-time digital processing. The FT II was selected for use in Global Oscillation Network Group (GONG) in about 1985 and has since then also been used in the space based helioseismometers — Micheson Doppler Imager (MDI) onboard Solar and Heliospheric Observatory (Scherrer et al. 1995) and Helioseismic Magnetic Imager (HMI) onboard Solar Dynamics Observatory (Scherrer et al. 2012). The FT II performance has increased over the years with the current HMI version having 4096 × 4096 pixels, or 0.5 × 0.5 arcsec for the HMI full disk facility, and a cadence of 45 seconds. However, except for some early observations at the Sacramento Peak, the Fourier Tachometer has not appeared to have been applied to non-helioseismology ground-based observations. In ground-based telescopes science full precise line profiles are generally desired making the FT II undesirable since it only measures something close to their center-of-gravity. For future very large diameter (1.5 - 8 m) ground-based solar telescopes that will also be the case. But complimentary FT II observations, for example from the spectrograph reflecting slit-jaws, would provide valuable, high time and spatial resolution complimentary observations. The HMI version would have pixel sizes of about 0.03 × 0.03 arcsec, closely matching the telescope resolution over a 2 × 2 arcmin field-of-view provided by its Multi-Conjugate Adaptive Optics system.

Beckers, J. M.; Brown, T. M.

2013-12-01

418

Low-dose, simple, and fast grating-based X-ray phase-contrast imaging  

PubMed Central

Phase sensitive X-ray imaging methods can provide substantially increased contrast over conventional absorption-based imaging and therefore new and otherwise inaccessible information. The use of gratings as optical elements in hard X-ray phase imaging overcomes some of the problems that have impaired the wider use of phase contrast in X-ray radiography and tomography. So far, to separate the phase information from other contributions detected with a grating interferometer, a phase-stepping approach has been considered, which implies the acquisition of multiple radiographic projections. Here we present an innovative, highly sensitive X-ray tomographic phase-contrast imaging approach based on grating interferometry, which extracts the phase-contrast signal without the need of phase stepping. Compared to the existing phase-stepping approach, the main advantages of this new method dubbed “reverse projection” are not only the significantly reduced delivered dose, without the degradation of the image quality, but also the much higher efficiency. The new technique sets the prerequisites for future fast and low-dose phase-contrast imaging methods, fundamental for imaging biological specimens and in vivo studies. PMID:20643971

Zhu, Peiping; Zhang, Kai; Wang, Zhili; Liu, Yijin; Liu, Xiaosong; Wu, Ziyu; McDonald, Samuel A.; Marone, Federica; Stampanoni, Marco

2010-01-01

419

Unsupervised malaria parasite detection based on phase spectrum.  

PubMed

In this paper, we propose a novel method for malaria parasite detection based on phase spectrum. The method first obtains the amplitude spectrum and phase spectrum for blood smear images through Quaternion Fourier Transform (QFT). Then it gets the reconstructed image based on Inverse Quaternion Fourier transform (IQFT) on a constant amplitude spectrum and the original phase spectrum. The malaria parasite areas can be detected easily from the reconstructed blood smear images. Extensive experiments have demonstrated the effectiveness of this novel method. PMID:22256196

Fang, Yuming; Xiong, Wei; Lin, Weisi; Chen, Zhenzhong