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1

Detection of left atrial myxoma by Fourier phase image.  

PubMed

A case of left atrial myxoma shown on an equilibrium radionuclide ventriculography is presented. A peculiar abnormality of the Fourier phase image appears more reliable than the other findings previously revealed by first-pass or equilibrium studies. The findings were perfectly consistent with the gross anatomy of the tumour. PMID:7160403

Tarolo, G L; Picozzi, R; Zatta, G; Baroffio, R; Bossi, M C

1982-01-01

2

Optical Fourier techniques for medical image processing and phase contrast imaging  

PubMed Central

This paper briefly reviews the basics of optical Fourier techniques (OFT) and applications for medical image processing as well as phase contrast imaging of live biological specimens. Enhancement of microcalcifications in a mammogram for early diagnosis of breast cancer is the main focus. Various spatial filtering techniques such as conventional 4f filtering using a spatial mask, photoinduced polarization rotation in photosensitive materials, Fourier holography, and nonlinear transmission characteristics of optical materials are discussed for processing mammograms. We also reviewed how the intensity dependent refractive index can be exploited as a phase filter for phase contrast imaging with a coherent source. This novel approach represents a significant advance in phase contrast microscopy.

Yelleswarapu, Chandra S.; Kothapalli, Sri-Rajasekhar; Rao, D.V.G.L.N.

2008-01-01

3

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

4

Novel Fourier-domain constraint for fast phase retrieval in coherent diffraction imaging.  

PubMed

Coherent diffraction imaging (CDI) for visualizing objects at atomic resolution has been realized as a promising tool for imaging single molecules. Drawbacks of CDI are associated with the difficulty of the numerical phase retrieval from experimental diffraction patterns; a fact which stimulated search for better numerical methods and alternative experimental techniques. Common phase retrieval methods are based on iterative procedures which propagate the complex-valued wave between object and detector plane. Constraints in both, the object and the detector plane are applied. While the constraint in the detector plane employed in most phase retrieval methods requires the amplitude of the complex wave to be equal to the squared root of the measured intensity, we propose a novel Fourier-domain constraint, based on an analogy to holography. Our method allows achieving a low-resolution reconstruction already in the first step followed by a high-resolution reconstruction after further steps. In comparison to conventional schemes this Fourier-domain constraint results in a fast and reliable convergence of the iterative reconstruction process. PMID:21996873

Latychevskaia, Tatiana; Longchamp, Jean-Nicolas; Fink, Hans-Werner

2011-09-26

5

Statistical texture image classification using two-dimensional nonminimum-phase Fourier series based model  

Microsoft Academic Search

Using the 2-D extension of Chi's real 1-D parametric nonminimum-phase Fourier series based model (FSBM) for or as an approximation to any arbitrary nonminimum-phase linear time-invariant (LTI) systems, we propose a system identification algorithm for 2-D nonminimum-phase linear shift-invariant (LSI) systems supported by some simulation results. The estimated 2-D FSBM parameters and second- and higher-order statistics obtained using the proposed

Chii-Horng Chen; Chong-Yung Chi

1999-01-01

6

Digital imaging of Giemsa-banded human chromosomes: eigenanalysis and the Fourier phase reconstruction  

Microsoft Academic Search

The new methodology of chromosome analysis based on eigenanalysis and iterative Fourier synthesis has been developed. The approach is inspired by the analysis developed in electron microscopy of particles, and has been modified to address particular problems of chromosome analysis. Preliminary results on data sets containing 40-80 images for each of the human chromosomes indicate that this methodology provides an

Zeljko Jericevic; Loris McGavran; Louis C. Smith

1991-01-01

7

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

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

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

10

Digital imaging of Giemsa-banded human chromosomes: eigenanalysis and the Fourier phase reconstruction  

NASA Astrophysics Data System (ADS)

The new methodology of chromosome analysis based on eigenanalysis and iterative Fourier synthesis has been developed. The approach is inspired by the analysis developed in electron microscopy of particles, and has been modified to address particular problems of chromosome analysis. Preliminary results on data sets containing 40-80 images for each of the human chromosomes indicate that this methodology provides an improvement of chromosome band resolution and potentially can provide cytogeneticist with some new insights. The proposed procedure is a novel approach in chromosome analysis and represents a significant contribution to quantitative cytogenetics. It opens the possibility of identifying defects in chromosome banding pattern automatically.

Jericevic, Zeljko; McGavran, Loris; Smith, Louis C.

1991-05-01

11

Multiple-image encryption based on nonlinear amplitude-truncation and phase-truncation in Fourier domain  

NASA Astrophysics Data System (ADS)

The classical double random phase encoding technique (DRPE) is vulnerable to chosen ciphertext attacks, known-plaintext attacks and chosen-plaintext attacks for its linearity. In order to avoid the disadvantages originated from the linearity and symmetric, an improved method for multiple-image encryption based on nonlinear operations in Fourier domain is proposed. The random phase masks (RPMs) for encryption and additive keys which are determined by the original images and generated by the nonlinear operations in encryption process, are necessary for image decoding. As a result of the nonlinear operations, the increase in the number of keys, removal of linearity and high robustness could be achieved in this cryptosystem. Computer simulations are presented to demonstrate its good performance, and the security is analyzed as well.

Wang, Xiaogang; Zhao, Daomu

2011-01-01

12

Removal of a mirror image and enhancement of the signal-to-noise ratio in Fourier-domain optical coherence tomography using an electro-optic phase modulator  

Microsoft Academic Search

A novel swept-laser-based Fourier-domain optical coherence tomography system using an electro-optic phase modulator was demonstrated. The imaging range was doubled by cancellation of the mirror image. The elimination of low-frequency noises resulting from dc and autocorrelation terms increased the sensitivity by 20 dB.

Jun Zhang; J. Stuart Nelson; Zhongping Chen

2005-01-01

13

Resampling Images in Fourier Domain  

NASA Astrophysics Data System (ADS)

When simulating sky images, one often takes a galaxy image F(x) defined by a set of pixelized samples and an interpolation kernel, and then wants to produce a new sampled image representing this galaxy as it would appear with a different point-spread function, a rotation, shearing, or magnification, and/or a different pixel scale. These operations are sometimes only possible, or most efficiently executed, as resamplings of the Fourier transform F˜(u) of the image onto a u-space grid that differs from the one produced by a discrete Fourier transform (DFT) of the samples. In some applications, it is essential that the resampled image be accurate to better than one part in 103, so in this paper, we first use standard Fourier techniques to show that Fourier-domain interpolation with a wrapped sinc function yields the exact value of F˜(u) in terms of the input samples and kernel. This operation scales with image dimension as N4 and can be prohibitively slow, so we next investigate the errors accrued from approximating the sinc function with a compact kernel. We show that these approximations produce a multiplicative error plus a pair of ghost images (in each dimension) in the simulated image. Standard Lanczos or cubic interpolators, when applied in Fourier domain, produce unacceptable artifacts. We find that errors less than one part in 103 can be obtained by (1) fourfold zero-padding of the original image before executing the x ? u DFT, followed by (2) resampling to the desired u-grid using a six-point, piecewise-quintic interpolant that we design expressly to minimize the ghosts, then (3) executing the DFT back to x-domain.

Bernstein, Gary M.; Gruen, Daniel

2014-03-01

14

Comment on: Novel image encryption/decryption based on quantum fourier transform and double phase encoding  

NASA Astrophysics Data System (ADS)

In this letter, we have pointed out some problems existed in (Yang et al. in Quantum Inf Process 12(11):3477-3493, 2013). Then, a new restricted quantum image color transformation method is proposed.

Song, Xian-Hua; Niu, Xia-Mu

2014-06-01

15

Laser Field Imaging Through Fourier Transform Heterodyne  

SciTech Connect

The authors present a detection process capable of directly imaging the transverse amplitude, phase, and Doppler shift of coherent electromagnetic fields. Based on coherent detection principles governing conventional heterodyned RADAR/LADAR systems, Fourier Transform Heterodyne incorporates transverse spatial encoding of the reference local oscillator for image capture. Appropriate selection of spatial encoding functions allows image retrieval by way of classic Fourier manipulations. Of practical interest: (1) imaging may be accomplished with a single element detector/sensor requiring no additional scanning or moving components, (2) as detection is governed by heterodyne principles, near quantum limited performance is achievable, (3) a wide variety of appropriate spatial encoding functions exist that may be adaptively configured in real-time for applications requiring optimal detection, and (4) the concept is general with the applicable electromagnetic spectrum encompassing the RF through optical.

Cooke, B.J.; Laubscher, B.E.; Olivas, N.L.; Galbraith, A.E.; Strauss, C.E.; Grubler, A.C.

1999-04-05

16

Image encryption algorithm by using fractional Fourier transform and pixel scrambling operation based on double random phase encoding  

NASA Astrophysics Data System (ADS)

To enhance the security of double random phase encoding, a kind of amplitude scrambling operation is designed and introduced into an image encryption process. The random data of the second phase mask in double random phase encoding is also employed for scrambling amplitude distribution in order to save the space of storage and transmission of the key information. The scrambling operator is changeable for generating the key. Some numerical simulations have been provided for testing the validity of the image encryption scheme.

Liu, Zhengjun; Li, She; Liu, Wei; Wang, Yanhua; Liu, Shutian

2013-01-01

17

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

18

Gas-Phase Plume from Laser-Irradiated Fiberglass-Reinforced Polymers via Imaging Fourier Transform Spectroscopy.  

PubMed

Emissive plumes from laser-irradiated fiberglass-reinforced polymers (FRP) were investigated using a mid-infrared imaging Fourier transform spectrometer, operating at fast framing rates (50 kHz imagery and 2.5 Hz hyperspectral imagery) with adequate spatial (0.81 mm(2) per pixel) and spectral resolution (2 cm(-1)). Fiberglass-reinforced polymer targets were irradiated with a 1064 nm continuous wave neodymium-doped yttrium aluminum garnet (Nd:YAG) laser for 60 s at 100 W in air. Strong emissions from H2O, CO, CO2, and hydrocarbons were observed between 1800 and 5000 cm(-1). A single-layer radiative transfer model was developed for the spectral region from 2000 to 2400 cm(-1) to estimate spatial maps of temperature and column densities of CO and CO2 from the hyperspectral imagery. The spectral model was used to compute the absorption cross sections of CO and CO2 using spectral line parameters from the high-temperature extension of the HITRAN. The analysis of pre-combustion spectra yields effective temperatures rising from ambient to 1200 K and suddenly increasing to 1515 K upon combustion. The peak signal-to-noise ratio for a single spectrum exceeds 60:1, enabling temperature and column density determinations with low statistical error. For example, the spectral analysis for a single pixel within a single frame yields an effective temperature of 1019 ± 6 K, and CO and CO2 column densities of 1.14 ± 0.05 and 1.11 ± 0.03 × 10(18) molec/cm(2), respectively. Systematic errors associated with the radiative transfer model dominate, yielding effective temperatures with uncertainties of >100 K and column densities to within a factor of 2-3. Hydrocarbon emission at 2800 to 3200 cm(-1) is well correlated with CO column density. PMID:25014838

Acosta, Roberto I; Gross, Kevin C; Perram, Glen P; Johnson, Shane M; Dao, Ly; Medina, David F; Roybal, Robert; Black, Paul

2014-07-01

19

Fourier Transform and Reflective Imaging Pyrometry  

SciTech Connect

A stationary Fourier transform pyrometer was used to record mid-wavelength IR spectra in dynamic shock experiments. The gated-IR camera used with this system was also used to record images of light produced and light reflected from shocked metals in order to constrain the dynamic emissivity and provide temperature estimates. This technique will be referred to as reflective imaging pyrometry.

Stevens, G. D.

2011-07-01

20

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

21

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

22

Fourier analysis of blood plasma laser images phase maps in the diagnosis of cancer in human organs  

NASA Astrophysics Data System (ADS)

A method of polarization mapping of the optico-anisotropic polycrystalline networks of the blood plasma albumin and globulin proteins with adjusted spatial-frequency filtering of the coordinate distributions of the azimuth and ellipticity of the polarization of laser radiation in the Fourier plane is proposed and substantiated. Comparative studies of the effectiveness of direct methods of mapping and a spatial-frequency selection in differentiating polarization azimuth and ellipticity maps of the field of laser radiation converted by the networks of albumin - globulin crystals of the blood plasma in healthy people and patients with prostate cancer have been carried out.

Angelsky, P. O.; Kushnerick, L. Ya.; Bachinskiy, V. T.; Vanchuliak, O. Ya.; Garazdiuk, M.; Pashkovska, N. V.; Andriychuk, D.

2013-12-01

23

Novel fringe scanning/Fourier transform method of synthetic imaging  

SciTech Connect

We have developed a one-dimensional theory and a computer model for synthetically imaging scenes using a novel fringe scanning/Fourier transform technique. Our method probes a scene using two interfering beams of slightly different frequency. These beams form a moving fringe pattern which scans the scene and resonates with any spatial frequency components having the same spatial frequency as the scanning fringe pattern. A simple, non-imaging detector above the scene observes any scattered radiation from the scene falling onto it. If a resonance occurs between the scanning fringe pattern and the scene, then the scattered radiation will be modulated at the difference frequency between the two probing beams. By changing the spatial period of the fringe pattern and then measuring the amplitude and phase of the modulated radiation that is scattered from the scene, the Fourier amplitudes and phases of the different spatial frequency components making up the scene can be measured. A synthetic image of the scene being probed can be generated from this Fourier amplitude and phase data by taking the inverse Fourier transform of this information. This technique could be used to image objects using light, ultrasonic, or other electromagnetic or acoustic waves.

Crawford, T.M.; Albano, R.K.

1993-08-01

24

Simultaneous encryption of a color and a gray-scale image using byte-level encoding based on single-channel double random-phase encoding architecture in fractional Fourier domain  

NASA Astrophysics Data System (ADS)

A technique for simultaneous encryption of a color and a gray-scale image is proposed, using single-channel double random-phase encoding in the fractional Fourier domain. Prior to the encryption, the segregated red, green, and blue components of the color image and the gray-scale image are encoded into a single image after changing their bit formats. The format of the encoded image is such that it cannot be perceived by the human eye. The fractional orders of the fractional Fourier transform and two random-phase masks act as key parameters for the encryption. Performance of the scheme is verified against chosen plain-text and known plain-text attacks, respectively. The effect of noise on the performance of the proposed technique is analyzed.

Joshi, Madhusudan; Singh, Kehar

2011-04-01

25

Phase information in coherent Fourier scatterometry  

NASA Astrophysics Data System (ADS)

Incoherent Optical Scatterometry (IOS) is widely used in semiconductor industry in applications related to optical metrology particularly in grating reconstruction. Recently, Coherent Fourier Scatterometry (CFS) has emerged as a strong alternative to the traditional IOS under suitable condition. When available, phase information is an added advantage in CFS to complement the intensity data. Phase information in the scattered far field is dependent on the structure and the composition of the grating. We derive and discuss the phase information accessible through the CFS. Phase difference between the diffracted orders is computed and the polarization dependent phase sensitivity of the grating parameters are discussed. The results are rigorously simulated and an experimental implementation of CFS demonstrates the functionality of the method.

Kumar, N.; El Gawhary, O.; Roy, S.; Pereira, S. F.; Urbach, H. P.

2013-04-01

26

Trends in Fourier transform infrared spectroscopic imaging  

Microsoft Academic Search

Fourier transform infrared (FTIR) spectroscopic imaging is a relatively new method that has received great attention as a\\u000a new field of analytical chemistry. The greatest benefit of this technique lies in the high molecular sensitivity combined\\u000a with a spatial resolution down to a few micrometers. Another advantage is the ability to probe samples under native conditions,\\u000a which allows new insights

Gerald Steiner; Edmund Koch

2009-01-01

27

Fresnel and Fourier hologram generation using orthographic projection images.  

PubMed

A novel technique for synthesizing a hologram of three-dimensional objects from multiple orthographic projection view images is proposed. The three-dimensional objects are captured under incoherent white illumination and their orthographic projection view images are obtained. The orthographic projection view images are multiplied by the corresponding phase terms and integrated to form a Fourier or Fresnel hologram. Using simple manipulation of the orthographic projection view images, it is also possible to shift the three-dimensional objects by an arbitrary amount along the three axes in the reconstruction space or invert their depths with respect to the given depth plane. The principle is verified experimentally. PMID:19365458

Park, Jae-Hyeung; Kim, Min-Su; Baasantseren, Ganbat; Kim, Nam

2009-04-13

28

Adaptive system correction for robust Fourier ptychographic imaging.  

PubMed

Fourier ptychography (FP) is a recently developed imaging approach that bypasses the resolution limit defined by the lens' aperture. In current FP imaging platforms, systematic noise sources come from the intensity fluctuation of multiple LED elements and the pupil aberrations of the employed optics. These system uncertainties can significantly degrade the reconstruction quality and limit the achievable resolution, imposing a restriction on the effectiveness of the FP approach. In this paper, we report an optimization procedure that performs adaptive system correction for Fourier ptychographic imaging. Similar to the techniques used in phase retrieval, the reported procedure involves the evaluation of an image-quality metric at each iteration step, followed by the estimation of an improved system correction. This optimization process is repeated until the image-quality metric is maximized. As a demonstration, we used this process to correct for illumination intensity fluctuation, to compensate for pupil aberration of the optics, and to recover several unknown system parameters. The reported adaptive correction scheme may improve the robustness of Fourier ptychographic imaging by factoring out system imperfections and uncertainties. PMID:24514833

Bian, Zichao; Dong, Siyuan; Zheng, Guoan

2013-12-30

29

Pseudo-log-polar Fourier transform for image registration  

Microsoft Academic Search

A new registration algorithm based on pseudo-log-polar Fourier transform (PLPFT) for estimating large translations, rotations, and scalings in images is developed. The PLPFT, which is calculated at points distributed at nonlinear increased concentric squares, approximates log-polar Fourier representations of images accurately. In addition, it can be calculated quickly by utilizing the Fourier separability property and the fractional fast Fourier transform.

Hanzhou Liu; Baolong Guo; Zongzhe Feng

2006-01-01

30

Construction of high frame rate images with Fourier transform  

NASA Astrophysics Data System (ADS)

Traditionally, images are constructed with a delay-and-sum method that adjusts the phases of received signals (echoes) scattered from the same point in space so that they are summed in phase. Recently, the relationship between the delay-and-sum method and the Fourier transform is investigated [Jian-yu Lu, Anjun Liu, and Hu Peng, ``High frame rate and delay-and-sum imaging methods,'' IEEE Trans. Ultrason. Ferroelectr. Freq. Control (submitted)]. In this study, a generic Fourier transform method is developed. Two-dimensional (2-D) or three-dimensional (3-D) high frame rate images can be constructed using the Fourier transform with a single transmission of an ultrasound pulse from an array as long as the transmission field of the array is known. To verify our theory, computer simulations have been performed with a linear array, a 2-D array, a convex curved array, and a spherical 2-D array. The simulation results are consistent with our theory. [Work supported in part by Grant 5RO1 HL60301 from NIH.

Peng, Hu; Lu, Jian-Yu

2002-05-01

31

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.

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

2013-01-01

32

Fourier transform digital holographic adaptive optics imaging system.  

PubMed

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

2012-12-10

33

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

34

DEFT: Direct electronic Fourier transforms of optical images  

Microsoft Academic Search

A family of novel devices for electronic imaging is described and several different realizations age presented. Direct electronic Fourier transform (DEFT) cameras employ coupling between surface strain waves, the image intensity, and electrical charge to produce electronic signals representing the spatial Fourier transform of the image at a single pair of terminals. This signal can be easily processed to accomplish

P. G. Kornreich; S. T. Kowel; D. J. Fleming; Neng-Tze Yang; A. Gupta; O. Lewis

1974-01-01

35

Least-squares Fourier phase estimation from the modulo 2? bispectrum phase  

Microsoft Academic Search

The recovery of Fourier phases from measurements of the bispectrum occupies a vital role in many astronomical speckle imaging schemes. In arecent paper (J. Opt. Soc. Am. A 7,14(1990)) it was suggested that a least-squares so- lution to this problem must fail if the bispectrum phase is known only modulo 27r. Here an alternative nonlinear least-squares algorithm is presented that

Christopher A. Haniff

1991-01-01

36

Color image encryption based on joint fractional Fourier transform correlator  

NASA Astrophysics Data System (ADS)

In this paper, an optical color image encryption/decryption technology based on joint fractional Fourier transform correlator and double random phase encoding (DRPE) is developed. In this method, the joint fractional power spectrum of the image to be encrypted and the key codes is recorded as the encrypted data. Different from the case with classical DRPE, the same key code was used both in the encryption and decryption. The security of the system is enhanced because of the fractional order as a new added key. This method takes full advantage of the parallel processing features of the optical system, and could optically realize single-channel color image encryption. The experimental results indicate that the new method is feasible.

Lu, Ding; Jin, Weimin

2011-06-01

37

Mosaic imaging Fourier transform spectrometer applications  

NASA Astrophysics Data System (ADS)

A high-speed passive FTIR imaging spectrometer has been developed and tested in airborne flight tests on both fixed wing and helicopter platforms. This sensor was developed and flown from 2000 to 2005 in conjunction with various organizations, and is known as the Turbo FT. The Turbo FT is a laser-less rotary high speed Fourier Transform Infra-Red (FTIR) spectrometer capable of very high speed, spectral resolution to 1 cm-1, and operation in rugged environments. For these tests, the sensor was run at 8 cm-1 resolution and 50-100 scans per second with either a single element or a 2x8 element LWIR detector. An on-board auto-calibrating blackbody accessory was developed and automated chemical detection software was developed. These features allow in-flight calibration, facilitated detection of target gas clouds, and reported detections to an on-board targeting computer. This paper will discuss the system specifications, sensor performance, and field results from various experiments. Current work on development of an 8x8 pixel Turbo FT system will also be presented.

Wadsworth, Winthrop; Dybwad, Jens Peter; Stone, Drew

2005-06-01

38

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

39

Imaging Fourier Transform Spectroscopy from a Space Based Platform -- The Herschel/SPIRE Fourier Transform Spectrometer  

NASA Astrophysics Data System (ADS)

The Herschel Space Observatory (Herschel), a flagship mission of the European Space Agency (ESA), is comprised of three cryogenically cooled instruments commissioned to explore the far-infrared/submillimetre universe. Herschel's remote orbit at the second Lagrangian point (L2) of the Sun-Earth system, and its cryogenic payload, impose a need for thorough instrument characterization and rigorous testing as there will be no possibility for any servicing after launch. The Spectral and Photometric Imaging Receiver (SPIRE) is one of the instrument payloads aboard Herschel and consists of a three band imaging photometer and a two band imaging spectrometer. The imaging spectrometer on SPIRE consists of a Mach-Zehnder (MZ)-Fourier transform spectrometer (FTS) coupled with bolometric detector arrays to form an imaging FTS (IFTS). This thesis presents experiments conducted to verify the performance of an IFTS system from a space based platform, Le. the use of the SPIRE IFTS within the Herschel space observatory. Prior to launch, the SPIRE instrument has undergone a series of performance verification tests conducted at the Rutherford Appleton Laboratory (RAL) near Oxford, UK. Canada is involved in the SPIRE project through provision of instrument development hardware and software, mission flight software, and support personnel. Through this thesis project I have been stationed at RAL for a period spanning fifteen months to participate in the development, performance verification, and characterization of both the SPIRE FTS and photometer instruments. This thesis discusses Fourier transform spectroscopy and related FTS data processing (Chapter 2). Detailed discussions are included on the spectral phase related to the FTS beamsplitter (Chapter 3), the imaging aspects of the SPIRE IFTS instrument (Chapter 4), and the noise characteristics of the SPIRE bolometer detector arrays as measured using the SPIRE IFTS (Chapter 5). This thesis presents results from experiments performed both on site at the RAL Space Science and Technology Department (SSTD) Assembly Integration Verification (AIV) instrument test facility as well as from the Astronomical Instrumentation Group (AIG) research laboratories within the Department of Physics & Astronomy at the University of Lethbridge.

Spencer, Locke Dean

40

The measurement uncertainty of CD measurement in the optical measurement technology using Fourier image  

NASA Astrophysics Data System (ADS)

Optical metrology system is used as high sampling CD measurement. The optical measurement technology using Fourier image can obtain much information with various optical conditions. We evaluated Fourier image method for CD metrology. Various issues of the optical measurement technology were found for CD measurement uncertainty. Measurement uncertainty depends on the number of position on Fourier image, and measurement uncertainty is improved by using multiple positions data. Top CD value is influenced by under layer pattern CD variance and under layer thickness variance. Optical CD measurement technology is influenced by various process variation like under-layer structure, stacked film thickness, material changes and so on. If optical measurement system applies to CD metrology, Fourier image method should be used in development phase for unfixed process because high number of data and speedy process feedback in no under layer situation is needed.

Nagashima, Kuniharu; Abe, Hideaki; Oote, Makoto; Yamazaki, Yuichiro

2014-04-01

41

Fourier hologram generation from multiple incoherent defocused images  

NASA Astrophysics Data System (ADS)

A novel method to capture a Fourier holography of the three-dimensional objects under regular incoherent illumination is proposed. Multiple images of the three-dimensional objects are captured by a camera while moving the focal plane along the optic axis over the whole object space. Captured multiple defocused images are processed considering the point spread function of the camera and the Fourier holography is finally synthesized. The principle is explained and verified experimentally.

Park, Jae-Hyeung; Seo, Seung-Woo; Chen, Ni; Kim, Nam

2010-04-01

42

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

43

Imaging Fourier transform spectrometer for NGST  

NASA Astrophysics Data System (ADS)

An imaging FTS would be capable of carrying out many of the programs in the DRM, namely all those which require imaging and/or low spectral resolution wide field/multi-object spectroscopy. We review the DRM science areas, describing the relevance of an imaging FTS. Required instrumental capabilities are then derived from the science goals. Our compact camera and imaging FTS instrument design emphasizes simplicity with a single optical train covering a field 6 X 3 arcmin2, with a fixed spatial sampling of 0.03 arcsec/pixel on a 12 k X 6 k detector array.

Posselt, Winfried; Wright, Gillian S.; Le Fevre, Oliver; Cornelisse, Koos W.; Jakobsen, Peter

2000-07-01

44

Phase averaging of image ensembles by using cepstral gradients  

SciTech Connect

The direct Fourier phase averaging of an ensemble of randomly blurred images has long been thought to be too difficult a problem to undertake realistically owing to the necessity of proper phase unwrapping. It is shown that it is nevertheless possible to average the Fourier phase information in an image ensemble without calculating phases by using the technique of cepstral gradients.

Swan, H.W.

1983-11-01

45

[Spatially modulated Fourier transform imaging spectrometer data compression research].  

PubMed

Fourier transform imaging spectrometer is a new technic, and has been developed very fast in recent ten years. When it is used in satellite, because of the limit by the data transmission, the authors need to compress the original data obtained by the Fourier transform imaging spectrometer, then, the data can be transmitted, and can be incepted on the earth and decompressed. Then the authors can do data process to get spectrum data which can be used by user. Data compression technic used in Fourier transform imaging spectrometer is a new technic, and few papers introduce it at home and abroad. In this paper the authors will give a data compression method, which has been used in EDIS, and achieved a good result. PMID:20302132

Huang, Min; Xiangli, Bin; Yuan, Yan; Shen, Zhong; Lu, Qun-bo; Wang, Zhong-hou; Liu, Xue-bin

2010-01-01

46

Generic pixel-wise speckle detection in Fourier-domain optical coherence tomography images.  

PubMed

We present a generic phase-domain processing method for detecting speckles in Fourier-domain optical coherence tomography (OCT) images. The physics behind the interferometry is revisited and analytically along with simulation results it indicates that the speckle formation comes with phase distortion to the complex OCT signal. The first and the second derivatives of phase along the imaging depth are then calculated for speckle identification. The phase-domain processing method was applied to images acquired by both spectral-domain OCT and swept-source OCT systems, and the experimental results show that this method enables pixel-wise speckle identification. PMID:25078185

Zhang, Anqi; Xi, Jiefeng; Liang, Wenxuan; Gao, Tianxin; Li, Xingde

2014-08-01

47

Geometrically robust image watermarking based on Jacobi-Fourier moments  

NASA Astrophysics Data System (ADS)

Rotation, scaling and translation (RST) attacks can desynchronize the watermark detection so that many watermark systems failed. A geometrically robust image watermarking strategy based on Jacobi-Fourier moments (JFMs) is proposed. The Jacobi moments of the original image are first extracted as original moments; then the watermark image is embedded into the global or local area of the original image, and the Jacobi moments of the area are extracted. When the watermarked image is not attacked, the watermark can be retrieved by using the margin of the original moments and the moments of the embedded area. When it is attacked, the watermark can also be got in that way, and the original moments need to be transformed. It can be concluded that Jacobi-Fourier moments perform better than Zernike moments (ZMs) for small images. Meanwhile, the watermark is also robust to scaling and rotation as well as regular attacks such as added noises.

Dong, Jia-Li; Yin, Guo-Rui; Ping, Zi-Liang

2009-09-01

48

A comparative image analysis of discrete radial Fourier transforms  

Microsoft Academic Search

Fourier transform is not often applied to pattern and object recognition, because of its inefficiency in image description and calculation. In order to solve this problem, a bi-discrete radial cosine transform is proposed. This new transform has two superior properties. Firstly, by using Mukundan’s square-to-circular transformation, it projects images in square to images in discrete circle girds. Secondly, different from

Guojun Zhang; Bo Li; Bo Fu; Li Li; Gaoxiang Liu

2010-01-01

49

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

50

Formation of Fourier phase shifts in the solar Ni I 6768 A line  

NASA Technical Reports Server (NTRS)

A formalism is developed to understand better how Doppler shifts of spectrum lines as inferred from phase shifts in the Fourier transforms of line profiles are related to the underlying velocity structures which they are intended to measure. With a standard model atmosphere and a simplified, quasi-LTE treatment of line formation, the formalism is applied to the Ni I 6768 A line, which has been selected for use with a network of imaging interferometers under development by the Global Oscillations Network Group for research in helioseismology. Fourier phase shifts are found to be a remarkably linear measure of velocity even in the presence of gradients and unresolved lateral variations in the assumed velocity field. An assumed outward increase in amplitude of a model oscillatory velocity is noticeably reflected in the center-to-limb behavior of the simulated velocity measure, and a sample model of solar granulation is found to have a strong influence on the formation of the Fourier phase.

Jones, Harrison P.

1989-01-01

51

Formation of Fourier phase shifts in the solar NI I 6768 A line  

NASA Astrophysics Data System (ADS)

A formalism is developed to understand better how Doppler shifts of spectrum lines as inferred from phase shifts in the Fourier transforms of line profiles are related to the underlying velocity structures which they are intended to measure. With a standard model atmosphere and a simplified, quasi-LTE treatment of line formation, the formalism is applied to the Ni I 6768 A line, which has been selected for use with a network of imaging interferometers under development by the Global Oscillations Network Group for research in helioseismology. Fourier phase shifts are found to be a remarkably linear measure of velocity even in the presence of gradients and unresolved lateral variations in the assumed velocity field. An assumed outward increase in amplitude of a model oscillatory velocity is noticeably reflected in the center-to-limb behavior of the simulated velocity measure, and a sample model of solar granulation is found to have a strong influence on the formation of the Fourier phase.

Jones, Harrison P.

52

Localized Fourier transform filter for noise removal in electronic speckle pattern interferometry wrapped phase patterns  

NASA Astrophysics Data System (ADS)

This article is concerned with frequency filtering for electronic speckle pattern interferometry wrapped phase patterns. We propose a robust localized Fourier transform filter which is an extension of the root filtering method (RFM). We improve the RFM from a simple technical process and a filter function in the frequency domain. In our method, the proposed filter function is taken as the power spectrum of the convolution of an image and a Gaussian function to the power ?. We test the proposed method on two computer-simulated wrapped phase fringe patterns and one experimentally obtained wrapped phase pattern, and compare our models with the widely used, well-known RFM and windowed Fourier filtering (WFF). The experimental results have demonstrated that our localized Fourier transform filter outperforms the RFM and is comparable to WFF. Our method depends on fewer parameters, as compared with WFF, and can achieve a better balance between the computational complexity and the filtered results.

Li, Cancan; Tang, Chen; Yan, Haiqing; Wang, Linlin; Zhang, Hao

2011-08-01

53

Localized Fourier transform filter for noise removal in electronic speckle pattern interferometry wrapped phase patterns.  

PubMed

This article is concerned with frequency filtering for electronic speckle pattern interferometry wrapped phase patterns. We propose a robust localized Fourier transform filter which is an extension of the root filtering method (RFM). We improve the RFM from a simple technical process and a filter function in the frequency domain. In our method, the proposed filter function is taken as the power spectrum of the convolution of an image and a Gaussian function to the power ?. We test the proposed method on two computer-simulated wrapped phase fringe patterns and one experimentally obtained wrapped phase pattern, and compare our models with the widely used, well-known RFM and windowed Fourier filtering (WFF). The experimental results have demonstrated that our localized Fourier transform filter outperforms the RFM and is comparable to WFF. Our method depends on fewer parameters, as compared with WFF, and can achieve a better balance between the computational complexity and the filtered results. PMID:21857715

Li, Cancan; Tang, Chen; Yan, Haiqing; Wang, Linlin; Zhang, Hao

2011-08-20

54

Image hiding in Fourier domain by use of joint transform correlator architecture and holographic technique.  

PubMed

Based on joint transform correlator (JTC) architecture and holographic techniques, a new method for image hiding is presented. A hidden image encrypted by JTC architecture is embedded in the Fourier hologram of the host image. Inverse Fourier transform can be used to obtain the watermarked image, and JTC architecture is used to decode the hidden image from the watermarked hologram. Unlike other watermarking techniques, by prechoosing information, the noise added to the recovered hidden image by the host can be reduced. Unlike other watermarking systems based on double random-phase encoding, no conjugate key is used to recover the hidden image. Theoretical analyses have shown the system's feasibility. Computer simulations are presented to verify the system's validity and efficiency. Numerical simulations also show that the proposed system is robust enough to resist attacks, such as occlusion, noise, and filtering. PMID:21343999

Shi, Xiaoyan; Zhao, Daomu

2011-02-10

55

Nonlinear effects of phase blurring on Fourier transform holograms  

Microsoft Academic Search

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 inter- modulation products to the diffraction patterns of computer-generated Fourier transform

Markus Duelli; Li Ge; Robert W. Cohn

2000-01-01

56

[Research on spatially modulated Fourier transform imaging spectrometer data processing method].  

PubMed

Fourier transform imaging spectrometer is a new technic, and has been developed very rapidly in nearly ten years. The data catched by Fourier transform imaging spectrometer is indirect data, can not be used by user, and need to be processed by various approaches, including data pretreatment, apodization, phase correction, FFT, and spectral radicalization calibration. No paper so far has been found roundly to introduce this method. In the present paper, the author will give an effective method to process the interfering data to spectral data, and with this method we can obtain good result. PMID:20496726

Huang, Min; Xiangli, Bin; Lü, Qun-Bo; Zhou, Jin-Song; Jing, Juan-Juan; Cui, Yan

2010-03-01

57

A Modified Fourier-Based Phase Unwrapping Algorithm With an Application to MRI Venography  

PubMed Central

Purpose To present a single-step deterministic procedure for unwrapping MRI phase maps. Materials and Methods Using an algorithm previously developed for optical applications, Laplacian operators were applied in the Fourier space of the MRI phase map. The original Fourier-based phase unwrapping algorithm was modified so that demodulation accomplished the required signal symmetrization in Fourier space. To evaluate the method's performance in the presence of thermal noise, a set of wrapped phase maps were simulated at different levels of noise in k-space, and the response of the algorithm at different levels of signal-to-noise ratio (SNR) was evaluated for stability. To demonstrate its utility in MRI, the algorithm was applied to the wrapped phase maps of susceptibility-weighted imaging (SWI) studies, which were then used to generate venograms. Results In simulated phase wrapping, the algorithm correctly reproduced the original phase for a wide range of phase gradients and noise. The procedure was fast and produced useful maps of venous structures in SWI images. Conclusion A fast and stable single-step deterministic method for unwrapping MRI phase maps is available for such applications as SWI and mapping of static magnetic field inhomogeneity.

Bagher-Ebadian, Hassan; Jiang, Quan; Ewing, James R.

2008-01-01

58

Time-Resolved Fourier Transform Infrared Spectroscopic Imaging  

Microsoft Academic Search

Fourier transform infrared (FT-IR) imaging allows simultaneous spectral characterization of large spatial areas due to its multichan- nel detection advantage. The acquisition of large amounts of data in the multichannel coné guration results, however, in a poor tem- poral resolution of sequentially acquired data sets, which limits the examination of dynamic processes to processes that have character- istic time scales

Rohit Bhargava; Ira W. Levin

2003-01-01

59

Scanning plasmonic microscopy by image reconstruction from the Fourier space.  

PubMed

We demonstrate a simple scheme for high-resolution imaging of nanoplasmonic structures that basically removes most of the resolution limiting allowed light usually transmitted to the far field. This is achieved by implementing a Fourier lens in a near-field scanning optical microscope (NSOM) operating in the leakage-radiation microscopy (LRM) mode. The method consists of reconstructing optical images solely from the plasmonic 'forbidden' light collected in the Fourier space. It is demonstrated by using a point-like nanodiamond-based tip that illuminates a thin gold film patterned with a sub-wavelength annular slit. The reconstructed image of the slit shows a spatial resolution enhanced by a factor ~/= 4 compared to NSOM images acquired directly in the real space. PMID:23263132

Mollet, Oriane; Huant, Serge; Drezet, Aurélien

2012-12-17

60

Quantification of fibre polymerization through Fourier space image analysis  

PubMed Central

Quantification of changes in the total length of randomly oriented and possibly curved lines appearing in an image is a necessity in a wide variety of biological applications. Here, we present an automated approach based upon Fourier space analysis. Scaled, band-pass filtered power spectral densities of greyscale images are integrated to provide a quantitative measurement of the total length of lines of a particular range of thicknesses appearing in an image. A procedure is presented to correct for changes in image intensity. The method is most accurate for two-dimensional processes with fibres that do not occlude one another.

Nekouzadeh, Ali; Genin, Guy M.

2011-01-01

61

Aperture-scanning Fourier ptychography for 3D refocusing and super-resolution macroscopic imaging.  

PubMed

We report an imaging scheme, termed aperture-scanning Fourier ptychography, for 3D refocusing and super-resolution macroscopic imaging. The reported scheme scans an aperture at the Fourier plane of an optical system and acquires the corresponding intensity images of the object. The acquired images are then synthesized in the frequency domain to recover a high-resolution complex sample wavefront; no phase information is needed in the recovery process. We demonstrate two applications of the reported scheme. In the first example, we use an aperture-scanning Fourier ptychography platform to recover the complex hologram of extended objects. The recovered hologram is then digitally propagated into different planes along the optical axis to examine the 3D structure of the object. We also demonstrate a reconstruction resolution better than the detector pixel limit (i.e., pixel super-resolution). In the second example, we develop a camera-scanning Fourier ptychography platform for super-resolution macroscopic imaging. By simply scanning the camera over different positions, we bypass the diffraction limit of the photographic lens and recover a super-resolution image of an object placed at the far field. This platform's maximum achievable resolution is ultimately determined by the camera's traveling range, not the aperture size of the lens. The FP scheme reported in this work may find applications in 3D object tracking, synthetic aperture imaging, remote sensing, and optical/electron/X-ray microscopy. PMID:24921553

Dong, Siyuan; Horstmeyer, Roarke; Shiradkar, Radhika; Guo, Kaikai; Ou, Xiaoze; Bian, Zichao; Xin, Huolin; Zheng, Guoan

2014-06-01

62

Radio astronomical imaging and phase information  

Microsoft Academic Search

Some basic concepts in use for making astronomical observations at radio wavelengths are introduced. In particular the importance of phase information for imaging in radio astronomy is highlighted. Using simple examples it is demonstrated how phase information is much more essential than that even of amplitude for an image reconstruction from its Fourier components.

Ashok K. Singal

2005-01-01

63

Astronomical imaging Fourier spectroscopy at far-infrared wavelengths  

NASA Astrophysics Data System (ADS)

The principles and practice of astronomical imaging Fourier transform spectroscopy (FTS) at far-infrared wavelengths are described. The Machâ??Zehnder (MZ) 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 MZ design are presented. The techniques for retrieving astrophysical parameters from the measured spectra are discussed using calibration data obtained with the Herschelâ??SPIRE instrument. The paper concludes with an example of imaging spectroscopy obtained with the SPIRE FTS instrument.

Naylor, David A.; Gom, Brad G.; van der Wiel, Matthijs H. D.; Makiwa, Gibion

2013-11-01

64

Globally optimized Fourier finite-difference method for ultrasound breast imaging  

NASA Astrophysics Data System (ADS)

Ultrasound reflection imaging is a promising imaging modality for detecting small, early-stage breast cancers. Properly accounting for ultrasound scattering from heterogeneities within the breast is essential for high-resolution and high-quality ultrasound breast imaging. We develop a globally optimized Fourier finite-difference method for ultrasound reflectivity image reconstruction. It utilizes an optimized solution of acoustic-wave equation and a heterogeneous sound-speed distribution of the breast obtained from tomography to reconstruct ultrasound reflectivity images. The method contains a finite-difference term in addition to the split-step Fourier implementation, and minimizes ultrasound phase errors during wavefield inward continuation while maintaining the advantage of high computational efficiency. The accuracy analysis indicates that the optimized method is much more accurate than the split-step Fourier method. The computational efficiency of the optimized method is one to two orders of magnitude faster than time-reversal imaging using a finite-difference time-domain wave-equation scheme. Our new optimized method can accurately handle ultrasound scattering from breast heterogeneities during reflectivity image reconstruction. Our numerical imaging examples demonstrate that the optimized method has the potential to produce high-quality and high-resolution ultrasound reflectivity images in combination with a reliable ultrasound sound-speed tomography method.

Huang, Lianjie; Hanson, Kenneth M.; Quan, Youli; Li, Cuiping; Duric, Neb

2008-04-01

65

Displacement estimation by the phase-shiftings of Fourier transform in present white noise  

NASA Astrophysics Data System (ADS)

Displacement estimation is a fundamental problem in Real-time video image processing. It can be typically approached by theories based on features in spatial domain. This paper presents an algorithm which improves the theory for estimating the moving object's displacement in spatial domain by its Fourier transform frequency spectrum. Because of the characters of Fourier transform, the result is based on all the features in the image. Utilizing shift theorem of Fourier transform and auto-registration, the algorithm employs the phase spectrum difference in polar coordinate of two frame images sequence with the moving target.The method needn't transform frequency spectrum to spatial domain after calculation comparing with the traditional algorithm which has to search Direc peak, and it reduces processing time. Since the technique proposed uses all the image information, including all the white noise in the image especially, and it's hard to overcome the aliasing from noises, but the technique can be an effective way to analyze the result in little white noise by the different characters between high and low frequency bands. It can give the displacement of moving target within 1 pixel of accuracy. Experimental evidence of this performance is presented, and the mathematical reasons behind these characteristics are explained in depth. It is proved that the algorithm is fast and simple and can be used in image tracking and video image processing.

Wu, Yuan-hao; Yu, Qian-yang

2006-01-01

66

Distortion- and Noise-Robust Digital Watermarking Using Input and Fourier-Plane Phase Encoding  

NASA Astrophysics Data System (ADS)

In this chapter, we propose a technique for information hiding using input and Fourier-plane phase encoding. The proposed method uses a weighed double-phase-encoded hidden image embedded within a host image as the transmitted image. We develop an analytical presentation for the system performance using the statistical properties of double-phase encoding. The peak signal-to-noise ratio (PSNR) metric is used as a measure for the degradation in the quality of the host image and the recovered hidden image. We test, analytically, the distortion of the hidden image due to the host image and the effect of occlusion of the pixels of the transmitted image (that is, the host image containing the hidden image). Moreover, we discuss the effect of using only the real part of the transmitted image to recover the hidden image. Computer simulations are presented to test the system performance against these types of distortions. Simulations illustrate the system's ability to recover the hidden image under distortions and the robustness of the hidden image against removal trials.

Kishk, Sherif; Javidi, Bahram

67

Denoising and deblurring of Fourier transform infrared spectroscopic imaging data  

NASA Astrophysics Data System (ADS)

Fourier transform infrared (FT-IR) spectroscopic imaging is a powerful tool to obtain chemical information from images of heterogeneous, chemically diverse samples. Significant advances in instrumentation and data processing in the recent past have led to improved instrument design and relatively widespread use of FT-IR imaging, in a variety of systems ranging from biomedical tissue to polymer composites. Various techniques for improving signal to noise ratio (SNR), data collection time and spatial resolution have been proposed previously. In this paper we present an integrated framework that addresses all these factors comprehensively. We utilize the low-rank nature of the data and model the instrument point spread function to denoise data, and then simultaneously deblurr and estimate unknown information from images, using a Bayesian variational approach. We show that more spatial detail and improved image quality can be obtained using the proposed framework. The proposed technique is validated through experiments on a standard USAF target and on prostate tissue specimens.

Nguyen, Tan H.; Reddy, Rohith K.; Walsh, Michael J.; Schulmerich, Matthew; Popescu, Gabriel; Do, Minh N.; Bhargava, Rohit

2012-02-01

68

Fourier phase contrast multimodal optical microscopy for real time display of phase and fluorescence at the same time  

NASA Astrophysics Data System (ADS)

Microorganisms, cells and thin tissue sections are transparent and not visible to view in ordinary microscope. Techniques such as phase contrast and Normarski/Differential interference contrast microscopy transform the phase variation information into intensity distribution to reveal the details of internal structures. Similarly fluorescence microscope uses intrinsic or extrinsic chromophores to reveal specific and hidden details. Advances achieved in recent years have greatly improved the versatility of microscopes to obtain more insightful information about different physiological functions that occur at cellular level. Understanding the cell response, involving both structural and functional changes within the cell, dictates ability to image cell structure and function at the same time. We report a novel optical Fourier phase contrast multimodal optical microscopy technique for real time display of phase and fluorescence features of biological specimens at the same time. It combines the principles of (a) Fourier phase contrast microscopy which exploits monochromaticity, intensity and phase coherence of the laser beam via optical Fourier transform and photoinduced birefringence of dye doped liquid crystal for phase contrast imaging, and (b) common-path multimodal optical microscopy for co-registered imaging of phase and fluorescence features of biological specimens in real time using a single optical path, single light source, and single camera with no requirement of image registration. Further the instrument also enables co-registered imaging of fluorescence and spatial filtering facilitating simultaneous display of structural and functional information. This comprehensive microscope has the capability of simultaneously providing both structural and functional information in a streamlined simplified design and may find applications in high-throughput screening and automated microscopy.

Yelleswarapu, Chandra S.; Das, Bhargab; Veraksa, Alexey; Rao, D. V. G. L. N.

2011-06-01

69

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

70

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

71

Laser and Fourier Transform Spectroscopy of Gas Phase Molecules  

Microsoft Academic Search

Laser and Fourier transform spectroscopy were used to study a variety of gas phase molecules. A series of calcium and strontium monoalkoxides, CaOR and SrOR (R=H, CH_3, CH _2CH_3, CH(CH _3)_2, CH_2CH _2CH_3, CH _2(CH_2)_2 CH_3, CH_2 (CH_3)CH_2 CH_3 and C(CH_3) _3) was studied by laser induced fluorescence and laser excitation techniques. The A - X and B - X

Leah Christine O'Brien

1987-01-01

72

Fourier analysis of high-spatial-frequency holographic phase gratings  

NASA Astrophysics Data System (ADS)

Plane-wave holograms were recorded on Agfa Gevaert 8E75HD holographic plates, in a wide range of bias exposures and fringe visibilities. Plates were processed by developer AAC and bleaching agent R-9. Phase gratings were studied by phase-contrast microscopy, using a high-power immersion (100×) objective. Phase-contrast photomicrographs were Fourier analysed. Thus first-, second- and third-order modulations of the refractive index as functions of bias exposure and visibility of the recording interference pattern could be determined. Relative amplitudes of the higher-order modulations to that of the first-order modulation can serve as a measure of the nonlinearity of the holographic recording. The results presented here can be used to check the validity of grating profile calculations based on higher-order coupled-wave theory.

Bányász, I.

2005-11-01

73

Integrated optics in an electrically scanned imaging Fourier transform spectrometer  

NASA Technical Reports Server (NTRS)

An efficient, lightweight and stable, Fourier transform spectrometer was developed. The mechanical slide mechanism needed to create a path difference was eliminated by the use of retro-reflecting mirrors in a monolithic interferometer assembly in which the mirrors are not at 90 degrees to the propagation vector of the radiation, but rather at a small angle. The resulting plane wave fronts create a double-sided inteferogram of the source irradiance distribution which is detected by a charge-coupled device image sensor array. The position of each CCD pixel in the array is an indication of the path difference between the two retro-reflecting mirrors in the monolithic optical structure. The Fourier transform of the signals generated by the image sensor provide the spectral irradiance distribution of the source. For imaging, the interferometer assembly scans the source of irradiation by moving the entire instrument, such as would occur if it was fixedly mounted to a moving platform, i.e., a spacecraft. During scanning, the entrace slot to the monolithic optical structure sends different pixels to corresponding interferograms detected by adjacent columns of pixels of the image sensor.

Breckinridge, James B. (inventor); Ocallaghan, Fred G. (inventor)

1982-01-01

74

Imaging the sun in hard x rays using Fourier telescopes  

NASA Technical Reports Server (NTRS)

For several years, solar flares have been observed with a variety of instruments confirming that tremendous amounts of energy are locally stored in the solar magnetic field and then rapidly released during the life of the flare. In concert with observations, theorists have attempted to describe the means by which these energetic events occur and evolve. Two competing theories have emerged and have stood the test of time. One theory describes the flare in terms of nonthermal, electron beam injection into a thick target while the other uses a thermal approach. Both theories provide results which are reasonably consistent with current observations; but to date, none have been able to provide conclusive evidence as to the validity of either model. Imaging on short time scales (1 s) and/or small size scales (1 arc s) should give definitive answers to these questions. In order to test whether a realistic telescope can indeed discriminate between models, we construct model sources based upon the thermal and the nonthermal models and calculate the emission as a function of time and energy in the range from 10 to 100 keV. In addition, we construct model telescopes representing both the spatial modulation collimator (SMC) and the rotating modulation collimator (RMC) techniques of observation using random photon counting statistics. With these two types of telescopes we numerically simulate the instrument response to the above two model flares to see if there are distinct x-ray signatures which may be discernable. We find that theoretical descriptions of the primary models of solar flares do indeed predict different hard x-ray signatures for 1 sec time scales and at 1-5 arc sec spatial resolution. However, these distinguishing signatures can best be observed early in the impulsive phase and from a position perpendicular to the plane of the loop. Furthermore, we find that Fourier telescopes with reasonable and currently attainable design characteristics can image these signatures and that the same sensitive areas and short temporal integration times relative to source evolution (i.e., 1 s), the RMC and the SMC will both provide about the same performance.

Campbell, J. W.

1993-01-01

75

The gridding method for image reconstruction by Fourier transformation  

SciTech Connect

This paper explores a computational method for reconstructing an n-dimensional signal f from a sampled version of its Fourier transform {cflx f}. The method involves a window function {cflx w} and proceeds in three steps. First, the convolution {cflx g} = {cflx w} * {cflx f} is computed numerically on a Cartesian grid, using the available samples of {cflx f}. Then, g = wf is computed via the inverse discrete Fourier transform, and finally f is obtained as g/w. Due to the smoothing effect of the convolution, evaluating {cflx w} * {cflx f} is much less error prone than merely interpolating {cflx f}. The method was originally devised for image reconstruction in radio astronomy, but is actually applicable to a broad range of reconstructive imaging methods, including magnetic resonance imaging and computed tomography. In particular, it provides a fast and accurate alternative to the filtered backprojection. The basic method has several variants with other applications, such as the equidistant resampling of arbitrarily sampled signals or the fast computation of the Radon (Hough) transform.

Schomberg, H. [Philips Research Lab., Hamburg (Germany)] [Philips Research Lab., Hamburg (Germany); Timmer, J. [Philips Medical Systems, Best (Netherlands)] [Philips Medical Systems, Best (Netherlands)

1995-09-01

76

Tests of a compact static Fourier-transform imaging spectropolarimeter.  

PubMed

A compact Fourier-transform imaging spectropolarimeter covering a 450-1000 nm spectral range is presented. The sensor, which is based on two birefringent retarders and a Wollaston interferometer, offers significant advantages over previous implementations. Specifically, with no internal moving parts, electrically controllable or micro polarization components, the full wavelength-dependent state of polarization, spectral and spatial information of a scene can be acquired simultaneously. Outdoor measurements of several cars and plants demonstrate the sensor's potential for color measurement, target identification, and agriculture monitoring applications. PMID:24921497

Li, Jie; Gao, Bo; Qi, Chun; Zhu, Jingping; Hou, Xun

2014-06-01

77

Fourier-processed images of dynamic lung function from list-mode data  

SciTech Connect

Time and volume correlated amplitude and phase images are computed from nuclear medical ventilation studies and for dynamic transmission scans of the lungs. This is made possible by a hardware interface and data acquisition system, developed in-house, allowing camera events and multiple ancillary physiological signals (including lung volume) to be acquired simultaneously in list mode. The first harmonic amplitude and phase images are constructed on an event by event basis. These are computed for both equal time and equal lung volume increments. Time and volume correlated Fourier images for ventilation studies have shown details and functional structures not usually seen in conventional imaging techniques. Processed transmission scans show similar results compared to ventilation images.

Zubal, I.G.; Rowe, R.W.; Bizais, Y.; Susskind, H.; Bennett, G.W.; Brill, A.B.

1983-01-01

78

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

79

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

80

High throughput full Stokes Fourier transform imaging spectropolarimetry.  

PubMed

A complete full Stokes imaging spectropolarimeter is proposed. Four separate polarized spectra are fed into the Sagnac Fourier transform spectrometer without slit using different angle combinations of the polarized elements. The four polarized spectra are separated without spatial aliasing. And the system has a good performance to resist the instrument noise due to its high light throughput. The mathematical model for the approach is derived and an optimization of the retardance is discussed. For acquiring the four spectra simultaneously, an improved robust polarization modulator using aperture division is outlined. Then the system is discussed in detail including the imaging principle and spectral resolution. Lastly, two proven experiments are carried out and the experimental results in visible light are outlined. PMID:24514802

Meng, Xin; Li, Jianxin; Xu, Tingting; Liu, Defang; Zhu, Rihong

2013-12-30

81

A Local Algorithm for the Computation of Image Velocity via Constructive Interference of Global Fourier Components  

Microsoft Academic Search

A novel Fourier-based technique for local motion detection from image sequences is proposed. In this method, the instantaneous\\u000a velocities of local image points are inferred directly from the global 3D Fourier components of the image sequence. This is\\u000a done by selecting those velocities for which the superposition of the corresponding Fourier gratings leads to constructive\\u000a interference at the image point.

Babette Dellen; Florentin Wörgötter

2011-01-01

82

Fourier transform infrared phase shift cavity ring down spectrometer  

NASA Astrophysics Data System (ADS)

OPTRA has developed a novel approach to phase shift cavity ring down spectroscopy (PS-CRDS) using a Fourier transform infrared (FTIR) modulator to impose the spectrally-dependent amplitude modulation on a broadband IR light source. As with previous PS-CRDS measurements, we excite a resonant cavity with amplitude modulated energy and measure the phase shift of the modulated signal exiting the cavity which is proportional to the ring down time and inversely proportional to the losses of the cavity including those due to molecular absorption. In contrast to previous efforts, we impose the amplitude modulation with the FTIR interferometer instead of an external electro-optical modulator and extract the phase from each interferogram thereby enabling broadband FTIR-PS-CRDS measurements at greater than 1 Hz update rates. The measured phase spectra can then be used for multicomponent analysis. The combined measurement can be viewed as a resonant cavity enhancement to traditional FTIR spectroscopy or a broadband enhancement to CRDS. In our paper we present the theory behind this measurement and describe the breadboard and test results from our feasibility study.

Rentz Dupuis, Julia; Engel, James R.

2012-05-01

83

Ultrahigh speed spectral/Fourier domain ophthalmic OCT imaging  

NASA Astrophysics Data System (ADS)

Ultrahigh speed spectral / Fourier domain optical coherence tomography (OCT) imaging using a CMOS line scan camera with acquisition rates of 70,000 - 312,500 axial scans per second is investigated. Several design configurations are presented to illustrate trade-offs between acquisition speed, sensitivity, resolution and sensitivity roll-off performance. We demonstrate: extended imaging range and improved sensitivity roll-off at 70,000 axial scans per second , high speed and ultrahigh resolution imaging at 106,382 axial scans per second, and ultrahigh speed imaging at 250,000-312,500 axial scans per second. Each configuration is characterized through optical testing and the trade-offs demonstrated with in vivo imaging of the fovea and optic disk in the human retina. OCT fundus images constructed from 3D-OCT data acquired at 250,000 axial scans per second have no noticeable discontinuity of retinal features and show that there are minimal motion artifacts. The fine structures of the lamina cribrosa can be seen. Long cross sectional scans are acquired at 70,000 axial scans per second for imaging large areas of the retina, including the fovea and optic disk. Rapid repeated imaging of a small volume (4D-OCT) enables time resolved visualization of the capillary network surrounding the INL and may show individual red blood cells. The results of this study suggest that high speed CMOS cameras can achieve a significant improvement in performance for ophthalmic imaging. This promises to have a powerful impact in clinical applications by improving early diagnosis, reproducibility of measurements and enabling more sensitive assessment of disease progression or response to therapy.

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

2009-02-01

84

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

85

Randomly displaced phase distribution design and its advantage in page-data recording of Fourier transform holograms.  

PubMed

For Fourier transform holography, an effective random phase distribution with randomly displaced phase segments is proposed for obtaining a smooth finite optical intensity distribution in the Fourier transform plane. Since unitary phase segments are randomly distributed in-plane, the blanks give various spatial frequency components to an image, and thus smooth the spectrum. Moreover, by randomly changing the phase segment size, spike generation from the unitary phase segment size in the spectrum can be reduced significantly. As a result, a smooth spectrum including sidebands can be formed at a relatively narrow extent. The proposed phase distribution sustains the primary functions of a random phase mask for holographic-data recording and reconstruction. Therefore, this distribution is expected to find applications in high-density holographic memory systems, replacing conventional random phase mask patterns. PMID:23434989

Emoto, Akira; Fukuda, Takashi

2013-02-20

86

Gaseous effluent monitoring and identification using an imaging Fourier transform spectrometer.  

National Technical Information Service (NTIS)

We are developing an imaging Fourier transform spectrometer for chemical effluent monitoring. The system consists of a 2-D infrared imaging array in the focal plane of a Michelson interferometer. Individual images are coordinated with the positioning of a...

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

1993-01-01

87

First Observations with the LLNL Optical Imaging Fourier Transform Spectrometer  

NASA Astrophysics Data System (ADS)

We present the results of the first observing run with an optical imaging Fourier transform spectrometer (FTS). We have designed and fabricated this FTS for low-background astronomical use as a testbed for a proposed imaging FTS for the Next Generation Space Telescope (NGST). The relatively low background in the optical allows us to mimic the long dwell, step-scan operation of the proposed infrared NGST FTS. In this first data set, we have demonstrated the operation of the system as a multi-band camera and as a medium-resolution 3D spectrometer. Our testbed FTS reflects our current design for the NGST FTS (IFIRS). It is a four-port (two input, two output) Michelson interferometer with two 45 degree, self-compensating beamsplitters and cube-corner retro-reflectors. This system was taken to the 1.5-m McMath-Pierce Solar Observatory (MPSO) in March 1999. MPSO provides a good facility for prototyping astronomical instruments with a horizontal focal plane projected onto a (de)rotating table. We collected data from one output port with an off-the-shelf PixelVision CCD camera with a 1024x1024, thinned SITe chip thermoelectrically cooled to 235K. Our final platescale was about 0.5 arcsec/pixel with an unvignetted field of about 4x4 arcmin. We collected imaging spectroscopy with resolutions of a few to 500 of well-known objects including globular clusters, open clusters, spiral galaxies, elliptical galaxies, and nebular regions. We describe our data reduction procedures with emphasis on the unique aspects of imaging FTS data. We present color-magnitude diagrams of star clusters to demonstrate the utility of the imaging FTS as a camera and compare the signal-to-noise performance with theoretical models and filter-based camera performance. Finally, we present datacubes demonstrating the ability of the imaging FTS to yield ``a spectrum for every pixel''.

Wurtz, R.; Abrams, M. C.; Bennett, C. L.; Bixler, J. V.; Carr, D. J.; Carr, J.; Cook, K. H.; Dey, A.; Graham, J. R.; Hertel, R. J.; Macoy, N. H.; Morris, S. L.; Najita, J. R.; Villemaire, A.; Wickham, D. R.; Wishnow, E.

1999-05-01

88

Feasibility Demonstration of Wide-Field Fourier-Spectroscopic-Imaging in Infrared Region  

NASA Astrophysics Data System (ADS)

We are aiming at the realization of living-environment sensor and non-invasive blood-sugar sensor by the proposed imaging type 2-D Fourier spectroscopy. This method is based on the phase-shift interference between the object beams. As a result, even if the object beams are spatially incoherent, we can observe the phase-shift interference phenomena. In the near infrared region, we can obtain the high-contrast blood vessel image of mouse's ear in the deeper part by InGaAs camera. Furthermore, in the mid-infrared region, we have successfully measured the radiation spectroscopic-imaging with wild field of view by the infrared module, such as the house plants.

Qi, Wei; Takuma, Takashi; Tsutsumi, Ryosuke; Inui, Asuka; Kagiyama, Hiroyasu; Kojima, Daisuke; Nishiyama, Akira; Ishimaru, Ichirou

89

Optical double image encryption employing a pseudo image technique in the Fourier domain  

NASA Astrophysics Data System (ADS)

A novel optical encryption method is proposed involving double image encryption in which one image is introduced as the pseudo image while the other is the original object image. The Double Random Phase Encoding technique is used to encrypt both the pseudo and object images into complex images. A unique binary image is then employed to first generate the random phase key for the object image encryption and then to embed the encrypted object image into the encrypted pseudo image, which acts as host image. Both the second random phase mask used for encoding the pseudo image and the binary image act as encryption keys. If an attacker attempts to crack the random phase key and decrypt the original object image, the pseudo image will be obtained instead. Simulation results and robustness tests are performed which demonstrate the feasibility of the algorithm.

Guo, Changliang; Liu, Shi; Sheridan, John T.

2014-06-01

90

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

91

A human identification system based on retinal image processing using partitioned fourier spectrum  

Microsoft Academic Search

Retinal image is one of the robust and accurate biometrics. A new biometric identification system base on Fourier transform and that special partitioning presented in this article. In this method, at first, optical disc is localized using template matching technique and use it for rotate the retinal image to reference position. Fourier transform coefficient and angular partitioning of these coefficients

A. Zahedi; H. Sadjedi

2010-01-01

92

RST invariant digital image watermarking: importance of phase information  

Microsoft Academic Search

Based on Fourier-Mellin transform, this paper presents a novel digital image watermarking scheme that is invariant to rotation, scaling, and translation (RST). We embed watermark in the log-polar mappings of Fourier magnitude spectrum of original image, and use the phase information of the original image to rectify the watermark positions. The scheme avoids computing inverse log-polar mapping (ILPM), therefore preserves

Dong Zheng; Jiying Zhao

2003-01-01

93

Iterative partial phase encoding based on joint fractional Fourier transform correlator adopting phase-shifting digital holography  

NASA Astrophysics Data System (ADS)

In this paper, digital holography based on two-step phase shifting interference (PSI) was applied to realize the iterative partial phase encoding with joint fractional transform correlator (JFTC). By this security system, the primitive image is encoded in two joint fractional power spectra (JFPS) corresponding to different phase-shifting values. The encrypted image can be deduced directly from the JFPSs by digital means, thus eliminating the noise interference of dc and conjugate terms. JFTC not only relaxes the alignment requirement but also avoids the beam splitting required by traditional holography. In the iterative partial phase encoding, the random phase masks (RPMs) are generated by chaotic mapping, and encoding areas are confined by a sequence of random binary masks. To recover the primitive image, decipher must regenerate the partial RPMs with correct chaotic conditions and perform inverse fractional Fourier transforms with correct orders. The decryption process can be realized by JFTC or by totally digital means. Simulation and experimental results have been presented to test security level and feasibility of the scheme.

Wang, Qu; Guo, Qing; Lei, Liang; Zhou, Jinyun

2014-02-01

94

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

95

Fast Fourier transform based image compression algorithm optimized for speckle interferometer measurements  

Microsoft Academic Search

In the framework of European Space Agency (ESA) FluidPac satellite mission, we have developed a fast, lossy image compression algorithm (ICA) based on a slight variation of the classical 2-D fast Fourier transform (FFT). In essence, given a monochrome picture, the ICA calculates (almost) its Fourier spectrum. It then applies a low-pass filter to eliminate all Fourier coefficients beyond a

Jorge L. Vago; Herman C. Vermeulen; Antonio Verga

1997-01-01

96

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

97

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.

98

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.

Ozcan, Alpay

2013-01-01

99

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

100

Membrane lipid phase transitions and phase organization studied by Fourier transform infrared spectroscopy.  

PubMed

Fourier transform infrared (FTIR) spectroscopy is a powerful yet relatively inexpensive and convenient technique for studying the structure and organization of membrane lipids in their various polymorphic phases. This spectroscopic technique yields information about the conformation and dynamics of all regions of the lipid molecule simultaneously without the necessity of introducing extrinsic probes. In this review, we summarize some relatively recent FTIR spectroscopic studies of the structure and organization primarily of fully hydrated phospholipids in their biologically relevant lamellar crystalline, gel and liquid-crystalline phases, and show that interconversions between these bilayer phases can be accurately monitored by this technique. We also briefly discuss how the structure and organization of potentially biologically relevant nonlamellar micellar or reversed hexagonal lipid phases can be studied and how phase transitions between lamellar and nonlamellar phases, or between various nonlamellar phases, can be followed as well. In addition, we discuss the potential for FTIR spectroscopy to yield fairly high resolution structural information about phospholipid packing in lamellar crystalline or gel phases. Finally, we show that many, but not all of these FTIR approaches can also yield valuable information about lipid-protein interactions in membrane protein- or peptide-containing lipid membrane bilayer model or even in biological membranes. This article is part of a Special Issue entitled: FTIR in membrane proteins and peptide studies. PMID:23098834

Lewis, Ruthven N A H; McElhaney, Ronald N

2013-10-01

101

3D quantitative Fourier analysis of second harmonic generation microscopy images of collagen structure in cartilage  

NASA Astrophysics Data System (ADS)

One of the main advantages of nonlinear microscopy is that it provides 3D imaging capability. Second harmonic generation is widely used to image the 3D structure of collagen fibers, and several works have highlighted the modification of the collagen fiber fabric in important diseases. By using an ellipsoidal specific fitting technique on the Fourier transformed image, we show, using both synthetic images and SHG images from cartilage, that the 3D direction of the collagen fibers can be robustly determined.

Romijn, Elisabeth I.; Lilledahl, Magnus B.

2013-02-01

102

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

103

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

104

Application of Fourier-Space Image-Restoration Techniques to Turbulence Compensation and Sparse-Aperture Imaging.  

National Technical Information Service (NTIS)

Image reconstruction is important in any application in which the sensing apparatus or the intervening medium significantly corrupts the recorded data. Deconvolution processes are the oldest and best understood, and for many practical problems Fourier dom...

R. R. Parenti

1994-01-01

105

In vivo blood flow imaging by a swept laser source based Fourier domain optical Doppler tomography  

Microsoft Academic Search

A swept source based Fourier domain optical Doppler tomography (FDODT) system was developed. The technique is based on a phase-resolved method where phase information was retrieved from the reconstructed complex fringe signals. The aliasing effects and artifacts caused by lateral scanning and sample movement were removed with a signal processing technique. The standard deviation of the phase shift of the

Jun Zhang; Zhongping Chen

2005-01-01

106

Theory of laser array phase locking by Fourier coupling  

SciTech Connect

The type of coupling in a fibre laser array phase locked with the help of an external mirror located at the focal distance from the plane of output ends of individual lasers is studied analytically. The explicit expression is derived for the eigenvalue of the resonator and the restriction on the width of the tuning range in which laser array phase locking is preserved is determined. The influence of the spread in the optical lengths of fibres on the phase-locking efficiency is considered. The phase-locking efficiency is analysed for the spread of optical lengths of fibres considerably exceeding the radiation wavelength. (control of laser radiation parameters)

Vysotskii, D V; Napartovich, A P; Troshchieva, V N [State Research Center of Russian Federation 'Troitsk Institute for Innovation and Fusion Research', Troitsk, Moscow Region (Russian Federation)

2007-04-30

107

Effect of motion on two-dimensional Fourier transformation magnetic resonance images. [Dogs, phantoms  

SciTech Connect

The effect of motion on two-dimensional Fourier transformation magnetic resonance (MR) images was investigated using phantoms, animals, and normal volunteers. Respiratory motion was simulated while imaging the phantoms. In addition to image blurring, motion produced ghost images, or image harmonics. Canine images, which were obtained during respiration and after the administration of curare, showed significant improvement after respiratory motion was eliminated. Images of normal volunteers were improved with respiratory and cardiac gating, but data acquisition time was significantly increased. These results indicate that MR image quality could be improved with a system that acquires all necessary data within a single breathhold.

Schultz, C.L.; Alfidi, R.J.; Nelson, A.D.; Kopiwoda, S.Y.; Clampitt, M.E.

1984-07-01

108

Phase Retrieval Between Overlapping Orders in Coherent Fourier Scatterometry Using Scanning  

NASA Astrophysics Data System (ADS)

Non-interferometric phase retrieval from the intensity measurements in Coherent Fourier Scatterometry (CFS) is presented using a scanningfocused spot. Formulae to determine the state of polarization of the scattered light and to retrieve the phase difference between overlappingscattered orders are given. The scattered far field is rigorously computed and the functionality of the method is proved with experimentalresults.

Kumar, N.; El Gawhary, O.; Roy, S.; Pereira, S. E.; Urbach, H. P.

2013-07-01

109

One-shot-phase-shifting Fourier domain optical coherence tomography by reference wavefront tilting  

Microsoft Academic Search

A novel optical scheme for a phase shifting method of Fourier domain optical coherence tomography is presented. With this method we avoid a mechanical scan for phase shifting (mechanical M-scan) by using a reference beam with tilted wavefront. The principle of this system is confirmed with a simple mirror object. This method is applied on a biological sample and used

Yoshiaki Yasuno; Shuichi Makita; Takashi Endo; Gouki Aoki; Hiroshi Sumimura; Masahide Itoh; Toyohiko Yatagai

2004-01-01

110

Image watermarking extraction using Fourier domain Wiener filter  

NASA Astrophysics Data System (ADS)

Digital watermarking is a vital process for protecting the copyright of images. This paper presents a method of embedding a private robust watermark into a digital image. The full complex form the Wiener filter is used to extract the signal from the watermarked image. This is shown to outperform the more conventional approximate notation. The results are shown to be extremely noise insensitive.

Birch, Philip; Pavlidis, Marios; Panwar, Ankit; Nnamadim, Ozoemena; Kypraios, Ioannis; Mitra, Bhargav; Young, Rupert; Chatwin, Chris

2008-03-01

111

Color holographic image by using digital lensless Fourier transform holography with optical fiber  

NASA Astrophysics Data System (ADS)

A new method of lensless Fourier transform holography for color reconstruction image is presented. With this method, the recording distance can be kept invariant in recording process. The resolutions of reconstruction images can be adjusted in the same recording distance. Three lasers with different wavelengths are used in an experimental setup to synthesize a color image in a reconstruction process. An optical fiber is used effectively, and the quality of the reconstruction image is improved after filter operation.

Chen, Li; Ma, Xiao; Wang, Qu

2012-04-01

112

Cross-Range Scaling Algorithm for ISAR Images Using 2-D Fourier Transform and Polar Mapping  

Microsoft Academic Search

This paper proposes a new method that solves the problem of inverse synthetic aperture radar image cross-range scaling by estimating the rotational velocity (RV) using the expansion-rotation-scale relationship between two range-Doppler (RD) images. This method is composed of three steps. The first step is preprocessing to construct 2-D Fourier transform images and initial polar-mapped images. In this step, two RD

Sang-Hong Park; Hyo-Tae Kim; Kyung-Tae Kim

2011-01-01

113

Optical encryption by combining image scrambling techniques in fractional Fourier domains  

NASA Astrophysics Data System (ADS)

In this paper, we propose a novel scheme for optical information hiding (encryption) of two-dimensional images by combining image scrambling techniques in fractional Fourier domains. The image is initially randomly shifted using the jigsaw transform algorithm, and then a pixel scrambling technique based on the Arnold transform (ART) is applied. The scrambled image is then encrypted in a randomly chosen fractional Fourier domain. These processes can then be iteratively repeated. The parameters of the architecture, including the jigsaw permutation indices, Arnold frequencies, and fractional Fourier orders, form a very large key space enhancing the security level of the proposed encryption system. Optical implementations are discussed as numerical implementation algorithms. Numerical simulation results are presented to demonstrate the system's flexibility and robustness.

Liu, Shi; Sheridan, John T.

2013-01-01

114

Iterative Image Reconstruction Using Inverse Fourier Rebinning for Fully 3-D PET  

Microsoft Academic Search

We describe a fast forward and back projector pair based on inverse Fourier rebinning for use in iterative image reconstruction for fully 3-D positron emission tomography (PET). The projector pair is used as part of a factored system matrix that takes into account detector-pair response by using shift-variant sinogram blur kernels, thereby combining the computational advantages of Fourier rebinning with

Sanghee Cho; Quanzheng Li; Sangtae Ahn; Bing Bai; Richard M. Leahy

2007-01-01

115

Quaternion image watermarking using the spatio-chromatic fourier coefficients analysis  

Microsoft Academic Search

In this paper, a new color watermarking algorithm that uses the quaternion fourier transform (QFT) to mark the La?b? components of color images is presented. First, we propose an interpretation of the QFT coe-cients using the Spatio- Chromatic Fourier analysis, so the efiects of any changes to the coe-cients can be predicted. Next, watermark casting is performed by modifying the

Tsz Kin Tsui; Xiao-ping Zhang; Dimitrios Androutsos

2006-01-01

116

Fourier-Mellin registration of line-delineated tabular document images  

Microsoft Academic Search

Image registration (or alignment) is a useful preprocessing tool for assisting in manual data extraction from handwritten forms, as well as for preparing documents for batch OCR of specific page regions. A new technique is presented for fast registration of lined tabular document images in the presence of a global affine transformation, using the Discrete Fourier--Mellin Transform (DFMT). Each component

Luke A. D. Hutchison; William A. Barrett

2006-01-01

117

Modified radon-Fourier transform for reflective tomography laser radar imaging  

NASA Astrophysics Data System (ADS)

This paper presents imaging result of computer simulation using a modified Radon-Fourier transform algorithm to reconstruct images from reflective tomography data. Since the signal returned is reflected off the illuminated outer surface of an opaque target, only information about the exterior of the target can be obtained, and the images reconstructed using reflective tomography techniques is an outline view of the target cross section. The projection p(r,? ) and p(r,? + 180°) contain different information about the target surface, and will lead different Fourier estimates along the same line through the origin based on the standard Fourier-Slice tomography theorem. Here, using the functional similarity between transmission tomography and reflective tomography, we add the collinear reflective projections to become corresponding transmissive projections before Fourier transform. Then the target can be reconstructed from the Fourier domain using the same operations in transmission tomography. The computer simulation result demonstrates the effectiveness of this modified algorithm to reconstruct image in reflective tomography using the diffuse reflection model (lamberts body). Future research will include the development of image reconstruction based on this modified algorithm for targets with much more complicated reflective characters.

Jin, Xiaofeng; Sun, Jianfeng; Yan, Yi; Zhou, Yu; Liu, Liren

2011-06-01

118

Avalanche and bit independence characteristics of double random phase encoding in the Fourier and Fresnel domains.  

PubMed

In this work, we evaluate the avalanche effect and bit independence properties of the double random phase encoding (DRPE) algorithm in the Fourier and Fresnel domains. Experimental results show that DRPE has excellent bit independence characteristics in both the Fourier and Fresnel domains. However, DRPE achieves better avalanche effect results in the Fresnel domain than in the Fourier domain. DRPE gives especially poor avalanche effect results in the Fourier domain when only one bit is changed in the plaintext or in the encryption key. Despite this, DRPE shows satisfactory avalanche effect results in the Fresnel domain when any other number of bits changes in the plaintext or in the encryption key. To the best of our knowledge, this is the first report on the avalanche effect and bit independence behaviors of optical encryption approaches for bit units. PMID:24979643

Moon, Inkyu; Yi, Faliu; Lee, Yeon H; Javidi, Bahram

2014-05-01

119

Optical correlator performance of binary phase-only filters using Fourier and Hartley transforms.  

PubMed

Theoretical studies of the performance capabilities of binary phase-only filters (BPOFs), constructed using both Fourier and Hartley transforms, are presented. A thorough analysis of the Fourier BPOF is given. We show that, although BPOFs constructed using Fourier transforms perform well in optical correlator systems, they are also subject to additional noise sources and have the possibility of generating large false correlation signals. We then present an analysis of BPOFs constructed using the Hartley transform. We show that BPOFs made using the Hartley transform provide superior false correlation rejection and more uniformly sized correlation signals for heavily multiplexed BPOFs, compared with those made using the Fourier transform. We also present a technique for constructing Hartley BPOFs. Therefore, although it is well known that the quality of the correlation signal depends on the object, this work demonstrates that the quality of the correlation signal can also depend on the technique used in the synthesis of the BPOF. PMID:20490138

Cottrell, D M; Lilly, R A; Davis, J A; Day, T

1987-09-15

120

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

121

Local quaternion Fourier transform and color image texture analysis  

Microsoft Academic Search

Color images can be treated as two-dimensional quaternion functions. For analysis of quaternion images, a joint space-wavenumber localized quaternion S transform (QS) is presented in this study for a simultaneous determination of the local color image spectra. The QS transform uses a two-dimensional Gaussian localizing window that scales with wavenumbers. Rotation invariance, invertibility and computational aspects of the QS transform

Dawit Assefa; Lalu Mansinha; Kristy F. Tiampo; Henning Rasmussen; Kenzu Abdella

2010-01-01

122

Two-dimensional 220 MHz Fourier transform EPR imaging  

NASA Astrophysics Data System (ADS)

In the last decade radiofrequency continuous-wave EPR spectrometers have been developed to detect and localize free radicals in vivo. Only recently, pulsed radiofrequency EPR spectrometers have been described for imaging applications with small samples. In the present work, we show the first two-dimensional image obtained at 220 MHz on a large phantom (40 ml) that simulates typical conditions of in vivo EPR imaging. This pulsed EPR apparatus has the potential to make the time required for three-dimensional imaging compatible with the biological half-life of normally used paramagnetic probes.

Placidi, Giuseppe; Brivati, John A.; Alecci, Marcello; Testa, Luca; Sotgiu, Antonello

1998-07-01

123

Fractional Fourier transform dual random phase encoding of time-varying signals  

NASA Astrophysics Data System (ADS)

Optical techniques have shown great potential in the field of information security to encode high-security images. Among several established methods, a double-random phase encryption technique (DRPE) for encoding a primary image into stationary white noise was developed by using the analogy between Fresnel diffraction patterns and the fractional Fourier transform (FrFT-DRPE). In this case, additional keys are obtained through the knowledge of the fractional orders of the FrFTs. In this work we propose an encoding setup for time-varying signals, mainly for short-haul fiber optics link applications, that can be considered as the temporal analogue of the spatial FrFT-DRPE. The behavior of the proposed method is analyzed by employing the Wigner distribution function. As a result, general expressions for both signal time width and spectral bandwidth, at all encryption stages are obtained. Numerical simulations have been carried out to illustrate the system performance. The obtained results indicate that this encryption method could be a good alternative to other well-established methods.

Cuadrado-Laborde, C.; Duchowicz, R.; Torroba, R.; Sicre, E. E.

2008-09-01

124

Pfaff equation and Fourier analysis to phase extraction from an interferogram with carrier frequency  

NASA Astrophysics Data System (ADS)

In the phase extraction techniques, one of the steps most used is to calculate the phase unwrapping from the wrapped phase, which is generally obtained via the inverse tangent function. With the idea to avoid this process, in the present manuscript a method based in the solution of the Pfaff equations is proposed. It is shown that the Pfaff equation is formed with the phase gradient and an auxiliary vector. The phase gradient is obtained from an interference patron with carrier frequency by applying the Fourier transform method and the partial derivatives. In the present manuscript, mathematical analysis, numerical simulation, and the phase extraction of some experimental interferograms are shown.

Lara-Cortez, Francisco; Meneses-Fabian, Cruz; Rodriguez-Zurita, Gustavo

2011-01-01

125

Reorganizational dynamics of multilamellar lipid bilayer assemblies using continuously scanning Fourier transform infrared spectroscopic imaging  

Microsoft Academic Search

We employ an implementation of rapid-scan Fourier transform infrared (FT-IR) microspectroscopic imaging to acquire time-resolved images for assessing the non-repetitive reorganizational dynamics of aqueous dispersions of multilamellar lipid vesicles (MLVs) derived from distearoylphosphatidylcholine (DSPC). The spatially and temporally resolved images allow direct and simultaneous determinations of various physical and chemical properties of the MLVs, including the main thermal gel to

Scott W Huffman; Sebastian Schlücker; Ira W Levin

2004-01-01

126

Data processing pipeline for a time-sampled imaging Fourier transform spectrometer  

Microsoft Academic Search

ABSTRACT Imaging Fourier transform spectrometers ,(IFTS) are becoming ,the preferred systems ,for remote ,sensing spectral imaging applications because of their ability to provide, simultaneously, both high spatial and spectral resolution images ofa scene. IFTS can be operated in either step-and-integrate or rapid-scan modes, where it is common practice to sample interferograms at equal optical path difference intervals. The step-and-integrate mode

David A. Naylor; Trevor R. Fulton; Peter W. Davis; Ian M. Chapman; Brad G. Gom; D Locke; John V. Lindner; Nathan E. Nelson-fitzpatrick; Margaret K. Tahic; Gary R. Davis

127

Feasibility breadboard demonstration of an imaging Fourier transform spectrometer using solid state time delay  

NASA Astrophysics Data System (ADS)

JPL has developed an innovative electro-optic time delay line and utilize it to build a prototype proof-of-principle completely non-mechanical Electro-optic Hyperspectral Imaging Fourier Transform Spectrometer (EOHIFTS). Due to the use of the EO time delay line, the EOHIFTS is lightweight, broad spectral band, hyperspectral resolution that cannot be achieved simultaneously by any of the Imaging Fourier Transform Spectrometers (IFTS) developed to date. We will report the recent progress in the development of a feasibility breadboard and its feasibility demonstration.

Chao, Tien-Hsin; Lu, Thomas T.

2011-04-01

128

RST-invariant digital image watermarking based on log-polar mapping and phase correlation  

Microsoft Academic Search

Based on log-polar mapping and phase correla- tion, this paper presents a novel digital image watermarking scheme that is invariant to rotation, scaling, and translation (RST). We embed watermark in the log-polar mappings of Fourier magnitude spectrum of original image, and use the phase correlation between the LPM of the original image and the LPM of the watermarked image to

Dong Zheng; Jiying Zhao; Abdulmotaleb El-saddik

2003-01-01

129

Target detection of hyperspectral images based on their Fourier spectral features  

NASA Astrophysics Data System (ADS)

Original spectral features contain information pertinent to certain target spectral features. Without an efficient spectral feature extraction method, the target detection performance might be degraded. We present spectral feature extraction techniques based on the Fourier domain for use in target detection. These feature extraction methods are the Fourier magnitude (FM), Fourier phase (FP), and Fourier coefficient selection (FCS) methods. In our target detection experiments, we compared the proposed methods to the principle component analysis (PCA) and independent component analysis (ICA) methods and the original spectral features. The experiment results show that the FCS target detection accuracy is 95.75%, whereas the accuracies of the FM, FP, PCA, ICA methods, and the original spectral features are 86.76%, 36.28%, 84.51%, 74.49%, and 78.92%, respectively. The average feature extraction times of the proposed methods are 223% faster than that found for the PCA and 304% faster than the ICA methods.

Saipullah, Khairul-Muzzammil; Kim, Deok-Hwan

2012-11-01

130

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

131

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.

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

2014-01-01

132

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

133

Image simulator for spatially imaging Fourier Transform spectrometer 'HJ1A-HSI'  

NASA Astrophysics Data System (ADS)

The simulation of remote sensing images is a useful tool for a variety of tasks, such as the definition of future Earth Observation systems, the optimization and evaluation of instrument specifications, especially for a new type sensor, and the development and validation of data processing algorithms. A scene simulator for optical hyperspectral data from 'HJ1A-HSI' is described in this paper. 'HJ1A-HSI' was carried on the Chinese small satellite HJ-1A, which was successfully launched on September 6th, 2008. Different from common hyperspectral sensor, 'HJ1A-HSI' belongs to the spatial imaging Fourier Transform spectrometer (IFTS). In contrast to the high-speed development of spatial IFTS, the corresponding image simulator is still at the starting stage and the simulation data is very ideal in most cases. To simulate more actual data, a simulation system is proposed in this paper, based on the analysis of spatial IFTS principle. This system puts emphasis on simulating the effects of typical artifacts, and consists of four parts: the calculation of input parameter, the radiance computation for one beam before interfered, the simulation of effects of typical artifacts and the interferogram acquisition. The methodology applied to the complete scene simulation and some sample results are presented and analyzed in this paper.

Zhang, Wen-Juan; Zhang, Bing; Gao, Lian-Ru; Zhang, Wei

2010-10-01

134

High-resolution imaging of the human retina with a Fourier deconvolution technique.  

PubMed

A high-resolution retinal imaging camera is described that uses a Shack-Hartmann wave-front sensor and a Fourier deconvolution imaging technique. The operation of the camera is discussed in detail and high-resolution retinal images of the human cone mosaic are shown for a retinal patch approximately 10 arc min in diameter from two different retinal locations. The center-to-center cone spacing is shown to be approximately 2.5 microm for the retinal images recorded at 2 degrees temporal from the central fovea and approximately 4 microm for the retinal images recorded at 3 degrees temporal from the central fovea. PMID:12152691

Catlin, David; Dainty, Christopher

2002-08-01

135

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

136

Bright versus dark schlieren imaging: quantitative analysis of quasi-sinusoidal phase objects  

Microsoft Academic Search

We discuss the schlieren imaging of quasi-sinusoidal phase objects. We demonstrate that, when the zero-order (Fourier) spatial component of the input image is not blocked by the schlieren-knife at the Fourier plane, the intensity distribution on the reconstructed image is a linear function of the phase amplitude. In contrast, if the zero order is completely blocked (i.e., dark Schlieren processing),

Ismael Núñez; José A. Ferrari

2007-01-01

137

Phase-shifting algorithm via wavelength tuning based on temporal Fourier transform  

NASA Astrophysics Data System (ADS)

The phase-shifting algorithm via wavelength tuning based on temporal Fourier transform is according to the Fourier transform technique and the difference technique to realize the processing of the interferogram. This algorithm is applied to test some course profiles or the topography with high steps. The paper describes its main idea and presents the shortcoming of the algorithm proposed by Takeda. Then it puts forward the improved algorithml. The pape describes the realization processing and the errors of the new algorithm. Finally, it supplies the measurement result.

Yu, Yingjie; Zhang, Benhao; Jiao, Yunfang

2003-11-01

138

Determination of doubly labeled water by gas-phase fourier transform infrared spectroscopy  

Microsoft Academic Search

Both 2H (deuterium) and 18O (oxygen 18) in isotopically enriched water have been detected by gas-phase Fourier transform infrared (FTIR) spectroscopy at 2,720 and 3,661.8 cm?1, respectively. A linear relationship between varying concentrations of each of these isotopes and their absorbance at the above frequencies indicates that gas-phase FTIR may provide a rapid and potentially less expensive approach to measure

M. A. Khaled; C. L. Krumdieck; J. L. Ong

1995-01-01

139

High pressure crystal phases of solid CH4 probed by Fourier transform infrared spectroscopy  

Microsoft Academic Search

High pressure infrared spectra of solid CH4 are reported in the range 0.8–30 GPa at room temperature, coupling a Fourier transform infrared spectrometer to a membrane diamond–anvil cell by means of a high efficiency beam condensing optical system. Two crystal phases, A and B, have been investigated. The phase transition is affected by hysteresis and occurs at 9±0.5 GPa during

Roberto Bini; Lorenzo Ulivi; Hans J. Jodl; Pier R. Salvi

1995-01-01

140

Modeling fourier transform infrared spectroscopic imaging of Prostate and Breast Cancer tissue specimens  

Microsoft Academic Search

Fourier transform infrared (FT-IR) spectroscopic imaging is an emerging technique that provides both spatially and chemically resolved information. The rich chemical content of data may be utilized for computer-aided determinations of structure and pathologic state (cancer diagnosis) in histological tissue sections for Prostate and Breast Cancer. Recent results show that tissue type (histological) classification can be performed to an accuracy

Rohith Reddy; Brynmor Davis; Paul Scott Carney; Rohit Bhargava

2011-01-01

141

Practical protocols for fast histopathology by Fourier transform infrared spectroscopic imaging  

Microsoft Academic Search

Fourier transform infrared (FT-IR) spectroscopic imaging is an emerging technique that combines the molecular selectivity of spectroscopy with the spatial specificity of optical microscopy. We demonstrate a new concept in obtaining high fidelity data using commercial array detectors coupled to a microscope and Michelson interferometer. Next, we apply the developed technique to rapidly provide automated histopathologic information for breast cancer.

Frances N. Keith; Rohith K. Reddy; Rohit Bhargava

2008-01-01

142

Iterative tomographic image reconstruction using Fourier-based forward and back-projectors  

Microsoft Academic Search

Iterative image reconstruction algorithms play an increasingly important role in modern tomographic systems, espe- cially in emission tomography. With the fast increase of the sizes of the tomographic data, reduction of the computation demands of the reconstruction algorithms is of great importance. Fourier- based forward and back-projection methods have the potential to considerably reduce the computation time in iterative recon-

Samuel Matej; Jeffrey A. Fessler; Ivan G. Kazantsev

2004-01-01

143

Lossless compression of the geostationary imaging Fourier transform spectrometer (GIFTS) data via predictive partitioned vector quantization  

Microsoft Academic Search

The Geostationary Imaging Fourier Transform Spectrometer (GIFTS), as part of NASA's New Millennium Program, is an advanced instrument to provide high-temporal-resolution measurements of atmospheric temperature and water vapor, which will greatly facilitate the detection of rapid atmospheric changes associated with destructive weather events, including tornadoes, severe thunderstorms, flash floods, and hurricanes. The Committee on Earth Science and Applications from Space

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

2007-01-01

144

Fast Registration of Tabular Document Images Using the Fourier-Mellin Transform  

Microsoft Academic Search

A new technique is presented for quickly identifying global affine transformations applied to tabular document images, and to correct for those transformations. This technique, based on the Fourier-Mellin transform, is used to register (align) a set of tabular documents to each other. Each component of the affine transform is handled separately, which dramatically reduces the total parameter space of the

Luke A. D. Hutchison; William A. Barrett

2004-01-01

145

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

146

Extreme Ultraviolet Phase Contrast Imaging  

SciTech Connect

The conclusions of this report are: (1) zone plate microscopy provides high resolution imaging of EUV masks; (2) using phase plates in the back focal plane of the objective lens can provide contrast mechanisms for measurement of the phase shift from defects on the mask; (3) the first high resolution EUV Zernike phase contrast images have been acquired; and (4) future work will include phase contrast mode in reflection from an EUV mask to directly measure the reflectivity and phase shift from defects.

Denbeaux, Gregory; Garg, Rashi; Aquila, Andy; Barty, Anton; Goldberg, Kenneth; Gullikson, Eric; Liu, Yanwei; Wood, Obert

2005-11-01

147

Fiber Fourier optics.  

PubMed

The Fourier transform of a coherent optical image can be evaluated physically by use of a single lens plus free-space propagation, thereby providing the basis for the field of Fourier optics. I point out that one can similarly evaluate the discrete Fourier transform of a sampled or pixelated optical array physically by passing the discrete array amplitudes through a network of single-mode fibers or optical waveguides. A passive optical network that evaluates the fast Fourier transform of a coherent array can be fabricated by use of (N/2)log(2)[N] optical 3-dB couplers plus small added phase shifts. Implementing such networks in fiber or integrated optical form could provide the basis for a possible technology of fiber Fourier optics. PMID:18049563

Siegman, A E

2001-08-15

148

Gaseous effluent monitoring and identification using an imaging Fourier transform spectrometer  

SciTech Connect

We are developing an imaging Fourier transform spectrometer for chemical effluent monitoring. The system consists of a 2-D infrared imaging array in the focal plane of a Michelson interferometer. Individual images are coordinated with the positioning of a moving mirror in the Michelson interferometer. A three dimensional data cube with two spatial dimensions and one interferogram dimension is then Fourier transformed to produce a hyperspectral data cube with one spectral dimension and two spatial dimensions. The spectral range of the instrument is determined by the choice of optical components and the spectral range of the focal plane array. Measurements in the near UV, visible, near IR, and mid-IR ranges are possible with the existing instrument. Gaseous effluent monitoring and identification measurements will be primarily in the ``fingerprint`` region of the spectrum, ({lambda} = 8 to 12 {mu}m). Initial measurements of effluent using this imaging interferometer in the mid-IR will be presented.

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

1993-10-01

149

Two-dimensional Kerr-Fourier imaging of translucent phantoms in thick turbid media  

NASA Astrophysics Data System (ADS)

Translucent scattering phantoms hidden inside a 5.5-cm-thick Intralipid solution were imaged as a function of phantom scattering coefficients by the use of a picosecond time-and space-gated Kerr-Fourier imaging system. A 2-mm-thick translucent phantom with a 0.1% concentration (scattering coefficient) difference from the 55-mm-thick surrounding scattering host can be distinguished at a signal level of approximately 10-10 of the incidence illumination intensity.

Liang, X.; Wang, L.; Ho, P. P.; Alfano, R. R.

1995-06-01

150

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

151

Efficient segmentation technique for noisy frontal view iris images using Fourier spectral density  

Microsoft Academic Search

In a less constrained capture of iris images to build a high-speed iris recognition system, the design of a robust and fast\\u000a iris segmentation method is important. In this paper, a new iris segmentation technique based on the Fourier spectral density\\u000a is proposed for noisy frontal view eye images captured with minimum cooperation from the subjects. The proposed segmentation\\u000a method

Niladri B. Puhan; Natarajan Sudha; Anirudh Sivaraman Kaushalram

2011-01-01

152

Hybrid acousto-optic Fourier processor for imaging spatially inhomogeneous acoustic fields  

NASA Astrophysics Data System (ADS)

A new method is proposed for imaging spatially inhomogeneous acoustic fields. The approach is based on the Fourier transform of a coherent light field formed as a result of the Bragg diffraction of a probing laser beam on an ensemble of quasi-plane acoustic waves in a lithium niobate crystal. These waves appear as a result of the transformation of an imaged acoustic field by a spherical acoustic lens. The proposed method has been experimentally verified using model multielement acoustic sources.

Kolotyrin, A. A.; Zimnyakov, D. A.; Nikishin, E. L.; Zdrazhevskii, R. A.; Zavarin, S. V.

2011-11-01

153

High-resolution Fourier-transform infrared chemical imaging with multiple synchrotron beams  

PubMed Central

Conventional Fourier-transform infrared (FTIR) microspectroscopic systems are limited by an inevitable trade-off between spatial resolution, acquisition time, signal-to-noise ratio (SNR) and sample coverage. We present an FTIR imaging approach that substantially extends current capabilities by combining multiple synchrotron beams with wide-field detection. This advance allows truly diffraction-limited high-resolution imaging over the entire mid-infrared spectrum with high chemical sensitivity and fast acquisition speed while maintaining high-quality SNR.

Nasse, Michael J; Walsh, Michael J; Mattson, Eric C; Reininger, Ruben; Kajdacsy-Balla, Andre; Macias, Virgilia; Bhargava, Rohit; Hirschmugl, Carol J

2013-01-01

154

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

155

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

156

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

157

High resolution imaging using phase retrieval, volume 2  

NASA Astrophysics Data System (ADS)

This report describes a technique for obtaining fine-resolution images, suitable for SDI midcourse discrimination, using an inexpensive, lightweight telescope that would ordinarily yield a poor image. If, instead of collecting a blurred image with the telescope, one sends the light through an amplitude interferometer, then the modulus, but not the phase, of the Fourier transform of the object can be measured, despite the aberrations. We have developed and analyzed phase retrieval algorithms that recover the unknown Fourier phase, which allows a fine-resolution image to be reconstructed despite the aberrations of the telescope. It will also correct aberrations due to atmospheric turbulence for a ground-based telescope, and can be used with several other imaging modalities. For the case of interferometry through a partially obscured aperture, an algorithm was developed that combines phase retrieval with interpolation in order to restore the information at the missing spatial frequencies while retrieving the phase at the unobscured spatial frequencies. Another new phase retrieval algorithm, based on the Ayers/Dainty blind deconvolution algorithm, was also developed. A new methodology for exploring the uniqueness of phase retrieval in a practical sense was developed and tested. It involves finding the ambiguous image which is closest to a given image by a reduced-gradient search technique. The computational requirements for the phase retrieval algorithm were quantified. Laboratory experiments to test the technique were initiated.

Fienup, J. R.; Gorman, J. D.; Seldin, J. H.; Cederquist, J. N.

1991-10-01

158

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

159

Crystallographic phase retrieval through image processing under constraints  

NASA Astrophysics Data System (ADS)

The crystallographic image processing techniques of Sayre's equation, molecular averaging, solvent flattening and histogram matching are combined in an integrated procedure for macromolecular phase retrieval. It employs the constraints of the local shape of electron density, equal molecules, solvent flatness and correct electron density distribution. These constraints on electron density image are satisfied simultaneously by solving a system of non- linear equations using fast Fourier transform. The electron density image is further filtered under the constraint of observed diffraction amplitudes. The effect of each constraint on phase retrieval is examined. The constraints are found to work synergistically in phase retrieval. Test results on 2Zn insulin are presented.

Zhang, Kam Y.

1993-11-01

160

[The meteorological satellite spectral image registration based on Fourier-Mellin transform].  

PubMed

The meteorological satellite spectral image is an effective tool for researches on meteorological science and environmental remote sensing science. Image registration is the basis for the application of the meteorological satellite spectral image data. In order to realize the registration of the satellite image and the template image, a new registration method based on the Fourier-Mellin transform is presented in this paper. Firstly, we use the global coastline vector map data to build a landmark template, which is a reference for the meteorological satellite spectral image registration. Secondly, we choose infrared sub-image of no cloud according to the cloud channel data, and extract the edges of the infrared image by Sobel operator. Finally, the affine transform model parameters between the landmark template and the satellite image are determined by the Fourier-Mellin transform, and thus the registration is realized. The proposed method is based on the curve matching in essence. It needs no feature point extraction, and can greatly simplify the process of registration. The experimental results using the infrared spectral data of the FY-2D meteorological satellite show that the method is robust and can reach a high speed and high accuracy. PMID:23705469

Wang, Liang; Liu, Rong; Zhang, Li; Duan, Fu-Qing; Lü, Ke

2013-03-01

161

Phase transfer function of digital imaging systems  

NASA Astrophysics Data System (ADS)

For the past several decades, optical engineering has relied heavily on Fourier analysis of linear systems as a valuable aid in realizing numerous imaging applications. Today, spatial frequency analysis via the optical transfer function (OTF) remains an integral tool for the design, characterization and testing of incoherent imaging systems. The magnitude of the complex OTF is known as the modulation transfer function (MTF) and its phase is given by the phase transfer function (PTF). The MTF represents the contrast reduction at each spatial frequency; whereas, the PTF represents the spatial shift of these frequencies. While the MTF has been used extensively to characterize imaging systems, the PTF has long been ignored because it was thought to have an insignificant presence and to be difficult to understand and measure. Through theoretical analysis and experimental demonstrations, this work addresses all of these issues and shows that the PTF is a valuable tool for modern-day digital imaging systems. The effects of optical aberrations on the PTF of an imaging system in the absence of aliasing have been analyzed in detail. However, for the digital imaging systems, the effect of aliasing on the overall system behavior becomes an important consideration. To this end, the effects of aliasing on the PTF of the sampled imaging system are described and its key properties are derived. The role of PTF as an essential metric in today's imaging systems necessitates practical PTF measurement techniques. Two, easy-to-implement, image-based methods for PTF measurement are described and experimentally validated. These measurement methods and the insights gained from the theoretical analysis are leveraged for several applications spanning diverse fields such as optical system characterization, computational imaging, and image processing.

Bhakta, Vikrant R.

162

Discrete Fourier preprocessing transforms for the binary phase-only filter  

NASA Astrophysics Data System (ADS)

Two useful discrete Fourier preprocessing transforms (DFPTs), say, class 1 and class 2, are applied to the binary phase-only filter. The class-1 DFPT is very close to the discrete Fourier transform (DFT); therefore it preserves the properties similar to those for the DFT. The Class-2 DFPT's are location sensitive and are able to recognize the partial-shape-like input pattern that is the partial set of the pattern in the filter. The Class-2 DFPT's generate a delta-function-like correlation peak whose intensity is larger than that obtained by the DFT. These are different from the DFT-based binary phase-only filter. The elements of the DFPT's are very simple, containing only +/-1 and 0; some even contain sparse +/-1 values and plenty of zeros. Therefore the DFPT's are suitable for either optical or electrical implementation.

Hu, Neng-Chung; Su, Chia-Hsien

1995-03-01

163

Autofocus using image phase congruency.  

PubMed

The key issue in passive autofocus is to choose robust focus measures to judge optical blur in defocused images. Existing focus measures are sensitive to image contrast (illumination) as they use image intensity. In this report we demonstrate a focus measure using phase congruency. The proposed focus measure is robust for noisy imaging sensors in varying illumination conditions, and has great balance of defocus sensitivity and effective range. Its advantages are shown with a number of synthetic image sequences. PMID:21263565

Tian, Yibin

2011-01-01

164

Remote Fourier transform-infrared spectral imaging system with hollow-optical fiber bundle.  

PubMed

A spectral imaging system consisting of a Fourier transform-infrared spectrometer, a high-speed infrared camera, and a bundle of hollow-optical fibers transmitting infrared radiation images was constructed. Infrared transmission spectra were obtained by carefully processing multiple interferograms taken by high-speed photography. Infrared spectral images of a variety of samples captured by the system were measured. We successfully detected existence maps of the oil and fat of biological samples by mapping the transmission of specific wavelengths in the spectrum. PMID:23052066

Huang, Chenhui; Kino, Saiko; Katagiri, Takashi; Matsuura, Yuji

2012-10-10

165

Saturated laser Fourier-amplifier as a source for half-tone images in laser projection  

NASA Astrophysics Data System (ADS)

A contradiction between high efficiency of an amplifier operating in a saturated mode, and nonlinear distortions in image reproduction characteristic for this regime is solved. A lasing medium is located in a Fourier-plane of the image, its gain profile being specially shaped, while the amplified image is illuminated by a laser beam which angular divergence is appropriately formed. Criteria for the gain shape and beam divergence are formulated. A possibility for correct amplification of binary and/or half-tone images with high efficiency of energy stored in the laser medium (up to 70%) is shown. The results are applicable for laser image projectors of systems of virtual reality, simulators, etc., providing images with high dynamic range (e.g., pictures of illuminated landing stripes, approaching car lights, etc.).

Kornev, Aleksey F.; Kuchma, Igor G.; Pokrovski, Vassiliy P.; Soms, Leonid N.

2008-03-01

166

Pulsation Detection from Noisy Ultrasound-Echo Moving Images of Newborn Baby Head Using Fourier Transform  

NASA Astrophysics Data System (ADS)

In order to detect pulsation from a series of noisy ultrasound-echo moving images of a newborn baby's head for pediatric diagnosis, a digital image processing system capable of recording at the video rate and processing the recorded series of images was constructed. The time-sequence variations of each pixel value in a series of moving images were analyzed and then an algorithm based on Fourier transform was developed for the pulsation detection, noting that the pulsation associated with blood flow was periodically changed by heartbeat. Pulsation detection for pediatric diagnosis was successfully made from a series of noisy ultrasound-echo moving images of newborn baby's head by using the image processing system and the pulsation detection algorithm developed here.

Yamada, Masayoshi; Fukuzawa, Masayuki; Kitsunezuka, Yoshiki; Kishida, Jun; Nakamori, Nobuyuki; Kanamori, Hitoshi; Sakurai, Takashi; Kodama, Souichi

1995-05-01

167

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.

Sertel, Elif

2009-01-01

168

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

169

Data reconstructing for windowing broom Fourier transform imaging spectrometers based on multi-core techniques  

NASA Astrophysics Data System (ADS)

The windowing broom Fourier transform imaging spectrometer, based on space-time modulation, has the characteristics of high luminous flux, static interference part etc. However, the large amount of raw data and the data reconstruction increase the difficulty of the whole data processing and extend the computing time. In this paper, a parallel calculation algorithm for reconstruction of raw data is proposed. The proposed algorithm is achieved by using Task Parallel Library (TPL), which is provided by .NET framework, and a visualized processing system is further established. A set of data collected from a windowing broom Fourier transform imaging spectrometer is processed using both the proposed method and the ordinary serial algorithm. The scalability of this presented algorithm is verified by employing it on computers with different number of cores. The experimental results show that, compared to the serial algorithm, the proposed method can greatly speed up the processing with the same hardware condition, and it also has ideal scalability with different hardware.

Dong, Zhi-gang; Liao, Ning-fang; Qu, Liang; Lv, Hang

2013-08-01

170

Theory and Application of Gain Ranging to Fourier Transform Infrared Spectroscopic Imaging  

Microsoft Academic Search

Gain ranging is incorporated into the data acquisition and process- ing protocol for a Fourier transform infrared (FT-IR) imaging spec- trometer employing a focal plane array (FPA) detector. A model for predicting the signal, noise, and signal-to-noise ratio (SNR) for an FPA in terms of the dynamic range of the analog-to-digital con- verter (ADC) is presented. Conventional gain ranging theory,

Rohit Bhargava; Daniel C. Fernandez; Michael D. Schaeberle; Ira W. Levin

2001-01-01

171

Effect of the fringe visibility on spectrum SNR of Fourier transform imaging spectrometer  

NASA Astrophysics Data System (ADS)

The principle of Fourier transform spectrometer is based on the relationship of Fourier-Transform between interferogram and spectrum. The spectral information of Fourier transform imaging spectrometer (FTIS) reconstructed from raw interferogram by data processing. So there are two kinds of signal-to-noise ratio (SNR) to evaluate instrument performance, one regarding interferogram and the other regarding reconstructed spectrum. Because the raw interferogram is intuitive, the interferogram SNR is studied usually. On the contrary, the spectrum SNR is studied less because of the complexity of the data processing from interferogram to spectrum. The research about the effect of the interference fringe visibility on the spectrum SNR is especially few. This paper present a research work on the relations between the interference fringe visibility and the spectrum SNR. Firstly, the reduction of fringe visibility caused by imaging lens defocus was analyzed. Secondly, the changes of the average spectrum signal and noise caused by the reduction of fringe visibility were calculated. For average spectrum signal, the math deductions are done base on Fourier transform theory. The average noise with different input signal optic-electrons number are simulated. the results show that the average spectrum signal is directly proportional to the fringe visibility, and the effect of fringe visibility on the noise related to signal can be ignorable. Finally, In order to demonstrate above results, the imaging experiment was done with white-light source, using LASIS (Large aperture static imaging spectrometer) based on Sagnac Interferometer. The average spectrum SNRs under different fringe visibility are calculated and analyzed. The experimental results show that: the average spectrum SNRs increase from 42.7 to 62.4.along with the fringe visibility increasing from 0.5051 to 0.687. the reconstructed spectrum SNR is directly proportional to the fringe visibility. As a result, the interferogram fringe visibility can be used to estimate the reconstructed spectrum SNR, and evaluate the performance of FTIS before data processing.

Wang, Shuang; Bin, Xiangli; Jing, Juanjuan; Pi, Haifeng

2013-08-01

172

Correlating Fourier phase information with real-space higher order statistics in CMB data  

NASA Astrophysics Data System (ADS)

We present a heuristic study on the correlations between harmonic space phase information and higher-order statistics. Using the spherical full-sky maps of the cosmic microwave background as an example, we demonstrate that known phase correlations at large spatial scales can gradually be diminished when subtracting a suitable best-fit (Bianchi-)template map of a given strength. The weaker phase correlations are attended by a vanishing signature of anisotropy when measuring the Minkowski functionals and scaling indices in real space with the aid of surrogate maps being free of phase correlations. Those investigations can open a new road to a better understanding of signatures of non-Gaussianities in complex spatial structures, especially by elucidating the meaning of Fourier phase correlations and their influence on higher-order statistics.

Modest, H. I.; Räth, C.; Banday, A. J.; Górski, K. M.; Morfill, G. E.

2014-06-01

173

Color image encryption based on fractional Fourier transforms and pixel scrambling technique  

NASA Astrophysics Data System (ADS)

Color image encryption based on fractional Fourier transform (FRT) and pixel scrambling technique is presented in this paper. In general, color (RGB) image cannot be directly encrypted using a traditional setup for optical information processing, because which is only adapted to process two-dimensional gray image. In the proposed method, a three-dimensional RGB image is decomposed to three two-dimensional gray images (R, G and B values of the color image), and the encryption operation will be done on each two-dimensional gray image, then the encoded color image is available by composing the three two-dimensional encrypted images. The decryption process is an inverse of the encryption. The optical encrypting systems based on the presented method is proposed and simulated. Some results of computer simulation are presented to verify the flexibility and the reliability of this method. The quality of decrypted images would be debased with the difference of the fractional order. The frustrated decryption of monochromic image will affect the color of decrypted image. At the end of this paper, an all-optical and photoelectric encryption/decryption systems solution are presented, and the principle of selecting optical devices are also given.

Zhao, Jianlin; Lu, Hongqiang; Fan, Qi

2007-01-01

174

Minimum image resolution for shape recognition using the generic Jacobi Fourier moments  

NASA Astrophysics Data System (ADS)

We consider the use of Jacobi-Fourier moments for the classification of objects from motion blurred images. A set of numerical features are extracted from an image. These features are invariant to the changes in the scale, orientation, position, and illumination of the objects in the vision field. The test images used here have been acquired when the objects are vibrating at different frequencies and moving at constant velocity. The blur extent by image motion can be obtained using moment descriptors of the motion. Also, the acquisition system is characterized by means the optical transfer function (OTF); which can be computed by the geometric moments of motion function of the object centroid. The classification method is tested using images from objects which have intrinsically little differences between them. Experimental results show that, the proposed classification method based in Jacobi Fourier moments can be well addressed to grade images smeared by motion. A comparison of effectiveness is done with motion descriptors based on geometric moments.

Toxqui-Quitl, C.; Padilla-Vivanco, A.; Santiago Tepantlán, C.

2011-08-01

175

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

176

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

177

High-resolution retinal imaging using adaptive optics and Fourier-domain optical coherence tomography  

DOEpatents

This invention permits retinal images to be acquired at high speed and with unprecedented resolution in three dimensions (4.times.4.times.6 .mu.m). The instrument achieves high lateral resolution by using adaptive optics to correct optical aberrations of the human eye in real time. High axial resolution and high speed are made possible by the use of Fourier-domain optical coherence tomography. Using this system, we have demonstrated the ability to image microscopic blood vessels and the cone photoreceptor mosaic.

Olivier, Scot S. (Livermore, CA); Werner, John S. (Davis, CA); Zawadzki, Robert J. (Sacramento, CA); Laut, Sophie P. (Pasedena, CA); Jones, Steven M. (Livermore, CA)

2010-09-07

178

High spectral resolution Fourier transform imaging spectroscopy in a Michelson interferometer with homodyne laser metrology control  

NASA Astrophysics Data System (ADS)

High spectral resolution Fourier transform imaging spectroscopy has been demonstrated at the Lockheed Martin Advanced Technology Center. A testbed was built using a Michelson interferometer with a two-stage end-mirror control system. Homodyne laser metrology was used to sense relative tip, tilt and piston in the interferometer, and a 3-degree of freedom fast steering mirror in conjunction with a linear actuator stage provided sub-nanometer actuation control over 20 millimeters of piston range. The range of piston over which signal was present allowed for spectral resolution at the nanometer level in the visible / near infrared (VNIR) band for every pixel in the reconstructed image.

Ni, Mel; Feller, Greg; Irwin, J. Wes; Mason, James; Mudge, Jason

2009-08-01

179

Integration and testing of FTS-2: an imaging Fourier transform spectrometer for SCUBA-2  

NASA Astrophysics Data System (ADS)

FTS-2 is an imaging Fourier transform spectrometer (IFTS) being developed for use with SCUBA-2, the second generation, wide-field, submillimetre camera which will operate at the James Clerk Maxwell Telescope (JCMT). The FTS-2 interferometer uses a folded Mach-Zehnder configuration and will provide simultaneous broadband spectral imaging across both the 850 and 450 ?m bands with variable resolution ranging from resolving powers of R ~10 to 5000. Details of the instrument design, optical modeling, data reduction pipeline and calibration plan which have changed since the project CDR are discussed, along with preliminary results of lab integration and testing.

Gom, Brad; Naylor, David; Zhang, Baoshe

2008-08-01

180

Fourier Imaging Correlation Spectroscopy for Studies of Sub-Cellular Dynamics and Biomolecular Conformation Transition Pathways  

NASA Astrophysics Data System (ADS)

Novel high signal-to-noise spectroscopic experiments that probe the dynamics of fluorescently labeled macromolecules have the potential to reveal complex intracellular biochemical mechanisms, or the slow relaxations of soft matter systems. Fourier imaging correlation spectroscopy (FICS) is a phase-selective approach to fluorescence fluctuation spectroscopy that employs a unique route to elevate signal levels while acquiring detailed information about microscopic coordinate trajectories. In this talk, I will illustrate the broad applicability of this approach by discussing two recent studies. The anomalous sub-diffusive dynamics of mitochondria in budding yeast are characterized using FICS, and provide detailed, length-scale dependent information about the influence of specific cytoskeletal elements on the movements of this organelle. We find that non-equilibrium forces associated with actin polymerization lead to a 1.5-fold enhancement of the long-time mitochondrial diffusion coefficient, and a transient sub-diffusive temporal scaling of the mean-square displacement. These non-equilibrium dynamics are a predominant factor in driving mitochondrial transport. In another set of experiments, polarization-modulated FICS simultaneously captures information about the internal conformation fluctuations and molecular translational dynamics of the fluorescent protein DsRed. By implementing a four-point correlation analysis, we construct two-dimensional spectral densities and joint distribution functions that determine temporal correlations of center-of-mass and anisotropy coordinates over successive time intervals. These four-point functions reveal statistically meaningful transition pathways between different optical conformations of the DsRed protein. The FICS method is well suited to investigate the dynamics of a broad range of heterogeneous systems, which include the molecular motions of glass forming liquids.

Marcus, Andrew

2010-03-01

181

In vivo imaging of the rodent eye with swept source/Fourier domain OCT  

PubMed Central

Swept source/Fourier domain OCT is demonstrated for in vivo imaging of the rodent eye. Using commercial swept laser technology, we developed a prototype OCT imaging system for small animal ocular imaging operating in the 1050 nm wavelength range at an axial scan rate of 100 kHz with ~6 µm axial resolution. The high imaging speed enables volumetric imaging with high axial scan densities, measuring high flow velocities in vessels, and repeated volumetric imaging over time. The 1050 nm wavelength light provides increased penetration into tissue compared to standard commercial OCT systems at 850 nm. The long imaging range enables multiple operating modes for imaging the retina, posterior eye, as well as anterior eye and full eye length. A registration algorithm using orthogonally scanned OCT volumetric data sets which can correct motion on a per A-scan basis is applied to compensate motion and merge motion corrected volumetric data for enhanced OCT image quality. Ultrahigh speed swept source OCT is a promising technique for imaging the rodent eye, proving comprehensive information on the cornea, anterior segment, lens, vitreous, posterior segment, retina and choroid.

Liu, Jonathan J.; Grulkowski, Ireneusz; Kraus, Martin F.; Potsaid, Benjamin; Lu, Chen D.; Baumann, Bernhard; Duker, Jay S.; Hornegger, Joachim; Fujimoto, James G.

2013-01-01

182

In vivo imaging of the rodent eye with swept source/Fourier domain OCT.  

PubMed

Swept source/Fourier domain OCT is demonstrated for in vivo imaging of the rodent eye. Using commercial swept laser technology, we developed a prototype OCT imaging system for small animal ocular imaging operating in the 1050 nm wavelength range at an axial scan rate of 100 kHz with ~6 µm axial resolution. The high imaging speed enables volumetric imaging with high axial scan densities, measuring high flow velocities in vessels, and repeated volumetric imaging over time. The 1050 nm wavelength light provides increased penetration into tissue compared to standard commercial OCT systems at 850 nm. The long imaging range enables multiple operating modes for imaging the retina, posterior eye, as well as anterior eye and full eye length. A registration algorithm using orthogonally scanned OCT volumetric data sets which can correct motion on a per A-scan basis is applied to compensate motion and merge motion corrected volumetric data for enhanced OCT image quality. Ultrahigh speed swept source OCT is a promising technique for imaging the rodent eye, proving comprehensive information on the cornea, anterior segment, lens, vitreous, posterior segment, retina and choroid. PMID:23412778

Liu, Jonathan J; Grulkowski, Ireneusz; Kraus, Martin F; Potsaid, Benjamin; Lu, Chen D; Baumann, Bernhard; Duker, Jay S; Hornegger, Joachim; Fujimoto, James G

2013-02-01

183

Fourier transform infrared imaging analysis in discrimination studies of St. John's wort (Hypericum perforatum).  

PubMed

In the present study, Fourier transform infrared (FTIR) imaging and data analysis methods were combined to study morphological and molecular patterns of St. John's wort (Hypericum perforatum) in detail. For interpretation, FTIR imaging results were correlated with histological information gained from light microscopy (LM). Additionally, we tested several evaluation processes and optimized the methodology for use of complex FTIR microscopic images to monitor molecular patterns. It is demonstrated that the combination of the used spectroscopic method with LM enables a more distinct picture, concerning morphology and distribution of active ingredients, to be gained. We were able to obtain high-quality FTIR microscopic imaging results and to distinguish different tissue types with their chemical ingredients. PMID:23053167

Huck-Pezzei, V A; Pallua, J D; Pezzei, C; Bittner, L K; Schönbichler, S A; Abel, G; Popp, M; Bonn, G K; Huck, C W

2012-10-01

184

Automated segmentation of intramacular layers in Fourier domain optical coherence tomography structural images from normal subjects  

PubMed Central

Abstract. Segmentation of optical coherence tomography (OCT) cross-sectional structural images is important for assisting ophthalmologists in clinical decision making in terms of both diagnosis and treatment. We present an automatic approach for segmenting intramacular layers in Fourier domain optical coherence tomography (FD-OCT) images using a searching strategy based on locally weighted gradient extrema, coupled with an error-removing technique based on statistical error estimation. A two-step denoising preprocess in different directions is also employed to suppress random speckle noise while preserving the layer boundary as intact as possible. The algorithms are tested on the FD-OCT volume images obtained from four normal subjects, which successfully identify the boundaries of seven physiological layers, consistent with the results based on manual determination of macular OCT images.

Zhang, Xusheng; Yousefi, Siavash; An, Lin; Wang, Ruikang K.

2012-01-01

185

Subwavelength Fourier-transform imaging without a lens or a beamsplitter  

NASA Astrophysics Data System (ADS)

The fourier-transform patterns of an object are usually observed in the far-field region or obtained in the near-field region with the help of lenses. Here we propose and experimentally demonstrate a scheme of Fourier-transform patterns in the Fresnel diffraction region with thermal light. In this scheme, neither a lens nor a beamsplitter is used, and only one single charge coupled device (CCD) is employed. It means that dividing one beam out of a light source into signal and reference beams is not as necessary as the one done by the use of a beamsplitter in usual ghost interference experiments. Moreover, the coincidence measurement of two point detectors is not necessary and data recorded on a single CCD are sufficient for reconstructing the ghost diffraction patterns. The feature of the scheme promises a great potential application in the fields of X-ray and neutron diffraction imaging processes.

Liu, Rui-Feng; Yuan, Xin-Xing; Fang, Yi-Zhen; Zhang, Pei; Zhou, Yu; Gao, Hong; Li, Fu-Li

2014-05-01

186

Solving differential equations for phase retrieval in Fourier-transform methods  

NASA Astrophysics Data System (ADS)

In this paper, a method for phase retrieval by using Fourier analysis and techniques to solve differential equations is presented. From the technique proposed by Takeda et al., the function c(x,y) = (1/2).b(x,y).exp[iø(x,y)] is first calculated from a certain interference pattern given by a(x,y)+b(x,y).cosø(x,y). By deriving c(x,y) and c*(x,y) with respect to x and y, it is then possible to find the corresponding phase gradient ?ø(x,y), from which a Pfaff equation can be obtained. In this paper, we show that the solution of the Pfaff equation is the desired phase function plus a constant phase offset accordingly to the theory of differential equations. From this point of view, the phase function consists of a family of potential functions, which are orthogonal to a vectorial field which is the phase gradient. With this technique, the phase function ø(x,y) can be calculated from an interference pattern without the need of any phase unwrapping stage. A theoretical analysis and both numerical and experimental results are shown.

Meneses-Fabian, Cruz; Rodriguez-Zurita, Gustavo; Cordero-Davila, Alberto; Robledo-Sanchez, Carlos

2010-04-01

187

High-resolution diffusion imaging using phase-corrected segmented echo-planar imaging.  

PubMed

Diffusion magnetic resonance imaging (MRI) was performed with a high-resolution segmented echo-planar imaging technique, which provided images with substantially less susceptibility artifacts than images obtained with single-shot echo-planar imaging (EPI). Diffusion imaging performed with any multishot pulse sequence is inherently sensitive to motion artifacts and in order to reduce motion artifacts, the presented method utilizes navigator echo phase corrections, performed after a one-dimensional Fourier transform along the frequency-encoding direction. Navigator echo phases were fitted to a straight line prior to phase correction to avoid errors from internal motion. In vivo imaging was performed using electro cardiographic (ECG) triggering. Apparent diffusion coefficient (ADC) maps were calculated on a pixel-by-pixel basis using up to seven diffusion sensitivities, ranging from b = 0 to 1129 x 10(6) s/m(2). PMID:10930774

Brockstedt, S; Moore, J R; Thomsen, C; Holtås, S; Ståhlberg, F

2000-07-01

188

A no-key-exchange secure image sharing scheme based on Shamir's three-pass cryptography protocol and the multiple-parameter fractional Fourier transform.  

PubMed

In this paper, we propose a novel secure image sharing scheme based on Shamir's three-pass protocol and the multiple-parameter fractional Fourier transform (MPFRFT), which can safely exchange information with no advance distribution of either secret keys or public keys between users. The image is encrypted directly by the MPFRFT spectrum without the use of phase keys, and information can be shared by transmitting the encrypted image (or message) three times between users. Numerical simulation results are given to verify the performance of the proposed algorithm. PMID:22330477

Lang, Jun

2012-01-30

189

Chemical Vapor Identification Using Field-Based Attenuated Total Reflectance Fourier Transform Infrared Detection and Solid Phase Microextraction.  

National Technical Information Service (NTIS)

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) technology is used to identify chemicals in a liquid or solid phase but not in a vapor phase. This research identified vapor phase chemicals using a field- portable ATR-FTIR spectrometer c...

C. K. Bryant

2004-01-01

190

Processing of medical images using real-time optical Fourier processing.  

PubMed

Optical image processing techniques are inherently fast in view of parallel processing. A self-adaptive optical Fourier processing system using photoinduced dichroism in a bacteriorhodopsin film was experimentally demonstrated for medical image processing. Application of this powerful analog all-optical interactive technique for cancer diagnostics is illustrated with two mammograms and a Pap smear. Microcalcification clusters buried in surrounding tissue showed up clearly in the processed image. By playing with one knob, which rotates the analyzer in the optical system, either the microcalcification clusters or the surrounding dense tissue can be selectively displayed. Bacteriorhodopsin films are stable up to 140 degrees C and environmentally friendly. As no interference is involved in the experiments, vibration isolation and even a coherent light source are not required. It may be possible to develop a low-cost rugged battery operated portable signal-enhancing magnifier. PMID:11213918

Panchangam, A; Sastry, K V; Rao, D V; DeCristofano, B S; Kimball, B R; Nakashima, M

2001-01-01

191

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

192

Analysis of nanostructure of red blood cells membranes by space Fourier transform of AFM images.  

PubMed

Atomic force microscopy (AFM) allows a researcher to obtain images of red blood cells (RBC) and their membranes. Various effects on blood lead to surface alterations of cell membranes. Such alterations are estimated by a corrugation of membrane surface. This problem is complicated for statistical analysis because the membrane is the ensemble of structures with different sizes. In the present work we used the space Fourier transform to decompose the complex AFM image of the surface into three simpler ones. The parameters of spectral windows were selected according to the natural structures of RBC membranes. This method allowed us to obtain high resolution images for the corresponding spectral windows, to establish specificity of alterations from each effect, to estimate quantitatively the membrane nanostructures at different space scales and to compare their sizes statistically after actions of different agents. The blood intoxication was modeled by adding hemin, furosemide, chlorpromazine and zinc ions into blood, in vitro. PMID:22854216

Kozlova, Elena K; Chernysh, Alexander M; Moroz, Victor V; Kuzovlev, Artem N

2013-01-01

193

Analysis of the Advantages and Limitations of Stationary Imaging Fourier Transform Spectrometer. Revised  

NASA Technical Reports Server (NTRS)

New developments in infrared sensor technology have potentially made possible a new space-based system which can measure far-infrared radiation at lower costs (mass, power and expense). The Stationary Imaging Fourier Transform Spectrometer (SIFTS) proposed by NASA Langley Research Center, makes use of new detector array technology. A mathematical model which simulates resolution and spectral range relationships has been developed for analyzing the utility of such a radically new approach to spectroscopy. Calculations with this forward model emulate the effects of a detector array on the ability to retrieve accurate spectral features. Initial computations indicate significant attenuation at high wavenumbers.

Beecken, Brian P.; Kleinman, Randall R.

2004-01-01

194

Assessment of fibre orientation in reinforced concrete using Fourier image transform.  

PubMed

In this study, ribbon-shaped amorphous cast-iron fibres were used to reinforce a concrete matrix. X-ray photographs have been taken to detect fibres in situ. Their orientation has been investigated by automatic image analysis methods. However, this measurement should not be influenced by the digitization on the square frame of the analyser. For that purpose, the Fourier transform was used rather than the rose of direction method. This analysis revealed the transverse isotropic nature of the spatial arrangement of these fibres, whose axis of revolution corresponds to the concrete casting axis. Such a morphological characterization of the fibre-reinforced concrete reveals its mechanical behaviour. PMID:9767490

Redon; Chermant; Chermant; Coster

1998-09-01

195

Functional common-path Fourier-domain OCT for hemoglobin oxygen saturation imaging  

NASA Astrophysics Data System (ADS)

In this paper, we propose and investigate a technique to deduce hemoglobin oxygen saturation (SO2) variation image using Spectroscopic Optical Coherence Tomography (OCT). The technique is based on Morlet wavelet transformation and make use of the different absorption properties of hemoglobin (Hb) and oxyhemoglobin (HbO2) around 800 nm. In order to test the technique, we combined three superluminescent light emitting diodes (SLED) together in a Fourier Domain Common Path OCT (FD-CP-OCT) set-up. The result using chicken embryo in vivo shows that we are able to obtain highly localized oxygen saturation variation.

Liu, Xuan; Kang, Jin U.

2009-11-01

196

Range-invariant anomaly detection applied to imaging Fourier transform spectrometry data  

NASA Astrophysics Data System (ADS)

This paper describes the end-to-end processing of image Fourier transform spectrometry data taken of surrogate tank targets at Picatinny Arsenal in New Jersey with the long-wave hyper-spectral camera HyperCam from Telops. The first part of the paper discusses the processing from raw data to calibrated radiance and emissivity data. The second part discusses the application of a range-invariant anomaly detection approach to calibrated radiance, emissivity and brightness temperature data for different spatial resolutions and compares it to the Reed-Xiaoli detector.

Borel, Christoph; Rosario, Dalton; Romano, Joao

2012-09-01

197

Phase demodulation using adaptive windowed Fourier transform based on Hilbert-Huang transform.  

PubMed

The phase demodulation method of adaptive windowed Fourier transform (AWFT) is proposed based on Hilbert-Huang transform (HHT). HHT is analyzed and performed on fringe pattern to obtain instantaneous frequencies firstly. These instantaneous frequencies are further analyzed based on the condition of AWFT to locate local stationary areas where the fundamental spectrum will not be interfered by high-order spectrum. Within each local stationary area, the fundamental spectrum can be extracted accurately and adaptively by using AWFT with the background, which has been determined previously with the presented criterion during HHT, being eliminated to remove the zero-spectrum. This method is adaptive and unconstrained by any precondition for the measured phase. Experiments demonstrate its robustness and effectiveness for measuring the object with discontinuities or complex surface. PMID:23038397

Wang, Chenxing; Da, Feipeng

2012-07-30

198

Phase difference map interpretation of Mach diamond interferometric patterns by Fourier Transform Methods  

NASA Astrophysics Data System (ADS)

The development of a new interferometric evaluation system has allowed the detailed quantitative characterization of complex Mach diamond patterns in quasi stationary jets of compressed air provided by a Laval nozzle usually employed for laser cutting of ceramic materials. The application of a Mach-Zehnder interferometer in order to observe the stationary shock wave patterns provides fringe patterns that are recorded through a CMOS camera. Their optical phase is extracted through two differential phase evaluation methods that use the Fourier Transform as a fundamental tool. On the basis of the available data, the analysis of the pressure distribution and also of the shock wave patterns that occur in the free jet stream allows us to confirm the hypothesis previously established related with the main characteristics of a free jet.

Rodríguez, F.; Dorrío, B. V.; Doval, A. F.

2008-04-01

199

Fourier transform spectroscopic imaging using an infrared focal-plane array detector.  

PubMed

A powerful new mid-infrared spectroscopic chemical imaging technique combining step-scan Fourier transform Michelson interferometry with indium antimonide focal-plane array (FPA) image detection is described. The coupling of an infrared focal-plane array detector to an interferometer provides an instrumental multiplex/multichannel advantage. Specifically, the multiple detector elements enable spectra at all pixels to be collected simultaneously, while the interferometer portion of the system allows all the spectral frequencies to be measured concurrently. With this method of mid-infrared spectroscopic imaging, the fidelity of the generated spectral images is limited only by the number of pixels on the FPA detector, and only several seconds of starting time is required for spectral image acquisition. This novel, high-definition technique represents the future of infrared chemical imaging analysis, a new discipline within the chemical and material sciences, which combines the capability of spectroscopy for molecular analysis with the power of visualization. In particular, chemical imaging is broadly applicable for noninvasive, molecular characterization of heterogeneous materials, since all solid-state materials exhibit chemical nonuniformity that exists either by design or by development during the course of material preparation or fabrication. Imaging, employing Raman and infrared spectroscopy, allows the precise characterization of the chemical composition, domain structure, and chemical architecture of a variety of substances. This information is often crucial to a wide range of activities, extending from the fabrication of new materials to a basic understanding of biological samples. In this study, step-scan imaging principles, instrument design details, and infrared chemical imaging results are presented. Since the prospect of performing high-resolution and high-definition mid-infrared chemical imaging very rapidly has been achieved with the step-scan approach, the implications for the chemical analysis of materials are many and varied. PMID:8686889

Lewis, E N; Treado, P J; Reeder, R C; Story, G M; Dowrey, A E; Marcott, C; Levin, I W

1995-10-01

200

Comparison of phase-shifting techniques for in vivo full-range, high-speed Fourier-domain optical coherence tomography  

PubMed Central

Single spectrometer-based complex conjugate artifact removal methods are evaluated for in vivo imaging with complementary metal-oxide semiconductor line scan camera based high-speed Fourier-domain optical coherence tomography (FD–OCT) at 100,000 axial scans per second. Performance of three different phase-shifting methods with the same OCT engine is evaluated using modified data acquisition schemes, depending on the requirements of each phase-shifting technique. The suppression ratio of complex conjugate artifact images using a paperboard is assessed for all tested methods. Several other characteristics, including a list of additional hardware requirements (beyond standard FD-OCT components) and data acquisition schemes for each of the methods is presented. In vivo full-range images of human fingerpad and nail are shown and compared with standard FD-OCT images. Additionally, a complex-conjugate-free human retinal volume acquired at the speed of 100,000 A-scans?s is presented.

Kim, Dae Yu; Werner, John S.; Zawadzki, Robert J.

2010-01-01

201

Diffusion-weighted imaging in the prostate: an apparent diffusion coefficient comparison of half-Fourier acquisition single-shot turbo spin-echo and echo planar imaging  

Microsoft Academic Search

Prostate cancer detection using diffusion-weighted imaging is highly affected by the accuracy of the apparent diffusion coefficient (ADC) values in an image. Echo planar imaging (EPI) is a fast sequence commonly used for diffusion imaging but has inherent magnetic susceptibility and chemical shift artefacts associated. A diffusion sequence that is less affected by these artefacts is therefore advantageous. The half-Fourier

Ben Babourina-Brooks; Gary J. Cowin; Deming Wang

202

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

203

Lateral shear interferometer using multiplexed holographic lenses and spatial Fourier transform: varying spectrum position and phase fluctuations  

NASA Astrophysics Data System (ADS)

Previously, we reported a simple method to obtain lateral shear in both the x- and y-directions using a multiplexing technique. The phase data was extracted using the inherent spatial carrier fringes formed due to the tilt in the two sheared beams. In this article, we report that an error in phase map is introduced when the band-pass-filtered Fourier transform (FT) spectrum is not centered prior to performing the inverse FT to obtain the phase. We also found that intentionally introducing aberrations when capturing dynamic fluctuations in the wave front, resulted in controlling the spread of the Fourier spectrum.

Joenathan, Charles; Bernal, Ashley; Sirohi, Rajpal S.

2013-08-01

204

Optimization of magnetic flux density for fast MREIT conductivity imaging using multi-echo interleaved partial fourier acquisitions  

PubMed Central

Background Magnetic resonance electrical impedance tomography (MREIT) has been introduced as a non-invasive method for visualizing the internal conductivity and/or current density of an electrically conductive object by externally injected currents. The injected current through a pair of surface electrodes induces a magnetic flux density distribution inside the imaging object, which results in additional magnetic flux density. To measure the magnetic flux density signal in MREIT, the phase difference approach in an interleaved encoding scheme cancels out the systematic artifacts accumulated in phase signals and also reduces the random noise effect by doubling the measured magnetic flux density signal. For practical applications of in vivo MREIT, it is essential to reduce the scan duration maintaining spatial-resolution and sufficient contrast. In this paper, we optimize the magnetic flux density by using a fast gradient multi-echo MR pulse sequence. To recover the one component of magnetic flux density Bz, we use a coupled partial Fourier acquisitions in the interleaved sense. Methods To prove the proposed algorithm, we performed numerical simulations using a two-dimensional finite-element model. For a real experiment, we designed a phantom filled with a calibrated saline solution and located a rubber balloon inside the phantom. The rubber balloon was inflated by injecting the same saline solution during the MREIT imaging. We used the multi-echo fast low angle shot (FLASH) MR pulse sequence for MRI scan, which allows the reduction of measuring time without a substantial loss in image quality. Results Under the assumption of a priori phase artifact map from a reference scan, we rigorously investigated the convergence ratio of the proposed method, which was closely related with the number of measured phase encode set and the frequency range of the background field inhomogeneity. In the phantom experiment with a partial Fourier acquisition, the total scan time was less than 6 seconds to measure the magnetic flux density Bz data with 128×128 spacial matrix size, where it required 10.24 seconds to fill the complete k-space region. Conclusion Numerical simulation and experimental results demonstrated that the proposed method reduces the scanning time and provides the recovered Bz data comparable to what we obtained by measuring complete k-space data.

2013-01-01

205

The wide-field Fourier spectroscopic-imaging of the radiation heat from the object itself in the middle infrared region for the health monitoring  

NASA Astrophysics Data System (ADS)

We are aiming at the realization of the wide-field spectroscopic-imaging-sensor that is available for the health monitoring or the plant factory. Conventionally, the body temperature is measured by the thermography as a total intensity of the middle infrared radiation. We are trying to analyze the spectroscopic characteristics of the radiation heat from the human body in detail to measure the blood glucose or the moisture-retaining properties of the human skin. The proposed imaging-type 2-dimensional Fourier spectroscopy can measure the radiation heat from the object itself with the wide field of view and the wide wavelength-band. In this proposed method, we install the phase-shifter on the optical Fourier-transform-plane of the imaging optics to give the arbitrary phase-shift to the half flux of the object beams. Thus, the interferogram can be formed on the imaging plane in each bright point by the phase-shift interference-phenomena between the object beams that are emitted from the each corresponding bright point on the objective surface. In this report, we mention the feasibility results of the wide-field spectroscopic-imaging using the black body for the basic optical evaluation and the house plants for measuring the glucose distribution with the infrared camera(wavelength: 8?m-14?m).

Qi, Wei; Takuma, Takashi; Inui, Asuka; Tsutsumi, Ryosuke; Yuzuriha, Takehiko; Kagiyama, Hiroyasu; Kojima, Daisuke; Nishiyama, Akira; Ishimaru, Ichirou

2012-02-01

206

On neutron phase contrast imaging  

NASA Astrophysics Data System (ADS)

Improving the spatial resolution conditions in a neutron imaging experiment enables the detection of phase-based contrast in addition to attenuation contrast. Addressing not only the amplitude but also the phase of radiation in an imaging experiment allows for obtaining additional information about the sample. The so-called neutron phase contrast method improves imaging results mainly by edge enhancement which increases the visibility of sub-resolution structures and of low attenuation contrast materials. These effects have been found at high intensity synchrotron X-ray sources before and have been applied to neutron imaging recently. However, the excellent coherence conditions and spatial resolution of imaging instruments at state-of-the-art synchrotron sources can hardly be compared to neutron imaging. Nevertheless, edge enhancement has been found for increased resolution (coherence) conditions in neutron experiments as well. As for X-ray instruments the effects have been explained by diffraction, although typical interference fringes have never been recorded. In contrast this article will explain the effects measured with neutron radiation by refraction and total reflection. Both of these do not require high spatial coherence. Therefore improved resolution and not increased coherence will be considered as precondition to obtain the reported signals and to understand the results. Considerations concerning relaxed collimation requirements for improved detector resolutions will be presented as a consequence.

Strobl, M.; Treimer, W.; Kardjilov, N.; Hilger, A.; Zabler, S.

2008-01-01

207

Progress in Fourier transform infrared spectroscopic imaging applied to venereal cancer diagnosis.  

PubMed

Fourier transform infrared imaging spectroscopy is a powerful technique that provides molecular and spatial information at the single-cell level. We report on the progress of this technology in the field of cancer research, focusing on human cervical cancer because of the inherent difficulty in grading this type of cancer and as a model for venereal cancers in dogs. Using a suite of multivariate imaging processing techniques, we demonstrate the potential of this technique to identify histologic features in the normal epithelium and cervical intraepithelial neoplasia stages I and III. We highlight the advantages and detail the barriers that need to be overcome before implementation of this technology in the clinical environment. PMID:24009268

Wood, B R; Kiupel, M; McNaughton, D

2014-01-01

208

Real-time Fourier transform spectrometry for fluorescence imaging and flow cytometry  

SciTech Connect

We present a Fourier transform (FT) spectrometer that is suitable for real-time spectral analysis in fluorescence imaging and flow cytometry. The instrument consists of a novel type of interferometer that can be modulated at frequencies of up to 100 kHz and has a high light throughput; and a dedicated, parallel array processor for the real-time computation of spectral parameters. The data acquisition array processor can be programmed by a host computer to perform any desired linear transform on the interferogram and can thus separate contributions from multiple fluorescence microscopy. The integration of a flow cytometer and a spectral imaging fluorescence microscope is discussed, and the concepts of direct and reversed virtual sorting'' are introduced. 9 refs., 8 figs.

Buican, T.N.

1990-01-01

209

4D imaging of embryonic chick hearts by streak-mode Fourier domain optical coherence tomography  

NASA Astrophysics Data System (ADS)

Recently, we developed the streak-mode Fourier domain optical coherence tomography (OCT) technique in which an area-scan camera is used in a streak-mode to record the OCT spectrum. Here we report the application of this technique to in ovo imaging HH18 embryonic chick hearts with an ultrahigh speed of 1,016,000 axial scans per second. The high-scan rate enables the acquisition of high temporal resolution 2D datasets (1,000 frames per second or 1 ms between frames) and 3D datasets (10 volumes per second), without use of prospective or retrospective gating technique. This marks the first time that the embryonic animal heart has been 4D imaged using a megahertz OCT.

Wang, Rui; Yun, Julie X.; Goodwin, Richard; Markwald, Roger; Borg, Thomas K.; Runyan, Raymond B.; Gao, Bruce

2012-02-01

210

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

211

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

212

Phase retrieval from speckle images.  

PubMed

In ground-based astronomy, the inverse problem of phase retrieval from speckle images is a means to calibrate static aberrations for correction by active optics. It can also be used to sense turbulent wavefronts. However, the number of local minima drastically increases with the turbulence strength, mainly because of phase wrapping ambiguities. Multifocal phase diversity has been considered to overcome some ambiguities of the phase retrieval problem. We propose an effective algorithm for phase retrieval from a single focused image. Our algorithm makes use of a global optimization strategy and an automatically tuned smoothness prior to overcome local minima and phase degeneracies. We push the limit of D/r(0)=4 achieved by Irwan and Lane [J. Opt. Soc. Am. A.15, 2302 (1998)] up to D/r(0)=11, which is a major improvement owing to the drastic increase in the problem complexity. We estimate the performances of our approach from consistent simulations for different turbulence strengths and noise levels (down to 1500 photons per image). We also investigate the benefit of temporal correlation. PMID:17912332

Rondeau, Xavier; Thiébaut, Eric; Tallon, Michel; Foy, Renaud

2007-10-01

213

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

214

Quantitative analysis of biological tissues using Fourier transform-second-harmonic generation imaging  

NASA Astrophysics Data System (ADS)

We demonstrate the use of Fourier transform-second-harmonic generation (FT-SHG) imaging of collagen fibers as a means of performing quantitative analysis of obtained images of selected spatial regions in porcine trachea, ear, and cornea. Two quantitative markers, preferred orientation and maximum spatial frequency are proposed for differentiating structural information between various spatial regions of interest in the specimens. The ear shows consistent maximum spatial frequency and orientation as also observed in its real-space image. However, there are observable changes in the orientation and minimum feature size of fibers in the trachea indicating a more random organization. Finally, the analysis is applied to a 3D image stack of the cornea. It is shown that the standard deviation of the orientation is sensitive to the randomness in fiber orientation. Regions with variations in the maximum spatial frequency, but with relatively constant orientation, suggest that maximum spatial frequency is useful as an independent quantitative marker. We emphasize that FT-SHG is a simple, yet powerful, tool for extracting information from images that is not obvious in real space. This technique can be used as a quantitative biomarker to assess the structure of collagen fibers that may change due to damage from disease or physical injury.

Ambekar Ramachandra Rao, Raghu; Mehta, Monal R.; Toussaint, Kimani C., Jr.

2010-02-01

215

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

PubMed Central

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.

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

2012-01-01

216

Fourier domain optical coherence tomography achieves full range complex imaging in vivo by introducing a carrier frequency during scanning  

Microsoft Academic Search

The author describes a Fourier domain optical coherence tomography (FDOCT) system that is capable of full range complex imaging in vivo .T his is achieved by introducing a constant carrier frequency into the OCT spectral interferograms at the time when imaging is performed. The complex functions of the spatial interferograms formed by each single wavelength are constructed before performing the

Ruikang K Wang

2007-01-01

217

Interferometric imaging with global phases  

NASA Astrophysics Data System (ADS)

A number of seismic methods exist to image the lithosphere below a collection of receivers, using distant earthquakes. Although both global and teleseismic phases could be used, in the current practice, especially teleseismic phases are utilized. We are working on a method that takes advantage of the availability of global phases. Nowadays it is known how to extract reflection responses from a collection of phase responses, using seismic interferometry. Reflections can be obtained between any two receivers at the Earth's surface. However, a wide distribution of earthquakes is required to achieve this. This distribution does not always exist or it might take ages to detect. In this abstract we propose a simple, but effective, alternative. We consider the extraction of zero-offset P-wave responses. A zero-offset response is obtained when a virtual source and a receiver are created at the same station position. We only need illumination with phases which impinge on the lithosphere with angles of incidence close to zero, considering the lithosphere is, grosso modo, horizontally layered. Thus, we use global phases, like PKP. A large advantage of these global phases is that the vertical component is already a good approximation of the P-wave response. Consequently, we can leave out of the equation, the lower signal-to-noise of the horizontal components and inaccuracies introduced by decomposition. Another advantage of global phases is that a large backazimuthal range may be included. For about any station on the globe, there exists a good distribution of earthquakes within the allowed range. From a sampling perspective, only a few global phases would suffice to retrieve a reflection response. However, global phases can be highly triplicated. These triplications lead to spurious cross terms. Therefore, still a large number of phases need to be used to unveil the actual reflectivity. We test the technique on data from the Hi-CLIMB experiment (2002-2005). This was a large and well-sampled seismic array, passing the Himalayas and a significant part of the Tibetan Plateau. For this array, a few images have been published, which were obtained by applying different techniques. This enables benchmarking of our own results. We select a number of high-quality (M>6) global phase responses from the Andes region. We apply seismic interferometry for each station position individually. After concatenating the obtained zero-offset responses, consistent reflections are shown. The zero-offset response is migrated to obtain a sharp image of the lithosphere. Along with the main crustal reflections, the image shows a double Moho below Southern Tibet, a complicated transition zone below the northern portion of the Lhasa block and again a clear Moho below the Qiangtang block.

Ruigrok, E. N.; Wapenaar, C. A.

2011-12-01

218

Neutron Phase Imaging and Tomography  

SciTech Connect

We report how a setup consisting of three gratings yields quantitative two- and three-dimensional images depicting the quantum-mechanical phase shifts of neutron de Broglie wave packets induced by the influence of macroscopic objects. Since our approach requires only a little spatial and chromatic coherence it provides a more than 2 orders of magnitude higher efficiency than existing techniques. This dramatically reduces the required measurement time for computed phase tomography and opens up the way for three-dimensional investigations of previously inaccessible quantum-mechanical phase interactions of neutrons with matter.

Pfeiffer, F.; Gruenzweig, C.; Bunk, O.; Frei, G.; Lehmann, E.; David, C. [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland)

2006-06-02

219

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

220

Fourier transform infrared imaging analysis in discrimination studies of squamous cell carcinoma.  

PubMed

Oral squamous cell carcinoma (OSCC) of the oral cavity and oropharynx represents more than 95% of all malignant neoplasms in the oral cavity. Histomorphological evaluation of this cancer type is invasive and remains a time consuming and subjective technique. Therefore, novel approaches for histological recognition are necessary to identify malignancy at an early stage. Fourier transform infrared (FTIR) imaging has become an essential tool for the detection and characterization of the molecular components of biological processes, such as those responsible for the dynamic properties of tumor progression. FTIR imaging is a modern analytical technique enabling molecular imaging of a complex biological sample and is based on the absorption of IR radiation by vibrational transitions in covalent bonds. One major advantage of this technique is the acquisition of local molecular expression profiles, while maintaining the topographic integrity of the tissue and avoiding time-consuming extraction, purification, and separation steps. With this imaging technique, it is possible to obtain unique images of the spatial distribution of proteins, lipids, carbohydrates, cholesterols, nucleic acids, phospholipids, and small molecules with high spatial resolution. Analysis and visualization of FTIR imaging datasets are challenging and the use of chemometric tools is crucial in order to take advantage of the full measurement. Therefore, methodologies for this task based on the novel developed algorithm for multivariate image analysis (MIA) are often necessary. In the present study, FTIR imaging and data analysis methods were combined to optimize the tissue measurement mode after deparaffinization and subsequent data evaluation (univariate analysis and MIAs). We demonstrate that it is possible to collect excellent IR spectra from formalin-fixed paraffin-embedded (FFPE) tissue microarrays (TMAs) of OSCC tissue sections employing an optimised analytical protocol. The correlation of FTIR imaging to the morphological tissue features obtained by histological staining of the sections demonstrated that many histomorphological tissue patterns can be visualized in the colour images. The different algorithms used for MIAs of FTIR imaging data dramatically increased the information content of the IR images from squamous cell tissue sections. These findings indicate that intra-operative and surgical specimens of squamous cell carcinoma tissue can be characterized by FTIR imaging. PMID:22792538

Pallua, J D; Pezzei, C; Zelger, B; Schaefer, G; Bittner, L K; Huck-Pezzei, V A; Schoenbichler, S A; Hahn, H; Kloss-Brandstaetter, A; Kloss, F; Bonn, G K; Huck, C W

2012-09-01

221

An effective approach for iris recognition using phase-based image matching.  

PubMed

This paper presents an efficient algorithm for iris recognition using phase-based image matching--an image matching technique using phase components in 2D Discrete Fourier Transforms (DFTs) of given images. Experimental evaluation using CASIA iris image databases (versions 1.0 and 2.0) and Iris Challenge Evaluation (ICE) 2005 database clearly demonstrates that the use of phase components of iris images makes possible to achieve highly accurate iris recognition with a simple matching algorithm. This paper also discusses major implementation issues of our algorithm. In order to reduce the size of iris data and to prevent the visibility of iris images, we introduce the idea of 2D Fourier Phase Code (FPC) for representing iris information. The 2D FPC is particularly useful for implementing compact iris recognition devices using state-of-the-art Digital Signal Processing (DSP) technology. PMID:18703828

Miyazawa, Kazuyuki; Ito, Koichi; Aoki, Takafumi; Kobayashi, Koji; Nakajima, Hiroshi

2008-10-01

222

Fourier transform infrared imaging analysis in discrimination studies of bladder cancer.  

PubMed

Bladder carcinoma represents more than 4% of all cancer diseases in Austria. The histomorphological evaluation is invasive and remains a subjective and time consuming technique. On account of this it is necessary to find novel non-invasive approaches which support the pathologists for histological recognition to identify malignancy at an early stage. In the present study, Fourier transform infrared (FTIR) microscopic imaging was combined with univariate and multivariate data analysis methods to study bladder carcinoma tissue sections in detail. The possibility to collect IR spectra of bladder carcinoma tissue sections employing an optimized analytical protocol is demonstrated. The correlation between FTIR microscopic imaging and the morphological tissue features obtained by histological staining of the sections demonstrated that many histomorphological tissue patterns can be visualized in the colour images. The routine generation of high quality imaging data is enabled because of the combination of FTIR technology and optimized sample preparation techniques. This opens a new quality of spectroscopic analyses of cancerous tissue, allowing exploration of molecular changes associated with the histopathological morphology. PMID:23897512

Pezzei, C; Brunner, A; Bonn, G K; Huck, C W

2013-10-01

223

Fourier analysis of a four-dimensional imaging spectrometer with a fiber optic dimension transform element  

NASA Astrophysics Data System (ADS)

A four-dimensional imaging spectrometer with a fiber optic dimension transform element has the ability to capture all four dimensions of data (2D spatial, spectral and temporal) with a single, radiometrically calibrated sensor at a single exposure, which satisfies the need to record transient events and fast changing phenomena of interest. In order to analyze the corresponding relation between the input light intensity and the output light intensity of a four-dimensional imaging spectrometer with a fiber optic dimension transform element, this paper utilizes the Fourier optics theory and complex Gaussian functions expansion method to derive and analyze the transmission characteristics of the imaging spectrometer optical system. This paper introduces the light intensity distribution formula when the detector is fixed on the negative first order spectral image plane and establishes and simulates the corresponding relation between the light intensity distribution of the detector and the spatial/spectral information on the target space. The research results show that the target information can be extracted and analyzed directly according to the corresponding relation.

Yan, Zongqun; Liu, Bingqi

2012-09-01

224

IFTSUV: an imaging Fourier transform spectrometer in UV for the next solar space missions  

NASA Astrophysics Data System (ADS)

The study of the Sun in the UV spectral domain is essential for a better understanding of the physical processes taking place in the solar atmosphere. The main tools for this study are imagers and spectrometers. Nevertheless, the analysis of imagery data is rapidly limited unless spectral information is available, and the association of spectrometers and imagers is limited by the lack of coherence between the instruments. Therefore, the design of an imaging spectrometer in UV is a priority for solar physicists. In the far UV, only all reflective optical systems can be used thus an imaging Fourier transform spectrometer (IFTS) is the ideal candidate for the realization of such an instrument. The performances of an IFTS are given by the modulation efficiency. Theoretical study of performances and scientific objectives lead to technical and operating specifications. A mock-up of an IFTSUV has been built at IAS to validate the working principle. Its optical design and alignment are described in this paper. The first results are shown and discussed. Planned modifications of the design are also discussed.

Millard, Anne A.; Lemaire, Philippe; Vial, Jean-Claude

2006-07-01

225

Simulating the Performance of a Fourier Transform Imaging Spectrometer on NGST  

NASA Astrophysics Data System (ADS)

Due to its simultaneous deep imaging and integral field spectroscopic capability, an Imaging Fourier Transform Spectrograph (IFTS) is ideally suited to the NGST mission, and offers opportunities for tremendous scientific return in many fields of astrophysical inquiry. We describe the operation and quantify the advantages of an IFTS for space applications. We present the expected signal-to-noise performance of an IFTS on NGST and show that its flexible imaging and spectroscopic capabilities can execute efficiently a substantial fraction of the design reference mission. We have built a high-fidelity model that simulates the interferometric data cubes produced by a space-borne IFTS. This artificial data is invaluable because it allows us to visualize directly the data products and performance of an IFTS for comparison with other instruments. We present simulations of deep ( =~ 10(5) s) NGST IFTS observations of rich star fields and the distant Universe. These simulations demonstrate that an IFTS on NGST will be able to spectroscopically classify stars in crowded fields approaching the confusion limit, find and classify distant supernovae on the basis of their spectral signatures alone in single-epoch images, and identify young, forming super star clusters out to redshifts of z =~ 12.

Dey, A.; Najita, J. R.; Graham, J. R.; Bennett, C. L.; Cook, K. H.; Wurtz, R.; Macoy, N. H.; Wickham, D. R.; Hertel, R. J.; Abrams, M. C.; Carr, J.; Morris, S. L.; Villemaire, A.; Wishnow, E.

1998-12-01

226

Combining the tape-lift method and Fourier transform infrared spectroscopic imaging for forensic applications.  

PubMed

Conventional Fourier transform infrared (FT-IR) spectroscopy and microscopy have been widely used in forensic science. New opportunities exist to obtain chemical images and to enhance the spatial resolution using attenuated total reflection (ATR) FT-IR spectroscopy coupled with a focal-plane array (FPA) detector. In this paper, the sensitivity limits of FT-IR imaging using three different ATR crystals (Ge, ZnSe, and diamond) in three different optical arrangements for the detection of model particles is discussed. Model systems of ibuprofen and paracetamol particles having sizes below 32 mum were studied. The collection of drug particles was achieved with the aid of two different tapes: common adhesive tape and a film of polydimethylsiloxane (PDMS). The surface of the film with collected particles was measured directly via ATR-FT-IR imaging. Since the removal of tape from porous surfaces can be difficult, the application of micro ATR-FT-IR imaging directly to the surface of a newspaper contaminated with particles of model drugs is also discussed. In order to assess the feasibility of the chosen method in a forensic case study, the detection of diacetylmorphine hydrochloride traces in PDMS matrix and the finger surface is investigated. The scenarios considered were that of the detection of evidence collected at a crime scene with the tape lift method and the analysis of the finger of an individual after drug handling. The results show broad implications in the detection of drugs of abuse. PMID:17002827

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

2006-09-01

227

High throughput operando studies using Fourier transform infrared imaging and Raman spectroscopy.  

PubMed

A prototype high throughput operando (HTO) reactor designed and built for catalyst screening and characterization combines Fourier transform infrared (FT-IR) imaging and Raman spectroscopy in operando conditions. Using a focal plane array detector (HgCdTe focal plane array, 128x128 pixels, and 1610 Hz frame rate) for the FT-IR imaging system, the catalyst activity and selectivity of all parallel reaction channels can be simultaneously followed. Each image data set possesses 16 384 IR spectra with a spectral range of 800-4000 cm(-1) and with an 8 cm(-1) resolution. Depending on the signal-to-noise ratio, 2-20 s are needed to generate a full image of all reaction channels for a data set. Results on reactant conversion and product selectivity are obtained from FT-IR spectral analysis. Six novel Raman probes, one for each reaction channel, were specially designed and house built at Pacific Northwest National Laboratory, to simultaneously collect Raman spectra of the catalysts and possible reaction intermediates on the catalyst surface under operando conditions. As a model system, methanol partial oxidation reaction on silica-supported molybdenum oxide (MoO3SiO2) catalysts has been studied under different reaction conditions to demonstrate the performance of the HTO reactor. PMID:18681719

Li, Guosheng; Hu, Dehong; Xia, Guanguang; White, J M; Zhang, Conrad

2008-07-01

228

The quantum state vector in phase space and Gabor's windowed Fourier transform  

NASA Astrophysics Data System (ADS)

Representations of quantum state vectors by complex phase space amplitudes, complementing the description of the density operator by the Wigner function, have been defined by applying the Weyl-Wigner transform to dyadic operators, linear in the state vector and anti-linear in a fixed 'window state vector'. Here aspects of this construction are explored, and a connection is established with Gabor's 'windowed Fourier transform'. The amplitudes that arise for simple quantum states from various choices of windows are presented as illustrations. Generalized Bargmann representations of the state vector appear as special cases, associated with Gaussian windows. For every choice of window, amplitudes lie in a corresponding linear subspace of square-integrable functions on phase space. A generalized Born interpretation of amplitudes is described, with both the Wigner function and a generalized Husimi function appearing as quantities linear in an amplitude and anti-linear in its complex conjugate. Schrödinger's time-dependent and time-independent equations are represented on phase space amplitudes, and their solutions described in simple cases.

Bracken, A. J.; Watson, P.

2010-10-01

229

Translational Diffusion of Fluorescent Proteins by Molecular Fourier Imaging Correlation Spectroscopy  

PubMed Central

The ability to noninvasively observe translational diffusion of proteins and protein complexes is important to many biophysical problems. We report high signal/noise (?250) measurements of the translational diffusion in viscous solution of the fluorescent protein, DsRed. This is carried out using a new technique: molecular Fourier imaging correlation spectroscopy (M-FICS). M-FICS is an interferometric method that detects a collective Fourier component of the fluctuating density of a small population of fluorescent molecules, and provides information about the distribution of molecular diffusivities. A theoretical analysis is presented that expresses the detected signal fluctuations in terms of the relevant time-correlation functions for molecular translational diffusion. Furthermore, the role played by optical orientational degrees of freedom is established. We report Fickian self-diffusion of the DsRed tetramer at short timescales. The long-time deviation of our data from Fickian behavior is used to determine the variance of the distribution of the protein self-diffusion coefficient. We compare our results to the expected outcomes for 1), a bi-disperse distribution of protein species, and 2), dynamic disorder of the host solvent.

Fink, Michael C.; Adair, Kenneth V.; Guenza, Marina G.; Marcus, Andrew H.

2006-01-01

230

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

231

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

PubMed

As a solution to iterative CT image reconstruction, first-order methods are prominent for the large-scale capability and the fast convergence rate [Formula: see text]. 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. PMID:24840019

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

2014-06-21

232

Nonlinear joint fractional Fourier transform correlation for target detection in hyperspectral image  

NASA Astrophysics Data System (ADS)

In this paper, we present a spectral joint fractional Fourier transform correlation (SJFRTC) for detecting and identifying very small target with only a few pixels using reflectance spectral information in the hyperspectral imagery. In this technique, fractional correlation (FC) between input spectral signature and known reference spectral signature is performed digitally or optically. Binary differential technique is utilized to enhance the performance of the SJFRTC, resulting in delta-function-like correlation peaks without dc interference. Distinctive and distinguishable correlation performance is obtained using peak-to-clutter ratio (PCR) instead of absolute correlation peak value, which makes the proposed technique independent from the intensity variation of the spectral signature. Simulation results using real-life hyperspectral images show that the binary SJFRTC can detect both single or/and multiple targets successfully with excellent detection capability, as compared to the other traditional hyperspectral detection algorithms.

Wang, Qu; Guo, Qing; Zhou, Jinyun; Lin, Qinghua

2012-09-01

233

The use of the fractional Fourier transform with coded excitation in ultrasound imaging.  

PubMed

Medical ultrasound systems are limited by a tradeoff between axial resolution and the maximum imaging depth which may be achieved. The technique of coded excitation has been used extensively in the field of RADAR and SONAR for some time, but has only relatively recently been exploited in the area of medical ultrasound. This technique is attractive because allows the relationship between the pulse length and the maximum achievable spatial resolution to be changed. The work presented here explores the possibility of using the fractional Fourier transform as an effective means for the processing of signals received after the transmission of linear frequency modulated chirps. Results are presented which demonstrate that this technique is able to offer spatial resolutions similar to those obtained with a single cycle duration signal. PMID:16602583

Bennett, Michael J; McLaughlin, Steve; Anderson, Tom; McDicken, Norman

2006-04-01

234

Fourier transform infrared spectroscopic imaging parameters describing acid phosphate substitution in biologic hydroxyapatite.  

PubMed

Acid phosphate substitution into mineralized tissues is an important determinant of their mechanical properties and their response to treatment. This study identifies and validates Fourier transform infrared spectroscopic imaging (FTIRI) spectral parameters that provide information on the acid phosphate (HPO4) substitution into hydroxyapatite in developing mineralized tissues. Curve fitting and Fourier self-deconvolution were used to identify subband positions in model compounds (with and without HPO4). The intensity of subbands at 1127 and 1110 cm(-1) correlated with the acid phosphate content in these models. Peak height ratios of these subbands to the ?3 vibration at 1096 cm(-1) found in stoichiometric apatite were evaluated in the model compounds and mixtures thereof. FTIRI spectra of bones and teeth at different developmental ages were analyzed using these spectral parameters. Factor analysis (a chemometric technique) was also conducted on the tissue samples and resulted in factor loadings with spectral features corresponding to the HPO4 vibrations described above. Images of both factor correlation coefficients and the peak height ratios 1127/1096 and 1112/1096 cm(-1) demonstrated higher acid phosphate content in younger vs. more mature regions in the same specimen. Maps of the distribution of acid phosphate content will be useful for characterizing the extent of new bone formation, the areas of potential decreased strength, and the effects of therapies such as those used in metabolic bone diseases (osteoporosis, chronic kidney disease) on mineral composition. Because of the wider range of values obtained with the 1127/1096 cm(-1) parameter compared to the 1110/1096 cm(-1) parameter and the smaller scatter in the slope, it is suggested that this ratio should be the parameter of choice. PMID:23380987

Spevak, Lyudmila; Flach, Carol R; Hunter, Tracey; Mendelsohn, Richard; Boskey, Adele

2013-05-01

235

Flow distributions in hollow fiber hemodialyzers using magnetic resonance Fourier velocity imaging.  

PubMed

Distribution of flow within the hollow fibers and the dialysate compartment of hemodialyzers is difficult to measure; previous work has suggested that flow distributions may be non uniform. Magnetic resonance Fourier velocity imaging was used to determine flow distributions within the hollow fibers and dialysate compartment of three commercial hemodialyzers (CA170, CT190, and F60A). Distilled water was pumped without pulsatility through the hollow fibers and the outflow was circulated in a countercurrent direction through the dialysate compartment. Steady state flow distributions were determined simultaneously in both directions using input flow rates of 300 and 600 ml/min. Flow distributions within the hollow fibers were relatively uniform in most hemodialyzer cross sections, approximately Gaussian, and similar for all hemodialyzers. Flow distributions in the dialysate compartment were non uniform and skewed to high flow rates. High flow in the dialysate compartment was largely outside the fiber bundle for the CA170 and CT190 hemodialyzers. Local regions containing both low flow within the hollow fibers and high flow in the dialysate compartment were observed for the F60A hemodialyzer, and these regions became more prominent at a flow rate of 600 ml/min. The results of this study demonstrate that flow distributions within the hollow fibers and dialysate compartment of hemodialyzers can be simultaneously determined using magnetic resonance Fourier velocity imaging. It is concluded that the distribution of flow within the hollow fibers of hemodialyzers is relatively uniform but in the dialysate compartment it is not uniform and depends upon hemodialyzer design. PMID:8573891

Zhang, J; Parker, D L; Leypoldt, J K

1995-01-01

236

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

237

The Wavenumber Algorithm: Fast Fourier-Domain Imaging Using Full Matrix Capture  

NASA Astrophysics Data System (ADS)

We develop a Fourier-domain approach to full matrix imaging based on the wavenumber algorithm used in synthetic aperture radar and sonar. The extension to the wavenumber algorithm for full matrix capture is described and the performance of the new algorithm is compared to the total focusing method (TFM), which we use as a representative benchmark for the time-domain algorithms. The wavenumber algorithm provides a mathematically rigorous solution to the inverse problem for the assumed forward wave propagation model, whereas the TFM employs heuristic delay-and-sum beamforming. Consequently, the wavenumber algorithm has an improved point-spread function and provides better imagery. However, the major advantage of the wavenumber algorithm is its superior computational performance. For large arrays and images, the wavenumber algorithm is several orders of magnitude faster than the TFM. On the other hand, the key advantage of the TFM is its flexibility. The wavenumber algorithm requires a regularly sampled linear array, while the TFM can handle arbitrary imaging geometries. The TFM and the wavenumber algorithm are compared using simulated and experimental data.

Hunter, A. J.; Drinkwater, B. W.; Wilcox, P. D.

2009-03-01

238

Visible imaging Fourier transform spectrometer based on a beam-folding technique  

NASA Astrophysics Data System (ADS)

A low-cost visible to Near-infrared Imaging Fourier Transform Spectrometer (IFTS) using a beam-folding technique instead of the spectral folding technique is presented. The retroreflectors are used to replace the plane mirrors to maintain the optical alignments without the adoption of complex active-alignment measures. Fast-scanning mechanism is adopted to avoid the high-cost precise-position control system. The interferogram images at sequential sampling points, spectral images at different wavenumbers and pixel interferograms and spectra of the multimode fiber ends illuminated by a He- Ne laser and a red LED source respectively, are given. The experimental results show that the IFTS based on the beamfolding technique can achieve a spectral resolution of ~15cm-1 (~0.5nm) when measuring the bright coherent light source (the end of a 600 ?m fiber coupled with the He-Ne laser). The resolution is mainly limited by the nonlinearity of the CCD output, the memory size of the PC and the data-transferring speed between the PC and the CCD camera PL-A741. Preliminary results showed that it is suited to the measurement of bright object sources. This restriction is only due to the poor performance of the CCD detector array used in the experiment. A fast-scanning visible-Near infrared IFTS for the objects of low light intensity is feasible when the high-sensitivity CCD camera is adopted.

Wang, Xuzhu; Chan, Robert K. Y.

2009-07-01

239

3D imaging of dental hard tissues with Fourier domain optical coherence tomography  

NASA Astrophysics Data System (ADS)

A fiber optical coherence tomography (OCT) probe is used for three dimensional dental imaging. The probe has a lightweight miniaturized design with a size of a pen to facilitate clinic in vivo diagnostics. The probe is interfaced with a swept-source / Fourier domain optical coherence tomography at 20K axial scanning rate. The tooth samples were scanned from occlusal, buccal, lingual, mesial, and distal orientations. Three dimensional imaging covers tooth surface area up to 10 mm x 10 mm with a depth about 5 mm, where a majority of caries affection occurs. OCT image provides better resolution and contrast compared to gold standard dental radiography (X-ray). In particular, the technology is well suited for occlusal caries detection. This is complementary to X-ray as occlusal caries affection is difficult to be detected due to the X-ray projectile scan geometry. The 3D topology of occlusal surface as well as the dentin-enamel junction (DEJ) surface inside the tooth can be visualized. The lesion area appears with much stronger back scattering signal intensity.

Chen, Yueli L.; Yang, Yi; Ma, Jing; Yan, Jun; Shou, Yuanxin; Wang, Tianheng; Ramesh, Aruna; Zhao, Jing; Zhu, Quing

2011-02-01

240

A sapphire fibre thermal probe based on fast Fourier transform and phase-lock loop  

NASA Astrophysics Data System (ADS)

A sapphire fibre thermal probe with Cr3+ ion-doped end is developed by using the laser heated pedestal growth method. The fluorescence thermal probe offers advantages of compact structure, high performance and ability to withstand high temperature in a detection range from room temperature to 450°C. Based on the fast Fourier transform (FFT), the fluorescence lifetime is obtained from the tangent function of phase angle of the non-zeroth terms in the FFT result. This method has advantages such as quick calculation, high accuracy and immunity to the background noise. This FFT method is compared with other traditional fitting methods, indicating that the standard deviation of the FFT method is about half of that of the Prony method and about 1/6 of that of the log-fit method. And the FFT method is immune to the background noise involved in a signal. So, the FFT method is an excellent way of processing signals. In addition, a phase-lock amplifier can effectively suppress the noise.

Wang, Yu-Tian; Wang, Dong-Sheng; Ge, Wen-Qian; Cui, Li-Chao

2006-05-01

241

Fast Imaging Detector Readout Circuits with In-Pixel ADCs for Fourier Transform Imaging Spectrometers  

NASA Technical Reports Server (NTRS)

Focal plane arrays (FPAs) with high frame rates and many pixels benefit several upcoming Earth science missions including GEO-CAPE, GACM, and ACE by enabling broader spatial coverage and higher spectral resolution. FPAs for the PanFTS, a high spatial resolution Fourier transform spectrometer and a candidate instrument for the GEO-CAPE mission are the focus of the developments reported here, but this FPA technology has the potential to enable a variety of future measurements and instruments. The ESTO ACT Program funded the developed of a fast readout integrated circuit (ROIC) based on an innovative in-pixel analog-to-digital converter (ADC). The 128 X 128 pixel ROIC features 60 ?m pixels, a 14-bit ADC in each pixel and operates at a continuous frame rate of 14 kHz consuming only 1.1 W of power. The ROIC outputs digitized data completely eliminating the bulky, power consuming signal chains needed by conventional FPAs. The 128 X 128 pixel ROIC has been fabricated in CMOS and tested at the Jet Propulsion Laboratory. The current version is designed to be hybridized with PIN photodiode arrays via indium bump bonding for light detection in the visible and ultraviolet spectral regions. However, the ROIC design incorporates a small photodiode in each cell to permit detailed characterization of the ROICperformance without the need for hybridization. We will describe the essential features of the ROIC design and present results of ROIC performance measurements.

Rider, D.; Blavier, J-F.; Cunningham, T.; Hancock, B.; Key, R.; Pannell, Z.; Sander, S.; Seshadri, S.; Sun, C.; Wrigley, C.

2011-01-01

242

Image-spectroscopy--II. The removal of plural scattering from extended energy-filtered series by Fourier deconvolution.  

PubMed

The increased spectral information obtained by acquiring an EFTEM image-series over several hundred eV allows plural scattering to be removed from loss images using standard deconvolution techniques developed for the quantification of EEL spectra. In this work, both Fourier-log and Fourier-ratio deconvolution techniques have been applied successfully to such image-series. Application of the Fourier-log technique over an energy-loss range of several hundred eV has been achieved by implementation of a novel method that extends the effective dynamic range of EFTEM image-series acquisition by over four orders of magnitude. Experimental results show that the removal of plural scattering from EFTEM image-series gives a significant improvement in quantification for thicker specimen regions. Further, the recovery of the single-scattering distribution using the Fourier-log technique over an extended energy-loss range is shown to result in an increase in both the ionisation-edge jump-ratio and the signal-to-noise ratio. PMID:11463197

Thomas, P J; Midgley, P A

2001-08-01

243

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

244

Comparative analysis on viewing angle change in Fresnel and Fourier holographic images reconstructed by a tilted plane wave.  

PubMed

We carry out a comparative analysis on a viewing angle change in Fresnel and Fourier holographic images reconstructed by a tilted plane wave. A tilted plane wave illuminating an on-axis hologram generates a diffractive wave carrying the holographic image in a paraxial region of a new diffraction axis. The reconstructed image in the Fresnel hologram is deformed along the new viewing direction, which is well described as Affine transformation. In the Fourier holographic image, the replica of the image is formed without its deformation when the hologram is placed in the front focal plane of the lens, whereas in the case of a hologram that is located at a distance different from a focal length, image deformation arises. This property is investigated through numerical simulation based on a wide-angle diffraction phenomenon. We also perform a similar interpretation for high-order diffraction images appearing in the sampled Fourier hologram and discuss a method for enlarging the viewing angle of the holographic image. PMID:24922205

Chae, Byung Gyu

2014-05-20

245

The Study of Small Biomolecules Using Chirped-Pulse Fourier Transform Microwave Cp-Ftmw Spectrometer in the Gas Phase  

Microsoft Academic Search

The microwave spectra of a large molecule is sensitive to both the structure of the molecule and as well as its motion along different vibrational coordinates. Chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is an exciting new technique that makes possible the reading of the complete microwave spectrum of a gas phase sample using a single 1 -s pulse. In this

Ryan G. Bird; David W. Pratt; Justin L. Neill; Brooks H. Pate

2009-01-01

246

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...

247

Imaging phased telescope array study  

NASA Technical Reports Server (NTRS)

The problems encountered in obtaining a wide field-of-view with large, space-based direct imaging phased telescope arrays were considered. After defining some of the critical systems issues, previous relevant work in the literature was reviewed and summarized. An extensive list was made of potential error sources and the error sources were categorized in the form of an error budget tree including optical design errors, optical fabrication errors, assembly and alignment errors, and environmental errors. After choosing a top level image quality requirment as a goal, a preliminary tops-down error budget allocation was performed; then, based upon engineering experience, detailed analysis, or data from the literature, a bottoms-up error budget reallocation was performed in an attempt to achieve an equitable distribution of difficulty in satisfying the various allocations. This exercise provided a realistic allocation for residual off-axis optical design errors in the presence of state-of-the-art optical fabrication and alignment errors. Three different computational techniques were developed for computing the image degradation of phased telescope arrays due to aberrations of the individual telescopes. Parametric studies and sensitivity analyses were then performed for a variety of subaperture configurations and telescope design parameters in an attempt to determine how the off-axis performance of a phased telescope array varies as the telescopes are scaled up in size. The Air Force Weapons Laboratory (AFWL) multipurpose telescope testbed (MMTT) configuration was analyzed in detail with regard to image degradation due to field curvature and distortion of the individual telescopes as they are scaled up in size.

Harvey, James E.

1989-01-01

248

Understanding the influence of turbulence in imaging Fourier transform spectroscopy of smokestack plumes  

NASA Astrophysics Data System (ADS)

A Telops Hyper-Cam Fourier-transform spectrometer (IFTS) was used to collect infrared hyper-spectral imagery of the smokestack plume from a coal-burning power facility to assess the influence of turbulence on spectral retrieval of temperature (T) and pollutant concentrations (Ci ). The mid-wave (1.5-5.5 ?m) system features a 320x256 InSb focal-plane array with a 326 ?rad instantaneous field-of-view (IFOV). The line-of-sight distance to the 76mtall smokestack exit was 350m(11.4 x 11.4 cm2 IFOV). Approximately 5000 interferogram cubes were collected in 30 minutes on a 128x128 pixel window corresponding to a spectral resolution of 20 cm-1. Radiance fluctuations due to plume turbulence were observed on a time scale much shorter than hyper-spectral image acquisition rate, suggesting scene change artifacts (SCA) would be present in the Fourier-transformed spectra. Time-averaging the spectra minimized SCA magnitudes, but accurate T and Ci retrieval requires a priori knowledge of the statistical distribution of temperature and other stochastic flow field parameters. A method of quantile sorting in interferogram space prior to Fourier-transformation is presented and used to identify turbulence throughout the plume. Immediately above the stack exit, T and CO2 concentration estimates from the median spectrum are 395 K and 6%, respectively, which compare well to in situ measurements. Turbulence is small above the stack exit and introduced systematic errors in T and Ci on the order of 0.5 K and 0.01%, respectively. In some plume locations, turbulent fluctuations introduced errors in T and Ci on the order of 8 K and 1%, respectively. While more complicated radiance fluctuations precluded straightforward retrieval of the temperature probability distribution, the results demonstrate the utility of additional information content associated with multiple interferogram quantiles and suggest IFTS may find use as a tool for non-intrusive flow field analysis.

Massman, Jennifer L.; Gross, Kevin C.

2011-05-01

249

Optical phase imaging using a synthetic aperture phase retrieval technique.  

PubMed

Optical phase imaging enables visualization of transparent samples, numerical refocusing, and other computational processing. Typically phase is measured quantitatively using interferometric techniques such as digital holography. Researchers have demonstrated image enhancement by synthetic aperture imaging based on digital holography. In this work we introduce a novel imaging technique that implements synthetic aperture imaging using phase retrieval, a non-interferometric technique. Unlike digital holography, phase retrieval obviates the need for a reference arm and provides a more compact, less expensive, and more stable experimental setup. We call this technique synthetic aperture phase retrieval. PMID:24787826

Lee, Dennis J; Weiner, Andrew M

2014-04-21

250

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

251

Quantitative analysis of diseased horse tendons using Fourier-transform-second-harmonic generation imaging  

NASA Astrophysics Data System (ADS)

Fourier transform-second-harmonic generation (FT-SHG) imaging is used to quantitatively assess the structural organization of collagen fibers in tendonitis-induced horse tendons. Fiber orientation, isotropy, and the ratio of forward to backward SHG signal (F/B ratio) are used to differentiate the fiber organization between the normal and diseased horse tendons. Each second-harmonic generation (SHG) image is divided into several smaller regions of interest (ROI) and the aforementioned quantitative metrics are calculated across the whole grid. ROIs are further labeled as dark (no or minimal presence of fibers), isotropic (random fiber organization), or anisotropic (regular fiber organization) regions. Results show that the normal tendon possesses minimal isotropic regions and small standard deviations in the histograms of orientation and F/B ratio, indicating an intact and highly regular fiber organization. However, the tendonitis-induced horse tendons possess higher number of dark and isotropic regions, and larger standard deviations of the measured parameters, suggesting significantly disoriented and disorganized collagen fibers. This type of quantification would be highly beneficial in diagnosing and determining the stage of tendonitis in clinical settings. Not limited to tendonitis, the technique could also be applied to other diseases that structurally affect collagen fibers. The advantage of FT-SHG over the conventional polarization microscopy is also discussed.

Sivaguru, Mayandi; Durgam, Sushmitha; Ambekar, Raghu; Luedtke, David; Fried, Glenn; Stewart, Allison; Toussaint, Kimani C., Jr.

2011-02-01

252

First imaging Fourier-transform spectral measurements of detonation in an internal combustion engine  

NASA Astrophysics Data System (ADS)

The Telops Hyper-Cam midwave (InSb 1.5-5.5?m) imaging Fourier-transformspectrometer (IFTS) observed repeated detonations in an ethanol-powered internal combustion (IC) engine. The IC engine is aMegatech Corporation MEG 150 with a 1in. bore, 4in. stroke, and a compression ratio of 3 : 1. The IC combustion cylinder is made from sapphire permitting observation in the visible and infrared. From a distance of 3m, the IFTS imaged the combustion cylinder on a 64×32 pixel array with each pixel covering a 0.1×0.1cm2 area. More than 14,000 interferograms were collected at a rate of 16Hz. The maximum optical path difference of the interferograms was 0.017cm corresponding to an unapodized spectral resolution of 36cm-1. Engine speed was varied between 600-1200RPM to de-correlate the observation time scale from the occurrence of detonations. A method is devised to process the ensemble of interferograms which takes advantage of the DC component so that the time history of the combustion spectrum can be recovered at each pixel location. Preliminary results of this analysis will be presented.

Gross, Kevin C.; Borel, Chris; White, Allen; Sakai, Stephen; Devasher, Rebecca; Perram, Glen P.

2010-08-01

253

Performance evaluation of the Herschel/SPIRE imaging Fourier transform spectrometer through ground-based measurements  

NASA Astrophysics Data System (ADS)

The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments onboard the European Space Agency (ESA)'s Herschel Space Observatory. Herschel was successfully launched on 14 May 2009; routine science observations commenced in late 2009. Medium resolution spectroscopy with SPIRE is accomplished via an imaging Fourier transform spectrometer (IFTS) of the Mach-Zehnder configuration. Although pre-launch performance verification and calibration measurements were conducted with the SPIRE instrument mounted in an evacuated cryostat at cryogenic temperatures, it was not possible to simulate fully the expected in-flight conditions. This paper compares the performance of the SPIRE IFTS, as measured during ground-based tests, with theoretical simulations. In turn, these results are used to provide an estimate of the in-flight instrument performance. This paper includes a discussion of key aspects of the SPIRE IFTS including the spectrometer dual-input compensation scheme, instrument line shape and the overall instrument sensitivity. As a case study, the derived instrument performance is used to investigate SPIRE's utility in observing astronomical line emission from the starburst galaxy M82.

Spencer, Locke D.; Naylor, David A.; Swinyard, Bruce M.

2010-06-01

254

Shape-based recognition of targets in synthetic aperture radar images using elliptical Fourier descriptors  

NASA Astrophysics Data System (ADS)

This paper primarily investigates the use of shape-based features by an Automatic Target Recognition (ATR) system to classify various types of targets in Synthetic Aperture Radar (SAR) images. In specific, shapes of target outlines are represented via Elliptical Fourier Descriptors (EFDs), which, in turn, are utilized as recognition features. According to the proposed ATR approach, a segmentation stage first isolates the target region from shadow and ground clutter via a sequence of fast thresholding and morphological operations. Next, a number of EFDs are computed that can sufficiently describe the salient characteristics of the target outline. Finally, a classification stage based on an ensemble of Support Vector Machines identifies the target with the appropriate class label. In order to experimentally illustrate the merit of the proposed approach, SAR intensity images from the well-known Moving and Stationary Target Acquisition and Recognition (MSTAR) dataset were used as 10-class and 3-class recognition problems. Furthermore, comparisons were drawn in terms of classification performance and computational complexity to other successful methods discussed in the literature, such as template matching methods. The obtained results portray that only a very limited amount of EFDs are required to achieve recognition rates that are competitive to well-established approaches.

Nicoli, Louis P.; Anagnostopoulos, Georgios C.

2008-05-01

255

Towards a practical Fourier transform infrared chemical imaging protocol for cancer histopathology.  

PubMed

Fourier transform infrared (FTIR) chemical imaging is a strongly emerging technology that is being increasingly applied to examine tissues in a high-throughput manner. The resulting data quality and quantity have permitted several groups to provide evidence for applicability to cancer pathology. It is critical to understand, however, that an integrated approach with optimal data acquisition, classification, and validation is necessary to realize practical protocols that can be translated to the clinic. Here, we first review the development of technology relevant to clinical translation of FTIR imaging for cancer pathology. The role of each component in this approach is discussed separately by quantitative analysis of the effects of changing parameters on the classification results. We focus on the histology of prostate tissue to illustrate factors in developing a practical protocol for automated histopathology. Next, we demonstrate how these protocols can be used to analyze the effect of experimental parameters on prediction accuracy by analyzing the effects of varying spatial resolution, spectral resolution, and signal to noise ratio. Classification accuracy is shown to depend on the signal to noise ratio of recorded data, while depending only weakly on spectral resolution. PMID:17786414

Bhargava, Rohit

2007-10-01

256

In situ permeation study of drug through the stratum corneum using attenuated total reflection Fourier transform infrared spectroscopic imaging  

Microsoft Academic Search

Infrared (IR) spectroscopy is one of the most chemically specific analytical methods that gives information about composition, structure, and interactions in a material. IR spectroscopy has been successfully applied to study the permeation of xenobiotics through the skin. Combining IR spectroscopy with an IR array detector led to the development of Fourier transform infrared (FTIR) spectroscopic imaging, which generates chemical

Jean-Michel Andanson; Jonathan Hadgraft; Sergei G. Kazarian

2009-01-01

257

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

Microsoft Academic Search

Examples are presented of applications of a Fast Fourier transform algorithm to analyse time series of images of Normalized Difference Vegetation Index (NDVI) 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

M. Menenti; S. Azzali; W. Verhoef; R. van Swol

1993-01-01

258

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

259

A Fourier-based implicit evolution scheme for active surfaces, for object segmentation in volumetric images  

NASA Astrophysics Data System (ADS)

Active contours (AC) and active surfaces (AS) have been used extensively for segmentation and measurement in two- and three-dimensional images. The small time steps used in discretizing the evolution equation of AC/AS with the explicit scheme result in slow execution, whereas the use of the implicit evolution of AS in matrix form imposes very high memory and computational requirements. In this work we present an approach for implementing the implicit scheme for the numerical solution of the partial differential equation of the evolution of an AC/AS. The proposed approach is formulated as a deconvolution of the current contour/surface points with a one-dimensional mask that is performed using the discrete Fourier transform and it is derived using the properties of circulant matrices. The proposed scheme can handle higher accuracy numerical approximation of the discrete derivatives necessary for the method of AC/AS. It also possesses the separability property along different dimensions and it is applicable to implicit evolution of deformable surfaces, without the need to store and invert large sparse matrices. Initial results from the application of the proposed scheme to synthetic and clinical volumetric data demonstrate the correctness and applicability of the method. The computational complexity of the proposed scheme is also derived.

Delibasis, Konstantinos K.; Tassani, Simone; Asvestas, Pantelis; Kechriniotis, Aristides I.; Matsopoulos, George K.

2013-07-01

260

Remote quantification of smokestack effluent mass flow rates using imaging Fourier transform spectrometry  

NASA Astrophysics Data System (ADS)

A Telops Hyper-Cam midwave infrared (1.5 - 5.5?m) imaging Fourier-transform spectrometer (IFTS) was used to estimate industrial smokestack total effluent mass flow rates by combining spectrally-determined species concentrations with flow rates estimated via analysis of sequential images in the raw interferogram cube. Measurements of the coalburning smokestack were made with the IFTS at a stand-off distance of 350m. 185 hyperspectral datacubes were collected on a 128(W)×64(H) pixel sub-window (11.4×11.4cm2 per pixel) at a 0.5cm-1 spectral resolution. Strong emissions from H2O, CO2, CO, SO2, and NO were observed in the spectrum. A previously established single-layer radiative transfer model was used to estimate gas concentrations immediately above stack exit, and results compared reasonably with in situ measurements. A simple temporal cross-correlation analysis of sequential imagery enabled an estimation of the flow velocity at center stack. The estimated volumetric flow rate of 106+/-23m/s was within 4% of the reported value. Final effluent mass flow rates for CO2 and SO2 of 13.5+/-3.8kg/s and 71.3+/-19.3g/s were in good agreement with in situ rates of 11.6+/-0.1kg/s and 67.8+/-0.5g/s. NO was estimated at 16.1+/-4.2g/s, which did not compare well to the total NOx (NO +NO2) reported value of 11.2+/-0.2g/s. Unmonitored H2O, HCl , and CO were also estimated at 7.76+/-2.25kg/s, 7.40+/-2.00g/s, and 15.0+/-4.1 g/s respectively.

Harley, Jacob L.; Gross, Kevin C.

2011-05-01

261

Fourier Transform Infrared Imaging and Infrared Fiber Optic Probe Spectroscopy Identify Collagen Type in Connective Tissues  

PubMed Central

Hyaline cartilage and mechanically inferior fibrocartilage consisting of mixed collagen types are frequently found together in repairing articular cartilage. The present study seeks to develop methodology to identify collagen type and other tissue components using Fourier transform infrared (FTIR) spectral evaluation of matrix composition in combination with multivariate analyses. FTIR spectra of the primary molecular components of repair cartilage, types I and II collagen, and aggrecan, were used to develop multivariate spectral models for discrimination of the matrix components of the tissues of interest. Infrared imaging data were collected from bovine bone, tendon, normal cartilage, meniscus and human repair cartilage tissues, and composition predicted using partial least squares analyses. Histology and immunohistochemistry results were used as standards for validation. Infrared fiber optic probe spectral data were also obtained from meniscus (a tissue with mixed collagen types) to evaluate the potential of this method for identification of collagen type in a minimally-invasive clinical application. Concentration profiles of the tissue components obtained from multivariate analysis were in excellent agreement with histology and immunohistochemistry results. Bone and tendon showed a uniform distribution of predominantly type I collagen through the tissue. Normal cartilage showed a distribution of type II collagen and proteoglycan similar to the known composition, while in repair cartilage, the spectral distribution of both types I and II collagen were similar to that observed via immunohistochemistry. Using the probe, the outer and inner regions of the meniscus were shown to be primarily composed of type I and II collagen, respectively, in accordance with immunohistochemistry data. In summary, multivariate analysis of infrared spectra can indeed be used to differentiate collagen type I and type II, even in the presence of proteoglycan, in connective tissues, using both imaging and fiber optic methodology. This has great potential for clinical in situ applications for monitoring tissue repair.

Hanifi, Arash; McCarthy, Helen; Roberts, Sally; Pleshko, Nancy

2013-01-01

262

Boundary layer moisture retrieval from Indian Ocean METOC Imaging (IOMI) mission for geostationary imaging Fourier transform spectrometer (GIFTS)  

NASA Astrophysics Data System (ADS)

The Navy Indian Ocean METOC Imaging (IOMI) mission for the Geostationary Imaging Fourier Transform Spectrometer (GIFTS) will begin in early 2006 for a period of five years. The IOMI-GIFTS will measure Earth's outgoing infrared radiation with spatial (~4 km), temporal (~half hour), and spectral (~0.625 cm-1) resolutions and spectral coverages from longwave (LW, 685 - 1150 cm-1) for temperature profiles and short midwave (SMW, 1650 - 2250 cm-1) for moisture profiles. Retrieval of boundary layer moisture from IOMI-GIFTS with high vertical resolution and accuracy, is a special interest of the Navy, can provide water vapor wind information over the ocean. The characteristics of boundary layer moisture retrievals from IOMI-GIFTS are demonstrated. Both theoretical analysis and a simulation study with a GIFTS forward model developed at UW-Madison show that the contrast between surface air temperature and surface skin temperature has significant impact on the accuracy of boundary layer moisture retrievals. A large contrast (> 5 K) will result in noticeable boundary layer moisture improvement over that with less contrast.

Li, Jun; Huang, Hung-Lung

2003-04-01

263

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

264

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

265

Studies on mechanism of phase transformation of carboxylated poly(phenylene oxide) and polystyrene blend by Fourier transform infrared spectrometry  

Microsoft Academic Search

The thermally-induced phase transformation behaviors of carboxylated poly(phenylene oxide)(CPPO)\\/polystyrene(PS), and PPO\\/PS blends were studied by using a difference-spectrum method of Fourier Transform Infrared Spectrometry (FTIR). The difference intensities(µ) and vibration frequency shifts(??) of the characteristic infrared absorption bands in both CPPO\\/PS and PPO\\/PS increased with raising temperature. A linear temperature dependence in the band frequency vs. temperature plots was observed

Bing Liao; Yuhui Huang; Mincai Cheng; Guangmin Cong

1996-01-01

266

A hybrid discrete Fourier transform-moment method for the fast analysis of large rectangular phased arrays  

Microsoft Academic Search

The fast analysis of large antenna phased arrays remains an interesting and challenging problem. This paper presents an approach to accelerate the MOM by employing a DFT (discrete Fourier transform) representation for the unknowns of conventional MOM. Such an approach combining DFT with MOM is called DFT-MoM. The DFT-MoM employs the coefficients of the DFT representation as the new unknowns

Hsi-Tseng Chou; Hsien-Kwei Ho; P. H. Pathak; P. Nepa; O. A. Civi

2001-01-01

267

Sub-pixel spatial resolution wavefront phase imaging  

NASA Technical Reports Server (NTRS)

A phase imaging method for an optical wavefront acquires a plurality of phase images of the optical wavefront using a phase imager. Each phase image is unique and is shifted with respect to another of the phase images by a known/controlled amount that is less than the size of the phase imager's pixels. The phase images are then combined to generate a single high-spatial resolution phase image of the optical wavefront.

Stahl, H. Philip (Inventor); Mooney, James T. (Inventor)

2012-01-01

268

Phase unwrapping of MR phase images using Poisson equation  

Microsoft Academic Search

The authors have developed a technique based on a solution of the Poisson equation to unwrap the phase in magnetic resonance (MR) phase images. The method is based on the assumption that the magnitude of the inter-pixel phase change is less than ? per pixel. Therefore, the authors obtain an estimate of the phase gradient by “wrapping” the gradient of

Samuel Moon-ho Song; Sandy Napel; Norbert J. Pelc; Gary H. Glover

1995-01-01

269

Temperature-dependent Fourier transform infrared spectroscopy and Raman mapping spectroscopy of phase-separation in a poly(3-hydroxybutyrate)-poly(L-lactic acid) blend.  

PubMed

Variable-temperature Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopic mapping measurements were applied to study the phase separation of a poly(3-hydroxybutyrate) (PHB)-poly(L-lactic acid) (PLA) (50 : 50 wt.%) polymer-blend film as a function of temperature between 25 and 175 °C. Because of the better band separation compared with the fundamental absorptions, the first overtones of the ?(C=O) bands of PHB and PLA were used to evaluate the temperature-dependent FT-IR images as PLA-PHB and PHB-PLA band-ratio contour plots, respectively. From the visualization of the band-ratio FT-IR images, it could be derived that even beyond the melting point of PLA (145 °C), the lateral position and the geometry of the PHB-rich and PLA-rich phases were retained up to 165 °C. Furthermore, the FT-IR images derived during and after the melting of PHB (174 °C) provided an interesting insight into the homogenization process of the polymer melt. By exploiting its higher lateral resolution, valuable additional information became available from the Raman mapping measurements. Based on the Raman data, the scenario of phase-separated PHB-rich and PLA-rich domains of about 50 ?m size, based on the FT-IR imaging measurements, had to be revised. Instead, the originally interpreted PHB-rich and PLA-rich domains are actually clusters of much smaller grains. Additionally, the Raman images measured in the same temperature interval revealed that the clusters of small PHB-rich grain structures aggregated as a function of temperature increase. These investigations prove that FT-IR and Raman imaging in combination with variable-temperature measurements can provide new (and so far unavailable) insights into structural phenomena of phase-separated polymer blends. PMID:23622432

Unger, Miriam; Sato, Harumi; Ozaki, Yukihiro; Fischer, Dieter; Siesler, Heinz W

2013-02-01

270

DIDA - Dynamic Image Disparity Analyzer. Phase 1.  

National Technical Information Service (NTIS)

This report summarizes the work accomplished under Phase I of the Dynamic Image Disparity Analyzer (DIDA) program. The DIDA program was initiated to investigate the problems associated with real-time or dynamic disparity analysis. Image disparity analysis...

L. A. Tamburino

1985-01-01

271

NOTE: Deconvolution of x-ray phase contrast images as a way to retrieve phase information lost due to insufficient resolution  

Microsoft Academic Search

When free-space propagation x-ray phase contrast imaging is implemented outside synchrotron radiation facilities, the combined effect of detector resolution and source size swamps the fine phase contrast fringes, often making them almost undetectable. In an attempt to mitigate this effect, a simple deconvolution procedure based on division in the Fourier space plus multiplication by an appropriate filter was applied to

A. Olivo; R. D. Speller

2009-01-01

272

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

2012-02-01

273

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

PubMed

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

274

Quantitative Fourier Transform Infrared Analysis of Gas Phase Cigarette Smoke and Other Gas Mixtures  

Microsoft Academic Search

A new method for the analysis of selected components in complex gas mixtures has been developed utilizing a relatively inexpensive Fourier transform infrared spectrometer and a continuous flow gas cell. the method was used to monitor nitric oxide and nitrogen dioxide concentrations in cigarette smoke with time.Using multivariate least-square regression analysis, it is possible to simultaneously quantitate both NO and

Rafael Cueto; Daniel R. Church; William A. Piyor

1989-01-01

275

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.

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

2013-01-01

276

X-Ray Phase Imaging with Single Phase Grating  

Microsoft Academic Search

X-ray phase imaging with a single phase grating based on the fractional Talbot effect is described. A phase grating with an 8 mum pitch was placed behind a weakly absorbing object and illuminated with partially coherent 17.7 keV X-rays. Intensity patterns downstream of the grating were recorded with a high-resolution image detector. By the fringe scanning method, an X-ray wavefront

Yoshihiro Takeda; Wataru Yashiro; Yoshio Suzuki; Sadao Aoki; Tadashi Hattori; Atsushi Momose

2007-01-01

277

Single-shot X-ray phase-contrast imaging using two-dimensional gratings  

SciTech Connect

We developed a two-dimensional gratings-based X-ray interferometer that requires only a single exposure for clinical radiography. The interferometer consisted of a checkerboard phase grating for {pi} phase modulation and a latticed amplitude grating. Using a synchrotron radiation source, the phase grating modulates the X-rays and generates a self-image, transformed to a moire fringe by the amplitude grating. To allow use of a conventional X-ray tube, the latticed source grating was installed downstream from the X-ray tube. Differential phase-contrast and scattering images in two orthogonal directions were obtained by Fourier analysis of the single moire fringe image and an absorption image. Results show that characteristic features of soft tissue in two orthogonal directions were clearly shown in the differential phase-contrast images.

Sato, Genta; Itoh, Hidenosuke; Nagai, Kentaro; Nakamura, Takashi; Yamaguchi, Kimiaki; Kondoh, Takeshi; Handa, Soichiro; Ouchi, Chidane; Teshima, Takayuki; Setomoto, Yutaka; Den, Toru [Frontier Research Center, Corporate R and D Headquarters, Canon Inc., 3-30-2 Shimomaruko, Ohta-ku, Tokyo 146-8501 (Japan); Optics Technology Development Center, Corporate R and D Headquarters, Canon Inc., 23-10, Kiyohara-Kogyodanchi, Utsunomiya Tochigi 321-3231 (Japan); Nanotechnology R and D Center, Corporate R and D Headquarters, Canon Inc., 3-30-2 Shimomaruko, Ohta-ku, Tokyo 146-8501 (Japan)

2012-07-31

278

Mitochondrial dynamics and optical conformation changes in DsRed as studied by Fourier imaging correlation spectroscopy  

NASA Astrophysics Data System (ADS)

Novel experiments that probe the dynamics of intracellular species, including the center-of-mass displacements and internal conformational transitions of biological macromolecules, have the potential to reveal the complex biochemical mechanisms operating within the cell. This work presents the implementation and development of Fourier imaging correlation spectroscopy (FICS), a phase-selective approach to fluorescence spectroscopy that measures the collective coordinate fluctuations of fluorescently labeled microscopic particles. In FICS experiments, a spatially modulated optical grating excites a fluorescently labeled sample. Phase-synchronous detection of the fluorescence, with respect to the phase of the exciting optical grating, can be used to monitor the fluctuations of partially averaged spatial coordinates. These data are then analyzed by two-point and four-point time correlation functions to provide a statistically meaningful understanding of the dynamics under observation. FICS represents a unique route to elevate signal levels, while acquiring detailed information about molecular coordinate trajectories. Mitochondria of mammalian cells are known to associate with cytoskeletal proteins, and their motions are affected by the stability of microtubules and microfilaments. Within the cell it is possible to fluorescently label the mitochondria and study its dynamic behavior with FICS. The dynamics of S. cerevisiae yeast mitochondria are characterized at four discrete length scales (ranging from 0.6--1.19 mum) and provide detailed information about the influence of specific cytoskeletal elements. Using the microtubule and microfilament destabilizing agents, Nocodazole and Latrunculin A, it is determined that microfilaments are required for normal yeast mitochondrial motion while microtubules have no effect. Experiments with specific actin mutants revealed that actin is responsible for enhanced mobility on length scales greater than 0.6 mum. The versatility of FICS expands when individual molecules are labeled with fluorescent chromophores. In recent experiments on the tetrameric fluorescent protein DsRed, polarization-modulated FICS (PM-FICS) is demonstrated to separate conformational dynamics from molecular translational dynamics. The optical switching pathways of DsRed, a tetrameric complex of fluorescent protein subunits, are examined. An analysis of PM-FICS coordinate trajectories, in terms of 2D spectra and joint probability distributions, provides detailed information about the transition pathways between distinct dipole-coupled DsRed conformations. This dissertation includes co-authored and previously published material.

Senning, Eric Nicolas

279

Influence of area focal plane arrays on the deterioration of interference modulation for Fourier transform spectral imaging  

NASA Astrophysics Data System (ADS)

The Imaging Fourier Transform Spectrometer (IFTS) is the temporal modulated Michelson interferometer in which a single-element detector is replaced by an area focal plane arrays. Each pixel of detector arrays records observed area radiation and then yield the corresponding spectrum by Fourier transforms. While, area focal plane arrays improve spatial resolution and expand area coverage. However, this innovation technology has many technical challenges to be overcome. In this paper, the challenges caused by area focal plane arrays are discussed. The simulations of interference modulation (IM) of Fourier transform spectral imaging are presented. The IM changes as the extensions of pixel are simulated and analyzed. And a phenomenon that interference modulation deteriorates with spectral resolution improvement is discussed. The results show that, the off-axis pixels are sampled at slightly shorter OPDs, compared with the pixel in the center. The decrease of interference modulation caused by area focal plane arrays is related to both the position of each pixel and maximum optical path difference. Interference modulation decline in the format of a quadratic function as the pixel position extends. And this decrease in short waveband is more significant than that in long waveband. It is noticed that there is a key spectral resolution for IFTS interference modulation. When the spectral resolution is set below the key point, the IM decrease smoothly and slowly at the high level. However, if the spectral resolution keeps improving over the key point, the modulation will decline abruptly.

Guo, Xiarui; Li, Yan; Fan, Dongdong

2012-10-01

280

A 64-point Fourier transform chip for video motion compensation using phase correlation  

Microsoft Academic Search

Details of a new low power fast Fourier transform (FFT) processor for use in digital television applications are presented. This has been fabricated using a 0.6-?m CMOS technology and can perform a 64 point complex forward or inverse FFT on real-time video at up to 18 Megasamples per second. It comprises 0.5 million transistors in a die area of 7.8×8

Colin Chiu; Wing Hui; Tiong Jiu Ding; J. V. McCanny

1996-01-01

281

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

282

Phase Tomography Using Diffraction-Enhanced Imaging  

SciTech Connect

Phase tomography using diffraction-enhanced imaging (DEI) is presented with the observation of a phantom consisting of polyvinyl-chloride tubes and water. The boundary between the tube and water was successfully differentiated in a resultant tomographic image obtained with 0.06-nm synchrotron X rays. The sensitivity of this method is discussed in comparison with an image obtained by conventional X-ray tomography. The spatial and density resolutions achieved by the phase tomography are also discussed.

Koyama, I.; Momose, A. [Department of Advanced Materials Science, Graduate School of Frontier Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Hamaishi, Y. [Department of Applied Physics, School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2004-05-12

283

ACQUISITION OF PHASE INFORMATION IN THERMAL IMAGES  

Microsoft Academic Search

Pulsed phased thermography technique was used to perform non-destructive testing in this paper. Temperature\\/phase images were analysed and compared in terms of defect resolution. A graphical user interface was made in MATLAB to aid image analysis. It is concluded that phase information convey more subsurface information for high thermal contrast targets. Non-destructive testing (NDT) was a method for checking the

Richard Yen-Hung Shih

284

Amplified Dispersive FourierTransform Imaging for Ultrafast Displacement Sensing and Barcode Reading  

Microsoft Academic Search

Dispersive Fourier transformation is a powerful technique in which the spectrum of an optical pulse is mapped into a time-domain waveform using chromatic dispersion. It replaces a diffraction grating and detector array with a dispersive fiber and single photodetector. This simplifies the system and, more importantly, enables fast real-time measurements. Here we describe a novel ultrafast barcode reader and displacement

Keisuke God; Kevin K. Tsi; Bahram Jalali

285

Phase unwrapping method based on image segmentation  

Microsoft Academic Search

In this Letter, a method is proposed for interferometric synthetic aperture radar (SAR) phase unwrapping based on image segmentation. An auxiliary phase map was generated and the interferometric phase was divided into many connected regions without discontinuity by separation and combination operations. A local optimal strategy was used to combine these regions with as few discontinuities as possible. The coherence

T. Xiong; W. Zhang; W.-M. Boerner

2008-01-01

286

Fourier transform infrared spectroscopy in the study of lipid phase transitions in model and biological membranes: practical considerations.  

PubMed

Fourier transform infrared (FTIR) spectroscopy is a powerful, nonperturbing technique that has been used to good effect for the detection and characterization of lipid phase transitions in model and natural membranes. The technique is also quite versatile, covering a wide range of sophisticated applications, from which fairly detailed information about the structure and organization of membranes and other lipid assemblies can be obtained. In this chapter, an introduction to this particular application of FTIR spectroscopy is presented. Special emphasis is put on how the technique can be used to study lipid phase transitions under biologically relevant conditions. The chapter is intended to give an overview of the capabilities of FTIR spectroscopy in the field of lipid and biomembrane research, and provide the reader with some practical guidelines for the design and execution of simple FTIR spectroscopic experiments suitable for the detection and characterization of lipid phase transitions in hydrated lipid bilayers. PMID:17951736

Lewis, Ruthven N A H; McElhaney, Ronald N

2007-01-01

287

A New Fourier-Type Phase Estimation Method for Sensorless Drives of Permanent-Magnet Synchronous Motors  

NASA Astrophysics Data System (ADS)

This paper proposes a new Fourier-type phase estimation method (FPEM) for estimating the rotor phase in the sensorless drives of salient-pole permanent-magnet synchronous motors. The method involves the use of a stator current induced by high-frequency voltage injection. The proposed FPEM has the following characteristics: 1) it is versatile, i.e., it can be applied to almost all voltage injections, 2) it does not require band-pass filters that extract the high-frequency component from the stator current, 3) it could have the potential to enhance the positive correlation between the rotor phase and high-frequency current, 4) it does not require redesigning of the integrated PLL when the amplitude and/or frequency of the injected high-frequency voltage is changed. The usefulness of the proposed method is verified through extensive experiments.

Shinnaka, Shinji

288

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

289

X-Ray Phase-Contrast Imaging: Phase Reconstructions  

Microsoft Academic Search

Clinical X-ray imaging has always been based on the biological tissue's differences in X-ray attenuation ever since Roentgen discovered X-ray over 100 years ago. However X-ray-tissue interaction causes X-ray phase changes as well. We have identified the four clinically important factors that affect the X-ray phase visibility in clinical imaging. These factors are: body part attenuation, the spatial coherence of

Xizeng Wu; Hong Liu

2005-01-01

290

High-resolution imaging by phase retrieval and discrimination using speckle. Volume 1. Final report, August 1987-January 1989  

SciTech Connect

Concepts for unconventional sensors capable of high-resolution imaging and parameter estimation for the SDI midcourse discrimination application were developed. The basic sensor consists of a large filled array of small-aperture receivers that measure a laser-illuminated object's Fourier intensity in the aperture of the receiver. Reconstruction of a high-resolution image using a phase-retrieval algorithm was investigated via theoretical analysis, computer simulations, and laboratory experiments. In particular, modification of the basic sensor to include a small-aperture, diffraction-limited imager within the array was studied. A method was developed to use the additional low-resolution image data in the process of reconstructing a high-resolution image. This method first retrieves the Fourier phase over the small aperture of the low resolution imager using the Gerchberg-Saxton algorithm and then proceeds with phase retrieval over the entire array aperture using the iterative Fourier-transform algorithm. This method was successfully demonstrated via computer simulations. Reconstruction of the image of a simple two-part object from Fourier intensity data gathered in a laboratory experiment was also achieved. Non-imaging, speckle correlation methods were developed that use the data provided by the large array of receivers to measure rotation rates and separation rates for multiple objects.

Not Available

1989-03-01

291

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 range 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 innovative 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.

2014-03-01

292

Generalized Implementation of Rapid-Scan Fourier Transform Infrared Spectroscopic Imaging  

Microsoft Academic Search

We describe a novel, generalized data acquisition sequence to allow rapid-scan Fourier transform infrared (FT-IR) spectroscopic im- aging using focal plane array (FPA) detectors. This technique de- rives its applicability from the reproducible performance of modern FT-IR instrumentation and the availability of FPAs with simulta- neous, full array acquisition, or snapshot electronics. Instead of sampling the entire interferogram in one

Scott W. Huffman; Rohit Bhargava; Ira W. Levin

2002-01-01

293

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

294

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

295

Coherent array imaging using phased subarrays  

NASA Astrophysics Data System (ADS)

This research was motivated by the need to reduce the front-end hardware complexity of 3D ultrasound imaging systems using 2D transducer arrays. The results apply to other coherent array imaging applications including sonar, radio astronomy, and seismic imaging. Conventional full phased array (FPA) imaging requires parallel front-end electronic hardware to process the signals from each element independently. While currently used for commercial 2D ultrasound imaging using 1D transducer arrays, FPA imaging does not scale well to 3D imaging due to the overwhelming number of transducer elements. Phased subarray (PSA) imaging has been proposed as a method to reduce the imaging system's front-end hardware complexity while achieving near-FPA image quality. Each scan line is formed using multiple subsets of adjacent elements---subarrays---that span the full array. PSA imaging reduces the number of front-end hardware channels to the number of elements in the subarray. This dissertation extends the capabilities of PSA imaging. A mathematical model of the imaging response in the spatial domain and spatial frequency domain, or k-space, is developed for PSA imaging. This model is used as the basis for two new methods of designing subarray reconstruction filters for wideband PSA imaging. PSA and FPA imaging are compared using experimental data for 2D imaging and simulated data for 3D imaging. Experimental images were formed of a wire phantom using a 128-element capacitive micromachined ultrasound transducer array. PSA imaging had little or no affect on the axial resolution and little or no effect on the lateral resolution within the focal region. The SNR of the PSA images was slightly lower than that of the FPA images when using 32-element subarrays, and decreased for smaller subarrays. The contrast-to-noise ratio of PSA and FPA imaging was compared using simulated pulse-echo data of a cyst phantom and was slightly lower for all PSA imaging methods. The results illustrate that PSA imaging reduces the front-end hardware complexity and can enable real-time 3D ultrasound imaging.

Johnson, Jeremy Aaron

296

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

NASA Astrophysics Data System (ADS)

The method of phasing broadband Fourier transform ion cyclotron resonance (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.

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.

2013-06-01

297

Quantitative Fourier transform infrared analysis of gas phase cigarette smoke and other gas mixtures  

SciTech Connect

A new method for the analysis of selected components in complex gas mixtures has been developed utilizing a relatively inexpensive Fourier transform infrared spectrometer and a continuous flow gas cell. The method was used to monitor nitric oxide and nitrogen dioxide concentrations in cigarette smoke with time. Using multivariate least-square regression analysis, it is possible to simultaneously quantitate both NO and NO{sub 2}, even in the presence of overlapping peaks. Using this method, the oxidation of nitric oxide in the presence of isoprene in cigarette smoke and in a model system was followed with time. The method also can be applied to other compounds in smoke or to any other gaseous mixture.

Cueto, R.; Church, D.F.; Pryor, W.A. (Louisiana State Univ., Baton Rouge (USA))

1989-03-01

298

Autofocusing in digital holographic phase contrast microscopy on pure phase objects for live cell imaging.  

PubMed

Digital holography enables a multifocus quantitative phase microscopy for the investigation of reflective surfaces and for marker-free live cell imaging. For digital holographic long-term investigations of living cells an automated (subsequent) robust and reliable numerical focus adjustment is of particular importance. Four numerical methods for the determination of the optimal focus position in the numerical reconstruction and propagation of the complex object waves of pure phase objects are characterized, compared, and adapted to the requirements of digital holographic microscopy. Results from investigations of an engineered surface and human pancreas tumor cells demonstrate the applicability of Fourier-weighting- and gradient-operator-based methods for robust and reliable automated subsequent numerical digital holographic focusing. PMID:18594573

Langehanenberg, Patrik; Kemper, Björn; Dirksen, Dieter; von Bally, Gert

2008-07-01

299

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.

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

2009-01-01

300

The effect of pressure on the phase transition behavior of tridecane, pentadecane, and heptadecane: A Fourier transform infrared spectroscopy study  

NASA Astrophysics Data System (ADS)

The effect of pressure on the phase transition behavior of tridecane (C13), pentadecane (C15), and heptadecane (C17) has been investigated up to 489, 220, and 387 MPa, respectively, using Fourier transform infrared spectroscopy at 25 °C. The transition between the high pressure ordered (HPO) and high pressure rotator (HPR) phases has been observed in the pressure ranges of 270-220, 106-95, and 152-181 MPa for C13, C15, and C17, respectively, and the transition between the HPR and liquid phases was observed in the pressure ranges of 171-112, 73-47, and 43-70 MPa for C13, C15, and C17, respectively. The P1+P3 band of the methylene rocking mode exhibits factor group splitting caused by intermolecular vibrational coupling. This was observed in both the HPO and HPR phases, while the P1+P3 band did not split in the liquid phase. The separation of the peaks in the P1+P3 band changed discontinuously at the HPO-HPR and HPR-liquid phase transitions, even though the separation is known to change continuously in the transition from the liquid to the high temperature rotator (HTR) phase. In the HPR phase, the ratio of the intensities of the higher and lower frequency components in the P1+P3 doublet is roughly unity independent of pressure, while it is known to be much less than unity in the HTR phase. The separation of the P1+P3 doublet in the HPR phase is found to be larger for longer alkanes. From the intensity ratio, a large proportion of alkane molecules is believed to participate in intermolecular vibrational coupling and possess herringbone-type short-range positional order in the HPR phase. Conversely, in the HTR phase only small proportion of alkane molecules participate in intermolecular vibrational coupling. From the pressure dependence of the separation of the doublet, intermolecular vibrational coupling and herringbone-type short-range positional order is considered to change discontinuously at the HPR-liquid phase transition, while they are reported to change continuously at the HTR-liquid phase transition. The HPR-liquid phase transition is governed by the effect of molecular packing while the HTR-liquid phase transition is predominantly governed by the difference in entropy between the herringbone-type and parallel-type packing.

Yamashita, Motoi; Hirao, Atsushi; Kato, Minoru

2011-04-01

301

Concentration profiles of collagen and proteoglycan in articular cartilage by Fourier transform infrared imaging and principal component regression  

NASA Astrophysics Data System (ADS)

Fourier-transform infrared imaging (FT-IRI) technique with the principal component regression (PCR) method was used to quantitatively determine the 2D images and the depth-dependent concentration profiles of two principal macromolecular components (collagen and proteoglycan) in articular cartilage. Ten 6 ?m thick sections of canine humeral cartilage were imaged at a pixel size of 6.25 ?m in FT-IRI. The infrared spectra extracted from FT-IRI experiments were imported into a PCR program to calculate the quantitative distributions of both collagen and proteoglycan in dry cartilage, which were subsequently converted into the wet-weight based concentration profiles. The proteoglycan profiles by FT-IRI and PCR significantly correlated in linear regression with the proteoglycan profiles by the non-destructive ?MRI (the goodness-of-fit 0.96 and the Pearson coefficient 0.98). Based on these concentration relationships, the concentration images of collagen and proteoglycan in both healthy and lesioned articular cartilage were successfully constructed two dimensionally. The simultaneous construction of both collagen and proteoglycan concentration images demonstrates that this combined imaging and chemometrics approach could be used as a sensitive tool to accurately resolve and visualize the concentration distributions of macromolecules in biological tissues.

Yin, Jianhua; Xia, Yang; Lu, Mei

2012-03-01

302

Concentration Profiles of Collagen and Proteoglycan in Articular Cartilage by Fourier Transform Infrared Imaging and Principal Component Regression  

PubMed Central

Fourier-transform infrared imaging (FT-IRI) technique with the principal component regression (PCR) method was used to quantitatively determine the 2D images and the depth-dependent concentration profiles of two principal macromolecular components (collagen and proteoglycan) in articular cartilage. Ten 6 ?m thick sections of canine humeral cartilage were imaged at a pixel size of 6.25 ?m in FT-IRI. The infrared spectra extracted from FT-IRI experiments were imported into a PCR program to calculate the quantitative distributions of both collagen and proteoglycan in dry cartilage, which were subsequently converted into the wet-weight based concentration profiles. The proteoglycan profiles by FT-IRI and PCR significantly correlated in linear regression with the proteoglycan profiles by the non-destructive ?MRI (the goodness-of-fit 0.96 and the Pearson coefficient 0.98). Based on these concentration relationships, the concentration images of collagen and proteoglycan in both healthy and lesioned articular cartilage were successfully constructed two dimensionally. The simultaneous construction of both collagen and proteoglycan concentration images demonstrates that this combined imaging and chemometrics approach could be used as a sensitive tool to accurately resolve and visualize the concentration distributions of macromolecules in biological tissues.

Yin, Jianhua; Xia, Yang; Lu, Mei

2011-01-01

303

Fast and noninterpolating method for subpixel displacement analysis of digital speckle images using phase shifts of spatial frequency spectra.  

PubMed

A fast noninterpolation method for calculating displacement of digital speckle images with subpixel precision was introduced. In this method, the precise displacement is obtained from phase shifts of spatial frequency spectra of two digital speckle images instead of digital correlation calculation. First, digital speckle images before and after displacement are windowed and fast Fourier transform is performed. Then, phase shifts of different spatial frequencies are linearly fitted in spectral space using the least square method, and a coarse displacement value is directly calculated according to the phase shift theorem of Fourier transform. By a window technique and iterative procedure, the influence of finite image size on the accuracy of the results is eliminated, and the accurate displacement is obtained finally. It is significant that the method obtains the subpixel-precision displacement without any interpolation operations. The test results show that the method has high computing efficiency, high precision, and good robustness to low image quality. PMID:24921864

Lu, Helin; Huang, Chaohong; Wang, Cheng; Wang, Xiaozhong; Fu, Hongyan; Chen, Ziyi

2014-05-01

304

Fourier fringe processing using a regressive Fourier-transform technique  

NASA Astrophysics Data System (ADS)

Since the introduction of a fourier fringe algorithm by Takeda, it has been possible to determine the phase of a particular light source impinging on an object from one sole image. This has led to applications in many whole field optical measurement techniques such as ESPI, holography, profilometry and so on. However, the basic processing technique, in case of the 2D-Fourier transform, is subject to a major drawback. Because this technique supposes periodicity in a fringe image, the so-called leakage effects occur. This gives rise to non-negligible errors, which can be resolved by using a regressive Fourier transformation technique. In the method introduced in this article, the fringe signal is represented by a model using sines and cosines where the frequency is not fixed (which is the case for classical FFT-techniques). The coefficients of those sines and cosines together with the frequency components are then estimated locally by means of a frequency domain system identification technique. This allows the fringe pattern to be unwrapped without any distortion. This method will be applied in particular to Fourier-transform profilometry (determines object geometry using shifts of projected fringes) although it can be used in any of the techniques mentioned above. Moreover, it will be shown that the proposed method can deal with other distortions that occur in practice such as over-modulation and varying fringe visibility. The proposed technique will be validated on both simulations and on a profile measurement of a pipe section.

Vanherzeele, J.; Guillaume, Patrick; Vanlanduit, Steve

2005-06-01

305

CONTROL OF LASER RADIATION PARAMETERS: Theory of laser array phase locking by Fourier coupling  

NASA Astrophysics Data System (ADS)

The type of coupling in a fibre laser array phase locked with the help of an external mirror located at the focal distance from the plane of output ends of individual lasers is studied analytically. The explicit expression is derived for the eigenvalue of the resonator and the restriction on the width of the tuning range in which laser array phase locking is preserved is determined. The influence of the spread in the optical lengths of fibres on the phase-locking efficiency is considered. The phase-locking efficiency is analysed for the spread of optical lengths of fibres considerably exceeding the radiation wavelength.

Vysotskii, D. V.; Napartovich, A. P.; Troshchieva, V. N.

2007-04-01

306

Phase characterization of polarimetric SAR images  

Microsoft Academic Search

High Resolution (HR) Synthetic Aperture Radar (SAR) Single Look Complex (SLC) observations, mainly of strong scattering scenes or objects show phase patterns. Phase patterns may occur due to the system behavior or they may be signatures of the imaged objects. Since state of the art stochastic models of SAR SLC data describe mainly the pixel information. Now studies are needed

Matteo Soccorsi; Mihai Datcu

2007-01-01

307

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

308

Geometric Analysis and Symbol Calculus: Fourier Transform Magnetic Resonance Imaging and Wavelets  

Microsoft Academic Search

Due to its unequalled advantages, the magnetic resonance imaging (MRI) modality has truly revolutionized the diagnosis and evaluation of pathology. Because many morphological anatomic details that may not be visualized by other high tech imaging methods can now be readily shown by diagnostic MRI, it has already become the standard modality by which all other clinical imaging techniques are measured.

Walter Schempp

1997-01-01

309

Multifilter phase imaging with partially coherent light.  

PubMed

A novel quantitative phase imaging method is shown to estimate phase accurately over a wide range of length scales using Köhler illumination from an extended incoherent source. The method is based on estimating the longitudinal intensity derivative in the transport-of-intensity equation via convolution with multiple Savitzky-Golay differentiation filters and generalizes methods previously developed for coherent imaging to the practical scenario of partially coherent imaging. The resulting noise and resolution performance are evaluated via numerical simulation and demonstrated experimentally using a blazed transmission grating as well as a single-mode fiber as test objects. PMID:24922441

Jenkins, Micah H; Long, Joshua M; Gaylord, Thomas K

2014-06-01

310

Cardiac phase-correlated image reconstruction and advanced image processing in pulmonary CT imaging  

Microsoft Academic Search

Image quality in pulmonary CT imaging is commonly degraded by cardiac motion artifacts. Phase-correlated image reconstruction\\u000a algorithms known from cardiac imaging can reduce motion artifacts but increase image noise and conventionally require a concurrently\\u000a acquired ECG signal for synchronization. Techniques are presented to overcome these limitations. Based on standard and phase-correlated\\u000a images that are reconstructed using a raw data-derived synchronization

Robert M. Lapp; Marc Kachelrieß; Dirk Ertel; Yiannis Kyriakou; Willi A. Kalender

2009-01-01

311

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

312

Correlation-Based Watermarking Method for Image Authentication Applications.  

National Technical Information Service (NTIS)

We propose a correlation-based digital watermarking technique for robust image pattern authentication. We hide a phase-based signature of the image back into its Fourier magnitude spectrum in the embedding stage. The detector computes the Fourier transfor...

F. Ahmed I. S. Moskowitz

2004-01-01

313

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  

Microsoft Academic Search

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

Alexander Popp; Martina Wendel; Lilla Knels; Thea Koch; Edmund Koch

2006-01-01

314

Phase retrieval from single frame projection fringe pattern with variational image decomposition  

NASA Astrophysics Data System (ADS)

Phase retrieval from single frame projection fringe pattern is of fundamental importance, and is also a challenging problem in fringe projection measurement. In this paper, we present a new method for phase retrieval from a single frame projection fringe pattern based on variational image decomposition (VID) methods. We propose a new image decomposition model TV-G-Shearlet in order to effectively split a projection fringe pattern into background part, fringe part and noise part. The performance of the proposed approach is verified by simulated and real projection fringes as well as the comparison with the widely used and well-known Fourier transform method and wavelet transform method.

Zhu, Xinjun; Tang, Chen; Li, Biyuan; Sun, Chen; Wang, Linlin

2014-08-01

315

Self-starting, self-regulating Fourier domain mode locked fiber laser for OCT imaging.  

PubMed

We present a Fourier domain mode locking (FDML) fiber laser with a feedback loop allowing automatic startup without a priori knowledge of the fundamental drive frequency. The feedback can also regulate the drive frequency making the source robust against environmental variations. A control system samples the energy of the light traversing the FDML cavity and uses a voltage controlled oscillator (VCO) to drive the tunable fiber Fabry-Perot filter in order to maximize that energy. We demonstrate a prototype self-starting, self-regulating FDML operating at 40 kHz with a full width tuning range of 140 nm around 1305 nm and a power output of ~40 mW. The laser starts up with no operator intervention in less than 5 seconds and exhibits improved spectral stability over a conventional FDML source. In OCT applications the source achieved over 120 dB detection sensitivity and an ~8.9-µm axial resolution. PMID:21750775

Murari, Kartikeya; Mavadia, Jessica; Xi, Jiefeng; Li, Xingde

2011-07-01

316

Self-starting, self-regulating Fourier domain mode locked fiber laser for OCT imaging  

PubMed Central

We present a Fourier domain mode locking (FDML) fiber laser with a feedback loop allowing automatic startup without a priori knowledge of the fundamental drive frequency. The feedback can also regulate the drive frequency making the source robust against environmental variations. A control system samples the energy of the light traversing the FDML cavity and uses a voltage controlled oscillator (VCO) to drive the tunable fiber Fabry-Perot filter in order to maximize that energy. We demonstrate a prototype self-starting, self-regulating FDML operating at 40 kHz with a full width tuning range of 140 nm around 1305 nm and a power output of ~40 mW. The laser starts up with no operator intervention in less than 5 seconds and exhibits improved spectral stability over a conventional FDML source. In OCT applications the source achieved over 120 dB detection sensitivity and an ~8.9-µm axial resolution.

Murari, Kartikeya; Mavadia, Jessica; Xi, Jiefeng; Li, Xingde

2011-01-01

317

Reconstruction of a complex-valued object in coherent imaging through a random-phase screen.  

PubMed

We consider the reconstruction of a complex-valued object that is coherently illuminated and then viewed through a random-phase screen. The reconstruction involves a phase retrieval based on two intensity measurements. The first is a measurement of the long-exposure averaged intensity of a Fourier transform of the image; it yields full information on the magnitude of the object Fourier transform but noi nformation on its phase. The second measurement is made with the image field modulated by an exponential function. This modulation has the effect of shifting the Fourier-transform function along the imaginary axis of the complex plane of its argument, thus making its intensity dependent on the unknown object phase. This method is capable of reconstructing the object except for an inherent ambiguity corresponding to a simple displacement. The effects of the noise arising from averaging over finite, instead of infinite, exposure times and the quantum noise were assessed. A computer-simulated example of reconstru ting a two-dimensional object demonstrated that the reconstruction is robust. The reconstruction error increases with an increase of the variance of the random-phase function and with a decrease of its correlation length. PMID:20862080

Nakajima, N; Saleh, B E

1994-02-10

318

Phase congruency assesses hyperspectral image quality  

NASA Astrophysics Data System (ADS)

Blind image quality assessment (QA) is a tough task especially for hyperspectral imagery which is degraded by noise, distortion, defocus, and other complex factors. Subjective hyperspectral imagery QA methods are basically measured the degradation of image from human perceptual visual quality. As the most important image quality measurement features, noise and blur, determined the image quality greatly, are employed to predict the objective hyperspectral imagery quality of each band. We demonstrate a novel no-reference hyperspectral imagery QA model based on phase congruency (PC), which is a dimensionless quantity and provides an absolute measure of the significance of feature point. First, Log Gabor wavelet is used to calculate the phase congruency of frequencies of each band image. The relationship between noise and PC can be derived from above transformation under the assumption that noise is additive. Second, PC focus measure evaluation model is proposed to evaluate blur caused by different amounts of defocus. The ratio and mean factors of edge blur level and noise is defined to assess the quality of each band image. This image QA method obtains excellent correlation with subjective image quality score without any reference. Finally, the PC information is utilized to improve the quality of some bands images.

Shao, Xiaopeng; Zhong, Cheng

2012-10-01

319

[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

320

IFTSUV: an imaging Fourier transform spectrometer in UV for the next solar space missions  

Microsoft Academic Search

The study of the Sun in the UV spectral domain is essential for a better understanding of the physical processes taking place in the solar atmosphere. The main tools for this study are imagers and spectrometers. Nevertheless, the analysis of imagery data is rapidly limited unless spectral information is available, and the association of spectrometers and imagers is limited by

Anne A. Millard; Philippe Lemaire; Jean-Claude Vial

2006-01-01

321

Fully 3D PET image reconstruction using a Fourier preconditioned conjugate-gradient algorithm  

Microsoft Academic Search

Since the data sixes in fully 3D PET imaging are very large, iterative image reconstruction algorithms must converge in very few iterations to be useful. One can improve the convergence rate of the conjugate-gradient (CG) algorithm by incorporating preconditioning operators that approximate the inverse of the Hessian of the objective function. If the 3D cylindrical PET geometry were not truncated

Jeffrey A. Fessler; Edward P. Ficaro

1996-01-01

322

Ultrahigh speed Spectral / Fourier domain OCT ophthalmic imaging at 70,000 to 312,500 axial scans per second  

PubMed Central

We demonstrate ultrahigh speed spectral / Fourier domain optical coherence tomography (OCT) using an ultrahigh speed CMOS line scan camera at rates of 70,000 - 312,500 axial scans per second. Several design configurations are characterized to illustrate trade-offs between acquisition speed, resolution, imaging range, sensitivity and sensitivity roll-off performance. Ultrahigh resolution OCT with 2.5 - 3.0 micron axial image resolution is demonstrated at ? 100,000 axial scans per second. A high resolution spectrometer design improves sensitivity roll-off and imaging range performance, trading off imaging speed to 70,000 axial scans per second. Ultrahigh speed imaging at >300,000 axial scans per second with standard image resolution is also demonstrated. Ophthalmic OCT imaging of the normal human retina is investigated. The high acquisition speeds enable dense raster scanning to acquire densely sampled volumetric three dimensional OCT (3D-OCT) data sets of the macula and optic disc with minimal motion artifacts. Imaging with ? 8 - 9 micron axial resolution at 250,000 axial scans per second, a 512 × 512 × 400 voxel volumetric 3D-OCT data set can be acquired in only ? 1.3 seconds. Orthogonal registration scans are used to register OCT raster scans and remove residual axial eye motion, resulting in 3D-OCT data sets which preserve retinal topography. Rapid repetitive imaging over small volumes can visualize small retinal features without motion induced distortions and enables volume registration to remove eye motion. Cone photoreceptors in some regions of the retina can be visualized without adaptive optics or active eye tracking. Rapid repetitive imaging of 3D volumes also provides dynamic volumetric information (4D-OCT) which is shown to enhance visualization of retinal capillaries and should enable functional imaging. Improvements in the speed and performance of 3D-OCT volumetric imaging promise to enable earlier diagnosis and improved monitoring of disease progression and response to therapy in ophthalmology, as well as have a wide range of research and clinical applications in other areas.

Potsaid, Benjamin; Gorczynska, Iwona; Srinivasan, Vivek J.; Chen, Yueli; Jiang, James; Cable, Alex; Fujimoto, James G.

2009-01-01

323

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

324

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

325

Phase contrast imaging with polycapillary optics  

NASA Astrophysics Data System (ADS)

Conventional diagnostic radiography is limited by the similarity between x-ray absorption coefficients of normal tissue and carcinoma, which results in poor inherent subject contrast. Differences in x-ray refractive indices are much larger, so phase imaging has the potential for higher contrast. Unfortunately, the spatial coherence necessary for simple in-line phase contrast requires small sources at large distances, and hence excessive exposure times. Other schemes such as grating techniques require multiple images and complex alignment. In this work, polycapillary optics were employed to increase the intensity of the x-ray beam for simple propagation in-line imaging. Focusing through pinhole apertures created a small virtual source of high intensity from which phase contrast edge effects were observed with tissueequivalent phantoms.

Abbas, Hassan; Sun, Tianxi; MacDonald, C. A.

2012-10-01

326

Blocked element compensation in phased array imaging.  

PubMed

In clinical applications using large apertures, a significant number of phased array elements may be blocked due to discontinuous acoustic windows into the body. These blocked elements produce undesired beamforming artifacts, degrading spatial and contrast resolution. To minimize these artifacts, an algorithm using multiple receive beams and the total-least-squares method is proposed. Simulations and experimental results show that this algorithm can effectively reduce imperfections in the point spread function of the imager. Combined with first-and second-order scatterer statistics derived from multiple receive beams, the algorithm is modified for blocked element compensation on distributed scattering sources. Results also indicate that compensated images are comparable to full array images, and that even full array images can be improved by removing undesired sidelobe contributions. This method, therefore, can enhance detection of low contrast lesions using large phased-array apertures. PMID:18263183

Li, P C; Flax, S W; Ebbini, E S; O'Donnell, M

1993-01-01

327

Molecular-scale imaging of unstained deoxyribonucleic acid fibers by phase transmission electron microscopy  

SciTech Connect

The molecular structure of deoxyribonucleic acid (DNA) fibers was observed by a phase reconstruction method called three-dimensional Fourier filtering using a 200 kV transmission electron microscope. The characteristic helical structure and the spacing of adjacent base pairs of DNA were partially resolved due to an improved signal-to-noise ratio and resolution enhancement by the phase reconstruction although the molecular structure was damaged by the electron beam irradiation. In the spherical aberration-free phase images, the arrangements of single atom-sized spots forming sinusoidal curves were sometimes observed, which seem to be the contrast originating in the sulfur atoms along the main chains.

Takai, Yoshizo; Nomaguchi, Tsunenori; Matsushita, Shuhei; Kimura, Yoshihide [Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0879 (Japan)

2006-09-25

328

X-ray phase contrast image simulation  

Microsoft Academic Search

A deterministic algorithm is proposed to simulate phase contrast (PC) X-ray images for complex three-dimensional (3D) objects. This algorithm has been implemented in a simulation code named VXI (virtual X-ray imaging). The physical model chosen to account for PC technique is based on the Fresnel–Kirchhoff diffraction theory.The algorithm consists mainly of two parts. The first one exploits the VXI ray-tracing

A. Peterzol; J. Berthier; P. Duvauchelle; C. Ferrero; D. Babot

2007-01-01

329

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

330

Direct, object brightness estimation from atmospheric turbulence degraded images using a new high-speed, modified phase diversity method  

Microsoft Academic Search

The well known phase diversity technique has long been used as a premier passive imaging method to mitigate the degrading effects of atmospheric turbulence on incoherent optical imagery. Typically, an iterative, slow method is applied that uses the Zernike basis set and 2-D Fourier transforms in the reconstruction process. In this paper, we demonstrate a direct method for estimating the

William W. Arrasmith

2008-01-01

331

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

332

Subcellular Biochemical Investigation of Purkinje Neurons Using Synchrotron Radiation Fourier Transform Infrared Spectroscopic Imaging with a Focal Plane Array Detector  

PubMed Central

Coupling Fourier transform infrared spectroscopy with focal plane array detectors at synchrotron radiation sources (SR-FTIR-FPA) has provided a rapid method to simultaneously image numerous biochemical markers in situ at diffraction limited resolution. Since cells and nuclei are well resolved at this spatial resolution, a direct comparison can be made between FTIR functional group images and the histology of the same section. To allow histological analysis of the same section analyzed with infrared imaging, unfixed air-dried tissue sections are typically fixed (after infrared spectroscopic analysis is completed) via immersion fixation. This post fixation process is essential to allow histological staining of the tissue section. Although immersion fixation is a common practice in this filed, the initial rehydration of the dehydrated unfixed tissue can result in distortion of subcellular morphology and confound correlation between infrared images and histology. In this study, vapor fixation, a common choice in other research fields where postfixation of unfixed tissue sections is required, was employed in place of immersion fixation post spectroscopic analysis. This method provided more accurate histology with reduced distortions as the dehydrated tissue section is fixed in vapor rather than during rehydration in an aqueous fixation medium. With this approach, accurate correlation between infrared images and histology of the same section revealed that Purkinje neurons in the cerebellum are rich in cytosolic proteins and not depleted as once thought. In addition, we provide the first direct evidence of intracellular lactate within Purkinje neurons. This highlights the significant potential for future applications of SR-FTIR-FPA imaging to investigate cellular lactate under conditions of altered metabolic demand such as increased brain activity and hypoxia or ischemia.

2013-01-01

333

Subcellular biochemical investigation of purkinje neurons using synchrotron radiation fourier transform infrared spectroscopic imaging with a focal plane array detector.  

PubMed

Coupling Fourier transform infrared spectroscopy with focal plane array detectors at synchrotron radiation sources (SR-FTIR-FPA) has provided a rapid method to simultaneously image numerous biochemical markers in situ at diffraction limited resolution. Since cells and nuclei are well resolved at this spatial resolution, a direct comparison can be made between FTIR functional group images and the histology of the same section. To allow histological analysis of the same section analyzed with infrared imaging, unfixed air-dried tissue sections are typically fixed (after infrared spectroscopic analysis is completed) via immersion fixation. This post fixation process is essential to allow histological staining of the tissue section. Although immersion fixation is a common practice in this filed, the initial rehydration of the dehydrated unfixed tissue can result in distortion of subcellular morphology and confound correlation between infrared images and histology. In this study, vapor fixation, a common choice in other research fields where postfixation of unfixed tissue sections is required, was employed in place of immersion fixation post spectroscopic analysis. This method provided more accurate histology with reduced distortions as the dehydrated tissue section is fixed in vapor rather than during rehydration in an aqueous fixation medium. With this approach, accurate correlation between infrared images and histology of the same section revealed that Purkinje neurons in the cerebellum are rich in cytosolic proteins and not depleted as once thought. In addition, we provide the first direct evidence of intracellular lactate within Purkinje neurons. This highlights the significant potential for future applications of SR-FTIR-FPA imaging to investigate cellular lactate under conditions of altered metabolic demand such as increased brain activity and hypoxia or ischemia. PMID:23638613

Hackett, Mark J; Borondics, Ferenc; Brown, Devin; Hirschmugl, Carol; Smith, Shari E; Paterson, Phyllis G; Nichol, Helen; Pickering, Ingrid J; George, Graham N

2013-07-17

334

Quantitative Fourier Domain Optical Coherence Tomography Imaging of the Ocular Anterior Segment  

NASA Astrophysics Data System (ADS)

Clinical imaging within ophthalmology has had transformative effects on ocular health over the last century. Imaging has guided clinicians in their pharmaceutical and surgical treatments of macular degeneration, glaucoma, cataracts and numerous other pathologies. Many of the imaging techniques currently used are photography based and are limited to imaging the surface of ocular structures. This limitation forces clinicians to make assumptions about the underlying tissue which may reduce the efficacy of their diagnoses. Optical coherence tomography (OCT) is a non-invasive, non-ionizing imaging modality that has been widely adopted within the field of ophthalmology in the last 15 years. As an optical imaging technique, OCT utilizes low-coherence interferometry to produce micron-scale three-dimensional datasets of a tissue's structure. Much of the human body consists of tissues that significantly scatter and attenuate optical signals limiting the imaging depth of OCT in those tissues to only 1-2mm. However, the ocular anterior segment is unique among human tissue in that it is primarily transparent or translucent. This allows for relatively deep imaging of tissue structure with OCT and is no longer limited by the optical scattering properties of the tissue. This goal of this work is to develop methods utilizing OCT that offer the potential to reduce the assumptions made by clinicians in their evaluations of their patients' ocular anterior segments. We achieved this by first developing a method to reduce the effects of patient motion during OCT volume acquisitions allowing for accurate, three dimensional measurements of corneal shape. Having accurate corneal shape measurements then allowed us to determine corneal spherical and astigmatic refractive contribution in a given individual. This was then validated in a clinical study that showed OCT better measured refractive change due to surgery than other clinical devices. Additionally, a method was developed to combine the clinical evaluation of the iridocorneal angle through gonioscopy with OCT.

McNabb, Ryan Palmer

335

Fabry-Perot-based Fourier-transform hyperspectral imaging allows multi-labeled fluorescence analysis.  

PubMed

We demonstrate the ability of our hyperspectral imaging device, based on a scanning Fabry-Perot interferometer, to obtain a single hyper-image of a sample marked with different fluorescent molecules, and to unambiguously discriminate them by observing their spectral fingerprints. An experiment carried out with cyanines, fluorescein, and quantum dots emitting in the yellow-orange region, demonstrates the feasibility of multi-labeled fluorescence microscopy without the use of multiple filter sets or dispersive means. PMID:24922016

Pisani, Marco; Zucco, Massimo

2014-05-10

336

Time-resolved Fourier-transform infrared reflection study on photoinduced phase transition of tetrathiafulvalene-p-chloranil crystal  

NASA Astrophysics Data System (ADS)

We have measured temporal change of infrared reflection spectrum of ionic phase of tetrathiafulvalene- p-chloranil (TTF-CA) crystal induced by 10 ns pulsed laser excitation at 2.35 eV with using a step-scan Fourier-transform infrared spectrometer. The excitation reduced the magnitude of the a g -mode bands around 980 cm-1 and 1380 cm-1 and enhanced reflection intensity at 1630 cm-1. The time evolution of both the a g -mode changes and the enhancement at 1630 cm-1 are described by the sum of two decay components: one decayed within 2 ?s and the other showed very gradual decay within the time range used in the present study. The fractional changes of reflectivity for the fast decay components were almost identical for all a g modes. The 1630 cm-1 enhancement can be ascribed to the carbonyl stretching vibration of CA. The position of this peak shifts slightly to low-wavenumber side from the CA peak of the neutral phase in thermal equilibrium. Consequently, the fast decay component is ascribed to the photoinduced phase. The slow decay component is conceivably due to the metastable center formed by the excitation, because we could not resolve the spectral change corresponding to the slow component in the range between 1595 and 1660 cm-1, where the carbonyl stretching vibration of TTF-CA is observed. The degree of charge transfer of the photoinduced phase is evaluated to 0.52 ± 0.08 by comparing the peak position of the transient enhancement with those of the carbonyl stretching vibration modes in ionic and neutral phases in thermal equilibrium.

Nagahori, Aya; Kubota, Nobuhiko; Itoh, Chihiro

2013-03-01

337

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

338

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

339

Extending single-molecule microscopy using optical fourier processing.  

PubMed

This article surveys the recent application of optical Fourier processing to the long-established but still expanding field of single-molecule imaging and microscopy. A variety of single-molecule studies can benefit from the additional image information that can be obtained by modulating the Fourier, or pupil, plane of a widefield microscope. After briefly reviewing several current applications, we present a comprehensive and computationally efficient theoretical model for simulating single-molecule fluorescence as it propagates through an imaging system. Furthermore, we describe how phase/amplitude-modulating optics inserted in the imaging pathway may be modeled, especially at the Fourier plane. Finally, we discuss selected recent applications of Fourier processing methods to measure the orientation, depth, and rotational mobility of single fluorescent molecules. PMID:24745862

Backer, Adam S; Moerner, W E

2014-07-17

340

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

341

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

342

Phased Contrast X-Ray Imaging  

SciTech Connect

The Pacific Northwest National Laboratory is developing a range of technologies to broaden the field of explosives detection. Phased contrast X-ray imaging, which uses silicon gratings to detect distortions in the X-ray wave front, may be applicable to mail or luggage scanning for explosives; it can also be used in detecting other contraband, small-parts inspection, or materials characterization.

Erin Miller

2010-02-01

343

X-Ray Imaging with Phase Contrast  

NASA Astrophysics Data System (ADS)

The easiest way to obtain X-ray images of the internal structure of condensed objects is to register projections on an area detector like a photographic plate or a CCD and analyze the intensity of the transmitted beam. In such an arrangement the main cause of structures seen on the image is usually absorption contrast which scales with Z(Z/E)m where Z is atomic number, E is X-ray energy, and m ~ 2.5 to 3.5. Hence for light elements (which often are of main importance in the medical field) absorption contrast is quite small and sometimes unspecific compared to contrast caused by X-ray phase shift which scales with Z/E. In recent years various methods capable of registering X-ray phase shift have been developed, which include double crystal topography, X-ray interferometry, in-line phase-contrast imaging, the use of Talbot-mode grid devices, and others. A survey of existing approaches and examples of recent results will be given. -An important aspect in the application of X-ray imaging in the medical field is the amount of unavoidable irradiation dose to be applied to the patient under investigation. There is some hope that in the future, with a suitable phase-contrast method, the dose can be lowered.

Bonse, Ulrich; Beckmann, Felix

2010-04-01

344

Estimation of Motions in Color Image Sequences Using Hypercomplex Fourier Transforms  

Microsoft Academic Search

Although the motion estimation problem has been extensively studied, most of the proposed estimation approaches deal mainly with monochrome videos. The most usual way to apply them also in color image sequences is to process each color channel separately. A different, more sophisticated approach is to process the color channels in a ldquoholisticrdquo manner using quaternions, as proposed by Ell

Dimitrios S. Alexiadis; George D. Sergiadis

2009-01-01

345

Computer-aided classification of zoom-endoscopical images using Fourier filters  

Microsoft Academic Search

This paper describes an application of machine learning techniques and evolutionary algorithms to colon cancer diagnosis. We propose an automated classification system for endoscopical images, which is supposed to support physicians in making correct decisions. Classification is done according to the pit-pattern scheme, which defines two\\/six different classes based on the occurrence of patterns on the mucosa. All discriminative information

Michael Häfner; Leonhard Brunauer; Hannes Payer; Robert Resch; Alfred Gangl; Andreas Uhl; Friedrich Wrba; Andreas Vécsei

2010-01-01

346

Structure solution by minimal-function phase refinement and Fourier filtering. II. Implementation and applications.  

PubMed

The minimal function, R(psi), has been used to provide the basis for a new computer-intensive direct-methods procedure that shows potential for providing fully automatic routine solutions for structures in the 200-400 atom range. This procedure, which has been called shake-and-bake, is an iterative process in which real-space filtering is alternated with phase refinement using a technique that reduces the value of R(psi). It has been successfully tested using experimental data for a dozen known structures ranging in size from 25 to 317 atoms and crystallizing in a variety of space groups. The details of this procedure, the parameters used and the results of these applications are described. PMID:8166952

Weeks, C M; DeTitta, G T; Hauptman, H A; Thuman, P; Miller, R

1994-03-01

347

Phase coherence imaging of grained materials.  

PubMed

Ultrasound detection and evaluation of flaws in materials showing structural noise (austenitic steels, titanium alloys, composites, etc.) is difficult because of the low flaw-to-grain noise ratio. Much research has been performed looking for methods to improve flaw detection in grained materials. Many approaches require a cumbersome tuning process to select the correct parameter values or to use iterative techniques. In this work, the technique of phase coherence imaging is proposed to improve the flaw-to-grain noise ratio. The technique weights the output of a conventional beamformer with a coherence factor obtained from the aperture data phase dispersion. It can be simply implemented in real-time and it operates automatically, without needing any parameter adjustment. This paper presents the theoretical basis of phase coherence imaging to reduce grain noise, as well as experimental results that confirm the expected performance. PMID:21622056

Camacho, Jorge; Fritsch, Carlos

2011-05-01

348

High Speed Adaptive Ultrasonic Phased Array Imaging System.  

National Technical Information Service (NTIS)

The present invention relates to improvements in ultrasonic imaging; and, more particularly, to a high speed adaptive ultrasonic phased array imaging system. The system employs an image sharpening process which maximizes the average brightness of image te...

S. W. Smith G. E. Trahey

1988-01-01

349

Application of a Newly Built Chirped-Pulse Fourier Transform Microwave (CP-FTMW) Spectrometer to Study Biomolecules in the Gas Phase  

Microsoft Academic Search

Chirped-pulse Fourier Transform Microwave (CP-FTMW) spectroscopy is an exciting new technique that makes possible the recording of the complete microwave spectrum of a gas phase sample using a single 1 mus pulse. In this report, we will describe the recent introduction of a laser ablation nozzle for the study of small biomolecules using this technique. Potential applications to samples such

Ryan Bird; David Pratt; Justin Neill; Brooks Pate

2009-01-01

350

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

351

Imaging retinal degeneration in mice by combining Fourier domain optical coherence tomography and fluorescent scanning laser ophthalmoscopy  

NASA Astrophysics Data System (ADS)

Visualization of the internal structures of the retina is critical for clinical diagnosis and monitoring of pathology as well as for medical research investigating the root causes of retinal degeneration. Optical Coherence Tomography (OCT) is emerging as the preferred technique for non-contact sub-surface depth-resolved imaging of the retina. The high resolution cross sectional images acquired in vivo by OCT can be compared to histology to visually delineate the retinal layers. The recent demonstration of the significant sensitivity increase obtained through use of Fourier domain (FD) detection with OCT has been used to facilitate high speed scanning for volumetric reconstruction of the retina in software. The images acquired by OCT are purely structural, relying on refractive index differences in the tissue for contrast, and do not provide information on the molecular content of the sample. We have constructed a FDOCT prototype and combined it with a fluorescent Scanning Laser Ophthalmoscope (fSLO) to permit real time alignment of the field of view on the retina. The alignment of the FDOCT system to the specimen is crucial for the registration of measurements taken throughout longitudinal studies. In addition, fluorescence detection has been integrated with the SLO to enable the en face localization of a molecular contrast signal, which is important for retinal angiography, and also for detection of autofluorescence associated with some forms of retinal degeneration, for example autofluorescence lipofuscin accumulations are associated with Stargardt's Macular Dystrophy. The integrated FD OCT/fSLO system was investigated for imaging the retina of the mice in vivo.

Hossein-Javaheri, Nima; Molday, Laurie L.; Xu, Jing; Molday, Robert S.; Sarunic, Marinko V.

2009-02-01

352

Phase and amplitude phase restoration in synthetic aperture radar imaging.  

PubMed

Methods for addressing two types of multiplicative noise in synthetic aperture radar (SAR) imaging are presented. The authors consider a multiplicative noise with a real phase (i.e. the SAR signal's phase is contaminated but its amplitude is uncorrupted) that possesses unknown functional characteristics with respect to the radar signal's temporal frequencies. A perturbation solution for phase reconstruction from amplitude is developed from a wave equation governing the SAR signal and a Riccati equation that relates the amplitude and phase functions of the SAR signal. This solution is converted into a noniterative analytical solution in terms of the moments and powers of the log amplitude function. Next, the authors consider a multiplicative noise with a complex phase (i.e. both the amplitude and phase of the SAR signal are contaminated) that varies linearly with respect to the radar signal's temporal frequencies. The two wave equations governing the SAR signal at two temporal frequencies of the radar signal are combined to derive a method to reconstruct the complex phase error function. PMID:18296157

Soumekh, M; Choi, J H

1992-01-01

353

Quantitative analysis of collagen fiber organization in injured tendons using Fourier transform-second harmonic generation imaging.  

PubMed

Fourier transform-second harmonic generation (FT-SHG) imaging is used as a technique for evaluating collagenase-induced injury in horse tendons. The differences in collagen fiber organization between normal and injured tendon are quantified. Results indicate that the organization of collagen fibers is regularly oriented in normal tendons and randomly organized in injured tendons. This is further supported through the use of additional metrics, in particular, the number of dark (no/minimal signal) and isotropic (no preferred fiber orientation) regions in the images, and the ratio of forward-to-backward second-harmonic intensity. FT-SHG microscopy is also compared with the conventional polarized light microscopy and is shown to be more sensitive to assessing injured tendons than the latter. Moreover, sample preparation artifacts that affect the quantitative evaluation of collagen fiber organization can be circumvented by using FT-SHG microscopy. The technique has potential as an assessment tool for evaluating the impact of various injuries that affect collagen fiber organization. PMID:21164843

Sivaguru, Mayandi; Durgam, Sushmitha; Ambekar, Raghu; Luedtke, David; Fried, Glenn; Stewart, Allison; Toussaint, Kimani C

2010-11-22

354

Rapid and sensitive screening of 17?-estradiol estrogenicity using Fourier transform infrared imaging spectroscopy (FT-IRIS).  

PubMed

It is important to develop rapid and sensitive screening assays to assess the biological effects of emerging contaminants. In this contribution, the ability to determine the molecular level effects of 17?-estradiol on single MCF-7 cells using Fourier transform infrared imaging spectroscopy (FT-IRIS) was investigated. The use of FT-IRIS enabled subcellular imaging of the cells and determination of a dose dependent response in mucin concentration at 24 and 48 h of incubation. The 48 h increase in mucin was comparable to increases in cellular proliferation (Pearson R = 0.978). The EC50 values for the E-screen and FT-IRIS assays were 2.29 and 2.56 ppt, respectively, indicating that the molecular changes, which are observed at the single cell level using FT-IRIS, are reflective of physiological changes that are observed as the cell population responds to 17ß-estradiol. The FT-IRIS method, when combined with principal component analysis, enabled differentiation and grouping of cells exposed to varying concentrations of 17ß-estradiol. The FT-IRIS method shows potential to be used as a rapid and sensitive screening technique for the detection of biological responses to different emerging contaminants in relevant cells or tissues. PMID:24650306

Johnson, Candice M; Pleshko, Nancy; Achary, Mohan; Suri, Rominder P S

2014-04-15

355

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

PubMed Central

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 =CH stretching mode at 3012 cm?1. The axonal, dendritic, and somatic layers of the hippocampus were examined in the mice at 13 weeks, 24 weeks, 40 weeks and 56 weeks old. Results showed that lipid unsaturation in the axonal layer is 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, Andreana C.; Kretlow, Ariane; Miller, Lisa M.

2010-01-01

356

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

357

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

PubMed Central

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 ?1 × 10–8 mbar vacuum. The range of motion is set to 100 mm × 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; Smith, Donald F.; Chargin, David A.; Ivanov, Sergei; Lin, Tzu-Yung; Heeren, Ron M. A.; O'Connor, Peter B.

2011-01-01

358

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

NASA Astrophysics Data System (ADS)

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 ~1 × 10-8 mbar vacuum. The range of motion is set to 100 mm × 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; Smith, Donald F.; Chargin, David A.; Ivanov, Sergei; Lin, Tzu-Yung; Heeren, Ron M. A.; O'Connor, Peter B.

2011-05-01

359

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

360

Diffusion-weighted imaging in the prostate: an apparent diffusion coefficient comparison of half-Fourier acquisition single-shot turbo spin-echo and echo planar imaging.  

PubMed

Prostate cancer detection using diffusion-weighted imaging is highly affected by the accuracy of the apparent diffusion coefficient (ADC) values in an image. Echo planar imaging (EPI) is a fast sequence commonly used for diffusion imaging but has inherent magnetic susceptibility and chemical shift artefacts associated. A diffusion sequence that is less affected by these artefacts is therefore advantageous. The half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence was chosen. The diffusion sequences were compared in image quality, repeatability of the ADC value and the effect on the ADC value with varied b values. Eight volunteers underwent three scans of each sequence, on a 1.5-T Siemens system, using b values of 0, 150, 300, 450, 600, 750, 900 and 1000 s/mm(2). ADC maps were created to address the reproducibility of the ADC value when using two b values compared to eight b values. The ADC value using all b values with the HASTE sequence gave the best performance in all tested categories. Both sequences gave significantly different ADC mean values for two b values compared to when using eight b values (P<.05) suggesting larger error is present when using two b values. HASTE was shown to be an improvement over EPI in terms of repeatability, signal variation within a region of interest and standard deviation over the volunteer set. The improved accuracy of the ADC value in the HASTE sequence makes it potentially a more sensitive tumor detection technique. PMID:22055748

Babourina-Brooks, Ben; Cowin, Gary J; Wang, Deming

2012-02-01

361

Toward Fourier interferometry fluorescence excitation/emission imaging of malignant cells combined with photoacoustic microscopy  

NASA Astrophysics Data System (ADS)

Dual excitation fluorescence imaging has been used as a first step towards multi-wavelength excitation/emission fluorescence spectral imaging. Target cells are transformed keratinocytes, and other osteosarcoma, human breast and color cancer cells. Mitochondrial membrane potential probes, e.g. TMRM (tetramethylrhodamine methyl ester), Mitotracker Green (Molecular Probes, Inc., Eugene OR,USA) and a recently synthesized mitochondrial oxygen probe, [PRE,P1"- pyrene butyl)-2-rhodamine ester] allow dual excitation in the UV plus in teh blue-green spectral regions. Also, using the natural endogenous probe NAD(P)H, preliminary results indicate mitochondrial responses to metabolic challenges (e.g. glucose addition), plus changes in mitochonrial distribution and morphology. In terms of application to biomedicine (for diagnostiscs, prognostsics and drug trials) three parameters have been selected in addition to the natural probe NAD(P)H, i.e. vital fluorescence probing of mitochondria, lysosomes and Golgi apparatus. It is hoped that such a multiparameter approach will allow malignant cell characterization and grading. A new area being introduced is the use of similar methodology for biotechnical applications such as the study of the hydrogen-producing alga Chlamydomonas Reinhardtii, and possible agricultural applications, such as Saccharomyces yeast for oenology. Complementation by Photoacoustic Microscopy is also contemplated, to study the internal conversion component which follows the excitation by photons.

Kohen, Elli; Hirschberg, Joseph G.; Berry, John P.; Ozkutuk, Nuri; Ornek, Ceren; Monti, Marco; Leblanc, Roger M.; Schachtschabel, Dietrich O.; Haroon, Sumaira

2003-10-01

362

Image reconstruction algorithm for recovering high-frequency information in parallel phase-shifting digital holography [Invited].  

PubMed

We propose an image reconstruction algorithm for recovering high-frequency information in parallel phase-shifting digital holography. The proposed algorithm applies three kinds of interpolations and generates three different kinds of object waves. A Fourier transform is applied to each object wave, and the spatial-frequency domain is divided into 3×3 segments for each Fourier-transformed object wave. After that the segment in which interpolation error is the least among the segments having the same address of the segment in the spatial-frequency domain is extracted. The extracted segments are combined to generate an information-enhanced spatial-frequency spectrum of the object wave, and after that the formed spatial-frequency spectrum is inversely Fourier transformed. Then the high-frequency information of the reconstructed image is recovered. The effectiveness of the proposed algorithm was verified by a numerical simulation and an experiment. PMID:23292396

Xia, Peng; Shimozato, Yuki; Tahara, Tatsuki; Kakue, Takashi; Awatsuji, Yasuhiro; Nishio, Kenzo; Ura, Shogo; Kubota, Toshihiro; Matoba, Osamu

2013-01-01

363

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

364

Matrix-free mass spectrometric imaging using laser desorption ionisation Fourier transform ion cyclotron resonance mass spectrometry  

PubMed Central

Mass spectrometry imaging (MSI) is a powerful tool in metabolomics and proteomics for the spatial localization and identification of pharmaceuticals, metabolites, lipids, peptides and proteins in biological tissues. However, sample preparation remains a crucial variable in obtaining the most accurate distributions. Common washing steps used to remove salts, and solvent-based matrix application, allow analyte spreading to occur. Solvent-free matrix applications can reduce this risk, but increase the possibility of ionisation bias due to matrix adhesion to tissue sections. We report here the use of matrix-free MSI using laser desorption ionisation performed on a 12 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. We used unprocessed tissue with no post-processing following thaw-mounting on matrix-assisted laser desorption ionisation (MALDI) indium-tin oxide (ITO) target plates. The identification and distribution of a range of phospholipids in mouse brain and kidney sections are presented and compared with previously published MALDI time-of-flight (TOF) MSI distributions. Copyright © 2011 John Wiley & Sons, Ltd.

Goodwin, Richard J A; Pitt, Andrew R; Harrison, David; Weidt, Stefan K; Langridge-Smith, Pat R R; Barrett, Michael P; Logan Mackay, C

2011-01-01

365

Matrix-free mass spectrometric imaging using laser desorption ionisation Fourier transform ion cyclotron resonance mass spectrometry.  

PubMed

Mass spectrometry imaging (MSI) is a powerful tool in metabolomics and proteomics for the spatial localization and identification of pharmaceuticals, metabolites, lipids, peptides and proteins in biological tissues. However, sample preparation remains a crucial variable in obtaining the most accurate distributions. Common washing steps used to remove salts, and solvent-based matrix application, allow analyte spreading to occur. Solvent-free matrix applications can reduce this risk, but increase the possibility of ionisation bias due to matrix adhesion to tissue sections. We report here the use of matrix-free MSI using laser desorption ionisation performed on a 12 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. We used unprocessed tissue with no post-processing following thaw-mounting on matrix-assisted laser desorption ionisation (MALDI) indium-tin oxide (ITO) target plates. The identification and distribution of a range of phospholipids in mouse brain and kidney sections are presented and compared with previously published MALDI time-of-flight (TOF) MSI distributions. PMID:21416534

Goodwin, Richard J A; Pitt, Andrew R; Harrison, David; Weidt, Stefan K; Langridge-Smith, Pat R R; Barrett, Michael P; Logan Mackay, C

2011-04-15

366

Imaging Fourier transform spectrometer with photoconductive detector arrays: an application to the AKARI far-infrared instrument  

NASA Astrophysics Data System (ADS)

We have developed an imaging Fourier transform spectrometer (iFTS) for space-based far-infrared astronomical observations. The iFTS employs newly developed photoconductive detector arrays with a capacitive transimpedance amplifier, which makes the iFTS a completely unique instrument. The iFTS 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 iFTS had worked properly in the space environment as well as in laboratory for more than one year before liquid helium ran out on August 26, 2007. The iFTS was operated nearly six hundreds of pointed observations. More than one hundred hours of astronomical observations and almost the same amount of time for calibrations have been carried out in the mission life. 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 iFTS and interesting phenomena related to FTSs using photoconductive detectors are described, and the calibration strategy of the iFTS is discussed briefly.

Kawada, Mitsunobu; Takahashi, Hidenori; Murakami, Noriko; Okada, Yoko; Yasuda, Akiko; Ootsubo, Toshifumi; Kaneda, Hidehiro; Matsuo, Hiroshi; Matsuura, Shuji; Shirahata, Mai; Doi, Yasuo; Fujiwara, Mikio; Yamamura, Issei; Nakagawa, Takao; Shibai, Hiroshi

2008-08-01

367

Optique de Fourier  

NASA Astrophysics Data System (ADS)

L'optique de Fourier doit son nom à l'emploi délibéré de la transformation de Fourier dans la représentation de phénomènes fondés sur la diffraction de la lumière1. Inscrite dans les limites d'une théorie scalaire, elle est, traditionnellement, liée à l'optique cohérente et les sujets développés dans ce livre se rattachent à ce thème. Le domaine et les applications ussuelles de l'optique de Fourier concernent la formation des images, la résolution des instruments d'optique, le traitement du signal optique, l'holographie, le transfert de la cohérence. Nous verrons comment y inclure la théorie des résonateurs optiques et celle des faisseaux gaussiens; celle de la dispersion dans les fibres optiques. L'optique de Fourier fournit ainsi un cadre général à la modélisation d'un grand nombre de phénomènes optiques2.

Pellat-Finet, Pierre

368

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

369

Recent Advances in X-ray Phase Imaging  

Microsoft Academic Search

Since the middle of the 1990s, X-ray phase imaging including phase tomography has been attracting increasing attention. The advantage of X-ray phase imaging is that an extremely high sensitivity is achieved for weak-absorbing materials, such as biological soft tissues, which generate a poor contrast by conventional methods. Medical and biological imaging is the main target of X-ray phase imaging, and

Atsushi Momose

2005-01-01

370

Entangled-photon imaging of a phase object  

Microsoft Academic Search

Previous experimental demonstrations of entangled-photon imaging have been limited to imaging amplitude objects. We report the first experimental results of entangled-photon imaging of a phase object in a reflection configuration.

A. F. Abouraddy; P. R. Stone; A. V. Sergienko; B. E. A. Saleh; M. C. Teich

2003-01-01

371

Turbulence Mitigation in Phase-Conjugated Two-Photon Imaging  

Microsoft Academic Search

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

2011-01-01

372

Holography and phase retrieval in terahertz imaging  

NASA Astrophysics Data System (ADS)

In this paper, we present review and latest results obtained in the scope of terahertz holographic and other methods for phase retrieval in terahertz imaging. Not only accurate change of amplitude, but also rigorous phase retrieval is essential for precise calculation of optical parameters of the samples in terahertz range. Pulse terahertz holography introduced some years ago shows itself as perfect method for overall-object phase retrieval technique, but in the same time it allows measurement with low signal to noise that leads to less precise derivation of sample optical parameters. And certainly just point-by-point terahertz time-domain spectroscopy provides the most precise information of sample phase, but it is rather time consuming and has low spatial resolution as well. The other possible way assumes, in contrary to pulse terahertz holography and spectroscopy, using narrow-band continuous terahertz source, which tunability might also make the measurement process easier. And diffraction patterns registered with microbolometer array or any other terahertz intensity sensor placed at several different distances from the object and/or taken for several different terahertz frequencies are used for phase retrieval in this case. We present both numerical predictions and experimental results for the proposed methods, estimate the achievable spatial and other limits of the techniques and compare them to the others used in different spectral ranges.

Petrov, Nikolay V.; Gorodetsky, Andrei A.; Bespalov, Victor G.

2013-09-01

373

Phased Array Feed Calibration, Beamforming, and Imaging  

NASA Astrophysics Data System (ADS)

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.; Fisher, J. Richard; Norrod, Roger D.

2010-03-01

374

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

375

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

376

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.

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

2012-01-01

377

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

378

Analysis of image noise in 3D cone-beam CT: spatial and Fourier domain approaches under conditions of varying stationarity  

NASA Astrophysics Data System (ADS)

The statistical properties of medical images are central in characterizing the performance of imaging systems. The noise in cone-beam CT (CBCT) is often characterized using Fourier-based metrics, such as the 3D noise-power spectrum (NPS). Under a stationarity assumption, the NPS provides a complete representation of the covariance of the images, since the covariance matrix of the Fourier transform of the image is diagonal. In practice, such assumptions are obeyed to varying degrees. The objective of this work is to investigate the degree to which such assumptions apply in CBCT and to experimentally characterize the NPS and off-diagonal elements under a range of experimental conditions. A benchtop CBCT system was used to acquire 3D image reconstructions of various objects (air and a water cylinder) across a range of experimental conditions that could affect stationarity (bowtie filter and dose). We test the stationarity assumption under such varying experimental conditions using both spatial and frequency domain measures of stationarity. The results indicate that experimental conditions affect the degree of stationarity and that under some imaging conditions, local descriptions of the noise need to be developed to appropriately describe CBCT images. The off-diagonal elements of the DFT covariance matrix may not always be ignored.

Pineda, Angel R.; Siewerdsen, Jeffrey H.; Tward, Daniel J.

2008-04-01

379

Comparison of retinal thickness by Fourier-domain optical coherence tomography and OCT retinal image analysis software segmentation analysis derived from Stratus optical coherence tomography images  

NASA Astrophysics Data System (ADS)

Purpose: To compare thickness measurements between Fourier-domain optical coherence tomography (FD-OCT) and time-domain OCT images analyzed with a custom-built OCT retinal image analysis software (OCTRIMA). Methods: Macular mapping (MM) by StratusOCT and MM5 and MM6 scanning protocols by an RTVue-100 FD-OCT device are performed on 11 subjects with no retinal pathology. Retinal thickness (RT) and the thickness of the ganglion cell complex (GCC) obtained with the MM6 protocol are compared for each early treatment diabetic retinopathy study (ETDRS)-like region with corresponding results obtained with OCTRIMA. RT results are compared by analysis of variance with Dunnett post hoc test, while GCC results are compared by paired t-test. Results: A high correlation is obtained for the RT between OCTRIMA and MM5 and MM6 protocols. In all regions, the StratusOCT provide the lowest RT values (mean difference 43 +/- 8 ?m compared to OCTRIMA, and 42 +/- 14 ?m compared to RTVue MM6). All RTVue GCC measurements were significantly thicker (mean difference between 6 and 12 ?m) than the GCC measurements of OCTRIMA. Conclusion: High correspondence of RT measurements is obtained not only for RT but also for the segmentation of intraretinal layers between FD-OCT and StratusOCT-derived OCTRIMA analysis. However, a correction factor is required to compensate for OCT-specific differences to make measurements more comparable to any available OCT device.

Tátrai, Erika; Ranganathan, Sudarshan; Ferencz, Mária; Debuc, Delia Cabrera; Somfai, Gábor Márk

2011-05-01

380

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

381

Medical Applications of X-Ray Phase Contrast Imaging  

Microsoft Academic Search

We report the use of an inline holographic x-ray imaging technique for medical purposes. In contrast to conventional x-ray radiography a phase-sensitive x-ray imaging method is employed. This phase-contrast x-ray imaging is fundamentally different from conventional x-ray shadowgraphy because the mechanism of image formation does not rely on differential absorption by tissues. Instead, x-ray beams undergo differential phase shifts in

Christoph Rose-Petruck; Christopher Laperle; Theron Hamilton; Guohua Cao; Philip Wintermeyer; Gerald Diebold; Jack Wands

2007-01-01

382

Reactions of metal ions and their clusters in the gas phase using laser ionization: Fourier transform mass spectrometry. Progress report, February 1, 1993--January 31, 1994  

SciTech Connect

This report focuses on progress in seven areas: (1) Gas-Phase Reactions of Fe(Benzyne){sup +} with Simple Alkyl Halides; (2) Photodissociation and Collision-Induced Dissociation of Molecular Ions From Methylphenol and Chloromethylphenol; (3) Isotopomer Differentiation Using Metal Ion Chemical Ionization Reagents; (4) Multiple Excitation Collisional Activation (MECA) in Fourier Transform Mass Spectrometry; (5) Chemistry of Fe{sup +}-Arene Ions with Halobenzenes; (6) Gas-Phase Photodissociaton Study of Ag(Benzene){sup +} and Ag(Toluene){sup +}; and (7) Reactivity of Ti{sup 2+} and V{sup 2+} with Small Alkanes.

Freiser, B.S.

1993-09-01

383

CHARACTERIZATION OF AMBIENT PM2.5 AEROSOL AT A SOUTHEASTERN US SITE: FOURIER TRANSFORM INFRARED ANALYSIS OR PARTICLE PHASE  

EPA Science Inventory

During a field study in the summer of 2000 in the Research Triangle Park (RTP), aerosol samples were collected using a five stage cascade impactor and subsequently analyzed using Fourier Transform Infrared Spectroscopy (FTIR). The impaction surfaces were stainless steel disks....

384

Acoustically modulated x-ray phase contrast imaging  

Microsoft Academic Search

We report the use of ultrasonic radiation pressure with phase contrast x-ray imaging to give an image proportional to the space derivative of a conventional phase contrast image in the direction of propagation of an ultrasonic beam. Intense ultrasound is used to exert forces on objects within a body giving displacements of the order of tens to hundreds of microns.

Theron J. Hamilton; Claude J. Bailat; Christoph Rose-Petruck; Gerald J. Diebold

2004-01-01

385

MRI of intracranial sinovenous thrombosis: The role of phase imaging  

SciTech Connect

Conventional spin-echo magnetic resonance (MR) imaging of venous thrombosis is complicated by the variable appearance produced by the stage of blood clot degradation and velocity of blood flow. Phase MR imaging is a simple method based primarily on whether protons are stationary or moving. A case of superior sagittal sinus thrombosis demonstrates the utility of phase imaging.

Nadel, L.; Braun, I.F.; Kraft, K.A.; Jensen, M.E.; Laine, F.J. (Medical College of Virginia, Richmond (USA))

1990-01-01

386

X-Ray Phase Imaging for Breast Cancer Detection.  

National Technical Information Service (NTIS)

Aiming to develop a low-dose and quantitative x-ray phase imaging technique for facilitating breast cancer detection, in this project we designed and built a high-voltage x-ray imaging prototype that enables x-ray phase imaging and radiation dose reductio...

X. Wu

2012-01-01

387

Reversible ischemia in severe stress Tc-99m-Sestamibi perfusion defects: Assessment with gated tomographic polar map Fourier amplitude and amplitude/perfusion ratio images and correlation with resting images  

SciTech Connect

Reversible ischemia in myocardial segments with severe hypoperfusion ({le}50% of normal activity) on stress Tc-99m-Sestamibi (MIBI) images was assessed with ECG-gated tomographic (GSPECT) indices of myocardial thickening, as reflected by an increase in regional count density during systole. GSPECT bullseye plots were generated for each of 8 frames acquired after stress MIBI injection in 39 patients with coronary artery disease and at least one severe perfusion defect on summed SPECT images. Using first harmonic Fourier amplitude (AMP) and AMP to perfusion ratio (APR) images, regional myocardial systolic thickening was assessed using a 5-segment model, scored 0 to 3, for absent, minimal, mildly reduced or normal thickening. These data were regionally compared with defect reversibility assessed using a separate-day or a preceding same-day resting MIBI injection images, in which these segments were scored from 0 to 3 for absent, minimal, partial or complete defect reversibility. Of 91 severe stress defects, 16 showed absent, 18 minimal, 43 partial, and 14 complete reversibility on resting images. Both AMP and APR scores were in statistically significant agreement (p=.0218 and .0006) with resting image reversibility grades, with 79% (p=.0324) and 86% (p=.0001) agreement on the presence of reversibility on resting imaging, respectively. AMP correctly identified 89% of the reversibility defects on rest images, while the APR identified 99% (p=.0248 vs. AMP). On analysis of segment scores, the AMP slightly underestimated the degree of rest image reversibility (p=.0235), while APR images indicated more reversibility thin did resting images (p=.0092). In conclusion, GSPECT MIBI bullseye Fourier AMP images correlate well with the pattern of reversibility on resting MIBI in severe stress perfusion defects. When indexed for the degree of hypoperfusion, the Fourier images depict a greater degree of defect reversibility than resting MIBI images.

Williams, K.A.; Taillon, L.A. [Univ. of Chicago, IL (United States)

1994-05-01

388

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

389

Full range polarization-sensitive Fourier domain optical coherence tomography  

Microsoft Academic Search

A swept source based polarization-sensitive Fourier domain optical coherence tomography (FDOCT) system was developed that can acquire the Stokes vectors, polarization diversity intensity and birefringence images in biological tissue by reconstruction of both the amplitude and phase terms of the interference signal. The Stokes vectors of the reflected and backscattered light from the sample were determined by processing the analytical

Jun Zhang; J. Stuart Nelson; Woonggyu Jung; Zhongping Chen

2004-01-01

390

Near-field x-ray phase contrast imaging and phase retrieval algorithm  

Microsoft Academic Search

Theoretical analyses of x-ray diffraction phase contrast imaging and near field phase retrieval method are presented. A new variant of the near field intensity distribution is derived with the optimal phase imaging distance and spatial frequency of object taken into account. Numerical examples of phase retrieval using simulated data are also given. On the above basis, the influence of detecting

Hua-Feng Zhu; Hong-Lan Xie; Hong-Yi Gao; Jian-Wen Chen; Ru-Xin Li; Zhi-Zhan Xu

2005-01-01

391

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

PubMed

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

392

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

393

3D pupil plane imaging of opaque targets  

Microsoft Academic Search

Correlography is a technique that allows image formation from non-imaged speckle patterns via their relationship to the autocorrelation of the scene. Algorithms designed to form images from this type of data represent a particular type of phase retrieval algorithm since the autocorrelation function is related to the Fourier magnitude of the scene but not the Fourier phase. Methods for forming

Stephen C. Cain

2010-01-01

394

On X-ray phase retrieval from polychromatic images  

Microsoft Academic Search

Methods for quantitative phase retrieval from polychromatic Fresnel-region images obtained at a fixed position along the optic axis are proposed. These methods eliminate the need for collecting images at multiple distances from the object, thus possibly simplifying the experimental procedure and allowing simultaneous recording of the image intensity data. Applications to hard X-ray in-line phase-contrast imaging with the use of

T. E. Gureyev; S. W. Wilkins

1998-01-01

395

Phase noise analysis of two wavelength coherent imaging system.  

PubMed

Two wavelength coherent imaging is a digital holographic technique that offers several advantages over conventional coherent imaging. One of the most significant advantages is the ability to extract 3D target information from the phase contrast image at a known difference frequency. However, phase noise detracts from the accuracy at which the target can be faithfully identified. We therefore describe a method for relating phase noise to the correlation of the image planes corresponding to each wavelength, among other parameters. The prediction of the phase noise spectrum of a scene will aid in determining our ability to reconstruct the target. PMID:24514640

Dapore, Benjamin R; Rabb, David J; Haus, Joseph W

2013-12-16

396

High-field fourier transform ion cyclotron resonance mass spectrometry for simultaneous trapping and gas-phase hydrogen\\/deuterium exchange of peptide ions  

Microsoft Academic Search

Gas-phase hydrogen\\/deuterium exchange of D2O with [M+H]+ ions of angiotensin II, angiotensin I, [Sar1]-angiotensin II, bradykinin, des-Arg1-bradykinin, des-Arg9-bradykinin, luteinizing hormone releasing hormone (LH-RH), and substance P has been examined by Fourier transform ion cyclotron\\u000a resonance mass spectrometry at 9.4 tesla. Because the FTICR dynamic range increases quadratically with magnetic field, parent\\u000a ions from a mixture of several peptides may be

Michael A. Freitas; Christopher L. Hendrickson; Mark R. Emmett; Alan G. Marshall

1998-01-01

397

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.

2012-02-01

398

2D quaternion Fourier spectral analysis and its applications  

Microsoft Academic Search

Hypercomplex Fourier transforms based on quaternions have been used for gray and color image processing. In this paper, we present the relations between the quaternion Fourier spectral coefficients. Using these relations, we can separate the scalar and vector part of quaternion image for frequency domain and find the constraints of the Fourier spectral coefficients which the quaternion Fourier transform of

Ja-han Chang; Soo-chang Pei; Jian-jiun Ding

2004-01-01

399

Snake in Phase Domain: A Method for Boundary Detection of Objects in Phase Images  

Microsoft Academic Search

This paper presents a snake algorithm for boundary detection of objects in phase images. Since phase image is a modulo-2pi field, the proper gradient vector field (GVF) for snake dynamics should be taken from an unwrapped phase. This paper proposes a procedure to avoid such unwrapping by applying modulo-2pi gradient estimation. Performance assessment is conducted by comparing a boundary detection

Andriyan Bayu Suksmono; Astri Handayani; Akira Hirose

2006-01-01

400

Fourier volume rendering  

Microsoft Academic Search

In computer graphics we have traditionally rendered images of data sets specified spatially, Here, we present a volume rendering technique that operates on a frequency domain representa-tion of the data set and that efficiently generates line integral projections of the spatial data it represents, The motivation for this approach is that the Fourier Projection-Slice Theorem allows us to compute 2-D

Thomas Malzbender

1993-01-01

401

Phase error correction by phase differential algorithm for synthetic aperture imaging ladar  

NASA Astrophysics Data System (ADS)

During the signal acquisition for synthetic aperture imaging ladar, any phase error will deteriorate the phase-matched filtering results. The phase differential algorithm (PDA) is presented to correct the phase error. The quadratic spatial phase history can be reconstructed from the phase information submerged by the phase error from platform line-of-sight translation-vibration and nonlinear chirp. The theoretical modeling results and experimental results are presented.

Zhi, Ya'nan; Sun, Jianfeng; Hou, Peipei; Dai, Enwen; Zhou, Yu; Liu, Liren

2012-10-01

402

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.

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

2014-01-01

403

Thermal wave imaging with phase sensitive modulated thermography  

Microsoft Academic Search

A technique of thermal wave imaging with phase-sensitive modulated thermography ('thermal wave thermography') is described that combines the advantages of both the low-frequency CW modulation (providing phase angle information and a maximum depth range) and rapid scanning as it is used in the conventional thermographic imaging technique. Compared with the usual thermal wave techniques, the new technique provides an increased

G. Busse; D. Wu; W. Karpen

1992-01-01

404

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

405

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

406

Schlieren confocal microscopy for phase-relief imaging.  

PubMed

We demonstrate a simple phase-sensitive microscopic technique capable of imaging the phase gradient of a transparent specimen, based on the Schlieren modulation and confocal laser scanning microscopy (CLSM). The incident laser is refracted by the phase gradient of the specimen and excites a fluorescence plate behind the specimen to create a secondary illumination; then the fluoresence is modulated by a partial obstructor before entering the confocal pinhole. The quantitative relationship between the image intensity and the sample phase gradient can be derived. This setup is very easy to be adapted to current confocal setups, so that multimodality fluorescence/structure images can be obtained within a single system. PMID:24690716

Xie, Hao; Jin, Dayong; Yu, Junjie; Peng, Tong; Ding, Yichen; Zhou, Changhe; Xi, Peng

2014-03-01

407

Photothermal modulation of x-ray phase contrast images  

Microsoft Academic Search

The in-line x-ray phase-contrast imaging method relies on changes in index of refraction within a body to produce image contrast. In soft tissue, index of refraction variations arise from density changes so that phase contrast imaging provides a map of density gradients within a body. An intense, short pulse laser beam that is differentially absorbed by an object within a

Christopher M. Laperle; Guohua Cao; Theron J. Hamilton; Christoph Rose-Petruck; Gerald J. Diebold

2007-01-01

408

Multichannel far-infrared phase imaging for fusion plasmas  

SciTech Connect

A 20-channel far-infrared imaging interferometer system has been used to obtain single-shot density profiles in the UCLA Microtor tokamak. This system differs from conventional multichannel interferometers in that the phase distribution produced by the plasma is imaged onto a single, monolithic, integrated microbolometer linear detector array and provides significantly more channels than previous far-infrared interferometers. The system has been demonstrated to provide diffraction-limited phase images of dielectric targets.

Young, P.E.; Neikirk, D.P.; Tong, P.P.; Rutledge, D.B.; Luhmann N.C. Jr.

1985-01-01

409

Multivariate Analysis of Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopic Data to Confirm Phase Partitioning in Methacrylate-Based Dentin Adhesive  

PubMed Central

Water is ubiquitous in the mouths of healthy individuals and is a major interfering factor in the development of a durable seal between the tooth and composite restoration. Water leads to the formation of a variety of defects in dentin adhesives; these defects undermine the tooth-composite bond. Our group recently analyzed phase partitioning of dentin adhesives using high-performance liquid chromatography (HPLC). The concentration measurements provided by HPLC offered a more thorough representation of current adhesive performance and elucidated directions to be taken for further improvement. The sample preparation and instrument analysis using HPLC are, however, time-consuming and labor-intensive. The objective of this work was to develop a methodology for rapid, reliable, and accurate quantitative analysis of near-equilibrium phase partitioning in adhesives exposed to conditions simulating the wet oral environment. Analysis by Fourier transform infrared (FT-IR) spectroscopy in combination with multivariate statistical methods, including partial least squares (PLS) regression and principal component regression (PCR), were used for multivariate calibration to quantify the compositions in separated phases. Excellent predictions were achieved when either the hydrophobic-rich phase or the hydrophilic-rich phase mixtures were analyzed. These results indicate that FT-IR spectroscopy has excellent potential as a rapid method of detection and quantification of dentin adhesives that experience phase separation under conditions that simulate the wet oral environment.

Ye, Qiang; Parthasarathy, Ranganathan; Abedin, Farhana; Laurence, Jennifer S.; Misra, Anil; Spencer, Paulette

2014-01-01

410

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

411

The Asymmetric Pupil Fourier Wavefront Sensor  

NASA Astrophysics Data System (ADS)

This article 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, which 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

2013-04-01

412

Fourier transform infrared investigation of the effects of irradiation on the 19 and 30/sup 0/C phase transitions in polytetrafluoroethylene. [Gamma rays  

SciTech Connect

Fourier transform infrared spectroscopy has been used in conjunction with differential scanning calorimetric measurements to investigate the nature of molecular degradation and its effect on the phase transition temperatures in irradiated polytetrafluoroethylene (PTFE). Both the 19 and 30/sup 0/C transitions are observed to exhibit similar shifts to low temperatures upon irradiation. Infrared absorbance subtraction data from irradiated PTFE indicate a continual decrease in sample crystallinity accompanied by an increase in the number of free and bonded - COOH groups with increasing dose consistent with molecular degradation by chain scission. By comparing infrared band intensities on a number of irradiated PTFE samples with those from short chain perfluoro n-alkanes, it was determined that the overall reduction in chain length caused by irradiation was primarily responsible for the observed reduction in both phase transition temperatures.

Vanni, H.; Rabolt, J.F.

1980-03-01

413

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

414

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

415

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

PubMed

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