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Point Spread Function (point + spread_function)

Distribution by Scientific Domains

Medical Sciences	63%

Selected Abstracts

3423: Measurement of straylight

ACTA OPHTHALMOLOGICA, Issue 2010
HS GINIS
Purpose Straylight in the human eye is associated with low light intensities scattered at angles large compared to the part of the Point Spread Function that is governed by refractive error and aberrations. It is the purpose of this talk to summarise existing methods for the measurement of straylight in the human eye and to discuss new developments. Methods Among psychophysical techniques are the most well-established and studied methods. Optical techniques to date are limited by signal to noise as well as dynamic range considerations. Results Improvements in optical techniques involve the creation of the appropriate imaging conditions where scattered light intensity can be calculated based on the effects of scatter on the acquired image. Conclusion Psychophysical methods, that have been particularly successful, require specially designed optical schemes (for the presentation of the stimulus), a specific task and a suitable data analysis method. Optical techniques may benefit from refinements in these directions also. [source]

Optimizing the point spread function in phase-encoded magnetic resonance microscopy

CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2004
A.G. Webb
Abstract Three-dimensional phase-encoded magnetic resonance microscopy is the most promising method for obtaining images with isotropic spatial resolutions on the order of a few micrometers. The attainable spatial resolution is limited by the available gradient strength (Gmax) and the molecular self-diffusion coefficient (D) of the sample. In this study, numerical simulations in the microscopic-size regime are presented in order to show that for given values of Gmax and D, there exists an optimum number of phase-encoding steps that maximize the spatial resolution in terms of minimizing the full-width at half-maximum (FWHM) of the image point spread function (PSF). Unlike the case of "macroscopic" imaging, in which diffusion plays an insignificant role in determining spatial resolution, acquiring data beyond this optimal value actually degrades the image PSF. An alternative version of phase encoding, using a variable phase-encoding time rather than a variable gradient strength, is analyzed in terms of improvements in the image PSF and/or reductions in the data acquisition time for a given spatial resolution. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 22A: 25,36, 2004. [source]

Convergence analysis of blind image deconvolution via dispersion minimization

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 7 2006
C. Vural
Abstract A new non-linear adaptive filter called blind image deconvolution via dispersion minimization has recently been proposed for restoring noisy blurred images blindly. This is essentially a two-dimensional version of the constant modulus algorithm that is well known in the field of blind equalization. The two-dimensional extension has been shown capable of reconstructing noisy blurred images using partial a priori information about the true image and the point spread function in a variety of situations by means of simulations. This paper analyses the behaviour of the algorithm by investigating the static properties of the cost function and the dynamic convergence of the parameter estimates. The theoretical results are supported with computer simulations. Copyright © 2006 John Wiley & Sons, Ltd. [source]

A novel blind super-resolution technique based on the improved Poisson maximum a posteriori algorithm

INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 6 2002
Min-Cheng Pan
Abstract Image restoration has received considerable attention. In many practical situations, unfortunately, the blur is often unknown, and little information is available about the true image. Therefore, the true image is identified directly from the corrupted image by using partial or no information about the blurring process and the true image. In addition, noise will be amplified to induce severely ringing artifacts in the process of restoration. This article proposes a novel technique for the blind super-resolution, whose mechanism alternates between de-convolution of the image and the point spread function based on the improved Poisson maximum a posteriori super-resolution algorithm. This improved Poisson MAP super-resolution algorithm incorporates the functional form of a Wiener filter into the Poisson MAP algorithm operating on the edge image further to reduce noise effects and speed restoration. Compared with that based on the Poisson MAP, the novel blind super-resolution technique presents experimental results from 1-D signals and 2-D images corrupted by Gaussian point spread functions and additive noise with significant improvements in quality. © 2003 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 12, 239,246, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10032 [source]

Age and gender dependence of human cardiac phosphorus metabolites determined by SLOOP 31P MR spectroscopy

MAGNETIC RESONANCE IN MEDICINE, Issue 4 2006
Herbert Köstler
Abstract The aim of this study was to apply 31P magnetic resonance spectroscopy (MRS) using spatial localization with optimal point spread function (SLOOP) to investigate possible age and gender dependencies of the energy metabolite concentrations in the human heart. Thirty healthy volunteers (18 males and 12 females, 21,67 years old, mean = 40.7 years) were examined with the use of 31P-MRS on a 1.5 T scanner. Intra- and interobserver variability measures (determined in eight of the volunteers) were both 3.8% for phosphocreatine (PCr), and 4.7% and 8.3%, respectively, for adenosine triphosphate (ATP). High-energy phosphate (HEP) concentrations in mmol/kg wet weight were 9.7 ± 2.4 (age < 40 years, N = 16) and 7.7 ± 2.5 (age , 40 years, N = 14) for PCr, and 5.1 ± 1.0 (age < 40 years) and 4.1 ± 0.8 (age , 40 years) for ATP, respectively. Separated by gender, PCr concentrations of 9.2 ± 2.4 (men, N = 18) and 8.0 ± 2.8 (women, N = 12) and ATP concentrations of 4.9 ± 1.0 (men) and 4.2 ± 0.9 (women) were measured. A significant decrease of PCr and ATP was found for volunteers older than 40 years (P < 0.05), but the differences in metabolic concentrations between both sexes were not significant. In conclusion, age has a minor but still significant impact on cardiac energy metabolism, and no significant gender differences were detected. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source]

Natural linewidth chemical shift imaging (NL-CSI)

MAGNETIC RESONANCE IN MEDICINE, Issue 1 2006
Adil Bashir
Abstract The discrete Fourier transform (FT) is a conventional method for spatial reconstruction of chemical shifting imaging (CSI) data. Due to point spread function (PSF) effects, FT reconstruction leads to intervoxel signal leakage (Gibbs ringing). Spectral localization by imaging (SLIM) reconstruction was previously proposed to overcome this intervoxel signal contamination. However, the existence of magnetic field inhomogeneities creates an additional source of intervoxel signal leakage. It is demonstrated herein that even small field inhomogeneities substantially amplify intervoxel signal leakage in both FT and SLIM reconstruction approaches. A new CSI data acquisition strategy and reconstruction algorithm (natural linewidth (NL) CSI) is presented that eliminates effects of magnetic field inhomogeneity-induced intervoxel signal leakage and intravoxel phase dispersion on acquired data. The approach is based on acquired CSI data, high-resolution images, and magnetic field maps. The data are reconstructed based on the imaged object structure (as in the SLIM approach) and a reconstruction matrix that takes into account the inhomogeneous field distribution inside anatomically homogeneous compartments. Phantom and in vivo results show that the new method allows field inhomogeneity effects from the acquired MR signal to be removed so that the signal decay is determined only by the "natural" R2 relaxation rate constant (hence the term "natural linewidth" CSI). Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source]

A QSO host galaxy and its Ly, emission at z= 6.43,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
Tomotsugu Goto
ABSTRACT Host galaxies of highest redshift quasi-stellar objects (QSOs) are of interest; they provide us with a valuable opportunity to investigate physics relevant to the starburst,active galactic nuclei (AGN) connection at the earliest epoch of the Universe, with the most luminous black holes. Here, we report an optical detection of an extended structure around a QSO at z= 6.43 in deep z,- and zr -band images of the Subaru/Suprime-Cam. Our target is CFHQS J2329-0301 (z= 6.43), the highest redshift QSO currently known. We have carefully subtracted a point spread function (PSF) constructed using nearby stars from the images. After the PSF (QSO) subtraction, a structure in the z, band extends more than 4 arcsec on the sky (Re= 11 kpc), and, thus, is well resolved (16, detection). The PSF-subtracted zr -band structure is in a similar shape to that in the z, band, but less significant with a 3, detection. In the z, band, a radial profile of the QSO+host shows a clear excess over that of the averaged PSF in 0.8,3 arcsec radius. Since the z, band includes a Ly, emission at z= 6.43, we suggest the z, flux is a mixture of the host (continuum light) and its Ly, emission, whereas the zr -band flux is from the host. Through a SED modelling, we estimate 40 per cent of the PSF-subtracted z,-band light is from the host (continuum) and 60 per cent is from Ly, emission. The absolute magnitude of the host is M1450=,23.9 (cf. M1450=,26.4 for the QSO). A lower limit of the SFR(Ly,) is 1.6 M, yr,1 with stellar mass ranging from 6.2 × 108 to 1.1 × 1010 M, when 100 Myr of age is assumed. The detection shows that a luminous QSO is already harboured by a large, star-forming galaxy in the early Universe only after ,840 Myr after the big bang. The host may be a forming giant galaxy, co-evolving with a super-massive black hole. [source]

Very high contrast integral field spectroscopy of AB Doradus C: 9-mag contrast at 0.2 arcsec without a coronagraph using spectral deconvolution,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
Niranjan Thatte
ABSTRACT We present an extension of the spectral deconvolution (SD) method to achieve very high contrast at small inner working radii. We apply the method to the specific case of ground-based adaptive optics fed integral field spectroscopy (without a coronagraph). Utilizing the wavelength dependence of the Airy and speckle patterns, we make an accurate estimate of the point spread function that can be scaled and subtracted from the data cube. The residual noise in the resulting spectra is very close to the photon noise from the starlight halo. We utilize the technique to extract a very high signal-to-noise ratio H - and K -band spectrum of AB Doradus (AB Dor) C, the low-mass companion to AB Dor A. By effectively eliminating all contamination from AB Dor A, the extracted spectrum retains both continuum and spectral features. The achieved 1, contrast is 9 mag at 0.2 arcsec, 11 mag at 0.5 arcsec, in 20 min exposure time, at an effective spectral bandwidth of 5.5 nm, proving that the method is applicable even in low-Strehl regimes. The SD method clearly demonstrates the efficacy of image slicer based integral field units in achieving very high contrast imaging spectroscopy at small angular separations, validating their use as high-contrast spectrographs/imagers for extreme adaptive optics systems. [source]

The SAURON project , VIII.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
OASIS/CFHT integral-field spectroscopy of elliptical, lenticular galaxy centres
ABSTRACT We present high spatial resolution integral-field spectroscopy of 28 elliptical (E) and lenticular (S0) galaxies from the SAURON representative survey obtained with the OASIS spectrograph during its operation at the Canada,France,Hawaii Telescope. These seeing-limited observations explore the central 8 × 10 arcsec2 (typically 1 kpc diameter) regions of these galaxies using a spatial sampling four times higher than SAURON (0.27-arcsec versus 0.94-arcsec spatial elements), resulting in almost a factor of 2 improvement in the median point spread function. These data allow accurate study of the central regions to complement the large-scale view provided by SAURON. Here we present the stellar and gas kinematics, stellar absorption-line strengths and nebular emission-line strengths for this sample. We also characterize the stellar velocity maps using the ,kinemetry' technique, and derive maps of the luminosity-weighted stellar age, metallicity and abundance ratio via stellar population models. We give a brief review of the structures found in our maps, linking also to larger-scale structures measured with SAURON. We present two previously unreported kinematically decoupled components (KDCs) in the centres of NGC 3032 and NGC 4382. We compare the intrinsic size and luminosity-weighted stellar age of all the visible KDCs in the full SAURON sample, and find two types of components: kiloparsec-scale KDCs, which are older than 8 Gyr, and are found in galaxies with little net rotation; and compact KDCs, which have intrinsic diameters of less than a few hundred parsec, show a range of stellar ages from 0.5 to 15 Gyr (with 5/6 younger than 5 Gyr), are found exclusively in fast-rotating galaxies, and are close to counter-rotating around the same axis as their host. Of the seven galaxies in the SAURON sample with integrated luminosity-weighted ages less than 5 Gyr, five show such compact KDCs, suggesting a link between counter-rotation and recent star formation. We show that this may be due to a combination of small sample size at young ages, and an observational bias, since young KDCs are easier to detect than their older and/or corotating counterparts. [source]