Deconvolution of the two-dimensional point-spread function of area detectors using the maximum-entropy algorithm

Graafsma, H.; Vries, R.Y. de

doi:10.1107/s0021889899003817

Cited by 9 publications

(3 citation statements)

References 8 publications

(8 reference statements)

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“…In the present study, noise makes a significant contribution to the experimental X-ray images, and we also have the situation of the width of the PSF being comparable in size with certain key sample features (especially the Cu wire). Graafsma & de Vries (1999), for example, have demonstrated the utility of the maximum-entropy method for the deconvolution of PSFs from experimental X-ray images and Laue diffraction patterns. We have investigated both the Richardson-Lucy algorithm (Richardson, 1972;Lucy, 1974) and regularized Wiener deconvolution [see Wiener (1949)], as implemented in the X-TRACT software, and will report briefly on results of the latter here.…”

Section: Discussionmentioning

confidence: 99%

Analysis and interpretation of the first monochromatic X-ray tomography data collected at the Australian Synchrotron Imaging and Medical beamline

Stevenson

Hall

Mayo

et al. 2012

J Synchrotron Radiat

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The first monochromatic X-ray tomography experiments conducted at the Imaging and Medical beamline of the Australian Synchrotron are reported. The sample was a phantom comprising nylon line, Al wire and finer Cu wire twisted together. Data sets were collected at four different X-ray energies. In order to quantitatively account for the experimental values obtained for the Hounsfield (or CT) number, it was necessary to consider various issues including the pointspread function for the X-ray imaging system and harmonic contamination of the X-ray beam. The analysis and interpretation of the data includes detailed considerations of the resolution and efficiency of the CCD detector, calculations of the X-ray spectrum prior to monochromatization, allowance for the response of the double-crystal Si monochromator used (via X-ray dynamical theory), as well as a thorough assessment of the role of X-ray phase-contrast effects. Computer simulations relating to the tomography experiments also provide valuable insights into these important issues. It was found that a significant discrepancy between theory and experiment for the Cu wire could be largely resolved in terms of the effect of the point-spread function. The findings of this study are important in respect of any attempts to extract quantitative information from X-ray tomography data, across a wide range of disciplines, including materials and life sciences.

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Section: Discussionmentioning

confidence: 99%

Analysis and interpretation of the first monochromatic X-ray tomography data collected at the Australian Synchrotron Imaging and Medical beamline

Stevenson

Hall

Mayo

et al. 2012

J Synchrotron Radiat

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“…In principle, one could obtain the corrected intensity by the deconvolution of the observed scattering pattern by the known PSF (Pedersen et al, 1990;Graafsma & Vries, 1999;Le Flanchec et al, 1996). This calculation is computationally intensive and dif®cult to perform without introducing artifacts, such as oscillations, unless the measured data extend over a very wide range beyond that of interest.…”

Section: Figurementioning

confidence: 99%

High-dynamic range SAXS data acquisition with an X-ray image intensifier

2002

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Data with a wide dynamic range of intensity can be collected with a pinhole high-brilliance small-angle X-ray scattering (SAXS) camera using an image-intensi®ed charge-coupled device (CCD) detector. The point spread function (PSF) of this detector has a narrow peak with a broad low tail such that a high level of scattered intensity at small angles can cause a signi®cant background in the detector elements at higher angles. A correction scheme for the long tail of the PSF of the detector is needed when this integrating area detector is used for measuring intensity that spans a dynamic range of four to ®ve orders of magnitude. A procedure is described for measuring the PSF contribution by masking a small part of the detector from the scattered radiation with an absorbing material. In order to measure the PSF, it is necessary to use a highintensity spot, which is readily achieved by using a sample that scatters strongly at small angles. Although this intensity is spread over many pixels, the sharp features in the scattering from the silica sample chosen for this study permit one to obtain simultaneously both the narrow and the broad parts of the PSF. The data are compared with the actual scattering function, which has been measured exactly with a point-geometry Bonse±Hart camera. The advantages of this procedure are discussed.

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“…It is possible to use the maximum entropy method to optimize the deconvolution of the PDF for two-dimensional detectors, and a signi¢cant improvement in both spatial resolution and the signal-to-noise ratio has been achieved by doing so for Laue images taken from a virus crystal. 74 The paper presents a clear explanation of the method and the underlying assumptions.…”

Section: Data Processingmentioning

confidence: 99%

5 Molecular structure from X-ray diffraction

Powell

2000

Annu. Rep. Prog. Chem., Sect. C

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The last of these reports appeared four years ago; 1 a number of major advances in structure elucidation have appeared in laboratories in that period, mostly in the ¢eld of macromolecular structure determination. This is largely because sub-100 non-hydrogen atom structure solution has become almost routine, with extremely robust solution and re¢nement programs being complemented by rapid data collection from single crystal samples. In many cases, the role of the in-house crystallographer in chemistry departments is to provide a service to synthetic chemists in an analogous way to that of NMR spectroscopists ¢fteen or twenty years ago. Many chemical crystallographers have used this as an opportunity to study more dif¢cult structures, for example larger molecules from both single crystal and powder methods, using twin datasets, and looking more closely at structures in charge density studies.This increased ease has not removed the perils of being ``Marshed''; the well-known investigator into errors in space group determination has examined structures deposited into the Cambridge Structural Database (CSD) with space group P1, of which more than 20% are incorrect. 2 The majority of errors appear to be due to typographical errors in the original publication, but a signi¢cant minority are due to incorrect space group assignment (usually authors missing a centre of inversion, and assigning P1 rather than P1, or not recognizing higher symmetry, e.g., assigning P1 (triclinic) rather than C2 (monoclinic). However, the author notes that in some cases of true P1 structures, the deviation from centrosymmetry is as small as 0.1 Ð, and would be expected to lead to dif¢culties in re¢nement unless the problem had been recognized, as the following example illustrates.The solution and re¢nement of the antibiotics Emycin E and D provides a warning not to abide by conventional wisdom under all circumstances. 3 Both antibiotics crystallize in a triclinic space group with two molecules in the asymmetric unit (Z 2). The dataset for Emycin E was in accordance with the normal measure of centricity, a mean hjE 2 À 1ji value of 0.978 (the expected value for a centrosymmetric dataset is 0.968, and is 0.736 for acentric), while that for Emycin D was 0.829. Both can be re¢ned to low residual indices (R-factors) in space group

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Deconvolution of the two-dimensional point-spread function of area detectors using the maximum-entropy algorithm

Cited by 9 publications

References 8 publications

Analysis and interpretation of the first monochromatic X-ray tomography data collected at the Australian Synchrotron Imaging and Medical beamline

Analysis and interpretation of the first monochromatic X-ray tomography data collected at the Australian Synchrotron Imaging and Medical beamline

High-dynamic range SAXS data acquisition with an X-ray image intensifier

5 Molecular structure from X-ray diffraction

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