Dr. Michael S. Westmore Profile

Dr. Michael S. Westmore

Principal Research Scientist at Eli Lilly and Co

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Publications (6)

Proceedings Article | 25 April 2000 Paper

Effect of fat content on single- and dual-energy CT measurements of bone mineral: determination using a new system of tissue-mimicking phantom materials

Michael Westmore, Masahjiko Sato

Proceedings Volume 3977, (2000) https://doi.org/10.1117/12.384538

KEYWORDS: Bone, Tissues, Computed tomography, Minerals, Signal attenuation, Mass attenuation coefficient, Calcium, Phase modulation, Carbonates, Chlorine

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Proceedings Article | 24 July 1998 Paper

Quantitative coherent-scatter-computed tomography

Deidre Batchelar, Michael Westmore, Hao Lai, Ian Cunningham

Proceedings Volume 3336, (1998) https://doi.org/10.1117/12.317076

KEYWORDS: Signal attenuation, Diffraction, X-ray computed tomography, Tomography, Tissues, Bone, X-rays, Scattering, Photons, X-ray diffraction

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Proceedings Article | 8 May 1995 Paper

Investigation of coherent-scatter computed tomography

Michael Westmore, Aaron Fenster, Ian Cunningham

Proceedings Volume 2432, (1995) https://doi.org/10.1117/12.208349

KEYWORDS: Diffraction, Tomography, X-ray computed tomography, Computed tomography, X-rays, Signal attenuation, X-ray diffraction, Medical research, Crystals, Sensors

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Conventional computed tomography (CT) images are `maps' of the x ray linear attenuation coefficient within a slice through an object. A novel approach to CT is being developed which instead produces tomographic images based on an object's low-angle (0 - 10 degree(s)) x-ray diffraction properties. The coherent-scatter cross sections of many materials vary greatly, and this coherent-scatter CT (CSCT) system gives material-specific information on this basis. The goal of this research is to produce tomographic maps of bone-mineral content (BMC), first in laboratory specimens, and potentially in patients. The concept of reconstructing tomographic images using coherently scattered x rays was first demonstrated by Harding et al. The approach described here is a modification of their method. First generation CT geometry is used in which a diffraction pattern is acquired for each pencil-beam using a CsI image intensifier coupled to a CCD. Each pattern is sectioned into concentric annular rings so that the integrated signal in each ring gives the scatter intensity at a particular scatter angle, integrated along the path through the object. An image is reconstructed for each ring, resulting in a series of tomographic images corresponding to the scatter intensity at a series of scatter angles. A test phantom was imaged (70 kVp, 50 mAs per exposure, 100 mSv average dose) to demonstrate CSCT. The phantom consists of a water-filled Lucite cylinder containing rods of polyethylene, Lucite, polycarbonate, and nylon. The resulting series of images was used to extract the angular-dependent scatter cross section for every pixel. Using pure material cross sections as basis functions, the cross section from each pixel was fitted using non-negative least squares. The results were used to create material-specific images. These results show that CSCT is feasible with this approach and that if the materials in an object have distinguishable scatter cross sections, the method has the ability to identify the materials. It may be possible to image the BMC distribution as trabecular bone mineral is replaced by lipids.

Proceedings Article | 8 May 1995 Paper

Effect of finite detector-element width on the spatial-frequency-dependent detective quantum efficiency

Ian Cunningham, Michael Westmore, Aaron Fenster

Proceedings Volume 2432, (1995) https://doi.org/10.1117/12.208331

KEYWORDS: Sensors, Convolution, Stochastic processes, Modulation transfer functions, Signal to noise ratio, Signal detection, Digital imaging, Quantum efficiency, Imaging systems, Image processing

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Proceedings Article | 1 May 1994 Paper

Visual impact of the nonzero spatial frequency quantum sink

Ian Cunningham, Michael Westmore, Aaron Fenster

Proceedings Volume 2163, (1994) https://doi.org/10.1117/12.174264

KEYWORDS: X-ray optics, X-rays, Visualization, Spatial frequencies, Quantum efficiency, Monte Carlo methods, Modulation transfer functions, Signal to noise ratio, X-ray imaging, Imaging systems

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Medical x-ray imaging systems must be carefully designed to ensure that images can be produced with the highest possible signal-to-noise ratio (SNR) for a given x-ray dose to the patient. In most practical systems, images result from the conversion of primary x-rays into secondary quanta such as optical photons or electrical charge, in multiple cascaded stages. The average number of quanta at each stage (per incident x ray) is often evaluated as the product of all preceding system gain factors and displayed graphically as a "quantum-accounting diagram" (QAD). The stage with the fewest quanta forms the quantum sink, and is generally the noise-determining stage. This "zero spatial-frequency" type analysis is simplistic, however, as it ignores the spatial spreading of secondary quanta that will further degrade image noise. We have recently extended the above approach by introducing a spatial-frequency dependent QAD, in which the number of quanta at each stage is expressed by the product of all preceding system gains and squared modulation transfer functions (MTFs). The results are displayed graphically and used to determine the quantum-sink stage as a function of spatial frequency. The visual impact of the non-zero spatial frequency quantum sink is illustrated in a Monte Carlo simulation of the cascading process. A hypothetical system consisting of a scintillating phosphor optically coupled to a CCD camera is used for illustrative purposes. It is shown that an inefficient optical system results in the addition of a quantum mottle to the images due to a secondary quantum sink in the number of optical quanta. The mottle appears to be uniform in frequencies, but in combination with the effect of the screen MTF masks high-frequency detail more than low-frequency detail. This secondary quantum sink can be minimized both by: i) increasing the efficiency of the optical system; and, ii) improving the highfrequency response of the screen. Increasing the optical efficiency reduces the secondary quantum mottle, thus improving visualization particularly at high frequencies. Improving the high-frequency response makes a slight improvement on the quantum mottle, and also increases the contrast of the high-frequency patterns. The combination improves visualization at high spatial frequencies. Interpretation of the QAD is assisted by a direct comparison with the corresponding Monte Carlo images. It is concluded that the secondary quantum sink results in a visible deterioration of image quality at any specified frequency when the QAD at that frequency is less than approximately five times the primary quantum sink QAD value.

Proceedings Article | 14 September 1993 Paper

Analysis of the detective quantum efficiency of coupling a CCD to a scintillating phosphor for x-ray microtomographic imaging

Michael Westmore, Ian Cunningham

Proceedings Volume 1896, (1993) https://doi.org/10.1117/12.154622

KEYWORDS: Modulation transfer functions, X-rays, Charge-coupled devices, Imaging systems, Sensors, X-ray optics, Quantum efficiency, X-ray imaging, X-ray detectors, Physics

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