Dr. Horace Xu Profile

Dr. Horace Xu

at GE Global Research

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Publications (2)

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Proceedings Article | 19 March 2014 Paper

Hybrid-model for computed tomography simulations and post-patient collimator design

Horace Xu, Kun Tao, Padmashree GK, Mingye Wu, Ximiao Cao, Yong Long, Ming Yan, Yangyang Yao, Bruno De Man

Proceedings Volume 9033, 90334R (2014) https://doi.org/10.1117/12.2043235

KEYWORDS: Monte Carlo methods, Modulation transfer functions, X-rays, Collimators, Computer simulations, Scintillators, X-ray imaging, Sensors, Computed tomography, Photon transport

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Ray-tracing based simulation methods are widely used in modeling X-ray propagation, detection and imaging. While most of the existing simulation methods rely on analytical modeling, a novel hybrid approach comprising of statistical modeling and analytical approaches, is proposed here. Our hybrid simulator is a unique combination of analytical modeling for evoking the fundamentals of X-ray transport through ray-tracing, and a look-up-table (LUT) based approach for integrating it with the Monte Carlo simulations that model optical photon-transport within scintillator. The LUT approach for scintillation-based X-ray detection invokes depth-dependent gain factors to account for intra-pixel absorption and light-transport, together with incident-angle dependent effects for inter-pixel X-ray absorption (parallax effect). The model simulates the post-patient collimator for scatter-rejection, as an X-ray shadow on scintillator, while handling its position with respect to the pixel boundary, by a smart over-sampling strategy for high efficiency. We have validated this simulator for computed tomography system-simulations, by using real data from GE Brivo CT385. The level of accuracy of image noise and spatial resolution is better than 98%. We have used the simulator for designing the post-patient collimator, and measured modulation transfer function (MTF) for different widths of the collimator plate. Validation and simulation study clearly demonstrates that the hybrid simulator is an accurate, reliable, efficient tool for realistic system-level simulations. It could be deployed for research, design and development purposes to model any scintillator-based X-ray imaging-system (2-dimensional and 3-dimensional), while being equally applicable for medical and industrial imaging.

Proceedings Article | 19 March 2014 Paper

Physics-based modeling of X-ray CT measurements with energy-integrating detectors

Yong Long, Hewei Gao, Mingye Wu, Jed Pack, Hao Xu, Kun Tao, Paul Fitzgerald, Bruno De Man

Proceedings Volume 9033, 90334S (2014) https://doi.org/10.1117/12.2043144

KEYWORDS: X-rays, Sensors, Photons, X-ray detectors, Monte Carlo methods, X-ray optics, Scintillators, Photodiodes, Systems modeling, X-ray computed tomography

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Computer simulation tools for X-ray CT are important for research efforts in developing reconstructionmethods, designing new CT architectures, and improving X-ray source and detector technologies. In this paper, we propose a physics-based modeling method for X-ray CT measurements with energy-integrating detectors. It accurately accounts for the dependence characteristics on energy, depth and spatial location of the X-ray detection process, which is either ignored or over simplified in most existing CT simulation methods. Compared with methods based on Monte Carlo simulations, it is computationally much more efficient due to the use of a look-up table for optical collection efficiency. To model the CT measurments, the proposed model considers five separate effects: energy- and location-dependent absorption of the incident X-rays, conversion of the absorbed X-rays into the optical photons emitted by the scintillator, location-dependent collection of the emitted optical photons, quantumefficiency of converting fromoptical photons to electrons, and electronic noise. We evaluated the proposed method by comparing the noise levels in the reconstructed images from measured data and simulations of a GE LightSpeed VCT system. Using the results of a 20 cm water phantom and a 35 cm polyethylene (PE) disk at various X-ray tube voltages (kVp) and currents (mA), we demonstrated that the proposed method produces realistic CT simulations. The difference in noise standard deviation between measurements and simulations is approximately 2% for the water phantom and 10% for the PE phantom.

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