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Proceedings Paper

Modeling scattered radiation from dose compensator in CT by forced detection Monte Carlo simulation
Author(s): Negar Bazargani; Richard A. Thompson; Yoad Yagil
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Paper Abstract

We model the scatter radiation from the dose compensator in computed tomography (CT) using Monte Carlo (MC) simulation. Dose compensator reduces the patient radiation dose but also adds some scatter radiation which can reach detectors and degrade image quality. This scattered radiation impacts high contrast edges such as bone-soft tissue and tissue-air interfaces, similar to the well known off-focal radiation from the X-ray tube. To the best of our knowledge, this is the first study that uses MC simulation to model and investigate the compensator scatter radiation. Since detectors are far from the scatter source and have small solid angle, traditional MC is not computationally efficient. We have implemented variance reduction technique called forced detection (FD) to improve the computational efficiency, and achieved an improvement factor of 42,800. The simulated scatter to primary ratio (SPR) ranges from a few percent to 11% across the detectors. Simulations of water phantoms indicate that such scatter can lead to significant effects along edges as large as 20-30 HU, necessitating the need for correction. We demonstrate a correction in FBP reconstruction, somewhat similar to off-focal correction, and show that it significantly reduces the level of the artifact along the edge of the phantom.

Paper Details

Date Published: 3 March 2012
PDF: 7 pages
Proc. SPIE 8313, Medical Imaging 2012: Physics of Medical Imaging, 83132L (3 March 2012);
Show Author Affiliations
Negar Bazargani, Philips Healthcare (United States)
Richard A. Thompson, Philips Healthcare (United States)
Yoad Yagil, Philips Healthcare (Israel)

Published in SPIE Proceedings Vol. 8313:
Medical Imaging 2012: Physics of Medical Imaging
Norbert J. Pelc; Robert M. Nishikawa; Bruce R. Whiting, Editor(s)

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