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Proceedings Paper

Theoretical investigation of very high-quantum-efficiency segmented crystalline detectors for low-contrast visualization in megavoltage cone-beam CT
Author(s): Yi Wang; Larry E. Antonuk; Youcef El-Mohri; Amit Sawant; Qihua Zhao; Hong Du; Yixin Li
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Paper Abstract

Megavoltage cone-beam computed tomography (CBCT) using active matrix flat-panel imagers (AMFPIs) is a promising candidate for providing image guidance in radiation therapy. Unfortunately, the practical clinical implementation of this technique is limited by the relatively low detective quantum efficiency (DQE) of conventional megavoltage AMFPIs. This limitation is due to the modest thickness of the phosphor screen employed to convert incident x-rays to optical photons and the trade-off that exists between phosphor thickness and spatial resolution. Recently, our group has begun pursuing the development of thick crystalline segmented scintillating detectors as x-ray converters for AMFPIs so as to circumvent this limitation. In order to examine the potential of such detectors for providing soft-tissue visualization by means of CBCT at megavoltage energies, a Monte Carlo-based method was used to simulate the acquisition of projection images of a contrast phantom. These images were used to perform CT reconstructions by means of a Feldkamp-based algorithm. In this study, various detector configurations involving CsI and BGO scintillators at thicknesses of 10 mm and 40 mm were evaluated. In addition, since the simulations only considered energy deposition, and did not include optical phenomena, both segmented and non-segmented (continuous) detector configurations were evaluated. For the segmented CsI detectors, septal wall materials with densities lower, equivalent and higher than that of the scintillator were considered. Performance was quantified in terms of the contrast-to-noise ratio obtained for lowcontrast, soft-tissue-equivalent objects (i.e., liver, brain, and breast) embedded in the phantom. The results obtained from these early studies suggest that such segmented converters can provide visualization of soft-tissue contrast in tomographic images at clinically practical doses. It is anticipated that the realization of optimized segmented detector designs will lead to clinically useful megavoltage AMFPIs exhibiting impressive performance.

Paper Details

Date Published: 7 March 2006
PDF: 11 pages
Proc. SPIE 6142, Medical Imaging 2006: Physics of Medical Imaging, 61421P (7 March 2006); doi: 10.1117/12.654873
Show Author Affiliations
Yi Wang, Univ. of Michigan (United States)
Larry E. Antonuk, Univ. of Michigan (United States)
Youcef El-Mohri, Univ. of Michigan (United States)
Amit Sawant, Univ. of Michigan (United States)
Qihua Zhao, Univ. of Michigan (United States)
Hong Du, Univ. of Michigan (United States)
Yixin Li, Univ. of Michigan (United States)

Published in SPIE Proceedings Vol. 6142:
Medical Imaging 2006: Physics of Medical Imaging
Michael J. Flynn; Jiang Hsieh, Editor(s)

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