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Proceedings Paper

Physical characterization and optimal magnification of a portal imaging system
Author(s): Jean-Pierre Bissonnette; David A. Jaffray; Aaron Fenster; Peter Munro
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Paper Abstract

One problem in radiation therapy is ensuring accurate positioning of the patient so that the prescribed dose is delivered to the diseased regions while healthy tissues are spared. Positioning is usually assessed by exposing film to the high-energy treatment beam. Unfortunately, these films exhibit poor image quality (primarily due to low subject contrast) and the development delays make film impractical to check patient positioning routinely. Therefore, we have been developing a digital video-based imaging system to replace film. The system consists of a copper plate/fluorescent screen detector, a 45 degree(s) mirror, and a TV camera equipped with a large aperture lens. We have determined the signal and noise transfer properties of the imaging system by measuring its MTF(f) and NPS(f) and used these valued to estimate the optimal magnification for the imaging system. We have found that the optimal magnification is 2.3 - 2.5 when optimizing signal transfer (spatial resolution) alone; however, the optimal magnification is only 1.5 - 2.0 if SNR transfer is considered.

Paper Details

Date Published: 1 June 1992
PDF: 7 pages
Proc. SPIE 1651, Medical Imaging VI: Instrumentation, (1 June 1992); doi: 10.1117/12.59396
Show Author Affiliations
Jean-Pierre Bissonnette, Univ. of Western Ontario and London Regional Cancer Ctr. (Canada)
David A. Jaffray, Univ. of Western Ontario and London Regional Cancer Ctr. (Canada)
Aaron Fenster, Univ. of Western Ontario and John P. Robarts Research Institute (Canada)
Peter Munro, Univ. of Western Ontario and London Regional Cancer Ctr. (Canada)

Published in SPIE Proceedings Vol. 1651:
Medical Imaging VI: Instrumentation
Rodney Shaw, Editor(s)

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