1 June 1992 Physical characterization and optimal magnification of a portal imaging system
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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.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jean-Pierre Bissonnette, Jean-Pierre Bissonnette, David A. Jaffray, David A. Jaffray, Aaron Fenster, Aaron Fenster, Peter Munro, Peter Munro, } "Physical characterization and optimal magnification of a portal imaging system", Proc. SPIE 1651, Medical Imaging VI: Instrumentation, (1 June 1992); doi: 10.1117/12.59396; https://doi.org/10.1117/12.59396
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