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Proceedings Paper

Portal imaging with flat-panel detector and CCD camera
Author(s): Hans Roehrig; Chuankun Tang; Chee-Way Cheng; William J. Dallas
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Paper Abstract

This paper provides a comparison of imaging parameters of two portal imaging systems at 6 MV: a flat panel detector and a CCD-camera based portal imaging system. Measurements were made of the signal and noise and consequently of signal-to-noise per pixel as a function of the exposure. Both systems have a linear response with respect to exposure, and the noise is proportional to the square-root of the exposure, indicating photon-noise limitation. The flat-panel detector has a signal- to-noise ratio, which is higher than that observed wit the CCD-camera based portal imaging system. This is expected because most portal imaging systems using optical coupling with a lens exhibit severe quantum-sinks. The paper also presents data on the screen's photon gain (the number of light-photons per interacting x-ray photon), as well as on the magnitude of the Swank-noise, (which describes fluctuation in the screen's photon gain). Images of a Las Vegas-type aluminum contrast detail phantom, located at the ISO-Center, were generated at an exposure of 1 MU. The CCD-camera based system permits detection of aluminum-holes of 0.01194 cm diameter and 0.228 mm depth while the flat-panel detector permits detection of aluminum holes of 0.01194 cm diameter and 0.1626 mm depth, indicating a better signal-to-noise ratio. Rank order filtering was applied to the raw images from the CCD-based system in order to remove the direct hits. These are camera responses to scattered x-ray photons which interact directly with the CCD of the CCD-camera and generate 'salt and pepper type noise,' which interferes severely with attempts to determine accurate estimates of the image noise.

Paper Details

Date Published: 7 July 1997
PDF: 11 pages
Proc. SPIE 3115, Hard X-Ray and Gamma-Ray Detector Physics, Optics, and Applications, (7 July 1997); doi: 10.1117/12.277701
Show Author Affiliations
Hans Roehrig, Univ. of Arizona (United States)
Chuankun Tang, Univ. of Arizona (United States)
Chee-Way Cheng, Univ. of Arizona (United States)
William J. Dallas, Univ. of Arizona (United States)

Published in SPIE Proceedings Vol. 3115:
Hard X-Ray and Gamma-Ray Detector Physics, Optics, and Applications
Richard B. Hoover; F. Patrick Doty, Editor(s)

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