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Proceedings Paper

Noise in hybrid photodiode array: CCD x-ray image detectors for digital mammography
Author(s): Justin M. Henry; Martin Joel Yaffe; Tumay O. Turner
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Paper Abstract

Phosphor based detectors proposed for digital mammography require multiple energy conversion and coupling stages which degrade imaging performance. We are investigating the potential of a hybrid photodiode array-CCD which will overcome this problem. The photodiode converts the x-ray energy directly into charge which is stored in the CCD. The detector is used in a slot-scan configuration to image the entire breast. Due to the large amount of charge generated in the photodiode, a charge divider is incorporated on the CCD to prevent detector saturation. Feasible values of design parameters such as photodiode thickness, operating voltages, and charge divider ratio were determined by modeling the signal and noise propagation through the detector. The quantum accounting diagram (QAD) and detective quantum efficiency (DQE) were used to measure imaging performance. A photodiode thickness of 1.5 mm ensures acceptable quantum efficiency. This thickness, however, causes significant geometric blur due to obliquely incident x-rays at edges of the detector unless the detector is curved by using a number of hybrid sections less than 2 cm long. No more than 90% of the photodiode charge can be discarded by the divider without causing a significant reduction in DQE due to direct x-ray interaction in the CCD. Using the design parameter values determined by the model, a high DQE up to the Nyquist frequency is achieved.

Paper Details

Date Published: 11 April 1996
PDF: 10 pages
Proc. SPIE 2708, Medical Imaging 1996: Physics of Medical Imaging, (11 April 1996); doi: 10.1117/12.237774
Show Author Affiliations
Justin M. Henry, Sunnybrook Health Sciences Ctr./Univ. of Toronto (Canada)
Martin Joel Yaffe, Sunnybrook Health Sciences Ctr./Univ. of Toronto (Canada)
Tumay O. Turner, NOVA R&D, Inc. (United States)

Published in SPIE Proceedings Vol. 2708:
Medical Imaging 1996: Physics of Medical Imaging
Richard L. Van Metter; Jacob Beutel, Editor(s)

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