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Charge‐coupled device detector: Performance considerations and potential for small‐field mammographic imaging applications
Author(s) -
Karellas Andrew,
Harris Lisa J.,
Liu Hong,
Davis Michael A.,
D'Orsi Carl J.
Publication year - 1992
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.596819
Subject(s) - detector , mammography , medical imaging , field (mathematics) , medical physics , physics , optics , medicine , radiology , cancer , breast cancer , mathematics , pure mathematics
The physical characteristics of a charge‐coupled device (CCD) image detector were evaluated, as well as its potential as a digital imaging device for small field mammographic applications such as preoperative needle localization. The detection system is based on a 2048×2048 pixel CCD operated in 1024×1024 mode. The CCD was optically coupled to an intensifying screen via a lens, without intermediate intensification. The thermal noise was suppressed to 0.15 electrons pixel −1 s −1 by cooling the CCD with liquid nitrogen. The dominant source of noise was attributed to the on‐chip amplifier during the readout process that was performed at 50 000 pixels s −1 . The measured readout noise level was 15 electrons per pixel. The low‐noise characteristics of this CCD prototype detector produced encouraging results under conditions simulating mammography, with a signal level close to one electron per pixel for each detected x ray. The mean glandular dose to the breast, based on the entrance exposure measured from a standard mammographic phantom would be 1.52 mGy (152 mrad). The ultimate spatial resolution of the system was approximately 8 cycles/mm but it was limited to about 5 cycles/mm when operated in the 1024×1024 imaging mode. Other physical characteristics of the system such as optical coupling efficiency, exposure response, and signal‐to‐noise ratio were evaluated. The results of this study suggest that the use of a scientific‐grade CCD allows for very good low‐contrast discrimination and moderate spatial resolution under conditions simulating mammography, but the current prototype is limited to a 9×9‐cm 2 field of view. The results of this study suggest that with realistic improvements in the optical coupling via a faster lens or fiberoptic coupling, additional improvements in image quality and dose are feasible.