Characterization of a full field digital mammography detector based on direct x-ray conversion in selenium

We describe a high-resolution digital x-ray detector suitable for producing high quality mammographic images. The detector consists of an array of 3584 by 4096 pixels on 70 micrometer centers covering an area of 25 cm by 29 cm. The conversion layer of the detector is 250 micrometer thick amorphous selenium. Each pixel of the array consists of a storage capacitor for collecting x-ray signals and an amorphous silicon switching transistor. The signal is read out by custom high-speed, low-noise electronics. The integration of this detector with a mammographic x-ray system and acquisition console is described, as well as algorithms for calibration of the full system. We review characterization of the imaging performance of our system based on quantitative analyses of MTF and DQE data, and compare experimental results with theoretical calculations. We compare the performance of our direct conversion system with that of screen/film analog systems and indirect conversion digital detectors, such as LORAD's CsI/CCD detector, operated under similar conditions. MTF degradation mechanisms and system noise sources and their effect on DQE are discussed. We review qualitative aspects of image quality from our detector and present preliminary observer performance characteristics on clinical studies run with our system.