Optimization of a high-resolution real-time solid state x-ray detection system for mammography

In this study we present Vista-Mamma 50, a novel detection system for high resolution real-time digital mammography. A matrix sensor (12 cm x 12 cm) consists of a high luminance CsI:Tl crystal grown with columnar structure on the top of a pin photodiode matrix driven by CMOS transistors. This imaging technology is known to allow achievement of a pixel size as small as 50 μm or less with a fill factor of the sensitive area of about 80%. The sensor is equipped with a fast real-time electronic system for readout and digitization of images with a dynamic range of 12 bits. Images can be obtained at a frame rate as high as 9 images per second in a 4 x 4 binning operation mode. Appropriate computerized control tools, real-time image treatment, data representation and off-line analysis have been developed. On-line image processing is automatically applied to each frame, including offset and gain corrections and masking of defective pixels. Quantitative measurements including dose response, modulation transfer function (MTF) and detective quantum efficiency are presented. It was found that the detector response shows linear dependence on the entrance dose. The results from the MTF showed that a resolution of equal to or greater than 8 lp/mm could be achieved. The high value of the DQE obtained could be ascribed to the large fill factor. The high resolution detector that we present is well adapted to the image quality which is required by the standards for applications in mammography. Some preliminary results have been obtained for microcalcifications performed on equivalent breast phantoms. Clinical tests are in progress.