Evaluation of a photon-counting X-ray imaging system

A digital imaging system has been developed for mammography using silicon strip detectors operated in a pulse-counting mode and configured in a scanned slit geometry. More than 90% of the photons are absorbed in the sensor. The scatter rejection is very efficient and the image formation is nearly optimal since each X ray is processed individually. The result is a very dose-efficient system. In this paper, we present measurements that verify that the performance of the readout electronics is sufficient to count photons at high rates with high quantum efficiency and a charge collection efficiency that does not limit the dose efficiency. The spatial resolution of the system was measured to provide a modulation transfer function of approximately 0.5 at a spatial frequency of 10 lp/mm. Images of a mammography phantom were recorded experimentally to test overall system performance.