High-resolution (20 cycles/mm) digital x-ray mammography using amorphous selenium directly coupled to CCD readout devices

A simple x-ray detector that utilizes amorphous selenium (a-Se) directly deposited on a specially-designed CCD (charge coupled device) with a 25 pm del (detector element) pitch is described. This simple detector has been used to test the feasibility of creating digital mammography detectors. To enable the use of electron transport CCDs with a-Se, we have developed a-Se hole blocking layers to permit the transfer of electrons to the CCD while suppressing hole leakage current in the presence of the high negative bias (similar to1000 V) required to make the a-Se x-ray sensitive. We report measurements of the charge transfer efficiency (CTE), dark signal, x-ray sensitivity, x-ray signal linearity, and x-ray MTF (modulation transfer function) of the simple detector. As the thickness of the a-Se hole blocking layer was increased, the MTF decreased. For a thin (less than or equal to 1mum) blocking layer the MTF at a spatial frequency of 20 mm(-1) was 0.4.