SAPHIRE: A New Flat-Panel Digital Mammography Detector With Avalanche Photoconductor and High-Resolution Field Emitter Readout

摘要

A new concept of flat-panel imager (FPI) with avalanche gain and high resolution (with 50 micron pixel size) is being investigated for improving the imaging performance of digital mammography at low dose and high spatial frequencies, which are critical for the detection of subtle breast abnormalities and the development of digital tomosynthesis. The detector employs an avalanche photoconductor - amorphous selenium (a-Se), called HARP, to detect and amplify the optical signal generated by a structured scintillator - cesium iodide (CsI), and form a charge image that is read out by a high- resolution field emitter array (FEA). We call the proposed detector SAPHIRE (Scintillator-Avalanche Photoconductor with High Resolution Emitter Readout). Our investigation showed that the avalanche gain of SAPHIRE permits the use of high resolution (HR) type CsI, which has not been used in existing FPI due to its low light output. HR Cs can provide better imaging performance at high spatial frequencies than existing digital mammography detectors. We also investigated the factors affecting the resolution and image lag of the FEA readout method. Our results showed that adding electrostatic focusing at the FEA substrate can significantly improve the image resolution and lag of the detector. Dividing the signal electrode into multiple (e.g. 32) strips will improve both the electronic noise and the readout speed of the detector.