CMOS active pixel image sensor for medical application and its radiation effects

Abstract

Radiographic imaging modalities and applications have been expending in medical and industrial fields as one of methods to see inside the world of animate and inanimate, due to the properties of X-rays and X-rays receptors. As one of radiographic solutions, digital X-ray imaging is an alternative instead of analog modality. This thesis presents two digital X-ray imaging of general radiography and mammography for medical application, and its radiation effects under X-ray exposure conditions, which are all based on Scintillator Coupled Complementary Metal Oxide Semiconductor Active Pixel Sensor (SC CMOS APS) imager. For the medical application, the experiments are performed to investigate the potential ability of the SC CMOS APS imager under clinical conditions. The image quality is evaluated by image evaluation matrix such as modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). Several candidate scintillators are considered to be coupled CMOS APS array imager. The considered commercially available scintillators are different types such as screen film, needle structured, and fiber optic structured (FOP-scint.). The evaluation results tells that the CMOS APS imager coupled with needle CsI type scintillator shows DQE of 35 % at the frequency of $3mm^{-1}$. The FOP CsI type also guarantees good DQE performance in that field. However, no scintillator satisfies good DQE in mammography condition although the Fine scintillator shows relatively high DQE among others about 5 % at the frequency of $6mm^{-1}$. For the discrete components of the CMOS APS and the SC CMOS APS imager, two experiments are performed to analyze the radiation effects. Through the radiation test of the discrete components of the CMOS APS, it is verified that the main radiation effect on the CMOS APS shows dark current and or leakage current increase generated in both photosensor and transistor parts. In X-ray imaging, the transmitted X-rays throu...