Empirical electro-optical and x-ray performance evaluation of CMOS active pixels sensor for low dose, high resolution x-ray medical imaging

Monolithic complementary metal oxide semiconductor(CMOS) active pixel sensors with high performance have gained attention in the last few years in many scientific and space applications. In order to evaluate the increasing capabilities of this technology, in particular where low dose high resolution x-raymedical imaging is required, critical electro-optical and physical x-ray performance evaluation was determined. The electro-optical performance includes read noise, full well capacity, interacting quantum efficiency, and pixels cross talk. The x-ray performance, including x-ray sensitivity, modulation transfer function,noise power spectrum, and detection quantum efficiency, has been evaluated in the mammographic energy range. The sensor is a 525×525525×525 standard three transistor CMOS active pixel sensor array with more than 75% fill factor and 25×25μmpixel25×25μmpixel pitch. Reading at 10f∕s10f∕s, it is found that the sensor has 114 electrons total additive noise,105105 electrons full well capacity with shot noise limited operation, and 34% interacting quantum efficiency at 530nm530nm. Two different structured CsI:Tl phosphors with thickness 95 and 115μm115μm, respectively, have been optically coupled via a fiber optic plate to the array resulting in two different system configurations. The sensitivity of the two different system configurations was 43 and 47 electrons per x-ray incident on the sensor. The MTF at 10% of the two different system configurations was 9.5 and 9cycles∕mm9cycles∕mm with detective quantum efficiency of 0.45 and 0.48, respectively, close to zero frequency at ∼0.44μC∕kg∼0.44μC∕kg (1.72mR)(1.72mR)detector entrance exposure. The detector was quantum limited at low spatial frequencies and its performance was comparable with high resolution a:Sia:Si and charge coupled device based x-rayimagers. The detector also demonstrates almost an order of magnitude lower noise than active matrix flat panel imagers. The results suggest that CMOS active pixel sensors when coupled to structured CsI:Tl can be used for conventional and advanced digital mammography due to their low noise, high resolution performance