A Low-Cost Monolithically Integrated Multi Pixel Photon Counting X-ray Dete...| Zain Hussain Warsi

Abstract: Existing technologies concerning X-ray film screen and computed radiography systems are being replaced globally by large-area digital X-ray detectors due to their improved imaging performance and effective work flows. However, there remains a need for improvement in high-resolution imaging for applications requiring low-doses of contrast-medium for patient’s safety such as mammography and angiography where a better contrast and spatial resolution is required to reduce the errors in medical diagnosis. In comparison to traditional integration mode X-ray detectors, Multi-pixel photon counting (MPPC) X-ray detectors provide energy discrimination for improved image contrast, as well as offering lesser noise and a high dynamic range.The recent advancements in column-buttable CMOS IC technology will be used to mitigate the readout integrated circuit (ROIC) scaling constraints. X-ray sensors for MPPC applications detect X-rays directly and are based on crystalline and poly-crystalline materials such as Silicon, Cadmium Zinc Telluride and Cadmium Telluride etc. However, scaling of these materials to suit large-area medical applications is faced by challenges that arise due to yield and high cost associated with the growth and the interfacing of the sensor to the readout IC using the required bonding technology. Therefore, a commercially viable alternative is using amorphous selenium (a-Se); a predominant technology for large-area mammography X-ray detectors. The use of a-Se would then call to overcome the following challenges: (1) Count-rate limitations due to slow-carrier properties of a-Se and (2) the low X ray-to-charge conversion gain effecting our Signal-to-noise ratio (SNR), by employing improved nano-fabrication techniques for sensor design.
Hence, a Monolithic CMOS-Integrated MPPC detector with a-Se photoconductor and it's ROIC is proposed. The MPPC detector would have sub-micron pixel sizes, allowing a faster count rate compared to the existing technologies. The proposed design would overcome the count rate limitations due to a-Se by leveraging the small-pixel geometry with amorphous semiconductors for which effective nano-fabrication techniques will be employed. The pixel circuit will be designed to achieve a sufficient signal-to-noise ratio (SNR) for photon counting with a-Se. The proposed research will be novel and unique in its way as the targeted pixel pitch will the smallest in the world for X-ray photon counting, proving its novelty.