PhD Defence: Assessment of Cadmium Telluride Photon-Counting Detectors for Breast Imaging Applications

Student: James Day

Supervisor: Dr. Jesse Tanguay

Abstract

Breast cancer is a common disease among Canadian women, with 1 in 8 women expected to develop it. Early detection is crucial for higher survival rates. Mammography with photon-counting detectors can improve the detection rate of early-forming lesions and the classification accuracy of suspected lesions. Cadmium telluride photon-counting detectors are under development for clinical applications. Because this material can be implemented as a large-area flat-panel detector, it is expected to have a practical advantage over silicon based systems. Currently, it is unknown what their potential is for breast imaging applications. Most mammography systems are utilized for standard mammography applications first and contrast-enhanced mammography second. The project aims to (1) develop an experimentally validated cadmium telluride flat-panel photon-counting detector model and compare its theoretical potential to currently used imaging systems for standard mammography applications. (2) Expand upon this model for spectroscopic imaging tasks to determine its capabilities for detecting iodinated lesions using two and three-bin techniques. (3) Adapt the methodologies of this model to a live imaging system and perform a similar assessment. Our models were validated against the XCounter Thor, a prototype flat-panel cadmium telluride photon-counting detector. We utilized imaging metrics such as the detective quantum efficiency and the detectability index to compare detector systems and measure the imaging performance of both our model detector and the live system. Our study found that cadmium telluride flat-panel photon-counting detectors are a good option for mammography. If optimized, they can (1) perform similarly to current detector systems for standard mammography. Our results demonstrated comparable performance to highperforming selenium energy integrating detectors and silicon photon counting detectors. If further optimized for contrast-enhanced spectral mammography (2), these detectors have excellent iodine detection with two or three-bin imaging techniques. Although there is a marked degradation in detectability for three-bin imaging over two-bin imaging, the modeled detector predicted that a 7mm diameter lesion is still visible at one-ninth of the average blood concentration for an exam. Our live-detector assessment demonstrated methods to measure the detectability of iodine lesions in practice. Ultimately, this assessment (3) supports the observations inferred from our models; however, lesion detectability is moderately reduced.
Keywords: Photon Counting, Cadmium Telluride, mammography, Contrast enhanced mammography, Monte-carlo, Experiment, Optimization, Breast, Imaging, Detectability index.