PhD Defence: FEASIBILITY OF ENERGY-RESOLVED ANGIOGRAPHY

Student: Sarah Aubert

Supervisor: Dr. Jesse Tanguay

Abstract

Cardiovascular disease (CVD) is the leading cause of death globally, with coronary heart disease being one of the most common types of CVD. Two dimensional x-ray based imaging of the coronary arteries is used to verify and guide interventions and to obtain a good quality image of the vasculature a contrast agent is administered. Currently, patients who are suspected of having coronary heart disease will receive a coronary angiogram. There is potential to improve the visualization of coronary heart disease by subtracting anatomic noise, such as bone or soft tissue, that surrounds the contrast-enhanced vasculature in angiographic images. Currently, there are two subtraction based methods that are used to remove anatomic noise from an x-ray image: digital subtraction angiography and dualenergy angiography with kV-switching. However, these techniques are not used to image the coronary arteries due to susceptibility to motion artifacts and high tube loading demands, respectively. Technological advancements have lead to the development of photon-counting x-ray detectors that can estimate the energy distribution of photons at rates adequate for x-ray imaging applications. As such, the use of photon-counting x-ray detectors would allow for dual-energy imaging with a single exposure, allowing for the removal of anatomic noise without compromising image quality with motion artifacts. The use of a single-exposure dual-energy technique implemented with a photon-counting x-ray detector may lead to better visualization and diagnosis of coronary heart disease. This research focuses on examining the feasibility of using a photon-counting x-ray detector for improved imaging of coronary heart disease, specifically when implemented using dual energy imaging methods.
The goals of this project are to (1) develop theoretical models that incorporate realistic models of x-ray detector response to quantify image quality of subtraction based angiography and energy-resolved angiography methods, (2) experimentally optimize single-exposure dual-energy angiography implemented with a two-bin photoncounting x-ray detector, and (3) compare optimized image quality in terms of iodine signal-difference-to-noise ratio of single-exposure dual energy images, dual-energy images acquired using kV-switching and digital subtraction angiography images, all acquired using a two-bin photon-counting x-ray detector. Our theoretical model of x-ray detector response included physical phenomena that have been shown to degrade image quality in photon-counting detectors, such as charge sharing. Our theoretical results guided our experimental design, where we investigated optimizing soft tissue suppressed dual-energy single-exposure imaging using a custom built imaging phantom that contained varying amounts of iodine contrast agent. We optimized single exposure dual-energy angiography using the signal-difference-to-noise ratio per root entrance air kerma. Results identified the tube voltage and energy threshold that optimized image quality for various phantom thicknesses and scatter conditions. We identified that to achieve optimal image quality a high tube voltage will be required. In addition, energy thresholds will need to allocate approximately two thirds of all primary photons to the low energy image used to form a dual-energy image. It was found that single-exposure dual-energy angiography implemented with a photon-counting detector was capable of producing images of comparable quality to the subtraction-based methods investigated (digital subtraction angiography and kV-switching dual-energy angiography), while requiring a much lower tube load. These findings indicate that single-exposure dualenergy angiography implemented with a photon counting detector may provide a suitable alternative to kV-switching dual-energy angiography, offering potential improved visualization for diagnosis and treatment of coronary heart disease.
Keywords: cardiac imaging, x-ray imaging, photon-counting, energy-resolved xray imaging, vascular imaging, dual-energy imaging