The case for single-exposure angiography using energy-resolving photon-counting detectors: a theoretical comparison of signal and noise with conventional subtraction angiography

Abstract

The use of energy-resolving photon-counting (EPC) x-ray detectors creates an opportunity for material specific x-ray imaging. An exciting potential application of this technique is energy-resolved angiography (ERA) in which the injected-iodine signal is determined from an analysis of x-ray energies in a single exposure rather than the subtraction of a mask image from a post-contrast-injection image, as used in conventional digital subtraction angiography (DSA). We explore the possibility of single-exposure angiography using EPC detectors by theoretically calculating the signal-difference-to-noise ratio (SDNR) per root entrance exposure (X) in an iodine-specific image that could be determined using spectral methods, and to compare this with the corresponding SDNR using DSA for the same x-ray exposure. We found that angiography using ideal EPC x-ray detectors can separate iodine-filled cavities of variable concentrations from a water-only background in a single x-ray exposure. For high iodine concentrations, the best SDNR for DSA is approximately 1.5 times the best SDNR for ERA and at low concentrations this factor reduces to 1.3 times. This difference of approximately 1.3 to 1.5 times is surprisingly small. While DSA in general provides better image quality for the same x-ray exposure, DSA has been unsuccessful in coronary applications because of motion-related image artifacts. X-ray imaging using ideal energy-resolving photon-counting detectors has the potential to provide DSA-like angiographic images of iodinated vasculature in a single x-ray exposure, therefore eliminating motion-related image artifacts that limit the use of DSA in cardiac applications. ERA may potentially be used in for background removal in situations where DSA cannot be used, such as in cardiac imaging.