Signal‐difference‐to‐noise comparison of temporal subtraction, kV‐switching dual‐energy and photon‐counting dual‐energy x‐ray angiography

Abstract

AbstractBackgroundDual‐energy (DE) x‐ray angiography with photon‐counting detectors (PCDs) may enable single‐exposure DE imaging of coronary vasculature.PurposeTo compare the iodine signal‐difference‐to‐noise ratio (SDNR) of single‐exposure DE angiography with digital subtraction angiography (DSA) and kV‐switching DE angiography for matched patient x‐ray exposure.MethodsIn a phantom study, we determined the technique parameters that maximized the iodine SDNR per root entrance air kerma for DSA, kV‐switching DE angiography and single‐exposure DE angiography. We measured SDNR from images of a phantom consisting of an iodine step‐wedge immersed in a water tank of either 20  or 30 cm in thickness. We also imaged a phantom with simulated vessels embedded in background clutter and measured vessel SDNR. For this second phantom, we also applied anti‐correlated noise reduction (ACNR) and calculated the resulting iodine SDNR. All images were acquired using a cadmium telluride PCD with two energy bins and analog charge summing for charge sharing suppression. The energy‐discrimination capabilities were only used for the single‐exposure DE approach. Optimized techniques were compared in terms of SDNR per root air kerma for two levels of x‐ray scatter.ResultsFor the same patient x‐ray exposure, the SDNR of single‐exposure DE imaging without ACNR was 75% to 85% of that of kV‐switching DE imaging (also without ACNR) and DSA, the latter two of which had nearly equal SDNR. The single‐exposure DE approach required ∼50% of the tube load of the kV‐switching approach to achieve the same SDNR. For matched patient air kermas, the single exposure approach required only ∼25% of the tube load of the kV‐switching approach. ACNR increased SDNR by 2.4 and 3.0 for kV‐switching and single‐exposure DE imaging, respectively.ConclusionsPhoton‐counting, single‐exposure DE angiography can suppress soft tissues and provide iodine SDNR levels comparable to DSA and kV‐switching DE angiography for matched patient radiation exposures. When ACNR is used to reduce DE image noise, the SDNR of single‐exposure DE imaging and kV‐switching DE imaging exceed that of DSA by more than a factor of two. Compared to kV‐switching DE imaging, single‐exposure DE imaging requires substantially lower tube loading to achieve the same SDNR.