Quantification of Coronary Calcification using High-Resolution Photon-Counting-Detector CT and an Image Domain Denoising Algorithm.

Coronary artery calcification (CAC) is an important indicator of coronary disease. Accurate volume quantification of coronary calcification, especially calcifications smaller than a few mm, using computed tomography (CT) is challenging due to calcium blooming, which is a consequence of limited spatial resolution. In this study, ex-vivo coronary specimens were scanned on a clinical photon-counting detector (PCD) CT scanner and the estimated coronary calcification volume were compared with a conventional energy-integrating detector (EID) CT. Scans were performed using the same tube potential and radiation dose (120 kV, 9.3 mGy CTDIvol). EID-CT images were reconstructed using our routine clinical protocol for CAC quantification. PCD-CT images were reconstructed using a sharper reconstruction kernel than that was supported by the EID-CT scanner, resulting in improved resolution but higher image noise levels. An image-based denoising algorithm was applied to the PCD-CT images to achieve similar noise levels as the EID-CT images. Calcifications were segmented to estimate the volume. Micro-CT images of the same calcifications were acquired and served as the reference standard. PCD-CT images showed reduced calcium blooming artifacts compared to EID-CT. Calcification volume estimates were found to overestimate the micro-CT volumes by 9 ± 12% for PCD-CT data, and 24 ± 18% for the EID-CT data. Volume quantification accuracy of the current PCD-CT system was also found to be superior to a previous-generation investigational PCD-CT scanner with larger detector pixels.