Coronary Artery Calcifications Assessment with Photon-counting Detector Computed Tomography

Coronary artery calcification (CAC) diagnoses have been commonly assessed since 1990 using the Agatston score (AS). AS is conventionally performed using low-dose CT and with limited resolution in the axial direction, performed with a tube potential of 120 kilovolt peak and a reconstructed slice thickness of 3 mm. The drawback of the protocol is the blooming artifact that occurs along the axial direction, making it subject to patient misclassification between risk categories. Recently, a new detector technology has been introduced for X-ray CT: the photon-counting detector (PCD). With PCDs, the contrast, noise, and resolution properties are improved. One of the first assessed clinical applications of these novel PCD-CT scanners has been CAC detection and quantification. This chapter will introduce the AS definition and illustrate the effect of the blooming artifact on phantom images. Results of the first phantom and clinical studies using PCDs for CAC assessment are then presented. It has been shown that ASs from PCD-CT are comparable to conventional energy-integrating detectors (EIDs). However, the enhanced resolution of PCD-CT reduces the blooming artifact leading to the detection of smaller calcifications, improving the reproducibility, and reducing the calcification volume overestimation. PCD-CT can also provide spectral information that can be used to compute virtual monoenergetic images (VMIs). VMIs computed around 70 keV provide an AS similar to the conventional image.