Photon-Counting Detector CT Virtual Monoenergetic Images for Coronary Artery Stenosis Quantification: Phantom and In Vivo Evaluation.

Background: Calcium blooming causes stenosis overestimation on coronary CTA. Objective: To evaluate the impact of virtual monoenergetic imaging (VMI) reconstruction level on coronary artery stenosis quantification using a photon-counting detector (PCD) CT. Methods: A phantom containing two custom-made vessels (25% and 50% stenoses) underwent PCD CT acquisitions without and with simulated cardiac motion. A retrospective analysis was performed of 33 patients (7 female, 26 male; mean age, 71.3±9.0 years; 64 coronary artery stenoses) who underwent coronary CTA by PCD CT followed by invasive coronary angiography (ICA). Scans were reconstructed at nine VMI levels (40-140 keV). Percentage diameter stenosis (PDS) was measured, and bias was determined from the ground-truth stenosis percentage in the phantom and ICA-derived quantitative coronary angiography measurements in patients. Extent of blooming artifacts was measured in the phantom and in calcified and mixed plaques in patients. Results: In the phantom, PDS decreased for the 25% stenosis from 59.9% (40 keV) to 13.4% (140 keV), and for the 50% stenosis from 81.6% (40 keV) to 42.3% (140 keV). PDS showed lowest bias for the 25% stenosis at 90 keV (bias, 1.4%), and for the 50% stenosis at 100 keV (bias, -0.4%). Blooming artifacts decreased for the 25% stenosis from 61.5% (40 keV) to 35.4% (140 keV), and for the 50% stenosis from 82.7% (40 keV) to 52.1% (140 keV). In patients, PDS for calcified plaque decreased from 70.8% (40 keV) to 57.3% (140 keV), for mixed plaque decreased from 69.8% (40 keV) to 56.3% (140 keV), and for non-calcified plaque was 46.6% at 40 keV and 54.6% at 140 keV. PDS showed lowest bias for calcified plaque at 100 keV (bias, 17.2%), for mixed plaque at 140 keV (bias, 5.0%), and for non-calcified plaque at 40 keV (bias, -0.5%). Blooming artifacts decreased for calcified plaque from 78.4% (40 keV) to 48.6% (140 keV), and for mixed plaque from 73.1% (40 keV) to 44.7% (140 keV). Conclusion: For calcified and mixed plaque, stenosis severity measurements and blooming artifacts decreased at increasing VMI. Clinical Impact: PCD CT with VMI reconstruction helps overcome current limitations in stenosis quantification on coronary CTA.