Ultra-high-resolution CT and multi-resolution visualization of calcified coronary artery plaques: an ex vivo human study

Background: With new advances in CT energy-integrating (EID) and photon-counting (PCD) detector technology, the spatial resolution of CT has significantly improved from 0.50 mm to less than 0.25 mm isotropic. Our goal was to explore the image quality improvements that are associated with UHR CT, specifically in imaging and characterization of atherosclerotic plaques. Methods: We imaged seven excised human hearts, with a known history of atherosclerosis, on an EID-CT scanner equipped with a UHR comb. The scans were performed at 120 kVp and 211 mAs, with 1-sec gantry rotation time. The images were reconstructed twice; first with a standard resolution (SR) reconstruction kernel (Uq36u) at 0.5x0.5x3.0 mm(3) voxel size, and second with a UHR kernel (Uq77u) at 0.2x0.2x1.5 mm(3). We measured calcium volume, Agatston score, and number of lesions with dense calcification (HU>1000). We propose a multi-resolution visualization scheme in which smooth soft tissue features are derived from the SR image, and the sharp hard plaque features blended from the UHR images. Results: We detected a total of 105 lesions in the seven hearts. The UHR images had significantly reduced blooming artifacts which leads to higher average HU values and smaller lesion volumes. The calcium volume for UHR was 67% of the SR volumes (r(2) = 0.81). Agatston scores were also systematically lower in UHR compared to SR 41% (r(2) = 0.81). In addition, we found 102 lesions with dense calcification compared to 4 in SR. Conclusion: UHR-CT can significantly reduce blooming artifacts and partial volume effects in atherosclerotic plaque imaging.