Author: Afrouz Ataei, Victor Moy, Mark P. Supanich 👨🔬
Affiliation: Rush University 🌍
Purpose: This study evaluates the impact of ultra-high resolution (UHR) mode on the visualization of small vessels in coronary computed tomography angiography (CTA) using a photon-counting CT scanner. Comparisons were made with standard reconstruction modes across varying dose levels and phantom sizes to assess visualization and image noise.
Methods:
Three iodine inserts (5 mg/mL) mimicking contrast-enhanced vessels (diameters: 2, 5, and 10 mm) were embedded in two phantoms (20 cm and 40 cm lateral dimensions). Scans were performed on a photon-counting CT system (NAEOTOM Alpha) at 120 and 140 kV in both standard and UHR modes, using three dose levels. Virtual monoenergetic images (VMIs) at 70 keV were reconstructed with a vascular kernel. Visualization of small vessels was qualitatively assessed. Image noise was quantified using root-mean-square (RMS) calculations in four circular regions of interest (ROIs) in the central and peripheral regions of each phantom.
Results: In the 20 cm phantom, all iodine rods (2, 5, and 10 mm) were discernible at all dose levels. In the 40 cm phantom, the 2-mm rod was visible only in UHR mode at higher dose levels (25 mGy) for both 120 kV and 140 kV scans. RMS noise in the 20 cm phantom decreased significantly with UHR mode compared to standard mode at equivalent doses (e.g., at 120 kV and 20 mGy: 0.65 vs. 2.39, respectively). In the 40 cm phantom, central noise measurements showed slightly higher RMS values in UHR mode (e.g., at 140 kV and 20 mGy: 4.07 vs. 7.69, respectively). Peripheral noise analysis revealed similar trends.
Conclusion: Ultra-high-resolution mode significantly improves visualization of small vessels in coronary CTA, particularly in larger phantoms and at higher doses. UHR mode reduces image noise in smaller phantoms while maintaining acceptable noise levels in larger phantoms, enhancing its utility for coronary CTA applications.