Author: Afrouz Ataei, Victor Moy, Mark P. Supanich 👨🔬
Affiliation: Rush University 🌍
Purpose: To evaluate iodine quantification and CT number accuracy in coronary CT angiography (CTA) using standard and ultra-high resolution (UHR) modes of photon-counting CT (PCCT) across different dose levels and phantom sizes.
Methods: Iodine rods (5, 10, 15, 20 mg/mL) were inserted into 20 cm (small) and 40 cm (large) phantoms. Scans were performed with a NAEOTOM Alpha PCCT system at 120 kV and 140 kV using standard and UHR modes at 15, 20, and 25 mGy. Virtual monoenergetic images (VMIs) at 70 keV were reconstructed with a vascular kernel. Measured iodine concentrations were compared to nominal values through linear regression (R²), and CT number accuracy was evaluated by absolute percentage errors (APEs) relative to NIST values.
Results: The measured iodine concentrations versus nominal values demonstrated linearity across all modes and dose levels, with minimal deviations for the small phantom, exhibiting mean absolute percentage differences (MAPDs) below 5%.In the large phantom, MAPDs increased to 25% at 120 kV and 15 mGy in standard mode, while at 140 kV in standard mode,MAPDs remained below 5%. At higher dose levels and in UHR mode, the 120 kV performance improved.Notably,at 140 kV,MAPDs in UHR mode increased with higher doses (13% to 27%) compared to the lower doses.CT number APEs varied by phantom size,dose, and mode:In small phantom the UHR mode showed APEs of 2–31% (120 kV) and 2–38% (140 kV), with higher errors at lower doses. In large phantom the APEs ranged from 0–31% (120 kV) and 0–46% (140 kV), with UHR mode showing greater variability at 15 mGy.UHR mode maintained superior iodine quantification despite increased CT number variability in large phantoms at lower doses.
Conclusion: UHR mode enhances small-vessel visualization and iodine quantification in coronary CTA. However, optimizing protocols for larger patients and lower doses is necessary to address scatter and beam-hardening effects.