Half-dose coronary artery calcium scoring. impact of Iterative reconstruction

Purpose: The purpose of this study was to assess the impact of adaptive statistical iterative reconstruction (ASiR) on half-dose coronary artery calcium scoring (CACS) acquisition protocol. Materials and Methods: Between September 2016 and October 2017, 89 patients (54 male patients, mean age 64.6±10.7 y) with a clinically indicated coronary computed tomography angiography were prospectively enrolled. On a 64-row computed tomography scanner, patients underwent a standard CACS protocol (120 kVp, 170 mAs) reconstructed by filtered-back projection, and a half-dose CACS protocol (120 kVp, 85 mAs) reconstructed by ASiR at different percentages, from 10% to 100%, in 10% increments. CACS determinants (Agatston score, number of plaques, volume, and mass), signal-to-noise ratio, contrast-to-noise ratio, and radiation dose of both protocols were calculated. Patient risk categories based on CACS were determined for each protocol, and analysis of risk reclassification of half-dose protocol was performed. Depending on their body mass index (BMI), patients were divided into nonobese (BMI<30 kg/m2) and obese (BMI≥30 kg/m2) groups to investigate the influence of BMI on CACS determinants and risk reclassification. Results: Half-dose protocol reconstructed with ASiR 70% showed no significant differences in any CACS determinant compared with the standard protocol for both nonobese and obese patients (all P≥0.070 and ≥0.066, respectively) and reclassified 1 (1.7%) and 6 (20.0%) patients, respectively, with excellent (κ=0.91) and good (κ=0.74) agreement with standard protocol, respectively. ASiR 70% also resulted in a higher signal-to-noise ratio (1.88±0.78) and contrast-to-noise ratio (7.10±2.73) compared with standard protocol (all P≤0.001). Half-dose protocol provided 52% less radiation dose than standard acquisition (0.31±0.06 vs. 0.64±0.10 mSv; P<0.001). Conclusions: ASIR 70% coupled with reduction of tube current by 50% allowed for significant dose reduction and no detrimental effects on image quality, with minimal patient reclassification in nonobese patients. In obese patients, excessive noise may lead to a clinically significant reclassification rate.