Ultra-low-dose coronary artery calcium scoring using novel scoring thresholds for low tube voltage protocols—a pilot study

Aims: To determine if tube-adapted thresholds for coronary artery calcium (CAC) scoring by computed tomography at 80 kilovolt-peak (kVp) tube voltage and 70-kVp yield comparable results to the standard 120-kVp protocol. Methods and results: We prospectively included 103 patients who underwent standard scanning with 120-kVp tube voltage and additional scans with 80 kVp and 70 kVp. Mean body mass index (BMI) was 27.9 ± 5.1 kg/m2. For the lowered tube voltages, we applied novel kVp-adapted thresholds for calculation of CAC scores and compared them with standard 120-kVp scans using intraclass correlation and Bland-Altman (BA) analysis. Furthermore, risk-class (CAC score 0/1-10/11-100/101-400/>400) changes were assessed. Median CAC score from 120-kVp scans was 212 (interquartile range 25-901). Thirteen (12.6%) patients had zero CAC. Using the novel kVp-adapted thresholds, CAC scores derived from 80-kVp scans showed excellent correlation (r = 0.994, P < 0.001) with standard 120-kVp scans with BA limits of agreement of -235 (-39.5%) to 172 (28.9%). Similarly, for 70-kVp scans, correlation was excellent (r = 0.972, P < 0.001) but with broader limits of agreement of -476 (-85.0%) to 270 (48.2%). Only 2 (2.8%) reclassifications were observed for the 80-kVp scans in patients with a BMI <30 kg/m2 (n = 71), and 2 (6.1%) for the 70-kVp scans in patients with a BMI <25 kg/m2 (n = 33). Mean effective radiation dose was 0.60 ± 0.07 millisieverts (mSv), 0.19 ± 0.02 mSv, and 0.12 ± 0.01 mSv for the 120-kVp, 80-kVp, and 70-kVp scans, respectively. Conclusion: The present study suggests that CAC scoring with reduced peak tube voltage is accurate if kVp-adapted thresholds for calculation of CAC scores are applied while offering a substantial further radiation dose reduction.