Automatic Coronary Calcium Scoring in Low-Dose Non-ECG-synchronized Chest Computed Tomography (CT) Scans from a Lung Cancer Screening Trial

PURPOSE: Coronary calcium scores from lung cancer screening computed tomography (CT) have been shown to be an independent predictor of cardiovascular events. Given the large number of cases and the inherent large variability induced by motion artifacts on these non-gated scans, automatic calcium scoring might be a feasible option. We therefore evaluated the performance of automatic coronary calcium scoring in this setting. METHOD AND MATERIALS: We included 1796 baseline scans from the Nelson trial, a lung cancer screening program with low-dose chest CT (16 x 0.75 mm, 30 mAs, no IV contrast, no ECG synchronization). All scans were reconstructed to 3.1 mm-sections with 1.4 mm increment. Scans with beam hardening artifacts due to metal implants were identified and excluded. Automatic calcium scoring was performed using a method based on multi-atlas registration and pattern recognition. Each scan was inspected by one of four trained observers. When needed, the observers corrected automatically identified calcifications. Because stents could not be securely differentiated, they were scored as calcifications. Agatston and volume scores were computed for the automatic method and after manual correction. Each subject was assigned to a cardiovascular risk category based on the Agatston score. To estimate the interobserver agreement, a subset of 45 scans was manually scored by two observers. Spearman's rank correlation was computed to assess the agreement between the automatically and manually corrected volume scores, and between observers. Linearly weighted kappa statistic was calculated to evaluate the agreement in cardiovascular risk category assignments. RESULTS: The mean volume score was 534 mm3 (range:0-11,778 mm3) based on the manually corrected scores. Fourteen (0.8%) scans with large metal implants had to be excluded. We found a correlation ? of 0.88 and an agreement ? of 0.79 between the automatic and manually corrected scores. Interobserver agreement resulted in ? = 0.89, and ? = 0.83. CONCLUSION: Fully automatic coronary calcium scoring in a lung cancer screening program is feasible. Agreement of automatic scores with observer scores is similar to interobserver agreement. CLINICAL RELEVANCE/APPLICATION: Automatic estimation of cardiovascular risk in lung cancer screening can expand the scope of screening and help identify high-risk subjects who might benefit from preventive cardiovascular treatment.