Coronary artery and thoracic calcium on noncontrast thoracic CT scans: comparison of ungated and gated examinations in patients from the COPD Gene cohort.

OBJECTIVE: Coronary artery calcification (CAC) and thoracic aortic calcification, (TAC) are frequently detected on ungated multidetector computed tomography (MDCT) performed for lung evaluations. We sought to evaluate concordance of CAC and TAC scores on ungated (thoracic) and electrocardiogaphically (ECG)-gated (cardiac) MDCT scans.
METHODS: Fifty patients, enrolled in the Genetic Epidemiology of COPD study (COPDGene), were recruited to undergo gated CAC scans with 64-detector row CT, in addition to the ungated thoracic studies already being obtained as part of their study evaluation. Coronary and thoracic calcium were measured similarly (Agatston score, requiring 3 contiguous voxels of >130 Hounsfield units) with low-dose ungated studies and ECG-gated MDCT performed at the same scanning session. Intertechnique scoring variability and concordance were calculated.
RESULTS: Correlations between gated and ungated CAC and TAC were excellent (r = 0.96). The relative differences (median variability) measured by ECG-gated versus ungated MDCT were relatively high for CAC (44%) but not for TAC (8%). Prevalence of depicted CAC (n = 33; 66%) and TAC (n = 21; 42%) were coincident between ECG-gated and ungated MDCT, respectively (intertechnique concordance, 100%). Bland-Altman plots for CAC showed mean differences of 354 (confidence interval, 169-538) and 16.1 (confidence interval, -89 to 121).
CONCLUSION: Low-dose ungated MDCT is reliable for prediction of the presence of CAC and assessment of Agatston score. Concordance between methods and between TAC and CAC is high. This technique should allow for atherosclerotic disease risk stratification among patients undergoing ungated lung CT evaluation without requiring additional scanning. Measurement of TAC is almost as accurate from gated CT, and CAC scores are highly concordant.