Coronary Artery Calcium Quantification at Multi–Detector Row CT: Influence of Heart Rate and Measurement Methods on Interacquisition Variability—Initial Experience

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Abstract
To assess the effect of heart rate on interacquisition variability in different coronary calcium quantification methods at multi-detector row computed tomography (CT). Fifty consecutive adults (39 men and 11 women; mean age, 57 years +/- 13 [SD]) with various heart rates were examined with two prospectively electrocardiographically triggered multi-detector row CT acquisitions in succession for detection and quantification of coronary artery calcification. Calcium score, volume, and mass were measured for each acquisition. Interacquisition variability was evaluated in association with heart rate and quantification method in subjects and individual coronary vessels by using t tests and analysis of variance. In 37 subjects with detected calcium, interacquisition variability in mass measurement (10.4%) was significantly lower than that in score (23.9%) and volume (15.7%) measurements (P <.02). The interacquisition variability in all quantification methods was well correlated with heart rate and was considerably greater when heart rates were higher than 70 beats per minute (bpm) than when heart rates were 70 bpm or lower (P <.002). There was a clear tendency for interacquisition variability to vary by vessel (P <.01). The correlation of interacquisition variability with heart rate and a significant difference in interacquisition variability between the group with heart rates of 70 bpm or lower and the group with rates higher than 70 bpm (P <.02) were found for the left main and left anterior descending arteries but not for the circumflex and right coronary arteries. Interacquisition variability in coronary calcium measurements at multi-detector row CT is significantly less at lower heart rates. The coronary calcium mass measurement is more reproducible than are score and volume measurements.