Purpose: To retrospectively evaluate the effect of a small variation of scan starting position on coronary artery calcium scores based on nonoverlapping 3-mm multidetector computed tomographic (CT) data sets.
Materials and methods: Informed consent and institutional review board approval were obtained. A retrospective study was performed by using prospective unenhanced electrocardiographically triggered cardiac multidetector CT scans in 228 women (mean age, 67 years +/- 5 [standard deviation]). From the original 1.5-mm data set, two sets of adjacent images with a section thickness of 3 mm and a variation in starting point of 1.5 mm were obtained. Calcium scoring was performed to acquire Agatston, volume, and mass scores. Subjects were assigned to one of five risk categories (I-V) according to the Agatston score of each 3-mm data set and the average score. Kappa value was calculated to assess agreement in risk category assignment. Differences and relative differences between scores obtained for both 3-mm data sets were calculated overall and according to risk category. The effect of scoring algorithm on the relative differences between scores was analyzed with the Wilcoxon signed rank test.
Results: Categories I-V contained 102, 35, 48, 31, and 12 subjects, respectively. For all scoring algorithms, median relative differences decreased from more than 130% in category II to less than 10% in category V. In the three highest categories, relative differences were significantly smaller for volume and mass scores than for Agatston scores (P < .05). Twenty-one subjects were assigned to different risk categories between the two data sets (kappa = 0.87). Eleven patients were assigned a nonzero score in one and a zero score in the other data set.
Conclusion: A small variation in scan starting position can substantially influence calcium measurements and poses an inherent limit to calcium scoring with contiguous 3-mm sections. Mass and volume scores are slightly less affected than are Agatston scores.