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Coronary Calcification: Effect of Small Variation of Scan Starting Position on Agatston, Volume, and Mass Scores¹

¹ From the Department of Radiology (A.R., M.P.) and Image Sciences Institute (I.I.), University Medical Center Utrecht, Heidelberglaan 100, Room E01.132, 3584 CX Utrecht, the Netherlands. Received January 3, 2007; revision requested March 2; revision received March 9; accepted April 13; final version accepted April 26. Address correspondence to A.R. (e-mail: a.rutten{at}umcutrecht.nl).

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. 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 ( = 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.

© RSNA, 2007

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