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Coronary Artery Calcium: Accuracy and Reproducibility of Measurements with Multi–Detector Row CT—Assessment of Effects of Different Thresholds and Quantification Methods¹

¹ From the Mallinckrodt Institute of Radiology, Washington University School of Medicine, Campus Box 8131, 510 S Kingshighway Blvd, St Louis, MO 63110. Received April 7, 2002; revision requested June 17; final revision received October 3; accepted October 23. Address correspondence to K.T.B. (e-mail: baet@mir.wustl.edu).

View larger version (28K): [in a new window]   Figure 1. Phantom study. Scatterplot shows relationship between CT threshold and error in volume measurement, expressed as a percentage of the original value. There is a clear tendency for the volume error to decrease as CT threshold increases (r = -0.50, P < .01). Small circles = 3-mm lesion, large circles = 5-mm lesion, white circles = calcium density of 200 mg/cm3, gray circles = 400 mg/cm3, black circles = 800 mg/cm3.

View larger version (27K): [in a new window]   Figure 2. Phantom study. Scatterplot shows relationship between CT threshold and error in mass measurement, expressed as a percentage of the original value. There is a clear tendency for the mass error to increase as CT threshold increases (r = 0.46, P < .01). Small circles = 3-mm lesions, large circles = 5-mm lesions, white circles = calcium density of 200 mg/cm3, gray circles = 400 mg/cm3, black circles = 800 mg/cm3.

View larger version (19K): [in a new window]   Figure 3. Phantom study. Scatterplot shows relationship between calcium density and error in mass measurement, expressed as a percentage of the original value. There is a clear tendency for mass error to be smaller with higher calcium densities. Differences in the means are statistically significant (analysis of variance, P < .01). Small circles = individual value, large circles = mean, error bar = SD.

View larger version (26K): [in a new window]   Figure 4. Phantom study. Scatterplot shows relationship between volume error and mass error, expressed as a percentage of the original value. There is a clear relationship between the relative size of the errors (r = 0.91, P < .01), although the volume errors have a much larger range. There are slight but consistent differences between 3-mm (small circles aligned along the lower curve) and 5-mm (large circles aligned along the upper curve) lesions, which increase with calcium density. White circles = calcium density of 200 mg/cm3, gray circles = 400 mg/cm3, black circles = 800 mg/cm3.

View larger version (21K): [in a new window]   Figure 5. Clinical study. Scatterplot shows comparison of mass measurements between the initial scan (scan 1) and the repeat (scan 2). Results of mass measurements with scans 1 and 2 are highly correlated (r > 0.99, P < .01), with an almost exact one-to-one correspondence.

View larger version (30K): [in a new window]   Figure 6. Clinical study. Scatterplot shows relationship between image noise and interscan percentage difference for score (), volume (), and mass () measurements. Percentage difference tends to increase with image noise (r > 0.48 and P < .01 for all measurements).

View larger version (21K): [in a new window]   Figure 7. Clinical study. Scatterplot shows interscan variability with the mass method for individual vessels. Interscan variability is not significantly different (analysis of variance, P = .19). = individual value, = mean, error bar = SD, Cx = circumflex, LM+LAD = left main and left anterior descending coronary arteries, RCA = right coronary artery.