Coronary artery calcium scoring: Influence of reconstruction interval and reconstruction increment using 64-MDCT

OBJECTIVE. Assessment of coronary artery calcification is increasingly used for cardiovascular risk stratification. However, a scanning protocol for modern MDCT has not been established. In this study, we evaluated the impact of the reconstruction interval within diastole and the reconstruction increment on the coronary calcium score. MATERIALS AND METHODS. In 40 consecutive patients Agatston scores and volumetric scores were assessed using a 64-MDCT scanner. The patients were assigned to two groups at random with 20 patients each: in group A, collimation was 64 x 0.6 mm; in group B, it was 20 x 1.2 mm. All CT examinations were performed with retrospective ECG gating. For each patient, five data sets were created throughout diastole (50%, 55%, 60%, 65%, and 70% of the R-R interval). For each reconstruction, two data sets were calculated with a reconstruction increment of 3.0 and 1.5 mm, respectively. For all reconstructions, the mean Agatston scores and volumetric scores ± SD and the coefficient of variance were assessed. Furthermore, for each reconstruction, patients were assigned a percentile rank that described the level of cardiovascular risk. RESULTS. Four patients had to be excluded from the study because no coronary calcium was detected on any of the reconstructions. In both groups, the mean Agatston score was not significantly different between reconstruction increment 3.0 mm and reconstruction increment 1.5 mm (group A, 112.1 ± 92.5 and 114.3 ± 93.6, p = 0.28; group B, 164.8 ± 203.0 and 169.4 ± 207.9, p = 0.29, respectively). However, in two cases, very small calcified lesions in the circumflex coronary artery were only detected using a reconstruction increment of 1.5 mm. In both groups, the mean coefficient of variation was not significantly different at reconstruction increment 1.5 mm (group A, 11.4 ± 8.2; group B, 12.5 ± 7.6) and reconstruction increment 3.0 mm (group A, 14.8 ± 9.3; group B, 14.2 ± 9.1; group A, p = 0.18; group B, p = 0.48). Based on the reconstruction increment and reconstruction interval, 77% of the patients (n = 14) in group A were assigned to one risk group and 23% (n = 4) to two different risk groups according to percentile strata. In group B, 83% of the patients (n = 15) were assigned to one risk group and 17% (n = 3) to two different risk groups. In contrast to the Agatston score, the volumetric score was significantly higher in both groups at reconstruction increment 1.5 mm (group A, 105.4 ± 78.5 mm ³ ; group B, 153.8 ± 182.5 mm ³ ) compared with reconstruction increment 3.0 mm (group A, 90.0 ± 73.11 mm ³ ; group B, 138.2 ± 166.8 mm ³ ; p < 0.05). CONCLUSION. Using a 64-MDCT scanner, the calcium score calculated from different reconstructions within early diastole is variable, but the difference can be minimized using overlapping slice reconstructions. The variation does not lead to a different risk estimation in most patients. In patients with mild coronary calcifications, the use of overlapping slices may help to detect small calcified plaques. Furthermore, we recommend the use of ECG-controlled tube current modulation to reduce the radiation exposure.