Influence of body size and section level on calcium phantom measurements at coronary artery calcium CT scanning.

Abstract

To determine whether differences in body mass index (BMI) and image section levels representing the proximal through the distal sections of the heart are associated with attenuation differences in images of calcium phantoms scanned during computed tomographic (CT) imaging of study subjects. Mean attenuation values for three calcium phantoms (each with a different calcium hydroxyapatite concentration), as measured at each of four different image section levels, were obtained for 691 participants in the Muscatine CT Vascular Calcium Study. The subjects were grouped according to sex-specific BMI quartiles, and the degree of attenuation in each phantom was investigated as a function of image section level and BMI quartile. Spearman rank order correlation coefficients and one-, two-, and three-factor repeated-measures analysis of variance were used to examine the association between section level and BMI and the mean phantom attenuations. Attenuation was, for the most part, significantly associated with both section level (P <.005) and BMI quartile (P <.0025-.05). The degree of attenuation tended to decrease in images obtained at the more distal cardiac levels and to increase with increasing BMI quartile. Differences in attenuation related to BMI and image section level appear to have a significant effect on current calcium scoring methods.