Influence of body mass index on coronary artery opacification in 64-slice CT angiography

Purpose: To evaluate the influence of the body mass index (BMI) on coronary artery opacification in 64-slice CT. Material and Methods: Sixty-two patients retrospectively underwent ECG-gated 64-slice CT coronary angiography (tube potential 120 kV, tube current time product 650 mAs) after intravenous injection of 80 ml of iodinated contrast agent (320 mg/ml, 5 ml/s). Attenuation values (HU) were measured and contrast-to-noise ratios (CNR) were calculated in the right coronary artery (RCA) and left main artery (LMA). The CNR was defined as the difference between the mean attenuation in the vessel and the mean attenuation in the perivascular fat tissue divided by the image noise in the ascending aorta. The height and weight of the patients at the time of the CT scan were recorded and the BMI was calculated. Results: The mean BMI was 26.2 +/- 3.2 kg/m(2) (range 19.7-32.2 kg/m(2)), the mean attenuation in the LMA was 330 +/- 64 HU, and the mean attenuation in the RCA was 309 +/- 68 HU. The CNR in the LMA was 16.7 +/- 3.8, and the CNR in the RCA was 15.9 +/- 3.6. The image noise in the ascending aorta significantly correlated with the BMI (r = 0.36, p < 0.01). A weak negative correlation was found between the BMI and LMA attenuation (r = -0.28, p < 0.05), whereas no significant correlation was found for the RCA (r = -0.21, p = 0.12). A significant negative correlation was found between the BMI and the CNR in the RCA (r = -0.41, p < 0.05) and the LMA (r = -0.47, p < 0.001). Conclusion: With constant scan parameters and a constant contrast medium amount, the CNR in both coronary arteries decreases while the BMI increases. This implies a modification of previously standardized and fixed examinations with respect to individually adapted protocols with variable parameters for CT coronary angiography.