Contrast injection protocols for coronary computed tomography angiography using a 64-detector scanner: comparison between patient weight-adjusted- and fixed iodine-dose protocols.

OBJECTIVE

To compare patient-weight-adjusted and fixed iodine-dose protocols at coronary computed tomography angiography (CTA) using a 64-detector scanner and computer-assisted bolus tracking.

MATERIALS AND METHODS

Approval from our institutional review board and patient prior informed consent were obtained before entering 60 patients with suspected coronary disease in this study. The patients were randomly assigned to one of 2 protocols. In the fixed iodine-dose protocol, they received a fixed dose of 80 mL Iopamidol-370; the injection duration was 20 seconds. In the weight-adjusted iodine-dose protocol, the dose was tailored to the patient body weight; this group received 1.0 mL/kg and the injection duration was shorter, ie, 15 seconds. Imaging was on a 64-detector CT scanner using a computer-assisted bolus tracking technique. A radiologist blinded to the protocol used measured the Hounsfield density number of the large vessels and coronary arteries. CT attenuation in the aortic root was compared in patients whose weight was less than 58 kg (group 1) or 58 kg or more (group 2). The standard deviation (SD) of CT attenuation in the aortic root and the myocardium was compared with evaluate image noise. Using a 3-point scale, 2 radiologists independently evaluated beam-hardening artifacts and coronary enhancement. Statistical analysis was with the two-tailed Student t test and the Mann-Whitney U test.

RESULTS

There was no significant difference between the protocols with respect to CT attenuation of the ascending aorta and coronary arteries. Under the fixed-iodine-dose protocol, mean CT attenuation in the aortic root was 421.3 +/- 51.5 Hounsfield unit (HU) in the lighter-, and 397.2 +/- 42.3 HU in the heavier weight group, respectively; the difference was statistically significant (P = 0.03). Under the weight-adjusted iodine-dose protocol, these values were 407.6 +/- 85.1 and 409.2 +/- 47.9 HU, respectively and the difference was not statistically significant (P = 0.17). The SD of the ascending aorta and myocardium was significantly higher for the fixed- than the weight-adjusted iodine-dose protocol. The mean visual score for beam-hardening artifacts was significantly lower in the weight-adjusted- than the fixed-iodine-dose protocol (P < 0.01), however, there was no significant difference in the enhancement of the coronary arteries (P = 0.82).

CONCLUSION

At 64-detector CTA of the heart, the patient weight-tailored dose protocol with the 15-second injection duration yielded significantly better image quality than the fixed-dose, 20-second injection duration protocol.