The aim of the study was to optimize low-dose scanning protocols for the test bolus technique in 64-detector computed tomography (CT) angiography (CTA) of the head and neck.

A total of 250 patients were randomly divided into 5 groups of 50 patients each: conventional group (group A: 120 kV, 100 mA) and low-dose groups (group B: 100 kV, 100 mA; group C: 100 kV, 50 mA; group D: 80 kV, 100 mA; and group E: 80 kV, 50 mA). Subjective scores and objective measurements (CT values of the aortic arch, image noise, and signal-to-noise ratio) were used to evaluate the image quality and compare the radiation doses of the 5 groups.

The image quality of the 5 groups met the diagnostic requirements, with no significant difference in the subjective evaluation findings (P > 0.05). There were significant differences in the CT values between the conventional group and low-dose groups (P < 0.05); however, there was no significant difference between groups B and C and between groups D and E (P > 0.05). Moreover, the volume CT dose index and dose length product of groups B, C, D, and E decreased by 37.62%, 70.45%, 65.28%, and 83.39%, respectively, compared with those of group A. Although the image noise of the low-dose groups increased, an appropriate reduction in the tube voltage enhanced the contrast medium-induced x-ray attenuation and increased the CT value, which resulted in a nonsignificant difference in the signal-to-noise ratio. Therefore, the image quality of the low-dose groups was not affected compared with that of the conventional group.

In the test bolus technique in 64-detector CTA, the low-dose protocol of using 80 kV and 50 mA reduces the radiation dose by 83.39% compared with the conventional scan, without affecting the image quality.