Image quality and radiation exposure with low-contrast-dose computed tomography angiography of the lower extremities

Introduction
Multidetector computed tomography is the reference standard for the diagnosis of peripheral arterial disease (PAD). The aim of this study is to optimise the image quality of computed tomography (CT) scanning for the diagnosis of PAD with the lowest possible radiation and contrast volume.

Material and methods
Seventy-two patients were referred for evaluation of suspected PAD with CT angiography. Patients were randomly assigned to an optimise care dose of kVp – group A, n = 36; 18 men, 18 women; mean age, 63 years with standard deviation 15; range, 20-88 years (contrast volume 80-85 ml was injected automatically with bolus tracking, and group B, n = 36; 18 men, 18 women; mean age, 61 years with standard deviation 16; range, 26-88 years (contrast volume 120-140 ml was injected automatically with bolus tracking). Other scanning parameters were kept constant. Lower extremities vessel enhancement and image noise were quantified, and the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Subjective vessel contrast was assessed by two radiologists in consensus.

Result
A total of 16 cases of PAD (22.2%) were found in the evaluated of subjects (10 in group A, and six in group B). All PAD cases were detected by the two readers. There was no significant difference in the size or location of the PAD between the two groups; the average image noise was 19 HU for group A and 16 HU for group B. The difference was not statistically significant (p = 0.183). Overall, the SNR and CNR were slightly higher in group B (25.5 and 24.1, respectively) compared with group A (20 and 17.4, respectively), but those differences were not statistically significant (p = 061 and p = 0.38, respectively).

Conclusions
All patients were evaluated by lower extremities CTA protocol allowing similar image quality to be achieved in both groups, with optimised care dose for both protocols, and contrast volume was reduced by 40% in the new protocol group compared to the conventional protocol group.