Feasibility study of low tube voltage (80 kVp) coronary CT angiography combined with contrast medium reduction using iterative model reconstruction (IMR) on standard BMI patients

Objective: To investigate the feasibility of low-tube-voltage (80kVp) coronary CT angiography (CCTA) combined with contrast medium (CM) reduction and iterative model reconstruction (IMR) on patients with standard body mass index compared with clinical routine protocol. Methods: Retrospectively gated helical CCTA scans were acquired using a 256-slice multi-slice CT (Brilliance iCT; Philips Healthcare, Cleveland, OH) on 94 patients with standard body mass index (20-25 kgm(-2)) who were randomly assigned into 2 groups. The scan protocol for Group 1 was 100kVp and 600mAs with 70 ml CM at an injection rate of 4.5-5.5 mls(-1); images were reconstructed by a hybrid iterative reconstruction technique (iDose(4); Philips Healthcare). Group 2 was scanned at 80kVp and 600mAs with 35 ml CM at an injection rate of 3.5-4.5 mls(-1); images were reconstructed with IMR. Objective measurements such as the mean image noise and contrast-to-noise ratio of the two groups were measured on CT images and compared using the paired t-test. In addition, a subjective image quality evaluation was performed by two radiologists who were blinded to the scan protocol, using a 5-point scale [1 (poor) to 5 (excellent)]. The results of the two groups were compared using Mann-Whitney U test. Results: The iodine delivery rate of Group 2 was 1.0 +/- 0.5 gls(-1) compared with 2.1 +/- 0.5 gls(-1) in Group 1 resulting in a reduction of 52.4%. In addition, an effective radiation dose reduction of 56.4% was achieved in Group 2 (2.4 +/- 1.2mSv) compared with Group 1 (5.5 +/- 1.4mSv). The mean CT attenuation, contrast-to-noise ratio and image quality of all segments in Group 2 were significantly improved compared with those in Group 1 (all, p<0.01). Conclusion: The use of IMR along with a low tube voltage (80kVp) combined with a low CM protocol for CCTA can reduce both radiation and CM dose with improved image quality. Advances in knowledge: In this study, we used a novel knowledge-based IMR which remarkably reduced the image noise. We compared the quality of the images obtained when the tube voltage was reduced to 80 kVp and that of those obtained according to the clinical routine protocols to determine whether ultra-low-dose imaging plus IMR is feasible in CCTA scans. We found that a low dose protocol combined with 80 kVp and reduced CM for CCTA can reduce both radiation dose and CM dosewith improved image quality by the use of IMR in non-obese patients.