Ultra low dose MDCT angiography of thoracic aorta using a combined ED-saving strategy and two contrast media with different iodine concentrations

Introduction: Aim of the study is to compare vascular contrast enhancement and feasibility of low dose multidetector computed tomography (MDCT) angiography of thoracic aorta using a combined ED-saving strategy and two contrast media with different iodine concentration (Iodixanol 320 mgI/mL and Iomeprol 400 mgI/mL) at different tube voltage (80 - 100 Kvp). Methods: We enrolled 86 patients referred to our hospital for thoracic aorta evaluation by MDCT. Patients were randomized into four groups: Group A (CT with Iodixanol 320 and 80 Kvp), Group B (CT with Iodixanol 320 and 100 Kvp), Group C (CT with Iomeprol 400 and 80 Kvp) and Group D (CT with Iomeprol 400 and 100 Kvp). The image quality was evaluated using a semiquantitative score (0: not evaluable, 1: average, 2: good) and for each patient, attenuation, image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and effective dose (ED) were measured and compared among groups. All MDCT were performed using prospective ECG triggering (padding 0) and adaptive statistical iterative reconstruction algorithm (ASIR). Attenuation values were measured at the level of the ascending aorta and liver parenchyma and for all groups different injection protocols were setted for mainteining the same iodine delivery rate. Results: No significant differences were found among the four groups in terms of age, genders and BMI. The two contrast media didn't show significant differences in attenuation, noise, SNR and CNR between groups with same kV, but attenuation values were statistically significant higher in group with low kV. We didn't found significant differences in terms of mean attenuation and noise between Group A and Group C (726±97-49±11.08 and 730.96±121.18-47.3±13.01 respectively) and between Group B and Group D (555.01±76.86- 28.47±10.16 and 577.73±88.80-33.12±7.69, respectively). On the contrary, attenuation values were significantly higher in Group A versus Group B (726±97 vs. 555.01±76.86, p<0.0005) and in Group C versus Group D (730.96±121.18 vs 577.73±88.80, p<0.0003). Significant differences in SNR and CNR were found among groups with 80 kV versus groups using 100 kV irrespective of the type of contrast media, but without a significant loss of image quality. ED was significantly lower in groups A and C with 80 kV (1.65±0.25 and 1.57±0.27 mSv respectively) than in groups B and D (3.03±0.41 and 2.8±0.40 mSv respectively). Conclusions: Iodixanol 320 and Iomeprol 400 injected at same iodine delivery rate did not show statistically significant differences in vascular contrast enhancement. CT protocols using 80 kV are feasible and allow significant reduction of radiation dose for CT angiography of the thoracic aorta without compromising image quality.