Novel single-source high-pitch protocol for CT angiography of the aorta: comparison to high-pitch dual-source protocol in the context of TAVI planning

Abstract

Purpose Computed tomography (CT) is increasingly being used for planning purposes prior to trans-arterial valve implantation (TAVI). High-pitch protocols using a 2nd generation dual-source CT (DSCT) allow for a comprehensive assessment of the aortic valve anulus, its distance to the coronary artery ostia, the aortic bulbus and the iliofemoral arteries with very low radiation exposure and low amount of contrast agent. The aim of this study was to evaluate the image quality of a comparable high-pitch scan mode in a modern single-source CT (SSCT) system. Methods 40 patients with severe symptomatic aortic valve stenosis have been examined for planning purposes prior to TAVI. The first 20 consecutive patients were examined with a 2nd generation DSCT system using a high-pitch scan mode (pitch value 3.4) and 60 ml of contrast agent. The second group of 20 consecutive patients were examined with a 128-slice SSCT system, using a high-pitch scan mode (pitch value of 1.7) and 60 ml of contrast agent. Image quality of the aortic valve, the ascending aorta, the coronary artery ostia, the iliofemoral arteries and overall image quality were graded in a blinded fashion using a 4-point-grading-scale. Furthermore, signal intensity and image noise were derived in the ascending aorta and in the ilio-femoral arteries. Results There was a minor but significant difference in the overall image quality score with lower image quality in SSCT (3.5 ± 0.6) when compared to DSCT (3.85 ± 0.4; p = 0.037). The mean image quality score was significantly higher in patients examined in DSCT when compared to SSCT regarding the evaluability of the coronary ostia (4.0 vs. 3.5; p < 0.01) and the image quality of the ascending aorta (4.0 vs. 3.5; p < 0.01). There was no significant difference in evaluation of the aortic valve and its anulus (3.85 for DSCT and 3.65 for SSCT; p = 0.149) and image quality of the iliofemoral arteries (3.65 for DSCT and 3.85 for SSCT; p = 0.140). Signal intensity and image noise did not differ significantly between both groups. Conclusions This study presents a novel high-pitch protocol for modern SSCT scanners, which allows CT angiography for TAVI planning with a similar radiation dose and contrast agent exposition and only small compromises in image quality compared to a high-pitch protocol on a DSCT scanner.