CT Angiography of the Aorta: Prospective Evaluation of Individualized Low-Volume Contrast Media Protocols

Purpose: To prospectively develop individualized low-volume contrast media (CM) protocols adapted to tube voltage in patients undergoing computed tomographic (CT) angiography of the aorta. Materials and Methods: The study was approved by the institutional review board and local ethics committee. All patients provided written informed consent. CT angiography was performed by using automated attenuation-based tube voltage selection (ATVS) (range, 70-150 kVp; 10-kVp increments). Iodine attenuation curves from an ex vivo experiment in a phantom were used to design CM protocols for CT angiography of the thoracoabdominal aorta in 129 consecutive patients (hereafter, cohort A). Further modified CM protocols based on results in cohort A were designed with the aim of homogeneous vascular attenuation of 300-350 HU across tube voltages and were applied to another 61 consecutive patients (cohort B). Three independent blinded radiologists assessed subjective image quality, and one reader determined objective image quality. The Kruskal-Wallis test was performed to test for differences in subjective image quality, and linear regression was performed to test for differences in objective image quality between the automatically selected tube voltages. Results: Experiments revealed tube voltage-dependent iodine attenuation curves, which were used to determine the CM protocols in cohort A; these ranged from 68 mL at 110 kVp to 45 mL at 80 kVp. In both cohorts, ATVS selected 80 kVp in 62 patients, 90 kVp in 84, 100 kVp in 33, and 110 kVp in 11. In cohort A, image quality that was satisfactory or better was attained in 126 (98%) of 129 patients who had no significant differences in subjective image quality between tube voltages (P =.106) but who did have significant differences in attenuation and contrast-to-noise ratio (CNR) (P<.001 for both). In cohort B, the furthermodified CM protocol (from 33 mL at 80 kVp to 68 mL at 110 kVp) yielded image quality that was satisfactory or better in all 61 (100%) patients, without significant differences in subjective image quality (P =.178), and without significant differences between tube voltage and attenuation (P =.108), noise (P =.250), or CNR (P =.698). Conclusion: Individualized low-volume CM protocols based on automatically selected tube voltages are feasible and yield diagnostic image quality for CT angiography of the aorta. (C) RSNA, 2016.