Retrospective assessment of low-dose and low-contrast agent protocols for photon-counting CT angiography of the aorta

Our objective was to assess dedicated low-dose (LD) and low-contrast (LC) scan protocols for aortic angiography, compared to standard protocols in photon-counting CT (PCD-CT) and energy-integrating CT (EID-CT). 57 patients (23 women) who underwent aortic PCD-CT angiography (Nov. 23 - July 24) were assessed retrospectively. 19 received a low-contrast protocol (LC; 14 mg iodine, image quality level IQ64), 18 a low-dose protocol (LD; 21 mg iodine, IQ42), and 20 a combined low-dose/low-contrast protocol (LD/LC) according to defined patient characteristics. In addition, two groups of 20 BMI-matched patients were created, one of which underwent CTA using the standard PCD-CT protocol and the other using EID-CT, and these were compared with the new protocols. CNR was calculated. Overall quality, luminal contrast, vessel sharpness, and artifacts were rated by four radiologists. LD enabled ~ 40% dose-reduction compared to EID-CT (3.3 ± 0.8 versus 5.3 ± 0.4mGy; p < 0.01) but higher CNR (33.5 ± 6.1 vs. 25.1 ± 6.4; p < 0.01). CNR of LC (26.3 ± 5.6) and LD/LC (25.6 ± 9.1) did not differ significantly to EID-CT (25.1 ± 6.4; p > 0.99). Image quality of LC was deemed superior to EID-CT (5 [5-5] vs. 4 [4-4]; p < 0.01). LD (4 [4-5]) and LD/LC (4 [4-4]) demonstrated comparable image quality to EID-CT (p = 0.52/0.94). In conclusion even the LD/LC protocol provided image quality comparable to EID-CT despite substantial reduction of radiation and contrast agent dose. Special dose-reduced and contrast-reduced protocols are feasible without compromising diagnostic image quality.