Ultra-low contrast agent dosage in photon-counting CT angiography of the thoracoabdominal aorta

To assess the viability of an ultra-low contrast agent protocol (ULC) for aortic photon-counting CT angiography (PCD-CTA).

For this retrospective, single-center study, 31 consecutive patients receiving PCD-CTA with 48 ml Imeron® 150mgI/ml (≙ 7.2 g iodine) were assessed. Virtual monoenergetic images with 45/55 keV were compared to a control sample scanned with radiation-dose-equivalent 55 keV protocols (120kVp; image-quality-level 42) employing standard (SC; 60 ml Imeron® 350mgI/ml ≙ 21 g iodine) and low contrast agent dose (LC; 40 ml Imeron® 350 mg/ml ≙ 14 g iodine). Luminal attenuation and image noise were measured, while contrast-to-noise ratios were calculated. Five radiologists rated overall image quality, luminal attenuation, and diagnostic confidence using a 5-point rating scale.

Radiation dose and body-mass-index did not differ significantly among groups (p > .999, each). ULC scans displayed significantly lower CNR (55 keV: 12.2 ± 2.7; 45 keV: 20.0 ± 4.6) than SC (35.3 ± 7.5) and LC studies (27.4 ± 10.7; each p ≤ .001) due to reduced luminal attenuation (ULC-55keV: 211.9 ± 27.3HU; ULC-45keV: 302.9 ± 42.8HU; SC 504.3 ± 70.9HU; LC: 380.8 ± 98.3HU; p < .001). Overall image quality of protocols was rated similar (each 4 [4-4]; p ≥ .395), while luminal attenuation of ULC-45keV (4 [4-4]) was rated inferior to SC (5 [5-5]; p < 0.001) but not to LC (4 [4-5]; p = 0.25). Diagnostic confidence was good for ULC (45 keV: 4 [4-4]); 55 keV: 3 [3-4]) and excellent for SC (5 [5-5]) and LC (5 [4-5]).

Despite inferior contrast, aortic PCD-CTA with ultra-low contrast agent dosage at 45 keV allows for diagnostic image quality. The proposed scan protocol may hold potential for kidney protection in vulnerable patient groups.