Color K-edge angiography with a dedicated gadolinium-based contrast agent for spectral photon-counting computed tomography.

Purpose: The purpose of this study was to investigate the feasibility of using a gadolinium (Gd)-based ultrasmall rigid platform (USRP) for angiography imaging using color K-edge imaging with spectral photon-counting CT technology in a rabbit model.

Materials and methods: Ten atherosclerotic rabbits with a mean weight of 3.1 ± 0.5 (standard deviation) kg, underwent intravenous administration of an USRP solution (15 mL; 2.5 mL/s; 0.27 mol Gd³⁺/L). A sub-group of six rabbits also received gadoteric acid (7.8 mL; 1.4 mL/s; 0.5 mol Gd³⁺/L) for paired comparisons. Rabbits were imaged using a clinical SPCCT prototype (120 kVp; 100 mAs; 0.5-s rotation time; 1.17 pitch). The whole aorta was scanned 6 s post-injection (first pass), followed by abdominal scanning at 30 s, 1-, 3- and 10 min. Two-readers assigned aneurysm grades (expressed as a % vessel dilatation). Median, 25^th, and 75^th percentiles were used to compare first-pass signals. Mean signal differences in biodistribution for both agents were compared in the aorta, vena cava, and renal pelvis using t-test or Wilcoxon signed-rank test. Signals from both conventional CT and color K-edge images were analyzed.

Results: Mean aneurysm grades for both image types were 45 %. A matching first-pass signal was achieved for both agents (P = 0.98), with median concentrations of 7.8 mg/mL (6.9, 8.4) vs. 7.6 mg/mL (6.4, 8.6) for USRP and gadoteric acid, respectively. Following timepoints showed similar blood pool signal among agents, but a minimal increase in average signal (mean signal difference = 17 Hounsfield unit or 0.2 mg/mL; P < 0.05) for both vessels in favor of USRP. High Gd concentrations in the renal pelvis for both agents indicated similar renal excretion profiles (mean signal difference of 0.9 mg/mL; P > 0.05).

Conclusion: Gd-based USRPs can be used for color K-edge angiography imaging, representing viable contrast media candidates for emerging spectral photon-counting CT applications.