Experimental Evaluation of a Hybrid Iodine-Gadolinium Contrast Medium in Photon-counting Detector CT

BACKGROUND: Photon-counting CT (PCD-CT) provides spectral imaging in every clinical scan through virtual monoenergetic image (VMI) reconstruction. However, because conventional iodine-based contrast medium has a low k-edge, image contrast in the VMIs decreases at high energies. Contrast media with higher k-edges may improve contrast in high-energy VMIs. Therefore, this study investigates BAY3685750, a novel iodine-gadolinium hybrid contrast medium. MATERIALS AND METHODS: In vitro experiments compared BAY3685750 with conventional iodine-based and gadolinium-based contrast agents in an anthropomorphic abdominal phantom. Relaxivity (r1) of BAY3685750 was measured at 1.41 T in water and human plasma to assess its potential for both MRI and CT applications. Next, 3 Göttingen minipigs underwent multiphasic contrast-enhanced upper abdominal CT on a first-generation PCD-CT. In 2 animals, BAY3685750 was administered for the first scan, followed by a 60-minute washout and a second multiphasic scan with a standard iodine-based contrast medium. In the third animal, the order was reversed. VMIs were reconstructed for all scans, enabling intraindividual comparison of the 2 contrast agents. RESULTS: In the phantom study, BAY3685750 produced higher attenuation than the iodine-based contrast medium and lower attenuation than the gadolinium-based medium. Relative to the iodine medium, BAY3685750 attenuation increased continuously with energy, reaching ~20% (70 keV), 36% (100 keV), and 78% (140 keV) higher values. In vivo, all measured structures (aorta, inferior vena cava, portal vein, liver) had higher attenuation with BAY3685750 than with iodine at all phases and VMIs. The r1 relaxivity of BAY3685750 in human plasma (1.41 T) was 8.95 L mmol -1 s -1 compared with 5.93 L mmol -1 s -1 for gadobutrol. CONCLUSION: The hybrid iodine-gadolinium contrast medium BAY3685750 provides higher attenuation than conventional iodine-based CT contrast, suggesting improved image quality in high-energy VMIs.