MRI-Derived Evaluation of Liver Function and Its Extension to K-Edge Photon-Counting CT: Focus on Gadolinium-Based Functional Biliary Imaging.

Accurate assessment of liver function is essential in the management of chronic liver disease, hepatobiliary malignancies, and surgical planning. In recent years, hepatobiliary magnetic resonance imaging (MRI) using gadolinium-based contrast agents has evolved from a purely morphological technique into a quantitative functional imaging modality capable of evaluating hepatocyte uptake, biliary excretion, and regional liver function. Quantitative MRI-derived biomarkers, including relative liver enhancement, liver-to-spleen ratio, T1 relaxometry, and pharmacokinetic modeling, have demonstrated significant correlations with established liver function tests and postoperative outcomes. At the same time, the introduction of photon-counting computed tomography (PCCT) and K-edge imaging has opened new perspectives in quantitative imaging. Energy-resolved photon-counting technology has demonstrated gadolinium discrimination and material decomposition under selected experimental conditions, raising the hypothesis that aspects of hepatobiliary contrast distribution might eventually be investigated with computed tomography (CT). However, reliable K-edge detection and quantitative hepatobiliary gadolinium imaging after standard clinical administration have not yet been established in humans. Phantom, simulation, preclinical, and limited non-hepatobiliary human studies have investigated gadolinium K-edge imaging, but direct evidence for functional hepatobiliary PCCT in humans remains lacking. This review aims to provide a comprehensive overview of MRI-derived evaluation of liver function, with particular attention to the experimental evidence exploring whether selected MRI-derived concepts might ultimately be investigated using PCCT and K-edge imaging, highlighting current evidence, technical challenges, translational applications, and future perspectives in precision hepatobiliary diagnostics.