Clinical applications of 4D flow magnetic resonance imaging in hepatic vascular disorders: practical biomarkers, protocol design, and translational implementation

Abstract

Hepatic vascular disorders include portal hypertension in cirrhosis, Budd-Chiari syndrome (BCS), hepatic vascular malformations, and vascular complications after liver transplantation. These diseases depend on blood-flow direction, flow redistribution, and pressure transmission, and not only on gross vessel shape. Doppler ultrasound, computed tomography angiography (CTA), and digital subtraction angiography (DSA) are widely used in current clinical practice, but each has distinct limits for full hemodynamic assessment, and repeated follow-up can be difficult to implement effectively in daily clinical work. Four-dimensional flow magnetic resonance imaging (4D flow MRI) is a time-resolved three-dimensional (3D) phase-contrast MRI method with three-directional velocity encoding (VENC). It provides volumetric flow and multidirectional velocity data across the cardiac cycle, and it allows flexible retrospective plane placement and comprehensive network-level analysis. It can accurately measure flow volume, peak and mean velocity, retrograde fraction, fractional flow change, and shear-related metrics. It also supports pressure-gradient estimation when combined with physics-based modeling in selected clinical settings. Hepatic imaging still faces multiple major constraints, including VENC tradeoffs, respiratory motion, limited small-vessel resolution, and the need for unified standardized acquisition and analysis. Workflow limits from segmentation and plane placement can be greatly reduced by modern automated analysis. This review systematically summarizes technical foundations, processing steps, disease-focused applications, and practical barriers for clinical translation.