Four-Dimensional Flow Magnetic Resonance Imaging—Basic Physics, Techniques, and Cardiovascular Applications

Phase contrast (PC) imaging is a cornerstone of cardiovascular magnetic resonance. While conventional two-dimensional PC magnetic resonance imaging (MRI) provides valuable flow data, it is constrained to a single spatial plane. Conversely, four-dimensional (4D) flow MRI captures time-resolved velocity data across all three spatial dimensions, offering a holistic representation of hemodynamics. This article reviews the fundamental physics, acquisition techniques, post-processing workflows, and expanding clinical applications of 4D flow MRI, incorporating recent advancements. Driven by advances in computing, compressed sensing, and recent breakthroughs in deep learning reconstruction, 4D flow MRI scan times have been drastically reduced to under 2 minutes. It provides qualitative flow visualization (streamlines, pathlines) and advanced quantitative insights—such as wall shear stress and kinetic energy loss. Its applications are broad, proving highly beneficial in complex congenital heart diseases (e.g., Fontan circulation, Tetralogy of Fallot), aortic pathologies (e.g., bicuspid aortopathy, Marfan syndrome, dissection), and increasingly in acquired heart diseases like heart failure with preserved ejection fraction, valvular disease, and pulmonary hypertension. 4D flow MRI represents a paradigm shift in cardiovascular imaging. By moving from single-plane functional assessment to comprehensive volumetric hemodynamic mapping, it bridges basic fluid dynamics and clinical pathophysiology. Ongoing standardization and deep learning–driven automated post-processing are cementing its role as an indispensable, routine clinical tool in modern cardiovascular care.