Clinical 4D flow MRI assessment in aortopathy—what the clinician needs to know

Interval cross-sectional imaging plays an important role in aortopathy surveillance. Often, cardiac magnetic resonance imaging (MRI) is used over computed tomography (CT) due to the lack of radiation in repeated surveillance and the option of additional hemodynamic assessment. Primarily, assessment includes the orthogonal measurement of aortic dimensions in a three-dimensional (3D) structure. Lately, four-dimensional (4D) flow MRI is becoming more widespread as it can be acquired within 1-5 minutes using advanced techniques. In addition to standard flow quantification, 4D flow MRI offers advanced hemodynamic quantification. This review discusses important advanced imaging biomarkers, including helical flow pattern, wall shear stress (WSS), flow displacement and systolic flow reversal ratio (sFRR). It focuses on those parameters that can be analyzed using commercially available post-processing platforms and are accessible for clinical centers without the need for research setup and collaboration. WSS plays a role in the assessment of bicuspid aortic valve disease. Here it is elevated even without the presence of stenosis. Flow displacement is also of value in bicuspid aortic valve disease and is abnormal in heart failure with preserved ejection fraction (HFpEF) as well as chronic aortic dissection. 4D flow MRI is also useful in understanding and assessing flow changes in aortic valve replacement.