MRI-Based Pressure Gradient Mapping in Patient-Specific Models of Coarctation of the Aorta

Accurate assessment of the pressure gradient ( $\Delta P$ ) across aortic coarctation (CoA) is critical for determining disease severity and the need for intervention. Current non-invasive methods are unreliable, while invasive catheterization remains the clinical gold standard. This study evaluates a novel MRI acquisition strategy, 4D-FlowP, that simultaneously encodes blood velocity and acceleration to enable reliable non-invasive pressure gradient mapping in CoA.

Patient-specific compliant aortic phantoms were created from clinical MRI data of two patients with CoA. Additional geometries were synthetically generated by increasing stenosis severity. Phantoms were studied in an MRI-compatible flow loop under physiologically realistic flow and pressure conditions. Pressure gradients were estimated using conventional 4D-Flow MRI, 4D-FlowP, and fluid-structure interaction (FSI) simulations. Results were compared against ground-truth catheter-based measurements across multiple flow rates and stenosis severities.

Conventional 4D-Flow consistently underestimated $\Delta P$ (slope = 0.63, $R^2=0.75$ ) relative to catheter measurements. In contrast, 4D-FlowP demonstrated substantially improved agreement (slope = 0.95, $R^2=0.75$ ). FSI simulations showed the highest overall agreement with catheter-derived $\Delta P$ (slope = 1.14, $R^2=0.82$ ). Scan times for 4D-FlowP were comparable to 4D-Flow (26 vs. 24 minutes).

4D-FlowP enables a more accurate MRI-based pressure gradient mapping in CoA than conventional 4D-Flow, when compared to ground truth catheter measurements. These findings support further in vivo evaluation of 4D-FlowP as a non-invasive alternative for functional assessment of CoA severity.