Pressure and Flow Interplay in Aortic Dilation Using 4D Flow Magnetic Resonance Imaging

Abstract

Ascending thoracic aortic aneurysms (ATAA) are defined by a silent dilation of the ascending aorta (AA). Although maximal aortic diameter is currently used for surgery planning, a high proportion of patients with low diameters ending up with aortic dissection. Our purpose was to propose a fine and comprehensive quantitative evaluation of pressure-flow-wall interplay from 4D flow MRI data in the setting of aortic dilation. We studied 12 patients with ATAA (67±14 years, 7 male) and 12 healthy subjects (63±12 years, 8 male) who underwent 4D flow MRI acquisition. The segmented velocity fields were used to estimate: 1) local AA pressure changes from Navier-Stokes-derived relative pressure maps (AADP), 2) AA wall shear stress (AAWSS) by estimating local velocity derivatives at the aortic borders, 3) aortic flow vorticity using the λ2 method (AAV). AADP was significantly and positively associated with both AAV (r=0.55, p=0.006) and AAWSS (r=0.69 p<0.001). Such associations remained significant after adjustment for maximal diameter, age and BSA. Local variations in pressures within the aorta, rendered possible while using 4D flow MRI, are associated with flow disorganization as quantified by vorticity and with the increase in the stress exerted on the aortic wall, as quantified by wall shear stress.