Session S62.4

Local Indices of Aortic Stiffness: A Magnetic Resonance Imaging Study

A Dogui*, A De Cesare, N Kachenoura, F Frouin,
M Lefort, E Mousseaux, A Herment

INSERM
Paris, France

Aim: Magnetic resonance imaging (MRI) is increasingly used for the analysis of mechanical properties of the aortic wall using aortic geometry and velocity profiles of blood flows. The aim of this study was to evaluate the stiffness of the aortic wall by coupling the morphological and the hemodynamic MR data. To achieve this aim : 1) the deformability of the ascending aorta, and 2) the Pulse Wave Velocity (PWV) derived from the propagation speed of the velocity waveform in the aortic arch were estimated. Then, we identified the relationship between deformability and PWV, and their variation according to aging.
Methods: We studied 36 volunteers aged between 14 and 77 years. For each subject, acquisitions of cine and phase contrast (PC) at the same level of the aorta were selected. The deformability is calculated as the ratio between the variation in the area of the aortic lumens between systole and diastole and the diastolic surface. These areas were measured on cine MR acquisitions using a snake based automatic contouring. The PWV was calculated from the PC sequences by using the transit time of the systolic flow curves between the ascending and descending aorta and the length of the aortic arch between these two locations. The transit time was automatically calculated from the normalized flow curves in the ascending and descending aorta using an algorithm based on the least squares minimization technique.
Results: PWV and deformability on the 36 volunteers were inversely related: decrease in deformability corresponds to increase in PWV. Two groups of subjects were identified: 1) volunteers with PWV= 8 m/s (mean 8.79m/s, SD 0.76) having deformability values =0.11 (mean 0.042, SD 0.039). 2). The volunteers with PWV <8 m/s (mean 4.98 m/s SD 1.13) having deformability values ranged between 0.12 and 0.6 (mean 0.26, SD 0.11). Importantly, the first group included subjects with age =50 years while the second group included subjects with age <50 years. In addition, changes in deformability and PWV according to aging were not linear: both relationships were better characterised with a second order polynomial (age-PWV: rē=0.62 / age-deformability: rē=0.70). Of note, deformability decreases with aging while PWV increases with aging.
Conclusions: The deformability and the PWV were independently calculated on the aortic arch, however they are well related: it confirms the robustness of our measurements. Aging has a significant influence on the aortic stiffness: the older volunteers (=50 years) have the highest PWV and the lowest deformability. Our local and automated approach for measurement of deformability and PWV characterises directly the stiffness of the aorta and our results were consistent with previous studies.

(Abstract Control Number: 202)