A dual-VENC 4D Flow MRI Framework for Analysis of Subject-Specific Heterogeneous non-linear Vessel Deformation

Abstract

Advancement of subject-specific in-silico medicine requires new imaging protocols tailored to specific anatomical features, paired with new constitutive model development based on structure/function relationships. In Part I of this two-part study we develop a new dual-VENC 4D Flow MRI protocol that provides unprecedented spatial and temporal resolution of in-vivo aortic deformation. Based on this dual-VENC subject-specific aortic imaging technique, in Part II we develop a new finite element framework that uncovers the link between spatial variance in vessel composition and biomechanical function. The imaging protocol developed in Part I provides high sensitivity to all blood flow velocities throughout the entire cardiac cycle, overcoming the challenge of accurately measuring the highly unsteady non-uniform flow field in the aorta. Cross sectional area change, volumetric flow rate, and compliance are observed to decrease with distance from the heart, while pulse wave velocity is observed to increase. A non-linear aortic lumen pressure-area relationship is observed throughout the aorta, such that a high vessel compliance occurs during diastole, and a low vessel compliance occurs during systole. This clearly demonstrates that vessel compliance during a cardiac cycle cannot be simplistically represented by a single value. This high-resolution MRI data provides key information on the spatial variation in non-linear aortic compliance. In Part II we demonstrate that such subject-specific data facilitates the development of finite element simulations that directly predict the relationship between spatial variations in vessel composition and biomechanical function. This MRI/FEA framework significantly advances the state-of-the-art of in-silico diagnostic techniques for the human aorta.