Aortopathy Assessment using a Wall Shear Stress Atlas of the Thoracic Aorta

Estimations of the number of death caused by thoracic aortic aneurysms per year range from 30.000 to 60.000 in the US. The disease is frequently related to aortic valve disease, aortic insufficiency (AI), tricuspid valve (TAV) stenosis (AS) and bicuspid aortic valve (BAV). Consensus-based guidelines for aortic valve or aorta repair, assessed with echocardiography, do not relate hemodynamic parameters to aortic wall remodeling, which may lead to aortic growth, dissection or rupture. Wall remodeling can be investigated in a more direct fashion by estimating wall shear stress (WSS) from, at Northwestern routinely used, 4D Flow MRI. To process an extensive amount of data in a well-ordered fashion and make the information easily accessible and interpretable for clinicians, we propose a technique to create 3D WSS atlases of healthy aortas, of aortopathies and of aortas with AS (both TAV and BAV). We hypothesize that a 3D WSS atlas created from healthy volunteers helps identify regions of significant different WSS with aortopathy atlases and that these regions correlate with outcome as defined by aortic diameter, AS/AI severity and/or type of aortopathy. Preliminary results comparing atlases created from 10 healthy controls, 10 dilated aortas with TAV, 10 dilated aortas with TAV stenosis, 10 aortas with BAV, 10 dilated aortas with BAV and 10 dilated aortas with BAV stenosis show clear distinction in WSS behavior between these groups. Furthermore, preliminary results of highlighting abnormal WSS 11 individual BAV patients by comparison with the control atlas are presented. To investigate whether differences between atlases and individual aortas can be attributed to the WSS values or the co-registration technique applied to create the atlases, 2D planes will be placed at anatomical landmarks in the atlas and 42+ individual aortas. An existing 4D Flow MRI database (n=700+) will be used to retrospectively add data to the different WSS atlases to increase power. The healthy volunteer atlas will be categorized according to age and gender to facilitate comparison between cohorts. Multivariate statistics will be applied to analyze disease progression (aortic diameter, AS/AI severity). One final step is to correlate growth of 42+ retrospectively available dilated aortas with WSS by using 4D Flow MRI and follow-up contrast-enhanced magnetic resonance angiography.