4D Flow MRI-based study of helical blood flow patterns in healthy and diseased thoracic aortas

One of the most prevalent congenital heart defects is the bicuspid aortic valve (BAV), which is frequently linked to dangerous side effects, notably thoracic aortic dilatation. Aortic dilatations can progress into aneurysms, which are typically not detected early and may not show symptoms until they reach a critical size or rupture, leading to unforeseen and fatal outcomes. The current standard clinical assessment of the risk of rupture based only on the aneurysm's diameter is insufficient, as evidenced by numerous studies. To improve current risk assessment, recent studies have investigated the role of hemodynamics in the progression of the abovementioned aortic diseases. The aim of the study is to examine in vivo helical flow in the thoracic aorta and to explore its characteristics in both healthy individuals and in patients with a bicuspid aortic valve (BAV) and thoracic aortic dilatation (DIL). This analysis aims to investigate potential correlations with other hemodynamic and geometric features. This study analyses 44 healthy subjects with tricuspid aortic valve and without aortic dilatation (H), comparing them to two groups of patients: one consisting of 23 subjects with bicuspid aortic valve (BAV) and another including 20 subjects with dilated aorta (DIL). Data were acquired using 4D flow MRI, the aortas were segmented to examine only the ascending portion (from the sino-tubular junction to the brachiocephalic trunk). Velocities obtained from 4D flow MRI were interpolated on unstructured mesh grids to compute helicity-based parameters. Statistical analysis was executed in MATLAB to compare parameters across all groups. The main results show that healthy subjects are characterized by more pronounced topological helical structures (higher |LNH|) with higher intensity (h2) compared to pathological (BAV and DIL) subjects, as well as by more balanced counter-rotating structures (low h4). Furthermore, from the correlation analysis conducted between helicity-based parameters and demographic, geometric and hemodynamic variables, it emerged a strong positive correlation between the aortic kinetic energy and the helicity intensity h2, both in the healthy (H) and in the diseased (BAV, DIL) groups of subjects. In conclusion, the outcomes of this study may contribute to enrich the current understanding of the mechanistic link between helical blood flow and aortic pathology, thus providing a valuable tool to discriminate between dangerous and non-dangerous hemodynamic situations. If supported by longitudinal data, this approach could result in significative implications for the clinical management of patients with bicuspid aortic valve and thoracic aorta dilatation.