Development of a new approach for the assessment of complex blood flow patterns in the left atrium from 4D flow MRI imaging

Mitral valve regurgitation is a common disorder affecting 2-3% of the general population. The morphological and functional remodelling of the left atrium caused by this disease could favour blood stagnation and consequently stroke risk. Several clinical studies suggest that stroke risk stratification may be improved by using hemodynamic information on the left atrium. The goal of this study was therefore to develop a new approach for the assessment of complex blood flow patterns in the left atrium which could quantify the hemodynamic implications of the mitral valve regurgitation on sick patients compared to healthy volunteers. This analysis may enable optimized patient risk stratification and therapy. 4D Flow MRI imaging on the subjects provides information of the anatomy and the velocity field in the three directions in space and time for all the acquisitions. We selected three time frames: the S, E and A wave corresponding to the reservoir, conduit and boosting pump function of the atrium, respectively. We derived the patient- specific anatomical model of the left atrium, by applying a Chan-Vese segmentation, furthermore, we derived the modulus of the velocities and calculated the vorticity performing the curl of the velocities field. We individuated and implemented four different criteria for the identification of vortex cores inside the left atrium, ω, Δ, Q and λ_2 criterion. We evaluated the N_k number defined as the quality of rotation of a vortex core and we proposed a scale to quantitatively quantify them. We also calculated other different features as kinetic energy, pressure gradient and Fourier transformation. In this preliminary testing, the interface and the method proposed, returned a good segmentation and velocities in the expected range. All the features and methods proposed seem to indicate that a reduced blood washout in the left atrium occurs in sick patients, which might facilitate clot formation and increase of the thromboembolic risk.