4D flow MRI-based assessment of atrial fibrillation


Atrial fibrillation (AF) is the most common cardiac arrhythmia, and associated with increased risk for ischemic stroke and mortality. While the risk of stroke has been shown to be reduced with the use of oral anticoagulants like Warfarin, these medications are predictably linked with an increased risk of bleeding, and thus patients need to be stratified for stroke risk. Empirical risk scoring systems based on broad demographic factors like age, gender, prior medical history, are the current clinical standard, however, these have been shown to have poor predictive value on whether or not a patient will actually develop stroke. Cardiac magnetic resonance imaging (MRI) studies using 4-dimensional flow MRI (3D spatial and velocity encoding + time), have found that 3D hemodynamics may provide more individualized stroke risk stratification techniques. However, current 4D flow techniques are limited by low scan times that are not always clinically feasible and low velocity dynamic range. In addition, 4D flow techniques are acquired over multiple heartbeats that are assumed to be the same length. Not only are arrhythmias often inefficiently handled or unaccounted for, but the influence of arrhythmias on 3D hemodynamics has not been thoroughly investigated. Thus, this dissertation was primarily focused on the development of highly accelerated 4D flow MRI acquisition techniques for improved evaluation of 3D hemodynamics in patients with AF. For the purpose of methods development and validation, patient studies also included non-arrhythmic patients with congenital heart disease, as well as patients with valvular and aortic disease. As AF could be considered one of the most challenging patient subgroups in cardiac MRI, the techniques developed as part of this doctoral work can be applied to many other cardiac diseases.

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