MRI-based Curvature Assessment and High-Resolution T1 Mapping to Detect Cardiac Structural Abnormalities

Atrial fibrillation (AF) is a devastating cardiovascular disease with 1.5 million people worldwide diagnosed every year. AF is an abnormal rhythm that affects the upper chambers of the heart resulting in a number of complications including ventricular tachycardia, stroke and even cardiac arrest. As the disease progresses, changes in tissue physiology occur as a result of increased pressure overload and stress in the chamber. This includes the development of fibrosis, which can further facilitate the maintenance of AF. Fibrosis characterization could help optimize treatment strategies and improve management of AF. This dissertation describes the development of magnetic resonance imaging (MRI) techniques to identify structural remodeling and the detection of fibrosis in the heart. Cardiac MRI, particularly of the atria, is challenging due to the movement of the beating heart and the thin walls. One approach studied is a novel high resolution T1 mapping method that was evaluated in an animal model of myocardial infarction. Secondly, an approach using magnetic resonance angiograms to characterize the size and shape of the left atrium was evaluated. Curvature measurements of the surface of the left atrium were correlated to other potential indicators of fibrosis from Late Gadolinium Enhancement (LGE) imaging and electrogram mapping. Validation of the high resolution T1 mapping technique was done using Bloch simulations, phantom studies and animal studies. An exponential relationship was seen between T1 values and signal intensity of high-resolution T1-weighted imaging. The high resolution maps of T1 showed an increased dynamic range of T1 in areas of infarction and detection of fibrosis not seen in lower resolution maps. Magnetic resonance angiograms of the left atrium in a cohort of patients with AF showed flatter curvature for patients with more persistent AF compared to those with lesser burden of AF (paroxysmal AF). Regional assessment showed strong correlation between the curvedness of the inferior left atrium with fibrosis detected with LGE. Curvature of the left atrial roof showed negative correlation with dominant frequency of AF electrograms. In the paroxysmal AF group, patients with flatter curvedness has worse AF ablation outcomes than patient with more curvedness. There was no difference in AF ablation outcomes between patients low and high curvedness for persistent AF group. The development of novel and reliable non-invasive techniques for diagnosis and risk stratification of patients with cardiac fibrosis is becoming more critical for patient care. The two novel techniques studied provide clinically meaningful information that can be easily adapted into currently available MRI platforms.