Non-invasive investigation of cardiac tissue compartments and components using MR microscopy

The heart responds to the ever-changing demands that the whole body places on the cardiovascular system. This life-time pump expels the blood out by generating a forceful and efficient contraction. The homogeneous function is the orchestrated outcome of morphologic, electrophysiological, molecular constituents that exhibit prominent heterogeneity in the heart. Non-invasive imaging of anatomical structure of the whole heart has increasing demand for the understanding of its role to normal function and pathological development.;Our hypothesis is that magnetic resonance imaging at high magnetic fields can distinguish different tissue compartments and cellular components in the mammalian heart and monitor their pathophysiological alterations, in-situ. In this thesis, we investigate non-invasively tissue compartments and cellular components comprising the rabbit heart using 17.6 T and 11.1 T magnets. The attenuation of MR diffusion signal intensity is used to reflect change in the tissue compartments. Magnetic resonance micro images contrasted by diffusion and transverse relaxation time of water molecules reveal anatomical features previously unavailable. Besides the myocardium, we visualize anatomical details of the cardiac conduction system from the bundle of His to terminal ramification of the Purkinje fibers in the ventricles using three-dimensional high resolution MR imaging and microscopic high angular resolution diffusion imaging (MHARDI). Anatomical relationship of constituents in the ventricular muscular interseptum is explored. The combined investigative technique of microscopic three-dimensional high resolution MRI and MHARDI is observed to be an effective method of monitoring morphological changes occurring in cardiac tissue with advancing age.