Dilated cardiomyopathy (DCM) is one of the most common forms of heart muscle disease. In this disease, chronic hemodynamic overload leads to increased wall stress. Subsequent adaptive responses of the heart include both ventricular chamber dilation and myocyte hypertrophy to equalize wall stress. While such adaptations help to maintain pump function over the short term, over the long term, inadequate compensation leads to heart failure. Understanding left ventrical remodeling in the dyssynchronous failing heart, including alteration of ventricular geometry as well as fiber architecture, is therefore of critical importance to understanding DCM.

We have employed diffusion tensor magnetic resonance imaging (DTMRI) to reconstruct whole heart geometry, fiber and laminar structure at a high resolution. In this technique, a tensor that represents the 3D diffusion of water in each image voxel is estimated. The local eigensystem of this diffusion tensor aligns with the cardiac fiber structure. We have used these methods to image and reconstruct the geometry and fiber structure of populations of normal and failing canine hearts. Shown in the top figure are the MR images and fiber orientation of 2 normal and 1 failing hearts. There is natural variation in both the geometry and fiber structure.

Using these imaging data, we have also developed novel mathematical and computational methods to quantify variation of anatomic structure both within and between populations of DTMRI reconstructed hearts. The method uses an atlas-based approach, whereby different anatomies are registered to an anatomical atlas and variation is quantified in the mapping. Structural differences within and across the population are observed within the reference frame of the anatomical atlas. Shown in the bottom images are sample comparisons of geometry, fiber and laminar architecture between a population of normal and failing hearts.