Quantitative Analysis of Hypertrophic Myocardium using Diffusion Tensor Magnetic Resonance Imaging

Systemic hypertension is a causative factor in left ventricular hypertrophy which has a range of co-morbidities. Pathologic hypertrophy may negatively impact essential cardiac function. Understanding the physical and biomechanical changes in the heart associated with hypertensive left ventricular hypertrophy is motivated by the potential to reverse or manage the dysfunction associated with structural remodeling of the myocardium in this pathology. Diffusion tensor imaging is a nondestructive magnetic resonance imaging technique that can be used to image myocardial tissue microstructure and determine the orientation of myocardial muscle fibers. In this study, we present an analysis of myocardial fiber and laminar sheet orientation using the covariance of the diffusion tensor to quantify changes in orientation associated with myocardial tissue remodeling. We performed an ex vivo evaluation of hypertrophic and normal rat hearts (N=11) using diffusion tensor magnetic resonance imaging. We observed that the hypertrophic myocardium exhibited significantly increased myocardial fiber derangement (p=0.033), having a mean dispersion of 40 degrees. In comparison, normotensive myocardium had a mean of 36 degrees of dispersion. The calculated dispersion of the laminar sheet normal in the wild-type population was 52 degrees, compared to 55 degrees in the hypertrophic population (p=0.056). The fiber orientation distribution and dispersion data we obtained could be used to further evaluate the biomechanics of myocardial hypertrophy.