Diffusion Tensor Magnetic Resonance of Cardiac Microstructure and Application to Coronary Artery Disease

Cardiovascular magnetic resonance (CMR) is indispensable for heart research because of its versatility, reproducibility, & tissue characterisation capability. A new technique called diffusion tensor (DT) CMR has recently become viable in-vivo in humans. DT-CMR quantifies water diffusion in the myocardium, which is constrained by the myocardial micro-architecture. Diffusion aligned to the orientation of myocytes is greater than the diffusion in the perpendicular directions, & therefore yields information on myocyte organisation. The diffusion can be visualised in 3D by an ellipsoid which can be described by a mathematical tensor, from which the 3 axes of the ellipsoid can be obtained. These axes are described by their magnitude (eigenvalues: E1, E2, E3) & direction (eigenvectors: E1a, E2a, E3a). Robust validation shows that E1 is aligned with myocyte orientation, & E2 is aligned with the sheetlet orientation (groups of myocytes ~6 thick separated by shear planes). In a recent breakthrough, we showed in-vivo impairment in sheetlet function with systolic & diastolic arrest in hypertrophic & dilated cardiomyopathy patients respectively. There is tremendous potential for further development & clinical application of this completely novel technology in cardiac disease especially in myocardial inafrction, cardiomyopathy and congenital heart disease.