Two-component diffusion tenser MRI of isolated perfused hearts

Nonmonoexponential MR diffusion decay behavior has been observed at high di ffusion-weighting strengths for cell aggregates and tissues, including the myocardium; however, implications for myocardial MR diffusion tenser imagin g are largely unknown. In this study, a slow-exchange-limit, two-component diffusion tenser model was fitted to diffusion-weighted images obtained in isolated, perfused rat hearts. Results indicate that there are at least two distinct components of anisotropic diffusion, characterized by a "fast" co mponent whose principal diffusivity is comparable to that of the perfusate, and a highly anisotropic "slow" component. It is speculated that the two c omponents correspond to tissue compartments and have a general agreement wi th the orientations of anisotropy, or fiber orientations, in the myocardium . Moreover, consideration of previous studies of myocardial diffusion sugge sts that the presently observed fast component may likely be dominated by d iffusion in the vascular space, whereas the slow component may include the intracellular and interstitial compartments. The implications of the result s for myocardial fiber orientation mapping and limitations of the current t wo-component model used are also discussed. (C) 2001 Wiley-Liss, Inc.