Submitted on March 16, 2007
Accepted on June 28, 2007
Transmural Heterogeneity of Diffusion Anisotropy in the Sheep Myocardium Characterized by MR Diffusion Tensor Imaging
Yi Jiang1*, Julius M Guccione2, Mark B Ratcliffe2, and Edward W Hsu3
1 Department of Biomedical Engineering, Duke University, Durham, North Carolina, United States
2 Department of Surgery, University of California, San Francisco, California, United States
3 Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States
* To whom correspondence should be addressed. E-mail: yi.jiang{at}duke.edu.
The orientation of MRI-measured diffusion tensor in the myocardium has been directly correlated to the tissue fiber direction and widely characterized. However, the scalar anisotropy indices have mostly been assumed to be uniform throughout the myocardium wall. The current study examines the fractional anisotropy (FA) as functions of transmural depth and circumferential and longitudinal locations in the normal sheep cardiac left ventricle (LV). Results indicate that the FA stays relatively constant from epicardium to midwall, and then decreases steadily toward the endocardium (25.7% lower). The decrease of FA corresponds to 7.9% and 12.9% increases in the secondary and tertiary diffusion tensor diffusivities, respectively. The transmural location of the FA transition coincides with the location where myocardial fibers run exactly circumferential. There is also significant difference in the midwall-endocardium FA slope between the septum and the posterior or lateral LV free wall. These findings are consistent with the known cellular microstructure from reported histological studies of the myocardium, and suggest a role of MR diffusion tensor imaging for characterizing in addition to fiber orientation other tissue parameters such as the extracellular volume fraction.
