Jiang Yi, Guccione Julius M, Ratcliffe Mark B, Hsu Edward W
Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA.
Am J Physiol Heart Circ Physiol. 2007 Oct;293(4):H2377-84. doi: 10.1152/ajpheart.00337.2007. Epub 2007 Jun 29.
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 indexes have mostly been assumed to be uniform throughout the myocardial wall. The present study examines the fractional anisotropy (FA) as a function of transmural depth and circumferential and longitudinal locations in the normal sheep cardiac left ventricle. Results indicate that FA remains relatively constant from the epicardium to the midwall and then decreases (25.7%) steadily toward the endocardium. 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 circumferentially. There is also a significant difference in the midwall-endocardium FA slope between the septum and the posterior or lateral left ventricular free wall. These findings are consistent with the cellular microstructure from histological studies of the myocardium and suggest a role for MR diffusion tensor imaging in characterization of not only fiber orientation but, also, other tissue parameters, such as the extracellular volume fraction.
心脏磁共振成像测量的心肌扩散张量的方向已被直接关联到组织纤维方向并得到广泛描述。然而，标量各向异性指数大多被假定在整个心肌壁中是均匀的。本研究检测了正常绵羊心脏左心室中分数各向异性（FA）作为透壁深度以及圆周和纵向位置的函数。结果表明，FA从心外膜到中层心肌保持相对恒定，然后朝心内膜稳定下降（25.7%）。FA的下降分别对应于二级和三级扩散张量扩散率增加7.9%和12.9%。FA转变的透壁位置与心肌纤维恰好沿圆周方向走行的位置一致。在室间隔与左心室后壁或侧壁之间，中层心肌 - 心内膜FA斜率也存在显著差异。这些发现与心肌组织学研究中的细胞微观结构一致，并表明磁共振扩散张量成像不仅在表征纤维方向方面，而且在表征其他组织参数（如细胞外体积分数）方面都发挥作用。
