In vivo diffusion tensor imaging of rat spinal cord with echo planar imaging.

The in vivo apparent diffusion tensor (ADT) of spinal cord was measured in nine rats at 2.0 T using an interleaved multi-shot echo planar imaging (EPI) diffusion sequence. A technique that combines sliding acquisition and phase correction, based on a calibration scan, to reduce ghosting artifacts in the images introduced by the strong diffusion-sensitizing gradients was described. Two rotationally invariant parameters, the trace (actually trace/3, to be consistent with the published values) and the lattice anisotropy index (LAI) were estimated from the ADT. In in vivo cords, the mean white matter (WM) trace value (1.05 +/- 0.13 x 10(-3) mm(2)/sec) was found to be significantly higher than the gray matter (GM) trace (0. 84 +/- 0.12 x 10(-3) mm(2)/sec, p < 0.0025). Significant anisotropic diffusion was observed in both WM and GM, with greater anisotropy in the WM (LAI=0.59 +/- 0.04) than in the GM (LAI=0.47 +/- 0.06, p < 0. 0001). These results are in agreement with the in vivo values determined using the conventional spin-echo sequence. Magn Reson Med 42:300-306, 1999.