DIFFUSION ANISOTROPY IN EXCISED NORMAL RAT SPINAL-CORD MEASURED BY NMR MICROSCOPY

A conventional spin-echo NMR imaging pulse sequence was used to obtain high-resolution images of excised normal rat spinal cord at 7 and 14 T, It was observed that the large pulsed-field gradients necessary for high-resolution imaging caused a diffusion weighting that dominated t he image contrast and that could be used to infer microscopic structur al organization beyond that defined by the resolution of the image mat rix (i.e., fiber orientation could be assigned based on diffusion anis otropy), Anisotropic diffusion coefficients were therefore measured us ing apparent diffusion tensor (ADT) imaging to assess more accurately fiber orientations in the spinal cord; structural anisotropy informati on is portrayed in the six unique images of the complete ADT, To reduc e the dimensionality of the data, a trace image was generated using a separate color scale for each of the three diagonal element images of the ADT, This new image retains much of the invariance of the trace to the relative orientations of laboratory and sample axes (inherent to a greyscale trace image) but provides, by the use of color, contrast r eflecting diffusion anisotropy, The colored trace image yields a pseud o-three-dimensional view of the rat spinal cord, from which it is poss ible to deduce fiber orientations. (C) 1997 Elsevier Science Inc.