Inglis B A, Yang L, Wirth E D, Plant D, Mareci T H
Department of Biochemistry and Molecular Biology, University of Florida, Gainesville 32610, USA.
Magn Reson Imaging. 1997;15(4):441-50. doi: 10.1016/s0730-725x(96)00242-1.
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 the image contrast and that could be used to infer microscopic structural organization beyond that defined by the resolution of the image matrix (i.e., fiber orientation could be assigned based on diffusion anisotropy). Anisotropic diffusion coefficients were therefore measured using apparent diffusion tensor (ADT) imaging to assess more accurately fiber orientations in the spinal cord; structural anisotropy information is portrayed in the six unique images of the complete ADT. To reduce 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 reflecting diffusion anisotropy. The colored trace image yields a pseudo-three-dimensional view of the rat spinal cord, from which it is possible to deduce fiber orientations.
采用传统的自旋回波核磁共振成像脉冲序列，在7T和14T磁场强度下获取切除的正常大鼠脊髓的高分辨率图像。观察到，高分辨率成像所需的大脉冲场梯度会导致扩散加权，这种加权主导了图像对比度，并且可用于推断超出图像矩阵分辨率所定义的微观结构组织（即，可基于扩散各向异性确定纤维方向）。因此，使用表观扩散张量（ADT）成像测量各向异性扩散系数，以更准确地评估脊髓中的纤维方向；完整ADT的六个独特图像描绘了结构各向异性信息。为降低数据维度，利用ADT的三个对角元素图像各自单独的颜色标度生成了一个迹图像。这一新图像保留了迹对实验室轴和样品轴相对方向的大部分不变性（灰度迹图像所固有的），但通过使用颜色提供了反映扩散各向异性的对比度。彩色迹图像产生了大鼠脊髓的伪三维视图，从中可以推断纤维方向。
