Reich D S, Smith S A, Jones C K, Zackowski K M, van Zijl P C, Calabresi P A, Mori S
Department of Neurology, Johns Hopkins University, Baltimore, MD, USA.
AJNR Am J Neuroradiol. 2006 Nov-Dec;27(10):2168-78.
White matter tract-specific imaging will probably become a major component of clinical neuroradiology. Fiber tracking with diffusion tensor imaging (DTI) is widely used, but variability is substantial. This article reports the ranges of MR imaging appearance and right-left asymmetry of healthy corticospinal tracts (CST) reconstructed with DTI.
For 20 healthy volunteers, whole-brain DTI data were coregistered with maps of absolute T1 and T2 relaxation times and magnetization transfer ratio (MTR), all acquired at 3T. For each individual, the 2 reconstructed CSTs and their asymmetry were analyzed with respect to the number of fibers reconstructed; tract volume; and individual MR imaging parameters restricted to the tracts. Interscan variability was estimated by repeat imaging of 8 individuals.
Reconstructed fiber number and tract volume are highly variable, rendering them insensitive to abnormalities in disease. Individual tract-restricted MR imaging parameters are more constrained, and their population averages and normal ranges are reported. The average population asymmetry is generally zero; therefore, normal ranges for an index of asymmetry are reported. By way of example, CST-restricted MR imaging parameters and their asymmetries are shown to be abnormal in an individual with multiple sclerosis who had a lesion affecting the CST.
The results constitute a normative dataset for the following imaging parameters of the CST: T1, T2, MTR, fractional anisotropy, mean diffusivity, transverse diffusivity, and the 3 diffusion tensor eigenvalues. These data can be used to identify, characterize, and establish the significance of changes in diseases that affect the CST.
白质束特异性成像可能会成为临床神经放射学的一个主要组成部分。利用扩散张量成像（DTI）进行纤维追踪被广泛应用，但变异性很大。本文报告了用DTI重建的健康皮质脊髓束（CST）的磁共振成像表现范围及左右不对称性。
对20名健康志愿者，将全脑DTI数据与绝对T1、T2弛豫时间及磁化传递率（MTR）图谱进行配准，所有数据均在3T条件下采集。对于每个个体，分析2条重建的CST及其不对称性，包括重建的纤维数量、束体积，以及仅限于这些束的个体磁共振成像参数。通过对8名个体进行重复成像来估计扫描间变异性。
重建的纤维数量和束体积高度可变，使其对疾病中的异常不敏感。个体束特异性磁共振成像参数受到更多限制，并报告了其总体平均值和正常范围。总体平均不对称性通常为零；因此，报告了不对称指数的正常范围。举例来说，一名患有影响CST病变的多发性硬化症个体的CST特异性磁共振成像参数及其不对称性显示为异常。
这些结果构成了CST以下成像参数的规范数据集：T1、T2、MTR、分数各向异性、平均扩散率、横向扩散率以及3个扩散张量特征值。这些数据可用于识别、表征和确定影响CST疾病中变化的意义。
