Sakai K, Yamada K, Nagakane Y, Mori S, Nakagawa M, Nishimura T
Center for Promotion of Excellence in Higher Education, Kyoto University, Yoshidanihonmatsu-cho, Sakyo-ku, Kyoto City, Kyoto 606-8501, Japan.
J Neurol Neurosurg Psychiatry. 2009 Sep;80(9):986-90. doi: 10.1136/jnnp.2008.163584.
The apparent diffusion coefficient (ADC) and anisotropy (eg, fractional anisotropy (FA)) of ischaemic tissue evolve over time. A reduction in diffusivity (ie, lambda(2) and lambda(3)) is an important marker for characterising hyperacute-stage infarction, as these parameters may reflect axonal membrane status. The study examines whether transverse diffusivity could be useful in assessing white matter infarcts of various ages.
Diffusion tensor imaging data from 44 adult patients (34 men, 10 women, aged 46 to 89 years, mean = 70.3) with acute white matter infarction (1-168 h) of the internal capsule were analysed. Relative eigenvalues were calculated as: (lambda(ipsi)-lambda(contra))/lambda(contra). Lesions were classified based on theoretically expected evolution of diffusivity over time as follows: stage I, FA higher than the contralesional region of interest (ROI); stage II, diffusivity lower than the contralesional side for all eigenvalues; stage III, one of two transverse eigenvalues (lambda(2) or lambda(3)) higher than the contralesional ROI.
Stage I infarcts (n = 5) were found primarily within 24 h of the onset of symptoms, with one case found on the third day. Stage II infarcts were found most commonly within 24 h (n = 18), and fewer after 24 h. After the first day, the ratio of stage III infarcts increased significantly. Thus, diffusivity-based classification of white matter infarcts seems to show a chronological trend.
Diffusion anisotropy may be useful for defining the biological tissue clock of white matter infarctions.
缺血组织的表观扩散系数（ADC）和各向异性（如分数各向异性（FA））随时间变化。扩散率降低（即λ₂和λ₃）是超急性期梗死的重要特征指标，因为这些参数可能反映轴突膜状态。本研究旨在探讨横向扩散率是否有助于评估不同时期的白质梗死。
分析44例成年患者（34例男性，10例女性，年龄46至89岁，平均70.3岁）内囊急性白质梗死（发病1至168小时）的扩散张量成像数据。相对特征值计算如下：（λ同侧-λ对侧）/λ对侧。根据扩散率随时间的理论预期变化，将病变分为以下几期：I期，FA高于对侧感兴趣区（ROI）；II期，所有特征值的扩散率均低于对侧；III期，两个横向特征值（λ₂或λ₃）之一高于对侧ROI。
I期梗死（n = 5）主要在症状出现后24小时内发现，1例在第三天发现。II期梗死最常见于24小时内（n = 18），24小时后较少。第一天后，III期梗死的比例显著增加。因此，基于扩散率的白质梗死分类似乎呈现出时间顺序趋势。
扩散各向异性可能有助于确定白质梗死的生物组织时钟。
