中文摘要：

目的：采用基于体素内不相干运动（IVIM）的影像技术来探讨缺血性卒中患者病灶内表观弥散系数（ADC）信号不均质的可能原因。方法：回顾性分析2014年6月至2015年7月在浙江大学医学院附属第二医院神经内科收治的20例起病第3—7天缺血性卒中患者的弥散加权成像（DWI）和IVIM扫描数据。IVIM技术经过图像处理得到慢弥散系数（D）、快弥散系数（D^＊）和灌注分数（f），其中D和D^＊分别反映脑实质内血管外和血管内水分子弥散速度，f反映微循环灌注改变。在DWI序列上分割出信号强度高于正常侧两倍标准差的感兴趣区域（ROI），在此范围内以ADC值0．55×10^-3mm^2／s为界限，将DWI高信号区分为核心梗死区（ADC≤0．55×10^-3mm^2／s）和核心周围区（ADC〉0．55×10^-3mm^2／s），然后镜像至非梗死侧得到正常侧ROI，然后分别计算这些ROI内的ADC值和IVIM参数（包括D值、D^＊值和f值）。校正ADC值定义为rADC：核心梗死区ADC彬对侧镜像ADC值，同理得核心梗死区的rD值、rD^＊值和rf值以及核心周围区的rADC值、rD值、rD^＊值和rf值。结果：核心梗死区的ADC值、D值、f值较正常侧分别降低45％（P〈0．001）、42％（P〈0．001）和32％（P〈0．001）；核心周围区的ADC值、D值、f值较正常侧分别降低22％（P〈0．001）、32％（P〈0．001）和8％（P=0．009）。同样，核心梗死区的rADC值（P〈0．001）、rD值（P〈0．001）和ff值（P〈0．001）低于核心周围区。Pearson相关分析结果提示核心周围区的rADC值和rf值呈正相关（r=0．467，P=0．038）。结论：亚急性期缺血性卒中的DwI高信号病灶中，核心周围区相对于核心梗死区有反映微结构的水分子弥散速度的D值增加以及反映微循环血容量灌注的f值增加，这些改变反映了ADC值不均质可能与细胞水肿消退以及微血管代偿引起血容量增加有关。

英文摘要：

Objective： To investigate the cerebral lesions of diffusion weighted imaging （DWI） hyperintensity in patients with subacute stroke with intravoxel incoherent motion （IVIM） technique. Methods： The clinical data of 20 patients with ischemic stroke （3 to 7 d after onset） who underwent DWI and IVIM scanning between June 2014 and July 2015, were retrospectively analyzed. The parameters from IVIM including slow diffusion coefficient （D）, fast diffusion coefficient （D ＊ ） and perfusion fraction （f） were processed. DWI hyperintensity was segmented by its signal intensity greater than the mean ＋ 2 standard deviations of the value in the homologous contralateral region. Then, DWt hyperintensity was classified into two regions of interest （ROIs） ： infarction core and peri-core with the ADC threshold of 0. 55 ×10^-3mm^2/s. The mirrored ROIs of infarction core and peri-core were also obtained. Then, we measured the values of ADC and D, D ^＊ and f in these ROIs. The ratios of ADC （rADC）, D （rD）, D^＊ （rD^＊） and f （rf） were also calculated （e. g., rADC = ADCinfarction core/ADCmirrored region）. Results： Compared with mirrored region, ADC, D and f in the infarction core region decreased by 45% （ P 〈 0. 001 ）, 42% （P 〈0. 001 ） and 32% （P 〈0. 001 ）, respectively; while ADC, D and f in the peri- core region decreased by 22% （P 〈0.001）, 32% （P 〈0.001） and 8% （P= 0. 009 ）, respectively. The values of rADC, rD, rD ^＊ and rf in the infarction core region were significantly lower than those in the peri-core region （all P 〈 0. 001 ）. Pearson analysis showed that rADC was positively correlated with rf in the peri-core region （ r = 0. 467, P = 0. 038 ）. Conclusion： During subacute stage of stroke, compared to the infarction core region within DWI hyperintensity, D and f increase in the peri-core region of DWI hyperintensity, reflecting the increased water diffusion in microstructure and perfusion volume in microvasculature. This