缺血性脑梗死双指数表观扩散系数的参数化研究

Bi-exponential apparent diffusion coefficient parameterization in ischemic cerebral infarction

目的:探讨不同时期缺血性脑梗死双指数表观扩散系数的参数化特征。方法:16例经临床综合确诊为缺血性脑梗死的患者作为病例组;6例无神经系统及其他系统病史的健康人作为正常组。所受试者均在GE signa HDxt 3.0T磁共振扫描仪上行b值为1000s/mm2的临床常规扩散加权成像(DWI)以及b值从0依次递增到5000s/mm2的多b值扩散加权成像,并对所得图像进行单指数或双指数模型拟合求得各量化参数,包括表观扩散系数(ADC)、快速和慢速表观扩散系数(ADCfast和ADCslow)以及快速扩散成分所占比例ffast。兴趣区(ROI)测量包括正常组额叶脑白质及皮层区域、病例组的梗死核心区及对侧镜像区。结果:正常组额叶白质ffast值(70.40%±3.54%)高于脑皮质(65.37%±4.66%),而ADC值[(84.89±3.59)%]低于脑皮质[(93.19±9.52)%]。亚急性期组患者,梗死核心区ffast(61.54%±6.34%)明显低于对侧镜像区(65.56%±4.45%),ADCfast[(140.57±65.13)%]和ADCslow[(13.52±8.68)%]亦低于对侧镜像区[分别为(212.90±123.79)和(21.60±10.23)×10-5 mm2/s],差异均有统计学意义(P<0.05)。慢性期组患者,三个双指数量化参数在梗死核心区及对侧镜像区差异均无统计学意义(P>0.05)。结论:正常时脑白质和灰质呈现不同的扩散状态,亚急性期梗死灶核心区的双指数模型参数指标均低于对侧镜像区,而慢性期无明显差异;双指数表观扩散系数的参数化研究可为我们揭示正常及疾病状态下脑组织内更丰富的信息,但其生理学机制有待进一步探讨。

Objective：To explore the characteristics of bi-exponential apparent diffusion coefficient parameterization and the evolution of brain water compartmentation in cerebral infarction. Methods： All studies were performed within the guidelines of our internal institutional review board, and informed consent was obtained from all the participants. Sixteen patients with only white matter infarction （subacute stage,n= 10;chronic stage,n= 6） and 6 healthy volunteers finished routine diffusion weighted imaging （DWI） with b value of 1000s/mm^2 ,as well as multi-b factor DWI with b values extending from 0 to 5000s/mm^2 on a 3.0T MR system. Regions of interest （ROIs） were selected in the frontal white matter （FWM） and cortex （Cor） of the volunteers,as well as in the ischemic core and the contralateral mirror zones of the patients. Quantitative parameters （ADC,ff ADCfast, ADCslow） of the ROIs were measured on the corresponding maps. Results： In normal group, ffast, in FWM was much higher than in Cor, with ADC baseline much lower than in Cor. In patients at subacute stage, ffast, in the infarct core decreased significantly compared to the mirror zone （P〈0.05）, so did the ADCfast, and ADCslow （P〈 0.05）. In patients at chronic stage, ffast, ADCfast and ADCslow showed no significant difference between the infarct core and the mirror zone （P）〉0.05）. Conclusion：In normal group, the diffusivity parameters based on bi-exponential model was different between white matter and gray matter. In patients at subacute stage, the infarct core showed decreased ffast, ADCfast, and ADCslow values compared to mirror zones,while no significant differences were found in patients at chronic stage. Although bi-exponential model may be more fitted to explore the diffusion state of water,its underlying pathophysiological mechanism still needs further investigation.