DWI动态评价大鼠脑缺血—再灌注损伤区的组织学特征

目的本研究运用磁共振弥散加权成像(DWI)技术动态评价大鼠脑缺血—再灌注损伤后不同时间脑损伤区DWI信号强度(SI)及表观扩散系数(ADC)的变化,结合组织学检测,分析损伤区组织学特征。方法健康成年SD雄性大鼠(n=80)随机分成8组,分别为脑缺血—再灌注1h、3h、6h、12h、1d、3d、7d组和假手术组,采用线栓法制作大鼠右侧大脑中动脉缺血—再灌注(MCAO/R)模型,Zea Longa评分评价神经功能损伤程度,Philips Achieva 3.0T MR扫描仪对假手术组和缺血—再灌注后不同时间点大鼠脑部行冠状位DWI扫描,在工作站上重建ADC图,测量基底核层面梗死灶DWI-SI和ADC值,计算相对ADC值(r ADC)和相对DWI-SI(r DWI-SI)值。2,3,5-氯化三苯基四氮唑(TTC)染色评价梗死体积的变化。苏木精—伊红染色观察组织形态学变化。结果假手术组动物麻醉苏醒后未见神经功能缺损,脑缺血—再灌注1h大鼠出现神经损伤,3h~1d时症状逐渐加重,3~7d时症状改善。假手术组DWI及ADC图均未见异常信号;MCAO/R后1h DWI上右侧纹状体及周围部分皮质区域出现高信号,相应部位ADC值降低,1h~1d DWI高信号范围随时间推移逐渐增大,信号强度逐渐增高,3~7d时开始降低;r ADC值随时间先降低后升高,6h达到最低,12h开始回升,1d时r ADC值较12h稍降低(P0.05),3d时r ADC升高,7d时与假手术组无明显差异(P0.05);1h~1d r DWI-SI持续升高,1d达最高峰,3~7d开始下降,7d时仍明显高于假手术组。苏木精—伊红染色显示假手术组右侧海马及皮质区结构未见明显异常;缺血—再灌注12h缺血侧海马区及皮质区出现可见部分浓染细胞和胞浆空泡形成,核固缩,但细胞排列尚好;1d时缺血侧神经元缺血损伤加重,细胞排列紊乱,细胞间隙增宽,出现大量胞浆空泡化,核固缩显著;3d时缺血侧海马区空泡化有所减轻。假手术组TTC染色未见梗死区域;脑缺血—再灌注1h可见右侧纹状体及周围少许皮质梗死;1h~1d梗死体积逐渐增大,1~3d时达到峰值,7d时梗死体积减小。1h~1d缺血侧脑水肿体积随时间持续增加,1d达到高峰,3d时开始下降,7d明显减轻。模型组各时间点神经功能评分与相应时间点基底核区梗死灶r DWI-SI呈显著性正相关(r=0.503,P=0.000);相应时间点脑梗死体积、水肿体积与r DWI-SI均呈显著性正相关(r=0.542,P=0.001;r=0.740,P=0.000)。结论磁共振弥散加权成像获得的DWI-SI及ADC值,对评价脑缺血再灌注损伤组织学特征具有高度的敏感性和特异性,对脑缺血—再灌注损伤后缺血区的动态改变具有直观的价值。

Dynamic evaluation of histologic features of ischemic rat brain tissues by DWI

Objective To observe the dynamic changes of diffusion weighted imaging signal intensity (DWI-SI) and apparent diffusion coefficient (ADC) in the damaged brain zones in rats after cerebral ischemia reperfusion by DWI, and combined with tissue detection to study the histological features in brain damage zone.Method Eighty SD male rats were randomly divided into 8 groups: cerebral ischemia-reperfusion 1h group, 3h group, 6h group, 12h group,
1d group, 3d group, 7d group and sham group. The right middle cerebral artery occlusion and reperfusion (MCAO/R) model in rats was induced with the intraluminal suture method. The Zea Longa score was used to evaluate the neurological function of the rats in the MCAO/R groups and sham group. Coronal sections were performed with Philips Achieva 3.0-tesla whole-body MR scanner in the sham group and ischemia reperfusion at different time points. All rats were underwent DWI scanning. The ADC map was reconstructed on the workstation, and the DWI signal intensity, ADC value and the relative apparent diffusion coefficient (rADC) value of each rat was calculated. The infarct volumes were measured at each time point by 2,3,5-Triphenyltetrazolium chloride (TTC) staining. The morphological changes were observed by HE staining at different reperfusion time points (12h, 1d, 3d, sham).Results There were no neurological deficits in sham group. The rats showed neurological deficits in 1h after cerebral ischemia reperfusion, The neurological deficits were significantly severer in 3h-1d, and the symptoms gradually improved on 3-7d. No abnormal signal was detected on DWI and ADC maps in the sham group. The DWI showed high signal in striatum, and the ADC value of the corresponding part was decrease on 1h after MCAO/R. The high signal area in DWI and the signal intensity increased gradually from 1h to 1d, decreased gradually from 3d to 7d. The rADC value took on a firstly decreasing and then increasing, reached the lowest at 6h, which began to rise on 12h and decreased on 1d. The rADC value increased on 3d. There was no significant difference between sham group and 7d group (P>0.05). The rDWI-SI increased continuesly from 1h to 1d, reached its peak on 1d, began to decrease on 3d, the rDWI-SI at 7d group was still higher than that of in sham group. HE staining showed that there was no significant abnormality on the structure of the hippocampus and the cortex in sham operated group. At 12h after MCAO/R, it has been observed that some dense staining cells, cytoplasmic vacuoles formed, and nuclear nuclear pyknosis in the hippocampus and cortex of ischemic side, but cell arrangement was acceptable. The ischemic neuronal injury aggravated on the first day, cell arrangement disordered, cell gap widened, a large number of cytoplasmic vacuoles and nuclear condensation were seen on the first day, the cytoplasmic vacuoles of the hippocampus was reduced slightly on 3d. The infarct area was not found in sham group. The model group rats showed white staining area in the right striatum and the surrounding cortex at 1h, infarct area gradually expanded from 1h to 1d, reached a peak on 1-3d and decreased on 7d. The ischemic brain edema volume of model group increased gradually over time, reached a peak at 1d group, began to decrease at 3d group, decreased significantly at 7d group. The neurological function score was positively correlated with the rDWI-SI of basal ganglia in the model group (r=0.503,P=0.000), the infarct volume and the volume of edema was positively correlated with the rDWI in the model group (r=0.542,P=0.001.r=0.740, P=0.000).Conclusion The DWI-SI and ADC values were obtained by magnetic resonance diffusion weighted imaging, it have a high specificity and sensitivity on the changes of cerebral ischemia reperfusion injury, it had a intuitive value on the dynamic change of ischemia reperfusion injury.