磁共振扩散加权成像参数对兔超急性期脑梗死诊断的影响

目的。探讨磁共振扩散加权成像(DWI)参数选择在超急性期脑梗死诊断中的价值。方法。新西兰大白兔24只，其中实验组20只，对照组4K。实验组经眶人路电凝大脑中动脉，选择DWI参数，分别在兔右大脑中动脉阻塞(MCAO)后0．5h、2h、4h、6h进行DWI检查；对照组仅暴露同侧大脑中动脉，不予电凝。比较单方向DWI与平均DWI，分析b值对DWI的影响及DWI伪彩图改变.结果。平均DWI较单方向DWI显示病灶更清楚。b值为1000s／mm^2、2000s／mm^2和3000s／mm^2的DWI上均可发现异常高信号，但b值为2000s／mm^2和3000s／mm^2时的信号对比与b值为1000s／mm^2时比较差异有统计学意义，且高信号边界更加清晰，但图像信噪比下降。与常规DWI相比，DWI伪彩图上梗死核心和缺血半暗带的分界更加清楚。结论。平均DWI、b值和DWI伪彩图对扩散加权成像有重要影响，选择合适的参数有利于超急性期脑梗死的诊断。

Effect of diffusion weighted imaging parameters on diagnosis of superacute cerebral infarction in rabbits

Aim: To explore the value of parameters of diffusion weighted imaging (DWI) in the diagnosis of the superacute cerebral infarction. Methods: A total of 24 New Zealand rabbits were randomly assigned into experimental group(n=20) and control group(n=4). For the experimental group, transorbital electrocoagulation was carried out to occlude the middle cerebral artery, then the rabbits were undergone DWI with different parameters at 0.5 h, 2 h, 4 h, and 6 h after the right middle cerebral artery occlusion. The control group only exposed the right middle cerebral artery, but did not occlude it.Single direction and mean DWI were compared,and b value effect on DWI and artificial colour map of DWI were analyzed. Results: Mean DWI showed the lesions more clearly compared with single direction DWI.High signal intensity could be found when b value increased from 1 000 s/mm 2 to 3 000 s/mm 2. Compared with 1 000 s/mm 2, there was significant difference of the contrast ratio when b value was 2 000s/mm 2 and 3 000 s/mm 2 respectively. Furthermore, the border of the high signal intensity was clearer, but the signal-to-noise of DWI decreased. Compared with conventional DWI, the border between cerebral infarction and ischemic penumbra became clearer on artificial colour map of DWI. Conclusion: Mean DWI, b value,and artificial colour map may have great influence on DWI, and the superacute cerebral infarction could be found easier with suitable DWI parameters.