超急性期脑梗死不同高b值磁共振扩散加权成像的实验研究

目的探讨超急性期脑梗死时不同高b值磁共振扩散加权成像(DWI)上图像对比、信号强度的变化特征。方法新西兰大白兔25只,实验组20只,对照组5只。实验组经眶内入路电凝大脑中动脉,术后0.5h、2h、4h、6h进行DWI检查后,立即取不同时间点的兔脑标本进行病理检查。DWI扫描序列依次为:TR/TE/激励次数为6817ms/116.5ms/1次,b值为1000s/mm2,一次扫描时间为40s;TR/TE/激励次数为7647ms/133.1ms/2次,b值为2000s/mm2,一次扫描时间为68s;TR/TE/激励次数为8284ms/145.8ms/4次,b值为3000s/mm2,一次扫描时间为120s。结果b值1000~3000s/mm2均可发现DWI上的高信号,但b值越高,DWI上的高信号边界越清晰,而图像背景信号越模糊,信噪比下降。结论b值对扩散加权成像有重要影响,选择合适的高b值更有利于诊断超急性期脑梗死。

An experimental research of superacute infarction by MR diffusion weighted imaging with different high-b-value

Objective To observe the features of image contrast,signal intensity of the superacute infarction on diffusion weighted imaging(DWI) with different high b values.Methods 25 New Zealand rabbits regardless of male or female were randomized into two groups,20 rabbits were classified as experimental group and 5 rabbits were classified as control group.For experimental group,transobital electrocoagulation was carried out to occlude the middle cerebral artery.Then the rabbits of experimental group were underwent DWI in 0.5h,2h,4h,6h.Specimens of the brain tissue obtained correspondently to DWI slice were observed by microscopy and electrical microscopy respectively.Imaging parameters included: 6817ms/116.5ms/1(TR/TE/excitations),b=1000/40s;7647ms/133.1ms/2,b=2000/68s;8284ms/145.8ms/4,b=3000/120s.Results All the high signal intensity could be found when b value increased from 1000 s/mm2 to 3000 s/mm2.When b value increased,the border of the high signal intensity became clearer,but the background became blurred,the signal-to-noise(SNR) of DWI decreased.ADC value of affected and contralateral side decreased with b value increased and time coursing within 6h.Conclusion b value may have great influence on DWI,and the superacute cerebral infarction can be found easier with suitable b value.