不同b值DWI成像在早期脑梗死中的应用

Usefulness of different-b-value diffusion-weighted imaging in early cerebral infarction

目的:探讨不同b值磁共振扩散加权成像(diffusion weighted imaging,DWI)在早期脑梗死患者中的应用价值,寻找早期脑梗死的最佳b值。方法:对临床高度怀疑早期脑梗死(发病在72 h以内)患者行常规MRI和b值分别为1 000、2000、3 000 s/mm^2的DWI检查,测量感兴趣区(病灶中心和对侧正常脑组织)不同b值DWI信号强度(signal intensity,SI)、平均表观扩散系数(apparent diffusion coefficient,ADC),并计算不同b值DWI和常规MRI对诊断早期脑梗死的敏感性。结果:40例早期脑梗死患者中,b值为3 000 s/mm^2时DWI(DWI_(b=3 000))诊断早期脑梗死的敏感性为100%,b值为1 000和2 000 s/mm^2时DWI诊断早期脑梗死的敏感性为97.5%,常规MRI的敏感性为72.5%。随着b值增加,感兴趣区信号强度及ADC值均降低,不同b值条件下,感兴趣区信号强度及ADC值差异均有统计学意义(P<0.05)。结论:DWI对早期脑梗死的监测明显优于常规MRI扫描。随着b值增加,对超早期脑梗死的敏感性也随之增高,信号对比亦明显,但图像信噪比也随之降低,在b值=1 000 s/mm^2时,脑组织中对比度及对新发脑梗死的敏感性较高。

Objective To investigate the usefulness of different-b-value diffusion weighted imaging（DWI）in patients with early cerebral infarction and obtain the optimal b value of early cerebral infarction.Methods DWI at b-value of 1,000,2,000,and 3,000 s/mm2was performed for 40 patients within 72 h after the onset of stroke using a GE Signa HDx 3.0T MRI scanner.Post-processing was done by the DWI specific software Function Tool to gain signal intensity and mean apparent diffusion coefficient in the lesions center and the contralateral normal brain tissue,respectively.The sensitivity of conventional MRI and different-b-value DWI was calculated in the diagnosis of early cerebral infarction.Results In 40 patients with early cerebral infarction,the sensitivity of b-values of 1,000,2,000,and 3,000 s/mm2（DWI_（b=1 000）,DWI_（b=2 000）,DWI_（b=3 000））and conventional MRI in the diagnosis of early cerebral infarction were 100%,97.5%,97.5%,72.5%,respectively.With b value increased,signal intensity and ADC value declined.Under the condition of different b values,signal intensity and ADC value were statistically significant in region of interest（P0.05）.Conclusion DWI is superior to conventional MRI scan in monitoring early cerebral infarction.With the increase of b value,the sensitivity is the higher to hyperacute cerebral infarction,the signal contrast is obvious,while signal to noise ratio of the image reduces.It is suggested that brain tissue contrast and the sensitivity to the new cerebral infarction is more predictable on b value=1,000 DWI than on the other DWIs.