双b值扩散加权成像在脑梗死诊断中的应用

目的:比较双b值DWI对脑梗死体积及ADC值测量的影响,探讨较高b值DWI在脑梗死诊断中的应用价值。方法:回顾性研究30例脑梗死患者,年龄44～84岁,平均67岁,发病时间3～6d,DWI取b值1000和2000s/mm2,分析脑梗死DWI及ADC图,测量兴趣区与对侧正常部位的扩散系数(ADC)并计算相对扩散系数(rADC),测量并计算梗死灶体积。结果:急性和亚急性脑梗死灶均扩散受限,DWI呈高信号、ADC图呈低信号。与b值1000s/mm2相比,b值2000s/mm2DWI示脑灰白质对比度增加,病灶显示更清晰,还能发现新病灶。不同b值下rADC比较没有统计学意义(P=0.884,P>0.05),同侧ADC有统计学意义(P=0.005,P<0.05);对侧ADC有显著统计学意义(P<0.001)。较高b值下梗死体积较低b值增加,且有统计学意义(P=0.04,P<0.05)。结论:DWI是检测脑梗死的重要技术手段,rADC不受b值影响,rADC降低可指导脑梗死诊断;较高b值DWI上脑梗死灶体积测量更准确,有利于观察病灶演变和指导临床治疗。

Application of Double b Value Diffusion-weighted Magnetic Resonance Imaging in Diagnosis of Brain Infarction

Objective:To assess the value of higher b value diffusion-weighted magnetic resonance imaging(DWI)in diagnosis of brain infarction.Methods:Retrospective analysis of 1.5T MR examination findings in 30 subjects(age average,67 years)3~6 days after onset was studied,including conventional and double b value serial(b=1000s/mm2 and 2000s/mm2).ROIs were placed on infarct lesion and symmetrical contralateral normal brain tissue.The infarct volume,apparent diffusion coefficient(ADC)and relatively apparent diffusion coefficient(rADC)were calculated.Results:The acute and subacute brain infact had restricted diffusion which displayed hyper-intensity in DWI and hypo-intensity in ADC map.In comparison with DWI of b value 1000s/mm2,DWI of b value 2000s/mm2 could improve the contrast of the grey and white matter,and find new lesion.No significant change of relative ADC values was found between different b value groups(P=0.884,P>0.05),but the isolateral and contralateral ADC values were significantly different between DWI at b value 1000s/mm2 and 2000s/mm2(P=0.005,P<0.001,P<0.05,respectively).The infarct volume on the higher b value DWI was larger than that on the lower b value DWI(P=0.04,P<0.05).Conclusion:DWI is an important method to detect infarct lesion.Different b values have no effect on relatively apparent diffusion coefficient which can guide the diagnosis of brain infarct.The higher b value DWI is superior to lower b value DWI in calculating infarct volume more exactly,which was helpful in finding the time course of lesion development and provideing meaningful information for clinical therapy.