不同弥散强度对脑组织ADC值及FA值测定的影响

探讨不同弥散强度对弥散张量成像中表观弥散系数值及部分各向异性指数值测定的影响.材料和方法:使用七个不同的弥散梯度(b值分别为b0=0、b1=500s/mm2、b2=1000s/mm2、b3=1500s/mm2、b4=2000s/mm2、b5=2500s/mm2和b6=3000s/mm2)对20名正常成人脑组织进行弥散张量成像,对7个不同的b值分别进行组合(组合方式为b0b1、b0b2、b0b3、b0b5、b0b6和b0b6)及后处理,分别获得其ADC图和FA图,然后在ADC图和FA图上分别测定尾状核头、内囊后肢、丘脑、半卵圆中心、侧脑室体部及胼胝体膝部和压部的数值并进行统计学分析.结果:脑内各个解剖部位的ADC值均随着弥散强度的增加而显著降低(P＜0.05);FA值不随弥散强度的改变而改变(P＞0.05).结论:FA值不随弥散强度的改变而发生改变;随着弥散强度的改变,ADC值也发生改变,在进行临床研究时要充分考虑弥散强度对ADC值测定的影响.

Effect of Different Diffusion Weighting on ADC and FA Measurements of Normal Brain

Purpose: To study the effect of different diffusion weighting on ADC and FA measurements of normal brain. Materials and Methods: Seven different diffusion weightings(b0 = 0, b1 = 500s/mm2, b2 = 1000s/mm2, b3 = 1500s/mm2, b4= 2000s/mm2, b5 = 2500s/mm2 and b6 = 3000s/mm2) were applied in twenty normal brains in diffusion tensor imaging. The brain ADC and FA maps were calculated using six combinations of the seven different b values(b0b1, b0b2, b0b3, b0h4,b0b5 and b0h6) . The average of the ADC and FA were measured and compared in the centrum semiovale, posterior limb of the internal capsule, genu of corpus callosum, sple-nium of corpus callosum, thalamus, caudate nucleus, and body part of lateral ventricle. Results: The measured ADC was significantly decreased accompanied with increase of b values(P < 0.05) . The measured FA was not affected by the strength of b values (P > 0.05) .Conclusion: The strength of b values influence measurement of ADC, but not FA. Attention must be paid to choice of diffusion strength regarding clinical study.