磁共振扩散张量成像对正常人脑结构的显示及各向异性研究

目的 探讨不同脑组织结构在扩散张量成像（DTI）中的信号特点及各向异性。资料与方法 对20名正常人行DTI，分析其平均扩散系数（ADC）图及部分各向异性（FA）图的特点，并对不同感兴趣区（ROI）进行ADC及FA值的测量，通过统计学分析得出其扩散和各向异性特点。结果男女之间比较，同一部位的ADC及FA值差异均无统计学意义（P〉0．05），对称结构而言，左右侧的ADC或FA值相比差异也无统计学意义（P〉0．05）。ADC图上脑脊液呈明显的高信号，而其余脑组织呈不同程度的较低信号，且信号差别不大。侧脑室体部内的脑脊液与其他ROIADC值相比，差异有统计学意义（P〈0．05），而其余ROI之间的ADC值则无差异（P〉0．05）。FA图可以清晰反映脑白质纤维，呈明显的高信号。不同白质纤维的FA值不一致，胼胝体压部的FA值最大，并与胼胝体膝部差异无统计学意义（P〉0．05）。与其他测量结构差异有统计学意义（P〈0．05）。脑白质的各向异性按胼胝体、内囊、半卵圆中心、外囊逐渐降低。侧脑室体部内脑脊液的FA值最低。结论 不同部位脑组织的各向异性及信号不同。ADC图主要体现脑脊液与其他脑组织的差异，而FA图可以清晰显示脑内的白质纤维，并能定量反映不同部位各向异性的特征。

A Study of Displaying Normal Adult Brain and Its Anisotropic Difference by Using Diffusion Tensor Magnetic Resonance Imaging

Objective To discuss the signal intensity and anisotropy of different structures of normal adult brain on diffusion tensor imaging.Materials and Methods 20 normal adults were examined by diffusion tensor imaging (DTI), the signal features of different brain structures on both ADC and FA maps were analyzed, the ADC and anisotropic values were measured, results were analyzed statistically.Results No significant difference of ADC or FA value was found in the same region of interest (ROI) between male and female(P>0.05). For the symmetric structures, ADC or FA value of the right side and the left side had no significant difference (P>0.05). Cerebral spinal fluid (CSF) in the lateral ventricle was appeared as obviously high signal on ADC map, and the rest brain tissues demonstrated as gray shadows with different grey levels, but not so distinct. Significant difference was found between CSF in lateral ventricle body and other ROIs according to ADC values (P<0.05), ADC value displayed no significant difference among other ROIs (P>0.05). On FA map, white matters were well illustrated as apparently high signal intensities with various FA values. The highest FA value was in the splenium of corpus callosum, then the genu of corpus callosum, internal capsule, centerum semiovale, external capsule in descending order. Significant difference was found between splenium of corpus callosum and the other ROIs (P<0.05), except genu of corpus callosum. For FA values, FA value of CSF in lateral ventricle body was the lowest one.Conclusion Diffusion anisotropy varies among different structures in normal adult brain. ADC maps can reflect difference between CSF and other brain structure. White matters in the brain can be demonstrated well on FA maps, anisotropic features can be quantitied using DTI.