正常成人视放射的磁共振扩散张量成像和扩散张量纤维束成像研究

Optic radiation in normal adults: a study using magnetic resonance diffusion tensor imaging and diffusion tensor tractography

目的利用磁共振扩散张量成像(DTI)研究正常成人视放射的部分各向异性和视放射纤维束构象特征。方法对30例健康志愿者进行常规磁先振成像(MRI)及DTI序列检查,重建各向异性(FA)图和DEC图,分别测量双侧视放射区的FA值和平均扩散率(MD)值。采用扩散张量纤维束跟踪软件对视放射纤维束进行追踪。结果方向编码彩色图能清晰显示视放射,正常视放射的FA值分别为左侧0.509±0.029、右侧0.502±0.026,MD值分别为左侧(0.763±0.050)×10^-3mm2/s、右侧(0.748±0.052)×10^-3mm2/s。双侧视放射的FA值和MD值均无统计学差异(P>0.05)。扩散张量纤维束成像(DTT)可显示视放射纤维束起自丘脑的外侧膝状体,位于侧脑室三角区旁的矢状层,分为3束投射到原始视皮质,背侧束和外侧束向后到达距状裂的上缘,腹侧束先向前形成Meyer环,再向后终止于距状裂的下缘,符合经典解剖学的研究。结论DTI和DTT可清晰显示视放射纤维束的各向异性和构象特征,为了解视功能与视觉通路之间的关系提供了新的研究手段。

Objective To study the fractional anisotropy （FA） and the architecture of the optic radiation fiber tracts of normal adults with magnetic resonance （MR） diffusion tensor imaging （DTI）. Methods Diffusion tensor images were obtained from 30 healthy volunteers without any cerebral abnormalities on conventional MRI. FA and the mean diffusivity （MD） of the optic radiation were measured in the directional encoded color （DEC） maps. The architecture of the optic radiation fiber tracts were displayed with the software of diffusion tensor fiber tracking. Results In all subjects, the optic radiation could be readily identified in the DEC maps. The FA value was 0.509±0.029 in the left and 0.502±0.026 in the right, with the MD value of （0.763±0.050）×10^-3 and 0.748±0.052）×10^3 mm^2/s, respectively. No significant differences were found in the FA or MD value of the bilateral optic radiation （P〉0.05）. Diffusion tensor tractography （DTr） demonstrated that the 3 bundles of the optic radiation fibers were located in the lateral sagittal stratum, passing from the lateral geniculate body of the thalamus to the primary visual cortex. The dorsal and lateral bundles passed posteriorly to the superior bank of the calcarine cortex, while the ventral bundle passed anteriorly before making a sharp turn, known as the Meyer loop, and subsequently coursed posteriorly to terminate in the inferior margin of the calcarine cortex, which was consistent with the results of classic anatomical studies. Conclusion As a novel method to study the relationship between visual function and optic pathway, DTI and DTT can show the FA and architecture of the optic radiation.