局灶性脑皮质发育不良的扩散张量成像初步研究

Diffusion tensor imaging of focal cortical dysplasia： a preliminary study

目的探讨DTI技术诊断局灶性脑皮质发育不良（FCD）的价值。方法回顾性分析12例FCD患者的临床、MRI及DTI等资料。DTI经过图像后处理，获得平均扩散系数（MD）和部分各向异性分数（FA）图及彩色编码张量图，于FCD的皮质下白质区及对侧相应皮质下白质区设置椭圆形ROI，测量每个ROI的MD及FA值。病灶侧与对侧MD、FA值的比较采用配对t检验。扩散张量纤维束示踪成像（DTT）以T2WI图像为参照，ROI设置同DTI，以ROI中的任一点作为种子点，获得通过该ROI区域的所有白质纤维束示踪图像。结果12例患者MR平扫均显示局灶性脑皮质增厚及灰白质界限不清，其中7例显示皮质下白质稍长T1、稍长T2信号，2例皮质下白质萎缩，3例皮质下白质无明显异常。DT1分析显示FCD邻近皮质下白质与对侧比较FA值明显下降（患侧0．31±0．05，对侧0．42±0．08，t=-3．995，P〈0．01），MD值明显上升[患侧（1．02±0．16）×10^-3mm2／s，对侧（0．86±0．13）×10^-3mm2／s，t=2．655，P〈0．05]，差异均有统计学意义。DTT显示10例FCD患者皮质下白质纤维束较对侧明确减少，2例较对侧可能减少，主要表现为皮质下白质纤维稀疏，与深部白质纤维间联系减少。结论FCD除了导致脑皮质结构异常外，也影响局部皮质下白质纤维的发育，DTI是常规MR检查的重要补充。

Objective To evaluate the subcortical white matter changes adjacent to focal cortical dysplasia（FCD） by applying diffusion tensor imaging（DTI）and to investigate its potential value in the diagnosis of FCD. Methods The clinical information, MRI images and DTI data of 12 patients with FCD were retrospectively evaluated. The DTI images were postprocessed. The mean diffusivity（MD） , fractional anisotrophy （FA） and color-encoded tensor images were acquired. Ellipsoid ROIs were set in the subcortical white matter under FCD lesions and corresponding areas on the contralateral side. The MD value and FA value were measured in each ROI. The paired t test was employed to compare the MD and FA values between the areas ipsilateral and contralateral to the lesion. In diffusion tensor tractography（DTT） , the same ROI as DTI measurement was set using T2WI images as reference. One ROI served as seed point, all the white matter fiber tracts crossing the ROI were acquired. Results Focal cortical thickening and blurring of the gray-white matter junction were found in all cases of FCD on conventional MRI images. Seven patients demonstrated hyperintensity on T2WI images and hypointensity on T1WI images in the subeortical white matter adjacent to FCD. Two patients demonstrated focal subcortical white matter atrophy. No abnormal findings were detected in the subcortical white matter in 3 patients. Quantitative analysis of DTI data showed significant fractional anisotrophy （FA） decrease （ ipsilateral side to FCD 0. 31±0.05, contralateral side 0.42±0.08,t = - 3. 995,P 〈 0.01）, and mean diffusivity （MD） increase in comnarison to the contralateral region[ ipsilateral side to FCD （1.02± 0. 16）×10^-3mm2/s, contralateral side （0.86 ± 0. 13）×10^-3mm2/s ,t = 2. 655 ,P 〈 0.05 ]. On diffusion tensor tractography （ DTT）, 10 patients showed definite reduction in the volume of subcortical white matter bundles and the connections between the subcortex and deep white matter were sparse. Two patients showed probable reduction compared with the contralateral normal side. Conclusions FCD not only has cortical abnormalities but also affects local white matter development. DTI is an important supplement to conventional MRI.