基于扩散张量的脑白质内神经纤维束的可视化技术

介绍了在功能磁共振成像的研究中发展非常快的扩散张量成像技术的基本原理，以及如何利用扩散张量数据来重建脑白质内的神经纤维柬图像。其中主要介绍了白质束成像技术及其优缺点，并且分析了神经纤维束可视化技术的应用前景及其局限性。     

磁共振弥散张量成像的脑白质纤维优化重建

磁共振弥散张量成像(DTI)可对大脑白质纤维束的三维几何结构进行无创研究,其主要方法为DTI纤维追踪成像.研究打破现有DTI纤维追踪成像从初始种子区域逐步追踪增长的框架,提出脑白质的纤维优化重建方法,从全局角度描述追踪纤维,通过其对弥散倾向和几何结构的优化估计,重构最优纤维路径.结果表明,该方法可提供连接两个感兴趣区域(ROI)的有效和对称连接,同时通过全局优化手段消除累积噪声及局部随机噪声,提高长距离成像的可靠性;在人工合成数据集和真实人体数据集中均能较好成像,较之现有纤维追踪成像具有更高的可靠性和可重复性.     

基于Log-Euclidean矩阵的脑白质扩散张量场的正则化处理

在临床诊断时为了较快获得数据,扩散张量图像的质量常常不能得到保证,其正则化处理特别重要。为此,本研究提出一种基于Log-Euclidean矩阵的新算法对张量图像进行评估预处理,首先对张量特征值进行自然指数运算以实现张量场到Log-Euclidean矢量场的转换,再通过有限差分法计算矢量场梯度函数最小值,从而实现矢量场的去噪平滑,之后对矢量场取自然对数运算映射回张量空间。在1名志愿者脑扩散张量图像上进行白质纤维束跟踪测试,结果表明该方法有效避免了白质纤维束跟踪中杂从的出现,提高了跟踪平滑性。     

Diffusion Tensor Imaging of White Matter Tracts in the Dog Brain

Diffusion weighted imaging sequences are now widely available on Magnetic Resonance Imaging (MRI) scanners. Diffusion Tensor Imaging (DTI) of the brain is able to show white matter tracts and is now commonly used in human medicine to study brain anatomy, tumors, structural pathways,… The purpose of this study was to show the interest of DTI to reveal the white matter fibers in the dogs' brain. DTI MR Images for this study were obtained with a 3 T system of 4 dogs euthanized for other reasons than neurological disorders. Combined fractional anisotropic (FA) and directional maps were obtained in the first 2 hours after death. The heads were amputated immediately after scanning and stored in 10% formalin until preparation for dissection. An experienced anatomist tracked white matter tracts with clinical relevance using the scanner software. The selected tracts were REFVIDume rendered and correlated with gross dissection. Using DTI we were able to track relevant neurological connections, such as the corticospinal tract, the optic and the cerebellar tract. The three dimensional anatomy is better presented using modern visualization techniques. DTI seems to be a valuable tool in order to present clinically relevant white matter tracts to neurological clinicians and researchers. Anat Rec, 296:340–349, 2013. © 2013 Wiley Periodicals, Inc.     

基于DT-MRI的纤维跟踪及可视化研究

磁共振扩散张量成像(DT-MRI)是一种新的成像技术,比传统的扩散加权成像(DWI)能够更加准确地反映分子扩散的方向.在脑白质这样具有大量纤维束的组织中,水分子的扩散表现出显著的各向异性,从而有可能从张量信息的各向异性入手,跟踪得到白质纤维束的走行方向.本文介绍了DTI的原理、数据采集与处理方法,提出了一种可变步长的纤维跟踪方法,并以VC /ITK/VTK为开发工具实现了DTI分析和纤维跟踪与可视化.     

基于扩散形状的DTI纤维跟踪算法研究

到目前为止，研究者们已经提出了许多种神经纤维束的三维可视化技术，其中，基于扩散跟踪的白质束成像技术在白质纤维束的可视化和分析中使用得最多。本文针对现有纤维跟踪算法存在的问题，提出了基于扩散形状的纤维跟踪算法，该算法结合了流线跟踪（streamline tracking，STT）法与张量弯曲（tensor deflection，TEND）法的优点，对不同的扩散形状采用不同的跟踪方向，尤其在平面扩散的情况提出了更接近纤维走行的跟踪方法，减少了跟踪方向与实际纤维走行的误差，能更完整、更准确地显示大脑白质的纤维走行。     

Clinical Use of Diffusion Tensor Image-Merged Functional Neuronavigation for Brain Tumor Surgeries: Review of Preoperative,Intraoperative, and Postoperative Data for 123 Cases

Purpose

To achieve maximal safe resection during brain tumor surgery, functional image-merged neuronavigation is widely used. We retrospectively reviewed our cases in which diffusion tensor image (DTI)-merged functional neuronavigation was performed during surgery.

Materials and Methods

Between November 2008 and May 2010, 123 patients underwent surgery utilizing DTI-merged neuronavigation. Anatomical magnetic resonance images (MRI) were obtained preoperatively and fused with DTI of major white matter tracts, such as the corticospinal tract, optic radiation, or arcuate fasciculus. We used this fused image for functional neuronavigation during brain tumor surgery of eloquent areas. We checked the DTI images together with postoperative MRI images and evaluated the integrity of white matter tracts.

Results

A single white matter tract was inspected in 78 patients, and two or more white matter tracts were checked in 45 patients. Among the 123 patients, a grossly total resection was achieved in 90 patients (73.2%), subtotal resection in 29 patients (23.6%), and partial resection in 4 patients (3.3%). Postoperative neurologic outcomes, compared with preoperative function, included the following: 100 patients (81.3%) displayed improvement of neurologic symptoms or no change, 7 patients (5.7%) experienced postoperative permanent neurologic deterioration (additional or aggravated neurologic symptoms), and 16 patients (13.0%) demonstrated transient worsening.

Conclusion

DTI-merged functional neuronavigation could be a useful tool in brain tumor surgery for maximal safe resection. However, there are still limitations, including white matter tract shift, during surgery and in DTI itself. Further studies should be conducted to overcome these limitations.     

基于弥散张量成像的儿童失神癫痫认知控制网络的结构连接研究

已有研究表明儿童失神癫痫患者的认知控制网络（CCN）中功能连接发生了改变。为了探索这些改变相应的结构基础,采用基于弥散张量成像（DTI）的纤维束追踪技术,对9名儿童失神癫痫患者和12名正常对照,分别构建了每个人CCN网络的结构连接,然后对两组间的纤维束连接的条数、长度、连接强度、平均部分各向异性值（FA）和平均弥散度（MD）等参数使用双样本T检验进行了统计比较。结果发现患者组CCN网络中主要纤维束上平均FA值显著降低,MD值显著增加（P_s<0.05,Bonferroni 校正）,并且左侧前额叶皮层到丘脑的纤维束上平均FA值与病程呈显著的负相关关系（P=0.011）。本研究结果为儿童失神癫痫患者CCN网络的功能连接异常提供了相应的结构基础,这些白质纤维异常的连接可能是导致患者认知控制功能异常的重要原因之一。