磁共振扩散张量成像在视觉通路成像中的研究进展

扩散张量成像(diffusion tenser i maging,DTI)是在扩散加权成像(diffusion weighted i maging,DWI)技术的基础上发展而来的一项新的磁共振成像技术,它是利用组织内水分子布朗运动在不同方向上信号差异的一种成像方法,能测量并量化组织内微观结构,是目前唯一无创性活体研究脑白     

磁共振扩散张量成像对脊髓疾病的研究进展

脊髓是中枢神经系统的重要组成部分,脊髓病变复杂多样,脊髓截瘫等严重功能障碍带来巨大的经济和社会负担。对于脊髓病变,临床需要客观精确无创的检查方法早期诊断、制订治疗方案、随访疗效。磁共振成像(MRI)是目前检测脊髓病变的最佳影像学方法,但近年动物实验及初步临床研究证实[1]常规MRI结果与功能残疾评价相关性差,与神经病学及组织学损伤程度不相关联,低估了脊髓病变程度,不能反映脊髓白质纤维束状态,不能有效定量观察轴突损伤及再髓鞘化过程,不适于评价脊髓的功能状态[2]。扩散加权成像(diffusion weighted imaging,DWI)技术通过…     

磁共振扩散张量成像在多发性硬化中的研究进展

磁共振扩散张量成像(diffusion tensor imaging,DTI)是在扩散加权成像(diffusion weighted imaging,DWI)基础上发展起来的一项新技术,主要用于中枢神经系统的组织形态学改变与病理学的细微分析研究。多发性硬化(multiple sclero-sis,MS)是中枢神经系统最常见的脱髓鞘性疾病,DTI     

青光眼视通路的磁共振扩散张量成像研究进展

磁共振扩散张量成像(DTI)可以无创追踪脑内白质纤维束走行,可用于研究视通路的形态和功能改变。研究发现青光眼不仅局限于眼部视网膜变性,中枢神经系统视通路同样也受到影响,视神经直径、视交叉、外侧膝状体、视辐射及视皮质均存在形态和功能的改变,且功能的改变出现较早。应用DTI技术可以早期发现青光眼视通路改变,为临床治疗提供依据。     

磁共振扩散张量成像在脊髓型颈椎病中的研究进展

脊髓型颈椎病(cervical spondylotic myelopathy,CSM)是以颈椎退行性变或椎间盘膨出或突出导致脊髓和(或)支配脊髓的血管受压,造成以脊髓功能障碍为主的临床症候群,是临床常见疾病~([1]).     

扩散张量磁共振成像基本原理及应用

扩散张量成像 (diffusiontensorimaging ,DTI)是由扩散加权成像 (diffusionweightedimaging ,DWI)技术改进和发展而来的一项新型磁共振成像技术 ,可利用扩散敏感梯度从多个方向对水分子的扩散各向异性进行量化 ,从而反映活体组织内的细微结构。此技术在中枢神经系统的应用已日趋成熟 ,在其他组织器官的研究也取得了较大进展 ,是一项有广阔发展前景的新型检查手段。本文总结国外相关文献 ,对扩散张量成像的基本原理及临床应用研究进行阐述。1　数据采集1.1　扩散各向异性　自由水的扩散是随机的 ,在不同方向上扩散程度相同 ,这种现象被称…     

大脑磁共振弥散张量成像研究进展

弥散张量成像(diffusion tensor imaging DTI)是一种新近应用于临床的具有无创伤性优点的新的磁共振成像方法,其可以定量分析大脑的微细结构,如可定量分析病变组织和正常组织的弥散特征,从而为疾病的诊断和鉴别诊断提供更多的信息.     

视神经萎缩的磁共振扩散张量成像研究

目的 探讨视神经萎缩的磁共振扩散张量成像特点.方法 对20例视神经萎缩患者进行视神经磁共振扩散张量成像,并与20例正常健康者作对照.结果 ①萎缩视神经均明显变细,在各向异性(FA)图和方向编码彩色(DEC)图上萎缩的视神经信号强度较对照组明显降低;②萎缩视神经的FA值(0.277±0.078)和λ∥值(1.808±0.307)较正常对照组明显降低,萎缩视神经的平均扩散率(MD)值(1.442±0.264)和λ⊥值(1.231±0.225)较正常对照组明显升高,比较均有明显显著性差异(P均＜0.001).结论 磁共振扩散张量成像对视神经萎缩的信号变化非常敏感,并且可以定量反映视神经萎缩后轴索和髓鞘的病理变化.     

Generalized diffusion tensor imaging and analytical relationships between diffusion tensor imaging and high angular resolution diffusion imaging.

A new method for mapping diffusivity profiles in tissue is presented. The Bloch-Torrey equation is modified to include a diffusion term with an arbitrary rank Cartesian tensor. This equation is solved to give the expression for the generalized Stejskal-Tanner formula quantifying diffusive attenuation in complicated geometries. This makes it possible to calculate the components of higher-rank tensors without using the computationally-difficult spherical harmonic transform. General theoretical relations between the diffusion tensor (DT) components measured by traditional (rank-2) DT imaging (DTI) and 3D distribution of diffusivities, as measured by high angular resolution diffusion imaging (HARDI) methods, are derived. Also, the spherical tensor components from HARDI are related to the rank-2 DT. The relationships between higher- and lower-rank Cartesian DTs are also presented. The inadequacy of the traditional rank-2 tensor model is demonstrated with simulations, and the method is applied to excised rat brain data collected in a spin-echo HARDI experiment.     

The b matrix in diffusion tensor echo-planar imaging

In diffusion tensor imaging (DTI) an effective diffusion tensor in each voxel is measured by using a set of diffusion-weighted images (DWIs) in which diffusion gradients are applied in a multiplicity of oblique directions. However, to estimate the diffusion tensor accurately, one must account for the effects of all imaging and diffusion gradient pulses on each signal echo, which are embodied in the b matrix. For DTI to be practical clinically, one must also acquire DWIs rapidly and free of motion artifacts, which is now possible with diffusion-weighted echo-planar imaging (DW-EPI). An analytical expression for the b matrix of a general DW-EPI pulse sequence is presented and then validated experimentally by measuring the diffusion tensor in an isotropic phantom whose diffusivity is already known. The b matrix is written in a convenient tabular form as a sum of individual pair-wise contributions arising from gradient pulses applied along parallel and perpendicular directions. While the contributions from readout and phase-encode gradient pulse trains are predicted to have a negligible effect on the echo, the contributions from other imaging and diffusion gradient pulses applied in both parallel and orthogonal directions are shown to be significant in our sequence. In general, one must understand and account for the multiplicity of interactions between gradient pulses and the echo signal to ensure that diffusion tensor imaging is quantitative.     

Clinical applications of diffusion tensor imaging

Directionally-ordered cellular structures that impede water motion, such as cell membranes and myelin, result in water mobility that is also directionally-dependent. Diffusion tensor imaging characterizes this directional nature of water motion and thereby provides structural information that cannot be obtained by standard anatomic imaging. Quantitative apparent diffusion coefficients and fractional anisotropy have emerged from being primarily research tools to methods enabling valuable clinical applications. This review describes the clinical utility of diffusion tensor imaging, including the basic principles of the technique, acquisition, data analysis, and the major clinical applications.     

DTI常用扫描序列原理及比较

磁共振弥散张量成像技术是利用水分子的弥散各向异性进行成像,可用于脑白质纤维研究,常用扫描技术包括单次激发平面回波成像(EPI),线阵扫描弥散成像,导航自旋回波弥散加权成像(LSDI),半傅立叶探测单发射快速自旋回波成像等。每种成像技术各有其优缺点,EPI扫描时间短,图像信噪比高,但存在化学位移伪影、磁敏感性伪影、几何变形;LSDI精确度高,几乎无伪影及变形,但扫描时间过长;导航自旋回波弥散加权成像运动伪影少,但扫描时间长;半傅立叶探测单发射快速自旋回波成像扫描时间短,但图像模糊。综合比较,单次激发平面回波成像是用于临床研究较适宜的方法。     

磁共振弥散张量成像在特发性震颤中的应用

目的：采用磁共振弥散张量成像研究特发性震颤患者基底节区核团及红核FA值、ADC值变化,希望为临床诊断和病理学研究提供支持。方法：ET患者13名为病例组,健康人8名为对照组,对每名患者进行临床评分（Fahn-Tolosa-Marin）,并予以全脑横断面DTI检查,检测患者双侧尾状核、壳核和苍白球、丘脑、红核的FA值、ADC值。结果：病例组双侧红核ADC值较对照组升高（0.89±0.13,0.78±0.08;P=0.002）,其他感兴趣区FA值、ADC值在两组间无明显差异。结论：患者双侧红核可能存在神经元退行性改变,DTI可能为临床诊断ET提供支持。     

扩散张量成像对胶质瘤分级的应用价值

胶质瘤是脑内最常见的恶性肿瘤,胶质瘤分级对其治疗方案的选择及预后判断尤为重要。扩散张量成像(DTI)是目前唯一可以在活体状态下无创性检测组织微观结构的功能成像方法。DTI对水分子运动敏感,尤其是沿着轴突纤维束分布的水分子,而胶质瘤肿瘤细胞浸润主要沿着白质神经束走行,低级别胶质瘤的神经轴扩散率为3.7%~5.3%,而高级别胶质瘤为10%~27%,因此DTI对胶质瘤的分级诊断具有重要的价值。现就近年来DTI对胶质瘤分级诊断的研究现状及研究前景等方面内容进行综述。     

梗阻性脑积水的弥散加权成像及弥散张量成像研究

目的探讨磁共振弥散加权成像(DWI)与弥散张量成像(DTI)对梗阻性脑积水的诊断价值。方法 25例梗阻性脑积水患者和30例志愿者均行3.0T磁共振常规序列以及DWI和DTI扫描,重建出ADC图、MD图、FA图、RA图、VR图及AI图,并对各参数图进行测量和记录,所得数据进行统计学分析。结果 30例志愿者及25例梗阻性脑积水患者分别测量双侧侧脑室周围脑白质、胼胝体膝部及压部区域的ADC、MD、FA、RA、VR及AI进行测量,ADC图中胼胝体膝部两组ADC值差异具有统计学意义(P<0.05),双侧侧脑室外侧脑白质两组所测得MD、FA、VR、AI值均有统计学意义(P<0.05),两组胼胝体压部RA值有统计学差异(P<0.05),两组间胼胝体膝部所有测得DTI各参数值均无统计学差异(P>0.05)。结论 DWI和DTI在脑积水的诊断中具有重要的诊断价值。