磁共振扩散张量成像在脊髓压迫症中的应用

脊髓压迫症是指一组具有占位效应的椎管内病变,脊髓由于受到压迫而发生一系列的病理生理变化。常规MRI检查已经能够很好地显示脊髓受压的原因、范围及程度,但它只能描述脊髓大体解剖上的形态改变,而不能显示脊髓受压后内部发生的微观变化。脊髓的磁共振扩散张量成像则能在分子水平上提供组织变化的量化信息,反映脊髓受压后病变的发展过程,有助于观察病变的动态变化并判断预后。综述脊髓压迫症的发病机制及磁共振扩散张量成像在脊髓压迫症中的应用。     

磁共振扩散张量成像在脊髓压迫症中的应用

脊髓压迫症是指一组具有占位效应的椎管内病变,脊髓由于受到压迫而发生一系列的病理生理变化.常规MRI检查已经能够很好地显示脊髓受压的原因、范围及程度,但它只能描述脊髓大体解剖上的形态改变,而不能显示脊髓受压后内部发生的微观变化.脊髓的磁共振扩散张量成像则能在分子水平上提供组织变化的量化信息,反映脊髓受压后病变的发展过程,有助于观察病变的动态变化并判断预后.综述脊髓压迫症的发病机制及磁共振扩散张量成像在脊髓压迫症中的应用.     

扩散张量MR成像

扩散张量成像(DTI)是在分子水平上研究组织中水分子随机运动的一种无创性的功能性磁共振成像技术。在人体生理条件下，水分子在各个方向上的扩散率不同，即扩散异向性，DTI能够测量到水分子在三维空间扩散的方向和扩散程度，描述组织的各向异性特点，精确地研究纤维走行方向。     

脑膜瘤MR扩散张量成像研究

目的探讨平均扩散系数(ADC)和各向异性分数(FA)在脑膜瘤诊断中的价值.资料与方法 28例脑膜瘤在治疗前行常规MRI及扩散张量成像(DTI).在T1WI增强、T2WI及FA图上确定肿瘤、水肿、肿瘤邻近及对侧正常白质区.测量、分析这些区域的FA值和ADC值.结果脑膜瘤Ⅰ级:水肿区ADC值高于肿瘤实体区、肿瘤邻近正常白质区及肿瘤对侧正常白质区(P<0.05).肿瘤邻近及对侧白质区FA值高于肿瘤实体区、水肿区(P<0.05).肿瘤实体区与水肿区FA值无显著性差异(P>0.05).脑膜瘤Ⅱ Ⅲ级:水肿区ADC值高于肿瘤实体区、肿瘤邻近及对侧白质区(P<0.05),实体区和肿瘤邻近及对侧白质区ADC值亦有显著性差异(P<0.05).肿瘤邻近白质区FA值高于实体区和水肿区(P<0.05).脑膜瘤Ⅰ级肿瘤实体区、水肿区、邻近白质区ADC值与脑膜瘤Ⅱ、Ⅲ间具有显著性差异(P<0.05),肿瘤邻近白质区FA值亦有显著性差异(P<0.05).结论 ADC图有助于区分肿瘤实体区和水肿区.FA图可清晰显示正常白质纤维和肿瘤的解剖关系,利于术前手术方案制定.结合常规MRI,DTI有助于脑膜瘤良、恶性分级.     

扩散张量成像在皮质脊髓束华勒变性中的应用

目的 利用扩散张量成像(DTI)研究皮质脊髓束(CST)不同程度华勒变性(WD)微结构变化特点及临床价值.方法 回顾性分析我院47例单侧运动区脑梗死患者,依据CST信号和体积是否异常将WD分成三组,Ⅰ组:CST白质纤维束无信号及形态学改变,共17例;Ⅱ组:CST白质纤维束呈高信号,但无萎缩,共12例;Ⅲ组:CST白质纤维束呈高信号伴萎缩,共18例.所有患者DTI数据经分析处理,在CST患侧和健侧内囊后支、大脑脚、中脑、延髓层面走行区获取FA、MD、λ1、λ2+3值,将各组WD不同部位健侧与患侧DTI各参数指标行t检验,将大脑脚层面神经生物学指标与NIHSS和MI评分行Spearman相关分析.结果 (1)Ⅰ组患侧与健侧皮质脊髓束λ1有统计学差异(P＜0.05),Ⅱ组患侧与健侧皮质脊髓束FA、MD、λ2+3差异有统计学意义(P＜0.05),Ⅲ组患侧与健侧皮质脊髓束FA、MD、λ1、λ2+3均有统计学差异(P＜0.05).(2)Ⅰ组患者大脑脚区CSTrλ1与NIHSS评分存在负相关(r=-0.747,P＜0.01),rλ1与运动力指数呈正相关(r=0.862,P＜0.01).结论 DTI判断CST WD的严重程度有一定特征,其中λ1可以作为早期发现WD微结构变化以及评价病情严重程度的神经生物学指标.     

正常肾脏扩散张量成像的初步研究

目的 探讨正常成人肾脏扩散张量成像(DTI)的特性及其临床意义.方法 21例志愿者行肾脏DTI检查.分析肾脏皮质、髓质的表观扩散系数(ADC)、分数各向异性(FA值),并行髓质纤维束成像.结果 肾皮质和肾髓质ADC值分别为(2.34±0.16)×10-3 mm2/s和(2.10±0.17)×10-3 mm2/s,两者间具有显著性差异(t=2.45,P<0.05).髓质扩散张量示踪图显示肾髓质内放射状指向皮质的放射束.结论 DTI 可显示正常肾脏超微结构变化.肾髓质中水分子扩散具有高各向异性,肾皮质各向异性较弱.肾髓质的高FA值与肾小管、集合管的放射性走行有关.     

扩散张量成像在视辐射成像中的应用

MR检查中扩散张量成像为研究脑白质纤维束（包括视辐射）的走行提供了可能，介绍各向异性扩散加权磁共振成像与扩散张量成像的原理、白质纤维束成像与功能磁共振成像的结合，探讨其在视辐射中的应用价值。     

健康成人视神经MR扩散张量成像研究

目的:探索成人视神经MR扩散张量成像的特点.方法:采用单次激发ZOOM自旋回波平面成像序列,对30例成人健康志愿者的视神经行MR扩散张量成像(DTI)研究.将DTI原始数据输入个人计算机,应用Volume-one1.72软件进行后处理.结果:双侧视神经在部分各向异性图(FA图)呈高信号,在方向编码彩色图(DEC图)为绿色高信号,图像清晰,无明显伪影和扭曲变形,视神经周围脑脊液及眶内脂肪被抑制,呈无信号.本研究初步获得了成人视神经的部分各向异性和平均扩散率的参数值.测得视神经的部分各向异性(FA)值分别为左侧0.595±0.067、右侧0.589±0.066,平均扩散率(MD)值分别为左侧(0.948±0.112)×10-3 mm2/s,右侧(0.932±0.088)×10-3mm2/s,双侧视神经的FA值及MD值差异均无显著性意义(P＞0.05).结论:MR-DTI检测视神经非常敏感.     

正常前列腺的磁共振扩散张量成像研究

目的探讨前列腺磁共振扩散张量成像(DTI)的可行性及正常外周带和中央腺区DTI特征。方法研究对象为20例健康男性志愿者,DTI都采用Siemens Sonata1.5T超导成像仪和腹部相控阵线圈,应用西门子Leonardo工作站相应的软件进行数据处理。DTI记录感兴趣区各向异性(FA)比值和平均ADC值,并绘制相应参数图和纤维示踪影像。对比不同感兴趣区的相应成像指标的差异。结果正常外周带(PZ)和中央区(CZ)的FA值分别为0.16±0.03和0.23±0.04,两者差异具有统计学意义(P0.05)。PZ和CZ的平均ADC值分别为(1.85±0.34)×10-3mm2/s和(1.37±0.27)×10-3mm2/s,两者差异具有统计学意义(P0.05)。结论正常前列腺DTI具有可行性,中央腺区与外周带DTI指标存在明显差异。     

磁共振扩散张量成像在颈髓病变中的应用

目的：探讨磁共振扩散张量成像（DTI）技术在颈髓病变诊断中的临床应用。方法：应用1.5T磁共振机器对39例颈髓病变患者和15例健康志愿者行MRI常规和DTI检查,测定病变区和对照部位的FA值、ADC值并进行对照分析,并重建白质纤维束图。结果：健康志愿者颈髓的FA值为0.66±0.06,ADC值为（0.96±0.14）×10^-3mm^2/s。颈椎病病例FA值为0.47±0.05、ADC值为（1.16±0.28）×10^-3mm^2/s;与对照组统计学分析FA值明显降低（P〈0.01）,ADC值明显增高（P〈0.01）。颈髓急性损伤病例FA值为0.38±0.08、ADC值为（0.89±0.25）×10^-3mm^2/s;与对照组统计学分析FA值明显降低（P〈0.01）,ADC值与对照组无明显差异（P=0.130〉0.05）。颈髓炎症：FA值为0.40±0.06、ADC值为（1.25±0.40）×10^-3mm^2/s;与对照组统计学分析FA值明显降低（P〈0.01）,ADC值明显增高（P〈0.01）。所有病例通过DTI技术成功显示了白质纤维束在病变区变形、移位及中断等改变。结论：DTI可以探测到颈髓病变中常规MR未能发现的病灶;白质纤维束成像可以显示白质束的受损情况。     

快速 DTI 在急性颈髓损伤的临床应用

目的：研究扩散张量成像(DTI)在急性颈髓损伤(CSCI)的成像特点,评估其临床应用价值。方法本组8例 CSCI 患者(发病72 h 内)均采用3.0T 磁共振仪进行快速颈髓 DTI 扫描,并在工作站进行扩散张量纤维束成像(DTT)。同时,在工作站分别测量并计算颈髓病变区及上下相对正常区的各向异性(FA)值和表观扩散系数(ADC)值,之后进行统计学组间配对 t 检验分析(SPSS 13.0)。结果急性 CSCI 以 C5~C6节段(占4/8)和 C4~C5节段(占3/8)多见,且快速 DTI 均获得了较好的图像质量。急性 CSCI 时病变区 FA 值和 ADC 值均明显低于相对正常区域数值(P <0.01),相应在 FA 图和 ADC 图均表现为低信号,而上下相对正常区 FA 值和 ADC 值间无明显区别;同时,DTT 有利于显示刀刺伤导致的颈髓纤维束断裂,颈髓闭合伤则主要表现为脊髓纤维束紊乱等。结论3.0T 快速 DTI 序列可以在2 min 扫描时间内获得临床较为满意的诊断图像,并通过 FA 值和 ADC 值更敏感地反映急性 CSCI 后髓鞘损伤导致的 FA 改变及细胞毒性水肿和血管源性水肿导致的水分子扩散的变化。     

Thoracic and lumbar spinal cord diffusion tensor imaging in dogs

Purpose:

To analyze four clinically applicable diffusion tensor imaging (DTI) protocols (two each in the transverse and sagittal planes) in the normal dog.

Materials and Methods:

Seven healthy Dachshund dogs were scanned with four DTI protocols. Within each plane, identical spatial resolution was used while the number of diffusion‐encoding directions and averages varied. Agreement of measured fractional anisotropy (FA) and apparent diffusion coefficient (ADC) was analyzed with Bland–Altman methods, subjective image quality within each plane was compared, and FA and ADC were explored as a function of anatomic location.

Results:

There was good agreement in FA and ADC values within each plane. FA had the smallest bias and most precision. No difference was detected in subjective image quality within each plane. FA and ADC were slightly higher cranial to the lumbar intumescence compared to within it.

Conclusion:

DTI is a promising tool in the assessment of spinal cord injury (SCI) in the study of dogs with intervertebral disk herniation as a preclinical model of human SCI. J. Magn. Reson. Imaging 2013;37:632–641. © 2013 Wiley Periodicals, Inc.     

A diffusion tensor imaging group study of the spinal cord in multiple sclerosis patients with and without T2 spinal cord lesions

Purpose

To examine the T₂‐normal appearing spinal cord of patients with multiple sclerosis (MS) using diffusion tensor imaging.

Materials and Methods

Diffusion tensor images of the spinal cord were acquired from 21 healthy subjects, 11 MS patients with spinal cord lesions, and 10 MS patients without spinal cord lesions on the T₂‐weighted MR images. Different diffusion measures were evaluated using both a region of interest (ROI) ‐based and a diffusion tensor tractography‐based segmentation approach.

Results

It was observed that the FA, the transverse diffusivity λ_?, and the ratio of the longitudinal and transverse diffusivities (λ_∥/λ _?) were significantly lower in the spinal cord of MS patients with spinal cord lesions compared with the control subjects using both the ROI method (P = 0.014, P = 0.028, and P = 0.039, respectively) and the tractography‐based approach (P = 0.006, P = 0.037, and P = 0.012, respectively). For both image analysis methods, the FA and the λ _∥/λ _? values were significantly different between the control group and the MS patient group without T₂ spinal cord lesions (P = 0.013).

Conclusion

Our results suggest that the spinal cord may still be affected by MS, even when lesions are not detected on a conventional MR scan. In addition, we demonstrated that diffusion tensor tractography is a robust tool to analyze the spinal cord of MS patients. J. Magn. Reson. Imaging 2009;30:25–34. © 2009 Wiley‐Liss, Inc.

     

Magnetic resonance imaging of mouse spinal cord.

The feasibility of performing high-resolution in vivo MRI on mouse spinal cord (SC) at 9.4 T magnetic field strength is demonstrated. The MR properties of the cord tissue were measured and the characteristics of water diffusion in the SC were quantified. The data indicate that the differences in the proton density (PD) and transverse relaxation time between gray matter (GM) and white matter (WM) dominate the contrast seen on the mouse SC images at 9.4 T. However, on heavily T(2)-weighted images these differences result in a reversal of contrast. The diffusion of water in the cord is anisotropic, but the WM exhibits greater anisotropy and principal diffusivity than the GM. The quantitative data presented here should establish a standard for comparing similar measurements obtained from the SCs of genetically engineered mouse or mouse models of SC injury (SCI).     

Diffusion tensor imaging of in vivo and excised rat spinal cord at 7 T with an icosahedral encoding scheme.

Regional values of fractional anisotropy (FA) and mean diffusivity (D(av)) of in vivo and excised rat spinal cords were measured using an iscosahedral encoding scheme that is based on 21 uniformly distributed and alternating gradient directions with an echo planar imaging (EPI) readout. Based on the water phantom studies, this scheme was shown to provide unbiased estimation of FA. The stability of the scanner during the acquisition of diffusion tensor imaging (DTI) data was evaluated. Repeated measurements of the FA values demonstrated excellent reproducibility, as assessed by the Bland-Altman analysis. These studies demonstrated a reduced anisotropy in excised samples relative to in vivo cords. Diffusion in the spinal cord gray matter was shown to be anisotropic. The FA value in the dorsal white matter (WM) was found to be higher relative to the ventral WM. Results from these studies should provide the necessary baseline data for serial in vivo DTI of injured spinal cord.     

In vivo diffusion tensor imaging of the rat spinal cord at 9.4T

PURPOSE: To determine differences in diffusion measurements in white matter (WM) and gray matter (GM) regions of the rat cervical, thoracic, and cauda equina spinal cord using in vivo diffusion tensor imaging (DTI) with a 9.4T MR scanner. MATERIALS AND METHODS: DTI was performed on seven rats in three slices at the cervical, thoracic, and cauda equina regions of the spinal cord using a 9.4T magnet. Axial diffusion weighted images (DWIs) were collected at a b-value of 1000 seconds/mm(2) in six directions. Regions of interest were identified via T2-weighted images for the lateral, dorsal, and ventral funiculi, along with GM regions. RESULTS: Analysis of variance (ANOVA) results indicated significant differences between every WM funiculus compared to GM for longitudinal apparent diffusion coefficient (lADC), transverse apparent diffusion coefficient (tADC), fractional anisotropy (FA), measured longitudinal anisotropy (MA1), and anisotropy index (AI). A significant difference in mean diffusivity (MD) between regions of the spinal cord was not found. Diffusion measurements were significantly different at each spinal level. In general, GM regions were significantly different than WM regions; however, there were few significant differences between individual WM regions. CONCLUSION: In vivo DTI of the rat spinal cord at 9.4T appears sensitive to the architecture of neural structures in the rat spinal cord and may be a useful tool in studying trauma and pathologies in the spinal cord.     

Quantitative assessment of the cervical spinal cord damage in neuromyelitis optica using diffusion tensor imaging at 3 Tesla

Purpose:

To investigate whether quantitative MRI measures of cervical spinal cord white matter (WM) using diffusion tensor imaging (DTI) in neuromyelitis optica (NMO) differed from controls and correlated with clinical disability.

Materials and Methods:

Ten referred patients and 12 healthy volunteers were imaged on a 3 Tesla scanner and patients were clinically assessed on the Expanded Disability Status Scale (EDSS). Two raters quantified DTI‐derived indices from all participants, including fractional anisotropy (FA), mean diffusivity (MD), parallel diffusivity (lambda[parallel]) and perpendicular diffusivity (lambda[perpendicular]) at C1–C6 for lateral and dorsal columns. After the inter‐rater reliability test, univariate correlations between DTI measures and disability were assessed using the Spearman's rho correlation coefficient. Multiple regression analysis was performed to investigate which DTI measures independently correlated with the clinical score.

Results:

Statistical test results indicated high reliability of all DTI measurements between two raters. NMO patients showed reduced FA, increased MD and lambda[perpendicular] compared with controls while lambda[parallel] did not show any significant difference. The former three DTI metrics also showed significant correlations with disability scores, and especially FA was found to be sensitive to mild NMO (EDSS ≤ 3)

Conclusion:

FA is a potentially useful quantitative biomarker of otherwise normal appearing WM damage in NMO. Such damage is associated with clinical disability. J. Magn. Reson. Imaging 2011;33:1312–1320. © 2011 Wiley‐Liss, Inc.