磁共振弥散张量成像的质量控制

磁共振弥散张量成像（DTI）是诊断和分析神经系统疾病的重要方法,但其目前发展受空间分辨率、信噪比及图像质量等限制。本文对近年来MRI系统基础质量保证方法、DTI参数定性测量方法、用于扩散成像的软件方法以及不同纤维跟踪方法等进行综述。     

磁共振扩散张量成像序列对脊髓型颈椎病的诊断价值

目的:分析3.0T磁共振（MR）扩散张量成像（DTI）序列对脊髓型颈椎病（CSM）的诊断价值。方法:选择福建中医药大学附属康复医院收治的30例CSM患者纳入观察组,另选择同期体检人群中年龄匹配的30例健康志愿者为对照组,均运用常规MRI序列及DTI技术进行扫描,运用DTI技术测量FA及ADC值,进行图像后处理及数据分析,观察组患者根据MR平扫结果分为A组（n=10,单纯硬膜囊受压）、B组（n=14,颈髓受压,信号正常）和C组（n=6,颈髓受压,T2WI高信号）,分析各组FA及DA值差异,评价DTI诊断脊髓型颈椎病的诊断价值。结果:对照组脊髓C2-3、C3-4、C4-5、C5-6、C6-7节段的ADC值与FA比较差异无统计学意义（P>0.05）;对照组与A、B、C组的ADC值、FA值存在显著性差异（P<0.05）,B组、C组的ADC值显著高于对照组（P<0.05）,FA值显著低于对照组（P<0.05）,A组ADC值、FA值与对照组比较差异无统计学意义（P>0.05）;从A组到C组,ADC值呈升高趋势,FA值呈降低趋势,差异显著（P<0.05）;MR T2WI、DTI序列扫描FA值、MR DTI序列扫描ADC值诊断扫描诊断CSM的敏感度与特异度为20.00%（6/30）与80.00%（24/30）,80.00%（24/30）与20.00%（6/30）,66.67%（20/30）与30.00%（9/30）。结论:DTI较常规MRI能更早期而准确地诊断CSM,是一种显示CSM病变和观察病变修复过程的有效手段。     

PM滤波方法对提高不同b值弥散张量成像图像质量的应用研究

目的在不同b值条件下,研究PM滤波方法对提高弥散张量成像（DTI）技术图像质量的作用。方法在b值为800～2800s／mm2的条件下分别对模体及志愿者实施DTI．利用改进的PM滤波方法对获得的弥散加权成像（DWI）图像进行处理后求解张量参数．得到反映水分子各向异性扩散程度的FA图。通过比较标准FA图与处理后FA图间的均方根误差（RMSE）．评价PM滤波的效果。结果随着b值的升高,图像信噪比逐渐降低．FA误差逐渐增大。当b值小于2000s／mm2时．经过PM滤波后．可得到RMSE较低的后处理图像。结论b值在1000．2000s／mm2范围内,应用PM滤波方法是提高人脑DTI图像质量的一种有效手段．     

In vivo visualization of the levator ani muscle subdivisions using MR fiber tractography with diffusion tensor imaging

Understanding the levator ani complex architecture is of major clinical relevance. The aim of this study was to determine the feasibility of magnetic resonance (MR) fiber tractography with diffusion tensor imaging (DTI) as a tool for the three-dimensional (3D) representation of normal subdivisions of the levator ani. Ten young nulliparous female volunteers underwent DTI at 1.5 T MR imaging. Diffusion-weighted axial sequence of the pelvic floor was performed with additional T2-weighted multiplanar sequences for anatomical reference. Fiber tractography for visualization of each Terminologia Anatomica-listed major levator ani subdivision was performed. Numeric muscular fibers extracted after tractography were judged as accurate when localized within the boundaries of the muscle, and inaccurate when projecting out of the boundaries of the muscle. From the fiber tracking of each subdivision the number of numeric fibers (inaccurate and accurate) and a score (from 3 to 0) of the adequacy of the 3D representation were calculated. All but two volunteers completed the protocol. The mean number of accurate fibers was 17 ± 2 for the pubovisceralis, 14 ± 6 for the puborectalis and 1 ± 1 for the iliococcygeus. The quality of the 3D representation was judged as good (score = 2) for the pubovisceralis and puborectalis, and inaccurate (score = 0) for the iliococcygeus. Our study is the first step to a 3D visualization of the three major levator ani subdivisions, which could help to better understand their in vivo functional anatomy.     

Effect of accurately calculated b matrix on the evaluation of the diffusion tensor using echoplanar diffusion tensor imaging

Diffusion-weighted magnetic resonance imaging is a recognised tool in early detection of infarction of the human brain. If diffusion weighted-images with different values of b matrix are acquired during one individual investigation, it is possible to calculate diffusion coefficient maps that are elements of the diffusion tensor: they represent the apparent diffusion coefficient of protons of water molecules in each pixel in the corresponding sample. The relationship between signal intensity in the diffusion-weighted images, diffusion tensor and b matrix is derived from the Bloch equations. Our goal is to establish the error made in the calculation of the elements of the diffusion tensor when imaging gradients are ignored in the calculation of the b matrix elements. The numerical calculation of the b matrices show that a systematic error of up to 7% is introduced in the derived diffusion tensor elements when neglecting imaging gradients.     

弥散张量成像在中枢神经系统中的应用

在磁共振成像(MRI)研究中,弥散张量成像(DTI)是最近几年提出并迅速发展的一个研究方向,本文介绍了弥散张量成像的原理以及国际上主要的研究热点,并结合实际介绍了弥散张量成像在中枢神经系统(CNS)中的应用。     

Reproducibility of tract‐specific magnetization transfer and diffusion tensor imaging in the cervical spinal cord at 3 tesla

Damage to specific white matter tracts within the spinal cord can often result in the particular neurological syndromes that characterize myelopathies such as traumatic spinal cord injury. Noninvasive visualization of these tracts with imaging techniques that are sensitive to microstructural integrity is an important clinical goal. Diffusion tensor imaging (DTI)‐ and magnetization transfer (MT)‐derived quantities have shown promise in assessing tissue health in the central nervous system. In this paper, we demonstrate that DTI of the cervical spinal cord can reliably discriminate sensory (dorsal) and motor (lateral) columns. From data derived from nine healthy volunteers, two raters quantified column‐specific parallel (λ_||) and perpendicular (λ_?) diffusivity, fractional anisotropy (FA), mean diffusivity (MD), and MT‐weighted signal intensity relative to cerebrospinal fluid (MTCSF) over two time‐points separated by more than 1 week. Cross‐sectional means and standard deviations of these measures in the lateral and dorsal columns were as follows: λ_||: 2.13 ± 0.14 and 2.14 ± 0.11 μm²/ms; λ_?: 0.67 ± 0.16 and 0.61 ± 0.09 μm²/ms; MD: 1.15 ± 0.15 and 1.12 ± 0.08 μm²/ms; FA: 0.68 ± 0.06 and 0.68 ± 0.05; MTCSF: 0.52 ± 0.05 and 0.50 ± 0.05. We examined the variability and interrater and test‐retest reliability for each metric. These column‐specific MR measurements are expected to enhance understanding of the intimate structure‐function relationship in the cervical spinal cord and may be useful for the assessment of disease progression. Copyright © 2009 John Wiley & Sons, Ltd.     

弥散张量成像评价中老年患者全身麻醉后海马区纤维的完整性

目的:应用弥散张量成像技术(diffusion tensor imaging,DTI)比较中老年患者术前与接受全凭静脉麻醉术后海马旁回以及后扣带回白质纤维束的完整性.方法:对20例接受全凭静脉麻醉的老年患者进行术前简明精神状态量表(mini-mental state examination,MMSE)评分,并且进行术前1天及术后3天的功能磁共振扫描.分为术前组与术后组.术前组与术后组均为相同的患者.采用FSL软件对获取的磁共振图像数据进行处理,分别计算双侧海马旁回(hippocampal gyrus,PH),双侧后扣带回(posterior cingulate cortex,PCC)的各向异性分数(fractional anisotropy,FA)和表观弥散系数(apparent diffusion coefficient,ADC),利用SPSS软件进行统计学分析.结果:术后组双侧PH,双侧PCC的FA值较术前有所降低,ADC值较术前有所升高,差异有统计学意义(P＜0.05).结论:全凭静脉麻醉术后老年患者的海马体部白质纤维束的完整性较术前有所损害.     

Amyotrophic lateral sclerosis: diffusion tensor tractography and voxel-based analysis

The purpose of this study is to investigate whether the diffusional anisotropy of water molecules is disrupted in the pyramidal and extra-pyramidal regions in patients with amyotrophic lateral sclerosis (ALS). We studied seven patients with probable ALS (four women, mean age +/- SD, 57.3 +/- 6.2 years old) according to the criteria of the World Federation of Neurology. A control group consisted of 11 age- and sex-matched volunteers (six women, 57.1 +/- 4.5) without disorders affecting the central nervous system. Voxel-based diffusion tensor analysis was made with statistical parametric mapping (SPM99). We also created the normalized corticospinal tractography from the diffusion tensor data. The significant fractional anisotropy (FA) decrease in the ALS group was found in the right frontal subgyral white matter and left frontal precentral white matter. These clusters with significant FA decrease corresponded well to the average group map of the corticospinal tract in a standard reference frame. These results suggested that the combination of voxel-based diffusion tensor analysis and diffusion tensor tractography might help determine the location of the affected neuronal tissues among ALS patients in a non-invasive manner.     

磁共振弥散张量成像联合纤维束成像在脑梗死中的应用研究

目的 分析脑梗死患者磁共振弥散张量成像(DTI)和纤维束成像(DTT)的特点,探讨DTI、DTT在对不同时期脑梗死患者诊断的价值。方法分别对58例不同时期脑梗死患者和25名健康志愿者行MRI检查,包括T1WI、T2WI成像、FLAIR及DTI成像,重建部分各向异性(FA)图,对梗死区、健侧相应部位及正常对照组相应部位进...     

Anatomically correct assessment of the orientation of the cardiomyocytes using diffusion tensor imaging

Diffusion tensor imaging has been used for assessing the orientation of cardiac myocytes for decades. Striking methodological differences exist between studies when quantifying these orientations. This limits the comparability between studies, and impedes collaboration and the drawing of appropriate physiological conclusions. We have sought to elucidate these differences, permitting us to propose a standardised “tool set” that might better establish consensus in future studies. We fixed hearts from seven 25 kg pigs in formalin, and scanned them using diffusion tensor imaging. Using various angle definitions as found in literature, we assessed the orientations of cardiomyocytes, comparing them in terms of helical and intrusion angles, along with the orientation of their aggregations. The difference between assessment of the helical angle with and without relation to the epicardial curvature was 25.2° (SD: 7.9) at the base, 5.8° (1.9) at the equatorial level, and 28.0° (7.0) at the apex, ANOVA P = 0.001. In comparable fashion, the intrusion angle differed by 25.9° (12.9), 7.6° (0.98) and 17.5° (4.7), P = 0.01, and the angle of the aggregates (E3‐angle) differed by 25.0° (13.5) at the base, 9.4° (1.7) at the equator, and 23.1° (6.2) apically, P = 0.003. When assessing 14 definitions used in literature to calculate the orientation of aggregates, only 4 rendered identical results. The findings show that any attempt to use projection of eigenvectors introduces considerable bias. The epicardial curvature of the ventricular cone needs to be taken into account when seeking to provide accurate quantification of the orientation of the aggregated cardiomyocytes, especially in the apical and basal regions. This means that projection of eigenvectors should be avoided prior to quantifying myocyte orientation, especially when assessing radial orientation. Based on our results, we suggest appropriate methods for valid assessment of myocyte orientation using diffusion tensor imaging.     

磁共振扩散张量成像评价小儿脑病的初步应用

目的应用扩散张量成像（DTI）来进一步评价小儿脑疾病，探讨DTI的诊断价值。方法对15例患各种脑病的小儿进行MRI检查，其中男性10例，女性5例，年龄为生后3天至11岁（平均年龄4．8岁）。采用Philips Intera Achieva 3．0 Tesla的超导MRI仪，用回波平面成像（EPI）的DTI技术，b为800s／mm^2，15个方向。观察彩色分数各向异性（FA）图和三维彩色编码图。结果15例患儿中，发育畸形2例，分别是胼胝体发育不良、巨脑回；脑室旁白质软化（PVL）7例；缺氧缺血性脑病3例；脑软化2例；脑积水1例。在巨脑回病例，常规MRI见右侧脑回发育不良，呈巨脑回畸形，右侧脑室扩大，在DTI上见右侧病变区白质束明显较对侧少。胼胝体发育不良病例在DTI张量图见胼胝体菲薄。在PVL和缺氧缺血性脑病病例均可见白质纤维束在放射冠颜色混杂，方向性混乱。脑软化病例可见白质纤维束部分中断。在脑积水病例可见白质束受压推移。结论DTI能够显示白质束的走向、绕行、交叉及推挤、中断等异常，可能对今后评估小儿脑病的预后转归有帮助。     

Directional colour encoding of the human thalamus by diffusion tensor imaging

The potential of diffusion tensor imaging (DTI) in brain imaging in terms of the in vivo mapping of neuroanatomy is generally accepted. Mostly, analyses of deep brain structures were based on complex methodical backgrounds. In the present study, the delineation of groups of thalamic nuclei with similar projection characteristics was investigated in healthy human subjects using a novel differentiated colour encoding approach of DTI data without the use of statistical calculations. With the application of this directional colour encoding of the longest eigenvector of every voxel-specific tensor, at least three functional groups in the thalamus with different projection directions could be differentiated. The method displayed, furthermore, a high symmetry and stability in the analysis of the individual subjects. In summary, substantial neuroanatomical information can be gained for deep subcortical gray matter structures such as the thalamus with an improved detection and directional differentiation of voxel-specific tensors.     

磁共振弥散张量成像在临床诊疗中的应用

磁共振弥散张量成像(diffusion tensor imaging,DTI)作为一种功能磁共振成像(magnetic resonance imaging,MRI),在临床诊疗中发挥了重要作用.本文先介绍了DTI临床应用的各个领域,重点阐述了其在脑部疾病的应用,后指出临床应用中存在的问题,并对其前景进行了展望.     

基于参考图像的压缩感知磁共振扩散张量成像

基于参考图像的压缩感知磁共振扩散张量成像方法,利用相邻方向的扩散加权图像差异较小的特点,采用压缩感知理论实现快速扩散张量成像,回顾性选取扩散张量图像数据进行实验研究,在采样率为50%的均匀分布辐射线欠采样方式下进行基于参考图像的压缩感知扩散张量图像重建,结果表明重建后的扩散加权图的平均结构相似性（MSSIM）和峰值信噪比（PSNR）分别为0.904±0.044、（37.92±3.89） dB,各向异性分数图的MSSIM和PSNR分别为0.992、41.64 dB。因此,该方法在保证重建图像质量的前提下,可显著缩短数据采集时间,减少由于时间过长引起的图像伪影等问题。     

健康儿童颈髓磁共振扩散张量成像

目的 应用扩散张量成像技术研究儿童颈髓发育规律。方法 使用单次激发自旋回波平面回波序列对90例健康儿童行颈髓扩散张量成像。在颈髓节段分别测量其表观扩散系数值（ADC）、各向异性分数值（FA）、纤维束平均长度（Ltract）以及纤维束体积（Vtract）。结果 各组的ADC值、FA值、Ltract及Vtract分别如下：0.9747±0.2777、0.8493±0.2236、0.8210±0.1432、0.9198±0.1444、0.9048±0.1676;0.4117±0.0391、0.4712±0.0199、0.4944±0.0439、0.5608±0.0443、0.6169±0.0551;25.61±8.63、24.66±7.14、27.03±7.23、34.93±10.99、37.63±10.22;3.07±1.49、3.00±1.52、3.81±1.33、5.41±2.35、6.64±2.84。各年龄组的FA值、Ltract和Vtract不完全相同（P<0.001）,而ADC值各年龄组的均值差异无统计学意义（F=1.758, P=0.145）。在组间的两两比较中：1、2组间FA值差异具有统计学意义;3、4组间FA值、Ltract和Vtract差异均具有统计学意义;4、5组间FA值差异具有统计学意义。FA值、Ltract和Vtract与年龄呈正相关。
结论 儿童颈髓发育具有阶段性,且具有阶段性特征;磁共振扩散张量技术可用于观测儿童颈髓并评价其发育。     

Longitudinal diffusion tensor imaging in a rat brain glioma model

In order to investigate the properties of water motion within and around brain tumors as a function of tumor growth, longitudinal diffusion tensor imaging (DTI) was carried out in a rat brain glioma (C6) model. As tumors grew in size, significant anisotropy of water diffusion was seen both within and around the tumor. The tissue water surrounding the tumor exhibited high planar anisotropy, as opposed to the linear anisotropy normally seen in white matter, indicating that cells were experiencing stress in a direction normal to the tumor border. When tumors were sufficiently large, significant anisotropy was also seen within the tumor because of longer-range organization of cancer cells within the tumor borders. These findings have important implications for diffusion-weighted MRI experiments examining tumor growth and response to therapy. Copyright (c) 2008 John Wiley & Sons, Ltd.     

基于弥散张量成像的脑结构网络参数研究

目的 利用复杂网络参数评估大脑特征,是探明大脑工作机制的新思路。方法 本研究基于弥散张量纤维束追踪和小世界网络理论构建脑结构网络。首先利用自动解剖标定（automated anatomical labeling,AAL）模板对大脑分区,并计算脑区间的纤维连接情况,对正常人的大脑结构进行网络建模。然后分析脑结构网络中节点度、簇系数和节点介数等网络参数,并通过引入小世界网络的介数和损伤性定义人脑结构网络的核心节点位置和特征。结果 脑结构网络具有小世界属性,且网络中存在少量的核心节点,具有较高的节点度和簇系数值。结论 利用弥散张量成像能够客观构建大脑结构网络,而核心节点的存在为揭示脑疾病的病理生理机制提供新的思路。     

弥散张量磁共振成像的新进展

弥散张量磁共振成像技术是近年来出现的一项新技术,由于其对脑白质纤维具有高度敏感性以致在临床上的应用日益广泛,并为人体中枢神经系统的深入研究提供了有效的工具。     

Association between sociability and diffusion tensor imaging in BALB/cJ mice

The purpose of this study was to use high-resolution diffusion tensor imaging (DTI) to investigate the association between DTI metrics and sociability in BALB/c inbred mice. The sociability of prepubescent (30-day-old) BALB/cJ mice was operationally defined as the time that the mice spent sniffing a stimulus mouse in a social choice test. High-resolution ex vivo DTI data on 12 BALB/cJ mouse brains were acquired using a 9.4-T vertical-bore magnet. Regression analysis was conducted to investigate the association between DTI metrics and sociability. Significant positive regression (p < 0.001) between social sniffing time and fractional anisotropy was found in 10 regions located in the thalamic nuclei, zona incerta/substantia nigra, visual/orbital/somatosensory cortices and entorhinal cortex. In addition, significant negative regression (p < 0.001) between social sniffing time and mean diffusivity was found in five areas located in the sensory cortex, motor cortex, external capsule and amygdaloid region. In all regions showing significant regression with either the mean diffusivity or fractional anisotropy, the tertiary eigenvalue correlated negatively with the social sniffing time. This study demonstrates the feasibility of using DTI to detect brain regions associated with sociability in a mouse model system.