MR扩散张量在临床脑梗死运动功能康复评估中的应用

目的使用扩散张量成像（DTI）研究脑梗死不同时期的扩散张量的变化规律，并试图通过扩散张量纤维束成像（DTT）探讨皮质脊髓束（CST）损伤与运动功能恢复的关系。方法26例脑梗死患者行常规MRI及DTI检查，测量各期病灶及对侧相应正常区域脑组织的平均扩散系数（DCavg）、部分各向异性系数（FA）、容积比（1-VR）及相对各向异性系数（RA）值，同时进行统计学分析；并行白质纤维束三维重建。结果各期病灶与对侧各参数值间的差异均有统计学意义（P〈0．01）；各期病灶各参数值间的差异亦有统计学意义（P〈0．01）。DTT可显示脑白质纤维束的破坏、推移或扭曲等征象，CST的损伤情况与运动功能的恢复有良好的相关。结论梗死灶DTI各参数值的变化具有规律性，DTT对观察CST的损害程度、预测恢复程度、指导临床康复治疗具有重要的参考价值。     

MR扩散张力成像原理及其在脑肿瘤中的研究进展

有关脑肿瘤研究的MRI新技术层出不穷,其中弥散加权成像(DWI)、灌注成像(PWI)、磁共振波谱(MRS)以及血氧水平依赖法(BOLD)脑功能成像研究在脑肿瘤的影像评价中均发挥着重要作用。但是,这些方法对于脑肿瘤与周围脑白质纤维关系的显示上都显得无能为力。随着扩散张力成像(diffusiontensorimaging,DTI)研究犤1-4犦的不断深入,目前已越来越多地应用于存在纤维定向组织的微观结构方面,在脑肿瘤的临床评价中也发挥重要的作用。1DTI的基本原理DTI是利用组织中水分子扩散运动存在的各向异性来探测组织微观结构的成像方法,是通过观察随扩散…     

Diffusion tensor imaging in episodic cluster headache

Background.— Cluster headache (CH) is a rare headache disorder with severe unilateral headache bouts and autonomic symptoms. The pathophysiology of CH is not completely understood. Using a voxel‐based morphometric paradigm or functional imaging, a key role of the hypothalamus and the pain matrix could be demonstrated during CH episodes. However, there are no diffusion tensor imaging (DTI) data investigating the white matter microstructure of the brain in patients with CH. Therefore, we used DTI to delineate microstructural changes in patients with CH in a headache‐free state. Methods.— Seven male patients with episodic CH and 7 healthy subjects were included and examined with a routine 1.5 T magnetic resonance imaging scanner. Whole‐head DTI scans measuring fractional anisotropy were analyzed without a priori hypotheses using track‐based spatial statistics. Results.— We found significant microstructural brain tissue changes bilaterally in the white matter of the brainstem, the frontal lobe, the temporal lobe, the occipital lobe, the internal capsule, and on the right side of thalamus and cerebellum. There were further lesions in the basal frontal lobe that were part of the olfactory system. Alterations of fractional anisotropy in the brainstem might indicate changes of the medial lemniscus and central sympathetic pathways. Conclusions.— Patients with episodic CH have microstructural brain changes in regions that belong to the pain matrix. Furthermore, we were able to detect structural changes suggesting an involvement of the olfactory system as well as lesions in the brainstem indicating an involvement of trigeminal and sympathetic systems.     

Diffusion tensor imaging: structural adaptive smoothing

Diffusion Tensor Imaging (DTI) data is characterized by a high noise level. Thus, estimation errors of quantities like anisotropy indices or the main diffusion direction used for fiber tracking are relatively large and may significantly confound the accuracy of DTI in clinical or neuroscience applications. Besides pulse sequence optimization, noise reduction by smoothing the data can be pursued as a complementary approach to increase the accuracy of DTI. Here, we suggest an anisotropic structural adaptive smoothing procedure, which is based on the Propagation-Separation method and preserves the structures seen in DTI and their different sizes and shapes. It is applied to artificial phantom data and a brain scan. We show that this method significantly improves the quality of the estimate of the diffusion tensor, by means of both bias and variance reduction, and hence enables one either to reduce the number of scans or to enhance the input for subsequent analysis such as fiber tracking.     

Diffusion tensor imaging and axonal tracking in the human brainstem

Diffusion tensor MRI was used to demonstrate in vivo anatomical mapping of brainstem axonal connections. It was possible to identify the corticospinal tract (CST), medial lemniscus, and the superior, medial, and inferior cerebellar peduncles. In addition, the cerebral peduncle could be subparcellated into component tracts, namely, the frontopontine tract, the CST, and the temporo-/parieto-/occipitopontine tract. Anatomical landmarks and tracking thresholds were established for each fiber and, using these standards, reproducibility of automated tracking as assessed by intra- and interrater reliability was found to be high (kappa > 0.82). Reconstructed fibers corresponded well to existing anatomical knowledge, validating the tracking. Information on the location of individual tracts was coregistered with quantitative MRI maps to automatically measure MRI parameters on a tract-by-tract basis. The results reveal that each tract has a unique spatial signature in terms of water relaxation and diffusion anisotropy.     

Diffusion tensor imaging of neurodevelopment in children and young adults

Diffusion tensor magnetic resonance imaging (DTI) was used to study regional changes in the brain's development from childhood (8-12 years, mean 11.1 +/- 1.3, N = 32) to young adulthood (21-27 years, mean 24.4 +/- 1.8, N = 28). Mean diffusivity (Trace/3 apparent diffusion coefficient, ADC) and fractional anisotropy (FA) were measured in 30 regions of interest (ROIs) in 13 distinct brain structures. Correlational analysis was performed to detect changes within 8-12 years and within 21-27 years, and group analysis to compare childhood diffusion properties with young adult values. Increases of fractional anisotropy were seen in the genu of the corpus callosum, splenium of the corpus callosum, corona radiata, putamen, and head of the caudate nucleus within 8-12 years, and also between childhood and young adulthood. Reductions in Trace/3 ADC were observed in 9 of 13 structures within 8-12 years and into young adulthood as well. DTI demonstrates more widespread changes in the brain's microstructure with maturation than previous reports using conventional T1-weighted MRI scans. These findings suggest a continuation of the brain's microstructural development through adolescence.     

Diffusion tensor spectroscopy and imaging of the arcuate fasciculus

The arcuate fasciculus (AF) is a fiber pathway in the human brain relevant for language processes and has recently been characterized by means of diffusion tensor tractography. The observations made concerning the left and right hemisphere AF include a characterization of the trajectories and quantification of physical properties such as fractional anisotropy, DTI-based fiber density and volume. However, these observations were based on the diffusion of water, which is not particular to either the intra- or extra-axonal compartments, and thus its usefulness for tissue characterization is limited. If the diffusion properties and in turn the geometric properties of only one tissue compartment can be isolated and characterized, a better microstructural characterization of AF is possible. In this study, water-based diffusion tensor probabilistic mapping was first implemented to segment the AF. Subsequently, diffusion tensor spectroscopic measurements of N-acetyl aspartate (NAA) were performed to measure the intra-axonal specific diffusion in left and right AF. Diffusion properties of NAA, which solely reflect the intra-axonal space, indicated possible leftward asymmetry in axonal diameter, where those of water, which are not compartment-specific, showed laterality to a lesser extent.     

Diffusion tensor imaging of adult age differences in cerebral white matter: relation to response time

Diffusion tensor imaging (DTI) measures the displacement of water molecules across tissue components, thus providing information regarding the microstructure of cerebral white matter. Fractional anisotropy (FA), the degree to which diffusion is directionally dependent, is typically higher for compact, homogeneous fiber bundles such as the corpus callosum. Previous DTI studies in adults have demonstrated an age-related decline in white matter FA, but whether the relation between FA and behavioral performance varies as a function of age has not been determined. We investigated adult age differences in FA, and age-related changes in the relation between FA and response time (RT), in a visual target-detection task. The results confirmed that, independently of age, FA is higher in the corpus callosum than in other brain regions. We also observed an age-related decline in FA that did not vary significantly across the brain regions. For both age groups, a lower level of integrity of the cerebral white matter (as indexed by FA), in specific brain regions, was associated with slower responses in the visual task. An age-related change in this relation was evident, however, in that the best predictor of RT for younger adults was FA in the splenium of the corpus callosum, whereas for older adults the best predictor was FA in the anterior limb of the internal capsule. This pattern is consistent with measures of the task-related cortical activation obtained from these same individuals and suggests an age-related increase in the attentional control of responses mediated by corticostriatal or corticothalamic circuits.     

Diffusion tensor imaging segments the human amygdala in vivo

The amygdala plays an important role in emotion, learning, and memory. It would be highly advantageous to understand more precisely its internal structure and connectivity for individual human subjects in vivo. Earlier cytoarchitectural research in post-mortem human and animal brains has revealed multiple subdivisions and connectivity patterns, probably related to different functions. With standard magnetic resonance imaging (MRI) techniques, however, the amygdala appears as an undifferentiated area of grey matter. Using high-quality diffusion tensor imaging (DTI) at 3 Tesla, we show diffusion anisotropy in this grey matter area. Such data allowed us to subdivide the amygdala for the first time in vivo. In 15 living subjects, we applied a spectral clustering algorithm to the principal diffusion direction in each amygdala voxel and found a consistent subdivision of the amygdala into a medial and a lateral region. The topography of these regions is in good agreement with the fibre architecture visible in myelin-stained sections through the amygdala of a human post-mortem brain. From these in vivo results we derived a probabilistic map of amygdalar fibre orientations. This segmentation technique has important implications for functional studies in the processing of emotions, cognitive function, and psychiatric disorders and in studying morphometry and volumetry of amygdala subdivisions.     

Diffusion tensor imaging of the corpus callosum in Autism

The corpus callosum is the largest commissural white matter pathway that connects the hemispheres of the human brain. In this study, diffusion tensor imaging (DTI) was performed on subject groups with high-functioning autism and controls matched for age, handedness, IQ, and head size. DTI and volumetric measurements of the total corpus callosum and subregions (genu, body and splenium) were made and compared between groups. The results showed that there were significant differences in volume, fractional anisotropy, mean diffusivity, and radial diffusivity between groups. These group differences appeared to be driven by a subgroup of the autism group that had small corpus callosum volumes, high mean diffusivity, low anisotropy, and increased radial diffusivity. This subgroup had significantly lower performance IQ measures than either the other individuals with autism or the control subjects. Measurements of radial diffusivity also appeared to be correlated with processing speed measured during the performance IQ tests. The subgroup of autism subjects with high mean diffusivity and low fractional anisotropy appeared to cluster with the highest radial diffusivities and slowest processing speeds. These results suggest that the microstructure of the corpus callosum is affected in autism, which may be related to nonverbal cognitive performance.     

Diffusion tensor magnetic resonance imaging of brain tumors

DTI seems to offer the possibility of adding important information to presurgical planning. Although experience is limited, DTI seems to provide useful local information about the structures near the tumor, and this seems to be useful in planning. In the future, DTI may provide an improved way to monitor intraoperative surgical procedures as well as their complications. Furthermore, evaluation of the response to treatment with chemotherapy and radiation therapy might also be possible. Although DTI has some limitations, its active investigation and further study are clearly warranted.     

代谢综合征患者的MR扩散张量成像研究

目的应用MRI扩散张量成像(DTI)检测病程5年以上代谢综合征(MS)患者的脑部各向异性(FA)值,早期发现亚临床脑神经纤维微结构损害。材料与方法分为病例组(代谢综合征15例)及对照组(17例健康体检者),对一般项目(身高、体重、血压、血糖、血脂、认知等神经功能相关量表评分)检查测定后,进行头颅MRI及DTI检查,对所测得结果进行统计学分析。结果 (1)病例组FA值(内囊后肢、放射冠区)明显低于对照组(P值均<0.01),3项代谢异常者FA值(内囊后肢和放射冠区)降低程度更显著(P值均<0.01),2项代谢异常者只在放射冠区FA值明显低于对照组(P<0.05),差异有统计学意义。(2)高血压组、糖尿病组、高血脂组、肥胖组内囊后肢及放射冠区FA值均明显低于对照组(P值均<0.05),差异有统计学意义。(3)以高血压、糖尿病、高脂血症、肥胖、年龄、病程年限为自变量,FA值为因变量,多元回归分析结果显示:FA值与高脂血症、高血压、肥胖负相关(r值分别为-0.103、-0.127、-0.012,P值均<0.05),放射冠区(CRA)FA值与年龄呈负相关(r=-0.04,P<0.05);与高血压年限呈负相关(r=-0.013,P<0.05)。结论 MS病程5年以上者脑部神经纤维微结构已有损害。脑部神经纤维微结构损害严重程度与代谢异常程度及病程年限明显相关。高血压、高脂血症、肥胖是脑神经纤维微结构损害的独立危险因素。     

磁共振弥散张量成像技术在新生儿脑白质发育中的研究

目的运用磁共振弥散张量成像(DTI)技术研究分析新生儿脑白质发育规律和特点。材料与方法本研究纳入38名新生儿,包括18例适于胎龄早产儿,20例正常出生体重足月儿,按胎龄分为3组,分别测量各兴趣区FA值进行分析。结果新生儿脑实质FA值无左右差异。外周白质FA值小于深部白质,在深部脑白质中,胼胝体压部FA值高于膝部,内囊后肢高于前肢,胼胝体压部高于内囊后肢;在外周脑白质中,半卵圆中心层面中部白质FA值最高,半卵圆中心前、后白质的FA值均无统计学差异(P0.05)。Ⅲ组各兴趣区FA值均高于Ⅰ组,且差异有统计学意义(P0.05),相邻胎龄组比较,只有部分兴趣区有统计学差异。结论 DTI技术在研究新生儿脑白质成熟方面具有重要价值,FA值可定量评估髓鞘发育。     

Diffusion tensor imaging of post mortem multiple sclerosis brain

Magnetic resonance imaging (MRI) is being used to probe the central nervous system (CNS) of patients with multiple sclerosis (MS), a chronic demyelinating disease. Conventional T(2)-weighted MRI (cMRI) largely fails to predict the degree of patients' disability. This shortcoming may be due to poor specificity of cMRI for clinically relevant pathology. Diffusion tensor imaging (DTI) has shown promise to be more specific for MS pathology. In this study we investigated the association between histological indices of myelin content, axonal count and gliosis, and two measures of DTI (mean diffusivity [MD] and fractional anisotropy [FA]), in unfixed post mortem MS brain using a 1.5-T MR system. Both MD and FA were significantly lower in post mortem MS brain compared to published data acquired in vivo. However, the differences of MD and FA described in vivo between white matter lesions (WMLs) and normal-appearing white matter (NAWM) were retained in this study of post mortem brain: average MD in WMLs was 0.35x10(-3) mm(2)/s (SD, 0.09) versus 0.22 (0.04) in NAWM; FA was 0.22 (0.06) in WMLs versus 0.38 (0.13) in NAWM. Correlations were detected between myelin content (Tr(myelin)) and (i) FA (r=-0.79, p<0.001), (ii) MD (r=0.68, p<0.001), and (iii) axonal count (r=-0.81, p<0.001). Multiple regression suggested that these correlations largely explain the apparent association of axonal count with (i) FA (r=0.70, p<0.001) and (ii) MD (r=-0.66, p<0.001). In conclusion, this study suggests that FA and MD are affected by myelin content and - to a lesser degree - axonal count in post mortem MS brain.     

扩散张量成像评价颈总动脉交感神经网剥脱术治疗儿童脑瘫的价值

目的应用磁共振扩散张量成像(diffusion tensor imaging,DTI)及扩散张量纤维束成像(diffusion tensor tracking,DTT),探讨其对脑瘫患儿颈总动脉交感神经网剥脱术后脑白质恢复的评估价值。材料与方法对30例痉挛型单侧脑瘫患儿手术前、后进行临床评估和常规MRI、DTI检查,测量并比较术前术侧和对侧、术前和术后双侧内囊后肢及大脑脚的各向异性分数(fractional anisotropy,FA)值,并对白质纤维束进行三维重建。运用粗大运动功能分级系统(gross motor function classification system,GMFCS)评价患儿运动功能。采用配对样本t检验比较术前术侧和对侧、术前和术后脑白质不同部位FA值的差异,以Spearman相关分析不同白质纤维束DTI参量与GMFCS的相关性。结果术前术侧不同部位白质纤维束FA值均显著低于对侧,差异有统计学意义(P0.01)。术后6个月脑瘫患儿术侧不同部位白质纤维束FA值与术前相比显著增加(P0.01),粗大运动功能获得改善。术后6个月患儿对侧不同部位白质纤维束FA值与术前相比差异无统计学意义(P0.05)。患儿临床GMFCS与FA值呈负相关(P0.01),且与内囊后肢、大脑脚的相关性都较高(r=-0.933,P0.01;r=-0.873,P0.01)。结论 DTI联合DTT可用于定量评价脑瘫患儿术后脑白质的恢复情况,对辅助临床治疗和预后评估具有重要作用。     

Diffusion tensor imaging in medial temporal lobe epilepsy with hippocampal sclerosis

Interictal diffusion imaging studies in patients with medial temporal lobe epilepsy (MTLE) accompanied by hippocampal sclerosis (HS) have shown an increased diffusivity in the epileptogenic hippocampus. In this study, we wanted to explore the whole brain in order to determine if MTLE could have an impact on the organization and the architecture of a large cerebral network and to identify clinical factors that could mediate diffusion abnormalities. Diffusion tensor imaging (DTI) and statistical parametric mapping of the entire brain were performed in 35 well-defined MTLE patients and in 36 healthy volunteers. SPM analyses identified three abnormal areas: an increased diffusivity was detected in the epileptic hippocampus and the ipsilateral temporal structures associated with a decreased anisotropy along the temporal lobe, a decreased diffusivity was found in the contralateral non-sclerotic hippocampus, the amygdala, and the temporal pole, and finally, a decreased anisotropy was noted ipsilaterally in posterior extratemporal regions. Duration of epilepsy, age at onset, and the frequency of generalized tonic-clonic seizures or partial complex seizures did not correlate with the presence of diffusion abnormalities. Region of interest analysis in the hippocampus/parahippocampus demonstrated a correlation between lower ipsilateral diffusivity values and occurrence of epigastric aura and between higher anisotropy values in both hemispheres and history of febrile seizures. In conclusion, this study showed that diffusion abnormalities are not restricted to the pathologic hippocampus and involve a larger network. This pattern may indirectly reflect the epileptogenic network and may be interpreted as a cause or a consequence of epilepsy.     

早产儿运动发育迟缓的磁共振扩散张量成像研究

目的 探讨磁共振扩散张量成像(DTI)技术在评价早产儿运动发育迟缓轻重程度方面的应用价值.方法 22例运动发育迟缓早产儿纠正胎龄后依据Peabody运动发育量表总运动商值(TMQ)评分分为轻、中、重三组并行常规MRI、DTI检查.测量各组患儿相同兴趣区的分数各向异性(FA)值.结果 FA值在大脑脚、内囊后肢、放射冠各个兴趣区的组间差异均有统计学意义(P＜0.05),FA值随病情加重而减低.Pearson相关分析显示患儿三个感兴趣区FA值与总运动商(TMQ)值的评分正相关(P＜0.05).结论 测定DTI的FA值能对运动发育迟缓早产儿白质髓鞘发育损伤程度能做出较准确、客观的预测.     

MRI弥散张量成像用于躯体化障碍患者小脑微结构研究

目的探讨躯体化障碍患者是否存在双侧小脑,尤其是小脑齿状核微观结构异常。方法应用3．0TMRI成像仪对28例躯体化障碍患者（SD组）及28例体检健康者（对照组）进行MRI弥散张量成像,测量2组双侧小脑髓质、齿状核表观弥散系数和各向异性分数值,比较2组左右侧小脑差异。结果SD组右侧小脑齿状核各向异性分数值较左侧升高（P〈0．05）,右侧表观弥散系数与左侧比较差异无统计学意义（P〉0．05）;对照组左、右侧小脑髓质和齿状核表观弥散系数、各向异性分数值比较差异无统计学意义（P〉0．05）;2组左、右侧小脑髓质、齿状核表观弥散系数和各向异性分数值比较差异均无统计学意义（P〉0．05）。结论SD患者双侧小脑齿状核不对称性较正常人增强,存在小脑结构侧化性类型异常。     

良性前列腺增生磁共振扩散张量成像的初步研究

目的探讨磁共振扩散张量成像（DTI）在评估良性前列腺增生（BPH）和正常外周带结构差异的应用价值。方法研究对象为经病理证实的25例BPH患者,DTI成像采用SIEMENS Sonata 1．5T超导成像仪和腹部相控阵线圈,应用Leonardo工作站相应的软件进行数据处理。记录BPH和正常外周带（PZ）的FA值和平均ADC值,绘制相应参数图和纤维示踪图像。对比不同感兴趣区的成像指标的差异。结果正常外周带和BPH的FA值分别为0．16±0．03和0．23±0．04（P〈0．05）,平均ADC值分别为（1．85±0．34）×10^-3mm^2和（1．37±0．27）×10^-3mm^2/s（P〈0．05）。PZ区和BPH区的纤维方向、形态和数量存在明显差异。结论DTI能评估BPH和PZ的结构差异,可作为BPH术前评估的影像学手段。