精神分裂症患者全脑白质纤维弥散张量成像的初步研究

目的运用能够提示白质纤维(white matter,WM)完整性的弥散张量成像(diffusion tensor imaging,DTI)技术,探讨精神分裂症患者全脑白质纤维是否受到损害。方法对21例精神分裂症患者(患者组)和21名健康人(对照组)进行全脑DTI扫描,用SPM2(Statistical Parametric Maps,SPM)软件对图像进行处理,采用以像素为基础的分析方法(voxel-based analysis,VBA)对两组的分数各向异性(fractional anisotropy,FA)值进行组间比较。结果患者组下列脑区的FA值显著低于对照组(P<0·001):左侧额眶区和右侧额中回的白质、双侧颞下回白质、双侧顶叶内侧白质、右侧前扣带、双侧海马、双侧大脑脚、双侧岛叶、右侧放射冠和右侧小脑上脚。结论精神分裂症多个部位脑白质纤维的完整性受到破坏。     

A meta-analysis of white matter changes in temporal lobe epilepsy as studied with diffusion tensor imaging

Purpose: Diffusion tensor imaging (DTI) is used increasingly to study white matter integrity in people with temporal lobe epilepsy (TLE). Most studies report fractional anisotropy (FA) decrease and mean diffusivity (MD) increase in multiple white matter regions. The disturbance of white matter integrity varies across studies and between regions. We aimed to obtain a more consistent estimate of white matter diffusion characteristics and relate these to the distance from the seizure focus. Methods: Studies comparing diffusion characteristics of people with epilepsy with those of healthy controls were systematically reviewed and quantified using random and mixed effects meta analysis. In addition to the overall meta‐analysis, pooled FA and MD differences were determined per hemisphere and white matter category separately. Key Findings: We included 13 cross‐sectional studies. The pooled FA difference for all white matter was ?0.026 (95% confidence interval [CI] ?0.033 to ?0.019) and MD difference was 0.028 × 10^?3 mm²/s (95% CI 0.015–0.04). FA was reduced significantly in people with TLE compared with healthy controls in both ipsilateral (mean difference ?0.03) and contralateral white matter (?0.02). MD was significantly increased ipsilaterally and contralaterally. MD differed significantly between white matter connected to the affected temporal lobe and remote white matter. Significance: The meta‐analysis provides a better estimation of the true diffusion characteristics. White matter structural integrity in TLE is disturbed more severely in the ipsilateral than in the contralateral hemisphere, and tracts closely connected with the affected temporal lobe are most disturbed. The exact underlying mechanisms remain to be elucidated.     

Longitudinal diffusion tensor imaging in Huntington's Disease

Serial diffusion tensor imaging scans were collected at baseline and 1 year follow-up to investigate the neurodegenerative profile of white matter (WM) in seven individuals with the Huntington's Disease (HD) gene mutation and seven control subjects matched on age and gender. In the HD subjects, but not controls, a significant reduction of fractional anisotropy (FA), a measure of WM integrity, between baseline and follow-up was evident throughout the brain. In addition, a DTI scalar associated with the stability of axons, axial diffusivity, showed significant longitudinal decreases from year 1 to year 2 in HD subjects, declines that overlapped to greater degree with FA discrepancies than longitudinal increases in radial diffusivity, a DTI variable sensitive to demylinization. These preliminary results provide the first longitudinal DTI evidence of WM degeneration in HD and support the notion that FA abnormalities in HD may be a result of axonal injury or withdrawal. These results suggest that longitudinal FA changes may serve as a neuropathological biomarker in HD.     

Direct evidence of the relationship between brain metastatic adenocarcinoma and white matter fibers: A fiber dissection and diffusion tensor imaging tractography study

It is commonly known that brain metastases usually have clear boundaries in magnetic resonance imaging. However, little is known regarding the trajectory of white matter fibers around the tumors, especially using the fiber dissection technique. Here, we focused on the anatomical interaction between white matter fibers and the tumor, using the fiber dissection in a postmortem brain with metastatic tumor and compared the findings with those of diffusion tensor imaging (DTI) tractography. One postmortem human brain hemisphere with metastatic adenocarcinoma in the Broca’s area was dissected using fiber dissection following the Klingler’s method. In order to compare the in vitro and in vivo results, additional brains from 15 patients with metastatic adenocarcinomas, the volumes of which were comparable to that of the adenocarcinoma in the brain used for fiber dissection, were analyzed using DTI tractographic reconstruction. Morphological findings of white matter bundles running around the tumor were compared between the two techniques. In the fiber dissection technique, the superior longitudinal fascicle, arcuate fascicle, and frontal aslant tract could be dissected, and the white matter bundles were curved and retracted to avoid the tumor. In all the cases analyzed, white matter fibers or streamlines surrounding the tumor avoided the lesion. Using the fiber dissection technique, this is the first direct evidence to elucidate the anatomy of white matter fibers affected by a metastatic brain. This suggests that brain metastatic adenocarcinoma is an intra-axial neoplasm with extra-axial white matter structures.     

Speed of lexical decision correlates with diffusion anisotropy in left parietal and frontal white matter: evidence from diffusion tensor imaging

Speed of visual word recognition is an important variable affecting linguistic competence. Although speed of visual word recognition varies widely between individuals, the neural basis of reaction time (RT) differences is poorly understood. Recently, a magnetic resonance technique called diffusion tensor imaging (DTI) has been shown to provide information about white matter (WM) microstructure in vivo. Here, we used DTI to explore whether visual word recognition RT correlates with regional fractional anisotropy (FA) values in the WM of healthy young adults. Participants completed a speeded lexical decision task that involved visual input, linguistic processes, and a motor response output. Results indicated that lexical decision RT was correlated negatively with FA in WM of inferior parietal and frontal language regions rather than in WM of visual or motor regions. Voxels within the inferior parietal and frontal correlation clusters were composed primarily of DTI-based tracts oriented in the anterior-posterior orientation at or near the superior longitudinal fasciculus (SLF) and likely including other smaller association fibers. These results provide new microstructural evidence demonstrating that speed of lexical decision is associated with the degree to which portions of frontal and parietal WM are directionally oriented.     

抑郁症患者脑奖赏环路相关结构的弥散张量成像研究进展

奖赏环路是脑内边缘系统的一部分,而奖赏系统则是愉快体验的核心,它可以促进人的学习,刺激和趋避行为.但奖赏系统的作用不仅局限于体验愉快,它同时也调节着人的认知与动机[1]. 弥散张量成像(Diffusion Tensor Imaging, DTI)由Basser等[2]在1996年首次提出,是目前唯一能在活体人脑组织的研究脑白质的非侵入性手段.DTI技术通过对水分子的自由热运动的各向异性进行量化分析,利用彩色图像显示白质纤维束的走行、方向、排列、紧密度、髓鞘化情况等信息[3],可以间接评价大脑白质纤维的完整性.DTI成像参数主要有两个:各向异性分数(Fractional Anisotropy,FA),反映细胞膜的完整性,受白质通道的调节,对纤维束的方向及一致性更加敏感;平均弥散率(Mean Diffusivity, MD),反映分子整体的弥散水平(平均椭球的大小)和弥散阻力的整体情况,MD越大,弥散阻力越大,信号传递速度越慢.本文对最近关于重性抑郁障碍(Major Depressive Disorder,MDD)奖赏环路的DTI的研究结果进行如下综述.     

White matter pathways associated with working memory in normal aging

Introduction

Previous studies by our group have found that white matter integrity as determined by Diffusion Tensor Imaging (DTI) is associated with working memory decline. It has been proposed that subtle white matter integrity loss may lead to the disruption of working memory in particular because it relies on the dynamic and reiterative activity of cortico-cortical pathways.

Methods

DTI and working memory measurement were acquired for 99 adults from our GENIE study of healthy middle aged and elderly individuals. Voxel-based statistics were used to identify clusters of voxels in mean diffusivity images specifically associated with variations in working memory performance. Tractography then identified the cortico-cortical white matter pathways passing through these clusters, between the temporal, parietal and frontal cortices.

Results

Significant clusters were identified which were associated with working memory in the white matter of the temporal and frontal lobes, the cingulate gyrus, and in the thalamus. The tracts that passed through these clusters included the superior parietal lobule pathway, the medial temporo-frontal pathway, the uncinate fasciculus, the fronto-parietal fasciculus, and the cingulum.

Conclusions

Significant clusters were identified in the white matter that were associated with working memory performance. Tractography performed through these clusters identified white matter fiber tracts which pass between grey matter regions known to be activated by working memory tasks and also mirror working memory pathways suggested by previous functional connectivity imaging.     

高功能孤独症患儿全脑白质纤维的弥散张量成像研究

目的 分析高功能孤独症患儿的全脑白质纤维的完整性.方法 对18例高功能孤独症患儿(病例组)以及10名年龄、性别、智商与病例组相匹配的健康儿童(对照组)进行全脑弥散张量成像(DTI)测量;应用基于体素的分析方法,比较两组全脑各向异性分数(FA)的差异.使用Spearman相关分析,分析病例组各感兴趣区FA值与儿章期孤独症评定表(CARS)总分及各项目之间的关系.结果 与对照组相比,病例组右侧额下回、左侧额中回及右侧颞下回邻近白质的FA值低(分别为0.67±0.10、0.57±0.09、0.50 ±0.12),左顶上小叶邻近白质的FA值高(0.55±0.15;P<0.001).病例组左额中回邻近白质的FA值与CARS中的与非生命物体的关系的得分呈负相关(r=-0.63,P=0.005).结论 高功能孤独症患儿多个部位的脑白质纤维的完整性受到破坏.     

Evaluation of changes in magnetic resonance diffusion tensor imaging of the bilateral optic tract in monocular blind rats

Some studies have used diffusion tensor imaging (DTI) to investigate white matter development of the visual pathway in humans and animals after visual deprivation. However, the alterations in the bilateral optic tract after the transection of unilateral optic nerve have not been well explored. In this study, we attempted to investigate the structural integrity of and pathological changes to the bilateral optic tract after transection of the unilateral optic nerve in rats using DTI. Eight healthy male Sprague-Dawley (SD) rats were randomly divided into 2 groups, with 4 in each group. Group A served as a control group. Transection of the unilateral (right) optic nerve was performed in the four rats in group B at seven days after birth to establish the early monocular blind model. Four months after the operation, MnCl₂ was injected into the left eyes of all rats, and MRI examinations were performed 24 h after injection. We detect the fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) values of the bilateral optic tract in all rats. In a comparison of the ipsilateral optic tract of group B with group A, a significant decrease in FA (P < 0.001) and an increase in RD (P < 0.01) of the left optic tract were found in group B, while no significant difference was found in the right optic tract. In group B, the FA and RD values of the left optic tract were significantly lower (P < 0.01) and significantly higher (P < 0.05), respectively, than those of the right optic tract. Consequently, transection of the right optic nerve can lead to structural integrity damage of and pathological changes to the left optic tract in rats. Some DTI-derived parameters (such as FA and RD) may serve as biomarkers of optic tract degeneration.     

首发未服药精神分裂症患者脑弥散张量成像的基于体素分析

目的分析首发未服药精神分裂症患者脑白质完整性的变化。 方法对40例首发未服药精神分裂症患者和68例健康对照者进行脑弥散张量磁共振成像检查,以DTI-studio软件和统计参数图(SPM)软件对所得图像进行预处理,得到的各向异性分数(FA)图像在SPM软件中进行两样本t检验,获得两组患者FA值差异统计参数图。 结果在P值小于0.001（未校正）水平下,首发未服药精神分裂症患者右侧杏仁核区(MNI：24,2,-14,cluster=347 voxels)、双侧前扣带区(MNI:6,42,2,cluster=586 voxels)、右侧前额叶眶上回区域(MNI：20,18,-10,cluster= 166 voxels)白质FA值较健康对照者下降,且未发现前者有脑区白质FA值较后者增高。 结论精神分裂症患者皮层一边缘系统环路存在结构连接障碍,这可能是精神分裂症的神经机制。     

Altered white matter integrity in primary restless legs syndrome patients: diffusion tensor imaging study

Abstract

Objectives:

A prior diffusion tensor imaging (DTI) of restless legs syndrome (RLS) subjects found alterations in brain white matter (WM). The aim of this study was to explore the possible mechanism of altered integrity of brain WM in RLS patients.

Methods:

The DTI measurement was performed in 22 subjects with RLS and 22 age-matched control subjects. Using a voxel-based analysis, fractional anisotropy (FA) and axial and radial diffusivities (AD and RD) were compared between RLS and control subjects with a two-sample t-test, and correlation analysis was performed in RLS subjects.

Results:

RLS subjects demonstrated decreased FA in the genu of the corpus callosum and frontal WM adjacent to the inferior frontal gyrus compared with the control subjects. For areas of decreased FA, both the AD and RD were higher than that in the control subjects.

Discussion:

Our findings suggest that loss of axonal density and myelin may account for WM changes seen in a prior study of RLS subjects.     

Sex interaction of white matter microstructure and verbal IQ in corpus callosum in typically developing children and adolescents

BackgroundChildhood is an extremely important time for neural development that has a critical role in human intelligence. Efficient information processing is crucial for higher intelligence, so the intra- or inter-hemispheric interaction is vital. However, the relationship between neuroanatomical connections and intelligence in typically developing children, as well as sex differences in this relationship, remains unknown.MethodsParticipants were 253 typically developing children (121 boys and 132 girls) aged 5–18. We acquired diffusion tensor imaging data and intelligence using an age-appropriate version of the IQ test; Wechsler Intelligence Scale for Children (WISC) or Wechsler Adult Intelligence Scale (WAIS). We conducted whole-brain multiple regression analysis to investigate the association between fractional anisotropy (FA), which reflects white matter microstructural properties, and each composite score of IQ test (full-scale IQ, performance IQ, and verbal IQ).ResultsFA was positively correlated with full-scale IQ in bilateral inferior occipitofrontal fasciculus, genu, and splenium of corpus callosum (CC). FA in the right superior longitudinal fasciculus, bilateral inferior longitudinal fasciculus, and splenium of CC were also positively correlated with performance IQ. Furthermore, we found significant sex interaction between FA in the CC and verbal IQ. FA was positively correlated in boys, and negatively correlated in girls.ConclusionResults suggest that efficient anatomical connectivity between parietal and frontal regions is crucial for children’s intelligence. Moreover, inter-hemispheric connections play a critical role in verbal abilities in boys.     

Aging white matter and cognition: Differential effects of regional variations in diffusion properties on memory, executive functions, and speed

Disruption of cerebral white matter has been proposed as an explanation for age-related cognitive declines. However, the role of specific regions in specific cognitive declines remains unclear. We used diffusion tensor imaging to examine the associations between regional microstructural integrity of the white matter and performance on age-sensitive cognitive tasks in a sample of healthy adults (N = 52, age 19-81 years). White matter integrity was assessed by fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in multiple regions of interest (genu and splenium of corpus callosum, internal capsule limbs, prefrontal, temporal, superior/posterior parietal, occipital white matter) and related to processing speed, working memory, inhibition, task switching, and episodic memory. We found that age and regional white matter integrity differentially influenced cognitive performance. Age-related degradation in anterior brain areas was associated with decreased processing speed and poorer working memory, whereas reduced inhibition and greater task switching costs were linked to decline in posterior areas. Poorer episodic memory was associated with age-related differences in central white matter regions. The observed multiple dissociations among specific age-sensitive cognitive skills and their putative neuroanatomical substrates support the view that age-related cognitive declines are unlikely to stem from a single cause.     

A comparative diffusion tensor imaging study of corpus callosum subregion integrity in bipolar disorder and schizophrenia

Structural magnetic resonance imaging (MRI) studies have provided evidence for corpus callosum (CC) white matter abnormalities in bipolar disorder (BD) and schizophrenia (SZ). These findings include alterations in shape, volume, white matter intensity and structural integrity compared to healthy control populations. Although CC alterations are implicated in both SZ and BD, no study of which we are aware has investigated callosal subregion differences between these two patient populations. We used diffusion tensor imaging (DTI) to assess CC integrity in patients with BD (n=16), SZ (n=19) and healthy controls (HC) (n=24). Fractional anisotropy (FA) of CC subregions was measured using region of interest (ROI) analysis and compared in the three groups. Significant group differences of FA values were revealed in five CC subregions, including the anterior genu, middle genu, posterior genu, posterior body and anterior splenium. FA values of the same subregions were significantly reduced in patients with SZ compared with HC. FA values were also significantly reduced in patients with BD compared to the HC group in the same subregions, excepting the middle genu. No significant difference was found between patient groups in any region. Most of the alterations in CC subregions were present in both the BD and SZ groups. These results imply an overlap in potential pathology, possibly relating to risk factors common to both disorders. The one region that differed between patient groups, the middle genu area, may serve as an illness marker and is perhaps involved in the different cognitive impairments observed in BD and SZ.     

Quantitative DTI assessment of periventricular white matter changes in neonatal meningitis

Neonatal meningitis is one of the important causes of infant mortality and morbidity. Periventricular white matter of neonatal brain is known to be vulnerable to oxidative and hypoxic/ischemic injury secondary to neuro-infections. The aim of this study was to assess periventricular white matter damage in neonatal bacterial meningitis using diffusion tensor imaging (DTI). DTI was performed in 7 age/sex matched controls and 14 neonates with proven bacterial meningitis at the time of diagnosis and after 3 weeks of antibiotic treatment. Region of interest were placed on periventricular white matter to quantify fractional anisotropy (FA) and mean diffusivity (MD). Based on the clinical prognosis and conventional MRI, patients were grouped into those with normal and with abnormal outcome. Compared to controls significantly decreased FA values were observed in entire periventricular white matter except for left parietal white matter in patients with abnormal outcome. Even in those with normal outcome significant decrease in FA values were observed in right parietal and bilateral occipital white matter compared to controls. Decreased FA values in the periventricular white matter regions in neonatal meningitis confirm microstructural white matter injury.     

弥散张量成像诊断弥漫性轴索损伤的敏感性及意识状态的研究

目的 研究弥散张量成像(DTI)诊断弥漫性轴索损伤(DAI)的敏感性,及探讨中脑区各向异性分数(FA)值与GCS评分的相关性以定量评估DAI的损伤程度. 方法 选择惠州市第一人民医院及惠州市中心人民医院神经外科自2007年1月至2013年1月临床诊断为DAI的105例患者为研究对象,对其在入院时行CT、MRI平扫及DTI扫描,观察比较3种不同影像学方法检测DAI损伤病灶的敏感性差异,并分析其中36例DAI患者中脑区FA值与入院时GCS评分的相关性. 结果 CT检测DAI损伤病灶的敏感性为70.48％,MRI平扫为82.86％,DTI为95.24％,3者比较差异具有统计学意义(P＜0.05),其中以DTI检查诊断的敏感性为最高.患者入院时GCS评分与中脑区FA值存在正相关关系(r=0.977,P=0.000). 结论 DTI不仅在诊断DAI敏感性方面优于CT和MRI平扫,且在一定程度上可客观地评估DAI的损伤程度.     

In vivo diffusion tensor imaging and ex vivo histologic characterization of white matter pathology in a post-status epilepticus model of temporal lobe epilepsy

Although epilepsy is historically considered a disease of gray matter, recent diffusion tensor imaging (DTI) studies have shown white matter abnormalities in patients with epilepsy. The histopathologic correlate of these findings, and whether they are a cause or consequence of epilepsy, remains unclear. To characterize these changes and their underlying histopathology, DTI was performed in juvenile rats, 4 and 8 weeks after pilocarpine‐induced status epilepticus (SE). In the medial corpus callosum (CC), mean diffusivity and axial diffusivity (MD and λ₁) as well as a myelin staining were significantly reduced at 4 weeks. Only the λ₁ decrease persisted at 8 weeks. In the fornix fimbriae (FF), λ₁ and myelin staining were decreased at both time points, whereas fractional anisotropy (FA) and MD were significantly reduced at 8 weeks only. We conclude that SE induces both transient and chronic white matter changes in the medial CC and FF that are to some degree related to myelin pathology.     

健康者三叉神经磁共振扩散张量成像研究

目的 测量三叉神经桥池段的表观扩散系数(ADC)值和部分各向异性分数(FA)值,了解三叉神经桥池段各参数的特点。 方法 选择50例健康志愿者三叉神经桥池段距离脑干发出点0mm、3mm、6mm、9mm共四处,利用DTI图像与B-TFE或THRIVE图像融合成像,提高三叉神经桥池段显示的空间分辨率,并利用该图像测量并分别记录ADC值与FA值,对所有受检者行三叉神经桥池段追踪成像。 结果 受检者左侧与右侧三叉神经桥池段的ADC值和FA值差异均无统计学意义(P＞0.05)。越靠近脑干发出点,左右两侧三叉神经桥池段的各导出量越呈现左右不对称的趋势。双侧三叉神经桥池段距脑干不同距离各位置的DTI导出量分析发现：相邻两距离间ADC值差异均有统计学意义(P＜0.05),出脑干后随距离增加ADC值逐渐升高,但行至6～9 mm间突然回转下降;FA值在0～6 mm间随距离增加而逐渐降低,且相邻两距离间差异均有统计学意义(P＜0.05),但行至6～9 mm间FA值不再有明显变化。 结论 DTI图像能够清晰分辨双侧三叉神经桥池段,可实现DTI各项导出量的测量。随着距脑干发出点距离的不同,各导出量发生有规律的变化,预示着DTI在明确区分三叉神经的中枢神经系统段、过渡段和周围神经系统段以及检出颅神经血管压迫方面的应用前景。     

弥散张量成像在颅脑损伤昏迷病人中的应用

目的初步探讨颅脑损伤昏迷病人上行网状激活系统(ARAS)弥散张量成像(DTI)和预后的相关性。方法以最近3年的颅脑损伤后昏迷病人为研究对象,在颅脑创伤后的3周和5周行DTI和纤维示踪成像(DTT)检查。种子兴趣区为中脑和桥脑被盖区,目标兴趣区为丘脑板内核。分析ARAS纤维束的部分各向异性(FA)、平均弥散率(MD)、纤维束量(TV),及其变异和病人颅脑创伤3月后意识状态的关系。采用Spearman相关分析,分析FA、MD、TV和预后评分的相关性。结果 3周时上行网状激动系统FA、MD和3月时的预后之间无相关性,TV和3月时的预后有统计学相关性(相关系数为0. 89,P 0. 001)。5周时,FA、TV和3月时的预后呈正相关性(P 0. 001),3周至5周间FA的变异与3月时的GCS评分和GOS评分呈正相关(P 0. 005,P 0. 05),TV变异和3月时GCS评分和GOS评分呈正相关(P 0. 001)。结论颅脑损伤后昏迷患者3月后的意识状态和DTI所模拟颅脑损伤后5周时ARAS的FA、MD、TV及动态变化有相关性。亚急性期上行网状激动系统纤维束的改变可以间接反映患者意识恢复能力。