磁共振弥散张量成像在神经疾病中的应用

磁共振弥散张量成像（DT）是近几年发展起来的水弥散成像技术，它通过脑水分子的弥散性定量反映脑白质纤维束的完整性。文章简要介绍了DTI的基本概念及其在脑梗死、多发性硬化、癫痫、Alzheimer病和颅内肿瘤等多种神经疾病中的应用。     

扩散张量成像在评价脑梗死预后的研究进展

<正>弥散张量成像(DTI)是利用组织中水分子弥散的各向异性,来探测组织微观结构的磁共振成像方法。在此基础上的扩散张量纤维束成像(DTT),是目前惟一可无创体内跟踪白质纤维束三维结构的方法,能直观三维显示白质束的走行方向。近年来,随着DTI技术日益发展成熟,已经越来越多     

磁共振DTI在脑梗死诊断中的应用价值

目的探讨磁共振弥散张量成像(DTI)对脑梗死诊断的价值。方法收集临床诊断考虑脑梗死并经常规磁共振成像(MRI)和弥散加权成像(DWI)检查证实为单侧脑梗死病人行DTI检查,共48例。重建ADVAV图、FA图及DTT图,测定脑梗死区及健侧相应部位脑组织的ADVAV值和FA值,对锥体束受累病人,测量双侧大脑脚、脑桥的ADVAV值和FA值测量。结果脑梗死后脑组织ADVAV值、FA值随病理生理演变呈一定规律性变化,在慢性期锥体束受累病例显示远离病变区患侧锥体束FA值下降,ADVAV变性则无统计学意义。与传统MRI及DWI相比DTI可清晰显示梗死灶与白质纤维束的空间位置关系及其受累程度。结论 DTI结合常规MRI及DWI对梗死灶的解剖定位更准确,ADVAV值与FA值联合应用有助于对脑梗死进行更精确的临床分期,DTI对脑梗死的诊断、治疗及评估预后具有重要临床应用价值。     

磁共振弥散张量成像在脑梗死诊断中的价值

目的分析脑梗死患者磁共振弥散张量成像(DTI)的特点,探讨DTI在不同时期对脑梗死患者诊断的价值。方法分别对40例不同时期脑梗死患者和40名健康志愿者行MR I检查,包括T1、T2加权成像、弥散加权成像及DTI,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行FA值、表观弥散系数(ADC)值测量。结果①DTI显示的梗死灶范围较常规MR I成像更加准确、清晰。②脑梗死组患者梗死区及梗死同侧内囊后肢、大脑脚、皮质脊髓束的FA值分别为0.12±0.01、0.29±0.03、0.36±0.12及0.35±0.04,低于对侧相应部位的0.35±0.08、0.50±0.13、0.53±0.14、0.56±0.07,差异均具有显著性(P<0.05);脑梗死患者健侧ADC、FA值与正常对照组相应部位对比,差异无显著性(P>0.05)。③脑梗死后脑组织FA值、ADC值随梗死时间呈一定规律性变化,在超早期患侧FA值较对侧无一致性变化,可轻度升高或轻度降低,随后(急性期、亚急性期、慢性期)降低;患侧ADC值随梗死时间延长呈明显减低、逐渐恢复正常、继而又升高的规律。结论DTI检查有助于明确脑梗死是否累及白质纤维束,ADC值与FA值联合能更精确对脑梗死进行临床分期和定位。     

老年缺血性脑梗死患者90例康复治疗前后的弥散张量成像

大多数脑梗死患者治疗后都一定程度上遗留生活不便。常规CT和MRI检查在显示病灶与其神经纤维的关系及白质束受损范围方面具有很大的局限性,而且很难准确显示其关系。最近几年才发展起来的弥散张量成像(DTI)是在常规磁共振和弥散加权成像的基础上开发的无创性成像方法,可比较直观地     

磁共振弥散张量成像在缺血性脑梗死中应用的研究进展

弥散张量成像(diffusion tensor imaging DTI)技术是一种新的无创性检查方法,在多种组织器官都有应用,近年来在中枢神经系统已经被广泛使用;由于对脑白质纤维显示敏感性较高,在评估脑梗死病情轻重、预后判断等方面具有重要临床意义。现就DTI基本原理、成像特点、常用参数及其在脑梗死中的应用进行综述。     

弥散张量成像在高级别星形细胞肿瘤诊断中的初步应用

对12例经病理证实的高级别（WHO分级Ⅲ-Ⅳ级）星形细胞肿瘤患者均行常规头颅MRI成像、磁共振弥散张量成像（DTI）检查,并获得部分各向异性指数（FA值）。结果显示,强化肿瘤实质区、强化肿瘤实质边缘区、坏死囊变区、瘤周水肿区FA值较对侧脑白质及同侧未受累白质明显下降（P〈0.05）;其余各区FA值无统计学差异（P〉0.05）。提示DTI可更好的区别肿瘤与周围白质纤维束,指导术前制定治疗方案。     

弥散张量成像在卒中后抑郁中的应用

卒中后抑郁(post-stroke depression, PSD)是卒中后常见的情感障碍, 可影响患者认知功能, 对卒中后康复造成不良影响。弥散张量成像(diffusion tensor imaging, DTI)可显示脑白质微结构, 目前已应用于各种疾病的发病机制研究。文章综述了DTI技术在抑郁症、卒中和PSD中的应用情况, 旨在从多方面对PSD进行早期预测以改善其转归。     

磁共振弥散张量在早期帕金森病中应用及普拉克索的疗效

目的探讨磁共振弥散张量成像(DTI)在早期帕金森病(PD)病情监测中的价值及普拉克索的疗效。方法早期PD患者40例,随机分为普拉克索用药组及未用药组,在入院时、治疗6个月、1年采用磁共振弥散张量成像检测FA、ADC、MD值。对照组为20例年龄性别、受教育程度等与PD患者对匹配的健康体检者。结果 PD患者用药组、未用药组6个月、1年时黑质FA值比较差异有统计学意义(P<0.05),且随着病程延长,黑质FA值逐渐下降。结论磁共振弥散张量成像可作为早期PD患者病情监测的一种可靠方法,为普拉克索疗效监测提供客观依据。     

弥散张量成像在评价急性缺血性脑梗死白质纤维束损伤中的价值

目的探讨磁共振弥散张量成像(DTI)在评价急性缺血性脑梗死白质纤维束损伤中的价值。方法对21例发病72 h内的急性缺血性脑梗死住院患者进行常规头部MR平扫、DWI、DTI扫描及DTT三维重建。对比测量梗死侧与健侧相对应部位脑白质的各向异性系数(FA),对皮质脊髓束(CST)进行弥散张量纤维束重建(DTT),并分级。结果急性脑梗死患侧FA减低,两者相比差异有统计学意义。病变侧CST表现为受压、变形、移位和中断,FA下降越明显,CST受累越严重。结论 DTI能够直接观察到白质纤维束的变化,从而对急性脑梗死白质纤维束损伤进行很好的评估。     

Evaluation of mannitol effect in patients with acute hepatic failure and acute-on-chronic liver failure using conventional MRI, diffusion tensor imaging and in-vivo proton MR spectroscopy

AIM： To evaluate the effect of an intravenous bolus of mannitol in altering brain metabolites, brain water content, brain parenchyma volume, cerebrospinal fluid （CSF） volume and clinical signs in controls and in patients with acute liver failure （ALF） and acute- on-chronic liver failure （ACLF）, by comparing changes in conventional magnetic resonance imaging （MRI）, in vivo proton magnetic resonance spectroscopy （PMRS） and diffusion tensor imaging （DTI） before and after its infusion.METHODS： Five patients each with ALF and ACLF in grade 3 or 4 hepatic encephalopathy and with clinical signs of raised intracranial pressure were studied along with five healthy volunteers. After baseline MRI, an intravenous bolus of 20% mannitol solution was given over 10 min in controls as well as in patients with ALF and ACLE Repeat MRI for the same position was acquired 30 rnin after completing the rnannitol injection. RESULTS： No statistically significant difference was observed between controls and patients with ALF and ACLF in metabolite ratios, DTI metrics and brain volume or CSF volume following 45 rain of mannitol infusion. There was no change in clinical status at the end of post-mannitol imaging. CONCLUSION： The osmotic effect of mannitol did not result in significant reduction of brain water content, alteration in metabolite ratios or any change in the clinical status of these patients during or within 45 min of mannitol infusion.     

Putaminal Diffusivity Correlates With Disease Progression in Parkinson's Disease: Prospective 6-Year Study

Diffusion tensor imaging (DTI) is an increasingly used noninvasive imaging tool. However its long-term clinical utility is unclear. Parkinson''s disease (PD) is a common neurodegenerative disease.We prospectively examined a cohort of 46 Parkinson''s disease (PD) patients who underwent diffusion tensor imaging (DTI) of the brain at baseline and 6 years later on a 1.5 Tesla scanner using a standardized protocol. DTI parameters of mean diffusivity (MD) and fractional anisotrophy (FA) were extracted using regions-of-interest (ROIs) analysis from various brain regions.Compared to the baseline scan, MD increased in all brain regions (P < 0.0001). FA increased in the substantia nigra and posterior putamen, but decreased in the frontal white matter (P < 0.0001). Linear regression analysis demonstrated that the MD in the anterior putamen increased 11.6 units (95% CI = [4.71, 18.43]) (P = 0.0003) for every unit increase of United PD Rating Scale (UPDRS).Our 6-year prospective longitudinal study demonstrated increased diffusivity in all brain regions and that in the anterior putamen correlated with disease progression. Serial diffusion data may be useful as an additional objective in vivo biomarker for motor progression in PD.     

Region-specific changes of cerebral white matter during normal aging: a diffusion-tensor analysis

With aging, the human brain tissue undergoes degeneration and a decline in cognitive function. Diffusion tensor imaging (DTI) is a sensitive method for detecting microstructural changes of the brain white matter (WM). We examined the age-dependent, region-specific, changing patterns in microstructures of the brain. This was preformed by DTI analysis of 58 healthy volunteers from Korea. The fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured for each region of interest (ROI) in 22 areas. The FA and ADC values of all 22 ROIs were, respectively, compared among the age groups, by linear regression analysis and analysis of variance. With aging, the ADC values tended to increase and the FA values tended to decrease. Patterns of regional changes of the FA were divided into three subgroups. The cingulum was affected earliest with aging and the age-related WM changes show an anterior to posterior gradient acceleration throughout the decades tested. This study suggests that DTI is sensitive enough a diagnostic tool to detect subtle microstructural changes. These results show that the WM has a region-specific vulnerability to the aging process.     

In vivo detection and functional correlates of white matter microstructural disruption in chronic alcoholism

BACKGROUND: Postmortem studies report degradation of brain white matter microstructure in chronic alcoholism, but until recently, in vivo neuroimaging could provide measurement only at a macrostructural level. The development of magnetic resonance diffusion tensor imaging (DTI) for clinical use offers a method for depicting and quantifying the diffusion properties of white matter expressed as intravoxel and intervoxel coherence of tracts and fibers. METHODS: This study used DTI to examine the intravoxel coherence measured as fractional anisotropy (FA) and intervoxel coherence (C) of white matter tracts of the genu and splenium of the corpus callosum and of the centrum semiovale in 15 detoxified alcoholic men and 31 nonalcoholic control subjects. Exploratory correlational analyses examined the relationships between regional DTI measures and tests of attention and working memory in the alcoholic patients. RESULTS: The alcoholic group had lower regional FA than the control group. C was lower in the alcoholics than controls in the splenium only. Working memory correlated positively with splenium FA, whereas attention correlated positively with genu C. CONCLUSIONS: These results provide in vivo evidence for disruption of white matter microstructure in alcoholism and suggest that interruption of white matter fiber coherence contributes to disturbance in attention and working memory in chronic alcoholism.     

Longitudinal Changes in the Brain Following Third Ventriculostomy in a Child With Hydrocephalus: A Case Report

The goal of this study was to detect the long-term effect of shunting on the integrity of white matter in young children with hydrocephalus.The authors reported the case of a 6-month-old boy with hydrocephalus who was evaluated by diffusion tensor imaging (DTI) before and after a shunt operation.When compared with normal children, the structures of the corpus callosum, internal capsule, and corona radiata in the patient showed a decrease in fractional anisotropy and an increase in radial diffusivity values before the shunt operation. Following successful cerebrospinal fluid shunting, long-term follow-up DTI demonstrated a trend toward normalization of the fractional anisotropy and radial diffusivity values.Shunt treatment can prevent further damage to the brain and grossly reconstitute the distorted anatomy. DTI could be a useful tool in detecting longitudinal changes after a shunt operation. Further studies involving larger case numbers are needed to detect the long-term effect of shunting on the brains of children with hydrocephalus.     

血管性痴呆的扩散张量成像研究

目的应用扩散张量成像(DTI)技术,探讨皮质下缺血性血管性痴呆(SIVD)患者脑白质变化的特点及不同脑区DTI参数改变与认知的关系。方法对34例SIVD患者(SIVD组)及26例健康老年人(对照组)行DTI扫描,测量双侧前额叶、额叶深部、眶额内侧、下额叶、颞叶、顶叶、枕叶白质及T_2WI高信号区、T_2WI高信号周围正常白质区的分量各向异性(FA)、主各向异性(PA)及表观弥散系数(ADC)值。结果对照组左侧前额叶白质PA值大于右侧,ADC值小于右侧。SIVD组双侧前额叶、双侧额叶深部、下额叶、眶额内侧的FA值及PA值明显下降,平均ADC值升高;双侧顶叶的FA值下降,平均ADC值升高;双侧颞叶、枕叶平均ADC值升高;左侧下额叶、眶额内侧白质的FA与PA值较右侧小;左侧下额叶ADC值较右侧大。病变区及病变周围区的FA和PA值小于正常区,ADC值大于正常区。前额叶FA与简易智能状态检查表评分呈正相关。结论 SIVD患者脑白质FA、PA和ADC改变具有区域选择性,前部及左侧脑区损伤明显,后部及右侧相对保留白质的完整性。DTI是研究SIVD脑白质损伤的一种理想的方法。     

Microstructural Change of the Brain in Chronic Obstructive Pulmonary Disease: A Voxel-Based Investigation by MRI

Abstract

Background: Cognitive deficit is a common problem in patients with chronic obstructive pulmonary disease (COPD). The aim of this study was to prospectively evaluate if MRI can demonstrate microstructural volume loss and the diffusion anisotropic change in subjects with COPD, compared with cognitively normal (CN) subjects. Methods: Six subjects with severe COPD, 13 with moderate COPD, and 12 CN subjects underwent isotropic volumetric T1-weighted imaging and diffusion tensor imaging (DTI). Voxel-based statistical analyses among groups were performed on brain volumes, fractional anisotropy (FA) and trace. Cognitive function tests were performed in all subjects, and the Cognitive function tests (CFT) scores were compared among the three groups. Results: No significant regional difference in volume was found in both the severe and moderate COPD groups relative to the CN group. Comparing between severe COPD and CN, FA was reduced in both the cerebral cortices, and in frontoparietal periventricular white matter. The trace value of the severe COPD group was significantly higher in the cerebral cortices, and in frontoparietal periventricular white matter, than that of the CN group. The severe COPD group showed significantly lower scores in the language-related, visuospatial, and frontal executive functions compared to those of the CN and moderate COPD group. Conclusion: This study demonstrated that COPD could affect the axonal integrity in multiple brain regions, and change in DTI might be related with the severity of the COPD.     

Evaluation of corpus callosum anisotropy in young adults with fetal alcohol syndrome according to diffusion tensor imaging

BACKGROUND: Fetal alcohol syndrome (FAS) and associated disorders resulting from maternal alcohol use during gestation are among the most common developmental disorders. However, they are rarely diagnosed and not fully understood in terms of their behavioral and neurocognitive phenotype. Prenatal exposure leads to alterations in facial morphology, growth, and neurocognition. The nature and extent of teratogenic effects on the brain and the relationship between such effects and observed behaviors remain in debate because there are no established markers for the neurological effects of exposure. In this study, we examined the impact of prenatal alcohol exposure on white-matter integrity in the corpus callosum by using diffusion tensor imaging (DTI) and herein describe the relationship between such effects and observed physical and behavioral outcomes. METHODS: DTI was used to evaluate diffusion anisotropy in the genu and splenium of corpus callosum in 16 low-income, primarily African-American volunteers. Volunteers were recruited from a cohort of young adults who had received neuropsychological evaluations during adolescence. Nine had been prenatally exposed to alcohol and had characteristics of FAS, and seven were nonexposed controls. RESULTS: Significant difference in the means for diffusion fractional anisotropy (t = 2.26, df = 9, p <0.002) and apparent diffusion coefficient (t = 2.14, df = 14, p < 0.008) were observed in the corpus callosum of alcohol-exposed youth compared with nonexposed youth. No significant differences were found in intracranial volume between these groups. CONCLUSIONS: Our results illustrate that DTI can be used in evaluating the integrity of corpus callosum in alcohol-exposed individuals. If future studies support these findings, diffusion anisotropy, represented by fractional anisotropy, has the potential to be used as a clinical marker in the diagnosis of FAS.     

Diffusion tensor magnetic resonance imaging as molecular diagnostic tool for leukoaraiosis

IntroductionDiffusion Tensor Imaging (DTI) is a magnetic resonance imaging (MRI) technique that measures mobility of water in biological tissues at molecular level. Useful quantitative parameters offered by DTI include mean diffusivity (MD) which indicates the diffusivity of water molecules in tissues, as well as fractional anisotropy (FA) which quantifies the degree of anisotropy in that particular region. DTI also allows for reconstruction of cerebral nerve fibre tracts through method called fibre tractography. Leukoaraiosis is a brain white-matter change detected as hyperintensity area on T2-weighted image of MRI. It is associated with age and various vascular risk factors, e.g. hypertension and diabetes mellitus. Its aetiology is thought to be related to ischaemia. DTI is expected to provide useful information for characterisation of leukoaraiosis.ObjectiveTo compare MD and FA values as well as fibre tractography between healthy and leukoaraiosis areas in the brain white-matter.MethodsTwelve volunteers with leukoaraiosis (5 male, 7 female; age: 57.0 ± 7.3) underwent brain scan using 1.5T MRI. Only two of them had hypertension, while none had diabetes. MD and FA values were measured for normal and leukoaraiosis areas in three different brain regions, namely the frontal, occipital, and parietal lobes. Fibre tractography was also performed. Comparison of obtained data for leukoaraiosis areas and healthy tissue in the corresponding lobe were performed. p<0.05 was considered statistically significant.Results & DiscussionSignificantly higher MD and reduced FA were observed in leukoaraiosis area compared to normal tissues in all lobes. Fibre tractography exhibits an obvious discontinuity of several nerve fibre tracts at the area of leukoaraiosis.ConclusionRelatively higher MD and reduced FA values seem to distinguish leukoaraiosis from normal tissues. Conventional MRI does not supply any quantitative value, whereas DTI provides molecular information for both healthy and leukoaraiosis areas.     

Pro-inflammatory cytokines are raised in extrahepatic portal venous obstruction, with minimal hepatic encephalopathy

Background and Aims: Minimal hepatic encephalopathy (MHE) and hyperammonemia are seen in patients with extrahepatic portal venous obstruction (EHPVO). Inflammation has been shown to play an important role in the pathogenesis of hepatic encephalopathy in cirrhotics. This study assessed serum pro‐inflammatory cytokines and their correlation with hyperammonemia, ¹H‐magnetic resonance (MR) spectroscopy‐derived brain glutamine, and diffusion tensor imaging (DTI)‐derived metrics in patients with EPHVO, with and without MHE. Methods: Neuropsychological tests, DTI, ¹H‐MR spectroscopy, and estimation of blood ammonia and pro‐inflammatory cytokines (tumor necrosis factor‐α[TNF‐α] and interleukin‐6 [IL‐6]) were done in 20 patients with EHPVO and eight healthy controls. Results: Pro‐inflammatory cytokines (TNF‐α and IL‐6), blood ammonia, brain glutamine, and mean diffusivity were increased in both patient groups, as compared to controls. Patients with MHE (n‐12) had significantly higher TNF‐α, IL‐6, blood ammonia, brain glutamine, and mean diffusivity, signifying brain edema, than controls. A significant, positive correlation was seen between TNF‐α and IL‐6 and between blood ammonia and TNF‐α, IL‐6, and brain glutamine. Significant, positive correlations of TNF‐α, IL‐6, and blood ammonia with mean diffusivity values were seen in various brain regions, including spectroscopy voxel‐derived mean diffusivity. Conclusion: Patients with extrahepatic portal vein obstruction have inflammation and hyperammonemia made evident by higher blood TNF‐α, IL‐6, ammonia, and brain glutamine levels. A significant correlation between hyperammonemia, pro‐inflammatory cytokines, and cerebral edema on DTI in various brain regions suggests that both these factors play a role in the pathogenesis of MHE in these patients.