DTI和fMRI在颅内肿瘤手术中的运用进展

颅内肿瘤手术治疗如何做到在最大程度切除肿瘤病变的同时保存患者更多的神经功能是神经外科医生长期所考虑的一大难题.DTI和fMRI通过将神经纤维束的形态以及大脑功能区的图像上传到神经导航系统,为神经外科手术提供了术前方案制定的良好依据,并对术后患者预后的评估起到了一定作用.现将近年来DTI和fMRI在颅内肿瘤手术中的运用综述如下.     

轻度认知障碍工作记忆的fMRI研究

目的 :运用血氧水平依赖 (bloodoxygenationleveldependent ,BOLD)法功能磁共振成像 (functionalmagneticresonanceimaging ,fMRI)对轻度认知障碍 (mildcognitiveimpairment ,MCI)与正常对照组在记忆的激活区域范围及强度方面进行比较。方法 :对 6例MCI患者 ,8例认知正常老人进行神经心理学测试 ,在 1 5TPick磁共振扫描仪上进行记忆过程中的EPI序列的扫描 ,并运用相关软件分析所得图像及数据。结果 :MCI患者在颞叶激活范围比正常对照组小 ,时间 信号强度变化曲线亦有差异 ,右侧颞叶激活的范围和强度均高于左侧。结论 :MCI患者的记忆功能下降在fMRI上主要表现为颞叶激活范围的变化及激活强度的下降 ,颞叶可能是MCI记忆功能下降反应比较敏感的区域。     

MRS联合DTI评估帕金森病认知障碍的初步研究

目的探讨1~H-磁共振波谱(1~H-MRS)及弥散张量成像(DTI)技术对早期诊断帕金森病(PD)患者认知障碍(PD-CI)患者脑部损害,探讨其在PD-CI的早期诊断及临床病情评估中的价值。方法采用Mo CA量表对14例PD患者及健康对照进行认知功能评定;应用1~H-MRS采集各感兴趣区(ROI)N-乙酰天门冬氨酸(NAA)、胆碱(Cho)及肌酸(Cr)浓度,计算NAA/Cr、Cho/Cr比值。然后对1~H-MRS所选ROI相同区域进行DTI扫描,测定各向异性分数(FA),并进一步分析三者之间及其与Mo CA评分之间的关系。结果 PD组Mo CA量表得分较对照组明显降低(P0.05),认知障碍明显。PD组额叶、颞叶、纹状体NAA/Cr值与对照组相比明显下降(P0.05),而两组黑质NAA/Cr值、各部位Cho/Cr值对比无明显差异。PD组额叶、黑质FA值与对照组相比明显降低(P0.05),而两组颞叶、纹状体FA值对比无明显差异。PD患者额叶、颞叶平均NAA/Cr值与Mo CA量表得分呈正相关(P0.05);额叶平均FA值与Mo CA量表得分呈正相关(P0.05)。PD患者额叶平均NAA/Cr值与FA值呈正相关(P0.05)。结论 1~H-MRS联合DTI扫描能更好地检测出PD认知障碍的患者可能存在的隐匿性损伤;分别从结构和代谢两方面为PD-CI的早期诊断提供客观指标;额叶NAA/Cr、FA值的下降与认知功能下降相关。     

fMRI与DTI联合应用在神经导航下切除运动区附近病变

目的 探讨fMRI与DTI联合应用在大脑皮层运动区附近病变手术中的价值.方法 对18例大脑皮层运动区附近病变的患者,采用组块设计,利用血氧水平依赖性功能磁共振成像(BOLD-fMRI)获得运动区皮层激活,利用磁共振弥散张量成像技术(DTI)获得白质纤维束走行,应用神经导航系统进行影像融合后,术中定位皮层运动区与锥体束,经神经电生理检查验证后,避开功能区在显微镜下切除病变.结果 fMRI确定的功能区与术中电生理检查结果基本一致.12例病变全切,6例大部切除.术后肢体肌力好转或无变化14例,3例出现一过性加重,1例遗留永久性功能损害.结论 在神经导航辅助下fMRI与DTI联合应用可以准确定位大脑皮层运动区和锥体束,提高病变切除程度,减少术后运动功能障碍.     

BOLD-fMRI联合DTI在脑肿瘤临床应用中的研究进展

血氧水平依赖功能磁共振成像(blood oxygenation level dependent functional magnetic resonanceimaging,BOLD-fMRI)是20世纪90年代发展起来的新技术.最先在1991年Belliveau等[1]应用功能磁共振成像(functional magnetic resonance imaging,fMRI)定位初级视觉皮层,此为人类第一次应用fMRI对人脑功能定位.     

弥散张量成像（DTI）在颅脑高级别胶质瘤中的应用初探

目的：初步探讨磁共振弥散张量成像（DTI）在颅脑高级别胶质瘤中的应用价值。方法：收集经手术病理证实高级别胶质瘤13例,均作了常规MRI平扫、增强扫描以及DTI,经计算机后处理获得平均弥散系数图（MD图）及部分各向异性指数图（FA图）,测定肿瘤实质区、囊变坏死区、瘤周水肿区及正常白质区的MD值、FA值,分析比较上述4个区MD值、FA值有无统计学差异。结果：肿瘤实质区、囊变坏死区、瘤周水肿区及正常白质区的MD值分别为0.976±0.171×10^-9mm^2/s、1.92±0.515×10^-9mm^2/s、1.414±0.288×10^-9mm^2/s、0.723±0.0525×10^-9mm^2/s,上述4个区域两两比较均有显著统计学差异（P〈0.01）;肿瘤实质区、囊变坏死区、瘤周水肿区及正常白质区的FA值分别为0.137±0.056、0.0824±0.061、0.148±0.09、0.522±0.073,囊变坏死区、肿瘤实质区、瘤周水肿区与正常白质区比较均有显著统计学差异（P〈0.001）,而囊变坏死区、肿瘤实质区及瘤周水肿区之间均无统计学差异（P〉0.05）。结论：DTIMD值可区分高级别胶质瘤肿瘤实质区、囊变坏死区、瘤周水肿区及正常白质区;FA值可区分肿瘤区与正常白质区,但不易区分肿瘤实质区、囊变坏死区与瘤周水肿区。     

首发抑郁症患者字母工作记忆fMRI研究

目的探讨首发抑郁症患者字母工作记忆的脑激活特征。方法12例首发抑郁症患者与12名健康对照配对进行字母工作记忆任务的功能磁共振成像(fMRI)。以AFNI软件对fMRI数据进行定位与定量分析。结果①两组任务执行正确率均大于75%,患者组字母工作记忆2-back任务正确率低于对照组[(0.79±0.04)%vs(0.83±0.03)%,t=4.69,P<0.05];②两组字母工作记忆激活的感兴趣脑区(ROI)均为左侧Broca区BA44/45、双侧前额叶腹侧BA9/46、顶叶后部BA7/40、前运动区BA6及辅助运动区(SMA)BA6/8(P<0.05);③患者组在右侧与左侧BA9/46、右侧与左侧BA6及左侧Broca区的激活强度分别为:1.38%、1.69%、1.21%、1.32%及0.52%,低于对照组的2.42%、3.53%、2.95%、3.51%及1.62%(P<0.05)。结论首发抑郁症患者存在字母工作记忆损害,而语音环路的双侧BA9/46、BA6与左侧Broca区激活减弱可能为其病理机制之一。     

脑梗死的DTI征像与临床分期的相关性研究

目的 分析脑梗死患者的磁共振弥散张量成像(DTI)表现与临床分期的关系. 方法 选择107例脑梗死患者进行常规MRI和DTI检查,采用旨法分析各向同性表观扩散系数(ADCiso)图和各向异性指数(FA)图上二病变区的信号特点,进行DTI征像的分型并分析其与临床分期的相关性. 结果 29例急性期脑梗死患者中DTI表现为Ⅰ型和Ⅱ型10例,Ⅲ型3例,Ⅳ型6例;34例亚急性期患者中I型2例,Ⅱ型20例,Ⅲ型8例,Ⅳ型4例;44例慢性期患者中DTI表现为Ⅱ型1例,Ⅲ型2例,Ⅳ型41例.脑梗死的DTI表现与临床分期呈正相关关系(r=0.693,P=0.000).结论脑梗死的DTI表现可直观地显示脑梗死的不同病期,为临床提供准确的影像学分期.     

弥漫性轴索损伤后早期磁共振弥散张量成像与工作记忆障碍的相关性研究

目的探讨磁共振弥散张量成像(DTI)对弥漫性轴索损伤(DAI)导致工作记忆障碍早期诊断及预后评估的价值。方法分别对10例DAI患者(DAI组)和10例健康志愿者(正常对照组)行DTI检查,并对两组DTI图像的钩束、皮质脊髓束、胼胝体和扣带回感兴趣区的部分各向异性(FA)值进行比较分析。DAI后6个月对患者与健康志愿者行认知量表评估,并行对比分析;另外将DAI组FA值与其认知量表评分行直线相关分析。结果与对照组相比,DAI患者4个感兴趣区的FA值显著降低(P<0.05),恢复期总体认知能力略降低,但无统计学意义(P>0.05),而工作记忆功能却显著降低(P<0.05)。DAI患者中的钩束和皮质脊髓束的FA值与工作记忆功能呈正相关(r分别为0.898和0.797,P<0.05);胼胝体和扣带回FA值与工作记忆功能无明显相关性(r分别为0.432和0.387,P>0.05)。结论 DTI技术可为DAI导致的工作记忆障碍早期诊断和预后评估提供依据。     

应用 DWI 和 DTI 勾画高级别胶质瘤术后放疗靶区的初步研究

目的：初步探讨MRI弥散加权成像（DWI）和弥散张量成像（DTI）在高级别胶质瘤（HGG）术后放疗靶区勾画中的应用价值。方法对复旦大学附属华山医院上海伽玛医院收治的 HGG术后残留患者做前瞻性研究。所有患者放疗前行DWI和DTI检查,在ADC图和FA图上分别测量残留肿瘤、肿瘤外1 cm区域内（定义为近瘤周区）、1～2 cm区域内（定义为中瘤周区）、2～3 cm区域内（定义为远瘤周区）及3～4 cm区域内（定义为瘤周区外）和对侧正常脑组织的ADC平均值、ADC最小值、FA平均值和FA最小值。结果2013年9月至2014年8月,共有55例HGG患者入组,ADC平均值和最小值呈现从残留肿瘤、近瘤周区到中瘤周区逐渐升高的趋势,并从中瘤周区、远瘤周区到瘤周区外逐渐降低;其中,残留肿瘤与近瘤周区,以及中瘤周区与远瘤周区、远瘤周区与瘤周区外比较,差异均有统计学意义（均P＜0．05）; FA平均值和最小值呈现从残留肿瘤、近瘤周区、中瘤周区、远瘤周区到瘤周区外逐渐升高的趋势,但各区差别无统计学意义（均P＞0．05）。结论本研究初步显示DWI技术可能有助于术后HGG及肿瘤周边组织性质的确定,指导HGG术后放疗靶区的勾画;FA值对于靶区勾画的价值有待进一步研究。     

Cortical activation during retrieval of arithmetical facts and actual calculation: a functional magnetic resonance imaging study

By using functional magnetic resonance imaging (fMRI), the neural substrates involved in mental recitation of the single-digit multiplication table and serial subtraction were studied. The former depends mostly on well-learned arithmetical facts, while the latter requires arithmetic processing. Activation during each task was compared with that in a number counting control. During the recitation of single-digit multiplication, the activated regions included the area lying along the left intraparietal sulcus, the premotor and supplementary motor areas, and the posterior portion of the left inferior frontal gyrus. The areas activated during serial subtraction included these areas as well as the bilateral prefrontal and right parietal areas. From the results obtained during retrieval of the multiplication table in this study and previous studies, it was concluded that semantic memory of the multiplication table is stored in the area lying along the intraparietal sulcus and that the frontal areas play an executive role in utilizing the semantic memory of arithmetical facts. It was assumed that the arithmetical facts requiring actual calculation are also stored in the same region. The additional activation during serial subtraction compared with the activation during retrieval of the multiplication table is probably due to the processes of actual calculation. These processes include proper alignment of digits, which may have caused the right parietal activation, and maintaining digits needed for the mental serial subtractions, which may have caused the bilateral prefrontal activation.     

Decoding Concurrent Representations of Pitch and Location in Auditory Working Memory

Multivariate analyses of hemodynamic signals serve to identify the storage of specific stimulus contents in working memory (WM). Representations of visual stimuli have been demonstrated both in sensory regions and in higher cortical areas. While previous research has typically focused on the WM maintenance of a single content feature, it remains unclear whether two separate features of a single object can be decoded concurrently. Also, much less evidence exists for representations of auditory compared with visual stimulus features. To address these issues, human participants had to memorize both pitch and perceived location of one of two sample sounds. After a delay phase, they were asked to reproduce either pitch or location. At recall, both features showed comparable levels of discriminability. Region of interest (ROI)-based decoding of functional magnetic resonance imaging (fMRI) data during the delay phase revealed feature-selective activity for both pitch and location of a memorized sound in auditory cortex and superior parietal lobule. The latter region showed higher decoding accuracy for location than pitch. In addition, location could be decoded from angular and supramarginal gyrus and both superior and inferior frontal gyrus. The latter region also showed a trend for decoding of pitch. We found no region exclusively coding pitch memory information. In summary, the present study yielded evidence for concurrent representations of pitch and location of a single object both in sensory cortex and in hierarchically higher regions, pointing toward representation formats that enable feature integration within the same anatomic brain regions.SIGNIFICANCE STATEMENT Decoding of hemodynamic signals serves to identify brain regions involved in the storage of stimulus-specific information in working memory (WM). While to-be-remembered information typically consists of several features, most previous investigations have focused on the maintenance of one memorized feature belonging to one visual object. The present study assessed the concurrent storage of two features of the same object in auditory WM. We found that both pitch and location of memorized sounds were decodable both in early sensory areas, in higher-level superior parietal cortex and, to a lesser extent, in inferior frontal cortex. While auditory cortex is known to process different features in parallel, their concurrent representation in parietal regions may support the integration of object features in WM.     

Involvement of the human frontal eye field and multiple parietal areas in covert visual selection during conjunction search

Searching for a target object in a cluttered visual scene requires active visual attention if the target differs from distractors not by elementary visual features but rather by a feature conjunction. We used functional magnetic resonance imaging (fMRI) in human subjects to investigate the functional neuroanatomy of attentional mechanisms employed during conjunction search. In the experimental condition, subjects searched for a target defined by a conjunction of colour and orientation. In the baseline condition, subjects searched for a uniquely coloured target, regardless of its orientation. Eye movement recordings outside the scanner verified subjects' ability to maintain fixation during search. Reaction times indicated that the experimental condition was attentionally more demanding than the baseline condition. Differential activations between conditions were therefore ascribed to top-down modulation of neural activity. The frontal eye field, the ventral precentral sulcus and the following posterior parietal regions were consistently activated: (i) the postcentral sulcus; (ii) the posterior; and (iii) the anterior part of the intraparietal sulcus; and (iv) the junction of the intraparietal with the transverse occipital sulcus. Parietal regions were spatially distinct and displayed differential amplitudes of signal increase with a maximal amplitude in the posterior intraparietal sulcus. Less consistent activation was found in the lateral fusiform gyrus. These results suggest an involvement of the human frontal eye field in covert visual selection of potential targets during search. These results also provide evidence for a subdivision of posterior parietal cortex in multiple areas participating in covert visual selection, with a major contribution of the posterior intraparietal sulcus.     

Changes in Effective Connectivity According to Working Memory Load: An fMRI Study of Face and Location Working Memory Tasks

Objective

The functional strategic mechanisms in the brain during performing visuospatial working memory tasks, especially tasks with heavy load, are controversial. We conducted the functional magnetic resonance imaging (fMRI) while sixteen subjects were performing face- and location-matching n-back tasks to examine causal relations within the frontoparietal networks.

Methods

We applied a sophisticated method, the structural equation modeling (SEM), to the fMRI data. The imaging data were analyzed by extracting the task-related eigenseries using the principal component analysis (PCA) and then by applying a form of data-driven model called the automated search method.

Results

The SEM analyses revealed a functional shift of network connectivity from the right to the left hemisphere with increasing load in the face-matching n-back tasks while the location-matching tasks required bilateral activation. In the locating matching n-back tasks, a pattern of parallel processing was observed in the left phonological loop and the right inferior parietal regions. Furthermore, object working memory-related activities in the left hemisphere reliably contributed to performance of both the face- and location-matching 2-back tasks.

Conclusion

Our results are consistent with previous reports in terms of demonstrating parallel and distributed information processing during performing working memory tasks with heavy loads. Our results additionally suggest a dynamic shift between the fast imagery circuit (right hemisphere) and the stable verbal circuit (left hemisphere), depending on task load.     

A systematic fMRI investigation of the brain systems subserving different working memory components in schizophrenia

Working memory impairment is one of the cardinal cognitive disturbances in schizophrenia and considerable evidence suggests that it can be traced to functional alterations in the brain. The exact allocation of specific deficits to regional specific dysfunctions, however, remains elusive. The aim of this study was to examine the functional integrity of three distinguishable brain systems underlying maintenance-related subprocesses of working memory (articulatory rehearsal, non-articulatory maintenance of phonological information, maintenance of visuospatial information) in patients with schizophrenia. Using an experimental paradigm, which had been designed to selectively activate these different brain systems, we assessed the brain activation of patients and controls with functional magnetic resonance imaging. Compared with controls, patients showed reduced activation of the fronto-opercular, intraparietal and anterior cingulate cortex during the non-articulatory maintenance of phonological information, as well as attenuated deactivation of the hippocampus. Additionally, we found prefrontal activation to depend critically on the patients' current symptom status. During visuospatial maintenance, patients showed impaired activation of the superior parietal, temporal and occipital cortex, combined with enhanced activation of the frontal eye field and the inferior parietal cortex. No abnormal activations were observed during the articulatory rehearsal task. All activation differences were independent of group differences in task performance. Our fine-grained analysis of dysfunctions in particular aspects of working memory circuitry provides evidence for a differential impairment of the brain systems supporting working memory subcomponents in schizophrenia and extends knowledge of the relationship between cognitive deficits, brain activation abnormalities and symptoms in schizophrenia.     

Effects of overnight fasting on working memory‐related brain network: An fMRI study

Glucose metabolism serves as the central source of energy for the human brain. Little is known about the effects of blood glucose level (BGL) on higher‐order cognitive functions within a physiological range (e.g., after overnight fasting). In this randomized, placebo‐controlled, double blind study, we assessed the impact of overnight fasting (14h) on brain activation during a working memory task. We sought to mimic BGLs that occur naturally in healthy humans after overnight fasting. After standardized periods of food restriction, 40 (20 male) healthy participants were randomly assigned to receive either glucagon to balance the BGL or placebo (NaCl). A parametric fMRI paradigm, including 2‐back and 0‐back tasks, was used. Subclinically low BGL following overnight fasting was found to be linked to reduced involvement of the bilateral dorsal midline thalamus and the bilateral basal ganglia, suggesting high sensitivity of those regions to minimal changes in BGLs. Our results indicate that overnight fasting leads to physiologically low levels of glucose, impacting brain activation during working memory tasks even when there are no differences in cognitive performance. Hum Brain Mapp 36:839–851, 2015. © 2014 Wiley Periodicals, Inc.     

Multi‐target attention and visual short‐term memory capacity are closely linked in the intraparietal sulcus

The existing literature suggests a critical role for both the right intraparietal sulcus (IPS) and the right temporo‐parietal junction (TPJ) in our ability to attend to multiple simultaneously‐presented lateralized targets (multi‐target attention), and the failure of this ability in extinction patients. Currently, however, the precise role of each of these areas in multi‐target attention is unclear. In this study, we combined the theory of visual attention (TVA) with functional magnetic resonance imaging (fMRI) guided continuous theta burst stimulation (cTBS) in neurologically healthy subjects to directly investigate the role of the right IPS and TPJ in multi‐target attention. Our results show that cTBS at an area of the right IPS associated with multi‐target attention elicits a reduction of visual short‐term memory capacity. This suggests that the right IPS is associated with a general capacity‐limited encoding mechanism that is engaged regardless of whether targets have to be attended or remembered. Curiously, however, cTBS to the right IPS failed to elicit extinction‐like behavior in our study, supporting previous suggestions that different areas of the right IPS may provide different contributions to multi‐target attention. CTBS to the right TPJ failed to induce a change in either TVA parameters or extinction‐like behavior.