Role of the corpus callosum in functional connectivity

BACKGROUND AND PURPOSE: Regional cerebral blood flow fluctuates synchronously in corresponding brain regions between the hemispheres. This synchrony implies neuronal connections between brain regions. The synchrony of blood flow changes is defined operationally as functional connectivity. Our purpose was to measure functional connectivity in patients with corpus callosal agenesis, in whom the interhemispheric connectivity is hypothetically diminished. METHODS: In three patients with agenesis of the corpus callosum, functional MR imaging was performed while patients performed text-listening and finger-tapping tasks. Functional images were also acquired while the patients performed no specific task (resting state). Regions of activation temporally correlated with the performance of the tasks were identified by cross-correlating the task data with a reference function. Voxel clusters (seed voxels) that corresponded to regions of activation in the task-activation data set were selected in the resting data set. All the voxels in the resting 3D data set that had a correlation coefficient exceeding 0.4 were identified. The number of these voxels in the ipsilateral and contralateral hemispheres was tabulated. RESULTS: In all patients, technically adequate functional MR and functional connectivity MR maps were obtained. For both tasks, activation was found in both hemispheres. For all of the seed voxels, significantly more functionally connected voxels were found in the ipsilateral hemisphere than in the contralateral hemisphere. For most seed voxels, no functionally connected voxels were found in the contralateral hemisphere. CONCLUSION: Interhemispheric functional connectivity in the motor and auditory cortices is diminished in patients with agenesis of the corpus callosum compared with that of healthy subjects.     

Mapping functionally related regions of brain with functional connectivity MR imaging

BACKGROUND AND PURPOSE: In subjects who are performing no prescribed cognitive task, functional connectivity mapped with MR imaging (fcMRI) shows regions with synchronous fluctuations of cerebral blood flow. When specific tasks are performed, functional MR imaging (fMRI) can map locations in which regional cerebral blood flow increases synchronously with the performance of the task. We tested the hypothesis that fcMRI maps, based on the synchrony of low-frequency blood flow fluctuations, identify brain regions that show activation on fMRI maps of sensorimotor, visual, language, and auditory tasks. METHODS: In four volunteers, task-activation fMRI and functional connectivity (resting-state) fcMRI data were acquired. A small region of interest (in an area that showed maximal task activation) was chosen, and the correlation coefficient of the corresponding resting-state signal with the signal of all other voxels in the resting data set was calculated. The correlation coefficient was decomposed into frequency components and its distribution determined for each fcMRI map. The fcMRI maps were compared with the fMRI maps. RESULTS: For each task, fcMRI maps based on one to four seed voxel(s) produced clusters of voxels in regions of eloquent cortex. For each fMRI map a closely corresponding fcMRI map was obtained. The frequencies that predominated in the cross-correlation coefficients for the functionally related regions were below 0.1 Hz. CONCLUSION: Functionally related brain regions can be identified by means of their synchronous slow fluctuations in signal intensity. Such blood flow synchrony can be detected in sensorimotor areas, expressive and receptive language regions, and the visual cortex by fcMRI. Regions identified by the slow synchronous fluctuations are similar to those activated by motor, language, or visual tasks.     

Frequencies contributing to functional connectivity in the cerebral cortex in "resting-state" data

BACKGROUND AND PURPOSE: In subjects performing no specific cognitive task ("resting state"), time courses of voxels within functionally connected regions of the brain have high cross-correlation coefficients ("functional connectivity"). The purpose of this study was to measure the contributions of low frequencies and physiological noise to cross-correlation maps. METHODS: In four healthy volunteers, task-activation functional MR imaging and resting-state data were acquired. We obtained four contiguous slice locations in the "resting state" with a high sampling rate. Regions of interest consisting of four contiguous voxels were selected. The correlation coefficient for the averaged time course and every other voxel in the four slices was calculated and separated into its component frequency contributions. We calculated the relative amounts of the spectrum that were in the low-frequency (0 to 0.1 Hz), the respiratory-frequency (0.1 to 0.5 Hz), and cardiac-frequency range (0.6 to 1.2 Hz). RESULTS: For each volunteer, resting-state maps that resembled task-activation maps were obtained. For the auditory and visual cortices, the correlation coefficient depended almost exclusively on low frequencies (<0.1 Hz). For all cortical regions studied, low-frequency fluctuations contributed more than 90% of the correlation coefficient. Physiological (respiratory and cardiac) noise sources contributed less than 10% to any functional connectivity MR imaging map. In blood vessels and cerebrospinal fluid, physiological noise contributed more to the correlation coefficient. CONCLUSION: Functional connectivity in the auditory, visual, and sensorimotor cortices is characterized predominantly by frequencies slower than those in the cardiac and respiratory cycles. In functionally connected regions, these low frequencies are characterized by a high degree of temporal coherence.     

Effect of focal and nonfocal cerebral lesions on functional connectivity studied with MR imaging

BACKGROUND AND PURPOSE: Functional connectivity MR (fcMR) imaging is used to map regions of brain with synchronous, regional, slow fluctuations in cerebral blood flow. We tested the hypothesis that focal cerebral lesions do not eradicate expected functional connectivity. METHODS: Functional MR (fMR) and fcMR maps were acquired for 12 patients with focal cerebral tumors, cysts, arteriovenous malformations, or in one case, agenesis of the corpus callosum. Task activation secondary to text listening, finger tapping, and word generation was mapped by use of fMR imaging. Functional connectivity was measured by selecting "seed" voxels in brain regions showing activation (based on the fMR data) and cross correlating with every other voxel (based on data acquired while the subject performed no task). Concurrence of the fMR and fcMR maps was measured by comparing the location and number of voxels selected by both methods. RESULTS: Technically adequate fMR and fcMR maps were obtained for all patients. In patients with focal lesions, the fMR and fcMR maps correlated closely. The fcMR map generated for the patient with agenesis of the corpus callosum failed to reveal functional connectivity between blood flow in the left and right sensorimotor cortices and in the frontal lobe language regions. Nonetheless, synchrony between blood flow in the auditory cortices was preserved. On average, there was 40% concurrence between all fMR and fcMR maps. CONCLUSION: Patterns of functional connectivity remain intact in patients with focal cerebral lesions. Disruption of major neuronal networks, such as agenesis of the corpus callosum, may diminish the normal functional connectivity patterns. Therefore, functional connectivity in such patients cannot be fully demonstrated with fcMR imaging.     

Changes in cerebellar functional connectivity and anatomical connectivity in schizophrenia: a combined resting-state functional MRI and diffusion tensor imaging study

Purpose:

To examine the functional and anatomical connectivity of the cerebellum and their relationship in schizophrenia through resting‐state functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI).

Materials and Methods:

Ten subjects with schizophrenia and 10 healthy controls underwent resting‐state fMRI and DTI. Left and right cerebellar seed regions were used in a voxel‐wise functional connectivity analysis of the cerebellum. Fractional anisotropy (FA) was measured to assess white matter integrity of the middle cerebellar peduncle (MCP) and superior cerebellar peduncle (SCP). Differences in functional connectivity and FA values between the two groups were determined by two‐sample t‐tests. The relationship between functional connectivity and FA values in both groups were assessed using Pearson s correlation.

Results:

Decreased functional connectivity to the left middle temporal gyrus, bilateral middle cingulate cortex, right paracentral lobule, right thalamus, and bilateral cerebellum were found in subjects with schizophrenia when compared to healthy controls; while decreased FA values in the left SCP were found in subjects with schizophrenia compared to healthy controls. Significant correlation was observed between the functional connectivity of the left cerebellum‐right paracentral lobule and right cerebellum‐right thalamus and the FA values of the MCP in healthy controls.

Conclusion:

Findings of this multi‐modal imaging study support functional and anatomical connectivity abnormalities and the role of the cerebellum in schizophrenia. They also indicate the need for further investigation regarding the relationship between functional and anatomical connectivity and its role in neuropathophysiology. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Metabolic connectivity by interregional correlation analysis using statistical parametric mapping (SPM) and FDG brain PET; methodological development and patterns of metabolic connectivity in adults

Purpose  Regionally connected areas of the resting brain can be detected by fluorodeoxyglucose-positron emission tomography (FDG-PET). Voxel-wise metabolic connectivity was examined, and normative data were established by performing interregional correlation analysis on statistical parametric mapping of FDG-PET data. Materials and methods  Characteristics of seed volumes of interest (VOIs) as functional brain units were represented by their locations, sizes, and the independent methods of their determination. Seed brain areas were identified as population-based gyral VOIs (n = 70) or as population-based cytoarchitectonic Brodmann areas (BA; n = 28). FDG uptakes in these areas were used as independent variables in a general linear model to search for voxels correlated with average seed VOI counts. Positive correlations were searched in entire brain areas. Results  In normal adults, one third of gyral VOIs yielded correlations that were confined to themselves, but in the others, correlated voxels extended to adjacent areas and/or contralateral homologous regions. In tens of these latter areas with extensive connectivity, correlated voxels were found across midline, and asymmetry was observed in the patterns of connectivity of left and right homologous seed VOIs. Most of the available BAs yielded correlations reaching contralateral homologous regions and/or neighboring areas. Extents of metabolic connectivity were not found to be related to seed VOI size or to the methods used to define seed VOIs. Conclusions  These findings indicate that patterns of metabolic connectivity of functional brain units depend on their regional locations. We propose that interregional correlation analysis of FDG-PET data offers a means of examining voxel-wise regional metabolic connectivity of the resting human brain. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Parkinson disease: pattern of functional MR imaging activation during deep brain stimulation of subthalamic nucleus--initial experience

PURPOSE: To prospectively determine the pattern of functional magnetic resonance (MR) imaging activation at 3 T produced by deep brain stimulation (DBS) of subthalamic nucleus (STN) for treatment of Parkinson disease and to determine the safety of DBS electrode stimulation during functional MR imaging at 3 T. MATERIALS AND METHODS: Informed consent was obtained from all subjects participating in the study, and the study protocol was approved by the institutional review board at the Cleveland Clinic Foundation and was HIPAA compliant. After extensive phantom safety testing of DBS lead systems, five patients (three men, two women; mean age, 49.4 years +/- 14.5 [standard deviation]; range, 31-74 years) with percutaneously extended bilateral DBS electrodes placed in the STN for treatment of Parkinson disease were examined at 3 T on the 1st or 2nd postoperative day. Imaging consisted of a three-dimensional anatomic data set with leads disconnected and a blood oxygen level-dependent functional MR image with a single lead connected to the external pulse generator in the MR imaging control room by using stimulation parameters previously determined to produce optimal stimulation for alleviation of symptoms. A total of nine leads were tested with the functional MR imaging protocol. Subjects underwent neurologic examination immediately before and after MR imaging. RESULTS: All five patients completed the study without change in their neurologic examination and with activation seen in eight of nine electrodes stimulated. Activation was seen in the ipsilateral basal ganglia in all subjects and ipsilateral thalamus in six of the electrodes tested. Two of the electrode stimulations demonstrated additional activation in the STN and/or substantia nigra region adjacent to the electrode tip. For three electrode stimulations, activation was seen in the contralateral superior cerebellum. CONCLUSION: Therapeutically effective DBS of STN can be performed safely during functional MR imaging at 3 T and produces a consistent pattern of ipsilateral activation of deep brain motor structures.     

Proton magnetic resonance spectroscopy of mesial temporal sclerosis: Analysis of voxel shape and position to improve diagnostic accuracy

OBJECTIVE: To determine if change in voxel shape and position improves the lateralization of magnetic resonance (MR) spectroscopy to the side of the MR imaging and/or electroencephalography (EEG) abnormality in mesial temporal sclerosis. METHODS: In 10 patients with unilateral mesial temporal sclerosis and 5 controls, MR spectroscopy was performed. Long echo time single-voxel spectroscopy was obtained in the right and left hippocampus. First, the standard 2-cm x 2-cm x 2-cm cubic voxels were placed bilaterally. Then, 1-cm x 2-cm x 4-cm rectangular voxels were used. With this rectangular voxel shape, more of the hippocampus and less of the adjacent medial temporal lobe were included in the interrogation voxel. N-acetylaspartate-to-creatine (NAA/Cr) ratios and choline-to-creatine (Cho/Cr) ratios were obtained. The difference between the affected and unaffected sides in the patients was calculated and compared with the controls. Additionally, the mean difference and standard deviation were determined. Predictive values and Student t tests were also performed. RESULTS: In all 10 patients, using the NAA/Cr ratios, the rectangular voxel correctly identified the abnormal side. The cubic voxel only identified the abnormal side in 6 of the 10 patients, however. Additionally, the mean difference between the affected and unaffected sides was 0.30 for the rectangular voxel but only 0.003 for the cubic voxel; that is, there was no overall significant difference when using the cubic voxel (P = 0.007). No significant correlation between the affected and unaffected sides was found using the Cho/Cr ratios. No significant difference between the right and left sides was found in the controls. CONCLUSION: Use of a 1-cm x 2-cm x 4-cm rectangular voxel places more of the hippocampus in the region of interrogation with less partial volume artifact from the adjacent brain parenchyma, which occurs with use of the standard 2-cm x 2-cm x 2-cm cubic voxel, resulting in improved correct lateralization of MR spectroscopy to the side of the MR imaging and/or EEG abnormality.     

正常人丘脑及岛盖功能连接的MRI研究

目的:探讨正常人在静息和认知任务状态下丘脑及岛盖功能连接的变化情况。方法:采用BOLD-fMRI方法,检测16例健康志愿者在静息和2-back任务状态下的脑功能连接,将前额叶内侧皮层作为种子点,应用SPM2、AFNI及Matlab软件进行图像数据处理,对2-back任务和静息状态行组内和组间2个水平的统计分析,统计阈值概率设定为P=0.005(未校正)。结果:与左侧丘脑前核相关的网络系统与默认网络一致,而丘脑背侧部属"任务正激活网络",且受试者反应正确率与左侧丘脑背侧的相关性差异有统计学意义(r=-0.52,P=0.04)。"岛盖相关网络"与"默认网络"呈负相关,前者在静息状态相关性高于任务状态,其主要脑区包括双岛叶、双顶下小叶、双中央旁小叶、双颞上回、双海马旁回等。结论:人脑在静息和任务状态下脑区间的功能连接不同,表现为丘脑前核和丘脑背侧部的功能分化,及"岛盖相关网络"与"默认网络"在静息状态的功能拮抗。     

Changes in fiber integrity, diffusivity, and metabolism of the pyramidal tract adjacent to gliomas: a quantitative diffusion tensor fiber tracking and MR spectroscopic imaging study

BACKGROUND AND PURPOSE: The underlying changes in the neuronal connectivity adjacent to brain tumors cannot always be depicted by conventional MR imaging. The hypothesis of this study was that preoperative sensorimotor deficits are associated with impairment in pyramidal fiber bundles. Hence, we investigated the potential of combined quantitative diffusion tensor (DT) fiber tracking and MR spectroscopic imaging (MRSI) to determine changes in the pyramidal tract adjacent to gliomas. MATERIALS AND METHODS: Quantitative DT fiber tracking and proton MRSI were performed in 20 patients with gliomas with WHO grades II-IV. Eight patients experienced preoperative sensorimotor deficits. Mean diffusivity (MD), fractional anisotropy (FA), and number of fibers per voxel (FpV) were calculated for the pyramidal tract of the ipsilateral and contralateral hemisphere. Metabolite concentrations for choline-containing compounds (Cho), creatine (Cr), and N-acetylaspartate (NAA) were computed, using LCModel, for all voxels located at the pyramidal tracts. RESULTS: For the whole pyramidal tract, quantitative DT fiber tracking resulted in significantly lower FpV and FA values (P < .001), but not MD values, for the ipsilateral hemisphere. For the section of the fiber bundle closest to the lesion, we found significantly decreased FpV and FA (P < .001) and increased MD (P = .002). MRSI showed, for the same volumes of interest, significantly decreased NAA (P = .001), increased Cho (P = .034) and Cho/NAA (P = .001) for the ipsilateral pyramidal tract. In patients suffering sensorimotor deficits, we found significantly lower FA (P = .022) and higher MD values (P = .026) and a strongly negative correlation between FA and MD (R = -0.710, P = .024) but no correlation in patients without deficits (R = 0.078, ns). CONCLUSION: Quantitative DTI was able to show significant differences in diffusivity of the pyramidal tract in patients with sensorimotor deficits in relation to patients without them. The additional use of proton MRSI may be helpful to discern whether these diffusivity changes in fiber tracts are caused by tumor infiltration or peritumoral edema.     

Optimized activation of the primary sensorimotor cortex for clinical functional MR imaging

BACKGROUND AND PURPOSE: One application of functional MR imaging is to identify the primary sensorimotor cortex (M1 and S1) around the central sulcus before brain surgery. However, it has been shown that undesirable coactivation of nonprimary motor areas, such as the supplementary motor area and the premotor area, can interfere with the identification of the primary motor cortex, especially in patients with distorted anatomic landmarks. We therefore sought to design a simple functional MR imaging paradigm for selective activation of the primary sensorimotor cortex. METHODS: Different paradigms using finger tapping for motor activation were examined and compared with respect to the distribution of activated voxels in primary and nonprimary cortical areas. Studies were conducted in 14 healthy volunteers using a blood oxygen level-dependent multislice echo-planar imaging sequence. RESULTS: The most selective activation of the primary sensorimotor cortex was obtained with a paradigm combining right-sided finger tapping as the activation condition with left-sided finger tapping as the control condition. Analysis of the signal time course of primary and nonprimary areas revealed that the highly selective primary motor activation was due to it being restricted to contralateral finger movements, as opposed to the nonprimary motor areas, which were activated by ipsilateral, contralateral, and bilateral finger movements alike. CONCLUSION: When performing functional MR imaging to determine the location of the primary sensorimotor cortex, one should compare unilateral voluntary movements as the activation condition with contralateral movements as the control condition to accentuate activation of the primary motor area and to suppress undesirable coactivation of nonprimary motor areas.     

静息状态下帕金森病患者脑部功能连接的MR研究

目的 探讨帕金森病患者在静息状态下脑部功能连接情况.方法 选取9例Ⅱ～Ⅲ级原发性帕金森病患者及8名年龄分布相同的健康志愿者在静息状态下进行MR扫描,选择双侧苍白球作为种子点,分析其脑部功能连接情况,并采用两样本t检验与健康对照组相比较.结果 正常健康对照组中,双侧颞极、双侧海马、双侧丘脑、扣带回后部、右侧枕中区、右侧顶上回等部位存在着功能连接.帕金森病患者的双侧小脑半球、左侧海马、双侧颞上回、后扣带同、左侧额下回、左侧额中回、左侧中央前回、左侧顶下回、左侧顶上回等部位存在功能联系,与对照纽相比,帕金森病患者的双侧小脑、双侧颞叶、左侧额叶、左侧运动前区、左侧顶叶等部位存在着功能连接增强,双侧丘脑的功能连接减弱.结论静息状态下,帕金森病脑部存在着功能连接异常现象.     

正常人工作记忆任务和静息状态下前额叶皮层内侧面的功能连接分析

目的 分析在工作记忆任务和静息两种状态下与前额叶皮层内侧面(MPFC)正、负相关脑区的分布,比较两种状态下MPFC功能连接的差异.资料与方法 采用GE 1.5 T MR扫描仪对25名正常自愿者行静息态及2-back工作记忆任务的功能磁共振成像(fMRI)实验,2-back实验采用组块设计,0-back作为对照,6个对照组块与5个任务组块交替进行.静息态全脑采集128个时相.采用SPM、AFNI对数据进行预处理.选择MPFC作为种子点与全脑其他像素进行Pearson相关分析,建立相关图.组内分析时采用随机效应模型单样本t检验,检测与MPFC明显正相关或负相关的脑区.组间分析采用配对样本t检验.检测MPFC功能连接图在2-back任务和静息状态下的差异.结果 两种状态下与MPFC正相关的脑区基本一致,属于"任务负激活网络".2-back任务状态下与MPFC负相关的脑区与"任务正激活网络"一致.静息状态下与MPFC负相关的脑区主要分布在双侧岛叶、双侧顶下小叶,且这些区域的负相关性明显高于任务状态.任务状态下负相关性高于静息状态的主要脑区包括双侧运动前区外侧(LPMA)、双侧顶叶后部(PPC)、左侧丘脑及右侧小脑半球.结论 静息及2-back任务状态下MPFC的功能连接情况不同,对于正常人在静息及任务状态下的功能连接对比研究为临床精神疾病患者的研究奠定了基础.     

MR单体素波谱和化学位移成像在颞叶癫痫中的研究

目的　应用MR氢质子波谱 (1HMRS)不同成像方法 ,包括单体素波谱 (SVS)、化学位移成像 (CSI) ,探讨1HMRS对颞叶癫痫 (TLE)的诊断价值。方法　设对照组 4 0例、颞叶癫痫组 (TLE) 2 0例。应用1HMRS分别进行海马结构 (HF)的SVS和CSI,应用SVS比较TLE患侧组、对侧组及对照组各代谢物比值 ,并行致痫灶定侧诊断。应用CSI分析TLE患侧组、对侧组及对照组HF从前到后各体素氮 乙酰天门冬氨酸 / (胆碱 肌酸复合物 ) [NAA/ (Cho Cr) ]的变化规律 ,并进行三组间、各体素间两两比较。结果　SVS示TLE组患侧组HF的NAA/ (Cho Cr) (0 4 8± 0 10 )、NAA/Cr(1 2 0± 0 19)下降 ,与对照组、对侧组 (分别为 0 71± 0 0 7、1 4 8± 0 16 ;0 6 1± 0 12、1 4 4± 0 2 3)差异有显著性意义 (F值分别为 4 1 95 8、15 5 75 ,P值 <0 0 0 0 1)。SVS对TLE定侧敏感度为 85 % ,特异度为 93%。CSI示对照组、TLE患侧、对侧组HF的NAA/ (Cho Cr)与HF部位间呈直线相关关系 ,后部较前部大 ;与正常组比较 ,患侧组前部NAA/ (Cho Cr)的降低程度较后部大。结论　SVS可帮助TLE致痫灶定侧。CSI显示HF从前到后存在NAA/ (Cho Cr)渐变现象 ,TLE患侧头部代谢改变较尾部大。在比较代谢改变时 ,保证定位于HF的相同部位很重要。     

Hippocampal structures: anteroposterior N-acetylaspartate differences in patients with epilepsy and control subjects as shown with proton MR spectroscopic imaging

PURPOSE: To determine the distribution of proton metabolites along the long axis of the hippocampus. MATERIALS AND METHODS: Proton magnetic resonance (MR) spectroscopic imaging measurements were performed in the hippocampi of 14 control subjects and nine patients with unilateral mesial temporal lobe epilepsy. RESULTS: Control subjects showed significantly lower ratios of N-acetylaspartate (NAA) to choline-containing compounds (Ch) and creatine plus phosphocreatine (CR) (NAA/[Cr + Ch]) in the anterior as compared with the posterior part of the hippocampus. Furthermore, a similar anteroposterior (AP) difference in NAA/(Cr + Ch) values was found in both ipsilateral and contralateral hippocampi of patients. In the patients compared with the control subjects, ipsilateral NAA/(Cr + Ch) levels were reduced in every part of hippocampal tissue with an average reduction of 17%, and contralateral NAA/(Cr + Ch) was reduced by about 10%. In the patients compared with the control subjects, the proportional reduction in ipsilateral NAA/(Cr + Ch) was greatest in voxels from anterior hippocampal regions. CONCLUSION: AP differences could be a result of fewer neurons in the anterior compared with the posterior hippocampus or of the increasing thickness of the hippocampus from posterior to anterior, which leads to different contributions from adjacent tissue. Measurements of T2 showed that T2 differences are probably not responsible for these changes.     

Evidence of neuronal injury outside the medial temporal lobe in temporal lobe epilepsy: N-acetylaspartate concentration reductions detected with multisection proton MR spectroscopic imaging--initial experience

PURPOSE: To determine whether magnetic resonance (MR) spectroscopic imaging reveals metabolic changes, especially decreased N-acetylaspartate (NAA) concentrations outside the medial temporal lobe in patients with mesial temporal lobe epilepsy (TLE), consistent with neuropathologic findings of extratemporal neuronal impairment. MATERIALS AND METHODS: Eleven patients with mesial TLE and 13 control subjects were examined with multisection MR spectroscopic imaging. Three MR spectroscopic imaging sections were acquired. Thirteen brain regions in each hemisphere and the midbrain were analyzed in each patient, and the NAA to creatine-phosphocreatine (Cr) plus choline-containing compounds (Ch) (NAA/[Cr + Ch]) ratios were determined. In addition, hemispheric and whole-brain values were calculated and statistically analyzed. RESULTS: The NAA/(Cr + Ch) ratio in the ipsilateral hippocampus was significantly reduced, compared with that in the contralateral hippocampus (P <.002) and compared with that in control subjects (P <.03), confirming findings in previous studies. In patients, whole-brain NAA/(Cr + Ch) ratio outside the hippocampus was significantly lower than that in control subjects (P <.002). For the ipsilateral hemisphere in patients, NAA/(Cr + Ch) ratio was significantly lower than that in control subjects (P <.0002). Comparisons between individual brain regions revealed trends toward lower NAA/(Cr + Ch) ratios in many areas of the ipsilateral and, to a lesser extent, the contralateral hemisphere outside the hippocampus and temporal lobe, suggesting diffuse impairment. CONCLUSION: Results suggest that repeated seizure activity damages neurons outside of the seizure focus.     

原发全面强直阵挛癫痫功能连接密度图研究

目的 采用静息态fMRI（rs-fMRI）功能连接密度图（functional connectivity density,FCD）方法观察全面强直阵挛癫痫（GTCS）发作间期脑网络水平的改变.方法 对40例GTCS患者（GTCS组）与40名性别、年龄相匹配的健康人（正常对照组）.采用3.0T超导MR仪采集rs-fMRI数据,计算并对比GTCS组相比正常对照组FCD改变的脑区,观察FCD改变的脑区与患者发作频率的相关性.结果 与正常对照组相比,GTCS患者发作间期FCD增加区域呈对称性分布,以双侧丘脑、双侧舌回、距状回及双侧楔叶为主（P＜0.05）;FCD减低的区域主要包括双侧颞叶、双侧海马旁回区域及双侧内侧前额叶.GTCS患者的发病频率与双侧丘脑FCD呈负相关（右侧为r=-0.315,P=0.048;左侧为r=0.349,P ＝0.027）.结论 本研究发现IGE-GTCS患者丘脑及DMN区域功能连接的异常,有助于进一步揭示GTCS的发病机制.     

Changes in thalamus connectivity in mild cognitive impairment: evidence from resting state fMRI

Purpose

The subcortical region such as thalamus was believed to have close relationship with many cerebral cortexes which made it especially interesting in the study of functional connectivity. Here, we used resting state functional MRI (fMRI) to examine changes in thalamus connectivity in mild cognitive impairment (MCI), which presented a neuro-disconnection syndrome.

Materials and methods

Data from 14 patients and 14 healthy age-matched controls were analyzed. Thalamus connectivity was investigated by examination of the correlation between low frequency fMRI signal fluctuations in the thalamus and those in all other brain regions.

Results

We found that functional connectivity between the left thalamus and a set of regions was decreased in MCI; these regions are: bilateral cuneus, middle occipital gyrus (MOG), superior frontal gyrus (SFG), medial prefrontal cortex (MPFC), precuneus, inferior frontal gyrus (IFG) and precentral gyrus (PreCG). There are also some regions showed reduced connectivity to right thalamus; these regions are bilateral cuneus, MOG, fusiform gyrus (FG), MPFC, paracentral lobe (PCL), precuneus, superior parietal lobe (SPL) and IFG. We also found increased functional connectivity between the left thalamus and the right thalamus in MCI.

Conclusion

The decreased connectivity between the thalamus and the other brain regions might indicate reduced integrity of thalamus-related cortical networks in MCI. Furthermore, the increased connectivity between the left and right thalamus suggest compensation for the loss of cognitive function. Briefly, impairment and compensation of thalamus connectivity coexist in the MCI patients.     

Improved MR imaging of the orbit at 1.5 T with surface coils

A method for obtaining localized high-resolution magnetic resonance (MR) images of the eye and orbit is demonstrated. The method uses modified surface receiver coils placed immediately adjacent to the anatomy to detect the MR signal. Surface coils provide enhanced sensitivity for imaging voxels close to the surface of the body while limiting the received patient-generated noise. The resulting improvement in signal-to-noise ratio allows for a reduction in the imaging voxel size to about 0.5 X 0.5 X 5 mm in scan times of 3.4-5 min. At this level of resolution, anatomic detail in the orbital region previously unobservable in MR images is seen.