Strategies for improving the detection of fMRI activation in trigeminal pathways with cardiac gating

Functional magnetic resonance imaging (fMRI) has become a powerful tool for studying the normal and diseased human brain. The application of fMRI in detecting neuronal signals in the trigeminal system, however, has been hindered by low detection sensitivity due to activation artifacts caused by cardiac pulse-induced brain and brainstem movement. A variety of cardiac gating techniques have been proposed to overcome this issue, typically by phase locking the sampling to a particular time point during each cardiac cycle. We sought to compare different cardiac gating strategies for trigeminal system fMRI. In the present study, we used tactile stimuli to elicit brainstem and thalamus activation and compared the fMRI results obtained without cardiac gating and with three different cardiac gating strategies: single-echo with TR of 3 or 9 heartbeats (HBs) and dual-echo T2*-mapping EPI (TR = 2 HBs, TE = 21/55 ms). The dual-echo T2* mapping and the single-echo with TR of 2 and 3 HBs cardiac-gated fMRI techniques both increased detection rate of fMRI activation in brainstem. Activation in the brainstem and the thalamus was best detected by cardiac-gated dual-echo EPI.     

Single-shot compensation of image distortions and BOLD contrast optimization using multi-echo EPI for real-time fMRI

Functional magnetic resonance imaging (fMRI) is most commonly based on echo-planar imaging (EPI). With higher field strengths, gradient performance, and computational power, real-time fMRI has become feasible; that is, brain activation can be monitored during the ongoing scan. However, EPI suffers from geometric distortions due to inhomogeneities of the magnetic field, especially close to air-tissue interfaces. Thus, functional activations might be mislocalized and assigned to the wrong anatomical structures. Several techniques have been reported which reduce geometric distortions, for example, mapping of the static magnetic field B(0) or the point spread function for all voxels. Yet these techniques require additional reference scans and in some cases extensive computational time. Moreover, only static field inhomogeneities can be corrected, because the correction is based on a static reference scan. We present an approach which allows for simultaneous acquisition and distortion correction of a functional image without a reference scan. The technique is based on a modified multi-echo EPI data acquisition scheme using a phase-encoding (PE) gradient with alternating polarity. The images exhibit opposite distortions due to the inverted PE gradient. After adjusting the contrast of the images acquired at different echo times, this information is used for the distortion correction. We present the theory, implementation, and applications of this single-shot distortion correction. Significant reduction in geometric distortion is shown both for phantom images and human fMRI data. Moreover, sensitivity to the blood oxygen level-dependent (BOLD) effect is increased by weighted summation of the undistorted images.     

Improved shimming for fMRI specifically optimizing the local BOLD sensitivity

In functional MRI, magnetic field inhomogeneities due to air-tissue susceptibility differences may lead to severe signal dropouts and geometric distortions in echo-planar images. Therefore, the inhomogeneities in the field are routinely minimized by shimming prior to imaging. However in fMRI, the Blood Oxygen Level Dependent (BOLD) effect is the measure of interest, so the BOLD sensitivity (BS) should be optimized rather than the magnetic field homogeneity. The analytical expression for an estimate of the BOLD sensitivity has been recently developed, allowing for the computation of BOLD sensitivity maps from echo-planar images and field maps. This report describes a novel shimming procedure that optimizes the local BOLD sensitivity over a region of interest. The method is applied in vivo and compared to a standard global shimming procedure. A breath-holding experiment was carried out and demonstrated that the BS-based shimming significantly improved the detection of activation in a target region of interest, the medial orbitofrontal cortex.     

三维双回波稳态序列观察正常腕关节软骨

目的 探讨3.0T MR三维双回波稳态（3D-DESS）序列在正常腕关节软骨成像中的价值。方法 对12名健康志愿者采用3D-DESS、常规T1W自旋回波（SE-T1W）序列、T2W脂肪抑制快速自旋回波（FS-FSE-T2W）序列、质子加权脂肪抑制快速自旋回波（FS-FSE-PDW）序列行腕关节扫描。测量并计算各序列上腕关节三角纤维软骨复合体（TFCC）、腕骨间软骨及腕骨骨髓SNR及CNR,比较3D-DESS与常规SE序列图像SNR、CNR的差异。结果 3D-DESS图像上TFCC、腕骨间软骨SNR均高于SE-T1W、FS-FSE-T2W、FS-FSE-PDW序列（P均<0.05）,而3D-DESS上骨髓SNR与FS-FSE-T2W、FS-FSE-PDW序列差异无统计学意义（P均>0.05）。3D-DESS显示腕骨间软骨/骨髓CNR明显高于SE-T1W、FS-FSE-T2W、FS-FSE-PDW序列（P均<0.05）,3D-DESS图像TFCC/骨髓CNR与FS-FSE-PDW序列差异无统计学意义（P>0.05）。结论 与常规SE序列相比,3D-DESS序列能更为清晰地显示腕关节软骨,对诊断腕关节软骨病变具有潜在价值。     

Hippocampus-specific fMRI group activation analysis using the continuous medial representation

We present a new shape-based approach for regional group activation analysis in fMRI studies. The method restricts anatomical normalization, spatial smoothing and random effects statistical analysis to the space inside and around a structure of interest. Normalization involves finding intersubject correspondences between manually outlined masks, and it leverages the continuous medial representation, which makes it possible to extend surface-based shape correspondences to the space inside and outside of structures. Our approach is an alternative to whole-brain normalization in cases where the latter may fail due to anatomical variability or pathology. It also provides an opportunity to analyze the shape and thickness of structures concurrently with functional activation. We apply the technique to the hippocampus and evaluate it using data from a visual scene encoding fMRI study, where activation in the hippocampus is expected. We produce detailed statistical maps of hippocampal activation, as well as maps comparing activation inside and outside of the hippocampus. We find that random effects statistics computed by the new approach are more significant than those produced using the Statistical Parametric Mapping framework (Friston, K.J., Holmes, A.P., Worsley, K.J., Poline, J.-P., Firth, C.D., Frackowiak, R.S.J. 1994, Statistical parametric maps in functional imaging: a general linear approach. Human Brain Mapping, 2(4): 189-210) at low levels of smoothing, suggesting that greater specificity can be achieved by the new method without a severe tradeoff in sensitivity.     

14例脑干海绵状血管瘤的显微手术治疗

目的探讨脑干海绵状血管瘤显微手术治疗的适应证及预后。方法对14例行显微手术治疗的脑干海绵状血管瘤患者的临床资料及手术效果进行分析总结。结果9例全切,4例次全切,其中1例于术后第3天再出血而死亡,另1例大部分切除。术后早期神经功能障碍改善6例,同术前5例,加重3例。随访6～38个月,仍有2例患者未恢复至术前状态。肿瘤未全切的4患者中有2例行放射治疗,肿瘤体积未见明确增大。肿瘤全切的9例患者生存良好,未见确切复发,亦无再次出血。结论对有手术指征的脑干海绵状血管瘤,积极行显微手术治疗效果良好。     

人脑运动皮层功能磁共振成像研究

目的采用功能用磁共振成像（fMRI）回波平面（EPI）技术,研究人脑运动皮质血氧水平依赖（BOLD）的功能磁共振成像。方法27名正常健康志愿者,右手挤压橡皮圈,在运动和静止两种对比条件下,采集运动皮层的回波平面图像（BOLD-fMRI）。分析运动状态和非运动状态信号对比的脑功能图像。结果fMRI图像显示运动刺激下脑功能活动激活区主要位于对侧感觉运动皮质区、辅助运动区等。结论fMRI可用于研究活体人脑各功能区的活动,fMRI可对运动刺激下的人脑运动皮质进行初步定位。     

Source localization of sensory gating: a combined EEG and fMRI study in healthy volunteers

Reduced sensory gating appears to be among the core features in schizophrenia. The sources of sensory gating however are largely unknown. The aim of the current study was to identify these sources, with concurrent EEG and fMRI methodology. Twenty healthy male volunteers were tested with identical P50 suppression paradigms in two separate sessions: an EEG setting, and an EEG concurrent with fMRI setting. The stimuli in the P50 paradigm consisted of weak electrical stimulation of the left median nerve. The stimuli were presented in pairs with either 500 ms or 1000 ms interstimulus intervals (ISI). No difference was found between the EEG setting and the concurrent EEG and fMRI setting. P50 suppression was, in both settings, found only in the 500 ms trials, not in the 1000 ms trials. EEG-dipole modeling resulted in 4 sources located in the medial frontal gyrus, the insula, the hippocampus, and primary somatosensory cortex. These sources corresponded to significant fMRI clusters located in the medial frontal gyrus, the insula, the claustrum, and the hippocampus. Activity in the hippocampus and the claustrum was higher in the trials with suppression, suggesting that these brain areas are involved in the inhibitory processes of P50 suppression. The opposite was found for activity in the medial frontal gyrus and the insula, suggesting that these brain areas are involved in the generation of the P50 amplitude. To our knowledge, this is the first study demonstrating that P50 suppression can be reliably assessed inside an MRI scanner.     

脑干肿瘤的显微手术治疗

目的探讨脑干肿瘤的外科治疗方法及其注意事项。方法48例脑干肿瘤依据MRI选择不同入路行显微手术治疗,术后给予呼吸、循环功能的对症处理。结果肿瘤全切除25例,次全切除10例,大部切除8例,部分切除5例;术后并发呼吸功能障碍10例,循环功能障碍4例,咳嗽反射减弱和上消化道出血各5例,肌力减弱9例;术后随访35例,神经系统功能明显好转29例。结论术前MRI检查和一定的手术技巧是脑干肿瘤手术治疗取得良好效果的关键,术后监护和并发症的处理可增加手术安全性。     

原发性脑干出血患者死亡因素分析

目的　调查分析影响原发性脑干出血患者死亡率的因素。方法　收集 2 0 0 1～ 2 0 0 3年在我院就诊 ,经CT检查明确为原发性脑干出血 ,年龄超过 18岁 ,在内科接受保守治疗的成年患者。从病例中提取数据分析患者的一般资料、出院时的结局及可能影响预后的因素。结果　共 78例纳入本研究 ,最终死亡 4 8例。痊愈出院 11例 ,伴有神经功能缺陷出院 19例 ,存活组和死亡组在下列项目上有显著差异 :出血量 >5mL、来院时神志不清、持续高血压、2 4h内出现呼吸抑制或呼吸衰竭、高热。存活组和死亡组在下列项目上无显著统计学差异 :年龄、性别、应激性溃疡、ICU的治疗。结论　原发性脑干出血患者死亡率仍很高 ,影响预后的因素包括出血量 >5mL、入院时神志不清、2 4h内出现呼吸抑制或呼吸衰竭、持续高血压、高热。     

脑干梗死MR成像的临床价值

目的：探讨脑干梗死的病理机理及MR表现特点。方法：本组72例，男42例，女30例，年龄21～86岁，平均66岁。采用GE 2．OT超导型磁共振仪。SE序列，T1加权，轴位；FSE序列，T2加权，轴位和冠状位。结果：72例中，中脑梗死16例，脑桥梗死52例（合并中脑梗死13例），延髓梗死4例。梗死灶在T1WI上表现为低信号、低～等信号或等信号，在T2WI上表现为高信号，随着病程的发展，T1和T2的延长愈明显，T2WI对脑干梗死灶最敏感。结论：MRI是诊断脑干梗死的最好检查方法，能够显示脑干梗死的部位、数目和大小。     

激光扫描共聚焦显微镜观察脑干中的神经轴突

目的 观察脑干组织中神经轴突的正常形态。方法 用荧光免疫组织化学技术显示神经丝蛋白,在荧光显微镜和激光扫描共聚焦显微镜下观察正常脑干组织中的神经轴突。结果 在荧光显微镜下,神经轴空粗细较均匀,少数有弯曲现象,未见不规则肿胀及断裂。激光扫描共聚焦显微镜分层扫描发现神经轴突的内部结构连续性好,三维重宾可见轴突的立体结构完整。结论 激光扫描共聚焦显微镜能观察到神经轴突的内部结构和立体结构,可用于观察神经     

Analysis of speech-related variance in rapid event-related fMRI using a time-aware acquisition system

Speech production introduces signal changes in fMRI data that can mimic or mask the task-induced BOLD response. Rapid event-related designs with variable ISIs address these concerns by minimizing the correlation of task and speech-related signal changes without sacrificing efficiency; however, the increase in residual variance due to speech still decreases statistical power and must be explicitly addressed primarily through post-processing techniques. We investigated the timing, magnitude, and location of speech-related variance in an overt picture naming fMRI study with a rapid event-related design, using a data acquisition system that time-stamped image acquisitions, speech, and a pneumatic belt signal on the same clock. Using a spectral subtraction algorithm to remove scanner gradient noise from recorded speech, we related the timing of speech, stimulus presentation, chest wall movement, and image acquisition. We explored the relationship of an extended speech event time course and respiration on signal variance by performing a series of voxelwise regression analyses. Our results demonstrate that these effects are spatially heterogeneous, but their anatomic locations converge across subjects. Affected locations included basal areas (orbitofrontal, mesial temporal, brainstem), areas adjacent to CSF spaces, and lateral frontal areas. If left unmodeled, speech-related variance can result in regional detection bias that affects some areas critically implicated in language function. The results establish the feasibility of detecting and mitigating speech-related variance in rapid event-related fMRI experiments with single word utterances. They further demonstrate the utility of precise timing information about speech and respiration for this purpose.     

Model-free characterization of brain functional networks for motor sequence learning using fMRI

Neuroimaging experiments have identified several brain regions that appear to play roles in motor learning. Here we apply a novel multivariate analytical approach to explore the dynamic interactions of brain activation regions as spatio-temporally coherent functional networks. We acquired BOLD fMRI signal during explicit motor sequence learning task to characterize the adaptive functional changes in the early phase of motor learning. Subjects practiced a 10-digit, visually cued, fixed motor sequence during 15 consecutive 30 s practice blocks interleaved with similarly cued random sequence blocks. Tensor Independent Component Analysis (TICA) decomposed the data into statistically independent spatio-temporal processes. Two components were identified that represented task-related activations. The first component showed decreasing activity of a fronto-parieto-cerebellar network during task conditions. The other exclusively related to sequence learning blocks showed activation in a network including the posterior parietal and premotor cortices. Variation in expression of this component across individual subjects correlated with differences in behavior. Relative deactivations also were found in patterns similar to those described previously as "resting state" networks. Some of these deactivation components also showed task- and time-related modulations and were related to the behavioral improvement. The spatio-temporal coherence within these networks suggests that their elements are functionally integrated. Their anatomical plausibility and correlation with behavioral measures also suggest that this approach allows characterization of the interactions of functional networks relevant to the task. Particular value for multi-variant, model-free methods such as TICA lies in the potential for generating hypotheses regarding functional anatomical networks underlying specific behaviors.     

直肠刺激的脑功能磁共振成像研究

目的：运用功能磁共振成像(fMRI)研究正常人和肠易激综合征(IBS)患者直肠刺激时脑内局部活动。方法：11名正常人和26例IBS患者为对象。以不同气体容量扩张直肠获得fMRI图像，并和T1W解剖图像融合，进行脑内活动区的面积和信号强度分析。结果：大多数正常人和IBS患者的直肠刺激明显激活扣带回前皮层(ACC)、脑岛皮层(IC)、前额叶皮层(PFC)和丘脑(THAL)。在正常人中，注气量达90ml和120ml时，均以ACC中的活动Ⅸ面积最大；在不同的注气量时，绝大多是以PFC和ACC中的活动区MR信号强度变化幅度最大。在相同容积直肠刺激时，IBS患者脑内活动区比正常人组活跃；IBS患者组在疼痛性直肠扩张时脑内活动区以PFC最为明显。结论：正常人直肠刺激时，中枢兴奋区主要位于ACC和PFC；而IBS患者在疼痛性直肠扩张时以PFC为主。     

功能性核磁共振对脑卒中评估的作用

脑卒中是常见病,是导致成年人残废的主要原因之一。功能性核磁共振(fMRI)是近年发展起来的研究和评估脑功能的新技术。对卒中后的脑功能成像研究发现:(1)在卒中后的康复中脑功能运动通路重构;(2)预先存在的非交叉通路恢复;(3)初级运动感觉皮层激活中心的局灶性后移。fMRI可以是监测和研究脑卒中后功能恢复的有用工具,并有助于我们理解掌握脑卒中后运动功能康复的机制。     

正常人体针灸效应功能性磁共振成像的研究

目的评价针刺体表穴位对脑部相应区域的功能性磁共振成像(fMRI)表现。方法17例健康志愿者，在1，5TMRI仪上进行针刺足三里(S36)、阳陵泉(G34)的实时动态fMRI检查，观察并分析针刺效果明显者的脑部功能变化情况，判断针刺效果及其意义。结果17例志愿者中13例检查成功，可见躯体感觉运动区(SMC)、运动前区(PMC)、副运动区(SMA)激活明显，额叶前部、扣带回、尾状核头部、豆状核及丘脑、岛叶、岛盖皮质大多有大面积明显激活，小脑和桥脑也可见有激活，在左侧丘脑、SMA、SMC、PMC激活区附近有信号减低的现象，但激活的像素数不多；信号减低区包括两侧额叶内侧面皮质，双侧扣带回前部皮质，两侧海马区，右侧眶回、基底节、尾状核头部等。结论针刺对脑部相关穴位的治疗效应显著，可产生广泛而复杂的脑功能变化，fMRI可清楚显示针刺效应引起的脑部功能变化，是针刺机制及效应良好且直观的评价途径。     

Torsade de pointes as a complication of brainstem encephalitis

A case of brainstem encephalitis complicated by torsade de pointes is described. The possible occurrence of ventricular arrhythmias may contribute to the mortality in this condition. We recommend the admission of patients with brainstem encephalitis to an intensivve care unit, for a period of electrocardiographic monitoring.

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Torsade de pointes as a complication of brainstem encephalitis

     

Glucose metabolism of the midline nuclei raphe in the brainstem observed by PET-MRI fusion imaging

The brainstem contains various important monoaminergic neuronal centers, including the raphe nuclei which contain serotonergic neurons. The raphe nuclei, however, are not easily identifiable and located by conventional neuroimaging.

Methods

Fluorodeoxyglucose positron emission tomography (PET) and magnetic resonance imaging (MRI) were performed in seven healthy subjects using a new PET-MRI, which consists of a high-resolution research tomograph (HRRT) PET and 7.0 T-MRI. Glucose metabolism of raphe nuclei was semiquantitatively measured and identified along the midline brainstem region in vivo.

Results

Midline nuclei clustered in four groups appeared to be the raphe nuclei and could be clearly visualized; specifically, we identified the groups as the dorsal raphe, raphe reticularis centralis superior, raphe pontis, and raphe magnus group.

Conclusion

FDG imaging of the midline raphe nuclei in vivo could potentially be an important tool for investigating brain diseases as well as conducting functional brain studies in the context of sleep disorders, depression, and neurodegenerative disease.     

三种不同脑干疾病的脑干听觉诱发电位的比较

目的 比较不同脑干疾病的脑干听觉诱发电位(BAEP)改变，总结其各自的特征点，为临床不同脑干疾病的诊断及鉴别诊断提供可参考的电生理依据。方法 对80例椎-基底动脉供血不足患者、56例听神经瘤患者、47例慢性小脑变性疾病患者分别作BAEP检查，并与50例健康者对照。结果 三组患者BAEP的异常率分别为73．75％，94．61％，89．36％，具体成分异常各有其特点。结论 三种不同性质的脑干疾病BAEP改变各有特点，对临床各种脑干疾病的诊断及鉴别诊断具有一定意义。