Simultaneous electroencephalographic recording and functional magnetic resonance imaging during pentylenetetrazol-induced seizures in rat

Truly simultaneous electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) were registered in curarized rats injected with convulsive doses of pentylenetetrazol (PTZ, 65 mg/kg, sc). Rigorous control of physiological parameters like body temperature and ventilation with control of blood gasses helped to avoid potential interference between systemic parameters, and central PTZ-induced blood oxygenation level-dependent (BOLD) changes. Simultaneous EEG/fMRI recordings demonstrated progressive epileptiform EEG discharges with concomitant BOLD changes, the latter gradually affecting most of the fore- and midbrain. Approximately 15 min after PTZ injection, the first BOLD contrast changes mainly occurred in neocortex, and coincided with the first minor EEG alterations. Most regions that displayed BOLD changes were regions with reportedly high GABA(A) receptor densities. Full-blown epileptiform discharges occurred on the EEG tracing, approximately 30 min after PTZ injection, and coincided with bilateral positive and/or negative BOLD contrast changes in cortical and subcortical regions. Behavioral observations demonstrated the first of several generalized clonic or clonic-tonic seizure episodes to occur also around this time. Approximately 90 min after injection, the electrographic paroxysms gradually decreased in amplitude and duration, whereas the BOLD signal changes still extended with alternating positive and negative traces, and spread to subcortical regions like caudate-putamen and globus pallidus.     

听觉脑功能磁共振成像

听觉脑功能磁共振成像是磁共振功能成像(functionalmagneticresonanceimaging,fMRI)的一种,fMRI是一种安全的影像学检查手段,在完全无创的条件下对人脑进行功能分析,一次成像可同时获得解剖与功能影像,而且对人体无辐射损伤。尽管fMRI技术和方法还在不断发展和完善,但其可靠性和实用性是不容置疑的。它对听觉障碍患者的术前诊断、手术计划的制定、术后患者康复程度的评估,将会发挥越来越重要的作用。     

Recent advances in recording electrophysiological data simultaneously with magnetic resonance imaging

Simultaneous recording of brain activity by different neurophysiological modalities can yield insights that reach beyond those obtained by each technique individually, even when compared to those from the post-hoc integration of results from each technique recorded sequentially. Success in the endeavour of real-time multimodal experiments requires special hardware and software as well as purpose-tailored experimental design and analysis strategies. Here, we review the key methodological issues in recording electrophysiological data in humans simultaneously with magnetic resonance imaging (MRI), focusing on recent technical and analytical advances in the field. Examples are derived from simultaneous electroencephalography (EEG) and electromyography (EMG) during functional MRI in cognitive and systems neuroscience as well as in clinical neurology, in particular in epilepsy and movement disorders. We conclude with an outlook on current and future efforts to achieve true integration of electrical and haemodynamic measures of neuronal activity using data fusion models.     

Human vestibular cortex as identified with caloric stimulation in functional magnetic resonance imaging

Anatomic and electrophysiological studies in monkeys have yielded a detailed map of cortex areas receiving vestibular afferents. In contrast, comparatively little is known about the cortical representation of the human vestibular system. In this study we applied caloric stimulation and fMRI to further characterize human cortical vestibular areas and to test for hemispheric dominance of vestibular information processing. For caloric vestibular stimulation we used cold nitrogen to avoid susceptibility artifacts induced by water calorics. Right and left side vestibular stimulation was repetitively performed inducing a nystagmus for at least 90 s after the end of the stimulation in all subjects. Only the first 60 s of this nystagmus period was included for statistical analysis and compared with the baseline condition. Activation maps revealed a cortical network with right hemispheric dominance, which in all subjects comprised the temporoparietal junction extending into the posterior insula and, furthermore, the anterior insula, pre- and postcentral gyrus, areas in the parietal lobe, the ventrolateral portion of the occipital lobe, and the inferior frontal gyrus extending into the inferior part of the precentral sulcus. In conclusion, caloric stimulation in fMRI reveals a widespread cortical network involved in vestibular signal processing corresponding to the findings from animal experiments and previous functional imaging studies in humans. Furthermore, this study demonstrates a strong right hemispheric dominance of vestibular cortex areas regardless of the stimulated side, consistent with the current view of a rightward asymmetrical cortical network for spatial orientation.     

Informing brain connectivity with optogenetic functional magnetic resonance imaging

Optogenetic functional magnetic resonance imaging (ofMRI) is a novel approach that combines optogenetic control of neural circuits with high-field functional MRI. Optogenetics is a neuro-modulation technology in which light-activated trans-membrane conductance regulators are introduced into specifically targeted cell types to allow temporally precise, millisecond-scale activity modulation in vivo. By combining optogenetic control with fMRI readout, neural activity arising from specific circuit elements defined by genetic identity, cell body location, and axonal projection targets can be monitored in vivo across the whole brain. These unique features of ofMRI open new vistas for in vivo characterization of the dense plexus of neural connections according to their type and functionality.     

Item analysis in functional magnetic resonance imaging

Behavioral and neuroimaging studies of cognition frequently test hypotheses regarding mental processing of different stimulus categories (e.g. verbs, faces, animals, scenes, etc.). The conclusions of such studies hinge upon the generalizability of their findings from the specific stimuli used in the experiment to the category as a whole. This type of generalizability is explicitly tested in behavioral studies, using "item analysis". However, generalizability to stimulus categories has up until now been assumed in neuroimaging studies, without employing item analysis for statistical validation. Here we apply item analysis to a functional magnetic resonance imaging study of nouns and verbs, demonstrating its theoretical importance and feasibility. In the subject-wise analysis, a left prefrontal and a left posterior-temporal region of interest showed putative grammatical class effects. An item-wise analysis revealed, however, that only the left posterior-temporal effect was generalizable to the stimulus categories of nouns and verbs. Taken together, the findings of the subject- and item-wise analyses suggest that grammatical-class effects in the left prefrontal cortex depend on the particular word stimuli used, rather than reflecting categorical differences between nouns and verbs. This empirical example illustrates that item analysis not only is sufficiently powered to detect task relevant changes in BOLD signal but also can make theoretically important distinctions between findings that generalize to the item populations, and those that do not.     

Simultaneous recording of laser-evoked brain potentials and continuous, high-field functional magnetic resonance imaging in humans

Simultaneous recording of event-related electroencephalographic (EEG) and functional magnetic resonance imaging (fMRI) responses has the potential to provide information on how the human brain reacts to an external stimulus with unique spatial and temporal resolution. However, in most studies combining the two techniques, the acquisition of functional MR images has been interleaved with the recording of evoked potentials. In this study we investigated the feasibility of recording pain-related evoked potentials during continuous and simultaneous collection of blood oxygen level-dependent (BOLD) functional MR images at 3 T. Brain potentials were elicited by selective stimulation of cutaneous Adelta and C nociceptors using brief radiant laser pulses (laser-evoked potentials, LEPs). MR-induced artifacts on EEG data were removed using a novel algorithm. Latencies, amplitudes, and scalp distribution of LEPs recorded during fMRI were not significantly different from those recorded in a control session outside of the MR scanner using the same equipment and experimental design. Stability tests confirmed that MR-image quality was not impaired by the evoked potential recording, beyond signal loss related to magnetic susceptibility differences local to the electrodes. fMRI results were consistent with our previous studies of brain activity in response to nociceptive stimulation. These results demonstrate the feasibility of recording reliable pain-related LEPs and fMRI responses simultaneously. Because LEPs collected during fMRI and those collected in a control session show remarkable similarity, for many experimental designs the integration of LEP and fMRI data collected in separate, single-modality acquisitions may be appropriate. Truly simultaneous recording of LEPs and fMRI is still desirable in specific experimental conditions, such as single-trial, learning, and pharmacological studies.     

Physiological noise modelling for spinal functional magnetic resonance imaging studies

Spinal cord functional imaging allows assessment of activity in primary synaptic connections made by sensory neurons relaying information about the state of the body. However, reported human data based on gradient-echo techniques have been largely inconsistent, with no clear patterns of activation emerging. One reason for this variability is the influence of physiological noise, which is typically not corrected for. By acquiring single-slice resting data from the spinal cord with a conventional gradient-echo EPI pulse sequence at TR=200 ms (critically sampled) and TR=3 s (under-sampled), we have characterised various sources of physiological noise. In 8 healthy subjects, the presence of physiologically dependent signal was explored using probabilistic independent component analysis (PICA). Based on the insights provided by PICA, we defined a new physiological noise model (PNM) based on retrospective image correction (RETROICOR), which uses independent physiological measurements taken from the subject to model sources of noise. Statistical significance of individual components included in the PNM was assessed by F-tests, which demonstrated that the optimal PNM included cardiac, respiratory, interaction and low-frequency regressors. In a group of 10 healthy subjects, activation data were acquired from the cervical spinal region (T1 to C5) during painful thermal stimulation of the right and left hands. The improvement obtained when using a PNM in estimating spinal cord activation was reflected in a reduction of false-positive activation (active voxels in the CSF space surrounding the cord), when compared to conventional GLM modelling without a PNM.     

k-Space based summary motion detection for functional magnetic resonance imaging

Functional MRI studies are very sensitive to motion; head movements of as little as 1-mm translations or 1 degrees rotations may cause spurious signals. An algorithm was developed that uses k-space MRI data to monitor subject motion during functional MRI time series. A k-space weighted average of squared difference between the initial scan and subsequent scans is calculated, which summarizes subject motion in a single quality parameter; however, the quality parameter cannot be used for motion correction. The evolution of this quality parameter throughout a time series indicates whether head motion is within a predetermined limit. Fifty functional MRI studies were used to calibrate the sensitivity of the algorithm, using the six rigid-body registration parameters (three translations and three rotations) from the statistical parametric mapping (SPM99) package as a reference. The average correlation coefficient between the new quality parameter and the reference value from SPM was 0.84. The simple algorithm correctly classified acceptable or excessive motion with 90% accuracy, with the remaining 10% being borderline cases. This method makes it possible to evaluate brain motion within seconds after a scan and to decide whether a study needs to be repeated.     

胎盘功能磁共振成像研究进展

胎盘是维持胎儿在子宫内发育的重要器官。MRI越来越多地用于胎儿及胎盘的解剖成像。随着影像技术的发展,功能MRI广泛应用于科研及临床,亦是评估胎盘功能重要的工具。本文对胎盘功能MRI的主要研究进展进行综述。     

亚急性脑卒中患者静息态功能磁共振成像

目的 探讨应用静息态功能磁共振成像(rs-fMRI)对缺血性脑卒中患者病灶区进行检测的可行性。方法 收集14例亚急性缺血性脑卒中患者,分析其rs-fMRI数据,包括病灶区和正常对照区平均信号的低频振幅、两区域间相位延迟前后的功能连接和相位延迟3项主要指标。结果 ①低频振幅分析:4例患者病灶区低频振幅增强,10例病灶区低频振幅减弱;14例患者病灶区和正常对照区低频振幅的差异无统计学意义(t=-1.6290,P=0.1273)。②功能连接分析:42.86%(6/14)的患者病灶区与正常区的功能信号存在相位差异。③相位延迟分析:对于正常区,6例患者与全脑信号无相位差异,4例相位超前,4例相位落后;对于病灶区,8例相位超前,6例相位落后。14例患者两侧区域相对全脑的时间延迟值差异无统计学意义(t=0.6288,P=0.5404)。结论 缺血性脑卒中会引起rs-fMRI相关特异性指标的改变,但各指标个体差异明显,一致性不高。     

功能磁共振在神经外科中的应用

功能磁共振(fMRI)是一种被广泛接受的成像手段,近年来已用于多种临床实践中,特别是在指导神经外科手术方面有了很大的进展.本文就fMRI基本原理和技术及其在有效性评估、指导神经外科手术和术后患者随访方面的作用予以综述.     

Acute opioid effects on human brain as revealed by functional magnetic resonance imaging

Functional magnetic resonance imaging has been widely used to study brain activation induced either by specific sensory stimulation or motor or cognitive task performance. We demonstrate that functional magnetic resonance imaging can provide information of brain regions involved in opioid-induced central nervous system effects. The reproducibility of the responses in the predefined regions of interest was confirmed by repeated boluses of ultra-short acting mu-opioid receptor agonist remifentanil and saline. We report spatially and temporally detailed information after remifentanil administration. Areas rich in mu-opioid receptors showed strong activations, whereas primary somatosensory cortex that has the lowest density of mu-opioid receptors showed negligible activation. The cingulate, orbitofrontal, posterior parietal and insular cortices, and amygdala showed activation, which was temporally closely related to most subjective sensations that were strongest at 80 to 90 s after drug administration. These areas belong to a circuitry that modulates the affective experience of sensory stimuli.     

Safety of adenosine stress magnetic resonance imaging using a mobile cardiac magnetic resonance system.

BACKGROUND: Contrast-enhanced magnetic resonance imaging (ceMRI) allows for the detection of ischemic heart disease. Aim of this prospective study was to show feasibility, practicability and safety of adenosine stress ceMRI in routine outpatients with a mobile scanner. METHODS: Consecutive patients were scanned in six different cardiac outpatient centers with a 1.5 T mobile ceMRI scanner. First-pass wash-in patterns of gadolinium chelate were evaluated after three minutes of adenosine infusion. After a second bolus of gadolinium chelate myocardial late enhancement (MLE) images of the left ventricle were acquired to visualize myocardial necrosis. RESULTS: Five hundred seventy-four patients were enrolled to the study. No major complications during examination and adenosine infusion were observed. One hundred seventy-three minor complications as temporary atrio-ventriculare blockade, mild chest pain or dyspnea and nausea were noticed. None of the complications led to further special treatment CONCLUSION: This ceMRI protocol is suitable for application in outpatient settings. CeMRI stress testing using a mobile scanner in an outpatient setting is feasible and safe.     

Correlation of sensorimotor activation with functional magnetic resonance imaging and magnetoencephalography in presurgical functional imaging: a spatial analysis.

In this study we investigated the spatial heterotopy of MEG and fMRI localizations after sensory and motor stimulation tasks. Both methods are frequently used to study the topology of the primary and secondary motor cortex, as well as a tool for presurgical brain mapping. fMRI was performed with a 1.5T MR system, using echo-planar imaging with a motor and a sensory task. Somatosensory and motor evoked fields were recorded with a biomagnetometer. fMRI activation was determined with a cross-correlation analysis. MEG source localization was performed with a single equivalent current dipole model and a current density localization approach. Distances between MEG and fMRI activation sites were measured within the same anatomical 3-D-MR image set. The central region could be identified by MEG and fMRI in 33 of 34 cases. However, MEG and fMRI localization results showed significantly different activation sites for the motor and sensory task with a distance of 10 and 15 mm, respectively. This reflects the different neurophysiological mechanisms: direct neuronal current flow (MEG) and secondary changes in cerebral blood flow and oxygenation level of activated versus non activated brain structures (fMRI). The result of our study has clinical implications when MEG and fMRI localizations are used for pre- and intraoperative brain mapping. Although both modalities are useful for the estimation of the motor cortex, a single modality may err in the exact topographical labeling of the motor cortex. In some unclear cases a combination of both methods should be used in order to avoid neurological deficits.     

慢性疼痛的功能MRI研究进展

慢性疼痛是一种关乎人体生理和心理的疾病,近年来学者应用功能MRI技术(functional magnetic resonance imaging,fMRI)对慢性疼痛进行了大量研究,作者从慢性疼痛的特点、静息态fMRI对慢性疼痛的研究方法、实验和分析等方面对慢性疼痛的静息态fMRI研究进展进行综述。     

偏头痛的功能MRI研究进展

偏头痛是一种以疼痛反复发作为特点的慢性功能障碍性疾病。近年来学者应用功能MRI技术对偏头痛进行了大量研究,作者拟从偏头痛的疾病机制、静息态脑功能网络异常和中医针刺干预等三个方面对偏头痛的功能MRI研究进展进行综述。     

功能磁共振成像临床应用及进展

近几十年来,多种模态的功能磁共振技术飞速发展,为临床医学的发展产生了重要影响,也为精神影像学的发展提供了重要手段,极大的深化了人类对神经系统疾病和疾病的认知.本文就功能磁共振的成像及图像后处理技术,及其在反映疾病亚临床阶段的功能改变、实时活体的个体化脑功能定位、探索中枢神经系统药物机制等方面的临床应用和进展进行了述评,同时阐明其技术缺陷及未来发展方向.     

疼痛的脑功能MRI研究进展

功能MRI(f MRI)是一种无创性的功能成像技术,近年来被广泛应用于疼痛方面的研究,使得人们对疼痛的生理有了进一步的认识。作者通过对不同类型疼痛的分析,从痛觉中枢的定位、临床疼痛的f MRI研究及疼痛治疗等方面综述了近年关于疼痛的脑f MRI研究进展。