Magnetic Source Imaging Research Articles

Magnetoencephalography assessment of evoked magnetic fields and cognitive function in subcortical ischemic vascular dementia patients

ObjectiveTo investigate the relationship between cognitive impairment and somatosensory evoked magnetic field and auditory evoked magnetic field changes in elderly male patients with subcortical ischemic vascular dementia (SIVD). MethodsMagnetoencephalography (MEG) was used to record evoked magnetic field changes from 4 SIVD patients (76–88 years), 3 patients with vascular cognitive impairment with no dementia (VCI-ND; 74–87 years), and 6 healthy volunteers (72–85 years). Latency peaks, equivalent current dipole (ECD) strength, and bilateral ECD position were recorded. The MEG data were superimposed on magnetic resonance imaging to produce magnetic source imaging. ResultsCompared to controls, SIVD patients showed increased M20 latency and ECD strength. There were no significant differences in M20 inter-hemispheric positions across diagnostic categories. At M100, SIVD patients showed delayed auditory evoked magnetic field latency compared to controls. However, ECD strength and 3-dimensional inter-hemispheric differences were similar across the groups at the M100 measurement. ConclusionsChanges in somatosensory and auditory evoked magnetic field changes correlated with cognitive impairment in SIVD patients. Magnetic field latency measures may provide an objective and sensitive index for early dementia detection and monitoring of cognitive function.

Magnetic source imaging and ictal SPECT in MRI‐negative neocortical epilepsies: Additional value and comparison with intracranial EEG

To investigate the utility of magnetic source imaging (MSI) and ictal single photon emission computed tomography (SPECT), each compared with intracranial electroencephalography (EEG) (ICEEG), to localize the epileptogenic zone (EZ) and predict epilepsy surgery outcome in patients with nonlesional neocortical focal epilepsy. Studied were 14 consecutive patients with nonlesional neocortical epilepsy who underwent presurgical evaluation including ICEEG, positive MSI, and localizing subtraction Ictal SPECT coregistered to MRI (SISCOM) analysis. Follow-up after epilepsy surgery was ≥ 24 months. ICEEG, MSI, and SPECT results were classified using a sublobar classification. Of 14 patients, 6 (42.9%) became seizure-free after surgery. Sublobar ICEEG focus was completely resected in 11 patients; 5 (45.5%) of them became seizure- free. Concordance of ICEEG and MSI and complete focus resection was found in 5 (35.7%) patients; 80% of them became seizure-free. Sublobar ICEEG-MSI concordance and complete focus resection significantly increased the chance of seizure freedom after epilepsy surgery (p = 0.038). In contrast, of the 6 patients (42.9%) with concordant ICEEG and SISCOM and complete focus resection, only 66.7% became seizure-free (p = 0.138). Assuming concordant results, the additive value to ICEEG alone for localizing the EZ is higher with ICEEG-MSI (odds ratio 14) compared to ICEEG-SISCOM (odds ratio 6). This study shows that combination of MSI and/or SISCOM with ICEEG is useful in the presurgical evaluation of patients with nonlesional neocortical epilepsy. Concordant test results of either MSI or SISCOM with ICEEG provide useful additive information for that provided by ICEEG alone to localize the EZ in this most challenging group of patients. When sublobar concordance with ICEEG is observed, MSI is more advantageous compared to SISCOM in predicting seizure-free epilepsy surgery outcome.

Improved Localization Accuracy in Magnetic Source Imaging Using a 3-D Laser Scanner

Brain source localization accuracy in magnetoencephalography (MEG) requires accuracy in both digitizing anatomical landmarks and coregistering to anatomical magnetic resonance images (MRI). We compared the source localization accuracy and MEG-MRI coregistration accuracy of two head digitization systems-a laser scanner and the current standard electromagnetic digitization system (Polhemus)-using a calibrated phantom and human data. When compared using the calibrated phantom, surface and source localization accuracy for data acquired with the laser scanner improved over the Polhemus by 141% and 132%, respectively. Laser scan digitization reduced MEG source localization error by 1.38mm on average. In human participants, a laser scan of the face generated a 1000-fold more points per unit time than the Polhemus head digitization. An automated surface-matching algorithm improved the accuracy of MEG-MRI coregistration over the equivalent manual procedure. Simulations showed that the laser scan coverage could be reduced to an area around the eyes only while maintaining coregistration accuracy, suggesting that acquisition time can be substantially reduced. Our results show that the laser scanner can both reduce setup time and improve localization accuracy, in comparison to the Polhemus digitization system.

Imaging techniques for presurgical evaluation of temporal lobe epilepsy

The surgical treatment of pharmaco-resistant focal epilepsy has increased dramatically in recent years. This evolution is undoubtedly due to an improvement of electrophysiological and neuroradiological investigations to localize the epileptic focus. Temporal lobe epilepsy is the most frequent pharmacoresistent epileptic syndrome in adults and responds better to surgery than the so-called extratemporal epilepsy. Apart from the history and the clinical semiology, the investigations for temporal lobe epilepsy are based on core investigations, including electroencephalography (long-term video-EEG recordings) and MRI. Additional noninvasive imaging techniques to improve the localization of the epileptic focus include PET ictal and interictal SPECT, electric source imaging and magnetic source imaging, and simultaneous EEG and functional MRI. Advanced sequences and analysis of structural MRI data allow us to map subtle structural abnormalities as well as important white matter tracts while functional MRI of language/memory helps to identify eloquent cortical area and estimate the risk of postoperative deficits. Our aim is to review the current literature and summarize all available data on these validated imaging techniques for the assessment of focal temporal lobe epilepsy.

Magnetic source imaging in non-lesional neocortical epilepsy: Additional value and comparison with ICEEG

ObjectiveTo investigate the utility of magnetic source imaging (MSI) for localizing the epileptogenic zone (EZ) and predicting epilepsy surgery outcome in non-lesional neocortical focal epilepsy (NLNE) patients. MethodsData from 18 consecutive patients with NLNE who underwent presurgical evaluation including intracranial electroencephalography (ICEEG) and MSI were studied. Follow-up after epilepsy surgery was ≥24months. Intracranial electroencephalography and MSI results were classified using a sublobar classification. ResultsSublobar ICEEG focus was completely resected in 15 patients; seizure-free rate was 60%. Eight patients showed sublobar-concordant ICEEG/MSI results and complete resection of both regions; seizure-free rate was 87.5%. Seizure-free rate in cases not matching these criteria was only 30% (p=0.013). ConclusionsMagnetoencephalography is a useful tool to localize the EZ and determine the site of surgical resection in NLNE patients. When sublobar concordance with ICEEG is observed, MSI increases the predictive value for a seizure-free epilepsy surgery outcome in these patients.

Inverse modeling in magnetic source imaging: Comparison of MUSIC, SAM(g2), and sLORETA to interictal intracranial EEG

Magnetoencephalography (MEG) is used in the presurgical work-up of patients with focal epilepsy. In particular, localization of MEG interictal spikes may guide or replace invasive electroencephalography monitoring that is required in difficult cases. From literature, it is not clear which MEG source localization method performs best in this clinical setting. Therefore, we applied three source localization methods to the same data from a large patient group for which a gold standard, interictal spikes as identified in electrocorticography (ECoG), was available. The methods used were multiple signal classification (MUSIC), Synthetic Aperture Magnetometry kurtosis [SAM(g2)], and standardized low-resolution electromagnetic tomography. MEG and ECoG data from 38 patients with refractory focal epilepsy were obtained. Results of the three source localization methods applied to the interictal MEG data were assigned to predefined anatomical regions. Interictal spikes as identified in ECoG were also assigned to these regions. Identified regions by each MEG method were compared to ECoG. Sensitivity and positive predictive value (PPV) of each MEG method were calculated. All three MEG methods showed a similar overall correlate with ECoG spikes, but the methods differ in which regions they detect. The choice of the inverse model thus has an unexpected influence on the results of magnetic source imaging. Combining inverse methods and seeking consensus can be used to improve specificity at the cost of some sensitivity. Combining MUSIC with SAM(g2) gives the best results (sensitivity = 38% and PPV = 82%).

Clinical added value of magnetic source imaging in the presurgical evaluation of refractory focal epilepsy

ObjectiveThis prospective, bicentre, blinded, intention to treat study assessed the clinical added value of magnetic source imaging (MSI) in the presurgical evaluation of patients with refractory focal epilepsy (RFE).Methods70 consecutive...

Cortical representation of high-frequency oscillations in Landau-Kleffner syndrome revealed by magnetic source imaging

Cortical representation of high-frequency oscillations in Landau-Kleffner syndrome revealed by magnetic source imaging

The fronto-cingulate executive function in recurrent depression revealed by the magnetic source imaging

Objective To investigate the variation of executive function of fronto-cingulate cortex in spatio-temporal sequence in recurrent depressed patients.Methods Eighteen recurrent depressed patients and twenty-one age-,gender- and education- matched healthy controls were involved in the Stroop word-color interference test to detect the executive function of anterior cingulate and prefrontal regions by magnetoencephaloraphy scanning.Results 1.Compared to healthy controls,the increased activation of brain regions in depressed patients during different time periods were separately shown as follows( t represents activation strength):( 1 ) 100 ～ 200 ms:the right anterior cingulate gyrus ( t =1.81,T value means activation strength),the bilateral medial frontal gyrus ( t =1.91,t =1.86),the left superior frontal gyms( t =1.79 ),the right middle frontal gyrus( t =1.82 ),the right inferior frontal gyrus ( t =1.82 ).( 2 ) 200 ～ 300 ms:the left anterior cingulate gyrus ( t =1.82 ).( 3 ) 250 ～ 350 ms:the left anterior cingulate gyrus ( t =2.67 ),the left medial frontal gyrus ( t =2.43 ),the left inferior frontal gyrus ( t=1.91 ).(4)300 ～400ms:the left anterior frontal gyrus(t=2.26),the bilateral inferior gyrus( t=1.97,t=2.66),the left medial frontal gyrus(t=2.35).(5)350 ～450ms:the left anterior cingulate gyrus(t=2.02),the left medial frontal gyrus ( t =2.00),the bilateral inferior frontal gyrus ( t =1.74,t =1.78 ).( 6 ) 400 ～ 500 ms:the left anterior cingulate gyrus( t=2.01 ),the left medial frontal gyrus( t =1.97).2.Compared to healthy controls,patients showed decreased activation in the left middle frontal gyms ( t =1.79) and the left superior gyrus(t =1.76) in 200 ～ 300 ms.Conclusion Executive dysfunction is reflected in depressed patients with the activation inefficiency in anterior cingulate and prefrontal regions in spatio-temporal sequence. Key words: Depression; Executive function; Magnetoencephaloraphy; Cingulate gyrus

Emerging imaging tools for use with traumatic brain injury research.

This article identifies emerging neuroimaging measures considered by the inter-agency Pediatric Traumatic Brain Injury (TBI) Neuroimaging Workgroup. This article attempts to address some of the potential uses of more advanced forms of imaging in TBI as well as highlight some of the current considerations and unresolved challenges of using them. We summarize emerging elements likely to gain more widespread use in the coming years, because of 1) their utility in diagnosis, prognosis, and understanding the natural course of degeneration or recovery following TBI, and potential for evaluating treatment strategies; 2) the ability of many centers to acquire these data with scanners and equipment that are readily available in existing clinical and research settings; and 3) advances in software that provide more automated, readily available, and cost-effective analysis methods for large scale data image analysis. These include multi-slice CT, volumetric MRI analysis, susceptibility-weighted imaging (SWI), diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), arterial spin tag labeling (ASL), functional MRI (fMRI), including resting state and connectivity MRI, MR spectroscopy (MRS), and hyperpolarization scanning. However, we also include brief introductions to other specialized forms of advanced imaging that currently do require specialized equipment, for example, single photon emission computed tomography (SPECT), positron emission tomography (PET), encephalography (EEG), and magnetoencephalography (MEG)/magnetic source imaging (MSI). Finally, we identify some of the challenges that users of the emerging imaging CDEs may wish to consider, including quality control, performing multi-site and longitudinal imaging studies, and MR scanning in infants and children.

Neural correlates of sentence reading in children with reading difficulties

In contrast to word-level skills, the neural basis of sentence comprehension in children with reading difficulties is not well understood. Using magnetic source imaging, we investigated the spatiotemporal dynamics of regional activity associated with silent passage reading in nonimpaired and students with reading difficulties. The latter exhibited underactivation of the temporoparietal and visual cortices, bilaterally, and of the left posterior cingulate region. Late activity in left temporoparietal and ventral occipitotemporal regions was found to be a significant predictor of individual reading ability in nonimpaired, but not in students with reading difficulties. These findings support the notion that reduced temporoparietal activation during word reading in context, is a hallmark of the functional deficit in reading disability.

Human Intracranial Recordings and Cognitive Neuroscience

The ultimate goal of neuroscience research is to understand the operating mechanism of the human brain and to exploit this understanding to devise methods for repair when it malfunctions. A key feature of this operating mechanism is electrical activity of single brain cells and cell assemblies. For obvious ethical reasons, scientists rely mostly on animal research in the study of such signals. Research in humans is often limited to electrical signals that can be recorded at the scalp or to surrogates of electrical activity, namely magnetic source imaging and measures of regional blood flow and metabolism. Invasive brain recordings performed in patients during various clinical procedures provide a unique opportunity to record high-resolution signals in vivo from the human brain-data that are otherwise unavailable. Of special value are the rare opportunities to record in awake humans the activity of single brain cells and small cellular assemblies. These recordings provide a unique view on aspects of human cognition that are impossible to study in animals, including language, imagery, episodic memory, volition, and even consciousness. In the current review we discuss the unique contribution of invasive recordings from patients to the field of cognitive neuroscience.

Optimizing estimation of hemispheric dominance for language using magnetic source imaging

The efficacy of magnetoencephalography (MEG) as an alternative to invasive methods for investigating the cortical representation of language has been explored in several studies. Recently, studies comparing MEG to the gold standard Wada procedure have found inconsistent and often less-than accurate estimates of laterality across various MEG studies. Here we attempted to address this issue among normal right-handed adults ( N = 12) by supplementing a well-established MEG protocol involving word recognition and the single dipole method with a sentence comprehension task and a beamformer approach localizing neural oscillations. Beamformer analysis of word recognition and sentence comprehension tasks revealed a desynchronization in the 10–18 Hz range, localized to the temporo-parietal cortices. Inspection of individual profiles of localized desynchronization (10–18 Hz) revealed left hemispheric dominance in 91.7% and 83.3% of individuals during the word recognition and sentence comprehension tasks, respectively. In contrast, single dipole analysis yielded lower estimates, such that activity in temporal language regions was left-lateralized in 66.7% and 58.3% of individuals during word recognition and sentence comprehension, respectively. The results obtained from the word recognition task and localization of oscillatory activity using a beamformer appear to be in line with general estimates of left hemispheric dominance for language in normal right-handed individuals. Furthermore, the current findings support the growing notion that changes in neural oscillations underlie critical components of linguistic processing.

E-019 Preoperative cortical localization by magnetic source imaging for endovascular treatment of arterial venous malformations in eloquent brain tissue

IntroductionPreoperative localization of functionally eloquent brain tissue helps plan and tailor the extent of endovascular embolization and surgical resection of AVMs. Combined magnetoencephalography and MR data can be used to...

The brain inhibitory function in unipolar depression revealed by the magnetic source imaging

Objective To investigate the variation of brain inhibitory function of depressed patients during the processes of the Stroop color-word interference task with the Magnetic source imaging ( MSI) technology. Methods Twenty-three depressed patients and twenty age-,gender- and education- matched healthy controls were involved in the Stroop word-color interference test to detect the variation of brain inhibitory function by magnetoen-cephaloraphy scanning. Results Compared with the healthy controls,the abnormal activities in depressed patients during different time periods were separately as follows: increased activation in the bilateral thalamus( t = 2.46, t = 2.92 ) ,the right temple fusiform gyrus ( t = 1. 81) , the right middle temporal gyrus ( t = 1. 76) , the right inferior frontal gyrus( t = 2.28) , the left anterior cingulate( t = 2.00) , the left caudate head( t=1.81) ,the precentral gy-rus( t = 2.17) ,the right parahippocampal gyrus( t = 2.04) ,the left superior temporal gyrus(t = 2.47) ; decreased activation in the right superior temporal gyrus( t=1.76) ,the bilateral middle frontal gyrus(t=1.95, t = 2.09), the right cuneus( t=1.97) ,the cingulate gyrus( t=1.70, t = 2.08) ,the postcentral gyrus( t = 2.57, t = 2.65) , the left supramarginal gyrus( t = 2. 16) ,the left lentiform nucleus putamen( t = 2.39) ,the bilateral middle temporal gyrus (t = 2.22, t= 1.90) ,the left insula( t= 1. 81) ,the left superior temporal gyrus( t= 1.90) ,the right parietal lobe( t= 3.26). Conclusion The abnormal activation inefficiency in the brain regions related with inhibition function is reflected in depressed patients,and the ability against interference information declines. Key words: Depression; Inhibitory function; Magnetoencephaloraphy

Supplementary motor cortex involvement in reading epilepsy revealed by magnetic source imaging

Reading epilepsy (RE) is an idiopathic reflex epilepsy syndrome characterized by perioral myoclonic jerks (PMJs) during reading associated with left-dominant frontotemporal spike-wave discharges (SWDs). To better understand the pathophysiology of this syndrome, we studied a 45-year-old patient using magnetic source imaging (MSI). The patient underwent two whole-head magnetoencephalography (MEG) recordings (Elekta Neuromag Oy) within 2 months while reading aloud. Forty-two SWDs associated with PMJs were recorded and averaged with respect to SWDs peak power. Epileptic discharges were then reconstructed using conventional equivalent current dipoles (ECDs) modeling, distributed sources sLORETA modeling, and beamformer approach. These methods identified two brain sources located in the left supplementary motor cortex (SMC) and the left primary sensorimotor face area (PSMFA). The spatiotemporal pattern of the sources was characterized by a cross-talk between these two brain regions, with an initial source in the left SMC. This MSI investigation suggests that RE-PMJs are associated with reading-induced activation of hyperexcitable neurons in the left SMC, followed by secondary propagation to the left PSMFA producing the myoclonus.

Realignment of Magnetoencephalographic Data for Group Analysis in the Sensor Domain

Magnetoencephalography (MEG) is a neuroimaging modality with high temporal resolution for studying functional brain processes in relatively small neural assemblies on the time scale of <100 milliseconds and with synchrony and coherence in the recorded signals at high frequencies. Advanced MEG signal analysis gained importance for clinical applications, e.g., as a sensitive classifier for the diagnosis of neuropsychiatric disorders. Despite tremendous improvements in magnetic source imaging, MEG analysis often does not require explicit source estimation and can be performed in the sensor domain. However, group analysis of MEG sensor data is complicated by variable positioning of the sensor array relative to the head and needs realignment of the sensor configuration. Here, the authors provide an algorithm for transforming the magnetic field data as recorded at various sensor positions onto a common sensor array. Based on the measured magnetic field at the original sensor position, they estimate a source distribution and project it onto a virtual sensor array using the leadfield description of the magnetic forward solution. First, they analyzed the variation of sensor positioning in a typical MEG study and reported the impact on the leadfield matrix. Then they evaluated the realignment algorithm and reported its properties. Including efficient regularization to the inverse solution, they demonstrated that the introduced error is in the order of the sensor noise, and smoothing of data is limited to the set of smallest eigenvalues of the data. They demonstrated the performance of the algorithm with dipole source modeling on group averaged MEG data and comparison of grand averaged auditory evoked responses with and without sensor realignment.

The gender differences of the magnetic source imaging during recognizing dynamically sad facial expression in depressed patients

Objective To explore the gender differences of brain activation between patients with depression in recognition of dynamically sad expression with magnetoencephalography (MEG) technology and the paradigm of expressional experiment,and further to examine its neurological basis. Methods Brain activities were detected using MEG during the recognition of dynamic facial video with 12 female depressed patients, 11 male depressed patients, and their corresponding normal controls matched by age and education. Results Compared with male depression,female depression showed increased activation during different time periods were in turn as follows: bilateral inferior frontal gyrus ( x, y, z = 58/- 60,12/22,20/20, T = 2.17,1.88 ), left anterior cingulate gyrus ( x, y, z = 64,12,4, T = 2.37 ), bilateral superior frontal gyrus ( x, y, z= 30/-24,64/- 4,0/50, T = 2.86,2.36 ),the left brainstem( x, y,z = - 12, - 16, - 18 ,T = 1.96) ,right middle frontal gyrus( x,y,z =40,60,4,T = 2.22 ),bilateral precentral gyrus(x,y,z = -62/56, 16/10, 10/8. T = 1.99,2.65 ) ,left hippocampus ( x,y,z = - 26,- 14, -20,T = 1.77) ,left parahippocampal gyrus(x,y,z = - 16, - 12, -20,T = 1.72) ,right middle occipital gyrus( x ,y ,z = 50, -76, -14 ,T = 1. 75 ),while the decreased brain activation were in turn in right superior temporal gyrus ( x, y, z = 68, - 18,2, T = 1.85 ), right parahippocampal gyrus ( x, y, z = 20, - 36, - 14, T = 1.92 ), left cuneus( x,y,z = -6, -98,14,T =2.46) ,bilateral temporal middle gyrus( x,y,z =52/-34, - 80/-62,20/28,T = 1.95,2.57 ), left pre-cuneus ( x, y, z = - 40, - 74,38, T = 2.58 ), right hippocampus( x, y, z = 24, - 32, - 18,T = 2.05 ) in recognition of dynamically sad expression. ( p ＜ 0. 05, corrected). Conclusion The data suggest that there may be significant gender differences of functional network in depressed patients during recognizing dynamical sad facial expression. Key words: Depression; Negative emotion recognition; Gender difference; Magnetoencephalography

Application of magnetic source imaging in localizing the epileptic foci in patients with grey matter heterotopia

Objective To evaluate the value of magnetic source imaging(MSI) in localizing the epileptic foci of patients with histologically proved grey matter heterotopia(GMH) and seizure. Methods MSI examinations were performed on 8 patients with GMH and seizure. The location of the epileptic foci defined by MSI was compared with the results of the ECoG. After imaging examinations, all patients received operation with 13-48 months follow up to observe the effectiveness of the operation. Results Among the 8 patients, 1 had hippocampal sclerosis,2 had focal cortical dysplasiaof type Ⅰ B and 1 had focal cortical dysplasia of type Ⅱ B. MRI showed normal findings in 2 cases, subcortical heterotopia in 4 cases, and nodulor heterotopia in 2 cases with one having schizencephaly. The epileptic foci defined by MSI were at right temporal lobe in 2 cases, left frontal lobe in 2 cases, biparietal lobe in1 case, left parietal lobe in 1 case, left temporal lobe in 1 case, and left frontal-parietal lobe in 1 case. The epileptic foci defined by MSI were completely overlaid with area of GMH in 4 cases, closely behind the area of GMH in case, and partly overlaid with area of GMH in 1 cases with size larger than that of the latter. One patient showed two epileptic foci with one located within the area of GMH and the other one 2 centimeters anterior to the area of GMH.One case's epileptic focus located 2 centimeters posteolateral to the area of GMH . The locations of the epileptic foci defined by MSI showed no difference with those defined by ECoG in all patients. According to Engel classification of treatment effect of epilepsy, 6 patients achieved Engle class Ⅰ ( seizure free after operation ), and 2 patients Engel class Ⅳ ( no changes in the frequcenty of occurrence of seizures before and after operation ). Conclusion MSI can noninvasively and precisely localize the epileptic foci before operation in patients with GMH and seizure. Key words: Epilepsy; Magnetoencephalography; Magnetic resonance imging

A Critical Review of Neuroimaging Applications in Sports Concussion

While abnormalities related to concussion are typically not identified on traditional clinical neuroimaging (i.e., computed tomography [CT] or magnetic resonance imaging [MRI]), more sophisticated neuroimaging techniques have the potential to reveal the complex neurometabolic processes related to concussion and its recovery. Clinically, these techniques may one day provide useful information to guide clinicians in the management and treatment of sports concussion. This article critically reviews the current state of the literature regarding neuroimaging and sports concussion, identifies challenges in the application of these techniques, and identifies areas for future research.