Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, 2011
Epilepsy patients with Landau-Kleffner syndrome (LKS) usually have a normal brain structure, whic... more Epilepsy patients with Landau-Kleffner syndrome (LKS) usually have a normal brain structure, which makes it a challenge to identify the epileptogenic zone only based on magnetic resonance imaging (MRI) data. A sparse source imaging technique called variation based sparse cortical current density (VB-SCCD) imaging was adopted here to reconstruct cortical sources of magnetoencephalography (MEG) interictal spikes from an LKS patient. Realistic boundary element (BE) head and cortex models were built by segmenting structural MRI. 148-channel MEG was recorded for 10 minutes between seizures. Total 29 epileptiform spikes were selected for analysis. The primary cortical sources were observed locating at the left intra- and perisylvian cortex. Multiple extrasylvian sources were identified as the secondary sources. The spatio-temporal patterns of cortical sources provide more insights about the neuronal synchrony and propagation of epileptic discharges. Our observations were consistent with presurgical diagnosis for this patient and observation of aphasia in LKS. The present results suggest that the promising of VB-SCCD technique in assisting with presurgical planning and studying the neural network for LKS in determining the lateralization of epileptic origins. It can further be applied to non-invasively localize and/or lateralize eloquent cortex for language for epilepsy patients in general in the future.
While the cerebral cortex in the human brain is of functional importance, functions defined on th... more While the cerebral cortex in the human brain is of functional importance, functions defined on this structure are difficult to analyze spatially due to its highly convoluted irregular geometry. This study developed a novel L1-norm regularization method using a newly proposed multi-resolution face-based wavelet method to estimate cortical electrical activities in electroencephalography (EEG) and magnetoencephalography (MEG) inverse problems. The proposed wavelets were developed based on multi-resolution models built from irregular cortical surface meshes, which were realized in this study too. The multi-resolution wavelet analysis was used to seek sparse representation of cortical current densities in transformed domains, which was expected due to the compressibility of wavelets, and evaluated using Monte Carlo simulations. The EEG/MEG inverse problems were solved with the use of the novel L1-norm regularization method exploring the sparseness in the wavelet domain. The inverse solutions obtained from the new method using MEG data were evaluated by Monte Carlo simulations too. The present results indicated that cortical current densities could be efficiently compressed using the proposed face-based wavelet method, which exhibited better performance than the vertex-based wavelet method. In both simulations and auditory experimental data analysis, the proposed L1-norm regularization method showed better source detection accuracy and less estimation errors than other two classic methods, i.e. weighted minimum norm (wMNE) and cortical low-resolution electromagnetic tomography (cLORETA). This study suggests that the L1-norm regularization method with the use of face-based wavelets is a promising tool for studying functional activations of the human brain.
Neuromodulation : journal of the International Neuromodulation Society, 2013
Development of effective chronic pain treatment strategies has been hampered by the lack of an ob... more Development of effective chronic pain treatment strategies has been hampered by the lack of an objective pain biomarker. Magnetoencephalography (MEG) has demonstrated cortical disorganization corresponding to the affected limb of complex regional pain syndrome (CRPS) patients and spinal cord stimulation (SCS) can acutely treat CRPS in a reversible and adjustable fashion. In order to better define a potential MEG-sensitive biomarker for chronic pain, our goal was to study the effects of therapeutic SCS on cortical disorganization in patients with unilateral limb CRPS. Two patients treated with either thoracic or cervical SCS with leg or arm CRPS were studied with MEG. Baseline and tactile-evoked responses were recorded with and without effective SCS therapy. All MEG recordings were obtained with minimal interference. In the patient with arm CRPS, with the stimulator off, first and fifth digit primary somatosensory (SI) cortical representations (D1/D5) were significantly disorganized and spatially inverted as compared with the opposite unaffected limb. Effective SCS therapy was then able to acutely normalize or restore hand cortical organization in the affected CRPS limb. This restoration of cortical organization was partially maintained with lingering pain relief when the stimulator was subsequently turned off. This is the first report of a MEG study showing D1/D5 cortical disorganization and its apparent reversal or restoration with cervical SCS therapy. Ours also is the first report of an apparent acute reversible interchange in the cortical representations of D1 and D5. Our limited data demonstrate that disorganization of SI cortex might be a neurophysiologic marker of chronic pain as shown with instantaneous normalization of SI disorganization or restoration of SI organization with therapeutic SCS. As a clinically proven tool for functional mapping, MEG might be shown to provide an objective measure of chronic pain. More data are required to further investigate this possibility.
Rasmussen's encephalitis (RE) is a cryptogenic progressive inflammatory disorder of the brain tha... more Rasmussen's encephalitis (RE) is a cryptogenic progressive inflammatory disorder of the brain that causes severe neurological problems, including intractable focal epilepsy. In select patients, aggressive treatment using cerebral hemispherectomy may ameliorate the devastating cognitive decline that accompanies this disease, even if the epileptic focus appears broadly distributed. We present a case of histopathologically-confirmed RE evaluated using a multimodal process that explored the physical and functional aspects of the associated epilepsy. This process included magnetic resonance imaging, single photo emission computed tomography, electroencephalography, and magnetoencephalography (MEG). The findings indicate that functional brain imaging data may greatly assist the surgical treatment decision-making process in RE, especially when structural imaging fails to reveal definitive localizing information. In addition, MEG may provide insights about the cortical reorganization of somatosensory cortex following hemispherectomy.
The configuration of language cortex in the dominant left hemisphere has been well described in t... more The configuration of language cortex in the dominant left hemisphere has been well described in the literature. However, language representation in the right hemisphere, particularly in patients with some degree of bilateral language, remains unclear. Herein, we report six patients who underwent electrocortical stimulation (ECS) for language mapping following implantation of a right subdural electrode array (SEA).The medical records of six bilateral language patients with right SEA implantation at the Minnesota Epilepsy Group between January 1996 and July 2004 were retrospectively reviewed. Language lateralization was based on the results of the intracarotid amobarbital procedure performed preoperatively. Anatomical localization of the SEA for each patient was verified using colored photographs of the cortical surface before and after SEA placement and by review of MRI scans taken with the SEA in place. Frontal and temporal language areas were identified by errors in any language modality including automatic speech, reading, naming, repetition, and comprehension during ECS.Language maps revealed the presence of frontal and/or temporal language areas analogous to the classic essential language areas of the dominant left hemisphere in four of six patients. One patient had a widespread distribution of single-language-error sites over the right temporal lobe. One patient had a silent language map.Our results identified the presence of language cortex in the right hemisphere in five of six patients classified with bilateral language based on intracarotid amobarbital procedure. These areas are assumed to be accessory language zones in relation to the left hemisphere. Further exploratory studies are needed to evaluate their clinical significance.
The purpose of this study is to investigate if multimodality neuroimaging evaluation increases th... more The purpose of this study is to investigate if multimodality neuroimaging evaluation increases the detection of subtle focal cortical dysplasia as part of an epilepsy surgery evaluation. Three patients with normal magnetic resonance imaging and histopathological findings of focal cortical dysplasia were reviewed. Their magnetoencephalography recordings were performed on whole-head magnetoencephalography system. Magnetic resonance images were re-evaluated with special inspection in limited regions guided by magnetoencephalography spike localization. Two patients had ictal and interictal single photon emission computed tomography study after administration of Tc99m ECD. In two patients we found tiny focal abnormalities including slightly increased cortical thickness and blurred gray-white matter junction at the locations of interictal events after re-evaluation of the MR images indicating focal cortical dysplasia. The third patient showed focal atrophic change. All patients are seizure free after surgery. Both ictal and interictal single photon emission computed tomography showed hyperperfusion in the dysplastic cortex regions. Multimodality neuroimaging study can improve the detection of focal cortical dysplasia. Normal magnetic resonance images should be re-evaluated for subtle signs of focal cortical dysplasia especially when magnetoencephalography recording demonstrate focal epileptic discharges.
Magnetoencephalography (MEG) is a novel noninvasive diagnostic tool used to determine preoperativ... more Magnetoencephalography (MEG) is a novel noninvasive diagnostic tool used to determine preoperatively the location of the epileptogenic zone in patients with epilepsy. The presence of focal slowing of activity recorded by electroencephalography (EEG) is an additional indicator of an underlying pathological condition in cases of intractable mesial temporal lobe epilepsy (MTLE). In the present study the authors examined the significance of focal, slow-wave and interictal spike activity detected using MEG in 29 patients who suffered from MTLE that was not associated with structural brain lesions. All patients underwent resective surgery after MEG and EEG monitoring. Equivalent single-dipole modeling was applied to focal low-frequency magnetic activity (LFMA) and interictal paroxysmal activity. Lateralized LFMA was defined as trains of rhythmic activity over the temporal area, with frequencies lower than 7 Hz, which were easily distinguished from background activity. Lateralized LFMA was found in 17 patients (58.6%); it always occurred on the side ipsilateral to the side of resection and displayed a maximum amplitude over the temporal area. Dipolar sources of magnetic flux computed during slow-wave trains were found in the majority of cases in the posterior superior temporal region and, occasionally, in mesial temporal structures that were subsequently resected. With respect to lateralization there was never disagreement between LFMA and MEG interictal spike sources. Thus, in patients with MTLE that is not associated with a mass lesion LFMA is topographically related to the epileptogenic area and, therefore, has value for reliable determination of the side and, possibly, the location of this area. Although focal slowing of EEG background activity is generally considered to be a nonspecific sign of functional disturbance, interictal LFMA in patients with MTLE should be conceptualized as a distinct electrographic phenomenon that is directly related to the epileptogenic abnormality. Analyzing the interictal MEG distribution of LFMA and sharp activity improves the diagnostic utility of MEG in patients with suspected TLE who are undergoing surgical evaluation.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, 2011
Epilepsy patients with Landau-Kleffner syndrome (LKS) usually have a normal brain structure, whic... more Epilepsy patients with Landau-Kleffner syndrome (LKS) usually have a normal brain structure, which makes it a challenge to identify the epileptogenic zone only based on magnetic resonance imaging (MRI) data. A sparse source imaging technique called variation based sparse cortical current density (VB-SCCD) imaging was adopted here to reconstruct cortical sources of magnetoencephalography (MEG) interictal spikes from an LKS patient. Realistic boundary element (BE) head and cortex models were built by segmenting structural MRI. 148-channel MEG was recorded for 10 minutes between seizures. Total 29 epileptiform spikes were selected for analysis. The primary cortical sources were observed locating at the left intra- and perisylvian cortex. Multiple extrasylvian sources were identified as the secondary sources. The spatio-temporal patterns of cortical sources provide more insights about the neuronal synchrony and propagation of epileptic discharges. Our observations were consistent with presurgical diagnosis for this patient and observation of aphasia in LKS. The present results suggest that the promising of VB-SCCD technique in assisting with presurgical planning and studying the neural network for LKS in determining the lateralization of epileptic origins. It can further be applied to non-invasively localize and/or lateralize eloquent cortex for language for epilepsy patients in general in the future.
While the cerebral cortex in the human brain is of functional importance, functions defined on th... more While the cerebral cortex in the human brain is of functional importance, functions defined on this structure are difficult to analyze spatially due to its highly convoluted irregular geometry. This study developed a novel L1-norm regularization method using a newly proposed multi-resolution face-based wavelet method to estimate cortical electrical activities in electroencephalography (EEG) and magnetoencephalography (MEG) inverse problems. The proposed wavelets were developed based on multi-resolution models built from irregular cortical surface meshes, which were realized in this study too. The multi-resolution wavelet analysis was used to seek sparse representation of cortical current densities in transformed domains, which was expected due to the compressibility of wavelets, and evaluated using Monte Carlo simulations. The EEG/MEG inverse problems were solved with the use of the novel L1-norm regularization method exploring the sparseness in the wavelet domain. The inverse solutions obtained from the new method using MEG data were evaluated by Monte Carlo simulations too. The present results indicated that cortical current densities could be efficiently compressed using the proposed face-based wavelet method, which exhibited better performance than the vertex-based wavelet method. In both simulations and auditory experimental data analysis, the proposed L1-norm regularization method showed better source detection accuracy and less estimation errors than other two classic methods, i.e. weighted minimum norm (wMNE) and cortical low-resolution electromagnetic tomography (cLORETA). This study suggests that the L1-norm regularization method with the use of face-based wavelets is a promising tool for studying functional activations of the human brain.
Neuromodulation : journal of the International Neuromodulation Society, 2013
Development of effective chronic pain treatment strategies has been hampered by the lack of an ob... more Development of effective chronic pain treatment strategies has been hampered by the lack of an objective pain biomarker. Magnetoencephalography (MEG) has demonstrated cortical disorganization corresponding to the affected limb of complex regional pain syndrome (CRPS) patients and spinal cord stimulation (SCS) can acutely treat CRPS in a reversible and adjustable fashion. In order to better define a potential MEG-sensitive biomarker for chronic pain, our goal was to study the effects of therapeutic SCS on cortical disorganization in patients with unilateral limb CRPS. Two patients treated with either thoracic or cervical SCS with leg or arm CRPS were studied with MEG. Baseline and tactile-evoked responses were recorded with and without effective SCS therapy. All MEG recordings were obtained with minimal interference. In the patient with arm CRPS, with the stimulator off, first and fifth digit primary somatosensory (SI) cortical representations (D1/D5) were significantly disorganized and spatially inverted as compared with the opposite unaffected limb. Effective SCS therapy was then able to acutely normalize or restore hand cortical organization in the affected CRPS limb. This restoration of cortical organization was partially maintained with lingering pain relief when the stimulator was subsequently turned off. This is the first report of a MEG study showing D1/D5 cortical disorganization and its apparent reversal or restoration with cervical SCS therapy. Ours also is the first report of an apparent acute reversible interchange in the cortical representations of D1 and D5. Our limited data demonstrate that disorganization of SI cortex might be a neurophysiologic marker of chronic pain as shown with instantaneous normalization of SI disorganization or restoration of SI organization with therapeutic SCS. As a clinically proven tool for functional mapping, MEG might be shown to provide an objective measure of chronic pain. More data are required to further investigate this possibility.
Rasmussen's encephalitis (RE) is a cryptogenic progressive inflammatory disorder of the brain tha... more Rasmussen's encephalitis (RE) is a cryptogenic progressive inflammatory disorder of the brain that causes severe neurological problems, including intractable focal epilepsy. In select patients, aggressive treatment using cerebral hemispherectomy may ameliorate the devastating cognitive decline that accompanies this disease, even if the epileptic focus appears broadly distributed. We present a case of histopathologically-confirmed RE evaluated using a multimodal process that explored the physical and functional aspects of the associated epilepsy. This process included magnetic resonance imaging, single photo emission computed tomography, electroencephalography, and magnetoencephalography (MEG). The findings indicate that functional brain imaging data may greatly assist the surgical treatment decision-making process in RE, especially when structural imaging fails to reveal definitive localizing information. In addition, MEG may provide insights about the cortical reorganization of somatosensory cortex following hemispherectomy.
The configuration of language cortex in the dominant left hemisphere has been well described in t... more The configuration of language cortex in the dominant left hemisphere has been well described in the literature. However, language representation in the right hemisphere, particularly in patients with some degree of bilateral language, remains unclear. Herein, we report six patients who underwent electrocortical stimulation (ECS) for language mapping following implantation of a right subdural electrode array (SEA).The medical records of six bilateral language patients with right SEA implantation at the Minnesota Epilepsy Group between January 1996 and July 2004 were retrospectively reviewed. Language lateralization was based on the results of the intracarotid amobarbital procedure performed preoperatively. Anatomical localization of the SEA for each patient was verified using colored photographs of the cortical surface before and after SEA placement and by review of MRI scans taken with the SEA in place. Frontal and temporal language areas were identified by errors in any language modality including automatic speech, reading, naming, repetition, and comprehension during ECS.Language maps revealed the presence of frontal and/or temporal language areas analogous to the classic essential language areas of the dominant left hemisphere in four of six patients. One patient had a widespread distribution of single-language-error sites over the right temporal lobe. One patient had a silent language map.Our results identified the presence of language cortex in the right hemisphere in five of six patients classified with bilateral language based on intracarotid amobarbital procedure. These areas are assumed to be accessory language zones in relation to the left hemisphere. Further exploratory studies are needed to evaluate their clinical significance.
The purpose of this study is to investigate if multimodality neuroimaging evaluation increases th... more The purpose of this study is to investigate if multimodality neuroimaging evaluation increases the detection of subtle focal cortical dysplasia as part of an epilepsy surgery evaluation. Three patients with normal magnetic resonance imaging and histopathological findings of focal cortical dysplasia were reviewed. Their magnetoencephalography recordings were performed on whole-head magnetoencephalography system. Magnetic resonance images were re-evaluated with special inspection in limited regions guided by magnetoencephalography spike localization. Two patients had ictal and interictal single photon emission computed tomography study after administration of Tc99m ECD. In two patients we found tiny focal abnormalities including slightly increased cortical thickness and blurred gray-white matter junction at the locations of interictal events after re-evaluation of the MR images indicating focal cortical dysplasia. The third patient showed focal atrophic change. All patients are seizure free after surgery. Both ictal and interictal single photon emission computed tomography showed hyperperfusion in the dysplastic cortex regions. Multimodality neuroimaging study can improve the detection of focal cortical dysplasia. Normal magnetic resonance images should be re-evaluated for subtle signs of focal cortical dysplasia especially when magnetoencephalography recording demonstrate focal epileptic discharges.
Magnetoencephalography (MEG) is a novel noninvasive diagnostic tool used to determine preoperativ... more Magnetoencephalography (MEG) is a novel noninvasive diagnostic tool used to determine preoperatively the location of the epileptogenic zone in patients with epilepsy. The presence of focal slowing of activity recorded by electroencephalography (EEG) is an additional indicator of an underlying pathological condition in cases of intractable mesial temporal lobe epilepsy (MTLE). In the present study the authors examined the significance of focal, slow-wave and interictal spike activity detected using MEG in 29 patients who suffered from MTLE that was not associated with structural brain lesions. All patients underwent resective surgery after MEG and EEG monitoring. Equivalent single-dipole modeling was applied to focal low-frequency magnetic activity (LFMA) and interictal paroxysmal activity. Lateralized LFMA was defined as trains of rhythmic activity over the temporal area, with frequencies lower than 7 Hz, which were easily distinguished from background activity. Lateralized LFMA was found in 17 patients (58.6%); it always occurred on the side ipsilateral to the side of resection and displayed a maximum amplitude over the temporal area. Dipolar sources of magnetic flux computed during slow-wave trains were found in the majority of cases in the posterior superior temporal region and, occasionally, in mesial temporal structures that were subsequently resected. With respect to lateralization there was never disagreement between LFMA and MEG interictal spike sources. Thus, in patients with MTLE that is not associated with a mass lesion LFMA is topographically related to the epileptogenic area and, therefore, has value for reliable determination of the side and, possibly, the location of this area. Although focal slowing of EEG background activity is generally considered to be a nonspecific sign of functional disturbance, interictal LFMA in patients with MTLE should be conceptualized as a distinct electrographic phenomenon that is directly related to the epileptogenic abnormality. Analyzing the interictal MEG distribution of LFMA and sharp activity improves the diagnostic utility of MEG in patients with suspected TLE who are undergoing surgical evaluation.
Uploads
Papers by Wenbo Zhang