1
|
Lagarde S, Modolo J, Yochum M, Carvallo A, Ballabeni A, Scavarda D, Carron R, Villeneuve N, Bartolomei F, Wendling F. Modification of brain conductivity in human focal epilepsy: A model-based estimation from stereoelectroencephalography. Epilepsia 2024; 65:1744-1755. [PMID: 38491955 DOI: 10.1111/epi.17957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Revised: 03/04/2024] [Accepted: 03/05/2024] [Indexed: 03/18/2024]
Abstract
OBJECTIVE We have developed a novel method for estimating brain tissue electrical conductivity using low-intensity pulse stereoelectroencephalography (SEEG) stimulation coupled with biophysical modeling. We evaluated the hypothesis that brain conductivity is correlated with the degree of epileptogenicity in patients with drug-resistant focal epilepsy. METHODS We used bipolar low-intensity biphasic pulse stimulation (.2 mA) followed by a postprocessing pipeline for estimating brain conductivity. This processing is based on biophysical modeling of the electrical potential induced in brain tissue between the stimulated contacts in response to pulse stimulation. We estimated the degree of epileptogenicity using a semi-automatic method quantifying the dynamic of fast discharge at seizure onset: the epileptogenicity index (EI). We also investigated how the location of stimulation within specific anatomical brain regions or within lesional tissue impacts brain conductivity. RESULTS We performed 1034 stimulations of 511 bipolar channels in 16 patients. We found that brain conductivity was lower in the epileptogenic zone (EZ; unpaired median difference = .064, p < .001) and inversely correlated with the epileptogenic index value (p < .001, Spearman rho = -.32). Conductivity values were also influenced by anatomical site, location within lesion, and delay between SEEG electrode implantation and stimulation, and had significant interpatient variability. Mixed model multivariate analysis showed that conductivity is significantly associated with EI (F = 13.45, p < .001), anatomical regions (F = 5.586, p < .001), delay since implantation (F = 14.71, p = .003), and age at SEEG (F = 6.591, p = .027), but not with the type of lesion (F = .372, p = .773) or the delay since last seizure (F = 1.592, p = .235). SIGNIFICANCE We provide a novel model-based method for estimating brain conductivity from SEEG low-intensity pulse stimulations. The brain tissue conductivity is lower in EZ as compared to non-EZ. Conductivity also varies significantly across anatomical brain regions. Involved pathophysiological processes may include changes in the extracellular space (especially volume or tortuosity) in epileptic tissue.
Collapse
Affiliation(s)
- Stanislas Lagarde
- Epileptology and Cerebral Rhythmology Department (member of the ERN EpiCARE Network), APHM, Timone Hospital, Marseille, France
- INS, Institut de Neurosciences des Systèmes, Aix Marseille University, INSERM, Marseille, France
- University Hospitals (HUG) and University of Geneva (UNIGE), Geneva, Switzerland
| | - Julien Modolo
- LTSI - U1099, University of Rennes, INSERM, Rennes, France
| | - Maxime Yochum
- LTSI - U1099, University of Rennes, INSERM, Rennes, France
| | | | - Alice Ballabeni
- Epileptology and Cerebral Rhythmology Department (member of the ERN EpiCARE Network), APHM, Timone Hospital, Marseille, France
- University of Modena and Reggio-Emilia, Modena, Italy
| | - Didier Scavarda
- INS, Institut de Neurosciences des Systèmes, Aix Marseille University, INSERM, Marseille, France
- Pediatric Neurosurgery Department, APHM, Timone Hospital, Marseille, France
| | - Romain Carron
- INS, Institut de Neurosciences des Systèmes, Aix Marseille University, INSERM, Marseille, France
- Stereotactic and Functional Neurosurgery Department, APHM, Timone Hospital, Marseille, France
| | | | - Fabrice Bartolomei
- Epileptology and Cerebral Rhythmology Department (member of the ERN EpiCARE Network), APHM, Timone Hospital, Marseille, France
- INS, Institut de Neurosciences des Systèmes, Aix Marseille University, INSERM, Marseille, France
| | | |
Collapse
|
2
|
Amirabdollahian A, Moeini M. An In Situ-Gelling Conductive Hydrogel for Potential Use in Neural Tissue Engineering. Tissue Eng Part A 2024. [PMID: 38445375 DOI: 10.1089/ten.tea.2023.0359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2024] Open
Abstract
Cerebral cavitation is usual following acute brain injuries, such as stroke and traumatic brain injuries, as well as after tumor resection. Minimally invasive implantation of an injectable scaffold in the cavity is a promising approach for potential regeneration of tissue loss. This study aimed at designing an in situ-gelling conductive hydrogel containing silk fibroin (SF), brain decellularized extracellular matrix (dECM), and carbon nanotubes (CNT) for potential use in brain tissue regeneration. Two percent w/v SF hydrogels with different concentrations of dECM (0.1%, 0.2%, or 0.3% w/v) and CNTs (0.05%, 0.1%, or 0.25% w/v) were fabricated and characterized. It was observed that with the addition of dECM, the porosity decreased, whereas swelling and electrical conductivity tended to increase. The addition of dECM also led to a faster resorption rate, but no significant change in compressive modulus. Addition of CNTs, on the other hand, led to a denser, stronger, and more regular porous structure, higher swelling ratio, faster gelation time, slower degradation rate, and a significant increase in electrical conductivity. dECM and CNTs combined together resulted in superior porosity, swelling, resorption rate, mechanical properties, and electrical conductivity compared with SF scaffolds containing only dECM or CNTs. Hydrogel samples containing 2% SF, 0.3% dECM, and 0.1% CNTs had a high porosity (58.9%), low swelling ratio (15.9%), high conductivity (2.35 × 10-4 S/m), and moderate degradation rate (37.3% after 21 days), appropriate for neural tissue engineering applications. Cell evaluation studies also showed that the hydrogel systems support the cell adhesion and growth, with no sign of significant cytotoxicity. Impact statement Tissue loss and formation of a fluid-filled cavity following stroke, traumatic brain injury, or brain tumor resection lead to sensorimotor and/or cognitive deficits. The lack of a healthy extracellular matrix in the cavity avoids the endogenous cell migration and axonal sprouting and may also worsen the secondary injuries to peri-lesional tissue. Due to the brain anatomy, simple implantation of tissue engineering scaffolds to the injured site is not possible in many cases. Therefore, the development of injectable scaffolds that support neural growth and differentiation is crucial for tissue repair or limiting the expansion of damage region.
Collapse
Affiliation(s)
- Atefeh Amirabdollahian
- Department of Biomedical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran
| | - Mohammad Moeini
- Department of Biomedical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran
| |
Collapse
|
3
|
Nishimoto H, Kodera S, Otsuru N, Hirata A. Individual and group-level optimization of electric field in deep brain region during multichannel transcranial electrical stimulation. Front Neurosci 2024; 18:1332135. [PMID: 38529268 PMCID: PMC10961445 DOI: 10.3389/fnins.2024.1332135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Accepted: 02/19/2024] [Indexed: 03/27/2024] Open
Abstract
Electrode montage optimization for transcranial electric stimulation (tES) is a challenging topic for targeting a specific brain region. Targeting the deep brain region is difficult due to tissue inhomogeneity, resulting in complex current flow. In this study, a simplified protocol for montage optimization is proposed for multichannel tES (mc-tES). The purpose of this study was to reduce the computational cost for mc-tES optimization and to evaluate the mc-tES for deep brain regions. Optimization was performed using a simplified protocol for montages under safety constraints with 20 anatomical head models. The optimization procedure is simplified using the surface EF of the deep brain target region, considering its small volume and non-concentric distribution of the electrodes. Our proposal demonstrated that the computational cost was reduced by >90%. A total of six-ten electrodes were necessary for robust EF in the target region. The optimization with surface EF is comparable to or marginally better than using conventional volumetric EF for deep brain tissues. An electrode montage with a mean injection current amplitude derived from individual analysis was demonstrated to be useful for targeting the deep region at the group level. The optimized montage and injection current were derived at the group level. Our proposal at individual and group levels showed great potential for clinical application.
Collapse
Affiliation(s)
- Hidetaka Nishimoto
- Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology, Nagoya, Japan
| | - Sachiko Kodera
- Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology, Nagoya, Japan
- Center of Biomedical Physics and Information Technology, Nagoya Institute of Technology, Nagoya, Japan
| | - Naofumi Otsuru
- Institute for Human Movement and Medical Sciences, Niigata University of Health and Welfare, Niigata, Japan
- Department of Physical Therapy, Niigata University of Health and Welfare, Niigata, Japan
| | - Akimasa Hirata
- Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology, Nagoya, Japan
- Center of Biomedical Physics and Information Technology, Nagoya Institute of Technology, Nagoya, Japan
| |
Collapse
|
4
|
Shindhelm AC, Thio BJ, Sinha SR. Modeling the Impact of Electrode/Tissue Geometry on Electrical Stimulation in Stereo-EEG. J Clin Neurophysiol 2023; 40:339-349. [PMID: 34482315 DOI: 10.1097/wnp.0000000000000892] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
PURPOSE Electrical stimulation through depth electrodes is used to map function and seizure onset during stereoelectroencephalography in patients undergoing evaluation for epilepsy surgery. Factors such as electrode design, location, and orientation are expected to impact effects of electrical stimulation. METHODS We developed a steady-state finite element model of brain tissue including five layers (skull through white matter) and an implanted electrode to explore the impact of electrode design and placement on the activation of brain tissue by electrical stimulation. We calculated electric potentials, current densities, and volume of tissue activated ( Volact ) in response to constant current bipolar stimulation. We modeled two depth electrode designs (3.5- and 4.43-mm intercontact spacing) and varied electrode location and orientation. RESULTS The electrode with greater intercontact spacing produced 8% to 23% larger Volact (1% to 16% considering only gray matter). Vertical displacement of the electrodes by half intercontact space increased Volact for upward displacement (6% to 83% for all brain tissue or -5% to 96% gray matter only) and decreased Volact (1% to 16% or 24% to 49% gray matter only) for downward displacement. Rotating the electrode in the tissue by 30° to 60° with respect to the vertical axis increased Volact by 30% to 90% (20%-48% gray matter only). CONCLUSIONS Location and orientation of depth electrodes with respect to surrounding brain tissue have a large impact on the amount of tissue activated during electrical stimulation mapping in stereoelectroencephalography. Electrode design has an impact, although modest for commonly used designs. Individualization of stimulation intensity at each location remains critical, especially for avoiding false-negative results.
Collapse
Affiliation(s)
- Alexis C Shindhelm
- Department of Neurology, Duke University Medical Center, Durham, North Carolina; and
| | - Brandon J Thio
- Department of Biomedical Engineering, Duke University, Durham, North Carolina
| | - Saurabh R Sinha
- Department of Neurology, Duke University Medical Center, Durham, North Carolina; and
| |
Collapse
|
5
|
Abboud T, Mielke D, Rohde V. Mini Review: Impedance Measurement in Neuroscience and Its Prospective Application in the Field of Surgical Neurooncology. Front Neurol 2022; 12:825012. [PMID: 35111132 PMCID: PMC8801870 DOI: 10.3389/fneur.2021.825012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 12/27/2021] [Indexed: 11/13/2022] Open
Abstract
Impedance measurement of human tissue can be performed either in vivo or ex vivo. The majority of the in-vivo approaches are non-invasive, and few are invasive. To date, there is no gold standard for impedance measurement of intracranial tissue. In addition, most of the techniques addressing this topic are still experimental and have not found their way into clinical practice. This review covers available impedance measurement approaches in the neuroscience in general and specifically addresses recent advances made in the application of impedance measurement in the field of surgical neurooncology. It will provide an understandable picture on impedance measurement and give an overview of limitations that currently hinders clinical application and require future technical and conceptual solutions.
Collapse
|
6
|
Mulinari Pinheiro Machado M, Voda A, Besançon G, Becq G, Kahane P, David O. Brain tissue classification from stereoelectroencephalographic recordings. J Neurosci Methods 2022; 365:109375. [PMID: 34627927 DOI: 10.1016/j.jneumeth.2021.109375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Revised: 09/29/2021] [Accepted: 10/01/2021] [Indexed: 10/20/2022]
Abstract
BACKGROUND Stereoelectroencephalographic (SEEG) recordings can be performed before final resective surgery in some drug-resistant patients with focal epilepsies. For good SEEG signal interpretation, it is important to correctly identify the brain tissue in which each contact is inserted. Tissue classification is usually done with the coregistration of CT scan (with implanted SEEG electrodes) with preoperative MRI. NEW METHOD Brain tissue classification is done here directly from SEEG signals obtained at rest by a linear discriminant analysis (LDA) classifier using measured SEEG signals. The classification operates on features extracted from Bode plots obtained via non-parametric frequency domain transfer functions of adjacent contacts pairs. Classification results have been compared with classification from T1 MRI following the labelling procedure described in Deman et al. (2018), together with minor corrections by visual inspection by specialists. RESULTS With the data processed from 19 epileptic patients representing 1284 contact pairs, an accuracy of 72 ± 3% was obtained for homogeneous tissue separation. To our knowledge only one previous study conducted brain tissue classification using the power spectra of SEEG signals, and the distance between contacts on a shaft. The features proposed in our article performed better with the LDA classifier. However, the Bayesian classifier proposed in Greene et al. (2020) is more robust and could be used in a future study to enhance the classification performance. CONCLUSIONS AND SIGNIFICANCE Our findings suggest that careful analysis of the transfer function between adjacent contacts measuring resting activity via frequency domain identification, could allow improved interpretation of SEEG data and or their co-registration with subject's anatomy.
Collapse
Affiliation(s)
| | - Alina Voda
- Univ. Grenoble Alpes, CNRS, Grenoble INP, GIPSA-lab, 38000 Grenoble, France.
| | - Gildas Besançon
- Univ. Grenoble Alpes, CNRS, Grenoble INP, GIPSA-lab, 38000 Grenoble, France.
| | - Guillaume Becq
- Univ. Grenoble Alpes, CNRS, Grenoble INP, GIPSA-lab, 38000 Grenoble, France.
| | - Philippe Kahane
- Univ. Grenoble Alpes, CHU Grenoble Alpes, Grenoble Institut des Neurosciences, GIN, 38000 Grenoble, France.
| | - Olivier David
- Univ. Grenoble Alpes, Grenoble Institut des Neurosciences, GIN, 38000 Grenoble, France; Aix Marseille Univ, Inserm, INS, Institut de Neurosciences des Systémes, Marseille, France.
| |
Collapse
|
7
|
Nissi J, Laakso I. Magneto- and electrophosphene thresholds in the retina: a dosimetry modeling study. Phys Med Biol 2021; 67. [PMID: 34965521 DOI: 10.1088/1361-6560/ac46df] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 12/29/2021] [Indexed: 11/12/2022]
Abstract
Objective:Sensations of flickering light produced by time-varying magnetic fields or electric currents are called magneto- or electrophosphenes. Phosphene thresholds have been used in international guidelines and standards as an estimate of the thresholds of exposure that produce effects in the central nervous system. However, the estimated threshold values have a large range of uncertainty.Approach:Phosphene thresholds were approximated by simulating five phosphene threshold experiments. Retinal electric fields and currents induced by electric and magnetic stimulation were calculated using the finite element method and 14 anatomically realistic computational models of human heads.Main results:The radial component of retinal current density was determined to be in the range of 6.0~--~20.6~mA/m$^2$. This study produces more accurate estimates for threshold current density in the retina using detailed anatomical models and the estimates had a reduced range of uncertainty compared to earlier studies.Significance:The results are useful for studying the mechanisms of retinal phosphenes and for the development of exposure limits for the central nervous system.
Collapse
Affiliation(s)
- Janita Nissi
- Department of Electrical Engineering and Automation, Aalto University, Otakaari 3, Espoo, 02150, FINLAND
| | - Ilkka Laakso
- Department of Electrical Engineering and Automation, Aalto University, Otakaari 3, Espoo, 02150, FINLAND
| |
Collapse
|
8
|
Abboud T, Hahn G, Just A, Paidhungat M, Nazarenus A, Mielke D, Rohde V. An insight into electrical resistivity of white matter and brain tumors. Brain Stimul 2021; 14:1307-1316. [PMID: 34481094 DOI: 10.1016/j.brs.2021.08.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Revised: 08/27/2021] [Accepted: 08/31/2021] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND There is a lack of information regarding electrical properties of white matter and brain tumors. OBJECTIVE To investigate the feasibility of in-vivo measurement of electrical resistivity during brain surgery and establish a better understanding of the resistivity patterns of brain tumors in correlation to the white matter. METHODS A bipolar probe was used to measure electrical resistivity during surgery in a prospective cohort of patients with brain tumors. For impedance measurement, the probe applied a constant current of 0.7 μA with a frequency of 140 Hz. The measurement was performed in the white matter within and outside peritumoral edema as well as in non-enhancing, enhancing and necrotic tumor areas. Resistivity values expressed in ohmmeter (Ω∗m) were compared between different intracranial tissues and brain tumors. RESULTS Ninety-two patients (gliomas WHO II:16, WHO III:10, WHO IV:33, metastasis:33) were included. White matter outside peritumoral edema had higher resistivity values (13.3 ± 1.7 Ω∗m) than within peritumoral edema (8.5 ± 1.6 Ω∗m), and both had higher values than brain tumors including non-enhancing (WHO II:6.4 ± 1.3 Ω∗m, WHO III:6.3 ± 0.9 Ω∗m), enhancing (WHO IV:5 ± 1 Ω∗m, metastasis:5.4 ± 1.3 Ω∗m) and necrotic tumor areas (WHO IV:3.9 ± 1.1 Ω∗m, metastasis:4.3 ± 1.3 Ω∗m), p=<0.001. No difference was found between low-grade and anaplastic gliomas, p = 0.808, while resistivity values in both were higher than the highest values found in glioblastomas, p = 0.003 and p = 0.004, respectively. CONCLUSIONS The technique we applied enabled us to measure electrical resistivity of white matter and brain tumors in-vivo presumably with a significant effect with regard to dielectric polarization. Our results suggest that there are significant differences within different areas and subtypes of brain tumors and that white matter exhibits higher electrical resistivity than brain tumors.
Collapse
Affiliation(s)
- Tammam Abboud
- Department of Neurosurgery, University Medical Center Göttingen, Robert-Koch-Straße 40, 37075, Göttingen, Germany.
| | - Günter Hahn
- Department of Anesthesiology, EIT Research Unit, University Medical Center Göttingen, Robert-Koch-Straße 40, 37075, Göttingen, Germany
| | - Anita Just
- Department of Anesthesiology, EIT Research Unit, University Medical Center Göttingen, Robert-Koch-Straße 40, 37075, Göttingen, Germany
| | - Mihika Paidhungat
- Department of Neurosurgery, University Medical Center Göttingen, Robert-Koch-Straße 40, 37075, Göttingen, Germany
| | - Angelina Nazarenus
- Department of Neurosurgery, University Medical Center Göttingen, Robert-Koch-Straße 40, 37075, Göttingen, Germany
| | - Dorothee Mielke
- Department of Neurosurgery, University Medical Center Göttingen, Robert-Koch-Straße 40, 37075, Göttingen, Germany
| | - Veit Rohde
- Department of Neurosurgery, University Medical Center Göttingen, Robert-Koch-Straße 40, 37075, Göttingen, Germany
| |
Collapse
|
9
|
Cost of focality in TDCS: Interindividual variability in electric fields. Brain Stimul 2020; 13:117-124. [DOI: 10.1016/j.brs.2019.09.017] [Citation(s) in RCA: 49] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 09/25/2019] [Accepted: 09/29/2019] [Indexed: 11/24/2022] Open
|
10
|
Carvallo A, Modolo J, Benquet P, Lagarde S, Bartolomei F, Wendling F. Biophysical Modeling for Brain Tissue Conductivity Estimation Using SEEG Electrodes. IEEE Trans Biomed Eng 2019; 66:1695-1704. [DOI: 10.1109/tbme.2018.2877931] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
11
|
Variation in Reported Human Head Tissue Electrical Conductivity Values. Brain Topogr 2019; 32:825-858. [PMID: 31054104 PMCID: PMC6708046 DOI: 10.1007/s10548-019-00710-2] [Citation(s) in RCA: 121] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Accepted: 04/13/2019] [Indexed: 01/01/2023]
Abstract
Electromagnetic source characterisation requires accurate volume conductor models representing head geometry and the electrical conductivity field. Head tissue conductivity is often assumed from previous literature, however, despite extensive research, measurements are inconsistent. A meta-analysis of reported human head electrical conductivity values was therefore conducted to determine significant variation and subsequent influential factors. Of 3121 identified publications spanning three databases, 56 papers were included in data extraction. Conductivity values were categorised according to tissue type, and recorded alongside methodology, measurement condition, current frequency, tissue temperature, participant pathology and age. We found variation in electrical conductivity of the whole-skull, the spongiform layer of the skull, isotropic, perpendicularly- and parallelly-oriented white matter (WM) and the brain-to-skull-conductivity ratio (BSCR) could be significantly attributed to a combination of differences in methodology and demographics. This large variation should be acknowledged, and care should be taken when creating volume conductor models, ideally constructing them on an individual basis, rather than assuming them from the literature. When personalised models are unavailable, it is suggested weighted average means from the current meta-analysis are used. Assigning conductivity as: 0.41 S/m for the scalp, 0.02 S/m for the whole skull, or when better modelled as a three-layer skull 0.048 S/m for the spongiform layer, 0.007 S/m for the inner compact and 0.005 S/m for the outer compact, as well as 1.71 S/m for the CSF, 0.47 S/m for the grey matter, 0.22 S/m for WM and 50.4 for the BSCR.
Collapse
|
12
|
Mikkonen M, Laakso I. Effects of posture on electric fields of non-invasive brain stimulation. ACTA ACUST UNITED AC 2019; 64:065019. [DOI: 10.1088/1361-6560/ab03f5] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
13
|
Vrba J, Janca R, Blaha M, Jezdik P, Belohlavkova A, Krsek P, Vrba D. Modeling of Brain Tissue Heating Caused by Direct Cortical Stimulation for Assessing the Risk of Thermal Damage. IEEE Trans Neural Syst Rehabil Eng 2019; 27:440-449. [PMID: 30763244 DOI: 10.1109/tnsre.2019.2898253] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This paper aims to employ the numerical simulations to assess the risk of cellular damage during the application of a novel paradigm of electrical stimulation mapping (ESM) used in neurosurgery. The core principle of the paradigm is the use of short, high-intensity and high-frequency stimulation pulses. We developed a complex numerical model and performed coupled electro-thermal transient simulations. The model was optimized by incorporating ESM electrodes' resistance obtained during multiple intraoperative measurements and validated by comparing them with the results of temperature distribution measurement acquired by thermal imaging. The risk of heat-induced cellular damage was assessed by applying the Arrhenius equation integral on the computed time-dependent spatial distribution of temperature in the brain tissue. Our results suggest that the impact of the temperature increase during our novel ESM paradigm is thermally non-destructive. The presented simulation results match the previously published thermographic measurement and histopathological examination of the stimulated brain tissue and confirm the safety of the novel ESM.
Collapse
|
14
|
Mikkonen M, Laakso I, Sumiya M, Koyama S, Hirata A, Tanaka S. TMS Motor Thresholds Correlate With TDCS Electric Field Strengths in Hand Motor Area. Front Neurosci 2018; 12:426. [PMID: 29988501 PMCID: PMC6026630 DOI: 10.3389/fnins.2018.00426] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Accepted: 07/06/2018] [Indexed: 12/05/2022] Open
Abstract
Transcranial direct current stimulation (TDCS) modulates cortical activity and influences motor and cognitive functions in both healthy and clinical populations. However, there is large inter-individual variability in the responses to TDCS. Computational studies have suggested that inter-individual differences in cranial and brain anatomy may contribute to this variability via creating varying electric fields in the brain. This implies that the electric fields or their strength and orientation should be considered and incorporated when selecting the TDCS dose. Unfortunately, electric field modeling is difficult to perform; thus, a more-robust and practical method of estimating the strength of TDCS electric fields for experimental use is required. As recent studies have revealed a relationship between the sensitivity to TMS and motor cortical TDCS after-effects, the aim of the present study was to investigate whether the resting motor threshold (RMT), a simple measure of transcranial magnetic stimulation (TMS) sensitivity, would be useful for estimating TDCS electric field strengths in the hand area of primary motor cortex (M1). To achieve this, we measured the RMT in 28 subjects. We also obtained magnetic resonance images from each subject to build individual three-dimensional anatomic models, which were used in solving the TDCS and TMS electric fields using the finite element method (FEM). Then, we calculated the correlation between the measured RMT and the modeled TDCS electric fields. We found that the RMT correlated with the TDCS electric fields in hand M1 (R2 = 0.58), but no obvious correlations were identified in regions outside M1. The found correlation was mainly due to a correlation between the TDCS and TMS electric fields, both of which were affected by individual's anatomic features. In conclusion, the RMT could provide a useful tool for estimating cortical electric fields for motor cortical TDCS.
Collapse
Affiliation(s)
- Marko Mikkonen
- Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland
| | - Ilkka Laakso
- Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland
| | - Motofumi Sumiya
- Department of System Neuroscience, National Institute for Physiological Sciences, Okazaki, Japan
| | - Soichiro Koyama
- School of Health Sciences, Faculty of Rehabilitation, Fujita Health University, Toyoake, Japan
| | - Akimasa Hirata
- Department of Computer Science and Engineering, Nagoya Institute of Technology, Nagoya, Japan
| | - Satoshi Tanaka
- Laboratory of Psychology, Hamamatsu University School of Medicine, Hamamatsu, Japan
| |
Collapse
|
15
|
Szabó N, Faragó P, Király A, Veréb D, Csete G, Tóth E, Kocsis K, Kincses B, Tuka B, Párdutz Á, Szok D, Tajti J, Vécsei L, Kincses ZT. Evidence for Plastic Processes in Migraine with Aura: A Diffusion Weighted MRI Study. Front Neuroanat 2018; 11:138. [PMID: 29387002 PMCID: PMC5776127 DOI: 10.3389/fnana.2017.00138] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2017] [Accepted: 12/26/2017] [Indexed: 01/03/2023] Open
Abstract
Background: Formerly white matter abnormalities in a mixed group of migraine patients with and without aura were shown. Here, we aimed to explore white matter alterations in a homogeneous group of migraineurs with aura and to delineate possible relationships between white matter changes and clinical variables. Methods: Eighteen patients with aura, 25 migraine patients without aura and 28 controls were scanned on a 1.5T MRI scanner. Diffusivity parameters of the white matter were estimated and compared between patients’ groups and controls using whole-brain tract-based spatial statistics. Results: Decreased radial diffusivity (p < 0.036) was found bilaterally in the parieto-occipital white matter, the corpus callosum, and the cingular white matter of migraine with aura (MwA) patients compared to controls. Migraine without aura (MwoA) patients showed no alteration compared to controls. MwA compared to MwoA showed increased fractional anisotropy (p < 0.048) in the left parieto-occipital white matter. In MwA a negative correlation was found between axial diffusivity and disease duration in the left superior longitudinal fascicle (left parieto-occipital region) and in the left corticospinal tract (p < 0.036) and with the number of the attacks in the right superior longitudinal fascicle (p < 0.048). Conclusion: We showed for the first time that there are white matter microstructural differences between these two subgroups of migraine and hence it is important to handle the two groups separately in further researches. We propose that degenerative and maladaptive plastic changes coexist in the disease and the diffusion profile is a result of these processes.
Collapse
Affiliation(s)
- Nikoletta Szabó
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary.,Central European Institute of Technology, Brno, Czechia
| | - Péter Faragó
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary.,Central European Institute of Technology, Brno, Czechia
| | - András Király
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary.,Central European Institute of Technology, Brno, Czechia
| | - Dániel Veréb
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
| | - Gergő Csete
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
| | - Eszter Tóth
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
| | - Krisztián Kocsis
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
| | - Bálint Kincses
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
| | | | - Árpád Párdutz
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
| | - Délia Szok
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
| | - János Tajti
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
| | - László Vécsei
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary.,MTA-SZTE Neuroscience Research Group, Szeged, Hungary
| | - Zsigmond T Kincses
- Neuroimaging Research Group, Department of Neurology, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
| |
Collapse
|
16
|
Minjoli S, Saturnino GB, Blicher JU, Stagg CJ, Siebner HR, Antunes A, Thielscher A. The impact of large structural brain changes in chronic stroke patients on the electric field caused by transcranial brain stimulation. NEUROIMAGE-CLINICAL 2017; 15:106-117. [PMID: 28516033 PMCID: PMC5426045 DOI: 10.1016/j.nicl.2017.04.014] [Citation(s) in RCA: 72] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 04/03/2017] [Accepted: 04/15/2017] [Indexed: 11/02/2022]
Abstract
Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (TDCS) are two types of non-invasive transcranial brain stimulation (TBS). They are useful tools for stroke research and may be potential adjunct therapies for functional recovery. However, stroke often causes large cerebral lesions, which are commonly accompanied by a secondary enlargement of the ventricles and atrophy. These structural alterations substantially change the conductivity distribution inside the head, which may have potentially important consequences for both brain stimulation methods. We therefore aimed to characterize the impact of these changes on the spatial distribution of the electric field generated by both TBS methods. In addition to confirming the safety of TBS in the presence of large stroke-related structural changes, our aim was to clarify whether targeted stimulation is still possible. Realistic head models containing large cortical and subcortical stroke lesions in the right parietal cortex were created using MR images of two patients. For TMS, the electric field of a double coil was simulated using the finite-element method. Systematic variations of the coil position relative to the lesion were tested. For TDCS, the finite-element method was used to simulate a standard approach with two electrode pads, and the position of one electrode was systematically varied. For both TMS and TDCS, the lesion caused electric field "hot spots" in the cortex. However, these maxima were not substantially stronger than those seen in a healthy control. The electric field pattern induced by TMS was not substantially changed by the lesions. However, the average field strength generated by TDCS was substantially decreased. This effect occurred for both head models and even when both electrodes were distant to the lesion, caused by increased current shunting through the lesion and enlarged ventricles. Judging from the similar peak field strengths compared to the healthy control, both TBS methods are safe in patients with large brain lesions (in practice, however, additional factors such as potentially lowered thresholds for seizure-induction have to be considered). Focused stimulation by TMS seems to be possible, but standard tDCS protocols appear to be less efficient than they are in healthy subjects, strongly suggesting that tDCS studies in this population might benefit from individualized treatment planning based on realistic field calculations.
Collapse
Affiliation(s)
- Sena Minjoli
- Danish Research Center for Magnetic Resonance, Copenhagen University Hospital, Hvidovre, Denmark
| | - Guilherme B Saturnino
- Danish Research Center for Magnetic Resonance, Copenhagen University Hospital, Hvidovre, Denmark; Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Jakob Udby Blicher
- Department of Clinical Medicine, Center of Functionally Integrative Neuroscience, Aarhus University, Denmark; Department of Neurology, Aalborg University Hospital, Aalborg, Denmark
| | - Charlotte J Stagg
- Centre for Functional MRI of the Brain (FMRIB), Nuffield Department of Clinical Neurosciences, University of Oxford, UK; Oxford Centre for Human Brain Activity (OHBA), Department of Psychiatry, University of Oxford, UK
| | - Hartwig R Siebner
- Danish Research Center for Magnetic Resonance, Copenhagen University Hospital, Hvidovre, Denmark; Department of Neurology, Copenhagen University Hospital Bispebjerg, Copenhagen, Denmark
| | - André Antunes
- Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Axel Thielscher
- Danish Research Center for Magnetic Resonance, Copenhagen University Hospital, Hvidovre, Denmark; Max Planck Institute for Biological Cybernetics, Tübingen, Germany; Center for Magnetic Resonance, Technical University of Denmark, Kgs. Lyngby, Denmark.
| |
Collapse
|
17
|
Koessler L, Colnat-Coulbois S, Cecchin T, Hofmanis J, Dmochowski JP, Norcia AM, Maillard LG. In-vivo measurements of human brain tissue conductivity using focal electrical current injection through intracerebral multicontact electrodes. Hum Brain Mapp 2016; 38:974-986. [PMID: 27726249 DOI: 10.1002/hbm.23431] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2016] [Revised: 09/23/2016] [Accepted: 09/30/2016] [Indexed: 11/08/2022] Open
Abstract
In-vivo measurements of human brain tissue conductivity at body temperature were conducted using focal electrical currents injected through intracerebral multicontact electrodes. A total of 1,421 measurements in 15 epileptic patients (age: 28 ± 10) using a radiofrequency generator (50 kHz current injection) were analyzed. Each contact pair was classified as being from healthy (gray matter, n = 696; white matter, n = 530) or pathological (epileptogenic zone, n = 195) tissue using neuroimaging analysis of the local tissue environment and intracerebral EEG recordings. Brain tissue conductivities were obtained using numerical simulations based on conductivity estimates that accounted for the current flow in the local brain volume around the contact pairs (a cube with a side length of 13 mm). Conductivity values were 0.26 S/m for gray matter and 0.17 S/m for white matter. Healthy gray and white matter had statistically different median impedances (P < 0.0001). White matter conductivity was found to be homogeneous as normality tests did not find evidence of multiple subgroups. Gray matter had lower conductivity in healthy tissue than in the epileptogenic zone (0.26 vs. 0.29 S/m; P = 0.012), even when the epileptogenic zone was not visible in the magnetic resonance image (MRI) (P = 0.005). The present in-vivo conductivity values could serve to create more accurate volume conduction models and could help to refine the identification of relevant intracerebral contacts, especially when located within the epileptogenic zone of an MRI-invisible lesion. Hum Brain Mapp 38:974-986, 2017. © 2016 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
- Laurent Koessler
- CNRS, CRAN, UMR 7039, Vandœuvre-lès-Nancy, France.,Université de Lorraine, CRAN, UMR 7039, Vandœuvre-lès-Nancy, 54516, France.,Service de Neurologie, Centre Hospitalier Universitaire de Nancy, Nancy, 54000, France
| | - Sophie Colnat-Coulbois
- Service de Neurochirurgie, Centre Hospitalier Universitaire de Nancy, Nancy, 54000, France
| | - Thierry Cecchin
- CNRS, CRAN, UMR 7039, Vandœuvre-lès-Nancy, France.,Université de Lorraine, CRAN, UMR 7039, Vandœuvre-lès-Nancy, 54516, France
| | - Janis Hofmanis
- Ventspils Engineering Research Institute, Ventspils University, Ventspils, LV3601, Latvia
| | - Jacek P Dmochowski
- Department of Biomedical Engineering, City College of New York, New York, New York
| | - Anthony M Norcia
- Department of Psychology, Stanford University, Stanford, California
| | - Louis G Maillard
- CNRS, CRAN, UMR 7039, Vandœuvre-lès-Nancy, France.,Université de Lorraine, CRAN, UMR 7039, Vandœuvre-lès-Nancy, 54516, France.,Service de Neurologie, Centre Hospitalier Universitaire de Nancy, Nancy, 54000, France
| |
Collapse
|
18
|
Beniczky S, Rosenzweig I, Scherg M, Jordanov T, Lanfer B, Lantz G, Larsson PG. Ictal EEG source imaging in presurgical evaluation: High agreement between analysis methods. Seizure 2016; 43:1-5. [PMID: 27764709 PMCID: PMC5176190 DOI: 10.1016/j.seizure.2016.09.017] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Revised: 09/24/2016] [Accepted: 09/30/2016] [Indexed: 11/17/2022] Open
Abstract
There was good agreement between different methods of ictal EEG source imaging. Ictal source imaging achieved an accuracy of 73% (for operated patients: 86%). Agreement between all methods did not necessarily imply accuracy of localization.
Purpose To determine the agreement between five different methods of ictal EEG source imaging, and to assess their accuracy in presurgical evaluation of patients with focal epilepsy. It was hypothesized that high agreement between methods was associated with higher localization-accuracy. Methods EEGs were recorded with a 64-electrode array. Thirty-eight seizures from 22 patients were analyzed using five different methods phase mapping, dipole fitting, CLARA, cortical-CLARA and minimum norm. Localization accuracy was determined at sub-lobar level. Reference standard was the final decision of the multidisciplinary epilepsy surgery team, and, for the operated patients, outcome one year after surgery. Results Agreement between all methods was obtained in 13 patients (59%) and between all but one methods in additional six patients (27%). There was a trend for minimum norm being less accurate than phase mapping, but none of the comparisons reached significance. Source imaging in cases with agreement between all methods was not more accurate than in the other cases. Ictal source imaging achieved an accuracy of 73% (for operated patients: 86%). Conclusion There was good agreement between different methods of ictal source imaging. However, good inter-method agreement did not necessarily imply accurate source localization, since all methods faced the limitations of the inverse solution.
Collapse
Affiliation(s)
- Sándor Beniczky
- Department of Clinical Neurophysiology, Danish Epilepsy Centre, Dianalund, Denmark; Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark.
| | - Ivana Rosenzweig
- Department of Clinical Neurophysiology, Danish Epilepsy Centre, Dianalund, Denmark; Sleep and Brain Plasticity Centre, Department of Neuroimaging, IOPPN, King's College and Imperial College, London, UK
| | | | | | | | - Göran Lantz
- Clinical Neurophysiology Unit, Department of Clinical Sciences, Lund University, Lund, Sweden; Electrical Geodesics, Inc., Eugene, OR, USA
| | - Pål Gunnar Larsson
- Clinical Neurophysiology Section, Department of Neurosurgery, Oslo University Hospital, Norway
| |
Collapse
|
19
|
Electric fields of motor and frontal tDCS in a standard brain space: A computer simulation study. Neuroimage 2016; 137:140-151. [DOI: 10.1016/j.neuroimage.2016.05.032] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Revised: 04/15/2016] [Accepted: 05/10/2016] [Indexed: 02/01/2023] Open
|
20
|
Liu B, Li H, Gao C, Zhang Y, Wang C, Wu H, Dong S, Tao Y, Zhang H. Occurrence predictors of the temporal interictal epileptic discharges in epilepsy patients with extratemporal lesions: A prospective cohort study. Int J Surg 2016; 31:52-7. [PMID: 27216454 DOI: 10.1016/j.ijsu.2016.05.040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2016] [Revised: 04/30/2016] [Accepted: 05/14/2016] [Indexed: 11/18/2022]
Abstract
OBJECTIVE Electrical kindling models of epilepsy suggest that medial temporal structures are more prone to be irritated. The aim of this study is to investigate the occurrence rate of temporal interictal epileptic discharges (TIEDs) in the epilepsy patients with extratemporal lesions (ETLs), and to determine the predictive factors for TIEDs in this cohort. METHODS Totally 221 patients were admitted for presurgical evaluation, and focal ETL were found in all of them by MRI examination. The occurrence rates of TIEDs in several groups with different brain lobe locations, durations; of epilepsy, seizure frequencies, and onset ages stages were assessed. We also evaluated the surgical outcome of; resection in this cohort. RESULTS The total occurrence rate of TIEDs in this cohort was 29.9%. The occurrence rate of TIEDs in the patients with longer durations (>5 or 10 years) was significantly higher than those with shorter duration (<1 year). These; patients with lower seizure frequency (<1 seizure/month) had a significantly decreased incidence of TIEDs; compared with those with higher frequency (>1 seizure/month or week). In the terms of the brain lobe locations; and age at onset, there were no differences between the groups. Furthermore, there were no differences in terms of the surgical outcomes between the patients with TIEDs and other patients in this series. CONCLUSIONS TIEDs were frequently recorded in these patients with ETLs, and the predictive factors for TIEDs included the epilepsy duration and seizure frequency. SIGNIFICANCE This study is instrumental for the presurgical EEG interpretationand the counseling of these ETLs patients considered for epilepsy surgery.
Collapse
Affiliation(s)
- Bei Liu
- Department of Neurosurgery, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi Province, China
| | - Huanfa Li
- Department of Neurosurgery, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi Province, China
| | - Chen Gao
- Department of Neurosurgery, AnNing Branch Hospital, Lanzhou General Hospital, Lanzhou Command, Lanzhou, Gansu Province, China
| | - Yu Zhang
- Department of Neurosurgery, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi Province, China
| | - Chao Wang
- Department of Neurosurgery, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi Province, China
| | - Hao Wu
- Department of Neurosurgery, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi Province, China
| | - Shan Dong
- Department of Neurosurgery, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi Province, China
| | - Ye Tao
- Department of Ophthalmology, General Hospital of Chinese PLA, Ophthalmology & Visual Science Key Lab of PLA, Beijing, China.
| | - Hua Zhang
- Department of Neurosurgery, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi Province, China.
| |
Collapse
|
21
|
Lau S, Güllmar D, Flemming L, Grayden DB, Cook MJ, Wolters CH, Haueisen J. Skull Defects in Finite Element Head Models for Source Reconstruction from Magnetoencephalography Signals. Front Neurosci 2016; 10:141. [PMID: 27092044 PMCID: PMC4823312 DOI: 10.3389/fnins.2016.00141] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Accepted: 03/18/2016] [Indexed: 11/24/2022] Open
Abstract
Magnetoencephalography (MEG) signals are influenced by skull defects. However, there is a lack of evidence of this influence during source reconstruction. Our objectives are to characterize errors in source reconstruction from MEG signals due to ignoring skull defects and to assess the ability of an exact finite element head model to eliminate such errors. A detailed finite element model of the head of a rabbit used in a physical experiment was constructed from magnetic resonance and co-registered computer tomography imaging that differentiated nine tissue types. Sources of the MEG measurements above intact skull and above skull defects respectively were reconstructed using a finite element model with the intact skull and one incorporating the skull defects. The forward simulation of the MEG signals reproduced the experimentally observed characteristic magnitude and topography changes due to skull defects. Sources reconstructed from measured MEG signals above intact skull matched the known physical locations and orientations. Ignoring skull defects in the head model during reconstruction displaced sources under a skull defect away from that defect. Sources next to a defect were reoriented. When skull defects, with their physical conductivity, were incorporated in the head model, the location and orientation errors were mostly eliminated. The conductivity of the skull defect material non-uniformly modulated the influence on MEG signals. We propose concrete guidelines for taking into account conducting skull defects during MEG coil placement and modeling. Exact finite element head models can improve localization of brain function, specifically after surgery.
Collapse
Affiliation(s)
- Stephan Lau
- Institute of Biomedical Engineering and Informatics, Technical University IlmenauIlmenau, Germany; Department of Neurology, Biomagnetic Center, University Hospital JenaJena, Germany; NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of MelbourneParkville, VIC, Australia; Centre for Neural Engineering, University of MelbourneParkville, VIC, Australia; Department of Medicine - St. Vincent's Hospital, University of MelbourneFitzroy, VIC, Australia
| | - Daniel Güllmar
- Medical Physics Group, Department of Diagnostic and Interventional Radiology, University Hospital Jena Jena, Germany
| | - Lars Flemming
- Department of Neurology, Biomagnetic Center, University Hospital Jena Jena, Germany
| | - David B Grayden
- NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of MelbourneParkville, VIC, Australia; Centre for Neural Engineering, University of MelbourneParkville, VIC, Australia
| | - Mark J Cook
- Department of Medicine - St. Vincent's Hospital, University of Melbourne Fitzroy, VIC, Australia
| | - Carsten H Wolters
- Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster Münster, Germany
| | - Jens Haueisen
- Institute of Biomedical Engineering and Informatics, Technical University Ilmenau Ilmenau, Germany
| |
Collapse
|
22
|
Emin D, Akhtari M, Ellingson BM, Mathern GW. Ionic charge transport between blockages: Sodium cation conduction in freshly excised bulk brain tissue. AIP ADVANCES 2015; 5:087133. [PMID: 26339528 PMCID: PMC4537479 DOI: 10.1063/1.4928652] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Accepted: 08/03/2015] [Indexed: 06/05/2023]
Abstract
We analyze the transient-dc and frequency-dependent electrical conductivities between blocking electrodes. We extend this analysis to measurements of ions' transport in freshly excised bulk samples of human brain tissue whose complex cellular structure produces blockages. The associated ionic charge-carrier density and diffusivity are consistent with local values for sodium cations determined non-invasively in brain tissue by MRI (NMR) and diffusion-MRI (spin-echo NMR). The characteristic separation between blockages, about 450 microns, is very much shorter than that found for sodium-doped gel proxies for brain tissue, >1 cm.
Collapse
Affiliation(s)
- David Emin
- Department of Physics and Astronomy, University of New Mexico , Albuquerque, NM 87131, USA
| | - Massoud Akhtari
- Semple Institutes for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California at Los Angeles , Los Angeles, CA 90095, USA
| | - B M Ellingson
- Department of Radiology, David Geffen School of Medicine, University of California at Los Angeles , Los Angeles, CA 90095, USA
| | - G W Mathern
- Department of Neurosurgery, David Geffen School of Medicine, University of California at Los Angeles , Los Angeles, CA 90095, USA
| |
Collapse
|
23
|
Phung J, Krogstad P, Mathern GW. Etiology associated with developing posthemispherectomy hydrocephalus after resection-disconnection procedures. J Neurosurg Pediatr 2013; 12:469-75. [PMID: 24011367 DOI: 10.3171/2013.8.peds13212] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
OBJECT The authors sought to determine if clinical epilepsy variables, maximum daily temperature (Tmax), and blood and CSF findings were associated with the risk of developing hydrocephalus after first-time resection-disconnection hemispherectomy. METHODS Patients who underwent cerebral hemispherectomy in whom a standardized perioperative protocol was used, including the use of ventriculostomies (n = 79), were classified into those who developed and those who did not develop hydrocephalus requiring CSF shunts. The authors compared these 2 groups for clinical variables, Tmax, and blood and CSF studies through postoperative Day 12. RESULTS In this cohort, 30% of the patients required CSF shunts, of which 8% developed late hydrocephalus up to 3 years posthemispherectomy. Multivariate analysis found that etiology was associated with developing posthemispherectomy hydrocephalus. Higher shunt rates were observed for patients with hemimegalencephaly (40%; n = 15) and a history of CNS infection (100%; n = 4) compared with cortical dysplasia (17%; n = 23) and Rasmussen encephalitis (17%; n = 12). In univariate analysis, other factors associated with developing hydrocephalus were elevated maximum daily temperatures, elevated white blood cell counts, decreased CSF protein, and increased CSF red blood cell counts. CONCLUSIONS The findings of the study indicate that etiology was the factor most strongly associated with developing posthemispherectomy hydrocephalus. These findings suggest that there are variable mechanisms for developing hydrocephalus after cerebral hemispherectomy depending on the procedure, and in resection-disconnection operations the mechanism may involve changes in CSF bulk flow that varies by histopathology.
Collapse
Affiliation(s)
- Jennifer Phung
- Departments of Neurosurgery and Psychiatry & Biobehavioral Sciences
| | | | | |
Collapse
|
24
|
Toschi N, Keck ME, Welt T, Guerrisi M. Quantifying uncertainty in Transcranial Magnetic Stimulation - A high resolution simulation study in ICBM space. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2013; 2012:1218-21. [PMID: 23366117 DOI: 10.1109/embc.2012.6346156] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Transcranial Magnetic Stimulation offers enormous potential for noninvasive brain stimulation. While it is known that brain tissue significantly "reshapes" induced field and charge distributions, most modeling investigations to-date have focused on single-subject data with limited generality. Further, the effects of the significant uncertainties which exist in the simulation (i.e. brain conductivity distributions) and stimulation (e.g. coil positioning and orientations) setup have not been quantified. In this study, we construct a high-resolution anisotropic head model in standard ICBM space, which can be used as a population-representative standard for bioelectromagnetic simulations. Further, we employ Monte-Carlo simulations in order to quantify how uncertainties in conductivity values propagate all the way to induced field and currents, demonstrating significant, regionally dependent dispersions in values which are commonly assumed "ground truth". This framework can be leveraged in order to quantify the effect of any type of uncertainty in noninvasive brain stimulation and bears relevance in all applications of TMS, both investigative and therapeutic.
Collapse
Affiliation(s)
- Nicola Toschi
- Medical Phsyics Section, Faculty of Medicine, University of Rome “Tor Vergata”.
| | | | | | | |
Collapse
|
25
|
Suh HS, Lee WH, Kim TS. Influence of anisotropic conductivity in the skull and white matter on transcranial direct current stimulation via an anatomically realistic finite element head model. Phys Med Biol 2012; 57:6961-80. [PMID: 23044667 DOI: 10.1088/0031-9155/57/21/6961] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
To establish safe and efficient transcranial direct current stimulation (tDCS), it is of particular importance to understand the electrical effects of tDCS in the brain. Since the current density (CD) and electric field (EF) in the brain generated by tDCS depend on various factors including complex head geometries and electrical tissue properties, in this work, we investigated the influence of anisotropic conductivity in the skull and white matter (WM) on tDCS via a 3D anatomically realistic finite element head model. We systematically incorporated various anisotropic conductivity ratios into the skull and WM. The effects of anisotropic tissue conductivity on the CD and EF were subsequently assessed through comparisons to the conventional isotropic solutions. Our results show that the anisotropic skull conductivity significantly affects the CD and EF distribution: there is a significant reduction in the ratio of the target versus non-target total CD and EF on the order of 12-14%. In contrast, the WM anisotropy does not significantly influence the CD and EF on the targeted cortical surface, only on the order of 1-3%. However, the WM anisotropy highly alters the spatial distribution of both the CD and EF inside the brain. This study shows that it is critical to incorporate anisotropic conductivities in planning of tDCS for improved efficacy and safety.
Collapse
Affiliation(s)
- Hyun Sang Suh
- Department of Biomedical Engineering, Kyung Hee University, Yongin, Gyeonggi, Republic of Korea
| | | | | |
Collapse
|
26
|
Dobiszewski KF, Deek MP, Ghaly A, Prodan C, Hill AA. Extracellular fluid conductivity analysis by dielectric spectroscopy for in vitro determination of cortical tissue vitality. Physiol Meas 2012; 33:1249-60. [PMID: 22735505 DOI: 10.1088/0967-3334/33/7/1249] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Brain tissue is extremely metabolically active in part due to its need to constantly maintain a precise extracellular ionic environment. Under pathological conditions, unhealthy cortical tissue loses its ability to maintain this precise environment and there is a net efflux of charged particles from the cells. Typically, this ionic efflux is measured using ion-selective microelectrodes, which measure a single ionic species at a time. In this paper, we have used a bio-sensing method, dielectric spectroscopy (DS), which allows for the simultaneous measurement of the net efflux of all charged particles from cells by measuring extracellular conductivity. We exposed cortical brain slices from the mouse to different solutions that mimic various pathological states such as hypokalemia, hyperkalemia and ischemia (via oxygen-glucose deprivation). We have found that the changes in conductivity of the extracellular solutions were proportional to the severity of the pathological insult experienced by the brain tissue. Thus, DS allows for the measurement of changes in extracellular conductivity with enough sensitivity to monitor the health of brain tissue in vitro.
Collapse
Affiliation(s)
- K F Dobiszewski
- Federated Department of Biological Sciences, New Jersey Institute of Technology and Rutgers University, Newark, NJ, USA
| | | | | | | | | |
Collapse
|
27
|
Rossi MA, Stebbins G, Murphy C, Greene D, Brinker S, Sarcu D, Tenharmsel A, Stoub T, Stein MA, Hoeppner TJ, Byrne RW, Moseley ME, Bammer RA, Bild S, Dennis J, Arnett N, Balabanov A, Bergen D, Kanner AM, Smith MC. Predicting white matter targets for direct neurostimulation therapy. Epilepsy Res 2010; 91:176-86. [DOI: 10.1016/j.eplepsyres.2010.07.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Revised: 07/06/2010] [Accepted: 07/18/2010] [Indexed: 12/13/2022]
|
28
|
Akhtari M, Mandelkern M, Bui D, Salamon N, Vinters HV, Mathern GW. Variable anisotropic brain electrical conductivities in epileptogenic foci. Brain Topogr 2010; 23:292-300. [PMID: 20440549 PMCID: PMC2914871 DOI: 10.1007/s10548-010-0144-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Accepted: 04/02/2010] [Indexed: 12/20/2022]
Abstract
Source localization models assume brain electrical conductivities are isotropic at about 0.33 S/m. These assumptions have not been confirmed ex vivo in humans. This study determined bidirectional electrical conductivities from pediatric epilepsy surgery patients. Electrical conductivities perpendicular and parallel to the pial surface of neocortex and subcortical white matter (n = 15) were measured using the 4-electrode technique and compared with clinical variables. Mean (±SD) electrical conductivities were 0.10 ± 0.01 S/m, and varied by 243% from patient to patient. Perpendicular and parallel conductivities differed by 45%, and the larger values were perpendicular to the pial surface in 47% and parallel in 40% of patients. A perpendicular principal axis was associated with normal, while isotropy and parallel principal axes were linked with epileptogenic lesions by MRI. Electrical conductivities were decreased in patients with cortical dysplasia compared with non-dysplasia etiologies. The electrical conductivity values of freshly excised human brain tissues were approximately 30% of assumed values, varied by over 200% from patient to patient, and had erratic anisotropic and isotropic shapes if the MRI showed a lesion. Understanding brain electrical conductivity and ways to non-invasively measure them are probably necessary to enhance the ability to localize EEG sources from epilepsy surgery patients.
Collapse
Affiliation(s)
- M Akhtari
- Neuropsychiatric Institutes, David Geffen School of Medicine, University of California, Los Angeles, CA 90015, USA.
| | | | | | | | | | | |
Collapse
|
29
|
Güllmar D, Haueisen J, Reichenbach JR. Influence of anisotropic electrical conductivity in white matter tissue on the EEG/MEG forward and inverse solution. A high-resolution whole head simulation study. Neuroimage 2010; 51:145-63. [PMID: 20156576 DOI: 10.1016/j.neuroimage.2010.02.014] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Revised: 01/12/2010] [Accepted: 02/08/2010] [Indexed: 01/27/2023] Open
|
30
|
Sekino M, Ohsaki H, Yamaguchi-Sekino S, Iriguchi N, Ueno S. Low-frequency conductivity tensor of rat brain tissues inferred from diffusion MRI. Bioelectromagnetics 2009; 30:489-99. [DOI: 10.1002/bem.20505] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
31
|
Lerner JT, Salamon N, Hauptman JS, Velasco TR, Hemb M, Wu JY, Sankar R, Donald Shields W, Engel J, Fried I, Cepeda C, Andre VM, Levine MS, Miyata H, Yong WH, Vinters HV, Mathern GW. Assessment and surgical outcomes for mild type I and severe type II cortical dysplasia: a critical review and the UCLA experience. Epilepsia 2009; 50:1310-35. [PMID: 19175385 DOI: 10.1111/j.1528-1167.2008.01998.x] [Citation(s) in RCA: 269] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Recent findings on the clinical, electroencephalography (EEG), neuroimaging, and surgical outcomes are reviewed comparing patients with Palmini type I (mild) and type II (severe) cortical dysplasia. Resources include peer-reviewed studies on surgically treated patients and a subanalysis of the 2004 International League Against Epilepsy (ILAE) Survey of Pediatric Epilepsy Surgery. These sources were supplemented with data from University of California, Los Angeles (UCLA). Cortical dysplasia is the most frequent histopathologic substrate in children, and the second most common etiology in adult epilepsy surgery patients. Cortical dysplasia patients present with seizures at an earlier age than other surgically treated etiologies, and 33-50% have nonlocalized scalp EEG and normal magnetic resonance imaging (MRI) scans. 2-((18)F)Fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) is positive in 75-90% of cases. After complete resection, 80% of patients are seizure free compared with 20% with incomplete resections. Compared with type I, patients with type II cortical dysplasia present at younger ages, have higher seizure frequencies, and are extratemporal. Type I dysplasia is found more often in adult patients in the temporal lobe and is often MRI negative. These findings identify characteristics of patients with mild and severe cortical dysplasia that define surgically treated epilepsy syndromes. The authors discuss future challenges to identifying and treating medically refractory epilepsy patients with cortical dysplasia.
Collapse
Affiliation(s)
- Jason T Lerner
- Department of Pediatric Neurology, University of California, Los Angeles, California, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Wu JY, Koh S, Sankar R, Mathern GW. Paroxysmal fast activity: an interictal scalp EEG marker of epileptogenesis in children. Epilepsy Res 2008; 82:99-106. [PMID: 18804956 DOI: 10.1016/j.eplepsyres.2008.07.010] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Revised: 07/07/2008] [Accepted: 07/13/2008] [Indexed: 11/29/2022]
Abstract
PURPOSE High-frequency oscillations (>100Hz) have been proposed as localized markers of epileptic networks, but require intracranial electroencephalographic (EEG) recordings. This study explored if beta- and gamma-frequency paroxysmal fast activity (PFA), recorded interictally during non-REM sleep, could be used as a scalp EEG marker of epileptogenesis in children. METHODS The presence and scalp location of PFA was visually identified in 681 patients with overnight video-EEG (age 0-18 years), and compared with ictal onset sites. The clinical features of patients with PFA were compared with patients without PFA along with evidence of PFA evolution in 35 patients who had multiple video-EEG records. RESULTS PFA was present in 16% of all patients and in 28% of those with seizures. PFA was more frequently observed in EEGs from patients 3 years of age or younger (>40%), and children with infantile spasms (85%). When present, PFA predicted if the patient had epilepsy with 97% accuracy, and was not found in individuals with non-epileptic events. PFA localized with EEG-ictal onset sites with 91% sensitivity and 82% accuracy. Ictal scalp EEG events began with beta- and gamma-frequencies in 80% of patients with PFA, and they had increased seizure frequencies compared with non-PFA cases. In patients with multiple video-EEG studies, PFA showed progression over increased numbers of electrodes in 74%, improvement in 15%, and remained unchanged in 12% and correlated with seizure evolution. PFA was not associated with other seizure types, anatomic location, type of antiepileptic drug, etiology, or histopathology. CONCLUSIONS While relatively infrequent, interictal PFA was specific in identifying younger children with epilepsy, co-localized with the ictal onset sites on scalp video-EEG, and progressed and correlated with seizure severity. We propose that PFA is a scalp EEG marker of epileptic networks with the advantage of being recorded non-invasively during interictal non-REM sleep.
Collapse
Affiliation(s)
- Joyce Y Wu
- Division of Pediatric Neurology, Mattel Children's Hospital at UCLA, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA 90095, United States.
| | | | | | | |
Collapse
|
33
|
Yu JT, Tan L. Diffusion-weighted magnetic resonance imaging demonstrates parenchymal pathophysiological changes in epilepsy. ACTA ACUST UNITED AC 2008; 59:34-41. [PMID: 18514917 DOI: 10.1016/j.brainresrev.2008.04.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2008] [Revised: 04/24/2008] [Accepted: 04/25/2008] [Indexed: 10/22/2022]
Abstract
Diffusion-weighted magnetic resonance imaging (DW-MRI) is a novel noninvasive technique probing the Brownian motion of water molecules. It has already proved very useful in the early identification of cerebral ischemia in human patients. Although a wide spectrum of peri-ictal, postictal or interictal DW-MRI abnormalities are recently being increasingly identified, clinicians are often in a dilemma about their significance in epilepsy. This article briefly reviews the whole dynamic ADC fluctuations and the implications of hypothetical pathophysiological evolution of effected zones in prolonged seizures or status epilepticus (SE) and their potential clinical applications in epilepsy.
Collapse
Affiliation(s)
- Jin-Tai Yu
- Department of Neurology, Qingdao Municipal Hospital, Affiliated Hospital of Qingdao University Medical College, Shandong Province, PR China
| | | |
Collapse
|
34
|
Affiliation(s)
- Chun Kee Chung
- Department of Neurosurgery, Seoul National University College of Medicine, Korea.
| |
Collapse
|