Effects of transcranial stimulating electrode montages over the head for lower-extremity transcranial motor evoked potential monitoring

2016 ◽  
Vol 126 (6) ◽  
pp. 1951-1958 ◽  
Author(s):  
Ryosuke Tomio ◽  
Takenori Akiyama ◽  
Takayuki Ohira ◽  
Kazunari Yoshida
Keyword(s):  
Finite Element ◽  
Lower Extremity ◽  
Electric Field ◽  
Motor Evoked Potentials ◽  
Motor Evoked Potential ◽  
Threshold Level ◽  
Lower Threshold ◽  
Transcranial Electrical Stimulation ◽  
Head Model ◽  
The Brain

OBJECTIVEThe aim of this study was to determine the most effective electrode montage to elicit lower-extremity transcranial motor evoked potentials (LE-tMEPs) using a minimum stimulation current.METHODSA realistic 3D head model was created from T1-weighted images. Finite element methods were used to visualize the electric field in the brain, which was generated by transcranial electrical stimulation via 4 electrode montage models. The stimulation threshold level of LE-tMEPs in 52 patients was also studied in a practical clinical setting to determine the effects of each electrode montage.RESULTSThe electric field in the brain radially diffused from the brain surface at a maximum just below the electrodes in the finite element models. The Cz-inion electrode montage generated a centrally distributed high electric field with a current direction longitudinal and parallel to most of the pyramidal tract fibers of the lower extremity. These features seemed to be effective in igniting LE-tMEPs.Threshold level recordings of LE-tMEPs revealed that the Cz-inion electrode montage had a lower threshold on average than the C3–C4 montage, 76.5 ± 20.6 mA and 86.2 ± 20.6 mA, respectively (31 patients, t = 4.045, p < 0.001, paired t-test). In 23 (74.2%) of 31 cases, the Cz-inion montage could elicit LE-tMEPs at a lower threshold than C3–C4.CONCLUSIONSThe C3–C4 and C1–C2 electrode montages are the standard for tMEP monitoring in neurosurgery, but the Cz-inion montage showed lower thresholds for the generation of LE-tMEPs. The Cz-inion electrode montage should be a good alternative for LE-tMEP monitoring when the C3–C4 has trouble igniting LE-tMEPs.

scholarly journals Effects of electrodes length and insulation for transcranial electric stimulation

2019 ◽  
Vol 10 ◽  
pp. 111
Author(s):  
Ryosuke Tomio
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Subcutaneous Fat ◽  
Motor Evoked Potential ◽  
Threshold Level ◽  
Lower Threshold ◽  
The Finite Element Method ◽  
Stimulation Threshold ◽  
Transcranial Electric Stimulation ◽  
The Brain

Background: The aim of this study is to investigate the effects of length and insulation of the corkscrew electrodes for transcranial motor evoked potential (tMEP) monitoring. Methods: We used the finite element method to visualize the electric field in the brain, which was generated by electrodes of different lengths (4, 7, and 12 mm). Two types of head models were generated: A model that included a subcutaneous fat layer and another without a fat layer. Two insulated needle types of conductive tip (5 and 2 mm) were studied. The stimulation threshold levels of hand tMEP were measured in a clinical setting to compare normal corkscrew and insulated 7-mm depth corkscrew. Results: The electric field in the brain depended on the electrode depths in the no fat layer model. The deeper the electrodes reached, the stronger the electric fields generated. Electrode insulation made a difference in the fat layer models. The threshold level recordings of tMEP revealed that the 7-mm insulated electrodes showed a lower threshold than the normal electrodes by one-side replacement in each patient: 33.6 ± 9.6 mA and 36.3 ± 11.0 mA (n =16, P < 0.001), respectively. The 7-mm insulated electrodes also showed a lower threshold than the normal electrodes when both sides, electrodes were replaced: 34.4 ± 8.6 mA and 37.5 ± 9.2 mA (n =10, P = 0.003), respectively. Conclusions: The electrodes depth reached enough to skull is considered to be efficient. Insulation of the electrodes with a conductive tip is efficient when there is subcutaneous fat layer.

scholarly journals Finite-element analysis of microwave scattering from a three-dimensional human head model for brain stroke detection

2018 ◽  
Vol 5 (7) ◽  
pp. 180319
Author(s):  
Awais Munawar Qureshi ◽  
Zartasha Mustansar ◽  
Samah Mustafa
Keyword(s):  
Finite Element ◽  
Dielectric Properties ◽  
Electric Field ◽  
Three Dimensional ◽  
Human Head ◽  
Head Model ◽  
Different Types ◽  
Brain Stroke ◽  
Human Head Model ◽  
Brain Stroke Detection

In this paper, a detailed analysis of microwave (MW) scattering from a three-dimensional (3D) anthropomorphic human head model is presented. It is the first time that the finite-element method (FEM) has been deployed to study the MW scattering phenomenon of a 3D realistic head model for brain stroke detection. A major contribution of this paper is to add anatomically more realistic details to the human head model compared with the literature available to date. Using the MRI database, a 3D numerical head model was developed and segmented into 21 different types through a novel tissue-mapping scheme and a mixed-model approach. The heterogeneous and frequency-dispersive dielectric properties were assigned to brain tissues using the same mapping technique. To mimic the simulation set-up, an eight-elements antenna array around the head model was designed using dipole antennae. Two types of brain stroke (haemorrhagic and ischaemic) at various locations inside the head model were then analysed for possible detection and classification. The transmitted and backscattered signals were calculated by finding out the solution of the Helmholtz wave equation in the frequency domain using the FEM. FE mesh convergence analysis for electric field values and comparison between different types of iterative solver were also performed to obtain error-free results in minimal computational time. At the end, specific absorption rate analysis was conducted to examine the ionization effects of MW signals to a 3D human head model. Through computer simulations, it is foreseen that MW imaging may efficiently be exploited to locate and differentiate two types of brain stroke by detecting abnormal tissues’ dielectric properties. A significant contrast between electric field values of the normal and stroke-affected brain tissues was observed at the stroke location. This is a step towards generating MW scattering information for the development of an efficient image reconstruction algorithm.

scholarly journals Integrating electric field modelling and neuroimaging to explain inter-individual variability of tACS effects

2019 ◽  
Author(s):  
Florian H. Kasten ◽  
Katharina Duecker ◽  
Marike C. Maack ◽  
Arnd Meiser ◽  
Christoph S. Herrmann
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Individual Variability ◽  
Transcranial Electrical Stimulation ◽  
Field Modelling ◽  
Novel Approach ◽  
Before And After ◽  
Transcranial Alternating Current Stimulation ◽  
The Brain ◽  
Field Variability

AbstractUnderstanding variability of transcranial electrical stimulation (tES) effects is one of the major challenges in the brain stimulation community. Promising candidates to explain this variability are individual anatomy and the resulting differences of electric fields inside the brain. We integrated individual simulations of electric fields during tES with source-localization to predict variability of transcranial alternating current stimulation (tACS) aftereffects on α-oscillations. In two experiments, participants received 20 minutes of either α-tACS (1 mA) or sham stimulation. Magnetoencephalogram was recorded for 10 minutes before and after stimulation. tACS caused a larger power increase in the α-band as compared to sham. The variability of this effect was significantly predicted by measures derived from individual electric field modelling. Our results directly link electric field variability to variability of tACS outcomes, stressing the importance of individualizing stimulation protocols and providing a novel approach to analyze tACS effects in terms of dose-response relationships.

Transcranial electrical stimulation and intraoperative neurophysiology of the corticospinal tract

2012 ◽  
Author(s):  
Vedran Deletis ◽  
Francesco Sala ◽  
Sedat Ulkatan
Keyword(s):  
Spinal Cord ◽  
Electrical Stimulation ◽  
Corticospinal Tract ◽  
Motor Evoked Potentials ◽  
Transcranial Electrical Stimulation ◽  
Irreversible Damage ◽  
Two Factors ◽  
Brain And Spinal Cord ◽  
The Brain ◽  
Wave Collision

Transcranial electrical stimulation is a well-recognized method for corticospinal tract (CT) activation. This article explains the use of TES during surgery and highlights the physiology of the motor-evoked potentials (MEPs). It describes the techniques and methods for brain stimulation and recording of responses. There are two factors that determine the depth of the current penetrating the brain, they are: choice of electrode montage for stimulation over the scalp and the intensity of stimulation. D-wave collision technique is a newly developed technique that allows mapping intraoperatively and finding the anatomical position of the CT within the surgically exposed spinal cord. Different mechanisms may be involved in the pathophysiology of postoperative paresis in brain and spinal cord surgeries so that different MEP monitoring criteria can be used to avoid irreversible damage and accurately predict the prognosis.

scholarly journals Brain Response Induced with Paired Associative Stimulation Is Related to Repetition Suppression of Motor Evoked Potential

2020 ◽  
Vol 10 (10) ◽  
pp. 674
Author(s):  
Shohreh Kariminezhad ◽  
Jari Karhu ◽  
Laura Säisänen ◽  
Jusa Reijonen ◽  
Mervi Könönen ◽  
...  
Keyword(s):  
Motor Evoked Potentials ◽  
Stable State ◽  
Motor Evoked Potential ◽  
Brain Response ◽  
Dynamic Component ◽  
Paired Associative Stimulation ◽  
Stable Component ◽  
Repetition Suppression ◽  
The Mean ◽  
The Brain

Repetition suppression (RS), i.e., the reduction of neuronal activity upon repetition of an external stimulus, can be demonstrated in the motor system using transcranial magnetic stimulation (TMS). We evaluated the RS in relation to the neuroplastic changes induced by paired associative stimulation (PAS). An RS paradigm, consisting of 20 trains of four identical suprathreshold TMS pulses 1 s apart, was assessed for motor-evoked potentials (MEPs) in 16 healthy subjects, before and following (at 0, 10, and 20 min) a common PAS protocol. For analysis, we divided RS into two components: (1) the ratio of the second MEP amplitude to the first one in RS trains, i.e., the “dynamic” component, and (2) the mean of the second to fourth MEP amplitudes, i.e., the “stable” component. Following PAS, five subjects showed change in the dynamic RS component. However, nearly all the individuals (n = 14) exhibited change in the stable component (p < 0.05). The stable component was similar between subjects showing increased MEPs and those showing decreased MEPs at this level (p = 0.254). The results suggest the tendency of the brain towards a stable state, probably free from the ongoing dynamics, following PAS.

Development and validation of a new finite element human head model

2018 ◽  
Vol 35 (1) ◽  
pp. 477-496 ◽  
Author(s):  
Fábio A.O. Fernandes ◽  
Dmitri Tchepel ◽  
Ricardo J. Alves de Sousa ◽  
Mariusz Ptak
Keyword(s):  
Finite Element ◽  
Design Methodology ◽  
Human Head ◽  
Design Tool ◽  
Head Model ◽  
Accident Reconstruction ◽  
Research Groups ◽  
Content Type ◽  
Development And Validation ◽  
The Brain

Purpose Currently, there are some finite element head models developed by research groups all around the world. Nevertheless, the majority are not geometrically accurate. One of the problems is the brain geometry, which usually resembles a sphere. This may raise problems when reconstructing any event that involves brain kinematics, such as accidents, affecting the correct evaluation of resulting injuries. Thus, the purpose of this study is to develop a new finite element head model more accurate than the existing ones. Design/methodology/approach In this work, a new and geometrically detailed finite element brain model is proposed. Special attention was given to sulci and gyri modelling, making this model more geometrically accurate than currently available ones. In addition, these brain features are important to predict specific injuries such as brain contusions, which usually involve the crowns of gyri. Findings The model was validated against experimental data from impact tests on cadavers, comparing the intracranial pressure at frontal, parietal, occipital and posterior fossa regions. Originality/value As this model is validated, it can be now used in accident reconstruction and injury evaluation and even as a design tool for protective head gear.

scholarly journals Development of a Finite Element Head Model for the Study of Impact Head Injury

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Bin Yang ◽  
Kwong-Ming Tse ◽  
Ning Chen ◽  
Long-Bin Tan ◽  
Qing-Qian Zheng ◽  
...  
Keyword(s):  
Finite Element ◽  
Brain Injuries ◽  
Current Knowledge ◽  
Human Head ◽  
Von Mises Stress ◽  
Head Model ◽  
Fe Model ◽  
Prediction And Prevention ◽  
Von Mises ◽  
The Brain

This study is aimed at developing a high quality, validated finite element (FE) human head model for traumatic brain injuries (TBI) prediction and prevention during vehicle collisions. The geometry of the FE model was based on computed tomography (CT) and magnetic resonance imaging (MRI) scans of a volunteer close to the anthropometry of a 50th percentile male. The material and structural properties were selected based on a synthesis of current knowledge of the constitutive models for each tissue. The cerebrospinal fluid (CSF) was simulated explicitly as a hydrostatic fluid by using a surface-based fluid modeling method. The model was validated in the loading condition observed in frontal impact vehicle collision. These validations include the intracranial pressure (ICP), brain motion, impact force and intracranial acceleration response, maximum von Mises stress in the brain, and maximum principal stress in the skull. Overall results obtained in the validation indicated improved biofidelity relative to previous FE models, and the change in the maximum von Mises in the brain is mainly caused by the improvement of the CSF simulation. The model may be used for improving the current injury criteria of the brain and anthropometric test devices.

scholarly journals Individual head models for estimating the TMS-induced electric field in rat brain

2019 ◽  
Author(s):  
Lari M. Koponen ◽  
Matti Stenroos ◽  
Jaakko O. Nieminen ◽  
Kimmo Jokivarsi ◽  
Olli Gröhn ◽  
...  
Keyword(s):  
Electric Field ◽  
Field Distribution ◽  
Magnetic Stimulation ◽  
Cortical Activation ◽  
Head Model ◽  
Spherically Symmetric ◽  
Simple Method ◽  
X Ray ◽  
Conductivity Profile ◽  
The Brain

AbstractIn transcranial magnetic stimulation (TMS), the initial cortical activation due to stimulation is determined by the state of the brain and the magnitude, waveform, and direction of the induced electric field (E-field) in the cortex. The E-field distribution depends on the conductivity geometry of the head. The effects of deviations from a spherically symmetric conductivity profile have been studied in detail in humans. In small mammals, such as rats, these effects are more pronounced due to their smaller and less spherical heads. In this study, we describe a simple method for building individual realistically shaped head models for rats from high-resolution X-ray tomography images. We computed the TMS-induced E-field with the boundary element method and assessed the effect of head-model simplifications on the estimated E-field. The deviations from spherical symmetry have large, non-trivial effects on the E-field distribution: in some cases, even the direction of the E-field in the cortex cannot be reliably predicted by the coil orientation unless these deviations are properly considered.

scholarly journals A simplified human head finite element model for brain injury assessment of blunt impacts

2020 ◽  
Vol 14 (2) ◽  
pp. 6538-6547 ◽  
Author(s):  
M.H.A. Hassan ◽  
Z. Taha ◽  
I. Hasanuddin ◽  
A.P.P.A. Majeed ◽  
H. Mustafa ◽  
...  
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Human Head ◽  
Brain Trauma ◽  
Head Model ◽  
Human Cadaver ◽  
Brain Responses ◽  
Dimensional Models ◽  
The Brain ◽  
Head Neck

Blunt impacts contribute more than 95% of brain trauma injuries in Malaysia. Modelling and simulation of these impacts are essential in understanding the mechanics of the injuries to develop a protective equipment that might prevent brain trauma. Various finite element models of human head have been developed, ranging from two-dimensional models to very complex three-dimensional models. The aim of this study is to develop a simplified three-dimensional human head model with low computational cost, yet capable of producing reliable brain responses. The influence of different head-neck boundary conditions on the brain responses were also examined. Our model was validated against an experimental work on human cadaver. The model with free head-neck boundary condition was found to be in good agreement with experimental results. The head-neck joint was found to have a significant influence on the brain responses upon impact. Further investigations on the head-neck joint modelling are needed. Our simplified model was successfully validated against experimental data on human cadaver and could be used in simulating blunt impact scenarios.

scholarly journals SimNIBS 2.1: A Comprehensive Pipeline for Individualized Electric Field Modelling for Transcranial Brain Stimulation

2018 ◽  
Author(s):  
Guilherme B. Saturnino ◽  
Oula Puonti ◽  
Jesper D Nielsen ◽  
Daria Antonenko ◽  
Kristoffer Hougaard H Madsen ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Brain Stimulation ◽  
Head Model ◽  
Non Invasive ◽  
Field Modelling ◽  
Transcranial Brain Stimulation ◽  
Automated Tools ◽  
Automated Placement ◽  
The Brain

Numerical simulation of the electric fields induced by Non-Invasive Brain Stimulation (NIBS), using realistic anatomical head models has gained interest in recent years for understanding the NIBS effects in individual subjects. Although automated tools for generating the head models and performing the electric field simulations have become available, individualized modelling is still not standard practice in NIBS studies. This is likely partly explained by the lack of robustness and usability of the previously available software tools, and partly by the still developing understanding of the link between physiological effects and electric field distributions in the brain. To facilitate individualized modelling in NIBS, we have introduced the SimNIBS (Simulation of NIBS) software package, providing easy-to-use automated tools for electric field modelling. In this article, we give an overview of the modelling pipeline in SimNIBS 2.1, with step-by-step examples of how to run a simulation. Furthermore, we demonstrate a set of scripts for extracting average electric fields for a group of subjects, and finally demonstrate the accuracy of automated placement of standard electrode montages on the head model. SimNIBS 2.1 is freely available at www.simnibs.org.

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