Realistic Human Head Model Research Articles

Microwave Technique for Linear Skull Fracture Detection-Simulation and Experimental Study Using Realistic Human Head Models.

Microwave (MW) sensing is regarded as a promising technique for various medical monitoring and diagnostic applications due to its numerous advantages and the potential to be developed into a portable device for use outside hospital settings. The detection of skull fractures and the monitoring of their healing process would greatly benefit from a rapidly and frequently usable application that can be employed outside the hospital. This paper presents a simulation- and experiment-based study on skull fracture detection with the MW technique using realistic models for the first time. It also presents assessments on the most promising frequency ranges for skull fracture detection within the Industrial, Scientific and Medical (ISM) and ultrawideband (UWB) ranges. Evaluations are carried out with electromagnetic simulations using different head tissue layer models corresponding to different locations in the human head, as well as an anatomically realistic human head simulation model. The measurements are conducted with a real human skull combined with tissue phantoms developed in our laboratory. The comprehensive evaluations show that fractures cause clear differences in antenna and channel parameters (S11 and S21). The difference in S11 is 0.1-20 dB and in S21 is 0.1-30 dB, depending on the fracture width and location. Skull fractures with a less than 1 mm width can be detected with microwaves at different fracture locations. The detectability is frequency dependent. Power flow representations illustrate how fractures impact on the signal propagation at different frequencies. MW-based detection of skull fractures provides the possibility to (1) detect fractures using a safe and low-cost portable device, (2) monitor the healing-process of fractures, and (3) bring essential information for emerging portable MW-based diagnostic applications that can detect, e.g., strokes.

Shielded Cone Coil Array for Non-Invasive Deep Brain Magnetic Stimulation.

Non-invasive deep brain stimulation using transcranial magnetic stimulation is a promising technique for treating several neurological disorders, such as Alzheimer's and Parkinson's diseases. However, the currently used coils do not demonstrate the required stimulation performance in deep regions of the brain, such as the hippocampus, due to the rapid decay of the field inside the head. This study proposes an array that uses the cone coil method for deep stimulation. This study investigates the impact of magnetic core and shielding on field strength, focality, decay rate, and safety. The coil's size and shape effects on the electric field distribution in deep brain areas are also examined. The finite element method is used to calculate the induced electric field in a realistic human head model. The simulation results indicate that the magnetic core and shielding increase the electric field intensity and enhance focality but do not improve the field decay rate. However, the decay rate can be reduced by increasing the coil size at the expense of focality. By adopting an optimum cone structure, the proposed five-coil array reduces the electric field attenuation rate to reach the stimulation threshold in deep regions while keeping all other regions within safety limits. In vitro and in vivo experimental results using a head phantom and a dead pig's head validate the simulated results and confirm that the proposed design is a reliable and efficient candidate for non-invasive deep brain magnetic stimulation.

A hybrid 2D-FDTD/3D-MoM method used for the analysis of MRI RF coils

The design of radiofrequency (RF) coils is crucial for ultra-high field (UHF) magnetic resonance imaging (MRI) systems. To analyze RF coils, various numerical methods, such as finite-difference time-domain (FDTD) and method of moments (MoM), are usually adopted. In this paper, we present a novel hybrid approach that combines a two-dimensional (2D) FDTD with a three-dimensional (3D) MoM to analyze MRI RF problems. In our algorithm, the MoM is utilized for calculating the coil current, and FDTD is assigned for solving the electromagnetic (EM) fields in the imaging region. The hybrid method achieves superior efficiency and acceptable accuracy than using either method individually. To validate the hybrid method, we analyze an ellipse coil loaded with a uniform phantom and a realistic human head model, with the objective of tailoring the magnetic field intensity by adding a multilayer dielectric pad (DP). The results show an improvement in the magnetic field after optimizing the DP configuration. These simulation studies indicate the potential of the new numerical method for the design and analysis of RF systems for ultra-high field applications.

Electromagnetic field exposure to human head model with various metal objects at sub-6 GHz frequencies

ABSTRACT In recent years, the interactions of metal objects in human body with electromagnetic fields caused by devices working at fifth-generation (5G) frequencies have been studied by various researchers. A motivation behind this research was to evaluate the human body absorption of electromagnetic energy operating at sub-6 GHz 5G applications. According to this, the specific absorption rate (SAR) caused by new generation mobile phones was investigated in human heads wearing metal-framed spectacles and having metallic implants or earrings to analyse electromagnetic field exposure. A realistic human head model, including some metal objects, was numerically calculated, and analysed in terms of non-ionizing dosimetry. Simulations were carried out with the finite integration technique (FIT) based commercial software in the frequencies of 0.9, 1.8, 2.1, 2.45, 3.5 and 5 GHz, respectively. The maximum SAR of 14 × 10−5 W/kg for 10 g average tissue was calculated at 2.45 GHz frequency in the head model with earrings. The highest electric field strength of 0.52 V/m was observed at a 1.8 GHz frequency in the head model with all metal objects equipped. Results show that metal objects such as spectacles, dental implants and earrings can cause an increase in the SAR values for external biological tissues, and metal objects can behave as a kind of shield for deeper tissues. However, the obtained values are below the limits of international organisations.

Robust Evaluation and Comparison of EEG Source Localization Algorithms for Accurate Reconstruction of Deep Cortical Activity

Accurately reconstructing deep cortical source activity from EEG recordings is essential for understanding cognitive processes. However, currently, there is a lack of reliable methods for assessing the performance of EEG source localization algorithms. This study establishes an algorithm evaluation framework, utilizing realistic human head models and simulated EEG source signals with spatial propagations. We compare the performance of several newly proposed Bayesian algorithms, including full Dugh, thin Dugh, and Mackay, against classical methods such as MN and eLORETA. Our results, which are based on 630 Monte Carlo simulations, demonstrate that thin Dugh and Mackay are mathematically sound and perform significantly better in spatial and temporal source reconstruction than classical algorithms. Mackay is less robust spatially, while thin Dugh performs best overall. Conversely, we show that full Dugh has significant theoretical flaws that negatively impact localization accuracy. This research highlights the advantages and limitations of various source localization algorithms, providing valuable insights for future development and refinement in EEG source localization methods.

Experimental and numerical analyses of ballistic resistance evaluation of combat helmet using Hybrid III headform

Combat helmets are the primary system for protecting the head against ballistic impacts. Generally, combat helmets have been evaluated using a ballistic plasticine head surrogate based on international standards. More realistic human head models have recently been introduced to assess combat helmet performance considering biomechanical requirements. In this work, the Hybrid III dummy head and neck has been introduced to evaluate the performance of the combat helmet against the ballistic impact of live ammunition at different impact locations, considering two different thicknesses of the padding system. A numerical model including a helmet and a Hybrid III head and neck, is developed and validated with our experimental data. The results reveal the influence of the location, where the rear impact leads to the highest risk of brain damage. The effect of pad thickness is closely related to the energy absorbed by the helmet, the backface deformation (BFD), the contact force and the acceleration measured on the head.

FDTD-based SAR calculation of a wearable antenna for wireless body area network devices

AbstractWireless-connected wearable electronics are finding extensive usage for diagnostic and therapeutic purposes after the globally spread pandemic disease of COVID-19. Although they are undoubtedly helpful for keeping physical distance, their health effects are still under investigation from different aspects and are still a concern for the end-users. In this study, a custom M-shaped wearable antenna covering the wireless body area network and wireless local area network frequencies is designed, built, and measured. A beret cap made from a 2 mm thick textile is used as a substrate. The specific absorption rate (SAR) in a realistic human-head model due to electromagnetic energy produced by the antenna is evaluated using the finite-difference time-domain method. The SAR distributions for 1-g and 10-g tissues are calculated at 2.4 and 5.8 GHz. It is shown that the obtained maximum SAR values for 1-g and 10-g tissues at each frequency of interest were less than the limits determined by IEEE RF exposure guidelines and standards.

Computation of Absorbed Power Densities in High-Resolution Head Models by Considering Skin Thickness in Quasi-Millimeter and Millimeter Wave Bands

The fifth-generation wireless communications system has been increasingly deployed by telecommunication companies worldwide. This system uses a high-frequency band ranging from 24 GHz to 28 GHz. However, the number of studies assessing the human protection from the electromagnetic fields is limited in this frequency band. In addition, two main international bodies—the International Commission on Non-Ionizing Radiation Protection and IEEE—have revised their guidelines and standard in 2020 and 2019, respectively. One primary change is the exposure metric and corresponding exposure limit at frequencies >6 GHz because the penetration depth of the electromagnetic waves in biological tissues is 1 cm or less for these frequencies. Therefore, modeling of the skin and subcutaneous tissues is important. This study evaluated the total absorbed power (TAP), the absorbed power density (APD), and variations in APD owing to skin thickness in seven types of realistic human head models with different skin thicknesses. Our results showed that the model without surface smoothing resulted in higher TAP than the model with smoothing. The amount of the TAP change in frequency domain in the model with realistically varied skin thickness was less than that in the model with uniform skin thickness because of the suppression of strong standing waves. The maximum variations in the APD, averaging over 4 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> or 1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with respect to skin thickness, were approximately 20% and 10%, respectively. For the limit of incident power density, APDs were below the guideline. These results will be useful for future revisions of international guidelines.

Non-invasive focalized stimulation in deep brain using the spatially symmetric array

As a non-invasive neuromodulation technology, transcranial magnetic stimulation (TMS) shows great potential in the treatment of mental diseases. Using TMS to stimulate deep brain targets has significant scientific research value for the exploration of the causes of psychiatric diseases. However, the focalized induced electrical field (E-field) generated by traditional TMS coils or coil arrays is largely restricted to superficial cortical targets. To achieve focalized stimulation in the deep brain, a novel spatially symmetric array based on curved θ-type coils (the θ-SSA) is proposed in this paper. Four θ-type coils in the array are symmetrical to the YZ and XZ planes. Each θ-type coil is placed tangent to the human scalp and bent away from the human head to reduce the non-longitudinal component accumulation of the induced E-field and enhance the stimulation focalization. The finite-element method is used to obtain the 3D spatial distributions of the intracranial induced E-field generated by the proposed array. Results show that the θ-SSA can form an obvious focusing area in the deep brain 11 cm below the scalp. Under identical stimulation current excitation, the θ-SSA can increase the intracranial longitudinal attenuation ratio by 77% compared to the traditional TMS coil. In addition, when generating the same focusing area, the stimulation depth of the θ-SSA is 1.67 times deeper than that of the traditional TMS coil. Meanwhile, the proposed array can dynamically steer the intracranial stimulated area, and the spatial coordinates of the intracranial stimulation target point can be flexibly and continuously adjusted when changing the stimulation current parameters applied to the array. An anatomically realistic human head model with gray matter is employed in this paper to verify our method.

An in-silico analysis of retinal electric field distribution induced by different electrode design of trans-corneal electrical stimulation

Objective. Trans-corneal electrical stimulation (TcES) produces therapeutic effects on many ophthalmic diseases non-invasively. Existing clinical TcES devices use largely variable design of electrode distribution and stimulation parameters. Better understanding of how electrode configuration paradigms and stimulation parameters influence the electric field distribution on the retina, will be beneficial to the design of next-generation TcES devices. Approach. In this study, we constructed a realistic finite element human head model with fine eyeball structure. Commonly used DTL-Plus and ERG-Jet electrodes were simulated. We then conducted in silico investigations of retina observation surface (ROS) electric field distributions induced by different return electrode configuration paradigms and different stimulus intensities. Main results. Our results suggested that the ROS electric field distribution could be modulated by re-designing TcES electrode settings and stimulus parameters. Under far return location paradigms, either DTL-Plus or ERG-Jet approach could induce almost identical ROS electric field distribution regardless where the far return was located. However, compared with the ERG-Jet mode, DTL-Plus stimulation induced stronger nasal lateralization. In contrast, ERG-Jet stimulation induced relatively stronger temporal lateralization. The ROS lateralization can be further tweaked by changing the DTL-Plus electrode length. Significance. These results may contribute to the understanding of the characteristics of DTL-Plus and ERG-Jet electrodes based electric field distribution on the retina, providing practical implications for the therapeutic application of TcES.

Microwave Hyperthermia of Brain Tumors: A 2D Assessment Parametric Numerical Study.

Due to the clinically proven benefit of hyperthermia treatments if added to standard cancer therapies for various tumor sites and the recent development of non-invasive temperature measurements using magnetic resonance systems, the hyperthermia community is convinced that it is a time when even patients with brain tumors could benefit from regional microwave hyperthermia, even if they are the subject of a treatment to a vital organ. The purpose of this study was to numerically analyze the ability to achieve a therapeutically relevant constructive superposition of electromagnetic (EM) waves in the treatment of hyperthermia targets within the brain. We evaluated the effect of the target size and position, operating frequency, and the number of antenna elements forming the phased array applicator on the treatment quality. In total, 10 anatomically realistic 2D human head models were considered, in which 10 circular hyperthermia targets with diameters of 20, 25, and 30 mm were examined. Additionally, applicators with 8, 12, 16, and 24 antenna elements and operating frequencies of 434, 650, 915, and 1150 MHz, respectively, were analyzed. For all scenarios considered (4800 combinations), the EM field distributions of individual antenna elements were calculated and treatment planning was performed. Their quality was evaluated using parameters applied in clinical practice, i.e., target coverage (TC) and the target to hot-spot quotient (THQ). The 12-antenna phased array system operating at 434 MHz was the best candidate among all tested systems for HT treatments of glioblastoma tumors. The 12 antenna elements met all the requirements to cover the entire target area; an additional increase in the number of antenna elements did not have a significant effect on the treatment quality.

Design of Antenna-Multiplexer for Seamless On-Body Internet of Medical Things (IoMT) Connectivity

Here, a compact design of antenna-multiplexer is engineered specifically to meet the stringent requirement imposed by intricate subsystems operating at 5.2, 5.5, and 5.8 GHz frequency bands for Internet of Medical Things (IoMT) applications. The proposed design includes a hexagonal-shaped substrate integrated waveguide (HSIW) cavity, tripole-shaped radiating slot, tuning vias, and three inset microstrip feedlines. A tripole-shaped slot is imprinted on the top of the SIW. This slot subdivides the cavity into trio-radiating segments and each segment offers a single frequency band. Further, the frequency bands are tuned at 5.2/5.5/5.8 GHz. The design maintains mutual port isolation better than 23.9 dB. Compared with the conventional tri-frequency antennas, the proposed design is highly compact and doesn’t need any additional circuitry to improve the port isolations. The measured results confirm the expected performance of the design. Furthermore, the proposed antenna is optimized within an implantable medical device (IMD) and simulated inside a realistic Human Head model at a depth of 3 mm and the Specific Absorption Rate (SAR) value is estimated. The SAR values are well below 0.362 W/Kg at the functioning bands due to the unidirectional radiation pattern from the antenna.

Simultaneous Bilateral Frontal and Bilateral Cerebellar Transcranial Direct Current Stimulation in Treatment-Resistant Depression-Clinical Effects and Electrical Field Modelling of a Novel Electrodes Montage.

Depressive disorders are one of the leading causes of disability worldwide. Transcranial direct current stimulation (tDCS) is a safe, simple, non-invasive brain stimulation technique showing considerable effectiveness in improving depressive symptoms. Most studies to date have applied anodal tDCS to the left dorsolateral prefrontal cortex (DLPFC), in line with the hypothesis that depressed patients exhibit relative hypoactivity in the left DLPFC compared to the right. Considering the emerging role of the cerebellum in emotional processes, we aimed to study the effect of combining bilateral cerebellar tDCS with the commonly used bifrontal stimulation in patients with severe depression. This open-label pilot study entailed the simultaneous administration of bilateral cerebellar (anode over the left cerebellum, cathode over the right cerebellum) and bilateral frontal (anode over the left DLPFC, cathode over the right DLPFC) tDCS to patients (N = 12) with treatment-resistant depression. The 21-item Hamilton Depression Rating Scale (HDRS) and Beck’s Depression Inventory-II (BDI-II) were selected as outcome measures. Electric fields distribution originating from this novel electrode montage was obtained by a computational method applied to a realistic human head model. We observed a 30% reduction of both clinician-rated and self-reported severity of depressive symptoms after only five days (10 sessions) of treatment. Younger age was associated with greater clinical improvement. Adverse events were similar to those of the conventional electrodes montage. The modelling studies demonstrated that the electric fields generated by each pair of electrodes are primarily distributed in the cortical areas under the electrodes. In conclusion, the cerebellum could represent a promising adjunctive target for tDCS interventions in patients with TRD, particularly for younger patients.

Guidelines for Burr Hole Surgery in Combination With Tumor Treating Fields for Glioblastoma: A Computational Study on Dose Optimization and Array Layout Planning.

Tumor treating fields (TTFields) is an anti-cancer technology increasingly used for the treatment of glioblastoma. Recently, cranial burr holes have been used experimentally to enhance the intensity (dose) of TTFields in the underlying tumor region. In the present study, we used computational finite element methods to systematically characterize the impact of the burr hole position and the TTFields transducer array layout on the TTFields distribution calculated in a realistic human head model. We investigated a multitude of burr hole positions and layouts to illustrate the basic principles of optimal treatment planning. The goal of the paper was to provide simple rules of thumb for physicians to use when planning the TTFields in combination with skull remodeling surgery. Our study suggests a number of key findings, namely that (1) burr holes should be placed directly above the region of interest, (2) field enhancement occurs mainly underneath the holes, (3) the ipsilateral array should directly overlap the holes and the contralateral array should be placed directly opposite, (4) arrays in a pair should be placed at far distance and not close to each other to avoid current shunting, and finally (5) rotation arrays around their central normal axis can be done without diminishing the enhancing effect of the burr holes. Minor deviations and adjustments (<3 cm) of arrays reduces the enhancement to some extent although the procedure is still effective in these settings. In conclusion, our study provides simple guiding principles for implementation of dose-enhanced TTFields in combination with burr-holes. Future studies are required to validate our findings in additional models at the patient specific level.

The significance of nanoparticles in brain cancer diagnosis and treatment: modeling and simulation

A numerical analysis of specific absorption rate (SAR) and temperature distributions in a realistic human head model is presented in this study. The key challenge is to rise cancer temperature to an optimal temperature without heating nearby healthy tissues. The model’s uniqueness is that it captures the effect of nanoparticles on both brain cancer diagnosis and treatment. A realistic human head model with a cancerous brain segmented from 2D magnetic resonance imaging (MRI) gained from an actual patient using 3D Slicer, modeled, and simulated using CST-Microwave Studio, and illuminated by Archimedes spiral antenna. At frequencies of 2450 MHz and 915 MHz, the model simulated the absence and presence of various nanoparticles. The obtained results suggest that when using nanoparticles, it is possible to achieve sufficient energy deposition and temperature rise to therapeutic values (greater than 42 °C) in brain cancers using the proposed noninvasive hyperthermia system at 915 MHz frequency, especially for gold nanoparticles, without harming surrounding healthy tissue. Our research might pave the way for a clinical applicator prototype that can heat brain cancer.

Key factors in the cortical response to transcranial electrical Stimulations—A multi-scale modeling study

Transcranial electrode stimulation (tES), one of the techniques used to apply non-invasive brain stimulation (NIBS), modulates cortical activities by delivering weak electric currents through scalp-attached electrodes. This emerging technique has gained increasing attention recently; however, the results of tES vary greatly depending upon subjects and the stimulation paradigm, and its cellular mechanism remains unclear. In particular, there is a controversy over the factors that determine the cortical response to tES. Some studies have reported that the electric field's (EF) orientation is the determining factor, while others have demonstrated that the EF magnitude itself is the crucial factor. In this work, we conducted an in-depth investigation of cortical activity in two types of electrode montages used widely—the conventional (C)-tES and high-definition (HD)-tES—as well as two stimulation waveforms—direct current (DC) and alternating current (AC). To do so, we constructed a multi-scale model by coupling an anatomically realistic human head model and morphologically realistic multi-compartmental models of three types of cortical neurons (layer 2/3 pyramidal neuron, layer 4 basket cell, layer 5 pyramidal neuron). Then, we quantified the neuronal response to the C-/HD-tDCS/tACS and explored the relation between the electric field (EF) and the radial field's (RF: radial component of EF) magnitude and the cortical neurons' threshold. The EF tES induced depended upon the electrode montage, and the neuronal responses were correlated with the EF rather than the RF's magnitude. The electrode montages and stimulation waveforms caused a small difference in threshold, but the higher correlation between the EF's magnitude and the threshold was consistent. Further, we observed that the neurons' morphological features affected the degree of the correlation highly. Thus, the EF magnitude was a key factor in the responses of neurons with arborized axons. Our results demonstrate that the crucial factor in neuronal excitability depends upon the neuron models' morphological and biophysical properties. Hence, to predict the cellular targets of NIBS precisely, it is necessary to adopt more advanced neuron models that mimic realistic morphological and biophysical features of actual human cells.

Comparison of Transcranial Focused Ultrasound and Transcranial Pulse Stimulation for Neuromodulation: A Computational Study

ObjectiveThe objective of the study was to investigate transcranial wave propagation through two low-intensity focused ultrasound (LIFU)–based brain stimulation techniques—transcranial focused ultrasound stimulation (tFUS) and transcranial pulse stimulation (TPS). Although tFUS involves delivering long trains of acoustic pulses, the newly introduced TPS delivers ultrashort (∼3 μs) pulses repeated at 4 Hz. Accordingly, only a single simulation study with limited geometry currently exists for TPS. We considered a high-resolution three-dimensional (3D) whole human head model in addition to water bath simulations. We anticipate that the results of this study will help researchers investigating LIFU have a better understanding of the effects of the two different techniques. ApproachWith an objective to first reproduce previous computational results, we considered two spherical tFUS transducers that were previously modeled. We assumed identical parameters (geometry, position, and imaging data set) to demonstrate differences, purely because of the waveform considered. For simulations with a 3D head data set, we also considered a parabolic transducer that has been used for TPS delivery. ResultsOur initial results successfully verified previous modeling workflow. The tFUS distribution was characterized by the typical elliptical profile, with its major axis perpendicular to the face of the transducer. The TPS distribution resembled two mirrored meniscus profiles, with its widest diameter oriented parallel to the face of the transducer. The observed intensity value differences were theoretical because the two waveforms differ in both intensity and time. The consideration of a realistic 3D human head model resulted in only a minor distortion of the two waveforms. SignificanceThis study simulated TPS administration using a 3D realistic image-derived data set. Although our comparison results are strictly limited to the model parameters and assumptions made, we were able to elucidate some clear differences between the two approaches. We hope this initial study will pave the way for systematic comparison between the two approaches in the future.

Numerical Analysis of RF-Induced Heating While Wearing Face Mask at Magnetic Resonance Imaging

In response to the unprecedented COVID-19 pandemic, wearing face masks in public places and common facilities has been strongly recommended to help prevent the further spread of the virus. However, conductive components of the face mask carry the potential risk of radio-frequency (RF)-induced heating when exposed to an RF electromagnetic field, particularly during magnetic resonance imaging (MRI). In this study, a realistic human head model wearing a face mask exposed to a strong RF electromagnetic field in 1.5 T, 3 T, and 7 T MRI was simulated. A nose wire in contact with the skin and a mask sheet with relatively high electrical conductivity, emulating a silver nanoparticle-coated face mask, was modeled to investigate the worst case of RF-induced heating that could occur during the MRI scan. 24 scenarios were simulated by using finite-difference time-domain (FDTD)-based electromagnetic solver and thermal-transient solver from Sim4Life commercial simulation software. According to the results, a notable enhancement in the specific absorption rate (SAR) and temperature rise was observed in the local region of the skin where the wire contacted the skin around the edge of the high-conductive mask sheet. In particular, a maximum of a 12-fold increase in mass-averaged SAR and a temperature increase of more than 8.0&#x00B0;C occurred because of the conductive face mask at 3 T, compared to the normal polymer-based face mask with low conductivity. Our results confirmed that the degree of RF-induced heating due to the face mask could be completely different depending on the RF frequency of the MRI, location where the nose wire contacted the skin, and conductivity of the mask sheet. To the best of our knowledge, this is the first study to assess the face mask as a factor for RF-induced heating during MRI. These findings are important for providing a safety guide that allows patients to safely undergo MRI while wearing a face mask during the COVID-19 pandemic.

Uncertainty quantification and sensitivity analysis of transcranial electric stimulation for 9-subdomain human head model

This paper deals with uncertainty quantification of transcranial electric stimulation (TES) of realistic human head model. The head model taken from Visible Human Project consists of 9 subdomains: scalp, skull, CSF, grey matter, white matter, cerebellum, ventricles, jaw and tongue. The deterministic computation of quasi-static induced electric scalar potential features boundary element method (BEM). Conductivities of each subdomain are modelled as uniformly distributed random variables and stochastic analysis features a non-intrusive stochastic collocation method (SCM). The input uncertainties impact only the magnitude of the electric scalar potential and not the position of the potential extrema. Skin and brain conductivities play the most important role, while CSF conductivity has negligible impact on the output potential variance. The significance of the skull conductivity is not high for the chosen input parameter setup. In the previous work authors considered 3-compartment head model which consisted of scalp, skull and brain compartments. The presented model is a step forward in SCM+BEM TES analysis, primarily in terms of model complexity. Comparing the results of the two analyses it can be concluded that the uncertainty in the added tissues’ conductivities do not impact the variation of the output electric potential.

Multi-channel transorbital electrical stimulation for effective stimulation of posterior retina

Transorbital electrical stimulation (tES) has been studied as a new noninvasive method for treating intractable eye diseases by delivering weak electrical current to the eye through a pair of electrodes attached to the skin around the eye. Studies have reported that the therapeutic effect of tES is determined by the effective stimulation of retinal cells that are densely distributed in the posterior part of the retina. However, in conventional tES with a pair of electrodes, a greater portion of the electric field is delivered to the anterior part of the retina. In this study, to address this issue, a new electrode montage with multiple electrodes was proposed for the effective delivery of electric fields to the posterior retina. Electric field analysis based on the finite element method was performed with a realistic human head model, and optimal injection currents were determined using constrained convex optimization. The resultant electric field distributions showed that the proposed multi-channel tES enables a more effective stimulation of the posterior retina than the conventional tES with a pair of electrodes.