Human Head Model Research Articles

A Model for Assessing the Electromagnetic Safety of an Inductively Coupled, Modular Brain-Machine Interface

Brain-Machine Interfaces (BMI) offer the potential to modulate dysfunctional neurological networks by electrically stimulating the cerebral cortex via chronically-implanted microelectrodes. Wireless transmitters worn by BMI recipients must operate within electromagnetic emission and tissue heating limits, such as those prescribed by the IEEE and International Commission on Non-Ionizing Radiation Protection (ICNIRP), to ensure that radiofrequency emissions of BMI systems are safe. Here, we describe an approach to generating pre-compliance safety data by simulating the Specific Absorption Rate (SAR) and tissue heating of a multi-layered human head model containing a system of wireless, modular BMIs powered and controlled by an externally worn telemetry unit. We explore a number of system configurations such that our approach can be utilized for similar BMI systems, and our results provide a benchmark for the electromagnetic emissions of similar telemetry units. Our results show that the volume-averaged SAR per 10g of tissue exposed to our telemetry field complies with ICNIRP and IEEE reference levels, and that the maximum temperature increase in tissues was within permissible limits. These results were unaffected by the number of implants in the system model, and therefore we conclude that the electromagnetic emissions our BMI in any configuration are safe.

Computational simulations establish a novel transducer array placement arrangement that extends delivery of therapeutic TTFields to the infratentorium of patients with brainstem gliomas.

Background and PurposeTumor treating fields (TTFields) are a non-invasive, efficacious treatment modality currently approved for supratentorial glioblastomas. Despite their ability to improve overall survival in supratentorial tumors, the current placement of arrays is limited to the supratentorial head, precluding its use in infratentorial tumors. Infratentorial malignancies are in need of new therapy modalities given their poor prognoses in both children and adults. The aim of this research is to determine whether rearrangement of TTFields may allow for management of infratentorial tumors.Materials and methodsDelivery of TTFields using Novocure’s prototype Optune™ device human male head model was simulated based on brain MRIs from patients with brainstem gliomas to develop a novel array layout designed to extend adequate infratentorial coverage.ResultsArray placement on the vertex, bilateral posterolateral occiput, and superior-posterior neck achieved intensities above 1.1 V/cm (average 1.7 V/cm; maximum 2.3 V/cm) in the vertical field direction and above 1 V/cm (average 2 V/cm; maximum 2.8 V/cm) in the horizontal field direction of the infratentorium. The calculated field intensity within the simulated tumors were in the therapeutic range and demonstrated the effective delivery of TTFields to the infratentorial brain.ConclusionsOur findings suggest that rearrangement of the TTFields standard array with placement of electrodes on the vertex, bilateral posterolateral occiput, and superior-posterior neck allows for adequate electric field distribution in the infratentorium that is within the therapeutic range.

Design of circularly polarized implantable antenna for wireless intracranial pressure monitoring system

Monitor of intracranial pressure (ICP) system is a life-saving instrument that monitors changes in brain pressure in real time. To implement wireless data transfer, antenna is an indispensable device. In this paper, an implantable antenna is designed with circularly polarized, wideband and compact in size to adapt the application of the ICP monitoring system. First, a one-layer human skin model to verify the basic characteristics of this antenna; and then a multilayered human head model is built to demonstrate the system performance of the designed antenna. In addition, we also considered the human safety to calculate the specific absorption rate value of the proposed antenna. The antenna can transmit different rates over to 1.5 m distance verified by the wireless communication link, which proved it has a good transitions characteristic. Finally, the sample of the antenna is fabricated and tested with help of fresh minced pork. Experiment results shows the antenna with a good property in the ICP monitoring system, as well as other remote medical telemetry system.

Low-profile high impedance surface on magneto-dielectric nanocomposite for wideband absorption of mobile phone radiation

An electrically thin (0.024𝜆0) high-impedance surface (HIS) on a magneto-dielectric nanocomposite (NC) is presented as an external shield for wideband absorption of mobile phone radiation. Characterization of the NC and numerical design and analysis of the miniaturized HIS unit cell on NC (0.088𝜆0 × 0.088𝜆0) are presented over 0.85–6 GHz, where 𝜆0 is the free space wavelength at the absorber resonant frequency. The absorber performance is assessed using a mobile phone handset at 0.9 and 1.8 GHz Global System for Mobile Communications (GSM) frequencies and 2.4 GHz Wireless Fidelity (WiFi) frequency. Handset specific absorption rate (SAR) measurements with the absorber recorded in head phantom indicated 83, 48 and 71% reduction in peak SAR at 0.9, 1.8 and 2.4 GHz, respectively without significantly affecting the handset radiation characteristics in free space. Simulation results of human head model with the hand showed SAR reduction of 69, 24 and 65% at 0.9, 1.8 and 2.4 GHz, respectively for 1 g SAR. It is concluded that the proposed absorber could be used to lower handset SAR levels and shield mobile communication signals over 0.85–6 GHz.

Analysis of SAR reduction to human head with plasma photonic crystals shield using ICCG-SFDTD method

A novel and effective biological electromagnetic method using plasma photonic crystals shield to protect the human head from electromagnetic radiation of an ultra-high-field magnetic resonance imaging (MRI) frequency is explored. An improved incomplete Cholesky conjugate gradient (ICCG)-based symplectic finite-difference time-domain (ICCG-SFDTD) method, which maintains the property of the Hamilton system and ensures energy conservation numerically with high precision, is applied to a bioelectromagnetic simulation of human head models without shield, with plasma shield and with plasma photonic crystals shield. Results show that plasma photonic crystals shield is superior to plasma shield with the same thickness in reducing the specific absorption rate (SAR) and electric field levels of the human head. In addition, the relationship of SAR and electric field in the human head models with the parameters of plasma photonic crystals, such as the plasma frequency, plasma collision frequency and dielectric constant of the medium is studied in order to provide a guidance to design plasma photonic crystals protective layer for biological tissue.

Scalp-Implantable MIMO Antenna for High-Data-Rate Head Implants

A quad-element multiple-input–multiple-output (MIMO) antenna is designed at 433 MHz industrial, scientific, and medical (ISM) band, to increase the transmission data-rate and minimize the multipath fading. The proposed MIMO antenna consists of semicircular meandered radiators with a shared ground. It is designed and optimized inside an implantable medical device in a human head model. The antenna’s results show a 10 dB fractional bandwidth of 38.26% (355–523 MHz) with a peak realized gain of −28.3 dBi. A high isolation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 32.6 dB) between MIMO elements is obtained using a central metallic via. Specific absorption rate and link budget are analyzed to validate the effectiveness of this antenna. The 4 × 4 MIMO channel parameters are calculated and validated. Furthermore, this antenna provides a channel capacity of 19.9 bps/Hz which is about three times higher than the single-input–single-output configuration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\approx$</tex-math></inline-formula> 5.89 bps/Hz. Hence, this MIMO configuration is a promising candidate for high-data-rate head implants.

Revisiting an analytical solution for the three-shell spherical human head model in electroencephalography

The complete three-shell spherical human head model in electroencephalography (EEG) is revisited and an analytical solution of the forward problem is derived. The introduced geometrical model involves four concentric spheres that represent the successive interfaces between the cerebrum, the cerebrospinal fluid, the skull and the skin, which are characterized by different conductivities, while the outer environment is evidently the non-conductive air. The neuronal operation of the brain is considered to be represented by an equivalent and arbitrarily orientated electric dipole that is located in the inner sphere. The dipole source produces a bipolar primary current and the electric activity is initiated by means of the generated electric field, which is associated with the corresponding potential functions within each one of the conductive compartments of the model, inferring crucial information about EEG effects outside the head. The potentials formulae are obtained in compact fashion via the solution of a sequence of interconnected elliptic-type boundary value problems with Dirichlet and Neumann transmission conditions, where the consistent behavior of the fields in the brain and far away from the system has been taken into account. The efficiency of the suggested mathematical model is numerically implemented and the impact of the brain electric response to the exterior measurable potential field is demonstrated, implying a solid and sufficient head representation for the EEG forward problem.

Small Triple-Band Meandered PIFA for Brain-Implantable Biotelemetric Systems: Development and Testing in a Liquid Phantom

We present a meandered triple-band planar-inverted-F antenna (PIFA) for integration into brain-implantable biotelemetric systems. The target applications are wireless data communication, far-field wireless power transfer, and switching control between sleep/wake-up mode at the Medical Device Radiocommunication Service (MedRadio) band (401–406 MHz) and Industrial, Scientific and Medical (ISM) bands (902–928 MHz and 2400–2483.5 MHz), respectively. By embedding meandered slots into the radiator and shorting it to the ground, we downsized the antenna to the volume of 11 × 20.5 × 1.8 mm3. We optimized the antenna using a 7-layer numerical human head model using full-wave electromagnetic field simulation. In the simulation, we placed the implant in the cerebrospinal fluid (CSF) at a depth of 13.25 mm from the body surface, which is deeper than in most works on implantable antennas. We manufactured and tested the antenna in a liquid phantom which we replicated in the simulator for further comparison. The measured gain of the antenna reached the state-of-the-art values of −43.6 dBi, −25.8 dBi, and −20.1 dBi at 402 MHz, 902 MHz, and 2400 MHz, respectively.

Investigation of effect of modulation frequency on high-density diffuse optical tomography image quality.

.Significance: By incorporating multiple overlapping functional near-infrared spectroscopy (fNIRS) measurements, high-density diffuse optical tomography (HD-DOT) images human brain function with fidelity comparable to functional magnetic resonance imaging (fMRI). Previous work has shown that frequency domain high-density diffuse optical tomography (FD-HD-DOT) may further improve image quality over more traditional continuous wave (CW) HD-DOT.Aim: The effects of modulation frequency on image quality as obtainable with FD-HD-DOT is investigated through simulations with a realistic noise model of functional activations in human head models, arising from 11 source modulation frequencies between CW and 1000 MHz.Approach: Simulations were performed using five representative head models with an HD regular grid of 158 light sources and 166 detectors and an empirically derived noise model. Functional reconstructions were quantitatively assessed with multiple image quality metrics including the localization error (LE), success rate, full width at half maximum, and full volume at half maximum (FVHM). All metrics were evaluated against CW-based models.Results: Compared to CW, localization accuracy is improved by >40% throughout brain depths of 13 to 25 mm below the surface with 300 to 500 MHz modulation frequencies. Additionally, the reliable field of view in brain tissue is enlarged by 35% to 48% within an optimal frequency of 300 MHz after considering realistic noise, depending on the dynamic range of the system.Conclusions: These results point to the tremendous opportunities in further development of high bandwidth FD-HD-DOT system hardware for applications in human brain mapping.

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.

808-nm Photobiomodulation Affects the Viability of a Head and Neck Squamous Carcinoma Cellular Model, Acting on Energy Metabolism and Oxidative Stress Production

Photobiomodulation (PBM) is a form of low-dose light therapy that acts through energy delivery from non-ionizing sources. During the recent two decades, there has been tremendous progress with PBM acceptance in medicine. However, PBM effects on potential stimulation of existing malignant or pre-malignant cells remain unknown. Thus, the primary endpoint was to assess the safety of PBM treatment parameters on head and neck squamous cell carcinoma (HNSCC) proliferation or survival. The secondary endpoint was to assess any putative anti-cancer effects of PBM treatments. Cell viability, energy metabolism, oxidative stress, and pro- and anti-apoptotic markers expression were investigated on a Human Head and Neck Squamous Cell Carcinoma cellular model (OHSU-974 FAcorr cell line). PBM therapy was administered through the 810 nm diode laser (GaAlAs) device (Garda Laser, 7024 Negrar, Verona, Italy) at the powers of 0, 0.25, 0.50, 0.75, 1.00, or 1.25 W in continuous wave (CW) mode for an exposure time of 60 s with a spot-size of 1 cm2 and with a distance of 1.86 cm from the cells. Results showed that 810-nm PBM affected oxidative phosphorylation in OHSU-971 FAcorr, causing a metabolic switch to anaerobic glycolysis. In addition, PBM reduced the catalase activity, determining an unbalance between oxidative stress production and the antioxidant defenses, which could stimulate the pro-apoptotic cellular pathways. Our data, at the parameters investigated, suggest the safeness of PBM as a supportive cancer therapy. Pre-clinical and clinical studies are necessary to confirm the in vitro evidence.

Microwave power penetration enhancement inside an inhomogeneous human head

The penetration of microwave power inside a human head model is improved by employing a dielectric loaded rectangular waveguide as the transmission source. A multi-layer reflection model is investigated to evaluate the combined material characteristics of different lossy human head tissues at 2.45 GHz. A waveguide loaded with a calculated permittivity of 3.62 is shown to maximise the microwave power penetration at the desired frequency. A Quartz (SiO2) loaded rectangular waveguide fed by a microstrip antenna is designed to validate the power penetration improvement inside an inhomogeneous human head phantom. A measured 1.33 dB power penetration increment is observed for the dielectric loaded waveguide over a standard rectangular waveguide at 50 mm inside the head, with an 81.9% reduction in the size of the transmission source.

Skull Thickness Calculation Using Thermal Analysis and Finite Elements

In this study, the skull bone thicknesses of 150 patients ranging in age from 0 to 72 years were calculated using a novel approach (thermal analysis), and thickness changes were analyzed. Unlike conventional thickness calculation approaches (Beam Propagation, Hildebrand), a novel heat transfer-based approach was developed. Firstly, solid 3D objects with different thicknesses were modeled, and thermal analyses were performed on these models. To better understand the heat transfer of 3D object models, finite element models (FEM) of the human head have been reported in the literature. The FEM can more accurately model the complex geometry of a 3D human head model. Then, thermal analysis was performed on human skulls using the same methods. Thus, the skull bone thicknesses at different ages and in different genders from region to region were determined. The skull model was transferred to ANSYS, and it was meshed using different mapping parameters. The heat transfer results were determined by applying different heat values to the inner and outer surfaces of the skull mesh structure. Thus, the average thicknesses of skull regions belonging to a certain age group were obtained. With this developed method, it was observed that the temperature value applied to the skull was proportional to the thickness value. The average thickness of skull bones for men (frontal: 7.8 mm; parietal: 9.6 mm; occipital: 10.1 mm; temporal: 6 mm) and women (frontal: 8.6 mm; parietal: 10.1 mm; occipital: 10 mm; temporal: 6 mm) are given. The difference (10%) between men and women appears to be statistically significant only for frontal bone thickness. Thanks to the developed method, bone thickness information at any desired point on the skull can be obtained numerically. Therefore, the proposed method can be used to help pre-operative planning of surgical procedures.

A Biomechanical Evaluation of a Novel Airbag Bicycle Helmet Concept for Traumatic Brain Injury Mitigation.

In this study, a novel expandable bicycle helmet, which integrates an airbag system into the conventional helmet design, was proposed to explore the potential synergetic effect of an expandable airbag and a standard commuter-type EPS helmet. The traumatic brain injury mitigation performance of the proposed expandable helmet was evaluated against that of a typical traditional bicycle helmet. A series of dynamic impact simulations on both a helmeted headform and a representative human head with different configurations were carried out in accordance with the widely recognised international bicycle helmet test standards. The impact simulations were initially performed on a ballast headform for validation and benchmarking purposes, while the subsequent ones on a biofidelic human head model were used for assessing any potential intracranial injury. It was found that the proposed expandable helmet performed admirably better when compared to a conventional helmet design—showing improvements in impact energy attenuation, as well as kinematic and biometric injury risk reduction. More importantly, this expandable helmet concept, integrating the airbag system in the conventional design, offers adequate protection to the cyclist in the unlikely case of airbag deployment failure.

Four-channel current switching device to enable multi-electrode magnetic resonance current density imaging.

Neurostimulation with multiple scalp electrodes has shown enhanced effects in recent studies. However, visualizations of stimulation-induced internal current distributions in brain is only possible through simulated current distributions obtained from computer model of human head. While magnetic resonance current density imaging (MRCDI) has a potential for direct in-vivo measurement of currents induced in brain with multi-electrode stimulation, existing MRCDI methods are only developed for two-electrode neurostimulation. A major bottleneck is the lack of a current switching device which is typically used to convert the DC current of neurostimulation devices into user-defined waveforms of positive and negative polarity with delays between them. In this work, we present a design of a four-electrode current switching device to enable simultaneous switching of current flowing through multiple scalp electrodes.

Design and SAR assessment of three compact 5G antenna arrays

In this paper three different multi stub antenna arrays at 27–29.5 GHz are designed. The proposed antenna arrays consist of eight single elements. The structure of feeding parts is the same but the radiation elements are different. The feeding network for array is an eight way Wilkinson power divider (WPD). To guarantee the simulation results, one of the proposed structures is fabricated and measured (namely the characteristics of S11, E-, and H-plane patterns) which shows acceptable consistency with measurement results. The simulation results by CST and HFSS show reasonable agreement for reflection coefficient and radiation patterns in the E- and H- planes. The overall size of the proposed antenna in maximum case is 29.5 mm × 52 mm × 0.38 mm (2.8 {{varvec{lambda}}}_{0}× 4.86{{varvec{lambda}}}_{0} × 0.036{{varvec{lambda}}}_{0}). Moreover, for Specific Absorption Rate (SAR) estimation, a three-layer spherical human head model (skin, skull, and the brain) is placed next to the arrays as the exposure source. The simulation results show that the performance of proposed antennas as low-SAR sources makes them ideal candidates for the safe usage and lack of impact of millimeter waves (mmW) on the human health. In all three cases of SAR simulations the value of SAR1g and SAR10g are below the standard limitations.

Rapid calculation of static magnetic field perturbation generated by magnetized objects in arbitrary orientations.

Most previous work on the calculation of susceptibility-induced static magnetic field (B0 ) inhomogeneity has considered strictly unidirectional magnetic fields. Here, we present the theory and implementation of a computational method to rapidly calculate static magnetic field vectors produced by an arbitrary distribution of voxelated magnetization vectors. Two existing B0 calculation methods were systematically extended to include arbitrary orientations of the magnetization and the magnetic field; they are (1) Fourier-domain convolution with k-space-discretized (KD) dipolar field, and (2) generalized susceptibility voxel convolution (gSVC). The methods were tested on an analytical ellipsoid model and a tilted human head model, as well as against experimentally measured B0 fields induced by a stainless-steel implant located in an inhomogeneous region of a clinical 3T MRI magnet. Both methods were capable of correctly calculating B0 fields inside a magnetized ellipsoid in all tested orientations. The KD method generally required a larger grid and longer computation time to achieve accuracy comparable to gSVC. Measured B0 fields due to the implant showed a good match with the gSVC-calculated fields that accounted for the spatial variation of the applied magnetic field including the radial components. Our method can provide a reliable and efficient computational tool to calculate B0 perturbation by magnetized objects under a variety of circumstances, including those with inhomogeneous magnetizing fields, anisotropic susceptibility, and a rotated coordinate system.

Force measurement of electrodes on a human head model

Abstract Electroencephalography (EEG) and transcranial electric stimulation (TES) require caps for holding the respective electrodes in place. To support the optimal design of such caps, knowledge of the force-displacement curves for each electrode position is desirable. We propose a calibrated setup to traceably measure force-displacement curves which consists of a human head model, a force sensor, a linear guide, a stepper motor, and a multiplexing multimeter. Repeated measures of a textile EEG-cap and a TES-cap show significant non-linearity and hysteresis effects for the force-displacement curves. Our setup will allow for the assessment of the fit of EEG and TES-caps for various head shapes and sizes.

WIRE-MESH CAPACITANCE TOMOGRAPHY FOR TREATMENT PLANNING SYSTEM OF ELECTRO-CAPACITIVE CANCER THERAPY

The wire-mesh capacitance tomography (WMCT) has been applied to visualize 2D of the distribution of electric field intensity in the treatment planning system (TPS) of electro-capacitive cancer therapy (ECCT) using human head model. WMCT is proposed in this study to estimate accurately the distribution of electric field intensity which is the main optimum factors of ECCT in order to compensate the inaccuracy of TPS ECCT simulation. The experimental and simulation studies were conducted with wire-mesh sensor consisted of 8×8 wire matrix of copper in human head model using two type of helmet ECCT. The result of electric field value at the intersection wire-mesh have been compared between experimental studies and simulation studies. The electric field average value resulted from ECCT helmet-1 is higher than ECCT helmet-2. The average electric field generated by the ECCT helmet-1 is 1585.72 V/m in an air medium, 97.43 V/m in grey matter and 80.58 V/m in the cancer. While the average electric field generated by the ECCT helmet-2 is 1413.28 V/m in an air medium, 64.20 V/m in grey matter and 52.65 V/m in the cancer. ECCT helmet-1 and helmet-2 result the different of electric field distribution pattern. ECCT helmet-1 is more optimal for used to patient has cancer position in the right and bottom, while ECCT helmet-2 is more optimal for used to patient has cancer position in the top and bottom.

Investigation of a defected ground structure inspired wideband printed monopole mobile antenna using characteristics mode analysis

In this research article, a wideband mobile antenna with defected ground structure (DGS) is designed using characteristics mode analysis. It consists of a modified crescent-shaped monopole antenna (M-mode), L-shaped stub (S-mode), and DGS element (slot modes). Here, the fundamental resonating modes of M- and S-mode are induced to operate in the integration mode (I-mode) to obtain good impedance bandwidth (IBW). The DGS is implemented in ground plane to get slot modes (1 and 2). By combining slot modes with M-mode and S-mode, it exhibits broadened IBW (i.e., C-mode), is suitable for the coverage of mobile bands (sub-6 GHz frequency bands). For the clarity, modal investigation is performed at each critical stages of antenna designing process and the modal metrics like modal significance, characteristics angle (βn), Eigen values (λn), modal currents, and modal patterns are extracted by using Computer Simulation Technology (CST) Studio Suite. The proposed monopole antenna operates in multiband for wireless applications, that is, 880–960 MHz, 2.3–2.4 GHz, 2.4–2.483 GHz, 3.3–4.2 MHz, 3.3–3.8 GHz, 5.15–5.85 GHz, and WLAN (IEEE 802.11 b/g/n) respectively with measured gain of 3–5.5 dBi. A prototype of proposed antenna is fabricated and measured, which shows good agreements with simulation. To validate, averaged specific absorption rate (SAR) is investigated with 3D voxel phantom human head and hand model. The observed SAR 1 g lies between 0.0014 and 0.0462 W/kg in the operating bands, which are under the limits prescribed by the Federal Communications Commission (FCC). From the above outcomes, it can be potentially used in the mobile handsets and also, can be extended to hybrid wireless cellular communication networks & potential applications like RF energy harvesting.