Realistic Human Body Models Research Articles

Effect of Anatomical Brain Development on Induced Electric Fields During Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) is increasingly becoming an established method for the treatment of drug-resistant major depressive disorder. It is also widely used in cognitive neuroscience and psychology to map brain function and modulate brain activity. The majority of studies utilizing TMS are performed with adult patients, but the method may also be of use for a variety of purposes for pediatric patients. To study the safety implications of performing TMS on patients of various ages, the induced electric field in the brain has been calculated with numerical methods with a variety of anatomically realistic human body models of different ages. The results of this paper show that large differences in induced electric field occur in patients of different ages and consideration of these differences must be taken into account to achieve the desired neurological effect.

Norton Surface Waves in the Scope of Body Area Networks

This paper presents an evaluation on how Norton surface waves can be used to analytically model the on-body propagation in wireless body area networks. Based on a brief review of the Norton surface wave theory, the general problem as defined for terrestrial propagation by Sommerfeld, is unified taking into account the further extensions by Norton and Bannister which motivates its evaluation for on-body propagations. A discussion of Sommerfeld's numerical distance reveals useful properties to evaluate the capability of a certain configuration to excite Norton surface waves in specific on-body scenarios. Based thereon antenna design guidelines for on-body propagation links can be derived. All investigations are carried out for human muscle, skin, and fat tissues in the frequency range from 0.4 GHz to 60 GHz. A comparison of the simplified model consisting of a planar homogeneous ground to a realistic inhomogeneous human body model shows good results for the attenuation of the electric field strength along the on-body path.

A novel RF resonator for human-body MRI at 3 T

A square-slot-loaded (SSL) radio-frequency (RF) resonator using a microstrip transmission line (MTL) is designed for human-body magnetic resonance imaging (MRI) at 3 T MRI. The SSL RF resonator shows improved RF magnetic fields resulting in more homogenous fields near the center of the phantom than traditional RF resonators using MTL. A multichannel body coil using the SSL RF resonators is also simulated and provides improved parallel excitation performance. In addition, RF shimming for homogenization can be effectively controlled by adjusting the inputs to the eight resonators. Numerical results are obtained by using a spherical phantom and a realistic human-body model at 3 T to calculate the B 1 + fields.

Characterization of path loss and absorption for a wireless radio frequency link between an in-body endoscopy capsule and a receiver outside the body

Abstract Physical-layer characterization is important for design of in-to-out body communication for wireless body area networks (WBANs). This paper numerically investigates the path loss and absorption of an in-to-out body radio frequency (RF) wireless link between an endoscopy capsule and a receiver outside the body using a 3D electromagnetic solver. A spiral antenna in the endoscopy capsule is tuned to operate in the Medical Implant Communication Service (MICS) band at 402 MHz, accounting for the properties of the human body. The influence of misalignment, rotation of the capsule, and three different human models are investigated. Semi-empirical path loss models for various homogeneous tissues and 3D realistic human body models are provided for manufacturers to evaluate the performance of in-body to out-body WBAN systems. The specific absorption rate (SAR) in homogeneous and heterogeneous body models is characterized and compliance is investigated.

Induced electric fields in the MAXWEL surface-based human model from exposure to external low frequency electric fields

This work presents calculations of internal induced electric fields in the anatomically realistic surface-based model of the male human body, MAXWEL, from exposure to external low frequency electric fields under grounded and isolated conditions. The maximum 99th percentile induced electric fields calculated in the MAXWEL central nervous system were 3.49 (grounded) and 1.54 (isolated) mV m(-1) per kV m(-1) at 50 Hz. The application of 2, 1 and 0.5 mm resolution voxel models derived from the surface-based version to the calculations of induced electric fields is described. 2 mm and 1 mm resolution maximum 99th percentile induced electric field values calculated in selected tissues of the eye at 50 Hz were within 30 % of those calculated at 0.5 mm resolution. The calculated electric field values in MAXWEL were compared with values from the male model NORMAN and female model NAOMI. The maximum 99th percentile value for NAOMI, calculated by Dimbylow in bone, was 49.4 mV m(-1) per kV m(-1) at 50 Hz under grounded conditions. The corresponding value calculated in MAXWEL was 15.7 mV m(-1) per kV m(-1), considerably lower due to anatomical differences between the male and female models.

Statistical multi‐path exposure method for assessing the whole‐body SAR in a heterogeneous human body model in a realistic environment

Assessing the whole-body absorption in a human in a realistic environment requires a statistical approach covering all possible exposure situations. This article describes the development of a statistical multi-path exposure method for heterogeneous realistic human body models. The method is applied for the 6-year-old Virtual Family boy (VFB) exposed to the GSM downlink at 950 MHz. It is shown that the whole-body SAR does not differ significantly over the different environments at an operating frequency of 950 MHz. Furthermore, the whole-body SAR in the VFB for multi-path exposure exceeds the whole-body SAR for worst-case single-incident plane wave exposure by 3.6%. Moreover, the ICNIRP reference levels are not conservative with the basic restrictions in 0.3% of the exposure samples for the VFB at the GSM downlink of 950 MHz. The homogeneous spheroid with the dielectric properties of the head suggested by the IEC underestimates the absorption compared to realistic human body models. Moreover, the variation in the whole-body SAR for realistic human body models is larger than for homogeneous spheroid models. This is mainly due to the heterogeneity of the tissues and the irregular shape of the realistic human body model compared to homogeneous spheroid human body models.

Dominant factors affecting temperature rise in simulations of human thermoregulation during RF exposure

Numerical models of the human thermoregulatory system can be used together with realistic voxel models of the human anatomy to simulate the body temperature increases caused by the power absorption from radio-frequency electromagnetic fields. In this paper, the Pennes bioheat equation with a thermoregulatory model is used for calculating local peak temperatures as well as the body-core-temperature elevation in a realistic human body model for grounded plane-wave exposures at frequencies 39, 800 and 2400 MHz. The electromagnetic power loss is solved by the finite-difference time-domain (FDTD) method, and the discretized bioheat equation is solved by the geometric multigrid method. Human thermoregulatory models contain numerous thermophysiological and computational parameters—some of which may be subject to considerable uncertainty—that affect the simulated core and local temperature elevations. The goal of this paper is to find how greatly the computed temperature is influenced by changes in various modelling parameters, such as the skin blood flow rate, models for vasodilation and sweating, and clothing and air movement. The results show that the peak temperature rises are most strongly affected by the modelling of tissue blood flow and its temperature dependence, and mostly unaffected by the central control mechanism for vasodilation and sweating. Almost the opposite is true for the body-core-temperature rise, which is however typically greatly lower than the peak temperature rise. It also seems that ignoring the thermoregulation and the blood temperature increase is a good approximation when the local 10 g averaged specific absorption rate is smaller than 10 W kg−1.

Abdominal Finite Element Model for Traffic Accidents Injury Analysis

The abdominal cavity is a vulnerable region of the human body. The severe and critical abdominal injuries arising during traffic accidents are the second most important bodily injuries after thoracic injuries. The injuries are predominantly caused by contact with the lap belt, steering wheel, armrest, dashboard, side door, etc. However in terms of investigating the biomechanical response of the abdomen, experimental studies have turned out to be particularly difficult to perform and the results obtained are not easy to interpret. Therefore attention should be paid to a generation of more realistic human body models with detailed inner organ models in order to be able to describe the organ injury mechanisms during accidents. In this study the abdominal finite element (FE) model was created to improve the abdominal part of the human body model ROBBY. This should ensure the ability of an updated model ROBBY to predict the abdominal injury during various impact conditions. The abdominal model geometry was created on the basis of real anatomical human data. Tissue characteristics completing the organ geometry were obtained from public sources. The created abdominal model was consequently scaled and embedded into the ROBBY model representing a 50th percentile male. The updated ROBBY model was validated with a comparison of the simulation results during abdominal oblique impactor tests and abdominal frontal rigid bar tests with available cadaver experimental results. It was found that the updated ROBBY model with the new deformable abdominal model is able to predict the response of the human abdomen during various impact conditions very well. Moreover due to the precision of the abdominal model the injury of individual abdominal organs can be predicted during impact. This allows the simulation of real vehicle accidents and the assessment of human abdomen injuries arising during accident to be performed.

A numerical evaluation of electromagnetic fields exposure on real human body models until 100 kHz

PurposeThe purpose of this paper is to describe how numerical models of human body have been applied for the evaluation of current density induced by strong magnetic field, to verify the respect of the basic restriction proposed by International Committee Non Ionizing Radiation Protection (ICNIRP) guidelines.Design/methodology/approachFinite element method has been used in order to compute the induced current density in a suitable human body model and a simplified model – a homogeneous cylinder – due to a time‐varying magnetic field.FindingsIn the practical case of a resistance welding equipment, the implemented computational technique has been used in order to evaluate both the magnetic flux density and the induced current density in different tissues. Their values have been also compared with the ones obtained in a homogeneous cylinder.Practical implicationsThe proposed method can be used in order to evaluate the compliance of the magnetic field produced by resistance welding equipments with ICNIRP limits.Originality/valueA realistic model of human body has been used. In the paper, the difference on magnetic flux density and corresponding current density values is pointed out for various source positions using a heterogeneous tetrahedral human body model.

Exposure of Working Population to Pulsed Magnetic Fields

Reference values of exposure for working population at extremely low frequency electromagnetic fields have been stated in ICNIRP Guidelines of 1998, and accepted by European Parliament in 2004. Nevertheless, quantification of coupling mechanism under pulsed field conditions is still an open question. The effect of complex non-sinusoidal or non-periodic waveforms is not univocally defined and several ways of estimating it have been proposed. This paper compares different ways of assessing effects of pulsed electromagnetic fields with frequency spectrum below 100 kHz and compare them to the eddy currents induced in one realistic model of human body by a resistance spot welding system supplied by in pulsed medium frequency direct current mode.

Corrections to, “Radiation Characteristics of Ingestible Wireless Devices in Human Intestine Following Radio Frequency Exposure at 430, 800, 1200, and 2400 MHz” [Aug 09

In order to assess the compliance of ingested wireless device (IWD) with related international safety guidelines, the studies on the biological effects and the signal intensity of an IWD in two realistic human body models using the finite-difference time-domain (FDTD) method are reported in this paper. Simulation studies are carried out in 21 scenarios where the IWD is placed at seven positions with three orientations, for each of the two human models. Specific absorption rate (SAR), temperature rise, near fields and far fields are analyzed in the 21 scenarios at four selected operation frequencies of 430 and 800 MHz, and 1.2 and 2.4 GHz, respectively. Our study indicates that the radiation intensity outside of the human body decreases with the increase of operation frequency. Furthermore, the radiation characteristics of the IWD are orientation and position dependent. The polarization of electric field outside of the human body is similar to that of the radio frequency (RF) source. As far as the compliance of safety is concerned, among all the simulated scenarios the maxima of the averaged-1 g and averaged-10 g SARs can reach 3.71 W/kg and 1.37 W/kg at the input power of 25 mW, respectively.

Effects of Dielectric Values of Human Body on Specific Absorption Rate Following 430, 800, and 1200 MHz RF Exposure to Ingestible Wireless Device

In order to assess the compliance of ingestible wireless device (IWD) within safety guidelines, the SAR, and near fields of IWD in two realistic human body models, whose dielectric values are increased from the original by +/-10% and +/- 20% are studied using the finite-difference time-domain method. The radiation characteristics of the IWD in the human body models with changed and unchanged dielectric values are compared. Simulations are carried out at 13 scenarios where the IWD is placed at center positions of abdomens in the two models at the operation frequency of 430, 800, and 1200 MHz, respectively. Results show that variation of radiation intensity near the surface of abdomen is around 2.5, 2.6, and 3.5 dB within 20% variation of dielectric values corresponding to the frequency of 430, 800, and 1200 MHz, respectively. Electric fields in the anterior of the human body models are higher than those in the posterior for all scenarios. SAR values increase with the increase of conductivities of human body tissues, and usually decrease with the increase of relative permittivities of human body tissues. The effect of the dielectric values of human body on SAR is orientation-, human-body-, and frequency-dependent. A variation up to 20% in conductivities and relative permittivities alone or simultaneously always causes a SAR variation less than 10%, 20%, and 30% at the frequency of 430, 800, and 1200 MHz, respectively. As far as the compliance of safety was concerned, the IWD was safe to be used at the input power less than 12.6, 9.3, and 8.4 mW, according to the IEEE safety standards at the frequency of 430, 800, and 1200 MHz, respectively.

Radiation Characteristics of Ingestible Wireless Devices in Human Intestine Following Radio Frequency Exposure at 430, 800, 1200, and 2400 MHz

In order to assess the compliance of ingested wireless device (IWD) with related international safety guidelines, the studies on the biological effects and the signal intensity of an IWD in two realistic human body models using the finite-difference time-domain (FDTD) method are reported in this paper. Simulation studies are carried out in 21 scenarios where the IWD is placed at seven positions with three orientations, for each of the two human models. Specific absorption rate (SAR), temperature rise, near fields and far fields are analyzed in the 21 scenarios at four selected operation frequencies of 430 and 800 MHz, and 1.2 and 2.4 GHz, respectively. Our study indicates that the radiation intensity outside of the human body decreases with the increase of operation frequency. Furthermore, the radiation characteristics of the IWD are orientation and position dependent. The polarization of electric field outside of the human body is similar to that of the radio frequency (RF) source. As far as the compliance of safety is concerned, among all the simulated scenarios the maxima of the averaged-1 g and averaged-10 g SARs can reach 3.71 W/kg and 1.37 W/kg at the input power of 25 mW, respectively.

Effects of Dielectric Parameters of Human Body on Radiation Characteristics of Ingestible Wireless Device at Operating Frequency of 430 MHz

In order to assess the sensitivities of the radiation characteristics and the compliance of ingestible wireless device (IWD) in human body due to the uncertainty and intersubject variability of dielectric properties of human body tissues, the specific absorption rate (SAR) and radiation characteristics of the IWD in two realistic human body models with changed and unchanged dielectric values are quantitatively compared using the finite-difference time-domain method. Simulations are carried out in 13 scenarios where the IWD is placed in the center positions of abdomens in the two body models at the operating frequency of 430 MHz with three orientations. Results show that the variation of radiation intensity near the surface of abdomen is around 2.5 dB within 20% variation of dielectric values. The maximum SAR values increase with the increase in conductivities of human body tissues and decrease with the increase in relative permittivities of human body tissues. A variation of up to 20% in conductivities and relative permittivities, alone or simultaneously, always causes a variation of SAR to be less than 10%. As far as the compliance of safety is concerned, the maxima of 1-g-averaged and 10-g-averaged SARs can reach 3.16 and 0.89 W/kg at the input power of 25 mW.

Specific Absorption Rates of Anatomically Realistic Human Models Exposed to RF Electromagnetic Fields From Mobile Phones Used in Elevators

This paper presents a detailed numerical investigation to determine whether or not an increased specific absorption rate (SAR) in an adult using a mobile phone inside an elevator due to the multireflections of electromagnetic fields from the walls exceed the RF-exposure guidelines. A fully realistic heterogeneous human body model and an actual elevator size were employed. The nonuniform mesh finite-difference time-domain technique and a supercomputer were employed to obtain the SAR and other important parameters. The mobile phone was modeled as a lambda/2 dipole antenna placed at a distance of 16 mm from the head. For computations, operating frequencies of 900, 1500, and 2000 MHz with transmitting power of 250 mW were used. Computed results show that the peak spatial-average 10-g SAR depends on the position of the passenger and the antenna against the elevator walls. We observed a substantial increase in the whole-body average SAR and peak 10-g SAR values of the passenger in the elevator over their respective free-space values. However, the maximum values obtained do meet the basic restrictions described in the international RF safety guidelines. For example, the maximum values of the whole-body average and peak spatial-average SAR were 4.4% and 78% of the international RF safety guideline, respectively.

An On-Body Channel Model for UWB Body Area Communications for Various Postures

On-body area ultrawideband (UWB) communication is of high importance for promising new biomedical applications. However, there are currently few measurements or models describing on-body area propagation channels which put an emphasis on various body postures. Using the frequency-dependent finite-difference time domain (FDTD) method and a realistic human body model, we simulate various body postures for modeling on-body channels. Based on the FDTD numerical results, we derive an on-body propagation model and determine the model parameters for some representative transmission links on the human body. A good match is obtained between the data derived from FDTD and the statistically implemented models in terms of key communication metrics. In addition, for the chest-to-right-waist transmission link, an experiment is performed in order to verify the results from the FDTD method, and it is found that the model parameters agree well between the two approaches.

Performance of convolutional PML absorbing boundary conditions in finite-difference time-domain SAR calculations

The performance of perfectly matched layer (PML) absorbing boundary conditions is studied for finite-difference time-domain (FDTD) specific absorption rate (SAR) assessment, using convolutional PML (CPML) implementation of PML. This is done by investigating the variation of SAR values when the amount of free-space layers between the studied object and PML boundary is varied. Plane-wave exposures of spherical and rectangular objects and a realistic human body model are considered for testing the performance. Also, some results for dipole excitation are included. Results show that no additional free-space layers are needed between the numerical phantom and properly implemented CPML absorbing boundary, and that the numerical uncertainties due to CPML can be made negligibly small.

Development of a platform for realistic garment drape simulation

An integrated platform for garment drape simulation system has been developed. In this system, garment patterns from conventional two-dimensional CAD systems can be assembled into a three-dimensional garment on a parametrically resizable realistic human body model. A fast and robust particle-based physical calculation engine has been developed for garment shape generation. Then a series of geometric and graphical techniques were applied to create realistic impressions on simulated garments. This system can be used as the rapid prototyping tool for garments in the future quick-response system.

Correlation Between Peak Spatial-Average SAR and Temperature Increase Due to Antennas Attached to Human Trunk

This paper discusses the correlation between peak spatial-average specific absorption rate (SAR) and maximum temperature increase for antennas attached to the human trunk. Frequency bands considered are 150, 400, and 900 MHz, which are assigned for occupational communications. This problem is throughly investigated with the aid of Green's function. In particular, the effect of variation of thermal constants on the temperature increase is revealed by using one-dimensional model. Computational results suggests that one of the most dominant factors which affect the correlation between peak SAR and maximum temperature increase is blood flow in tissues. This is confirmed by considering a three-dimensional realistic human body model. Uncertainties caused by the calculation of peak SAR and the difference in the body model shape are also quantified.

EM Interaction between a 5 GHz Band Antenna Mounted PC and a Realistic Human Body Model

A sub-grid finite-difference time-domain (FDTD) method was applied to analyze electromagnetic (EM) interaction between a 5 GH band antenna mounted laptop personal computer (PC) and a human body model in realistic use situations. The investigated situations were a typing and a non-typing PC users, who were simulated with a realistic whole body or half body model. It was found that the body proximity effect was mainly blocking the radiation up to 20 dB towards the body side, and the hands on the keyboard were mainly blocking the radiation up to 10 dB towards the direction at an angle to the head. It was also found that the highest EM absorption in the typing and non-typing situations occurred in the hand and in the chest, respectively, and the hands on the keyboard had a significantly blocking effect for the SAR spread to the head region. The peak SAR levels were low enough compared to the safety guidelines.