Whole-body Average Specific Absorption Rate Research Articles

Statistical analysis of whole-body absorption depending on anatomical human characteristics at a frequency of 2.1 GHz

In this paper, we propose identification of the morphological factors that may impact the whole-body averaged specific absorption rate (WBSAR). This study is conducted for the case of exposure to a front plane wave at a 2100 MHz frequency carrier. This study is based on the development of different regression models for estimating the WBSAR as a function of morphological factors. For this purpose, a database of 12 anatomical human models (phantoms) has been considered. Also, 18 supplementary phantoms obtained using the morphing technique were generated to build the required relation. This paper presents three models based on external morphological factors such as the body surface area, the body mass index or the body mass. These models show good results in estimating the WBSAR (<10%) for families obtained by the morphing technique, but these are still less accurate (30%) when applied to different original phantoms. This study stresses the importance of the internal morphological factors such as muscle and fat proportions in characterization of the WBSAR. The regression models are then improved using internal morphological factors with an estimation error of approximately 10% on the WBSAR. Finally, this study is suitable for establishing the statistical distribution of the WBSAR for a given population characterized by its morphology.

Acute Dosimetry and Estimation of Threshold-Inducing Behavioral Signs of Thermal Stress in Rabbits at 2.45-GHz Microwave Exposure

In the current international guidelines and standards for human exposure to microwaves (MWs), the basic restriction is determined by the whole-body average specific absorption rate (SAR). The basis for the guidelines is the adverse effect such as work stoppage in animals for whole-body average SARs above a certain level. Although it is known that absorbed MW energy causes the behavioral sign of thermal stress, the relationship of whole-body average SAR with temperature/temperature elevation has not been sufficiently investigated. In the present study, we performed experiments on rabbits exposed to 2.45-GHz MWs. A total of 24 measurements were conducted for power densities from approximately 100 to 1000 W/m(2). Our computational code for electromagnetic-thermal dosimetry was used to set the exposure time duration and incident power density. Our experimental results suggest that a core temperature elevation of 1 degrees C is an estimate of the threshold-inducing complex behavioral signs of MW-induced thermal stress in rabbits for different whole-body average SARs and exposure time durations. The whole-body average SAR required for MW-induced behavioral sign in rabbits was estimated as approximately 1.3 W/kg for 2.45-GHz MWs.

Estimation of Whole-Body Average SAR in Human Models Due to Plane-Wave Exposure at Resonance Frequency

This study proposes an equation for estimating whole-body average specific absorption rate (WBSAR) in human body models for plane-wave exposure at whole-body resonance frequency. This study is important because the WBSAR takes maximal at this frequency and approaches the basic restrictions in the international guidelines/standards for human protection. Therefore, the variability of the WBSAR at this frequency has attracted a great deal of attention. First, the dominant factors influencing the resonance frequency of the human body models are investigated for plane-wave exposures. An equation for estimating the WBSAR at the resonance frequency is then proposed based on an analogy to an antenna. This equation can estimate the WBSAR with the body mass index of the human body only for a given incident power density. The uncertainty of the WBSAR estimated with the proposed equation is approximately 10%, which is mainly attributed to the electrical constants of tissue, including the inhomogeneity of the human body model. The variability of the WBSAR due to the body shape was found to be 30% for humans of the same age.

Basic Construction of Whole-Body Averaged SAR Estimation System Using Cylindrical-External Field Scanning for UHF Plane Wave Irradiation of Human Models

The purpose of this study is to establish a whole-body averaged specific absorption rate (WB-SAR) estimation method using the power absorbed by humans; a cylindrical-external field scanning technique is used to measure the radiated RF (radio-frequency) power. This technique is adopted with the goal of simplifying the estimation of the exposure dosimetry of humans who have different postures and/or sizes. In this paper, to validate the proposed measurement method, we subject numerical human phantom models and cylindrical scanning conditions to FDTD analysis. We design a radiation system that uses a dielectric lens to achieve plane-wave irradiation of tested human phantoms in order to develop an experimental WB-SAR measurement system for UHF far-field exposure condition. In addition, we use a constructed SAR measurement system to confirm absorbed power estimations of simple geometrical phantoms and so estimate measurement error of the measurement system. Finally, we discuss the measurement results of WB-SARs for male adult and child human phantom models.

Experimental Quasi-Microwave Whole-Body Averaged SAR Estimation Method Using Cylindrical-External Field Scanning

The aim of this study is to develop a new whole-body averaged specific absorption rate (SAR) estimation method based on the external-cylindrical field scanning technique. This technique is adopted with the goal of simplifying the dosimetry estimation of human phantoms that have different postures or sizes. An experimental scaled model system is constructed. In order to examine the validity of the proposed method for realistic human models, we discuss the pros and cons of measurements and numerical analyses based on the finite-difference time-domain (FDTD) method. We consider the anatomical European human phantoms and plane-wave in the 2GHz mobile phone frequency band. The measured whole-body averaged SAR results obtained by the proposed method are compared with the results of the FDTD analyses.

2-GHz Band CW and W-CDMA Modulated Radiofrequency Fields Have No Significant Effect on Cell Proliferation and Gene Expression Profile in Human Cells

We investigated the mechanisms by which radiofrequency (RF) fields exert their activity, and the changes in both cell proliferation and the gene expression profile in the human cell lines, A172 (glioblastoma), H4 (neuroglioma), and IMR-90 (fibroblasts from normal fetal lung) following exposure to 2.1425 GHz continuous wave (CW) and Wideband Code Division Multiple Access (W-CDMA) RF fields at three field levels. During the incubation phase, cells were exposed at the specific absorption rates (SARs) of 80, 250, or 800 mW/kg with both CW and W-CDMA RF fields for up to 96 h. Heat shock treatment was used as the positive control. No significant differences in cell growth or viability were observed between any test group exposed to W-CDMA or CW radiation and the sham-exposed negative controls. Using the Affymetrix Human Genome Array, only a very small (< 1%) number of available genes (ca. 16,000 to 19,000) exhibited altered expression in each experiment. The results confirm that low-level exposure to 2.1425 GHz CW and W-CDMA RF fields for up to 96 h did not act as an acute cytotoxicant in either cell proliferation or the gene expression profile. These results suggest that RF exposure up to the limit of whole-body average SAR levels as specified in the ICNIRP guidelines is unlikely to elicit a general stress response in the tested cell lines under these conditions.

In Vitro Evaluation of MR Imaging Issues at 3T for Aneurysm Clips Made from MP35N: Findings and Information Applied to 155 Additional Aneurysm Clips

Aneurysm clips need to be tested at 3T to characterize MR imaging concerns, including magnetic field interactions, MR imaging-related heating, and artifacts. Therefore, we evaluated these risks for aneurysm clips. Three different MP35N aneurysm clips (Codman Slim-Line Aneurysm Clip, straight, blade length 25-mm; Codman Slim-Line Aneurysm Clip Graft, 5-mm diameter x 5-mm width; Codman Slim-Line Aneurysm Clip, reinforcing 30 degrees angle, 6-mm x 18-mm) that represented the largest mass for 155 additional clips made from MP35N were tested. The clips were evaluated at 3T for magnetic field interactions, heating, and artifacts. We studied MR imaging-related heating, placing the clip in a gelled-saline-filled phantom with MR imaging performed by using a transmit/receive radio-frequency body coil at a whole-body average SAR of 3 W/kg for 15 minutes. Artifacts were characterized by using T1-SE and GRE pulse sequences. Each aneurysm clip showed relatively minor magnetic field interactions, which would not cause movement in situ. Heating was not excessive (highest temperature change, <1.8 degrees C). Artifacts may create problems if the area of interest is in the same area or close to the aneurysm clip. The results of this investigation demonstrated that it would be acceptable (ie, "MR conditional" using current terminology) for patients with these aneurysm clips to undergo MR imaging at < or =3T. Notably, on the basis of the sizes of the clips that underwent testing, these findings pertain to 155 additional aneurysm clips made from the same material.

Lack of Teratogenicity after Combined Exposure of Pregnant Mice to CDMA and WCDMA Radiofrequency Electromagnetic Fields

Concern about the possible adverse effects of radiofrequency (RF)-field exposure on public health has increased because of the extensive use of wireless mobile phones and other telecommunication devices in daily life. The murine fetus is a very sensitive indicator of the effects of stress or stimuli in the environment. Therefore, we investigated the teratogenic effects of multi-signal radiofrequency electromagnetic fields (RF EMFs) on mouse fetuses. Pregnant mice were simultaneously exposed to two types of RF signals, single code division multiple access (CDMA) and wideband code division multiple access (WCDMA). Mice received two 45-min RF-field exposures, separated by a 15-min interval, daily throughout the entire gestation period. The whole-body average specific absorption rate (SAR) of CDMA or WCDMA was 2.0 W/kg. The animals were killed humanely on the 18th day of gestation and fetuses were examined for mortality, growth retardation, changes in head size and other morphological abnormalities. From the results, we report for the first time that simultaneous experimental exposure to CDMA and WCDMA RF EMFs did not cause any observable adverse effects on mouse fetuses.

Nocturnal urinary melatonin levels and urine biochemistry in microwave-irradiated rats

The aim of this study was to explore whether, during the course of a 15 days-lasting experiment, a two hours per day and five days per week, 2.45 GHz microwave whole-body irradiation may substantially and therefore provably affect rats’ nocturnal urinary 6-hydroxy-melatonin sulphate (aMT6s) excretion and urinalysis parameters. The average whole-body specific absorption rate (SAR) equalled to 1.25 (± 0.36 SE) W/kg. To collect nocturnal urine samples, animals were held in individual metabolic cages every experimental night from 7:00 PM till 7:00 AM next day. The concentration of aMT6s in rat urine samples was determined by a direct radioimmunoassay. Bilirubin, ketones, and urine protein content have been determined via multiple-use reagent strips. In comparison to the sham-exposed group, no significant changes in body temperature and food or water intake were observed in the exposed group. A decline in aMT6s, determined in the exposed rats, was observed from day 8 to day 11 of the experiment (P < 0.05). The aMT6s level remained consistently low until the end of the experiment, but not significantly lower than the control values. The results of the urine samples biochemical workup failed to reveal any significant differences between the exposed and the control animal groups. The results of this study suggest that, under the above described experimental conditions, repeated 2.45 GHz irradiation could act as a stressor and therefore influence the melatonine balance in rat.

Effects of 915 MHz Electromagnetic-Field Radiation in TEM Cell on the Blood-Brain Barrier and Neurons in the Rat Brain

The aim of this study was to determine whether albumin leakage and dark neurons were present in rat brains 14 and 50 days after a single 2-h exposure to a 915 MHz electromagnetic field, as reported by Salford et al. (Environ. Health Perspect. 111, 881-883, 203). Sixty-four male F344 rats (12 weeks old) were exposed to a 915 MHz electromagnetic field at whole-body average specific absorption rates of 0, 0.02, 0.2 and 2.0 W/kg in TEM cells for 2 h, following the protocol reported by Salford et al. The brains were examined histologically and immunohistochemically. No albumin immunoreactivity was observed in the exposed groups. In addition, dark neurons, assessed using hematoxylin and eosin staining, were rarely present, with no statistically significant difference between exposed and sham-exposed animals. This study thus failed to confirm the results of Salford et al.

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.

Dependence of the Occupational Exposure to Mobile Phone Base Stations on the Properties of the Antenna and the Human Body

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This study assesses human exposure in the close vicinity of mobile phone base station antennas by finite-difference time-domain simulations. The peak spatial average specific absorption rate (SAR) and the whole-body average SAR are analyzed in three different anatomical models (55–101 kg) with respect to the basic restrictions for occupational exposure. The models are at distances between 0.5 and 4 m from various antenna types operating at frequencies ranging from 450 to 2140 MHz. The validity of the simulations is confirmed by an analysis of the impact of the mesh resolution on local and whole-body average SAR and by experimental validation of the numerical models. The results demonstrate that the whole-body absorption generally determines the maximum permissible antenna output power for collinear array antennas. Local exposure depends on various effects that fluctuate strongly among individuals. In particular for short antennas, the peak spatial average SAR can be more restrictive than the whole-body absorption because they may only expose a fraction of the body. Therefore, compliance must be demonstrated for both quantities. </para>

Spatial averaging of fields from half-wave dipole antennas and corresponding SAR calculations in the NORMAN human voxel model between 65 MHz and 2 GHz

If an antenna is located close to a person, the electric and magnetic fields produced by the antenna will vary in the region occupied by the human body. To obtain a mean value of the field for comparison with reference levels, the Institute of Electrical and Electronic Engineers (IEEE) and International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommend spatially averaging the squares of the field strength over the height the body. This study attempts to assess the validity and accuracy of spatial averaging when used for half-wave dipoles at frequencies between 65 MHz and 2 GHz and distances of λ/2, λ/4 and λ/8 from the body. The differences between mean electric field values calculated using ten field measurements and that of the true averaged value were ∼15% in the 600 MHz to 2 GHz range. The results presented suggest that the use of modern survey equipment, which takes hundreds rather than tens of measurements, is advisable to arrive at a sufficiently accurate mean field value. Whole-body averaged and peak localized SAR values, normalized to calculated spatially averaged fields, were calculated for the NORMAN voxel phantom. It was found that the reference levels were conservative for all whole-body SAR values, but not for localized SAR, particularly in the 1–2 GHz region when the dipole was positioned very close to the body. However, if the maximum field is used for normalization of calculated SAR as opposed to the lower spatially averaged value, the reference levels provide a conservative estimate of the localized SAR basic restriction for all frequencies studied.

RETRACTED: Evaluation of basal DNA damage and oxidative stress in Wistar rat leukocytes after exposure to microwave radiation

The aim of this study was to assess whether microwave-induced DNA damage is basal or it is also generated through reactive oxygen species (ROS) formation. After having irradiated Wistar rats with 915MHz microwave radiation, we assessed different DNA alterations in peripheral leukocytes using standard and formamidopyrimidine DNA-glycosylase (Fpg)-modified comet assay. The first is a sensitive tool for detecting primary DNA damage, and the second is much more specific for detecting oxidative damage. The animals were irradiated for 1h a day for 2 weeks at a field power density of 2.4W/m(2), and the whole-body average specific absorption rate (SAR) of 0.6W/kg. Both the standard and the Fpg-modified comet assay detected increased DNA damage in blood leukocytes of the exposed rats. The significant increase in Fpg-detected DNA damage in the exposed rats suggests that oxidative stress is likely to be responsible. DNA damage detected by the standard comet assay indicates that some other mechanisms may also be involved. In addition, both methods served proved sensitive enough to measure basal and oxidative DNA damage after long-term exposure to 915MHz microwave radiation in vivo.

Specific absorption rate and electric field measurements in the near field of six mobile phone base station antennas

In this article, the exposure to radio frequency electromagnetic fields was studied in close proximity (distances of 10, 100, 300, and 600 mm) to six base station antennas. The specific absorption rate (SAR) in 800 mm x 500 mm x 200 mm box phantom as well as unperturbed electric field (E) in air was measured. The results were used to determine whether the measurement of local maximum of unperturbed electric field can be used as a compliance check for local exposure. Also, the conservativeness of this assessment method compared to the ICNIRP basic restriction was studied. Moreover, the assessment of whole-body exposure was discussed and the distance ranges presented in which the ICNIRP limit for local exposure could be exceeded before the limit for whole-body SAR. These results show that the electric field measurement alone can be used for easy compliance check for the local exposure at all distances and for all antenna types studied. However, in some cases when the local peak value of E was compared directly to the ICNIRP reference level for unperturbed E, the exposure was overestimated only very slightly (by factor 1.1) compared to the basic restriction for localized SAR in a human, and hence these results can not be generalized to all antenna types. Moreover, it was shown that the limit for localized exposure could be exceeded before the limit for the whole-body average SAR, if the distance to the antenna was less than 240 mm.

Influence of electromagnetic polarization on the whole-body averaged SAR in children for plane-wave exposures

The present study investigated the whole-body averaged specific absorption rate (WBSAR) in an infant model with the finite-difference time-domain method. The focus of the present study is the effect of polarization of incident electromagnetic waves on the WBSAR. This is because most previous studies investigated the WBSAR for plane-wave exposure with a vertically aligned electric field. Our computational results revealed that the WBSAR for plane-wave exposure with a vertically aligned electric field is smaller than that with a horizontally aligned electric field for frequencies above 2 GHz. The main reason for this difference is attributed to be the component of the surface area perpendicular to the electric field of the incident wave.

Conservative Estimation of Whole-body Average SAR in Infant Model for 0.3-6GHz Far-Field Exposure

From an anatomically-based Japanese model of three-year-old child with a resolution of 1 mm, we developed a nine-month Japanese infant with linear shrink. With these models, we calculated the whole-body average specific absorption rate (WBA-SAR) for plane-wave exposure from 0.1 to 6 GHz. A conservative estimate of the WBA-SAR was also investigated by using three kinds of simple-shaped models: cuboid, ellipsoid and spheroid, whose parameters were determined based on the above three-year-old child model. As a result, the cuboid and ellipsoid were found to provide an overestimate of the WBA-SAR compared to the realistic model, whereas the spheroid does an underestimate. Based on these findings for different body models, we have specified the incident power density required to produce WBA-SAR of 0.08 W/kg, which is the basic restriction for public exposure in the guidelines of International Commission on Non-Ionizing Radiation Protection.

SAR Computation inside Fetus by RF Coil during MR Imaging Employing Realistic Numerical Pregnant Woman Model

This paper presents the computational electromagnetic dosimetry inside an anatomically based pregnant woman models exposed to electromagnetic wave during magnetic resonance imaging. The two types of pregnant woman models corresponding to early gestation and 26 weeks gestation were used for this study. The specific absorption rate (SAR) in and around a fetus were calculated by radiated electromagnetic wave from highpass and lowpass birdcage coil. Numerical calculation results showed that high SAR region is observed at the body in the vicinity of gaps of the coil, and is related to concentrated electric field in the gaps of human body such as armpit and thigh. Moreover, it has confirmed that the SAR in the fetus is less than International Electrotechnical Commission limit of 10W/kg, when whole-body average SARs are 2W/kg and 4W/kg, which are the normal operating mode and first level controlled operating mode, respectively.

Computational Electromagnetic Dosimetry of a Human Body in a Vehicle for Plane-wave Exposure

The present study investigated whole-body specific absorption rate of a human body in a vehicle cabin for plane-wave exposure. The rationale for this investigation is that fields in the vehicle without human have been enhanced in particular frequency region due to standing waves, and thus power absorption in the human body is of interest. For our computational results, the whole-body average specific absorption rate of the human in the vehicle was found to be 60% smaller than that in free space. The reason for this upset is that the standing wave over the vehicle cabin was suppressed due to power absorption by the human.

Conservative estimation of whole-body-averaged SARs in infants with a homogeneous and simple-shaped phantom in the GHz region

We calculated the whole-body-averaged specific absorption rates (WBSARs) in a Japanese 9-month-old infant model and its corresponding homogeneous spheroidal and ellipsoidal models with 2/3 muscle tissue for 1–6 GHz far-field exposure. As a result, we found that in comparison with the WBSAR in the infant model, the ellipsoidal model with the same frontally projected area as that of the infant model provides an underestimate, whereas the ellipsoidal model with the same surface area yields an overestimate. In addition, the WBSARs in the homogenous infant models were found to be strongly affected by the electrical constant of tissue, and to be larger in the order of 2/3 muscle, skin and muscle tissues, regardless of the model shapes or polarization of incident waves. These findings suggest that the ellipsoidal model having the same surface area as that of the infant model and electrical constants of muscle tissue provides a conservative WBSAR over wide frequency bands. To confirm this idea, based on the Kaup index for Japanese 9-month-old infants, which is often used to represent the obesity of infants, we developed linearly reduced 9-month-old infant models and the corresponding muscle ellipsoidals and re-calculated their whole-body-averaged SARs with respect to body shapes. Our results reveal that the ellipsoidal model with the same surface area as that of a 9-month-old infant model gives a conservative WBSAR for different infant models, whose variability due to the model shape reaches 15%.