Specific Absorption Rate Estimation for a Typical Hibiscus Flower Model as per ICNIRP Electromagnetic Guidelines

Surface coils are widely used in magnetic resonance (MR) studies due to their superior signal to noise properties. Application of excessive power levels to transmit surface coils may result in local tissue damage.A homogeneous muscle tissue model for the conservative prediction of surface coil specific absorption rate (SAR) is introduced. Based on this model, sequence parameters can be limited to provide operational levels within safety guidelines. It is demonstrated that this model provides worst-case SAR estimates at MR frequencies of 25.75 MHz and 63.6 MHz. The dependence of SAR on model structure and geometry is analysed and conclusions on the relationship between SAR levels and local anatomy are drawn. By making a worst-case assumption for the tissue parameters the model provides safe operational levels for all tissue types. Power-demanding proton-decoupled 31P magnetic resonance spectroscopy experiments are possible based on the SAR estimates provided.To date SAR values are calculated for 1 g of tissue. Changes in regulations to calculate SAR values for 10 g tissue masses, and the according averaging of local SAR over a larger volume, have been proposed by the International Electrotechnical Commission. A comparative study shows that up to 100% more energy may be applied to surface coils if SAR values are determined for 10 g tissue masses rather than 1 g tissue masses.

We propose a local Specific Absorption Rate (SAR) estimation system using solid phantom and fixed E‐field probe for application to portable wireless devices such as cell phones. This system is constructed from a solid phantom molded from a lossy dielectric and an electric field (E‐field) probe inserted into the phantom. The advantage of this system is the ability to easily measure in a relatively short time the local SAR with measurement deviations of about ±30% compared to the measurements made by the conventional technique using a liquid phantom. First, we perform numerical analysis using the finite‐difference time‐domain (FDTD) method in the basic parameter design to clearly show the effects of the size of the insertion hole for the E‐field probe in the solid phantom and the complex dielectric permittivity on the antenna input impedance and local SAR. Next, we develop a local SAR estimation system using solid phantom and fixed E‐field probe, and measure and evaluate the antenna input impedance and local SAR of two solid phantoms having different complex dielectric permittivities. We confirmed that their properties tend to nearly agree with the calculated results. Finally, we measure the local SARs of 32 portable phones using this system. We confirmed that compared to the measurements by the E‐field probe scanning method, the measurements of about 77% of the phones have deviations within 30%, and the target measurement accuracy during development could almost be achieved. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(9): 46–56, 2003; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/ecja.10082

We propose a fast, patient-specific workflow for on-line specific absorption rate (SAR) supervision. An individualized electromagnetic model is created while the subject is on the table, followed by rapid SAR estimates for that individual. Our goal is an improved correspondence between the patient and model, reducing reliance on general anatomical body models. A 3D fat-water 3T acquisition (~2minutes) is automatically segmented using a computer vision algorithm (~1minute) into what we found to be the most important electromagnetic tissue classes: air, bone, fat, and soft tissues. We then compute the individual's EM field exposure and global and local SAR matrices using a fast electromagnetic integral equation solver. We assess the approach in 10 volunteers and compare to the SAR seen in a standard generic body model (Duke). The on-the-table workflow averaged 7'44″. Simulation of the simplified Duke models confirmed that only air, bone, fat, and soft tissue classes are needed to estimate global and local SAR with an error of 6.7% and 2.7%, respectively, compared to the full model. In contrast, our volunteers showed a 16.0% and 20.3% population variability in global and local SAR, respectively, which was mostly underestimated by the Duke model. Timely construction and deployment of a patient-specific model is computationally feasible. The benefit of resolving the population heterogeneity compared favorably to the modest modeling error incurred. This suggests that individualized SAR estimates can improve electromagnetic safety in MRI and possibly reduce conservative safety margins that account for patient-model mismatch, especially in non-standard patients.

The Near field communication technology (NFC) is applied for transferring data over short distances by maintaining an inductive coupling of the transmitter and the receiver at 13.56MHz. The relatively high magnetic field strength in the immediate surrounding of NFC devices give rise to the question about the local personal exposure of the user holding such a device in the hand or close to the body. In the present paper personal exposure in terms of the maximum 10g-averaged specific absorption rate (SAR) while using NFC was estimated for different scenarios using MRI-based anatomically correct body models. The simulations were performed with the method of Finite Differences in Time Domain (FDTD). The numerical models of the considered NFC devices were validated by SAR measurements using a simplified homogeneous body phantom and acceptable agreement between measurements and simulations was achieved. Several exposure scenarios with a cell phone comprising NFC functionality and a stationary NFC reader were investigated considering two different body models (male 34 years, male 14 years). The results showed maximum 10g-averaged SAR-values more than two orders of magnitude below the basic restriction recommended by the International Commission for Non Ionizing Radiation Protection (ICNIRP). The absolute maximum value of the maximum 10g-averaged SAR found in the considered scenarios was 11.18 mW/kg. Therefore, it can be concluded that personal exposure due to NFC devices typically cause SAR levels far below the basic restrictions of safety guidelines.

The specific absorption rate (SAR) measurement procedure for radio base station antennas using flat phantoms has been investigated and standardized by the International Electrotechnical Commission (IEC). This paper discusses the effectiveness of this procedure for considering Japanese human models based on numerical simulations with validation of whole-body average SAR (WBSAR) measurement. The WBSAR in two Japanese anatomical human models (adult male and 3-year-old child) and two box-shaped phantoms (large and small) using a standardized SAR measurement procedure are compared at 788 MHz and 3.5 GHz. Computational results show that the SAR measurement procedure in the IEC leads to overestimated WBSAR compared to those in Japanese anatomical human models. These results imply that the SAR measurement procedure above is applicable to not only some commonly used but Japanese human models. The WBSAR obtained using SAR estimation formulae in the IEC is also overestimated compared to those in Japanese anatomical human models. In addition, to reduce the measurement time and simplify the post-processing, this paper introduces a SAR measurement procedure based on the two-dimensional SAR distribution around the surface of the bottom of the phantom and the one-dimensional exponential decay of the SAR distribution in the direction of the phantom depth. SAR measurement examples of antennas for small radio base stations are also presented.

The procedure for measuring the 10g averaged specific absorption rate (SAR) next to an ear is specified in the IEC standard document (IEC 62209-1). It generally consists of two parts: an initial area scan and a following zoom scan. However, the measurement based on IEC62209-1 takes considerably long time to determine the peak spatial average SAR. Therefore, IEC 62209-1 also provides the procedure for a fast SAR measurement instead of the full/ordinary SAR measurement as described above. In this study, to verify the validity of the procedure for the fast SAR measurement, we measured the peak spatial average SAR of some cellular phones by both the fast and full SAR measurement procedures. Then we compared peak SAR values between the fast and full SAR measurement procedures. Our results show that the fast-procedure SAR values almost matched with the full-procedure SAR values within the range of the uncertainty assumed for the SAR measurements. In addition, the measurement time of the fast SAR measurement procedure was evaluated and found to be reduced by around 30% compared with the measurement time for the full SAR measurement procedure.

Independent assessment of MRI-induced temperature change and SAR distributions in phantoms

In this study, we present a new approach based on radial basis function neural networks (RBFNN) for estimation of specific absorption rate (SAR) in 2D cylindrical human model with three layers. The simulation results obtained using RBFNN were compared with the FDTD results. The estimated local SAR values using RBFNN has proved to be an impressive approximation to the FDTD results. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1958–1961, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23535

Since the diversification of the electromagnetic (EM) environment is spreading, it is essential to estimate the EM energy absorption rate [specific absorption rate (SAR)] of a pregnant woman's body and her fetus under various exposure situations. For example, if pregnant women work in jobs where they might wear business portable radios around their abdomens, they should also be concerned about this issue, because the fetuses are in their abdomens. In this paper, in order to evaluate the SAR in the pregnant woman and her fetus when wearing the wireless radio terminal on her abdomen, the SAR distribution in the fetus is calculated using the numerical model of the pregnant woman by exposed to near-field of a normal mode helical antenna (NHA) with a metallic case at 150 MHz. In addition, the SAR in the fetus will be evaluated under two fetal positions. It was found that the fetal SARs are greatly affected by the distance and penetration path from the antenna to the fetal surface. In addition, the fetal SARs are lower than the RF safety guidelines for occupational exposure.

In advanced wireless communication systems, multiantenna mobile handsets are developed for high data rate transmissions. In compliance with international standards and guidelines for human exposure to radio-frequency (RF) fields from these devices, it is necessary to evaluate the maximum specific absorption rate (SAR) of them. In this paper, we present low-error estimation models, which can be useful for fast and accurate determinations of the maximum SAR of a multi-antenna mobile handsets. Fundamentals of the estimation models, built from physical and mathematical perspectives, are first presented and analyzed. For validating the effectiveness of the models, we conduct several SAR measurements for a simple two-antenna mobile handset prototype. By using the estimation models, we perform SAR estimations and compare the estimated SAR with measured data. It is confirmed that the proposed low-error estimation models can provide more accurate estimated SARs, compared with the estimation techniques in previous studies. For example, the maximum estimation error caused by a conventional technique of about 3% can be decreased to 1% by the proposed estimation technique with an estimation order of three.

Background: Specific Absorption Rate (SAR) is radiofrequency power delivered to tissue duringa Magnetic Resonance Imaging (MRI) examination, expressed as watts per kg (W/kg). Radiofrequencypower deposition results in increased heating of patient tissues; thus, the use of MRI has to becontrolled to ensure patient safety.
 Objective: The study aimed to evaluate SAR among patients using the 3 Tesla MRI (MRI 3T) and 1.5Tesla MRI (MRI 1.5T) machines.
 Methods: Data were obtained from patients who were examined using MRI 3T (1,159 patients, 8,225series) and MRI 1.5T (1,423 patients, 8,605 series) machines. Age, body weight, SAR, repetition time(TR), type of radiofrequency (RF) pulse and anatomical region exposed were studied.
 Results: Average SAR for all patients using the MRI 3T was lower than that of the MR 1.5T in everypart (p <0.001) = 0.92 ± 0.57 W/Kg, 2.45 ± 1.01 W/Kg, accordingly. The SAR that the patients receivedusing the spin echo technique revealed that T2 weighted image had lower SAR than T1 weighted imagefrom both MRI 3T and MRI 1.5T (p < 0.001), 0.87 and 0.98 W/kg for MRI 3T, 2.20 and 2.83 W/kg forMRI 1.5T, respectively. For underweight patients, the lowest SAR was 0.89 W/Kg (MRI 3T) and 2.40W/Kg (MRI 1.5T), respectively. Whereas, among overweight patients, the SAR was the highest at 0.97W/Kg (MRI 3T) and 2.52 W/Kg (MRI 1.5T). For SAR categorized by the flip angle of the RF pulse,and patients evaluated by the MRI 3T, the study revealed that the group with the flip angle of the RFpulse <75 degrees had lower SAR than the flip angle of the RF pulse >75 degrees, 0.77 W/Kg and 0.94W/Kg, accordingly (p < 0.001) similar to the MRI 1.5T.
 Conclusion: The average SAR of patients evaluated using the MRI 3T was lower than those of patientsevaluated using the MRI 1.5T in every body part examined. SAR was lower when the TR was increasedand flip angle was decreased.

This study evaluates the radiation safety implications of electromagnetic field (EMF) from electrical distribution sub-stations in Aguata Local Government Area (LGA), Anambra State, Nigeria, using the EMF meter with a laser distance meter in-situ. Ten (10) locations of 11KV distribution sub-stations were mapped out and used for the study. The results of the in-situ measurement of Electric Field (E) and Magnetic Field (H) were used to evaluate the Power Density (S), Specific Absorption Rate (SAR) and Statistical analysis which includes descriptive statistics, inferential statistical tests (T-test) and graphical analysis to evaluate significant differences of EMF levels between different locations. The EMF emitted by these distribution substations was examined using data from the various locations. The results obtained show that EEDC Office has the highest electric field of 0.6633 V/m, while Oko Road has the second highest of 0.7783 V/m. The magnetic field intensity varies across locations, with Oko Road having the largest of 1.3317 A/m. Power density varied, with Oko Road having the highest 1.0365 W/m2 and Stadium having the lowest 0.1011 W/m2. The Specific Absorption Rate (SAR) ranging from 0.0001 to 0.0005 W/Kg showed consistent rates across locations. The International Commission on Non-Protection of Electromagnetic Fields (ICNIRP) sets EMF exposure regulations from 0-300 GHz at the exposure values of, E = 10,000V/m, H = 4×104 A/m, S = 50W/m2, SAR = 10W/kg. In this study, electric field, magnetic field, power density, and specific absorption rate (SAR) values varied widely between stations, with the magnetic field accounting for 45.25% of total electromagnetic exposure. The exposure to EMF emanating from distribution substations in Aguata LGA does not pose any health effect or any health hazards to the general public comparing the measured data with the standard guideline of ICNIRP.

The International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines and the IEEE C95.1 standard are currently under revision. In the guidelines/standard, the dominant effect for electromagnetic field exposures at frequencies above 100 kHz is the thermal effect. The whole-body-and 10g-averaged specific absorption rates (SARs), which are surrogates for core and local temperature elevations, respectively, are set as metrics for exposure evaluation. The external field strengths or incident power density, corresponding to the limit for SARs, are also used as metrics for practical compliance purposes. Although the limits for the SARs are identical amongst the guidelines/standard, the limits for the external field strengths differ by a factor of 7.4–12.9 in an intermediate frequency range (100 kHz–100 MHz). Due to the fact that the standard/guidelines were published before the computation with anatomical human models was available, it is worth revisiting the relationship between the SARs and external field strengths by computations using the human models. Intercomparison using different numerical codes was also performed to verify the results. For the main finding, as expected, the 10g-averaged SAR was a less restrictive factor for whole-body exposure over the frequencies considered in this paper. It was also found that the relationship between SARs and external field strength was satisfied, but was more conservative in the ICNIRP guidelines, whereas there were slight discrepancies below 30 MHz in the IEEE standard. The computational results would be useful for revising the permissible external field strength based on scientific results.

A 2-mm-thick plastic shell with 5-10-mm-thick tapered plastic spacer in the shape of a pinna-specific anthropomorphic mannequin (SAM) head model is being used for determination of the specific absorption rate (SAR) of cellular telephones for compliance testing against IEEE and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) Safety Guidelines used in the U.S. and Europe, respectively. We have used three-dimensional computer-aided design files of the SAM Model with 1-mm resolution to calculate peak 1- and 10-g SAR for cheek and 15/spl deg/-tilted positions of some typical telephones for comparison with those for three anatomic models of the head to show that the SAR obtained for SAM is up to two or more times smaller than for anatomic models. This is due to the shift of the high SAR locations to a low radiated fields region away from the antenna, particularly at 835 MHz, and a substantial physical separation from the absorptive phantom at 1900 MHz. Due to the use of lossless plastic for the pinna, another handicap of the SAM model is the total lack of knowledge of 1- or 10-g SAR in the pinna tissues required by all safety guidelines (current or proposed). To remedy this situation, we propose a modified SAM with a lossy pinna, for which 1- and 10-g SARs are relatively close to those for anatomic models, provided we use a fluid of higher conductivity than that currently used for compliance testing at 835 MHz. Lastly, we compare the implications of the current IEEE and ICNIRP guidelines and the newly proposed IEEE guidelines with a relaxed limit of 4.0 W/kg for any 10-g of tissue of the pinna for maximum allowable powers for cellular telephones at 835 and 1900 MHz to show that the newly proposed relaxed IEEE limits will allow radiated powers that may be 8-16 times those permitted by the current IEEE Standard and up to two times higher than those permitted under ICNIRP guidelines used in over 30 countries.

Spinal cord stimulation (SCS) is an accepted treatment in patients with failed back surgery (FBS), complex regional pain syndrome (CRPS) and persistent radicular pain following surgery. In order to avoid patient hazards or device malfunction manufacturers advise to abstain from magnetic resonance imaging (MRI) in patients with implanted electrodes or pulse generators. In a prospective study, 13 patients harbouring an implanted Medtronic Spinal Cord Stimulation (SCS) device underwent MRI (1.5 T) of the lumbar (n=13), the cervical (n=2) or the thoracic spine (n=1) following the development of new spinal symptoms. An adapted MRI protocol was used limiting the transmitted energy and specific absorption rate. Tolerability and safety were assessed by means of a standardized patient evaluation form documenting pain on a visual analogue scale (0-10), neurologic deficit, and discomfort during the scan. In addition, overall satisfaction with the examination procedure was rated on a Likert scale (1-5). Image quality was rated independently and blinded to the presence of a SCS device by the radiologist and the surgeon as equivalent, superior or inferior compared to the standard spine MRI examination. None of the 13 patients investigated by the modified spinal MRI protocol experienced new neurological deficits, worsening of symptoms or a defect/malfunction of the implant device. Three patients (23.1 %) reported transient warm sensation in the location of the electrode and in one case intermittent slight tingling in the lower extremities. Overall satisfaction with the examination was 1.13 ± 0.34 according to Likert scale (1-5). The image quality was rated - not statistically significant - slightly inferior to standard lumbar spine imaging (0.82 ± 0.54) with a kappa value of 0.68 between the two investigators. MRI examinations detected relevant and new lesions in 9 (69.2 %) patients which affected treatment in 8 (61.5 %) individuals. Using a protocol with a reduced specific energy absorption rate, spinal MRI examinations in patients with SCS can be considered safe. The current view that neurostimulators are a general contraindication to MR examinations has to be reconsidered in patients with new or progressive spinal symptoms.