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High-resolution MRI images are essential for the accurate diagnosis of diseases. Increasing the magnetic field strength achieves this but also raises the Specific Absorption Rate (SAR) of electromagnetic waves in the body, leading to safety concerns. Currently, SAR is managed by assuming an even distribution of electromagnetic waves; however, high-field MRI can cause localized concentrations. No direct method for SAR visualization exists that relies on numerical analysis, resulting in conservative management and inefficiency. This paper presents a method for converting temperature images from magnetic resonance imaging (MRI) into SAR images using Pennes' bioheat equation and Fourier transformation with gentle low-pass filtering. The method was tested using an agar-gel phantom heated with a heating RF coil, and the temperature changes were measured using the proton resonance frequency shift (PRFS) technique in a 3T MRI system. The results are validated by electromagnetic numerical simulations using xFDTD. Experimental results showed SAR images could be reconstructed from temperature images with a maximum error of 3.6 % compared with numerical simulations. The reconstruction took 5.2 s on a PC. This method can aid in managing electromagnetic safety in MRI and verifying the RF coil performance during development. Future studies will validate this method using different phantom configurations and in vivo experiments. [ABSTRACT FROM AUTHOR]

The increased magnetic field strength in MRI improves the spatial resolution and image quality of the metabolic activity of the human body by increasing the SNR. As the magnetic field increases, the level of RF exposure increases; therefore, extra care should be taken with high-field MRI scans. MRI regulated by IEC 60601-2-33 has been reported in several studies to be inefficient in MRI operation owing to overly conservative SAR-based regulations. The latest revisions to the IEC and ICNIRP show a dramatic increase in the use of temperature-based analytical descriptions. This is mainly because SAR does not consider the thermoregulatory mechanisms of the human body, which makes the SAR exposure levels conservative, whereas temperature-based analyses assume that the thermoregulatory mechanisms of the human body are inherently present. In this study, we synthesized the results of a primate numerical model and thermal simulation in a 1.5 T MRI to analyze the exposure to electromagnetic waves in the MRI and the resulting temperature increase. In addition, we analyzed the results of numerical observations of the impact on body temperature rise when blood flow, a major factor in thermoregulation, was decreased by 90 %, showing a temperature rise of 39.3°C and a CEM43 value of 0.07 min. [ABSTRACT FROM AUTHOR]

This article describes the computational analysis of Radio Frequency - Electromagnetic Field (RF-EMF) exposure of Uterus-Fetus Units (UFUs) embedded inside the body of a 26 year old human female. Realistic UFU models are obtained from ultrasound images acquired for different fetuses and at specific development stages (7 weeks, 9 weeks and 11 weeks old), for which a deep-learning based segmentation method is developed. Each UFU model is then inserted into a computational electromagnetic model of a 26 year old female. The Specific Absorption Rate (SAR) of the fetus at commonly used wireless communication frequencies is estimated using a commercially available numerical electromagnetic solver. The Inverted F antenna (IFA), which is a commonly used mobile phone antenna was used as the excitation source. Fetus SAR values are reported for different combinations of excitation frequencies, phone positions and UFU ages. It was found that the fetus SAR for all the cases is well below the maximum allowable exposure limit of 80 mW/kg, as prescribed by ICNIRP. Furthermore, we replaced the embryo with uterus tissues and calculated the SAR in the uterus tissues (i.e. uterus tissues with same volume and shape, and at the same location as that of UFU). The uterus SAR values were found to be only marginally different from that of fetus SAR.

This paper proposes a novel approach for fast human exposure absorbed power density assessment, based on a combination of over-the-air radiative field measurements and full-wave electromagnetic simulations. This so-called augmented OTA technique relies on the computation of an equivalent source or digital twin, which reproduces the radiation properties of the device under test. At short separation distances, the interaction between the human model and the device is however not negligible. A novel solution to model the influence of multiple reflections is introduced, where the inside of the equivalent source box is partially filled with a perfect electric conductor, thereby creating a reflective digital twin model. Simulation and measurement results demonstrate the relevance of this technique for enabling accurate absorbed power density evaluations. A discussion on aspects influencing the measurement time and uncertainty is also provided, where a new demonstration is delivered how spatial-averaging contributes positively to the accuracy of the method.

Purpose: Radiofrequency (RF) exposure during MR examination is limited by IEC 60601‐2‐33 to prevent thermal hazards to patients. These limits are also the basis to derive the maximum induced field for the demonstration of MR safety of implants per ISO/TS 10974 (2018). One limit is the head‐averaged specific absorption rate (SAR), for which the head extent is defined differently by MR and implant vendors. The purpose of this technical note is to inform MR safety stakeholders on the sensitivity of safety evaluations due to different head extent definitions. Methods: RF distributions from the validated MRIxViP exposure libraries of 12 high‐resolution human anatomical models were scaled to the normative SAR limits for different definitions of the head extent to compare the corresponding induced SAR and electric (E‐)field levels. Results: The definitions of the head extent used by major implant vendors and defined in ISO/TS 10974 (2018) are larger than those introduced in IEC 60601‐2‐33 (2022), resulting in lower RF head exposure by up to 2.4 dB (factor 1.7). Other proposed definitions of the head result in intermediate values. Conclusion: The different head extents result in different maximum RF exposures affecting the risk assessment by up to a factor of 1.7. The results of this study can be used to estimate the additional uncertainty in safety assessments. Future revisions of MR standards should eliminate this inconsistency. [ABSTRACT FROM AUTHOR]

Herein, we present a new method for the calculation of the specific absorption rate (SAR) of rats (named time-weighted SAR) to practically consider the effect of the ever-changing movements of rats on their SARs. First, nine rats in separate cages were recorded for approximately 22 h, and the footage every 1 min was collected to obtain 1,307 still shots per rat. Next, five representative postures, which were classified according to the similarity of the still shots, were selected. Subsequently, the percentage of each posture was calculated by computing the number of still shots classified into the corresponding representative postures. Lastly, we demonstrated that although each rat exhibited relatively different and diverse movements during the observation period, the application of this percentage to the SARs of each posture resulted in very similar SAR levels among the rats. This indicates that the time-weighted SAR can be a suitable parameter for accounting for various behavior patterns of rats, as it can measure the total amount of real RF exposure more precisely and practically.

This study addressed an important but not yet thoroughly investigated topic regarding human exposure to radio-frequency electromagnetic fields (RF-EMF) generated by vehicular connectivity. In particular, the study assessed, by means of computational dosimetry, the RF-EMF exposure in road users near a car equipped with vehicle-to-vehicle (V2V) communication antennas. The exposure scenario consisted of a 3D numerical model of a car with two V2V antennas, each fed with 1 W, operating at 5.9 GHz and an adult human model to simulate the road user near the car. The RF-EMF dose absorbed by the human model was calculated as the specific absorption rate (SAR), that is, the RF-EMF power absorbed per unit of mass. The highest SAR was observed in the skin of the head (34.7 mW/kg) and in the eyes (15 mW/kg); the SAR at the torso (including the genitals) and limbs was negligible or much lower than in the head and eyes. The SAR over the whole body was 0.19 mW/kg. The SAR was always well below the limits of human exposure in the 100 kHz–6 GHz band established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The proposed approach can be generalized to assess RF-EMF exposure in different conditions by varying the montage/number of V2V antennas and considering human models of different ages. [ABSTRACT FROM AUTHOR]

BackgroundThe use of electromagnetic (EM) technologies for military applications is gaining increasing interest to satisfy different operational needs, such as improving battlefield communications or jamming counterpart's signals. This is achieved by the use of high-power EM waves in several frequency bands (e.g., HF, VHF, and UHF). When considering military vehicles, several antennas are present in close proximity to the crew personnel, which are thus potentially exposed to high EM fields.MethodsA typical exposure scenario was reproduced numerically to evaluate the EM exposure of the human body in the presence of an HF vehicular antenna (2–30 MHz). The antenna was modeled as a monopole connected to a 3D polygonal structure representing the vehicle. Both the EM field levels in the absence and in the presence of the human body and also the specific absorption rate (SAR) values were calculated. The presence of the operator, partially standing outside the vehicle, was simulated with the virtual human body model Duke (Virtual Population, V.3). Several exposure scenarios were considered. The presence of a protective helmet was modeled as well.ResultsIn the area usually occupied by the personnel, E-field intensity radiated by the antenna can reach values above the limits settled by international safety guidelines. Nevertheless, local SAR values induced inside the human body reached a maximum value of 14 mW/kg, leading to whole-body averaged and 10-g averaged SAR values well below the corresponding limits.ConclusionA complex and realistic near-field exposure scenario of the crew of a military vehicle was simulated. The obtained E-field values radiated in the free space by a HF vehicular antenna may reach values above the safety guidelines reference levels. Such values are not necessarily meaningful for the exposed subject. Indeed, SAR and E-field values induced inside the body remain well below safety limits.

This study addressed an important but not yet thoroughly investigated topic regarding human exposure to radio-frequency electromagnetic fields (RF-EMF) generated by vehicular connectivity. In particular, the study assessed, by means of computational dosimetry, the RF-EMF exposure in road users near a car equipped with vehicle-to-vehicle (V2V) communication antennas. The exposure scenario consisted of a 3D numerical model of a car with two V2V antennas, each fed with 1 W, operating at 5.9 GHz and an adult human model to simulate the road user near the car. The RF-EMF dose absorbed by the human model was calculated as the specific absorption rate (SAR), that is, the RF-EMF power absorbed per unit of mass. The highest SAR was observed in the skin of the head (34.7 mW/kg) and in the eyes (15 mW/kg); the SAR at the torso (including the genitals) and limbs was negligible or much lower than in the head and eyes. The SAR over the whole body was 0.19 mW/kg. The SAR was always well below the limits of human exposure in the 100 kHz–6 GHz band established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The proposed approach can be generalized to assess RF-EMF exposure in different conditions by varying the montage/number of V2V antennas and considering human models of different ages.

Medical Physics Department (Medical School, University of Thessaly) participated in a Greek National EMF research program (EDBM34) with the scope to measure and evaluate radiofrequency (RF) exposure (27-3000 MHz) in areas of sensitive land use. A thousand (1000) measurements were carried out at two "metropolitan locations" (Athens and Thessaloniki: 624 points) and several rest urban/rural locations (376 points). SRM 3006 spectrum analyzer manufactured by Narda Safety Test Solutions was used. The broadband mean electric field in metropolitan areas was 0.41 V/m, while in the rest of Greece was 0.36 V/m. In metropolitan areas, the predominant RF source was the TV and Radio FM signals (36.2% mean contribution to the total RF exposure level). In the rest areas, the predominant source was the systems of the meteorological and military/defensive service (31.1%). The mobile sector contributed 14.9% in metropolitan areas versus 12.2% in the rest of Greece. The predominant mobile source was 900 MHz in both cases (4.5% in metropolitan areas vs. 3.3% in the rest of Greece). The total exposure from all RF sources complied with the International Commission on Non-Ionizing Radiation Protection (ICNIRP) 2020 safety guidelines [ICNIRP, 2020]. The maximum exposure level was 0.129% of the limit for the metropolitan areas vs. 0.110% for the rest of Greece. Nonremarkable differences between metropolitan areas' exposure and the rest of Greece. In most cases, new 5 G antennas will be added to the existing base stations. Thus, the total exposure may be increased, leading to higher safety distances. © 2023 Bioelectromagnetics Society., (© 2023 Bioelectromagnetics Society.)

Background: The use of electromagnetic (EM) technologies for military applications is gaining increasing interest to satisfy different operational needs, such as improving battlefield communications or jamming counterpart's signals. This is achieved by the use of high-power EM waves in several frequency bands (e.g., HF, VHF, and UHF). When considering military vehicles, several antennas are present in close proximity to the crew personnel, which are thus potentially exposed to high EM fields., Methods: A typical exposure scenario was reproduced numerically to evaluate the EM exposure of the human body in the presence of an HF vehicular antenna (2-30 MHz). The antenna was modeled as a monopole connected to a 3D polygonal structure representing the vehicle. Both the EM field levels in the absence and in the presence of the human body and also the specific absorption rate (SAR) values were calculated. The presence of the operator, partially standing outside the vehicle, was simulated with the virtual human body model Duke (Virtual Population, V.3). Several exposure scenarios were considered. The presence of a protective helmet was modeled as well., Results: In the area usually occupied by the personnel, E-field intensity radiated by the antenna can reach values above the limits settled by international safety guidelines. Nevertheless, local SAR values induced inside the human body reached a maximum value of 14 mW/kg, leading to whole-body averaged and 10-g averaged SAR values well below the corresponding limits., Conclusion: A complex and realistic near-field exposure scenario of the crew of a military vehicle was simulated. The obtained E-field values radiated in the free space by a HF vehicular antenna may reach values above the safety guidelines reference levels. Such values are not necessarily meaningful for the exposed subject. Indeed, SAR and E-field values induced inside the body remain well below safety limits., Competing Interests: MM, RP, and TC are employees at Larimart S.p.A. DF, AD, MCap, GP, and EM are employees at CEPOLISPE. Larimart and Cepolispe provided information about vehicle and antenna dimensions. This work was carried out in the frame of the HEPROSYS project funded by Lariamrt S.p.A. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Colella, Biscarini, de Meis, Patrizi, Ciallella, Ferrante, De Gaetano, Capuano, Pellegrino, Martini, Cavagnaro, Apollonio and Liberti.)