Induced radiofrequency fields in patients undergoing MR examinations: insights for risk assessment.

Purpose. To characterize and quantify the induced radiofrequency (RF) electric (E)-fields andB1+rmsfields in patients undergoing magnetic resonance (MR) examinations; to provide guidance on aspects of RF heating risks for patients with and without implants; and to discuss some strengths and limitations of safety assessments in current ISO, IEC, and ASTM standards to determine the RF heating risks for patients with and without implants.Methods. InducedE-fields andB1+rmsfields during 1.5 T and 3 T MR examinations were numerically estimated for high-resolution patient models of the Virtual Population exposed to ten two-port birdcage RF coils from head to feet imaging landmarks over the full polarization space, as well as in surrogate ASTM phantoms.Results. Worst-caseB1+rmsexposure greater than 3.5µT (1.5 T) and 2µT (3 T) must be considered for all MR examinations at the Normal Operating Mode limit. Representative inducedE-field and specific absorption rate distributions under different clinical scenarios allow quick estimation of clinical factors of high and reduced exposure.B1shimming can cause +6 dB enhancements toE-fields along implant trajectories. The distribution and magnitude of inducedE-fields in the ASTM phantom differ from clinical exposures and are not always conservative for typical implant locations.Conclusions.Field distributions in patient models are condensed, visualized for quick estimation of risks, and compared to those induced in the ASTM phantom. InducedE-fields in patient models can significantly exceed those in the surrogate ASTM phantom in some cases. In the recent 19ε2revision of the ASTM F2182 standard, the major shortcomings of previous versions have been addressed by requiring that the relationship between ASTM test conditions andin vivotangentialE-fields be established, e.g. numerically. With this requirement, the principal methods defined in the ASTM standard for passive implants are reconciled with those of the ISO 10974 standard for active implantable medical devices.

Compliance Assessment of the Epithelial or Absorbed Power Density Below 10 GHz Using SAR Measurement Systems.

The introduction of new dosimetric quantities, in particular, epithelial or absorbed power density for frequencies above 6 GHz, in exposure guidelines and safety standards requires the development of new experimental assessment procedures for compliance testing. In this study, we propose to approximate the peak spatial-average absorbed power density (psSab ) using the same measured data and algorithms that are used for determining the peak spatial-average specific absorption rate psSAR, which is currently limited to frequencies up to 10 GHz. The uncertainty component for the transformation of psSAR to psSab was evaluated as less than 0.55 dB (13.5%) for any source as close as 0.02 λ from the tissue simulating media. The approach is easy to implement and allows determining compliance with the basic restrictions of the latest safety guidelines. In the next project, we will expand dosimetric probes, phantoms, and procedures for frequencies above 10 GHz. © 2021 Bioelectromagnetics Society.

Assessment of Genotoxicity in Human Cells Exposed to Modulated Electromagnetic Fields of Wireless Communication Devices.

Modulated electromagnetic fields (wEMFs), as generated by modern communication technologies, have raised concerns about adverse health effects. The International Agency for Research on Cancer (IARC) classifies them as "possibly carcinogenic to humans" (Group 2B), yet, the underlying molecular mechanisms initiating and promoting tumorigenesis remain elusive. Here, we comprehensively assess the impact of technologically relevant wEMF modulations on the genome integrity of cultured human cells, investigating cell type-specificities as well as time- and dose-dependencies. Classical and advanced methodologies of genetic toxicology and DNA repair were applied, and key experiments were performed in two separate laboratories. Overall, we found no conclusive evidence for an induction of DNA damage nor for alterations of the DNA repair capacity in cells exposed to several wEMF modulations (i.e., GSM, UMTS, WiFi, and RFID). Previously reported observations of increased DNA damage after exposure of cells to GSM-modulated signals could not be reproduced. Experimental variables, presumably underlying the discrepant observations, were investigated and are discussed. On the basis of our data, we conclude that the possible carcinogenicity of wEMF modulations cannot be explained by an effect on genome integrity through direct DNA damage. However, we cannot exclude non-genotoxic, indirect, or secondary effects of wEMF exposure that may promote tumorigenesis in other ways.

Efficient and Reliable Assessment of the Maximum Local Tissue Temperature Increase at the Electrodes of Medical Implants under MRI Exposure.

Standard risk evaluations posed by medical implants during magnetic resonance imaging (MRI) includes (i) the assessment of the total local electromagnetic (EM) power (P) absorbed in the vicinity of the electrodes and (ii) the translation of P into a local in vivo tissue temperature increase ∆T (P2∆T) in animal experiments or simulations. We investigated the implant/tissue modeling requirements and associated uncertainties by applying full-wave EM and linear bioheat solvers to different implant models, incident field conditions, electrode configurations, and tissue models. Results show that the magnitude of the power is predominately determined by the lead, while the power distribution, and the P2∆T conversion, is determined by the electrode and surrounding tissues. P2∆T is strongly dependent on the size of the electrode, tissue type in contact with the electrode, and tissue inhomogeneity (factor of >2 each) but less on the modeling of the lead (<±10%) and incident field distribution along the lead (<±20%). This was confirmed by means of full-wave simulations performed with detailed high-resolution anatomical phantoms exposed to two commonly used MRI clinical scenarios (64 and 128 MHz), resulting in differences of less than 6%. For the determination of P2∆T, only the electrode and surrounding tissues must be modeled in great detail, whereas the lead can be modeled as a computationally efficient simplified structure exposed to a uniform field. The separate assessments of lead and electrode reduce the overall computational effort by several orders of magnitude. The errors introduced by this simplification can be considered by uncertainty terms. Bioelectromagnetics. 2019;40:422-433. © 2019 Bioelectromagnetics Society.

Theoretical and numerical assessment of maximally allowable power-density averaging area for conservative electromagnetic exposure assessment above 6 GHz.

The objective of this paper is to determine a maximum averaging area for power density (PD) that limits the maximum temperature increase to a given threshold for frequencies above 6 GHz. This maximum area should be conservative for any transmitter at any distance >2 mm from the primary transmitting antennas or secondary field-generating sources. To derive a generically valid maximum averaging area, an analytical approximation for the peak temperature increase caused by localized exposure was derived. The results for a threshold value of 1 K temperature rise were validated against simulations of a series of sources composed of electrical and magnetic elements (dipoles, slots, patches, and arrays) that represented the spectrum of relevant transmitters. The validation was successful for frequencies in which the power deposition occurred superficially (i.e., >10 GHz). In conclusion, the averaging area for a PD limit of 10 W/m2 that conservatively limits the temperature increase in the skin to less than 1 K at any distance >2 mm from the transmitters is frequency dependent, increases with distance, and ranges from 3 cm2 at <10 GHz to 1.9 cm2 at 100 GHz. In the far-field, the area depends additionally on distance and the antenna array aperture. The correlation was found to be worse at lower frequencies (<10 GHz) and very close to the source, the systematic evaluation of which is part of another study to investigate the effect of different coupling mechanisms in the reactive near-field on the ratio of temperature increase to incident power density. The presented model can be directly applied to any other PD and temperature thresholds. Bioelectromagnetics. 39:617-630, 2018. © 2018 Wiley Periodicals, Inc.

Life-Time Dosimetric Assessment for Mice and Rats Exposed in Reverberation Chambers of the 2-Year NTP Cancer Bioassay Study on Cell Phone Radiation.

In this paper, we present the detailed life-time dosimetry analysis for rodents exposed in the reverberation exposure system designed for the two-year cancer bioassay study conducted by the National Toxicology Program of the National Institute of Environmental Health Sciences. The study required the well-controlled and characterized exposure of individually housed, unrestrained mice at 1900 MHz and rats at 900 MHz, frequencies chosen to give best uniformity exposure of organs and tissues. The wbSAR, the peak spatial SAR and the organ specific SAR as well as the uncertainty and variation due to the exposure environment, differences in the growth rates, and animal posture were assessed. Compared to the wbSAR, the average exposure of the high-water-content tissues (blood, heart, lung) were higher by ~4 dB, while the low-loss tissues (bone and fat) were less by ~9 dB. The maximum uncertainty over the exposure period for the SAR was estimated to be <49% (k=2) for the rodents whereas the relative uncertainty between the group was <14% (k=1). The instantaneous variation (averaged over 1 min) was <13% (k=1), which is small compared to other long term exposure research projects. These detailed dosimetric results empowers comparison with other studies and provides a reference for studies of long-term biological effects of exposure of rodents to RF energy.

Effects of body habitus on internal radiation dose calculations using the 5-year-old anthropomorphic male models.

Computational phantoms are commonly used in internal radiation dosimetry to assess the amount and distribution pattern of energy deposited in various parts of the human body from different internal radiation sources. Radiation dose assessments are commonly performed on predetermined reference computational phantoms while the argument for individualized patient-specific radiation dosimetry exists. This study aims to evaluate the influence of body habitus on internal dosimetry and to quantify the uncertainties in dose estimation correlated with the use of fixed reference models. The 5-year-old IT'IS male phantom was modified to match target anthropometric parameters, including body weight, body height and sitting height/stature ratio (SSR), determined from reference databases, thus enabling the creation of 125 5-year-old habitus-dependent male phantoms with 10th, 25th, 50th, 75th and 90th percentile body morphometries. We evaluated the absorbed fractions and the mean absorbed dose to the target region per unit cumulative activity in the source region (S-values) of F-18 in 46 source regions for the generated 125 anthropomorphic 5-year-old hybrid male phantoms using the Monte Carlo N-Particle eXtended general purpose Monte Carlo transport code and calculated the absorbed dose and effective dose of five 18F-labelled radiotracers for children of various habitus. For most organs, the S-value of F-18 presents stronger statistical correlations with body weight, standing height and sitting height than BMI and SSR. The self-absorbed fraction and self-absorbed S-values of F-18 and the absorbed dose and effective dose of 18F-labelled radiotracers present with the strongest statistical correlations with body weight. For 18F-Amino acids, 18F-Brain receptor substances, 18F-FDG, 18F-L-DOPA and 18F-FBPA, the mean absolute effective dose differences between phantoms of different habitus and fixed reference models are 11.4%, 11.3%, 10.8%, 13.3% and 11.4%, respectively. Total body weight, standing height and sitting height have considerable effects on human internal dosimetry. Radiation dose calculations for individual subjects using the most closely matched habitus-dependent computational phantom should be considered as an alternative to improve the accuracy of the estimates.

Extremely low-frequency magnetic fields and risk of childhood leukemia: A risk assessment by the ARIMMORA consortium.

Exposure to extremely low-frequency magnetic fields (ELF-MF) was evaluated in an International Agency for Research on Cancer (IARC) Monographs as "possibly carcinogenic to humans" in 2001, based on increased childhood leukemia risk observed in epidemiological studies. We conducted a hazard assessment using available scientific evidence published before March 2015, with inclusion of new research findings from the Advanced Research on Interaction Mechanisms of electroMagnetic exposures with Organisms for Risk Assessment (ARIMMORA) project. The IARC Monograph evaluation scheme was applied to hazard identification. In ARIMMORA for the first time, a transgenic mouse model was used to mimic the most common childhood leukemia: new pathogenic mechanisms were indicated, but more data are needed to draw definitive conclusions. Although experiments in different animal strains showed exposure-related decreases of CD8+ T-cells, a role in carcinogenesis must be further established. No direct damage of DNA by exposure was observed. Overall in the literature, there is limited evidence of carcinogenicity in humans and inadequate evidence of carcinogenicity in experimental animals, with only weak supporting evidence from mechanistic studies. New exposure data from ARIMMORA confirmed that if the association is nevertheless causal, up to 2% of childhood leukemias in Europe, as previously estimated, may be attributable to ELF-MF. In summary, ARIMMORA concludes that the relationship between ELF-MF and childhood leukemia remains consistent with possible carcinogenicity in humans. While this scientific uncertainty is dissatisfactory for science and public health, new mechanistic insight from ARIMMORA experiments points to future research that could provide a step-change in future assessments. Bioelectromagnetics. 37:183-189, 2016. © 2016 Wiley Periodicals, Inc.

Virtual population-based assessment of the impact of 3 Tesla radiofrequency shimming and thermoregulation on safety and B1 + uniformity.

PURPOSE: To assess the effect of radiofrequency (RF) shimming of a 3 Tesla (T) two-port body coil on B1 + uniformity, the local specific absorption rate (SAR), and the local temperature increase as a function of the thermoregulatory response. METHODS: RF shimming alters induced current distribution, which may result in large changes in the level and location of absorbed RF energy. We investigated this effect with six anatomical human models from the Virtual Population in 10 imaging landmarks and four RF coils. Three thermoregulation models were applied to estimate potential local temperature increases, including a newly proposed model for impaired thermoregulation. RESULTS: Two-port RF shimming, compared to circular polarization mode, can increase the B1 + uniformity on average by +32%. Worst-case SAR excitations increase the local RF power deposition on average by +39%. In the first level controlled operating mode, induced peak temperatures reach 42.5°C and 45.6°C in patients with normal and impaired thermoregulation, respectively. CONCLUSION: Image quality with 3T body coils can be significantly increased by RF shimming. Exposure in realistic scan scenarios within guideline limits can be considered safe for a broad patient population with normal thermoregulation. Patients with impaired thermoregulation should not be scanned outside of the normal operating mode. Magn Reson Med 76:986-997, 2016. © 2015 Wiley Periodicals, Inc.

COMPUTATIONAL ASSESSMENT OF PREGNANT WOMAN MODELS EXPOSED TO UNIFORM ELF-MAGNETIC FIELDS: COMPLIANCE WITH THE EUROPEAN CURRENT EXPOSURE REGULATIONS FOR THE GENERAL PUBLIC AND OCCUPATIONAL EXPOSURES AT 50 Hz.

The Recommendation 1999/529/EU and the Directive 2013/35/EU suggest limits for both general public and occupational exposures to extremely low-frequency magnetic fields, but without special limits for pregnant women. This study aimed to assess the compliance of pregnant women to the current regulations, when exposed to uniform MF at 50 Hz (100 µT for EU Recommendation and 1 and 6 mT for EU Directive). For general public, exposure of pregnant women and fetus always resulted in compliance with EU Recommendation. For occupational exposures, (1) Electric fields in pregnant women were in compliance with the Directive, with exposure variations due to fetal posture of <10 %, (2) electric fields in fetuses are lower than the occupational limits, with exposure variations due to fetal posture of >40 % in head tissues, (3) Electric fields in fetal CNS tissues of head are above the ICNIRP 2010 limits for general public at 1 mT (in 7 and 9 months gestational age) and at 6 mT (in all gestational ages).

Near-field radiofrequency electromagnetic exposure assessment.

Personal wireless telecommunication devices, such as radiofrequency (RF) electromagnetic field (EMF) sources operated in vicinity of human body, have possible adverse health effects. Therefore, the correct EMF assessment is necessary in their near field. According to international near-field measurement criteria, the specific absorption rate (SAR) is used for absorbed energy distribution assessment in tissue simulating liquid phantoms. The aim of this investigation is to validate the relationship between the H-field of incident EMF and absorbed energy in phantoms. Three typical wireless telecommunication system frequencies are considered (900, 1800 and 2450 MHz). The EMF source at each frequency is an appropriate half-wave dipole antenna and the absorbing medium is a flat phantom filled with the suitable tissue simulating liquid. Two methods for SAR estimation have been used: standard procedure based on E-field measured in tissue simulating medium and a proposed evaluation by measuring the incident H-field. Compared SAR estimations were performed for various distances between sources and phantom. Also, these research data were compared with simulation results, obtained by using finite-difference time-domain method. The acquired data help to determine the source near-field space characterized by the smallest deviation between SAR estimation methods. So, this region near the RF source is suitable for correct RF energy absorption assessment using the magnetic component of the RF fields.

Experimental and numerical assessment of low-frequency current distributions from UMTS and GSM mobile phones.

The evaluation of the exposure from mobile communication devices requires consideration of electromagnetic fields (EMFs) over a broad frequency range from dc to GHz. Mobile phones in operation have prominent spectral components in the low-frequency (LF) and radio-frequency (RF) ranges. While the exposure to RF fields from mobile phones has been comprehensively assessed in the past, the LF fields have received much less attention. In this study, LF fields from mobile phones are assessed experimentally and numerically for the global system for mobile (GSM) and universal mobile telecommunications system (UMTS) communication systems and conclusions about the global (LF and RF) EMF exposure from both systems are drawn. From the measurements of the time-domain magnetic fields, it was found that the contribution from the audio signal at a normal speech level, i.e., -16 dBm0, is the same order of magnitude as the fields induced by the current bursts generated from the implementation of the GSM communication system at maximum RF output level. The B-field induced by currents in phones using the UMTS is two orders of magnitude lower than that induced by GSM. Knowing that the RF exposure from the UMTS is also two orders of magnitude lower than from GSM, it is now possible to state that there is an overall reduction of the exposure from this communication system.

Analysis of human brain exposure to low-frequency magnetic fields: a numerical assessment of spatially averaged electric fields and exposure limits.

Compliance with the established exposure limits for the electric field (E-field) induced in the human brain due to low-frequency magnetic field (B-field) induction is demonstrated by numerical dosimetry. The objective of this study is to investigate the dependency of dosimetric compliance assessments on the applied methodology and segmentations. The dependency of the discretization uncertainty (i.e., staircasing and field singularity) on the spatially averaged peak E-field values is first determined using canonical and anatomical models. Because spatial averaging with a grid size of 0.5 mm or smaller sufficiently reduces the impact of artifacts regardless of tissue size, it is a superior approach to other proposed methods such as the 99th percentile or smearing of conductivity contrast. Through a canonical model, it is demonstrated that under the same uniform B-field exposure condition, the peak spatially averaged E-fields in a heterogeneous model can be significantly underestimated by a homogeneous model. The frequency scaling technique is found to introduce substantial error if the relative change in tissue conductivity is significant in the investigated frequency range. Lastly, the peak induced E-fields in the brain tissues of five high-resolution anatomically realistic models exposed to a uniform B-field at ICNIRP and IEEE reference levels in the frequency range of 10 Hz to 100 kHz show that the reference levels are not always compliant with the basic restrictions. Based on the results of this study, a revision is recommended for the guidelines/standards to achieve technically sound exposure limits that can be applied without ambiguity.

Application of an induced field sensor for assessment of electromagnetic exposure from compact fluorescent lamps.

The development of scientifically sound instrumentation, methods, and procedures for the electromagnetic exposure assessment of compact fluorescent lamps (CFLs) is investigated. The incident and induced fields from 11 CFLs have been measured in the 10 kHz-1 MHz range, and they are compared with the levels for incandescent and light emitting diode (LED) bulbs. Commercially available equipment was used to measure the incident fields, while a novel sensor was built to assess the induced fields in humans. Incident electric field levels significantly exceed the International Commission on Non-Ionizing Radiation Protection (ICNIRP) reference levels at close distances for some sources, while the induced fields are within the ICNIRP basic restrictions. This demonstrates the importance of assessing the induced fields rather than the incident fields for these sources. Maximum current densities for CFLs are comparable to the limits (in the range of 9% to 56%), demonstrating the need for measurements to establish compliance. For the frequency range investigated, the induced fields were found to be considerably higher for CFLs than for incandescent light bulbs, while the exposure from the two LED bulbs was low. The proposed instrumentation and methods offer several advantages over an existing measurement standard, and the measurement uncertainty is significantly better than the assessment of electric and magnetic fields at close distances.

Assessment of the radio-frequency electromagnetic fields induced in the human body from mobile phones used with hands-free kits.

In this study, the radiation emission from mobile phones when used with wireless and wired hands-free kits (HFK) was evaluated to determine the necessity for a dedicated compliance procedure and the extent to which the use of wired and wireless HFK can reduce human exposure. The specific absorption rates (SAR) from wireless HFK were determined experimentally. Wired HFK were evaluated dosimetrically while connected to mobile phones (GSM900/1800, UMTS1950) under maximized current coupling onto the HFK cable and various wire routing configurations. In addition, experimentally validated simulations of a wired HFK and a mobile phone operating on anatomical whole-body models were performed. The maximum spatial peak SAR in the head when using wired HFK was more than five times lower than ICNIRP limits. The SAR in the head depends on the output power of the mobile phone, the coupling between the antenna and cable, external attenuation and potential cable specific attenuation. In general, a wired HFK considerably reduces the exposure of the entire head region compared to mobile phones operated at the head, even under unlikely worst-case coupling scenarios. However, wired HFK may cause a localized increase of the exposure in the region of the ear inside the head under worst-case conditions. Wireless HFK exhibit a low but constant exposure.

Amplitude-modulated electromagnetic fields for the treatment of cancer: discovery of tumor-specific frequencies and assessment of a novel therapeutic approach.

PURPOSE: Because in vitro studies suggest that low levels of electromagnetic fields may modify cancer cell growth, we hypothesized that systemic delivery of a combination of tumor-specific frequencies may have a therapeutic effect. We undertook this study to identify tumor-specific frequencies and test the feasibility of administering such frequencies to patients with advanced cancer. PATIENTS AND METHODS: We examined patients with various types of cancer using a noninvasive biofeedback method to identify tumor-specific frequencies. We offered compassionate treatment to some patients with advanced cancer and limited therapeutic options. RESULTS: We examined a total of 163 patients with a diagnosis of cancer and identified a total of 1524 frequencies ranging from 0.1 Hz to 114 kHz. Most frequencies (57-92%) were specific for a single tumor type. Compassionate treatment with tumor-specific frequencies was offered to 28 patients. Three patients experienced grade 1 fatigue during or immediately after treatment. There were no NCI grade 2, 3 or 4 toxicities. Thirteen patients were evaluable for response. One patient with hormone-refractory breast cancer metastatic to the adrenal gland and bones had a complete response lasting 11 months. One patient with hormone-refractory breast cancer metastatic to liver and bones had a partial response lasting 13.5 months. Four patients had stable disease lasting for +34.1 months (thyroid cancer metastatic to lung), 5.1 months (non-small cell lung cancer), 4.1 months (pancreatic cancer metastatic to liver) and 4.0 months (leiomyosarcoma metastatic to liver). CONCLUSION: Cancer-related frequencies appear to be tumor-specific and treatment with tumor-specific frequencies is feasible, well tolerated and may have biological efficacy in patients with advanced cancer. TRIAL REGISTRATION: clinicaltrials.gov identifier NCT00805337.

Assessment of induced radio-frequency electromagnetic fields in various anatomical human body models.

The reference levels for testing compliance of human exposure with radio-frequency (RF) safety limits have been derived from very simplified models of the human. In order to validate these findings for anatomical models, we investigated the absorption characteristics for various anatomies ranging from 6 year old child to large adult male by numerical modeling. We address the exposure to plane-waves incident from all major six sides of the humans with two orthogonal polarizations each. Worst-case scattered field exposure scenarios have been constructed in order to test the implemented procedures of current in situ compliance measurement standards (spatial averaging versus peak search). Our findings suggest that the reference levels of current electromagnetic (EM) safety guidelines for demonstrating compliance as well as some of the current measurement standards are not consistent with the basic restrictions and need to be revised.