Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> C. Recent Proposal on EMF Exposure Measurement Methodology <s> : The National Toxicology Program rodent cancer bioassay program design evolved from that of the National Cancer Institute in the 1970s. Groups of 50 or more mice are assigned to control or treatment groups. Test substances are given at three dose levels by intubation, dietary or drinking water consumption, or dermal or inhalation exposure. Dosing starts at age 5–6 weeks and lasts for 2 years, when surviving animals receive a complete histopathologic examination. Statistical approaches accommodate survival differences and no longer require differentiation between fatal and incidental tumors. Photocarcinogenicity studies, employing SKH-1 hairless mice, evaluate onset of skin papillomas and incidences at 1 year. Top doses are chosen to expose animals to a minimally toxic challenge and lower doses to operate within the linear range of kinetics. This dosing allows comparison of results across studies. Bioassay and ancillary studies successfully identify tumor-causing agents in rodents, provide information on dose-response, and characterize other chemical-related toxicities. NTP and Ramazzini Foundation bioassay designs differ in several aspects, but bioassays at both institutions provide chemical-specific information for predicting human carcinogens, thus providing for protection of public health. Bioassays constitute an essential information reference set for new assay development and further investigations into mechanisms of action. The scientific community and the public owe a huge debt of gratitude to Dr. Cesare Maltoni of the European Foundation of Oncology and Environmental Sciences and to Dr. David P. Rall of the National Institute of Environmental Health Sciences for their foresight and wisdom in creating and nurturing these bioassay programs. <s> BIB001 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> C. Recent Proposal on EMF Exposure Measurement Methodology <s> The specific absorption rate (SAR) is an indicator of the thermal effects caused by microwave exposure in biological tissue. Conventionally, an electric field probe scanning method is used for SAR evaluation. Although many countries have confirmed the validity of the electric field probe scanning method used in many SAR evaluation devices, a comparison between physically different measurement techniques is an important goal for validating a standard and for evaluating the uncertainty of a measurement system. Hence, the authors developed a thermal SAR measurement method using an optical fiber thermal sensor. In this paper, the results of comparison measurements between the electric field probe scanning system and the proposed thermal SAR measurement system are presented. The results show that the SAR measurements by each system overlap within the range of the expanded standard uncertainty in the frequency range of 2-6 GHz. <s> BIB002 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> C. Recent Proposal on EMF Exposure Measurement Methodology <s> Specific absorption rate management and excitation fidelity are key aspects of radio frequency pulse design for parallel transmission at ultra high magnetic field strength. The design of radio frequency pulses for multiple channels is often based on the solution of regularized least squares optimization problems for which a regularization term is typically selected to control the integrated or peak pulse waveform amplitude. Unlike single channel transmission, the specific absorption rate of parallel transmission is significantly influenced by interferences between the electric fields associated with the individual transmission elements, which a conventional regularization term does not take into account. This work explores the effects upon specific absorption rate of incorporating experimentally measurable electric field interactions into parallel transmission pulse design. Results of numerical simulations and phantom experiments show that the global specific absorption rate during parallel transmission decreases when electric field interactions are incorporated into pulse design optimization. The results also show that knowledge of electric field interactions enables robust prediction of the net power delivered to the sample or subject by parallel radio frequency pulses before they are played out on a scanner. <s> BIB003 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> C. Recent Proposal on EMF Exposure Measurement Methodology <s> In ultra-high-field magnetic resonance imaging, parallel radiofrequency (RF) transmission presents both opportunities and challenges for specific absorption rate management. On one hand, parallel transmission provides flexibility in tailoring electric fields in the body while facilitating magnetization profile control. On the other hand, it increases the complexity of energy deposition as well as possibly exacerbating local specific absorption rate by improper design or delivery of RF pulses. This study shows that the information needed to characterize RF heating in parallel transmission is contained within a local power correlation matrix. Building upon a calibration scheme involving a finite number of magnetic resonance thermometry measurements, this work establishes a way of estimating the local power correlation matrix. Determination of this matrix allows prediction of temperature change for an arbitrary parallel transmit RF pulse. In the case of a three transmit coil MR experiment in a phantom, determination and validation of the power correlation matrix were conducted in less than 200 min with induced temperature changes of <4°C. Further optimization and adaptation are possible, and simulations evaluating potential feasibility for in vivo use are presented. The method allows general characteristics indicative of RF coil/pulse safety determined in situ. <s> BIB004 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> C. Recent Proposal on EMF Exposure Measurement Methodology <s> A method is described for measuring absorbed electromagnetic energy radiated from cell phone antennae into ex vivo brain tissue. NMR images the 3D thermal dynamics inside ex vivo bovine brain tissue and equivalent gel under exposure to power and irradiation time-varying radio frequency (RF) fields. The absorbed RF energy in brain tissue converts into Joule heat and affects the nuclear magnetic shielding and the Larmor precession. The resultant temperature increase is measured by the resonance frequency shift of hydrogen protons in brain tissue. This proposed application of NMR thermometry offers sufficient spatial and temporal resolution to characterize the hot spots from absorbed cell phone radiation in aqueous media and biological tissues. Specific absorption rate measurements averaged over 1 mg and 10 s in the brain tissue cover the total absorption volume. Reference measurements with fiber optic temperature sensors confirm the accuracy of the NMR thermometry. <s> BIB005 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> C. Recent Proposal on EMF Exposure Measurement Methodology <s> Radiofrequency (RF) emitting wireless devices such as mobile phones are required to undergo standardized safety testing prior to entering the consumer market. Strict regulations are imposed on the amount of RF energy these devices are allowed to emit to prevent excessive deposition of RF energy into the body. In this work, a novel safety evaluation test for wireless devices using magnetic resonance thermometry is proposed. <s> BIB006 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> C. Recent Proposal on EMF Exposure Measurement Methodology <s> In this paper, we present the novel design features, their technical implementation, and an evaluation of the radio frequency exposure systems developed for the National Toxicology Program (NTP) of the National Institute of Environmental Health Sciences studies on the potential toxicity and carcinogenicity of second and third generation mobile-phone signals. The system requirements for this second-year NTP cancer bioassay study were the tightly controlled lifetime exposure of rodents (1568 rats and 1512 mice) to three power levels plus sham simulating typical daily, and higher, exposures of users of GSM and CDMA (IS95) signals. Reverberation chambers and animal housing were designed to allow extended exposure time per day for free-roaming individually housed animals. The performance of the chamber was characterized in terms of homogeneity, stirred to unstirred energy and efficiency. The achieved homogeneity was 0.59 and 0.48 dB at 900 and 1900 MHz, respectively. The temporal variation in the electric field strength was optimized to give similar characteristics to that of the power control of a phone in a real network using the two stirrers. Experimental dosimetry was performed to validate the SAR sensitivity and determine the SAR uniformity throughout the exposure volume; SAR uniformities of 0.46 and 0.40 dB, respectively, for rats and mice were achieved. <s> BIB007
In order to address the aforementioned issues on the current SAR measurement methodology, recent studies have proposed alternative approaches to assess the human EMF exposure. 1) Temperature Measurement: In addition to the electric field probe dosimetry systems, a temperature-based dosimetry system was proposed using an array of optical fiber thermal sensors positioned inside a phantom, showing good agreement with electric field probe measurements BIB002 . However, spatial resolution has been limited because of the large number of temperature probes that need to be positioned inside the phantom invasively. Recently, it has been shown that magnetic resonance imaging (MRI) temperature mapping has been used to quantify EMF energy deposition induced by MRI coils BIB003 - BIB004 and other antennas BIB005 BIB006 , where both radio frequency (RF) heating and temperature mapping were conducted inside the bore of the MRI scanner. 2) Chronic Exposure: The National Toxicology Program (NTP) BIB001 of the National Institute of Environmental Health Sciences (NIEHS) defines a cancer bioassay as "exposure of laboratory animals to a chemical, biological, or physical agent for at least 2 years." The NTP test also requires that the exposure level be practically constant over the lifetime of the subjects and that the animals be free to move within the individual cages. A recent work BIB007 presented results of tests in a room-size exposure chamber capable of housing a large number of rodents for an NTP assessment of the toxicity and carcinogenicity of RF signals emitted from widely used cell phones.