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Rabbit polymorphonuclear leucocytes (PMN, neutrophils) obtained from peritoneal exudate were exposed in vitro for one-half or one hour to continuous wave or amplitude-modulated (20-Hz) 100-MHz RF radiation in a temperature-controlled coaxial exposure chamber at field strengths from 2.5 to 4.1 V/cm (SARs of 120 to 341 W/kg). RF exposure at 37 +/- 0.2 degrees C had no detectable effect on PMN viability or phagocytosis compared to sham-exposed cells simultaneously subjected to the same time-temperature regime. Temperature control studies indicated that at 37 degrees C no effect on PMN viability would be expected but phagocytosis would be reduced by approximately 6%/degrees C temperature increase. The absence of an effect of RF exposure suggests that there was minimal undetected intrasample heating and that phagocytosis was not affected by 100-MHz RF radiation under the conditions of this study.

Studies were conducted utilizing improved methodology that examined the effects of radio-frequency (RF) radiation on heart rate (HR), deep body temperature (Tco), and electrocardiographic (ECG) waveform parameters in anesthetized rats. One group of animals was exposed to two power levels of continuous-wave RF radiation averaging 1.0 and 7.4 W/kg at a frequency of 600 MHz. A second group of animals, treated identically but not exposed to RF radiation, served as a control. The electrodes used for monitoring the ECG during RF exposure were fabricated from carbon-loaded Teflon wire, a semiconductor material that does not perturb the RF field. Analyses of the ECG were conducted by use of a recently developed computer-assisted procedure that quantitates HR and waveform intervals over 25-40 individual ECG complexes. There were no artifacts or arrhythmias in the ECGs of the animals exposed to RF radiation. There was a significant linear correlation between HR and Tco in the RF-exposed group that was not present in the control group.

Superficial- and deep-tissue heating was measured in five dogs during high-specific-absorption-rate radiofrequency (RF) irradiation to see whether significant temperature changes could be produced by a 1.5-T clinical magnetic resonance imager. The RF power output employed was 6.3 times that required for routine imaging. Temperature probes were placed in both deep and superficial tissues, and temperatures were recorded before, during, and after exposure. In each dog, there was a linear temperature increase of several degrees during RF exposure; the maximal average change was 4.6 degrees C in the urinary bladder. The temperature increase was slightly greater in deep tissues than in superficial tissues. The calculated specific absorption rate, based on the temperature change, averaged 7.9 W/kg for all five dogs. These findings argue for continued caution in the design and operation of imagers capable of high specific absorption rates, particularly when they are used for imaging infants or patients with altered thermoregulatory capability.

A previous study showed a substantial increase in the colonic temperature of rhesus monkeys (Macaca mulatta) exposed to radiofrequency (RF) fields at a frequency near whole-body resonance and specific absorption rates (SAR) of 2-3 W/kg. The present experiments were conducted to determine the metabolic and vasomotor responses during exposures to similar RF fields. We exposed five adult male rhesus monkeys to 225 MHz radiation (E orientation) in an anechoic chamber. Oxygen consumption and carbon dioxide production were measured before, during, and after RF exposure. Colonic, tail and leg skin temperatures were continuously monitored with RF-nonperturbing probes. The monkeys were irradiated at two carefully-controlled ambient temperatures, either cool (20 degrees C) or thermoneutral (26 degrees C). Power densities ranged from 0 (sham) to 10.0 mW/cm2 with an average whole-body SAR of 0.285 (W/kg)/(mW/cm2). We used two experimental protocols, each of which began with a 120-min pre-exposure equilibration period. One protocol involved repetitive 10-min RF exposures at successively higher power densities with a recovery period between exposures. In the second protocol, a 120-min RF exposure permitted the measurement of steady-state thermoregulatory responses. Metabolic and vasomotor adjustments in the rhesus monkey exposed to 225 MHz occurred during brief or sustained exposures at SARsmore » at or above 1.4 W/kg. The SAR required to produce a given response varied with ambient temperature. Metabolic and vasomotor responses were coordinated effectively to produce a stable deep body temperature. The results show that the thermoregulatory response of the rhesus monkey to an RF exposure at a resonant frequency limits storage of heat in the body. However, substantial increases in colonic temperature were not prevented by such responses, even in a cool environment.« less

The study is designed to simulate the chronic exposure of man to 450-MHz radio-frequency (RF) radiation at an incident power density of 1 mW/cm2. This paper presents a plan for conducting a lifetime exposure study involving two phases of work. The first phase, up to March 1980, is being spent in preparation for the chronic study. During the second phase, 200 rats, 100 experimental and 100 control, will be exposed 22 h/day over their lifetime to pulse-modulated 2450- MHz RF fields at an incident power density less than 500 µW/cm2. The state of health of each animal will be assessed periodically throughout the exposure period until the death of the animal. Blood chemistry parameters, mortality rates, histopathology, body weight, and water and food consumption will be the biological endpoints of this study. The modulation consists of 16 pulse groups/s (25 pulses/group) with a pulse duration of 10 µs and a period of 500µs.

Four experiments were performed in which six pregnant rats were exposed from day 12 of pregnancy to parturition, for 4 hours a day in a temperature-controlled environment, to 425-MHz (CW) radiation, using a multimode rectangular strip transmission line. Four male pups born to each dam were subsequently irradiated under the same RF exposure condition for 20-21 days of age (2 pups) and 40-41 days of age (2 pups). Specific absorption rates (SARs) for rats of different ages were determined by twin-well calorimetry as well as from calculations of power measurements of incident, reflected, and transmitted energy. Values of SARs between 3.1 and 6.7 mW/g were obtained for rats so exposed at 425 MHz. At selected times, rats were weighed to determine if the irradiation affected growth. Two rats from each litter (4 pups) were euthanized at 20-21 and two at 40-41 days of age and blood was obtained for complete blood counts. The in vitro blastogenic response of blood and lymph-node lymphocytes was measured by 3H-thymidine incorporation into DNA following stimulation of cells with T- or B-lymphocyte mitogens. No difference was observed in the weights of irradiated compared with sham-irradiated rats. No consistent change in the peripheral blood picture was observed between irradiated and sham-irradiated rats. Significant increases in the response of lymph-node but not of blood lymphocytes from irradiated rats following stimulation with mitogens was observed in two of four experiments. These changes were observed for both T- and B-lymphocytes. In another experiment at the same frequency, six pregnant rats were irradiated for 16 hours daily from day 6 through day 19 of pregnancy. The pups born to these dams were not subsequently irradiated. These rats, born to irradiated dams, showed a similar increased response of node but not of blood lymphocytes to T-cell mitogens at 42 days of age. These results indicate that exposure to 425-MHz microwave radiation, under the conditions described, may lead to increased responsiveness of node lymphocytes to in vitro stimulation by mitogen.

A continuously recording exposure meter has been developed for radio-frequency (RF) hazard measurements in FM/TV broadcasting towers for the frequency range 47-790 MHz. The instrument consists of an electrically-small dipole, loop probes and recording electronics. The dipole and loop are attached to the safety helmet; their distance from the head is approximately 7 cm. The dipole and loop respond to the tangential E field and radial H field, respectively. The error due to body proximity and one-dimensionality is 1 to 2 dB at 100 MHz and 2 to 3 dB at 200 MHz (for average power density measurements) if the probes move continuously and the measurement period is sufficiently long. Measurements in Finnish FM/TV towers showed that the average power density inside the tower increases with increasing power and decreasing antenna surface area. The highest levels have been found near UHF and FM antennas. For the FM band (100 MHz) the average H field exposures exceed the new ANSI standard value 10 W/m2, but remain in most cases below 100 W/m2. Local maxima may exceed 300 W/m2.

This paper presents the results of an environmental investigation in a plastic-ware industry using RF sealers. Environmental measurements have demonstrated the presence of strong electric fields the intensity of which: (1) reaches significant levels from the health-protection point of view only in proximity to the applicators; (2) often exceeds the maximal levels allowed by all standards (including the most permissive) for short duration exposures, especially in the region of the hands. Results of a cross-sectional study on the health of 63 female workers are related to the observed RF exposure. A statistically significant correlation was found to exist between RF exposure and some minor health effects—eye irritation, upper limb paresthesias, and vitreous body disorganization.

A number of retrospective studies have been done on human populations exposed or believed to have been exposed to RF/MW energies. There have been a few epidemiological studies of MW/RF exposure but these have generally been limited in scope (Silverman, 1979, 1980). Persons exposed while assigned to the military services or occupationally exposed in industrial settings have been the principal groups studied. A few other populations living or working near generating sources or exposed to medical diathermy have been or are being investigated (Silverman, 1979, 1980; Bureau of Radiological Health, 1980; Ruggera, 1980). Information about health status has come from medical records, questionnaires, physical and laboratory examination, and vital statistics. Sources of exposure data include personnel records, questionnaires, environmental measurements, equipment emission measurements, and (assumed adherence to) established exposure limits. Although there have been advances in measurement, microwave dosimetry still presents formidable problems for meaningful assessment in most epidemiological studies (Roberts and Michaelson, 1985; Silverman, 1979, 1980).

Purpose To compare a novel combined acquisition technique (CAT) of turbo-spin-echo (TSE) and echo-planar-imaging (EPI) with conventional TSE. CAT reduces the electromagnetic energy load transmitted for spin excitation. This radiofrequency (RF) burden is limited by the specific absorption rate (SAR) for patient safety. SAR limits restrict high-field MRI applications, in particular. Material and Methods The study was approved by the local Medical Ethics Committee. Written informed consent was obtained from all participants. T2- and PD-weighted brain images of n = 40 Multiple Sclerosis (MS) patients were acquired by CAT and TSE at 3 Tesla. Lesions were recorded by two blinded, board-certificated neuroradiologists. Diagnostic equivalence of CAT and TSE to detect MS lesions was evaluated along with their SAR, sound pressure level (SPL) and sensations of acoustic noise, heating, vibration and peripheral nerve stimulation. Results Every MS lesion revealed on TSE was detected by CAT according to both raters (Cohen’s kappa of within-rater/across-CAT/TSE lesion detection κCAT = 1.00, at an inter-rater lesion detection agreement of κLES = 0.82). CAT reduced the SAR burden significantly compared to TSE (p