摘要:

A microwave heating technique, a direct parallel to the parallel‐opposed treatment field that is used in therapeutic ionizing radiation, has been developed. The sources of radiation are two oppositely directed TEM applicators that operate at 2450 MHz. The applicator's design consists of an open‐ended rectangular waveguide that is partially loaded with low‐loss dielectric slabs. Such a structure can support a TEM mode of propagation. On direct contact with a tissue‐equivalent slab, the TEM applicator heats uniformly in the transverse plane. Exposed C3H mouse tumors, 1 cm in diameter and transplanted to grow on the flank of mice, were encapsulated within simulated phantom materials with dielectric properties that are similar to that of the tumor to form a rectangular slab. The TEM applicators were used to heat from opposite sides at alternating intervals of 5 to 50 seconds. The technique is capable of producing a uniform temperature of 42 (±0.25) °C over the ent

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00081

年代:1977

数据来源: WILEY

摘要:

A system was developed for exposing a sample of cells in a culture medium for short periods to broadband electromagnetic energy under controlled conditions of field and temperature. The system can produce a reasonably uniform electric field of strengths to 100 V/cm in a 5‐ml sample; the system has a continuously controllable input power to 600 W and a frequency range from dc to 100 MHz and beyond. Control of the sample's temperature over a wide range is achieved through a high‐rate, circulating‐liquid heat exchanger. The cooling capacity is sufficient to maintain one of a wide range of steady‐state temperatures during exposure of the sample to a CW field of strength in excess of 20 V/cm. Accurate monitoring of the sample's temperature at frequencies below 100 MHz is achieved during exposures through on‐line measurement of feedline impedance. Nonperturbing thermal measurement of sample can be made at all frequencies by a Teflon‐insulated sensor of spe

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00087

年代:1977

数据来源: WILEY

摘要:

A longitudinal‐shunt slot array with reflectors has been designed, built, and tested. The antenna is easily matched near the design frequency. The radiation pattern has an intensity within ±0.5 dB over a total angle of 15.6° in theHplane and 15.5° in theEplane. Gain is 19.7 dB which is 3.9 dB above that of a horn with a similar work area. By using energy‐absorbing material, it is possible to produce a pattern in which the fields drop suddenly from the nearly constant values to nearl

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00097

年代:1977

数据来源: WILEY

摘要:

Development of a system for exposing nonhuman primates of sizes to and including stumptail macaques (Macaca arctoides) at 2.45 GHz for long periods without constraining the animals (except for cage confinement) is described. The exposure chamber is a multimode mode‐stirred cubical microwave cavity of edge length about 90 cm internally; within the cavity is a dielectric cage sufficiently large to house a 15‐kg primate. The cavity is excited by a Type 2M53 magnetron. Radiopaque windows are provided for viewing and ventilation. Forward and reflected powers are measured with calibrated diode detectors in a bidirectional coupler between the magnetron and the cavity. Power values are set by phase‐angle selection and are held constant by detector‐output feedback to a thyristor control circuit. Containers of saline were used as phantoms, i.e., as first approximations to the RF loads presented by monkeys. Calorimetric measurements were made to determine energy absorption values for various quantities and spatial distributions of saline. The results indicate that the dose rate at any given input power is insensitive to phantom location (indicative of isotropy) and is inversely related to the mass of saline within. After the development of the prototype, 12 units were constructed for concurrent chronic irradiation of two squirrel monkeys in each module. A summary is presented of calorimetric measurements on saline‐containing dolls serving as phantoms; these measurements were performed to determine net values of RF input power into a cavity unit that are thermally equivalent to specified power‐density values of plane‐wave irradiation for the same duratio

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00103

年代:1977

数据来源: WILEY

摘要:

Heating patterns, induced in planar and limb phantoms of simulated fat and muscle tissue by large and by small, direct‐contact microwave diathermy applicators operating at 2.45 GHz, were studied. Teflon slab‐loaded rectangular waveguides, circularly polarized horns, and other large radiators were investigated as well as the only two low‐power direct‐contact emitters presently in noninvasive clinical use. The integrity of temperature measurements by a thermographic camera was established and probe thermometry was used to compare polyethelene with a silk screen as the midplane phantom film. The width and depth of penetration of microwave heating were determined to evaluate energy deposition inside simulated muscle tissue. The results of temperature profiles show that a Teflon slab‐loaded rectangular waveguide and a circularly polarized horn provide uniform heating in the center of the phantom's midplane and that the focusing effects of limb phantoms enhance depth of penetration. Measurements of the electric field demonstrated that direct‐contact applicators can be designed to maintain leakage levels below 5 mW/cm2per 100 watts of forward power for large applicators, and below 5 mW/cm2per 10 watts of forward power for small applicators at a distance of 5 cm. Leakage of a circular aperture horn can be minimized with an output f

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00111

年代:1977

数据来源: WILEY

摘要:

Conventional metal electrodes as used to record electrophysiological events are likely to introduce artifactual stimulation and spurious signals when the preparation to which they are attached or in which they are implanted is exposed to electromagnetic (EM) fields of high frequency. To combat these artifacts, electrodes of high linear resistance (>100 kΩ/m) were devised for use in chronic and in acute experiments. The electrodes minimize diffractive problems and control for artifactual stimulation by eliminating spurious currents at the junction between the electrode tip and the biological preparation. Contamination of amplifier‐recording circuits by demodulation artifact is prevented by proper filtrati

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00121

年代:1977

数据来源: WILEY

摘要:

Thirty‐six neonatal rats were exposed daily at a power density of zero or 40 mW/cm2to 2450‐MHz CW radiation for five minutes from day one through day six ofpostpartumlife. On day seven, control and experimental rats either were euthanized, were exposed to sham or microwave radiation for a seventh time, or were injected with ACTH. The two treated groups of pups were euthanized 20 minutes after the final exposure or injection. Trunk blood and adrenal glands were saved. No difference was found in concentration of plasma corticosterone between exposed rats and controls. Basal plasma concentration of corticosterone was less than 2 μg% in both groups. Following either microwave exposure or injection of ACTH on day seven, levels of plasma corticosterone remained low (<3 μg%) both in radiated and in control animals but were significantly higher in the former (2.08 μg% ±0.85 SD) as compared with the latter (0.72 μg% ±0.60 SD). A statistically significant increase in the wet mass of adrenal glands was noted in animals that were exposed to microwaves during the first six postnatal days. The cause and the biological significance of this enlargement are unknown. Because the first two to three weeks of postnatal life are critical in the development of the rat, the effects of exposure to microwave radiation during this period may be readily manifested at this time or at a later stag

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00125

年代:1977

数据来源: WILEY

摘要:

Controversy exists over thermal versus nonthermal biological effects of microwave radiation. Rectal measurements of temperature, which are often used as indicators of thermal stress, may not be sufficiently reliable. In this investigation, the oxygen‐consumption rate was used as a biological indicator of thermal stress from microwave radiation. Male CFI mice were irradiated with 2450‐MHz CW microwave energy in a waveguide at forward power levels of 0 (sham), 0.09, 0.3, 0.6, 1.7, and 3.3 W, which resulted in corresponding averaged dose rates of 0, 1.6, 5.5, 10.4, 23.6, and 44.3 mW/g. The environmental conditions were: temperature 24 °C, relative humidity 55% and rate of air flow 78 ml/min. The rate of oxygen consumption of the mouse was determined for successive 5‐minute periods by means of a paramagnetic oxygen analyzer, before, during, and after irradiation. Each of the stages lasted for 30 minutes. Across time, there was a reduction of oxygen consumption which correlated with a reduction in the averaged rate of energy absorption. The rate of oxygen consumption also decreased across time when the dose rate did not exceed 10.4 mW/g. The mouse apparently compensates homeostatically for large doses of microwave radiation by adjusting its metabolic rate downward to compensate for thermal loading from the radiation. Rebound of metabolic activity occurred after irrad

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00131

年代:1977

数据来源: WILEY

摘要:

Eight male rats were exposed for 13 weeks to 918‐MHz CW microwaves at an averaged power density of 2.5 mW/cm2. The rats were exposed ten hours every night for a total of 910 hours of irradiation. The exposure system consisted of (1) cylindrical waveguides that were capable of delivering guided, circularly polarized waves (TE11mode); and (2) Plexiglas living chambers that provided standard laboratory conditions for the rodents. The waveguides allowed for easy quantification of incident and absorbed energy in each chamber independent of the number of rodents being simultaneously exposed. Daily measures of body mass and of intake of food and water revealed no significant differences between the eight irradiated and the eight sham‐irradiated controls. Blood sampled after 4, 8, and 12 weeks showed no differences in most parameters of serum chemistry (e.g., calcium, sodium, potassium, chlorine, blood urea nitrogen, carbon dioxide, ion gap and glucose). During the 11th week, serial assessments were made of colonic temperature and behavioral repertoire but neither demonstrated a significant effect of the microwave exposures. Serum corticosterone levels sampled after 910 hours of radiation gave no indication of stress. Finally, neither one‐ nor two‐bottle preference tests for a saccharin solution suggested the presence of radiation‐related malaise. The significance of these results is discussed with respect to comparable exposures of rats to 10 mW/cm2, which do influence several of the assessed p

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00139

年代:1977

数据来源: WILEY

摘要:

Eighty‐six male Long‐Evans rats, 63–64 days of age, were subjected to 2450‐MHz CW microwave irradiation after a two‐week “gentling” procedure and three daily sessions of sham exposure. Exposures occurred without anesthesia at power densities of 0, 1, 5, 10, or 20 mW/cm2for 1, 2, 4, or 8 hours. Rectal temperatures of exposed rats were found to be higher than those of sham‐irradiated rats at power densities of 1 mW/cm2for four hours, 5 mW/cm2for one and two hours, 10 mW/cm2for two and four hours, and 20 mW/cm2for all of the durations of exposure. Circadian rhythmicity of rectal temperature was noted in sham‐irradiated rats. Except for rats exposed at 20 mW/cm2for four and eight hours, none of the averaged rectal temperatures of exposed groups reliably exceeded those of sham‐irradiated rats after eight hours of exposure. We concluded that the effect of exposure to microwaves at power densities below 10 mW/cm2accelerated the appearance of the peak rectal temperature to an earlier time of day. Serum corticosteroid (CS) levels were signficantly lower in rats exposed at 20 mW/cm2for eight hours than in animals sham exposed for the same duration. A significant correlation between rectal temperature and CS level was observed in the sham‐irradiated rats. Certain combinations of duration of exposure and power density of incident energy could dissociate this relationship, i.e., temperature increased sometimes without corresponding elevation of CS level. Serum thyroxine levels were depressed in rats exposed to radiation at 20 mW/cm2for four or for eight hours. A stimulatory effect of microwaves on thyroid function was noted in rats exposed at 1 mW/cm2for four hours, but the effect was transitory. Levels of growth h

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00147

年代:1977

数据来源: WILEY