Biomedical subjects

E G Moros

Publications and source records attributed to E G Moros.

At least 19 recordsLinked to original sources

PubMed2006

Gene expression does not change significantly in C3H 10T(1/2) cells after exposure to 847.74 CDMA or 835.62 FDMA radiofrequency radiation.

In vitro experiments with C3H 10T(1/2) mouse cells were performed to determine whether Frequency Division Multiple Access (FDMA) or Code Division Multiple Access (CDMA) modulated radiofrequency (RF) radiations induce changes in gene expression. After the cells were exposed to either modulation for 24 h at a specific absorption rate (SAR) of 5 W/ kg, RNA was extracted from both exposed and sham-exposed cells for gene expression analysis. As a positive control, cells were exposed to 0.68 Gy of X rays and gene expression was evaluated 4 h after exposure. Gene expression was evaluated using the Affymetrix U74Av2 GeneChip to detect changes in mRNA levels. Each exposure condition was repeated three times. The GeneChip data were analyzed using a two-tailed t test, and the expected number of false positives was estimated from t tests on 20 permutations of the six sham RF-field-exposed samples. For the X-ray-treated samples, there were more than 90 probe sets with expression changes greater than 1.3-fold beyond the number of expected false positives. Approximately one-third of these genes had previously been reported in the literature as being responsive to radiation. In contrast, for both CDMA and FDMA radiation, the number of probe sets with an expression change greater than 1.3-fold was less than or equal to the expected number of false positives. Thus the 24-h exposures to FDMA or CDMA RF radiation at 5 W/kg had no statistically significant effect on gene expression.

Animals↗

PubMed2005

Experience with a small animal hyperthermia ultrasound system (SAHUS): report on 83 tumours.

An external local ultrasound (US) system was developed to induce controlled hyperthermia of subcutaneously implanted tumours in small animals (e.g., mice and rats). It was designed to be compatible with a small animal positron emission tomography scanner (microPET) to facilitate studies of hyperthermia-induced tumour re-oxygenation using a PET radiopharmaceutical, but it is applicable for any small animal study requiring controlled heating. The system consists of an acrylic applicator bed with up to four independent 5 MHz planar disc US transducers of 1 cm in diameter, a four-channel radiofrequency (RF) generator, a multiple thermocouple thermometry unit, and a personal computer with custom monitoring and controlling software. Although the system presented here was developed to target tumours of up to 1 cm in diameter, the applicator design allows for different piezoelectric transducers to be exchanged and operated within the 3.5-6.5 MHz band to target different tumour sizes. Temperature feedback control software was developed on the basis of a proportional-integral-derivative (PID) approach when the measured temperatures were within a selectable temperature band about the target temperature. Outside this band, an on/off control action was applied. Perfused tissue-mimicking phantom experiments were performed to determine optimum controller gain constants, which were later employed successfully in animal experiments. The performance of the SAHUS (small animal hyperthermia ultrasound system) was tested using several tumour types grown in thighs of female nude (nu/nu) mice. To date, the system has successfully treated 83 tumours to target temperatures in the range of 41-43 degrees C for periods of 65 min on average.

Algorithms↗

PubMed2005

Localized versus regional hyperthermia: comparison of xenotransplants treated with a small animal ultrasound system and waterbath limb immersion.

The response of xenotransplants were compared with waterbath immersion vs focal ultrasound (US) hyperthermia using tumour growth delay, immunhistochemistry and histopathology assays. Waterbath hyperthermia was performed by limb immersion. Precautions were taken to minimize total body heating by surrounding the mouse with plastic insulators. Thermometry was performed with clinical-grade, 20-gauge needle thermocouples and monitored with a Labthermics unit. Significant differences in cytotoxicity between ultrasound and waterbath treatment of tumors at 43 degrees C were observed as determined by TUNNEL assay. Conversely, contralateral (non-treated) tumours in animals treated with similar temperature demonstrated no significant differences between modalities. Western blot analysis revealed increased hsp70 induction at 43 degrees C in waterbath vs focal ultrasound hyperthermia. Comparison of tumour growth delay between tumours heated with waterbath vs ultrasound at 43 degrees C but not at 41 degrees C revealed significant differences. This is the first study comparing localized vs regional hyperthermia using the small animal ultrasound system (SAHUS) delivery system. Consistent ultrasound hyperthermia can be achieved throughout a xenotransplant. At equivalent temperature of 43 degrees C for 60?min, waterbath hyperthermia demonstrated greater local response vs ultrasound hyperthermia.

Animals↗

PubMed2005

Non-invasive estimation of hyperthermia temperatures with ultrasound.

Ultrasound is an attractive modality for temperature monitoring because it is non-ionizing, convenient, inexpensive and has relatively simple signal processing requirements. This modality may be useful for temperature estimation if a temperature-dependent ultrasonic parameter can be identified, measured and calibrated. The most prominent methods for using ultrasound as a non-invasive thermometer exploit either (1) echo shifts due to changes in tissue thermal expansion and speed of sound (SOS), (2) variation in the attenuation coefficient or (3) change in backscattered energy from tissue inhomogeneities. The use of echo shifts has received the most attention in the last decade. By tracking scattering volumes and measuring the time shift of received echoes, investigators have been able to predict the temperature from a region of interest both theoretically and experimentally in phantoms, in isolated tissue regions in vitro and preliminary in vivo studies. A limitation of this method for general temperature monitoring is that prior knowledge of both SOS and thermal-expansion coefficients is necessary. Acoustic attenuation is dependent on temperature, but with significant changes occurring only at temperatures above 50 degrees C, which may lead to its use in thermal ablation therapies. Minimal change in attenuation, however, below this temperature range reduces its attractiveness for use in clinical hyperthermia. Models and measurements of the change in backscattered energy suggest that, over the clinical hyperthermia temperature range, changes in backscattered energy are dependent on the properties of individual scatterers or scattering regions. Calibration of the backscattered energy from different tissue regions is an important goal of this approach. All methods must be able to cope with motion of the image features on which temperature estimates are based. A crucial step in identifying a viable ultrasonic approach to temperature estimation is its performance during in vivo tests.

Animals↗

PubMed2004

MicroPET-compatible, small animal hyperthermia ultrasound system (SAHUS) for sustainable, collimated and controlled hyperthermia of subcutaneously implanted tumours.

An external ultrasound system was developed for the heating of subcutaneously implanted tumours in small animals. This small animal hyperthermia ultrasound system (SAHUS) was designed to be compatible with a microPET (small animal positron emission tomography) scanner to facilitate studies of hyperthermia effects on tumour hypoxia. Collimation and localization of energy deposition, a specific goal for the new device to avoid regional and/or systemic heating of small animals, was demonstrated using thermoradiography following high-power short-time heating of a layered gel phantom. The in vivo heating capabilities of the SAHUS were tested using PC3 cell line tumours (2000-2700 mm(3)) grown in the lateral proximal thighs of Nu-/Nu- nuBR nude mice. Intratumour temperatures were recorded during heating trials with deep and superficial interstitial thermocouples. The experimental data showed that the SAHUS could produce hyperthermia in 8 +/- 2 mm diameter tumours in small animals to a target temperature of 41.5 degrees C and maintain it within a narrow temperature range (+/- 0.3 degrees C) for up to 4 h without raising the core temperature of the animals. PET imaging studies, data to be published separately, were conducted before and during SAHUS-induced hyperthermia. Both devices performed as expected and there was no significant decrease in image quality. In this paper, the new SAHUS is described and data from phantom and in vivo experiments presented.

Acrylic Resins↗

PubMed2004

Modelling heat-induced radiosensitization: clinical implications.

Clinically achievable minimum tumour temperatures are in the order of about 41 degrees C. Therefore, it is important to evaluate mechanisms by which temperatures in this range might enhance cytotoxicity. Previous in vitro studies have demonstrated that 1-4 h (depending on the sequencing of modalities) of heating at 41 degrees C produces substantial heat-induced radiosensitization with little or no cell killing by heat alone. The increased radiation sensitivity is best modelled as a change in the single hit, alpha, parameter (with no significant effect on the two-hit parameter, beta) of the cell survival curve. The implications of heat-induced radiosensitization being mediated by a change in alpha on the traditional thermal enhancement ratio (for various radiation doses/fraction and alpha/beta) are reviewed. Response rates for a cohort of 60 patients enrolled on a prospective thermal dose escalation study are modelled assuming that the thermal dose dependence of heat-induced radiosensitization is modulated by a heat-induced delta alpha. The clinical data are fitted with delta alpha about 0.05-0.1 Gy-1. Randomized trials reported in the literature and the implication for the design of future prospective trials are reviewed in light of these observations.

Animals↗

PubMed2004

Transfection of human tumour cells with Mre11 siRNA and the increase in radiation sensitivity and the reduction in heat-induced radiosensitization.

Double-strand DNA breaks (DSBs) are potentially lethal DNA lesions induced by ionizing radiation. In eukaryotes, DSBs can be repaired by homologous recombination (HR) or non-homologous end-joining (NHEJ). DNA repair protein Mre11 participates in both the NHEJ and HR DNA repair pathways. Hyperthermia has been used clinically as a radiosensitizer. However, the mechanisms by which radiosensitization is induced by hyperthermia, especially moderate hyperthermia (41 degrees C) are not fully understood. Previous studies suggest that 41 degrees C reduces the nuclear Mre11 protein level in a manner that correlates with heat-induced changes in radiation sensitivity. Therefore, siRNA technology was used in the present study to reduce Mre11 gene expression to determine if reduced Mre11 protein levels induced radiosensitization and if such radiosensitization is similar to that induced by moderate hyperthermia. The results show that (1) the cellular level of the Mre11 protein was reduced about 60 +/- 18% by a 24-h treatment with siRNA. Results from the Mre11 protein turnover assay showed a half-life of 11.6 +/- 0.5 h for the Mre11 protein, which is consistent with reduction in protein level in 24 h after Mre11 siRNA treatment assuming a delay of 4-8 h to reduce RNA levels. After 48 h in siRNA, cellular Mre11 protein levels increased to approximately pretreatment levels. NSY cells were sensitized to ionizing radiation after 24 h of treatment with Mre11 siRNA. Two hours at 41 degrees C did not increase the radiation sensitivity of cells with a reduced Mre11 protein level following a 24-h siRNA treatment. These data support the conclusion that the DSB repair protein, Mre11, appears to be a target for radiosensitization by moderate hyperthermia.

Adenocarcinoma↗

PubMed2004

Measurement of DNA damage after acute exposure to pulsed-wave 2450 MHz microwaves in rat brain cells by two alkaline comet assay methods.

PURPOSE: To investigate the effect of 2450 MHz pulsed-wave microwaves on the induction of DNA damage in brain cells of exposed rats and to discover whether proteinase K is needed to detect DNA damage in the brain cells of rats exposed to 2450 MHz microwaves. MATERIALS AND METHODS: Sprague-Dawley rats were exposed to 2450 MHz pulsed-wave microwaves and sacrificed 4 h after a 2-h exposure. Rats irradiated whole-body with 1 Gy (137)Cs were included as positive controls. DNA damage was assayed by two variants of the alkaline comet assay on separate aliquots of the same cell preparation. RESULTS: Significant DNA damage was observed in the rat brain cells of rats exposed to gamma-rays using both versions of the alkaline comet assay independent of the presence or absence of proteinase K. However, neither version of the assay could detect any difference in comet length and/or normalized comet moment between sham- and 2450 MHz pulsed-wave microwave-exposed rats, regardless of the inclusion or omission of proteinase K in the comet assay. CONCLUSIONS: No DNA damage in brain cells was detected following exposure of rats to 2450 MHz microwaves pulsed-wave at a specific absorption rate of 1.2 W kg(-1) regardless of whether or not proteinase K was included in the assay. Thus, the results support the conclusion that low-level 2450 MHz pulsed-wave microwave exposures do not induce DNA damage detectable by the alkaline comet assay.

Animals↗

PubMed2004

Measurements of alkali-labile DNA damage and protein-DNA crosslinks after 2450 MHz microwave and low-dose gamma irradiation in vitro.

In vitro experiments were performed to determine whether 2450 MHz microwave radiation induces alkali-labile DNA damage and/or DNA-protein or DNA-DNA crosslinks in C3H 10T(1/2) cells. After a 2-h exposure to either 2450 MHz continuous-wave (CW) microwaves at an SAR of 1.9 W/kg or 1 mM cisplatinum (CDDP, a positive control for DNA crosslinks), C3H 10T(1/2) cells were irradiated with 4 Gy of gamma rays ((137)Cs). Immediately after gamma irradiation, the single-cell gel electrophoresis assay was performed to detect DNA damage. For each exposure condition, one set of samples was treated with proteinase K (1 mg/ml) to remove any possible DNA-protein crosslinks. To measure DNA-protein crosslinks independent of DNA-DNA crosslinks, we quantified the proteins that were recovered with DNA after microwave exposure, using CDDP and gamma irradiation, positive controls for DNA-protein crosslinks. Ionizing radiation (4 Gy) induced significant DNA damage. However, no DNA damage could be detected after exposure to 2450 MHz CW microwaves alone. The crosslinking agent CDDP significantly reduced both the comet length and the normalized comet moment in C3H 10T(1/2) cells irradiated with 4 Gy gamma rays. In contrast, 2450 MHz microwaves did not impede the DNA migration induced by gamma rays. When control cells were treated with proteinase K, both parameters increased in the absence of any DNA damage. However, no additional effect of proteinase K was seen in samples exposed to 2450 MHz microwaves or in samples treated with the combination of microwaves and radiation. On the other hand, proteinase K treatment was ineffective in restoring any migration of the DNA in cells pretreated with CDDP and irradiated with gamma rays. When DNA-protein crosslinks were specifically measured, we found no evidence for the induction of DNA-protein crosslinks or changes in amount of the protein associated with DNA by 2450 MHz CW microwave exposure. Thus 2-h exposures to 1.9 W/ kg of 2450 MHz CW microwaves did not induce measurable alkali-labile DNA damage or DNA-DNA or DNA-protein crosslinks.

Alkalies↗

PubMed2001

Energy deposition processes in biological tissue: nonthermal biohazards seem unlikely in the ultra-high frequency range.

The prospects of ultra high frequency (UHF, 300--3000 MHz) irradiation producing a nonthermal bioeffect are considered theoretically and found to be small. First, a general formula is derived within the framework of macroscopic electrodynamics for the specific absorption rate of microwaves in a biological tissue; this involves the complex Poynting vector, the mass density of the medium, the angular frequency of the electromagnetic field, and the three complex electromagnetic constitutive parameters of the medium. In the frequency ranges used for cellular telephony and personal communication systems, this model predicts that the chief physical loss mechanism will be ionic conduction, with increasingly important contributions from dielectric relaxation as the frequency rises. However, even in a magnetite unit cell within a magnetosome the deposition rate should not exceed 1/10 k(B)T per second. This supports previous arguments for the improbability of biological effects at UHF frequencies unless a mechanism can be found for accumulating energy over time and space and focussing it. Second, three possible nonthermal accumulation mechanisms are then considered and shown to be unlikely: (i) multiphoton absorption processes; (ii) direct electric field effects on ions; (iii) cooperative effects and/or coherent excitations. Finally, it is concluded that the rate of energy deposition from a typical field and within a typical tissue is so small as to make unlikely any significant nonthermal biological effect.

Biophysical Phenomena↗

PubMed2001

Micronuclei in the peripheral blood and bone marrow cells of rats exposed to 2450 MHz radiofrequency radiation.

PURPOSE: To determine the incidence of micronuclei in peripheral blood and bone marrow cells of rats exposed continuously for 24h to 2450 MHz continuous wave radiofrequency radiation (RFR) at an average whole-body specific absorption rate (SAR) of 12W/kg. MATERIALS AND METHODS: Eight adult male Sprague-Dawley rats were exposed to 2450 MHz RFR in circularly polarized waveguides. Eight sham-exposed rats were kept in similar waveguides without the transmission of RFR. Four rats were treated with mitomycin-C (MMC) and used as positive controls. All rats were necropsied 24h after the end of RFR and sham exposures, and after the 24h treatment with MMC. Peripheral blood and bone marrow smears were examined to determine the frequency of micronuclei (MN) in polychromatic erythrocytes (PCE). RESULTS: The results indicated that the incidence of MN/2000 PCE were not significantly different between RFR- and sham-exposed rats. The group mean frequencies of MN in the peripheral blood were 2.3+/-0.7 in RFR-exposed rats and 2.1+/-0.6 in sham-exposed rats. In bone marrow cells, the average MN incidence was 3.8+/-1.0 in RFR-exposed rats and 3.4+/-0.7 in sham-exposed rats. The corresponding values in positive control rats treated with MMC were 23.5+/-4.7 in the peripheral blood and 33.8+/-7.4 in bone marrow cells. CONCLUSION: There was no evidence for the induction of MN in peripheral blood and bone marrow cells of rats exposed for 24h to 2450 MHz continuous wave RFR at a whole body average SAR of 12 W/kg.

Animals↗

PubMed2001

Cytogenetic studies in human blood lymphocytes exposed in vitro to radiofrequency radiation at a cellular telephone frequency (835.62 MHz, FDMA).

Freshly collected peripheral blood samples from four healthy human volunteers were diluted with RPMI 1640 tissue culture medium and exposed in sterile T-75 tissue culture flasks in vitro for 24 h to 835.62 MHz radiofrequency (RF) radiation, a frequency employed for customer-to-base station transmission of cellular telephone communications. An analog signal was used, and the access technology was frequency division multiple access (FDMA, continuous wave). A nominal net forward power of 68 W was used, and the nominal power density at the center of the exposure flask was 860 W/m(2). The mean specific absorption rate in the exposure flask was 4.4 or 5.0 W/kg. Aliquots of diluted blood that were sham-exposed or exposed in vitro to an acute dose of 1.50 Gy of gamma radiation were used as negative or positive controls. Immediately after the exposures, the lymphocytes were stimulated with a mitogen, phytohemagglutinin, and cultured for 48 or 72 h to determine the extent of genetic damage, as assessed from the frequencies of chromosomal aberrations and micronuclei. The extent of alteration in the kinetics of cell proliferation was determined from the mitotic indices in 48-h cultures and from the incidence of binucleate cells in 72-h cultures. The data indicated no significant differences between RF-radiation- and sham-exposed lymphocytes with respect to mitotic indices, incidence of exchange aberrations, excess fragments, binucleate cells, and micronuclei. In contrast, the response of the lymphocytes exposed to gamma radiation was significantly different from both RF-radiation- and sham-exposed cells for all of these indices. Thus, under the experimental conditions tested, there is no evidence for the induction of chromosomal aberrations and micronuclei in human blood lymphocytes exposed in vitro for 24 h to 835.62 MHz RF radiation at SARs of 4.4 or 5.0 W/kg.

Adult↗

PubMed2001

Neoplastic transformation in C3H 10T(1/2) cells after exposure to 835.62 MHz FDMA and 847.74 MHz CDMA radiations.

The effect of radiofrequency (RF) radiation in the cellular phone communication range (835.62 MHz frequency division multiple access, FDMA; 847.74 MHz code division multiple access, CDMA) on neoplastic transformation frequency was measured using the in vitro C3H 10T(1/2) cell transformation assay system. To determine if 835.62 MHz FDMA or 847.74 MHz CDMA radiations have any genotoxic effects that induce neoplastic transformation, C3H 10T(1/2) cells were exposed at 37 degrees C to either of the above radiations [each at a specific absorption rate (SAR) of 0.6 W/kg] or sham-exposed at the same time for 7 days. After the culture medium was changed, the cultures were transferred to incubators and refed with fresh growth medium every 7 days. After 42 days, the cells were fixed and stained with Giemsa, and transformed foci were scored. To determine if exposure to 835.62 MHz FDMA or 847.74 MHz CDMA radiation has any epigenetic effects that can promote neoplastic transformation, cells were first exposed to 4.5 Gy of X rays to induce the transformation process and then exposed to the above radiations (SAR = 0.6 W/kg) in temperature-controlled irradiators with weekly refeeding for 42 days. After both the 7-day RF exposure and the 42-day RF exposure after X irradiation, no statistically significant differences in the transformation frequencies were observed between incubator controls, the sham-exposed (maintained in irradiators without power to the antenna), and the 835.62 MHz FDMA or 847.74 MHz CDMA-exposed groups.

Animals↗

PubMed2001

Measurement of DNA damage in mammalian cells exposed in vitro to radiofrequency fields at SARs of 3-5 W/kg.

In the present study, we determined whether exposure of mammalian cells to 3.2-5.1 W/kg specific absorption rate (SAR) radiofrequency fields could induce DNA damage in murine C3H 10T(1/2) fibroblasts. Cell cultures were exposed to 847.74 MHz code-division multiple access (CDMA) and 835.62 frequency-division multiple access (FDMA) modulated radiations in radial transmission line (RTL) irradiators in which the temperature was regulated to 37.0 +/- 0.3 degrees C. Using the alkaline comet assay to measure DNA damage, we found no statistically significant differences in either comet moment or comet length between sham-exposed cells and those exposed for 2, 4 or 24 h to CDMA or FDMA radiations in either exponentially growing or plateau-phase cells. Further, a 4-h incubation after the 2-h exposure resulted in no significant changes in comet moment or comet length. Our results show that exposure of cultured C3H 10T(1/2) cells at 37 degrees C CDMA or FDMA at SAR values of up to 5.1 W/kg did not induce measurable DNA damage.

Animals↗

PubMed2001

Chromosome damage and micronucleus formation in human blood lymphocytes exposed in vitro to radiofrequency radiation at a cellular telephone frequency (847.74 MHz, CDMA).

Peripheral blood samples collected from four healthy nonsmoking human volunteers were diluted with tissue culture medium and exposed in vitro for 24 h to 847.74 MHz radiofrequency (RF) radiation (continuous wave), a frequency employed for cellular telephone communications. A code division multiple access (CDMA) technology was used with a nominal net forward power of 75 W and a nominal power density of 950 W/m(2) (95 mW/cm(2)). The mean specific absorption rate (SAR) was 4.9 or 5.5 W/kg. Blood aliquots that were sham-exposed or exposed in vitro to an acute dose of 1.5 Gy of gamma radiation were included in the study as controls. The temperatures of the medium during RF-radiation and sham exposures in the Radial Transmission Line facility were controlled at 37 +/- 0.3 degrees C. Immediately after the exposures, lymphocytes were cultured at 37 +/- 1 degrees C for 48 or 72 h. The extent of genetic damage was assessed from the incidence of chromosome aberrations and micronuclei. The kinetics of cell proliferation was determined from the mitotic indices in 48-h cultures and from the incidence of binucleate cells in 72-h cultures. The data indicated no significant differences between RF-radiation-exposed and sham-exposed lymphocytes with respect to mitotic indices, frequencies of exchange aberrations, excess fragments, binucleate cells, and micronuclei. The response of gamma-irradiated lymphocytes was significantly different from that of both RF-radiation-exposed and sham-exposed cells for all of these indices. Thus there was no evidence for induction of chromosome aberrations and micronuclei in human blood lymphocytes exposed in vitro for 24 h to 847.74 MHz RF radiation (CDMA) at SARs of 4.9 or 5.5 W/kg.

Adult↗

PubMed2001

Radiofrequency electromagnetic fields do not alter the cell cycle progression of C3H 10T and U87MG cells.

The effects of exposure to radiofrequency electromagnetic fields (RF EMFs) on cell cycle progression of mouse fibroblasts C3H 10T(1/2) and human glioma U87MG cells were determined by the flow cytometric bromodeoxyuridine pulse-chase method. Cells were exposed to a frequency-modulated continuous wave at 835.62 MHz or a code division multiple access RF EMF centered on 847.74 MHz at an average specific absorption rate of 0.6 W/kg. Five cell cycle parameters, including the transit of cells through G(1), G(2) and S phase and the probability of cell division, were examined immediately after the cells were placed in the fields or after they had been kept in the fields for up to 100 h. The only significant change observed in the study was that associated with C3H 10T(1/2) cell cultures moving into plateau phase toward the later times in the long-exposure experiment. No changes in the cell cycle parameters were observed in cells exposed to either mode of RF EMFs when compared to sham-exposed cells in either of the cell lines studied during the entire experimental period. The results show that exposure to RF EMFs, at the frequencies and power tested, does not have any effect on cell progression in vitro.

Animals↗

PubMed2000

Experimental and numerical determination of SAR distributions within culture flasks in a dielectric loaded radial transmission line.

The effect of dielectric loading on the cell layer specific absorption rate (SAR) within a T-75 culture flask being irradiated within a transverse electromagnetic (TEM) cell was studied both experimentally and numerically. Direct thermal measurements of a T-75 containing 40 mL of culture medium and resting upon a 3-mm-thick slab of alumina ceramic (epsilon r = 9.6) revealed that, compared to the same flask resting upon a foam slab (epsilon r = 1.0) of the same thickness, the average SAR at the cell layer was increased roughly fourfold. This fourfold increase is significant experimentally because it allows biologists to perform experiments over a larger range of SAR values needed to determine possible dose-response curves without the costs and difficulties of a fourfold increase in amplifier power. Finite-difference time-domain (FDTD) simulations of the SAR distribution were in good quantitative agreement with the experimental measurements. It is concluded that FDTD modeling can be a cost effective and scientifically acceptable means of obviating the thermal measurement of SAR.

Absorption↗

PubMed1999

The radial transmission line as a broad-band shielded exposure system for microwave irradiation of large numbers of culture flasks.

The problem of simultaneously exposing large numbers of culture flasks at nominally equivalent incident power densities and with good thermal control is considered, and the radial transmission line (RTL) is proposed as a solution. The electromagnetic design of this structure is discussed, and an extensively bench-tested realization is described. Referred to 1 W of net forward power, the following specific absorption rate (SAR) data were obtained: at 835.62 MHz, 16.0+/-2.5 mW/kg (mean+/-SD) with range (11-22); at 2450 MHz, 245+/-50 mW/kg with range (130-323). Radio-frequency interference from an RTL driven at roughly 100 W is so low as to be compatible with a cellular base station only 500 m distant. To avoid potential confounding by temperature differences among as many as 144 T-75 flasks distributed over 9 RTLs (six irradiates and three shams), temperature within all flasks was controlled to 37.0+/-0.3 degrees C. Experience with over two years of trouble-free operation suggests that the RTL offers a robust, logistically friendly, and environmentally satisfactory solution to the problem of large-scale in vitro experiments in bioelectromagnetics.

Absorption↗