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PubMedDate not supplied

A new method for thermal dosimetry in microwave hyperthermia using microwave radiometry for temperature control.

Microwave radiometry has been used during the last few years in some clinical centres (Lille, Freiburg, Strasbourg, Brussels) for the non-invasive control of temperature during microwave hyperthermia. The principal objective of this paper is to present an atraumatic thermal dosimetry system based on numerical simulations of hyperthermia and radiometric temperature measurements for TEM propagation. To gauge the feasibility and performance of the method, a one-dimensional model in a homogeneous medium is considered, neglecting the curvature of the tissue layer. The good correlation between the theoretical and experimental values obtained allowed the likely thermal profile on the probe axis to be computed using the dielectric and thermal properties of the medium and measurement of the radiometric and cutaneous temperatures.

Computer Simulation↗
PubMedDate not supplied

Non-invasive microwave multifrequency radiometry used in microwave hyperthermia for bidimensional reconstruction of temperature patterns.

Microwave radiometry, used routinely since 1984 for non-invasive temperature measurements during hyperthermia sessions for superficial tumours treatment has proven its efficiency for temperature control. From radiometric temperature measurements in two frequency ranges (around 1 and 3 GHz) and superficial (or cutaneous) temperature measurements achieved during hyperthermia sessions, a numerical method to obtain the two-dimensional thermal profile has been developed and implemented. This method is based on hyperthermia simulation from the bioheat equation, the absorbed microwave power calculation in the medium taking into account the radiative diagram of the applicator, and the calculation of radiometric temperatures. From these experimental measurements (radiometric and superficial temperatures, heating power, dielectric and thermal characteristics), a program to determine the bidimensional distribution of temperature during the hyperthermia session has been developed, tested and used during and after clinical treatments.

Biophysical Phenomena↗
PubMed2002

Determination of methylmercury and butyltin compounds in marine biota and sediments using microwave-assisted acid extraction, solid-phase microextraction, and gas chromatography with microwave-induced plasma atomic emission spectrometric detection.

A method is described for the determination of methylmercury and butyltin compounds in marine sediment and tissue using microwave-assisted acid extraction or digestion and solid-phase microextraction (SPME) followed by analysis using gas chromatography with microwave-induced plasma atomic emission spectrometric detection (GC-MIP-AES). Using the SPME-GC-MIP-AES method, enrichment factors for methylmercury and butyltin compounds of 50-100 were achieved, as compared to the typical hexane extraction, and measurements in marine tissue and sediment matrixes were possible at 1-2 microg/kg (methylmercury) and 10-100 ng/kg (butyltins). The SPME-GC-MIP-AES method was validated using several marine sediment and tissue matrix certified reference materials (CRMs) with certified values for methylmercury and butyltin compounds. The SPME-GC-MIP-AES method was used to measure methylmercury in four marine tissue CRMs ranging from oyster tissue at 13.0 +/- 1.0 microg/kg to fish tissue at 397 +/- 13 microg/kg (as Hg dry mass). Results from the SPME-GC-MIP-AES method were used in conjunction with results from other techniques to assign certified values for methylmercury in oyster, mussel, and fish tissue CRMs. Mono-, di-, and tributyltin were measured in three sediment CRMs at concentration levels of (0.08 +/- 0.03)-(0.35 +/- 0.05) mg/kg (as Sn dry mass).

Animals↗
PubMed2004

Fourier transform microwave spectroscopy and Fourier transform microwave-millimeter wave double resonance spectroscopy of the ClOO radical.

Pure rotational spectra of the ClOO radical for the (35)Cl and (37)Cl isotopomers have been observed using Fourier transform microwave and Fourier transform microwave-millimeter wave double resonance spectroscopy. The rotational, centrifugal, spin-rotation coupling, and hyperfine coupling constants have been determined by least-squares fits of the observed transition frequencies. The molecular constants indicate that the electronic ground state is 2A". The r(0) structure is determined to be r(0)(ClO)=2.075 A, r(0)(OO)=1.227 A, and theta;(0)(ClOO)=116.4 degrees . Several highly accurate ab initio calculations have also been performed. Some of them turned out to be inaccurate because it is necessary to take into account both static and dynamic electronic correlations. Only multireference (single and double) configuration interaction calculations with large basis sets reproduce the present experimental results. The anharmonic force constants obtained by the ab initio calculations are used to determine the r(e) structure, r(e)(ClO)=2.084(1) A, r(e)(OO)=1.206(2) A, and theta;(e)(ClOO)=115.4(1) degrees . Unique features of the ClOO radical have become clear by the present experiment and the ab initio calculations.

Journal Article↗
PubMed2003

Correlated adiabatic and isocurvature cosmic microwave background fluctuations in the wake of the results from the wilkinson microwave anisotropy probe.

In general correlated models, in addition to the usual adiabatic component with a spectral index n(ad1) there is another adiabatic component with a spectral index n(ad2) generated by entropy perturbation during inflation. We extend the analysis of a correlated mixture of adiabatic and isocurvature cosmic microwave background fluctuations of the Wilkinson Microwave Anisotropy Probe (WMAP) group, who set the two adiabatic spectral indices equal. Allowing n(ad1) and n(ad2) to vary independently we find that the WMAP data favor models where the two adiabatic components have opposite spectral tilts. Using the WMAP data only, the 2sigma upper bound for the isocurvature fraction f(iso) of the initial power spectrum at k(0)=0.05 Mpc(-1) increases somewhat, e.g., from 0.76 of n(ad2)=n(ad1) models to 0.84 with a prior n(iso)<1.84 for the isocurvature spectral index.

Journal Article↗
PubMed2005

Microwave assisted IMDAF# reaction: microwave irradiation applied with success to cycloaddition reaction of N-propargyl-N-p-tolyl-N-2-furfurylamines.

The new tertiary furfurylamine with triple bond as a dienophylic part i.e. N-(5-methyl-2-furfuryl)-N-prop-2-ynyl-p-toluidine (1) was prepared and the intramolecular Diels-Alder reaction of the amine (1) was performed under microwave irradiation conditions and by heating a benzene solution of the amine under nitrogen. Comparing the results of the usual thermal and the MAOS reaction, we confirmed our expectations that MAOS could promote the outcome of IMDA reaction of the suitably N-substituted tertiary 2-furfuryl-amines. In the present example, N-p-tolyl-5-methyl-5,7a-dihydro-5,7a-epoxyisoindoline was obtained in much better yield and of higher purity.

Cyclization↗
PubMed1985

In vitro studies of microwave-induced cataract: reciprocity between exposure duration and dose rate for pulsed microwaves.

Rat ocular lenses exposed to pulsed microwave irradiation were maintained at constant temperature by circulating phosphate buffered saline in a thermostatically-controlled chamber. Irradiations with pulsed radiation (10 musec, 24 kW pulses) of 918 MHz were done at several different specific absorption rates (SAR) for durations up to 1 hr in order to explore a possible reciprocal relationship. The extent of damage was measured by the maximum depth of granular degeneration in the equatorial region of lenses fixed immediately after irradiation. The parameters of the pulses were increased to 20 musec and 48 kW to explore the variation in the biological effects and threshold with respect to average power, as well as pulse parameters (pulse width, peak power and energy per pulse). A total of 47 lenses were used in 3 X 4 factorial experimental design to explore effects observed at different average powers and durations (6, 20 and 60 min). The results were statistically analyzed by ANOVA and multiple regression analysis with logarithmic transformation. The results are summarized as follows. This data showed clear trends towards increasing depth of granular degeneration with increasing duration of exposure and dose rate. There was considerable evidence to confirm such reciprocity suggesting that total dose is an important parameter. A model postulating reciprocity was shown to explain observed variation in depth of damage as well as one allowing for separate effects of duration and dose rate. Lens fibre cell effects were detected by scanning electron microscopy after 6 min irradiation at the SAR values of 40 and 20 mW g-1. Light microscopic evidence of lens fiber cell damage can be detected at an SAR of 10 mW g-1 after a 1 hr exposure.

Animals↗
PubMed1987

In vitro studies of microwave-induced cataract. II. Comparison of damage observed for continuous wave and pulsed microwaves.

Depth of damage caused by pulsed (PU) and continuous wave (CW) microwaves was estimated by scanning electron microscopy in rat lenses fixed immediately, after irradiation in vitro in circulating thermostatically controlled buffered saline. Pulses of 10 microseconds width and 24 kW peak power were delivered to the lens at different repetition rates in order to permit the same total energy to be delivered during 6, 20 or 60 min of irradiation at specific absorption rate (SAR) values of 0, 5.75, 11.5, 23, 69, 231 and 750 mW g-1; total energy [power (pow) x time] deposited in the lens was 0, 0.23, 0.46, 1.38, 4.6, and 15 W min g-1. Damage (granular degeneration of cells at the lens equator) was measured at the apex of penetration of the degeneration. The depth of degeneration (dep) of Pu or CW was compared either: (1) by a one-way analysis of variance (ANOVA) for the CW data alone and the 11 combinations of (pow x time); or (2) by using two alternative models to fit the data, to permit experimental distinguishment between: (a) reciprocal effects of pow x time; and (b) separate effects. Using the ANOVA analysis, the Pu mode of irradiation resulted in more damage at the same average power for every combination tested except one (23 mW g-1, 6 min). Although the separate-effects models explained more of the variation in depth of damage, the reciprocal effects model may provide an adequate fit for practical purposes and has the advantage of greater simplicity. For both models, the pulsed irradiation mode produced 4.7 times the depth of damage caused by CW irradiation. These results are discussed in relation to previous Pu-CW comparisons. It is proposed that this additional damage at the same average power is caused by thermoelastic expansion (TEE).

Animals↗
PubMed2002

Environmental remediation by an integrated microwave/ UV-illumination method. 1. Microwave-assisted degradation of rhodamine-B dye in aqueous TiO2 dispersions.

The photocatalytic decomposition of the cationic rhodamine-B (RhB) dye was examined in aqueous TiO2 dispersions using an integrated microwave/UV-illumination (PD/MW) method. This procedure proved to be superior in the degradation of the dye than the TiO2 photocatalytic degradative method alone. With few exceptions, the integrated PD/MW method also proved superior for other chemical systems. The greater efficacy of the PD/MW technique appears to be the result of the following two considerations: (i) there is enhanced formation of reactive oxygen species (.OH radicals), as attested to by DMPO spin-trap ESR methods and their attack on the dye; and although speculative at this time, (ii) the activity of bulk water or the TiO2 particle surface is somehow affected by microwave radiation. The greater efficacy of the PD/MW degradation method was also observed at low concentrations of molecular oxygen and at low radiant excitance of the light source. A brief mechanistic description is given on the basis of results obtained on the two model compounds, (i) benzoic acid and (ii) pyronin-B dye.

Coloring Agents↗
PubMed2004

Ultra-rapid microwave-stimulated tissue processing with a modified protocol incorporating microwave fixation.

AIMS: To develop an ultra-rapid microwave (MW)-stimulated histoprocessing protocol that incorporates MW fixation and produces consistent, high quality sections. METHODS: A range of fresh autopsy tissues was divided into three groups composed of equal numbers of small and large tissue blocks. Group 1 tissues were fixed for 8 hours in 4% buffered formaldehyde and processed in a conventional tissue processor through a 15-hour cycle. Group 2 tissues were processed in a MW histoprocessor according to the manufacturer's recommended protocol of irradiation in a proprietary reagent before embedding in paraffin. Group 3 tissues were processed with our protocol that incorporated the addition of MW fixation in 4% buffered formaldehyde and MW irradiation in isopropyl alcohol after irradiation in the proprietary reagent. RESULTS: The manufacturer's protocol resulted in 'grey' and 'wet look' artefacts in large tissue blocks. These artefacts did not occur in our protocol which produced sections that were indistinguishable from those obtained with conventional 23-hour processing. Histochemical and immunohistochemical stains were also indistinguishable and the tissue blocks cut very smoothly. CONCLUSIONS: The incorporation of an additional step to ensure adequate tissue fixation and one to ensure optimal dehydration and clearing resulted in a MW histoprocessing protocol that produced consistent results for both large and small tissue blocks. Paraffin-impregnated blocks can be produced very rapidly from fresh small and large tissue blocks in 45 and 100 minutes, respectively.

Artifacts↗
PubMed1979

The role of water in microwave absorption by biological material with particular reference to microwave hazards.

The problem of the absorption of the energy of plane electromagnetic radiation by an aqueous solution of macromolecules is considered. A simplified model for the hydrated molecule is employed, consisting of a spherical shell of bound water surrounding a spherical core. The power deposition per unit volume of the shell is calculated in the frequency range 100 MHz-100 GHz for several bound water relaxation frequencies. In each case the corresponding values are also calculated for free water for comparison. The values obtained for the bound water are shown to be significantly higher than those for the free water up to frequencies of at least 1 GHz. The maximum difference between these two sets of values is of the order of a factor of five and occurs roughly at the bound water relaxation frequency. Because of the strong coupling between the bound water molecules and the macromolecules present in biological material this result could be a significant factor in the explanation of the biological effects of microwaves at a molecular level.

Macromolecular Substances↗
PubMed1981

Exposure of physiotherapists to microwave radiation during microwave diathermy treatment.

Power density was measured during several microwave diathermy treatment sessions in order to determine levels to which the physiotherapist might be exposed during normal practice. Measurements were made at a distance of 30 cm from the patient. In half the cases investigated readings were less than 10 mW cm-2, the maximum permissible level for continuous exposure during an 8-hour working day. In the other cases levels exceeded 10 mW cm-2 at some sites. The results indicate that physiotherapists are unlikely to be exposed to radiation levels which would be considered harmful, provided reasonable care is taken.

Diathermy↗
PubMedDate not supplied

Microwave interrogation of dielectric targets. Part II: by microwave time delay spectroscopy.

A method is described which overcomes the problems of multipath propagation and range ambiguity that is suffered by the single-frequency continuous-wave microwave-imaging system described in part I. This technique is essentially a variation of chrip radar techniques, which have been adapted to time delay and attenuation measurements through a target. The feasibility of discriminating between paths whose differential time delay is on the order of 100 ps is demonstrated. Further, the need for small physical aperture in the transmitting and receiving antennas is demonstrated.

Electric Conductivity↗
PubMed1995

Rapid primary microwave-aldehyde and microwave-osmium fixation: improved detection of rat parotid acinar cell secretory granule alpha-amylase using a post-embedding immunogold ultrastructural morphometric analysis.

Studies of methods for improved fixation are becoming increasingly important in the field of quantitative immunocytochemistry. We used microwave (MW)-assisted chemical fixation to show improved retention of salivary gland acinar cell secretory granule alpha-amylase detected by a quantitative immunogold method. Blocks (4-mm3) of rat parotid gland were fixed by the following methods: (a) MW irradiation in an aldehyde fixative (AF) for 6 sec; (b) immersion in AF for 1.5 hr; (c) MW irradiation in osmium tetroxide (OT) for 9 sec; (d) immersion in OT for 1.5 hr; or (e) Sequential MW AF, 10 sec, MW OT rapid treatment (SMAORT), 10 sec. Specimens were processed routinely for transmission electron microscopy. Thin sections of Epon-embedded tissues were exposed first to rabbit IgG anti-human salivary alpha-amylase and second to gold-conjugated goat anti-rabbit IgG. Granule area was obtained by a point counting method. Labeling density was calculated as the number of gold particles/micron 2 +/- SD. Specimens fixed in seconds by MW-AF, MW-OT, or SMAORT showed ultrastructural preservation similar to immersion fixation in AF or OT for 1.5 hr. Immunogold labeling density of granule alpha-amylase was highest for SMAORT (874 microns 2) compared to MW-AF (295 microns 2), MW-OT (248 microns 2), routine sequential immersion in AF and OT (229 microns 2), or immersion in OT (no aldehyde) (190 microns 2). This study establishes the improved retention of salivary gland acinar cell secretory granule alpha-amylase and markedly enhanced fixation speed for ultrastructural studies made possible by MW-chemical fixation protocols that use aldehydes and osmium.

Animals↗
PubMed2004

[Comparison of shaft temperature related treatment efficacy between "air-cooled" microwave coagulation and traditional microwave coagulation].

BACKGROUND & OBJECTIVE: The application and development of traditional percutaneous microwave coagulation therapy (PMCT) has been limited by high shaft temperature. The "air-cooled" PMCT is the newest advancement. This study was to compare shaft temperature related treatment efficacy between "air-cooled" PMCT and traditional PMCT. METHODS: Two pigs underwent traditional PMCT, and "air-cooled" PMCT at 80 W for 10 min separately. Skin injury, surface temperature of guide-needle, charring tissue sticking to the shaft, and lesion shape in 2 pigs were compared. Five patients with liver tumor received traditional PMCT, and 8 patients with liver tumor received "air-cooled" PMCT. Feeling of pain, skin injury, charring tissue sticking to the shaft, local therapeutic efficacy, and recurrence of these 2 groups of patients were compared. RESULTS: In the pig underwent traditional PMCT, surface temperature of guide-needle reached 119-160 Centigrade; skin burn around puncture points was serious; charring tissue stuck to the front of electrodes; a trail sign was observed in coagulated lesion. In the pig underwent "air-cooled" PMCT, surface temperature of guide-needle was 28.8-39.9 Centigrade; no skin injury was found around puncture points; no charring tissue stuck to the front of electrodes; no obvious trail sign was observed in coagulated lesion. In 5 patients received traditional PMCT, 3 had skin injury; 2 had charring tissue stuck to the front of electrode; all felt moderate or serious epigastric pain lasted for 1-8 weeks; 4 had complete coagulation; 1 had local recurrence. In 8 patients received "air-cooled" PMCT, no one had skin injury, and charring tissue stuck to "air-cooled" electrode; 4 felt slight epigastric pain within 1 week; all had complete coagulation; no local recurrence was found. CONCLUSIONS: The technique of "air-cooled" electrode may decrease temperature of shaft safely and reliably, and eliminate side effects arose from high temperature of shaft. Treatment efficacy of "air-cooled" PMCT is better than that of traditional PMCT.

Animals↗