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PubMed1979

Middle-ear structures contribute little to auditory perception of microwaves.

The contribution of the ossicles (middle-ear bones) to auditory perception of microwaves was evaluated by the brain-stem evoked response (BER). Amplitude and latency of BERs were recorded from guinea pigs that were stimulated at various intensities by acoustic pulses coupled to the auditory canal or via bone conduction, and by microwave pulses. Blocking of the external ear, middle-ear damping, and middle-ear destruction produced little change in the BERs that were elicited by microwave pulses. Results indicate that activity in the central auditory pathway as induced by pulsed microwaves only requires stimulation of the cochlea. Conduction of pressure waves through the bones of the calvarium appears to be the mechanism responsible in perception of pulsed microwaves.

Animals↗

PubMed1983

Microwave methods of measuring changes in lung water.

Two microwave methods for measuring changes in lung water content have been investigated. The first is based on measuring changes in the phase of an active microwave signal transmitted through the thorax, while the other is based on measuring the natural microwave radiation emitted by the body with a radiometer. The feasibility of using the active microwave method is investigated by making measurements on phantoms, on anesthetized dogs with induced pulmonary edema, and on isolated dog lungs. The obtained results clearly illustrated that the method is sensitive enough to measure small changes in lung water content. In the radiometer method, on the other hand, both calculations and preliminary measurements in phantoms indicate that the natural microwave emission changes with lung water content and that conventional radiometry systems should be able to detect as little as three to four percent change in lung water content. Initial results from both methods, therefore, indicate the soundness of the basic ideas and justify further development of these methods for clinical use.

Adult↗

PubMedDate not supplied

Rapid Bielschowsky silver impregnation method using microwave heating.

The Bielschowsky silver impregnation method has been used extensively to demonstrate neuronal processes including dendrites, axons and neurofibrils. In this study, we examined the differences in the time required for and the staining quality of the Bielschowsky method for neuronal processes when microwave heating was used instead of processing at room temperature. For this purpose, a control group of sections stained according to the conventional method at room temperature was compared to an experimental group stained in a microwave oven at 180 W for 2, 4 and 1 min in 2% silver nitrate, ammoniacal silver nitrate and gold chloride, respectively. Light microscopic examination demonstrated that the normal structure was preserved in both groups and that there was no difference in the staining quality between the control and the microwave groups. In addition, staining time for this procedure was reduced to 8 min by using the microwave oven. Our study revealed that microwave irradiation can be used safely for Bielschowsky silver impregnation of neuronal tissues.

Animals↗

PubMed2003

Feasibility of salvage interstitial microwave thermal therapy for prostate carcinoma following failed brachytherapy: studies in a tissue equivalent phantom.

Thermal therapy is an experimental treatment to destroy solid tumours by heating them to temperatures ranging from 55 degrees C to 90 degrees C, inducing thermal coagulation and necrosis of the tumour. We are investigating the feasibility of interstitial microwave thermal therapy as a salvage treatment for prostate cancer patients with local recurrence following failed brachytherapy. Due to the electrical and thermal conductivity of the brachytherapy seeds, we hypothesized that the seeds could scatter the microwave energy and cause unpredictable heating. To investigate this, a 915 MHz helical antenna was inserted into a muscle-equivalent phantom with and without brachytherapy seeds. Following a 10 W, 5 s input to the antenna, the temperature rise was used to calculate absorbed power, also referred to as specific absorption rate (SAR). Plane wave models based on Maxwell's equations were also used to characterize the electromagnetic scattering effect of the seeds. In addition, the phantom was heated with 8 W for 5 min to quantify the effect of the seeds on the temperature distribution during extended heating. SAR measurements indicated that the seeds had no significant effect on the shape and size of the SAR pattern of the antenna. However, the plane wave simulations indicated that the seeds could scatter the microwave energy resulting in hot spots at the seed edges. Lack of experimental evidence of these hot spots was probably due to the complex polarization of the microwaves emitted by the helical antenna. Extended heating experiments also demonstrated that the seeds had no significant effect on the temperature distributions and rates of temperature rise measured in the phantom. The results indicate that brachytherapy seeds are not a technical impediment to interstitial microwave thermal therapy as a salvage treatment following failed brachytherapy.

Brachytherapy↗

PubMed1988

Quantitative assessment of impedance tomography for temperature measurements in microwave hyperthermia.

The objective of this study is a non-invasive assessment of the thermal dose in microwave hyperthermia. We intend to monitor the induced temperature rise via the change in the resistivity of body tissue, and hence control the microwave power during treatment. An initial feasibility study using electrical impedance tomography in vivo has indicated that a microwave induced temperature difference of a suitable magnitude can be mapped from a knowledge of the temperature coefficient of conductivity for tissue (typically 2% per degrees C). The accuracy of the currently employed reconstruction algorithm is assessed from data simulated by finite element prediction methods. A circular arrangement of electrodes surrounding a conductive sheet is used to evaluate the voltage distribution on the boundary of the sheet. A range of regions inside the circular field are chosen and the conductivity is changed uniformly by steps of 1% up to 10%. Images of these changes are produced. It is noticed that the algorithm underestimates the values of resistivity change for the small areas and overestimates the change for the larger areas. We are studying results for a variety of shapes of surface regions of the body that undergo resistivity change with microwave heating applied. Further work is necessary to account for three-dimensional current paths. Preliminary results are also presented of experimental investigations of the microwave-induced temperature rise in layers of carbon-loaded paper sheet.

Body Temperature↗

PubMed2005

Renal-tissue damage induced by laparoscopic partial nephrectomy using microwave tissue coagulator.

BACKGROUND AND PURPOSE: The microwave coagulator is a useful instrument that enables surgeons to perform partial nephrectomy without vascular clamping. The extent of postoperative thermal damage in surgically spared renal tissue has not been well examined. The present study was conducted to evaluate the tissue damage caused by microwave coagulation in laparoscopic partial nephrectomy (LPN) for small renal tumors. MATERIALS AND METHODS: Seven cases of LPN with a microwave tissue coagulator were entered in the present study. The median tumor diameter was 1.5 cm, and the median size of the resected specimen was 2.2 cm. Postoperative tissue damage was evaluated by contrast-enhanced CT 1 month after surgery. Surgically spared renal-tissue volume and functioning renal-tissue volume were estimated from the images by NIH Image 1.62 software. RESULTS: Postoperative CT revealed unenhanced renal tissue adjacent to the surgical margin. The median estimated volumes of surgically spared and functioning renal tissue were 96.1% (range 74.3%-99.8%) and 88.4% (range 68.0%-92.7%) of preoperative normal renal tissue, respectively. The percentile volume of functioning to surgically spared renal tissue ranged from 89.9% to 96.0% (median 92.8%). CONCLUSIONS: The microwave coagulator enables us to carry out partial nephrectomy without vascular clamping. Although 96% of normal renal tissue was surgically spared, 4% to 10% of this tissue was nonfunctioning as a result of microwave-induced thermal damage.

Aged↗

PubMed1985

A rapid method of staining ultrathin sections for surgical pathology TEM with the use of the microwave oven.

A rapid microwave method is described for staining ultrathin sections for surgical pathology transmission electron microscopy (TEM). Three sets of Epon sections of human heart biopsy were mounted on unsupported 200-mesh Rhodium-coated copper grids and were stained with uranyl acetate (UA) and lead citrate. The first set of grids was stained for 15 seconds in each solution with the aid of a microwave oven, and the second set was stained routinely for 30 minutes in UA and 10 minutes in lead citrate at room temperature. The third control set was stained for 15 seconds in each solution without microwave bombardment. The overall image quality of the TEM micrographs generated by the "quick-stained" microwave enhanced sections was better than routine stained and control sections. The microwave-treated sections have more contrast, less artifacts in the form of precipitate, and a more uniform overall staining.

Humans↗

PubMed2006

Effect of plant extracts on physicochemical properties of chicken breast meat cooked using conventional electric oven or microwave.

This study evaluated effects of vacuum-infused fresh chicken breast meats with grape seed extracts, green tea extracts, or tertiary butyl hydroquinone on pH, texture, color, and thiobarbituric reactive substances after cooking using a microwave or conventional electric oven for 12 d storage at 5 degrees C. Thiobarbituric reactive substances values of uncooked (raw) chicken breast meats for 0 to 12 d of storage ranged from 1.12 to 3.5 mg of malonaldehyde/100 g of chicken. During 0 to 12 d of storage, thiobarbituric reactive substances values ranged from 2.50 to 7.80 and from 2.4 to 7.35 mg of malonaldehyde/100 g of chicken breast meat cooked by microwave and conventional electric oven, respectively. Meats cooked by microwave had higher redness and lower lightness values than those cooked by conventional electric oven. Also, meats cooked by microwave had higher maximum shear force, working of shear, hardness, springiness, cohesiveness, and chewiness values than meats cooked by conventional electric oven. Tertiary butyl hydroquinone was the most effective in raw and cooked meats in reducing lipid oxidation, followed by grape seed and green tea extracts. Plant extracts are effective in preventing undesirable changes in chemical properties in chicken breast meat caused by microwave and conventional electric oven cooking.

Animals↗

PubMed1986

A transient hypotensive episode (Bezold-Jarisch effect) occurring in a patient treated with microwave hyperthermia.

A case report of a hypotensive episode occurring during a microwave hyperthermia treatment is reported. Microwave hyperthermia was delivered using 915 MHz externally applied energy. The tumor being treated was either a superficial lymph node or local recurrence in the subdigastric region overlying the carotid artery. During the patient's treatment, she reported symptomatology consistent with a neuropathy which is characterized by its association with microwave energy. As the treatment progressed the patient developed syncopy, hypotension, and bradycardia similar to a Bezold-Jarisch reflex. All of these conditions promptly self-corrected when the microwave energy was discontinued. This event can be explained by a transient microwave induced neuropathy specifically involving the carotid body or sinus.

Bradycardia↗

PubMed2001

Microwave treatment of contact lens cases contaminated with acanthamoeba.

PURPOSE: Microbially contaminated contact lens cases are a predisposing risk factor for Acanthamoeba keratitis. Several findings have shown that microwave irradiation kills the six Food and Drug Administration test challenge microorganisms. We aimed to determine what effect microwave irradiation has on Acanthamoeba trophozoites and cysts. METHODS: Different types of contact lens cases were contaminated with trophozoites and cysts of three different Acanthamoeba species (A. comandoni, A. castellanii, A. hatchetti) and were exposed to microwave irradiation for 3, 5, and 8 minutes, respectively. RESULTS: Trophozoites, as well as cysts of the different Acanthamoeba strains, were effectively killed, even by only 3 minutes of microwave irradiation, and there were no negative effects of irradiation on the contact lens cases themselves. CONCLUSION: We demonstrate that microwave treatment is a very effective, easy, and cheap method to keep contact lens cases free of Acanthamoeba, thus considerably reducing the risk of an Acanthamoeba keratitis.

Acanthamoeba↗

PubMed1984

Decreased body weight in fetal rats after irradiation with 2450-MHz (CW) microwaves.

Female Sprague-Dawley (CD) rats were exposed to 2450-MHz (CW) microwave radiation at incident power densities of 0 or 40 mW/cm2 (SAR = 6.0 W/kg) for 100 min daily on the sixth through 15th day of gestation. One-time exposure to the same conditions increased average colonic temperatures 2 degrees C at the end of irradiation in pregnant rats of similar size. There were 23 sham-irradiated and 24 microwave-irradiated females. When these groups were compared on the 21st day of gestation, no significant differences were found in pregnancy rates; in the numbers of live, dead or total fetuses; nor in the incidences of external, visceral or skeletal anomalies or variations. However, mean fetal body weight was significantly (p = 0.0008) lower after microwave irradiation and was 9% less than that of sham-irradiated litters. Sternal ossification was also significantly delayed in the microwave-irradiated fetuses (p = 0.007). It is concluded that even though a change in the malformation rate is not effected in rats, a fetotoxic effect does occur due to microwave-exposure conditions which raise maternal rectal temperatures to approx. 40 degrees C and produce a specific absorption rate (SAR) greater than or equal to 6 W/kg in the dam.

Animals↗

PubMed1990

In-office microwave disinfection of soft contact lenses.

We evaluated the effectiveness of an in-office microwave disinfection procedure which allowed for the disinfection of up to 40 soft contact lenses at one time. Ciba AOSept cases filled with sterile unpreserved saline were contaminated with one of six FDA test challenge microorganisms at a concentration of approximately 10(3) colony forming units per milliliter (CFU/ml). Twenty cases were placed on the rotating plate of a standard 2450 MHz 650 W microwave oven in a 10-cm diameter circle. The cases were exposed to high intensity microwave irradiation for periods of 0 to 15 min. None of the 6 microorganisms evaluated survived 2 min or longer of microwave exposure. Our findings indicated that microwave irradiation can be a convenient, rapid, and effective method of disinfecting a number of soft contact lenses at one time and thus adaptable as an in-office soft contact lens disinfection procedure.

Bacteria↗

PubMed2004

Testing of a dual-mode microwave care regimen for hydrogel lenses.

PURPOSE: To test the design of a patient care regimen for soft lenses that aims to provide the highest standards of disinfecting through use of domestic microwave cookers, while also providing storage equipment and solution that enable patients to follow a conventional cold disinfecting regimen when traveling. The cleaning efficacy of surfactant agents during microwave treatment was also considered. METHODS: The microbiologic performance of the regimen and its disinfecting apparatus was tested according to the Food and Drug Administration (FDA) protocols for contact lens heat disinfectors. Subsequently, a prospective pilot clinical trial of the regimen involving 15 subjects was carried out to the protocols of the FDA and International Standards Organization 11,980:1997. RESULTS: Lenses inoculated with 10(7) colony-forming units (cfu) of Enterococcus faecalis were disinfected to 0 cfu by a 12-s irradiation of a compact disinfecting case that held the lenses suspended in 12 ml saline. A proof of operation indicator performed correctly for all 10 cases tested. No adverse reactions were found in the pilot patient trial, using Renu multipurpose (Bausch and Lomb, Rochester, NY) as the test solution, and no statistically significant difference was found between test and control groups in respect of any sign. However, the greater incidence of edema, palpebral hyperemia, and lens front-surface deposition in the microwave test group may be clinically significant. CONCLUSIONS: The design of the test care regimen proved easy for patients to follow in either hot or cold disinfecting mode. The greater incidence of certain signs in the microwave test group suggests the need to continue using a rub and rinse step for the microwave mode and for additional investigation into the choice of an appropriate multipurpose solution formulation for this proposed regimen, preferably one that does not use a block copolymer-type surfactant agent.

Contact Lens Solutions↗

PubMed1992

Evaluation of microwave and radio frequency catheter ablation in a myocardium-equivalent phantom model.

A highly localized burst of energy applied to the myocardium via a transvenous catheter-mounted power source can be used to destroy endocardial tissue regions which mediate life-threatening arrhythmias. In the past, high-voltage direct current pulses, radio-frequency (RF) current, and laser light have been used as energy sources. In this paper, the use of 2450 MHz microwave energy applied via a miniature coaxial cable-mounted helical coil antenna designed specifically for this application was investigated as a means to increase the treated volume of cardiac tissue in a controllable and efficient manner during ablation. Using an array of fiber optic temperature probes implanted in a saline-perfused, tissue-equivalent gel phantom model designed to simulate the myocardium during ablation, the heating pattern from the microwave antenna was characterized and compared to that induced by a commercial RF electrode catheter at 550 kHz. Effects of variable contact angle between the heat source and heart wall were assessed in terms of the radial penetration and overall volume of heated tissue. Heating patterns from the RF electrodes dropped off much more abruptly both radially and axially than the microwave antenna such that the volume of effectively heated tissue was more than ten times larger for the microwave antenna when the heat sources were well-coupled to the tissue, and more than four times larger for the microwave antenna when the sources were angled 30 degrees away from the tissue surface.

Catheter Ablation↗

PubMed1996

Effect of high-power microwave on indicator bacteria for sterilization.

According to the superiority sterilization, a specially-designed microwave disinfector using high-power microwave energy was made. A series of sterilizing experiments have been made to determine the effect of microwave energy on several typical indicator bacteria such as Bacillus subtilis var. niger, Bacillus stearothermophilus, Bacillus pumilus E601, Staphylococcus aureus, Bacillus cereus. Under the conditions of different sterilization duration and unequal intensity of microwave power irradiation onto the bacteria, a useful result of killing bacteria has been observed, i.e., the Bacillus subtilis can be considered as an optimum indicator bacterium for microwave sterilization.

Bacillus↗

PubMed1998

Quantification of the 3-D electromagnetic power absorption rate in tissue during transurethral prostatic microwave thermotherapy using heat transfer model.

Experiments were performed in a tissue microwave-equivalent phantom gel to quantitatively examine the volumetric heating produced by a microwave antenna with a peripheral cooling system for the transurethral prostatic thermotherapy. Based on previous research, expression for the specific absorption rate (SAR) of microwave energy in the gel was extended to three dimensions, which includes its dependence on radial, angular, and axial direction. A theoretical heat transfer model was developed to study the temperature distribution in the gel by introducing this proposed SAR expression. The parameters in this expression and the convection coefficient due to the chilled water running around the antenna were determined using a least-square residual fit of the theoretical temperature predictions to the experimentally measured steady-state temperature field within the gel. The analytical expression of the three-dimensional SAR distribution obtained in this study will help provide a better understanding of the microwave heating pattern in the prostatic tissue and, thus, to aid in designing improved applicators. It can also be used in the future as an accurate input to heat transfer models which predict temperature distributions during the transurethral microwave thermotherapy.

Gels↗

PubMed2000

Microwave life-detection systems for searching human subjects under earthquake rubble or behind barrier.

A new sensitive microwave life-detection system which can be used to locate human subjects buried under earthquake rubble or hidden behind various barriers has been constructed. This system operating at 1150 MHz or 450 MHz can detect the breathing and heartbeat signals of human subjects through an earthquake rubble or a construction barrier of about 10-ft thickness. The basic physical principle for the operation of a microwave life-detection system is rather simple. When a microwave beam of appropriate frequency (L or S band) is aimed at a pile of earthquake rubble covering a human subject or illuminated through a barrier obstructing a human subject, the microwave beam can penetrate the rubble or the barrier to reach the human subject. When the human subject is illuminated by a microwave beam, the reflected wave from the human subject will be modulated by the subject's body movements, which include the breathing and the heartbeat. If the clutter consisting of the reflected wave from stationary background can be completely eliminated and the reflected wave from the human subject's body is properly modulated, the breathing and heartbeat signals of the subject can be extracted. Thus, a human subject buried under earthquake rubble or hidden behind barriers can be located. This system has been tested extensively in a simulated earthquake rubble in the laboratory and also in a field test using realistic earthquake rubble conducted by a Federal Emergency Management Agency (FEMA) Task Force.

Diagnosis, Computer-Assisted↗

PubMed1994

Microwave oven antigen retrieval applied to the immunostaining of cytopathology specimens.

Microwave oven antigen retrieval has been developed to extend the range of antibodies that can be used upon sections of fixed and processed tissue. It has the additional advantages of improving immunostain intensity and reducing background positivity. It can also be employed as an alternative to proteolytic digestion. In this study the effects of microwave oven heating upon immunochemical staining of cytopathological specimens with a range of selected antibodies have been investigated. Microwaving did not result in loss of cells, and there was no need to use adhesive-coated slides. The method improved the staining intensity and reduced background with antibodies against a variety of antigens that are difficult or impossible to detect in formaldehyde-fixed cytological material. Microwave heating was also used successfully as an alternative to trypsin digestion, and had the advantage of reduced morphological distortion. The technique was useful in demonstrating the soluble formalin-sensitive antigen p19 on cytospins fixed in formaldehyde vapour. Microwave oven heating thus shows promise of extending the scope of immunostaining in clinical cytopathology.

Antigens↗