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At least 919 records · Page 51Linked to original sources
PubMed2003

Evaluation of the inhibiting effects from exposure to microwaves on the respiratory activity of yeast cells or on enzyme activity.

Microwaves are used in medical applications, so their eventual toxicity effects must be carefully evaluated. An integral toxicity test, based on the monitoring of the respiratory activity of yeast cells, is proposed to evaluate the damage from microwave exposure. Different exposure times and microwave powers were considered. On supposing that the damages occur at enzymatic levels, the inhibiting effects of microwave exposure on two enzymes (glucose oxidase (GOD) and superoxide dismutase (SOD)), assumed like models as present in the human organism, was evaluated.

Animals↗
PubMed1980

Microwave thermography in the detection of breast cancer.

Microwave thermography, a method of sensing subcutaneous temperatures, was used in a breast cancer detection study of about 5,000 female patients. The data were taken at wavelengths of 9.1 and 23 cm. Microwave thermography at 23 cm has true-positive and true-negative detection rates of 0.8 and 0.6, respectively, comparable to those of infrared thermography (0.7) and inferior to those of xeromammography (0.9). However, a potential advantage results if microwave and infrared thermography are used together for screening, and if mammography is used only for follow-up on those patients who were positive on either the microwave or the infrared thermograms. It is then possible to obtain true-positive and true-negative detection rates of 0.9 and 0.9, respectively, while only half the number of patients need be subjected to x-rays.

Breast Neoplasms↗
PubMed2003

Percutaneous sonographically guided microwave coagulation therapy for hepatocellular carcinoma: results in 234 patients.

OBJECTIVE: The objective of our study was to evaluate the long-term results of percutaneous microwave coagulation therapy for the treatment of hepatocellular carcinoma in a large patient population. SUBJECTS AND METHODS: Survival rates were determined in 234 patients with 339 nodules of hepatocellular carcinoma who had undergone percutaneous microwave coagulation therapy (208 men, 26 women; mean age, 54.8 years; mean tumor size, 4.1 +/- 1.9 cm; range, 1.2-8.0 cm; mean follow-up period, 27.9 months). Patients were those who had been rejected as candidates for surgery by the surgery department, who fit our study's criteria, and who agreed to participate. After baseline imaging studies were performed, the patients were followed up using the same combination of imaging (sonography, CT, or MR imaging) and posttreatment biopsy. RESULTS: After percutaneous microwave coagulation therapy, color Doppler flow signals disappeared in 92.0% (263/286) of the lesions. No enhancement was apparent in 89.2% (190/213) and 89.1% (41/46) of the lesions on contrast-enhanced CT and MR imaging, respectively. Posttreatment biopsies of 194 nodules showed no evidence of surviving tumor tissue in 180 nodules (92.8%). Resections of six lesions revealed complete tumor necrosis in five. The 1-, 2-, 3-, 4-, and 5-year cumulative survival rates were 92.70%, 81.60%, 72.85%, 66.37%, and 56.70%, respectively. The relationships between survival curves and the degree of hepatocellular carcinoma tumor differentiation and between survival curves and tumor size were statistically significant (p = 0.021). No severe complications were seen. CONCLUSION: Sonographically guided microwave coagulation proved to be safe and effective for the treatment of hepatocellular carcinoma. This therapy resulted in a high percentage of cases without evidence of residual tumor and satisfactory long-term results.

Administration, Cutaneous↗
PubMedDate not supplied

Microwave radiation effects on the thermally driven oxidase of erythrocytes.

Sheep red blood cells (SRBCs) were labelled with a concanavalin A-luminol-bovine serum albumin conjugate specific for the transmembrane anion transport protein (Band 3) and exposed to 2450 MHz continuous wave microwave radiation at an average specific absorption rate of 91 W/kg for 10 min. The temperature was held constant at 25, 37, 40, 42 or 45 degrees C with an airflow heat exchange system. Following exposure to microwave or air heating, the decrease in residual base-activated chemiluminescence (CL) of the SRBCs was measured as an indication of infield oxidase activity. Air heating resulted in a significant decrease in residual CL at temperatures above 37 degrees C (74 per cent decrease at 45 degrees C). Microwave radiation inhibited the decline in residual CL above 37 degrees C. At 45 degrees C the inhibition was 40 per cent. The results suggest microwave radiation either reversibly altered the thermodynamics of oxygen binding to haemoglobin or failed to energize a significant portion of the haemoglobin molecules in each sample to the thermal threshold of haemoglobin autoxidation.

Animals↗
PubMedDate not supplied

Microwave-induced hyperthermia and radiotherapy in human superficial tumours: clinical results with a comparative study of combined treatment versus radiotherapy alone.

Eighty-five evaluable superficial recurrent malignant tumours, mainly adenocarcinomas (78 per cent), in 38 patients were treated with either combined local hyperthermia (41-45 degrees C for four sessions) and low dose radiotherapy (30.0 Gy) or the same low dose radiotherapy alone. The treatment was given for two weeks. Hyperthermia was induced externally with 2450 MHz or 915 MHz microwaves. Totally 57 tumours were given combined treatment with a complete and partial response rate of 46 and 30 per cent, respectively (duration 1-38 months). In 18 patients with 2-10 superficial tumours each, 56 tumours were used in a comparative study, comparing the effect of combined hyperthermia and low dose radiotherapy versus the same low dose radiotherapy alone, the patients acting as their own controls. The total response rates were 89 and 50 per cent, respectively, in the two treatment modality groups. The difference in response rates is significant (p = 0.0039) in favour of the combined treatment, and this is also found when comparing complete remissions only (p = 0.0027). Local pain and normal tissue reactions presented problems during and after 2450 MHz microwave-induced hyperthermia treatment, performed without a coupling water bag system. Introduction of 915 MHz microwave-induced hyperthermia with a coupling deionized water bag system and refinement of microwave applicators, as well as the temperature control system considerably reduced these problems.

Adenocarcinoma↗
PubMedDate not supplied

Interstitial microwave-induced hyperthermia and iridium brachytherapy for the treatment of obstructing biliary carcinomas.

In a phase I clinical study, 10 patients with obstructive biliary carcinomas were treated with single-antenna interstitial microwave hyperthermia and iridium-192 brachytherapy. For each patient a standard biliary drainage catheter was implanted percutaneously through the obstructed common bile duct. This catheter accommodated a single microwave antenna which operated at 915 MHz, and one or two fibreoptic thermometry probes for temperature measurement. Under fluoroscopic guidance the microwave antenna and temperature probes were positioned in the CT-determined tumour mass. The 60-min heat treatment achieved a central tumour temperature of 45-55 degrees C while keeping temperatures at the proximal and distal margins at 43 degrees C. Immediately following the hyperthermia treatment the microwave antenna and temperature probes were removed, and a single strand of iridium-192 double-strength seeds was inserted to irradiate the tumour length. A dose of 5500-7900 cGy calculated at 0.5 cm radially from the catheter was administered over 5-7 days. Upon removal of the iridium a second hyperthermia treatment was performed. A total of 18 hyperthermia treatments were administered to the 10 patients. In two cases the second hyperthermia treatment after brachytherapy was not possible due to a kink in the catheter, or bile precipitation in the catheter. All patients tolerated the procedure well, and there were no acute complications. To evaluate the volumetric heating potential of this hyperthermia method, specific absorption rate (SAR) values were measured at 182 planar points in muscle phantom. Insulated and non-insulated antenna performance was tested at 915 MHz in a biliary catheter filled with air, saline, or bile to mimic clinical treatments. The insulated antenna exhibited the best performance. Differences between antenna performance in saline and bile were also noted. In summary, this technique may have potential for tumours which obstruct biliary drainage and are accessible to percutaneous decompression using standard diagnostic radiological procedures.

Biliary Tract Neoplasms↗
PubMedDate not supplied

Clinical system for simultaneous external superficial microwave hyperthermia and cobalt-60 radiation.

A system for simultaneous thermoradiotherapy was devised to investigate the possible benefits and/or complications of thermal radiosensitization in human superficial tumours. The system combines the well-known treatment modalities of external 915 MHz microwave hyperthermia and cobalt-60 teletherapy. Single waveguide applicators are utilized either attached to blocking trays, so that the gamma beam travels through a waveguide and into the patient (en face setup), or in a conventional way with the microwave propagation vector orthogonal to the gamma beam (orthogonal setup). With these setups a radiation fraction can be delivered in the middle of a 60-min, non-interrupted hyperthermia treatment. Temperatures and power level are remotely monitored and recorded outside the Cobalt room. Extensive measurements and testing showed that the operation of the hyperthermia system (generator, applicators, thermometry unit and temperature sensors) was not disrupted by irradiation and that the microwaves were confined to the treatment room and did not interfere with the operation of the Cobalt unit, of an adjacent linear accelerator or of an adjacent radiotherapy simulator. For the en face setup the dose distributions induced in solid water phantoms were uniform with the exception of a narrow (< 0.5 cm) region under the applicators' internal probes where 10-18% reduction exists. This dose defect is clinically smoothed using feathering techniques. The system has been successfully used without technical problems in 51 treatments in 15 patients (18 lesions) in a phase I/II clinical trial. An analysis of the thermal data showed that the temperature distributions achieved during simultaneous delivery have the same general characteristics of those achieved in conventional sequential hyperthermia with microwaves, and that the steady state distributions are maintained during the time of simultaneous irradiation. The tests performed in addition to the preliminary clinical experience clearly indicate that this type of combined therapy is technically feasible and safe. Here the system for simultaneous, external, superficial thermoradiotherapy and the implementation tests performed are described in detail. Preliminary clinical experience and results are also reported.

Cobalt Radioisotopes↗
PubMed1996

Aflatoxin destruction by microwave heating.

Microwaves were used in the present work in order to destroy pure aflatoxins (model system), and yellow corn and peanuts containing aflatoxins (food system). Pure aflatoxins (B1, B2, G1 and G2) were individually coated on a silica gel and exposed to microwaves at various power settings and periods. The same technique was adopted for peanuts and yellow corn deliberately infected by Aspergillus flavus. The aflatoxins were extracted, fractionated by thin-layer chromatographic technique and quantitatively determined by spectrodensitometry. In all cases, the content of different aflatoxins in the deliberately infected yellow corn was in the decreasing order B1 = G1 > B2 > G2. Infected peanuts were characterized by the highest B1 level, being approximately 3, 2, and 4.4 times as great as that in B2, G1 and G2, respectively. The rate of aflatoxin destruction of model and food systems increased with the increase of microwave oven power setting (low, moderate and high) and exposure time to microwaves.

Aflatoxin B1↗
PubMed1996

Tolazoline decreases survival time during microwave-induced lethal heat stress in anesthetized rats.

Effects of alpha-adrenergic antagonists have been studied during environmental heating but not during microwave-induced heating. Tolazoline may exert some of its effects via alpha-adrenegic blockade. In the present study, ketamine-anesthetized Sprague-Dawley rats were exposed to 2450-MHz microwaves at an average power density of 60 mW/cm2 (whole-body specific absorption rate of approximately 14 W/kg) until lethal temperatures were attained. The effects of tolazoline (10 mg/kg body weight) on physiological responses (including changes in body temperature, heart rate, blood pressure, and respiratory rate) were examined. Survival time was significantly shorter in the tolazoline group than in saline-treated animals. In general, heart rate and blood pressure responses were similar to those that occur during environmental heat stress. Heart rate, however, was significantly elevated in animals that received tolazoline, both before and during terminal microwave exposure. It is possible that changes associated with the elevated heart rate (e.g., less cardiac filling) in tolazoline-treated animals resulted in greater susceptibility to microwave-induced heating and the lower survival time.

Adrenergic alpha-Antagonists↗
PubMed1986

Quality characteristics, cholesterol, and sodium content of turkey as affected by conventional, convection, and microwave heating.

Six treatment combinations for evaluation of quality characteristics, sodium, and cholesterol content of turkey breast roasts were studied: three oven types (conventional, convection, and microwave) and two internal endpoint heating temperatures (77 C and 82 C). The microwave oven was the most energy efficient, and the conventional oven was the least efficient. Overall, drip loss was highest in the microwave oven, and heating to 82 C increased total cooking loss. Cook drip from the microwave oven contained less fat but the same amount of cholesterol as cook drip from the other two oven types. Instron shear values were not affected by oven type or internal endpoint temperature. Generally, when comparing raw to cooked samples, heating increased (concentrated) the cholesterol content and decreased the sodium content of the turkey. Cholesterol content of the heated roasts was not affected by type of oven; however, heating to the higher internal endpoint temperature increased (concentrated) the cholesterol. Sodium content was not affected by oven type or internal endpoint heating temperature. Cholesterol and sodium retentions of the roasts after heating were 96 and 64%, respectively, when averaged over the three oven types.

Animals↗
PubMedDate not supplied

Microwave thermal keratoplasty for myopia: keratoscopic evaluation in porcine eyes.

PURPOSE: Microwave thermal keratoplasty applies microwave energy to elevate the temperature of the paracentral stroma of the cornea to its thermal shrinkage temperature of about 60 degrees C. A suitable pattern of shrinkage in the paracentral cornea can flatten the central cornea. A surface cooling system preserves the epithelium during the procedure. METHODS: Fourteen enucleated porcine eyes were treated with a prototype microwave thermal keratoplasty applicator that heated in a ring pattern with inner diameter of 3.2 mm and width of 0.7 mm. The change in corneal power was quantified by a videokeratoscope. Slit-lamp microscope examinations and histological assessments were made. RESULTS: The 3-mm simulated keratometry reading showed an average of 6.60+/-6.00 D (standard deviation) of flattening. The region of opacity associated with shrinkage extended to 62% (+/-26%) of the corneal thickness. The epithelium was intact in all eyes. CONCLUSIONS: Microwave thermal keratoplasty applied in the paracentral cornea may flatten the central cornea.

Animals↗
PubMed1990

Development of a method of continuous temperature measurement for microwave denture processing.

A method of continuously measuring temperature during microwave irradiation was developed using a metal sheathed thermocouple. The temperatures recorded by this method were compared with those measured intermittently with a mercury thermometer. Samples of Sydney tap water (50 ml) were heated using a domestic microwave oven at High and Low powers which were the maximum (500 W) and minimum (50 W or 10%) powers of the oven, respectively. At 500 W, boiling was seen to occur within 1 min and the measurement with the mercury thermometer was omitted. The continuous temperature measurement with the thermocouple showed that the boiling point was reached at about 45 s. At 50 W the 10% work was shown by the delivery of 3 s microwave radiation which was repeated every 32 s. The boiling point was recorded at about 6 min, which was much earlier than the time (10 min) noted visually. The boiling point could not be registered with the mercury thermometer method. Visual observation or intermittent temperature measurement can result in an underestimation of temperature reached during microwave irradiation.

Denture Bases↗
PubMed2001

Use of a transurethral microwave thermotherapeutic device with permanent pacemakers and implantable defibrillators.

OBJECTIVE: To determine whether a device (Urologix Targis system) used for transurethral microwave treatment interferes with sensing, pacing, and arrhythmia detection by permanent pacemakers and implantable cardioverter-defibrillators (ICDs). METHODS: We tested 13 pacemakers in both bipolar and unipolar sensing configurations and 8 ICDs in vitro. Pacemakers and ICDs were programmed to their most sensitive settings. Energy outputs of the microwave device were typical of those used clinically. The probe of the microwave device was anchored 1.2 cm from the pacemaker or ICD being tested. RESULTS: No sensing, pacing, or arrhythmic interactions were noted with any ICD or any pacemaker programmed to the bipolar configuration. One pacemaker (Guidant Vigor 1230) showed intermittent tracking when programmed to the unipolar configuration. CONCLUSIONS: Most patients with permanent pacemakers or ICDs can safely undergo transurethral microwave therapy using the device tested. Pacemakers and ICDs should be programmed to the bipolar configuration (if available) during therapy. The pacemaker or ICD should be interrogated before and after therapy to determine whether programming changes occurred as a result of treatment. However, our findings suggest that this is unlikely.

Artifacts↗
PubMed1998

Inactivation of microorganisms with microwaves at reduced temperatures.

We developed a pilot-plant nonthermal flow process using microwave energy to inactivate microorganisms. The process consists of multiple passes through the microwave generator. Each passed material goes to a receiving tank for subsequent passes. The flow rate was 0.96 to 1.26 kg/min and the dwell time per pass was 1.1 to 1.5 min. Five passes were used. The microwave energy is instantaneously and simultaneously applied to the system, and thermal energy is removed by a cooling tube within the process line in the microwave generator. The cooling tube maintains the temperature below 40 degrees C. There was significant reduction in microorganisms in water, 10% glucose solution, and apple juice, and in yeast in beer. There was a slight decrease in microorganisms in tomato juice, pineapple juice, apple cider, and beer; and no effect in skim milk.

Beer↗
PubMed2003

[Non-ischemic partial nephrectomy using microwave tissue coagulator].

PURPOSE: The indications and the safety of non-ischemic partial nephrectomy using a microwave tissue coagulator were studied. MATERIALS AND METHODS: Non-ischemic partial nephrectomy was performed on 17 kidneys of 16 patients using a microwave tissue coagulator. The diagnosis was renal tumor and renal stones in eleven and five patients, respectively. Renal tumors were less than 4 centimeters in diameter, while the stones were associated with a caliceal diverticulum or secondary cortical atrophy. Excision of the tumors was done via the retroperitoneal approach through an oblique lumbar incision. The needle of the microwave tissue coagulator was inserted around the tumor (stone) 10 to 20 times, and the coagulator was activated. Then the tumor (stone) was excised with a sharp knife or scissors. Patients were encouraged to walk on the first postoperative day. RESULTS: Vascular clamping was necessary in one patient to reduce bleeding. Nephrectomy was done after partial nephrectomy in one patient because it was difficult to close the urinary collecting system after it was widely exposed. Although urine leakage was seen postoperatively in two patients, it ceased spontaneously at 14 and 23 days after surgery. Postoperative complications developed in one of seven patients (14%) with protruding renal tumor, in three of five patients (60%) with non-protruding renal tumor and in two patients with renal stone. Allogenic or autologous blood transfusion was not necessary, nor was any bleeding noticed post-operatively. In one patient, atrophy of the renal parenchyma occurred gradually after surgery and function was eventually lost. However, renal function was well preserved and recurrence of the problem was not observed in the other 15 patients, excluding one who died of esophageal cancer. CONCLUSIONS: The microwave tissue coagulator is a useful surgical instrument for non-ischemic partial nephrectomy, not only in patients with renal tumors but also in patients with complicated kidney stones. However, non-protruding renal tumor in a patient with solitary kidney should be avoided for this surgery. Thermal injury to the renal parenchyma or large vessels should be avoided and urine leakage from the collecting system should be meticulously treated during the operation.

Adult↗
PubMed1998

Validation of microwave digestion method for determination of trace metals in mushrooms.

A microwave digestion method for mushrooms, developed in the study, allows fast preparation of samples and reduces the contamination risk in the process of determining trace metals. Concentrations of six trace elements, Fe, Mn, Cu, Zn, Pb, and Cd were measured in 50 samples of different species of edible mushrooms (fam. Boletaceae) using atomic absorption spectrometry after microwave and dry ashing procedure. The methods were validated through certified Standard Reference Material SRM 1577b (Bovine Liver) which was treated and analysed using the same procedures as for the mushrooms. The samples were either digested with concentrated HNO3 in closed Teflon PFA vessels in a microwave oven, or ashed in quartz crucibles at 450 degrees C. The respective recoveries of Fe, Mn, Zn, Cu, Pb, and Cd obtained by measuring SRM were 112, 107, 104, 115, 111 and 95% after microwave digestion procedure and 86, 101, 109, 111, 98, and 110% after dry ashing procedure. The correlation between concentrations obtained by the two different methods of sample preparation was high for all metals.

Agaricales↗
PubMed1999

Effects of microwave irradiation on bacteria attached to the hospital white coats.

A test to sterilize pieces of cloths, which are the material of hospital white coats (doctors and nurses wears), by microwave irradiation in place of autoclaving was done using a commercial 2,450 MHz microwave oven. When pieces of cloths made of cotton (35%) and polyester (65%) were contaminated experimentally with Escherichia coli or Staphylococcus aureus and irradiated by microwave, the bacteria were killed quite rapidly according to almost first-order reaction kinetics. Only after a 20-sec irradiation, when the water content of cloths was decreased from the original 48% to 35%, the relative survivals of these bacteria fell to below 1% that of the non-irradiated control. The cloths were neither browned nor crisped, even after a 10-min irradiation of microwaves.

Clothing↗
PubMedDate not supplied

[Microwave technology in dental and eye prosthesis].

The paper outlines the specific features of using microwave technologies in dental and eye prostheses designed in Russia in 1992-1998. Thermal, microwave, and combined polymerizations of plastic materials used in prosthesis are compared. A Denta microwave unit is presented, which realizes a combined microwave technology.

Dental Prosthesis↗