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Biomedical subjects

R D Tucker

Publications and source records attributed to R D Tucker.

At least 19 recordsLinked to original sources
PubMed2001

The Archean Dongwanzi ophiolite complex, North China craton: 2.505-billion-year-old oceanic crust and mantle.

We report a thick, laterally extensive 2505 +/- 2.2-million-year-old (uranium-lead ratio in zircon) Archean ophiolite complex in the North China craton. Basal harzburgite tectonite is overlain by cumulate ultramafic rocks, a mafic-ultramafic transition zone of interlayered gabbro and ultramafic cumulates, compositionally layered olivine-gabbro and pyroxenite, and isotropic gabbro. A sheeted dike complex is rooted in the gabbro and overlain by a mixed dike-pillow lava section, chert, and banded iron formation. The documentation of a complete Archean ophiolite implies that mechanisms of oceanic crustal accretion similar to those of today were in operation by 2.5 billion years ago at divergent plate margins and that the temperature of the early mantle was not extremely elevated, as compared to the present-day temperature. Plate tectonic processes similar to those of the present must also have emplaced the ophiolite in a convergent margin setting.

Journal Article↗
PubMed2000

Defining the heating characteristics of ferromagnetic implants using calorimetry.

The induction heating of small, cylindrical ferromagnetic implants for localized tumors is currently under investigation. These thermal rods are implanted within a lesion in 1 cm(2) arrays and subsequently exposed to an externally applied alternating magnetic field. Implants absorb energy from the field and transfer it as heat to the surrounding tissue. To achieve a uniform temperature rise throughout the tissue volume and to account for any field-rod misalignment, 400 mW of power per implant is used as the design specification. The temperature to necrose cells must be greater than 46 degrees C. A calorimeter was constructed to confirm that the rod power output specification is satisfied at temperatures adequate for inducing cell death. The rods were designed to undergo a ferromagnetic to paramagnetic transition at temperatures of 55 degrees C, 60 degrees C, 65 degrees C, and 70 degrees C; this transition produces rods that are temperature self-regulating. Calorimetric results demonstrated that 55 degrees C, 60 degrees C, 65 degrees C, and 70 degrees C rods provided 400 mW at 47-51 degrees C, 51-53.5 degrees C, 57 degrees C, and 62.5-63.5 degrees C, respectively. Thermal rods provide sufficient power output at the temperatures necessary to cause thermal ablation of tumors. The higher-temperature rods give a greater margin to ensure that necrotizing temperatures can be achieved throughout the rod array even with minor misalignment.

Algorithms↗
PubMed2000

Use of permanent interstitial temperature self-regulating rods for ablation of prostate cancer.

BACKGROUND AND PURPOSE: We have examined a new technique for the thermal treatment of prostate cancer involving the percutaneous placement of small magnetic alloy rods into the gland in a procedure analogous to the placement of permanent brachytherapy seeds. When the patient and the implanted rods are placed in an extracorporeal alternating magnetic field, the rods heat and can produce tissue necrosis. The rods are temperature self-regulating and produce temperatures no higher than their preprogrammed regulation value. The rods are biocompatable permanent implants, comprised of cobalt and palladium. MATERIALS AND METHODS: We examined rods that heat to 55 degrees, 60 degrees, and 70 degrees C. Patients are treated for 1-hour sessions and easily have multiple sessions. RESULTS: Isolated rods produced little or asymmetrical necrosis. However, arrays of 70 degrees C rods placed within 1 cm of each other caused consistent necrosis between the rods. The temperature at the edge of the array dropped off quickly, and therefore, the rods can be placed within 2 mm of the capsule even posteriorly near the rectum. CONCLUSIONS: Arrays of high-temperature rods can be employed for tissue ablation, while lower-temperature arrays could be used to produce hyperthermia in order to achieve synergism with adjuvant radiation therapy. The technique is applicable in an outpatient setting.

Electromagnetic Fields↗
PubMed1997

Corrosion analysis of NiCu and PdCo thermal seed alloys used as interstitial hyperthermia implants.

Ferromagnetic materials with low Curie temperatures are being investigated for use as interstitial implants for fractionated hyperthermia treatment of prostatic disease. Previous investigations of the system have utilized alloys, such as NiCu, with inadequate corrosion resistance, requiring the use of catheters for removal of the implants following treatment or inert surface coatings which may interfere with thermal characteristics of the implants. We are evaluating a palladium-cobalt (PdCo) binary alloy which is very similar to high palladium alloys used in dentistry. Electrochemical corrosion tests and immersion tests at 37 degrees C for both NiCu and PdCo alloy samples in mammalian Ringer's solution were performed. Long-term corrosion rates are 5.8 x 10(-5) microm per year (NiCu) and 7.7 x 10(-8) microm per year (PdCo) from average immersion test results, indicating higher corrosion resistance of PdCo (P < 0.02); immersion corrosion rates were much lower than initial corrosion rates found electrochemically. Both alloys had significantly lower corrosion rates than standard surgical implant rates of 0.04 microm per year (P < 0.001 for both alloys). Scanning electron microscopy illustrates changes in the NiCu alloy surface due to pitting corrosion; no difference is observed for PdCo. The data indicate that the PdCo alloy may be suitable as a long-term implant for use in fractionated hyperthermia.

Alloys↗
PubMed1997

Histologic characteristics of electrosurgical injuries.

STUDY OBJECTIVE: To describe the wide variation of histologic characteristics produced by electrosurgical burns. DESIGN: Retrospective analysis. SETTING: University-associated teaching hospital. SUBJECTS: Pigs and dogs. INTERVENTIONS: Various power settings were employed with both monopolar and bipolar electrodes to incur electrosurgical damage. Animals were followed for up to 96 hours after injury. MEASUREMENTS AND MAIN RESULTS: Histologic analysis yielded characteristics of electrosurgical damage including areas of complete necrosis and coagulation, perivascular changes, endothelial damage, and hyperchromic pyknotic nuclei. White cell infiltration was seen only at the margin of necrotic zones of coagulation. CONCLUSION: The wide spectrum of histology from electrosurgical burns is primarily a result of the area that is sampled. Surgeons should actively investigate any postsurgical complications involving electrosurgery to obtain a definitive cause.

Animals↗
PubMed1997

Thermal ablation of canine prostate using interstitial temperature self-regulating seeds: new treatment for prostate cancer.

An interstitial temperature self-regulating implantable thermal seed for ablation of the prostate was investigated for the treatment of cancer. The technique is analogous to brachytherapy implants with three important advantages: highly localized temperatures may reduce complications, the thermal seed can be activated for retreatment at any point in time, and the seeds pose no radiation hazard to the clinical staff. Thermal seeds were implanted in the left lobe of the prostates in four dogs; the right lobe was a control to evaluate undesired heating outside the seed array. Linear-array thermometry probes were placed in both lobes, and the induction field for heating the implants was activated for 1 hour. After treatment, biopsies were taken from both lobes at 4-hour intervals up to 28 hours to evaluate thermal damage and thermotolerance as measured by expression of heat shock protein (hsp) 70. Only 5 minutes was required to heat the left lobe to 45 degrees to 55 degrees C. The maximum and minimum cumulative equivalent minutes at 43 degrees C (CEM43) thermal doses in the treated lobe were 174 and 4.4 hours, respectively; less than a 1-minute CEM43 was observed in the control lobe. Elevated hsp70 expression was detected in tissue of the treated lobe between 12 and 24 hours after treatment; minimal increases occurred in the control lobe. The thermal seed system was effective at heating the prostatic volume without damage to normal tissues outside the implant array, and subsequent treatments were simplified in comparison with other hyperthermia devices. Expression of hsp70 implies that retreatment of the prostate at intervals as short as 48 to 72 hours may avoid thermotolerance making weekly treatment an appropriate regimen.

Animals↗
PubMed1996

Evaluation of inductively heated ferromagnetic alloy implants for therapeutic interstitial hyperthermia.

Ferromagnetic alloys heated by magnetic induction have been investigated as interstitial hyperthermia delivery implants for over a decade, utilizing low Curie temperatures to provide thermal self-regulation. The minimally invasive method is attractive for fractionated thermal treatment of tumors which are not easily heated by focused microwave or ultrasound techniques. Past analyses of ferromagnetic seeds by other authors depict poor experimental correlation with theoretical heating predictions. Improvements in computer hardware and commercially available finite element analysis software have simplified the analysis of inductively heated thermal seeds considerably. This manuscript examines end effects of finite length implants and nonlinear magnetic material properties to account for previous inconsistencies. Two alloys, Ni-28 wt% Cu (NiCu) and Pd-6.15 wt% Co (PdCo), were used for comparison of theoretical and experimental calorimetric results. Length to diameter (L/d) ratios of over 20 for cylindrical seeds are necessary for minimization of end effects. Magnetic properties tested for alloys of NiCu and PdCo illustrate considerable nonlinearity of these materials in field strength ranges used for induction heating. Field strength dependent magnetic permeabilities and calorimetric data illustrate that more detailed material information must be included to accurately estimate induction power loss for these implants.

Alloys↗
PubMed1995

Laparoscopic electrosurgical complications and their prevention.

Insulation failures, direct coupling, and capacitive coupling around active electrodes may cause serious burns and tissue damage to patients undergoing laparoscopic procedures. A coordinated team effort between perioperative nurses and surgeons can prevent life-threatening complications from laparoscopic electrosurgical procedures. Knowledge of the biophysics of electrosurgery, the mechanisms of electrosurgery complications, and prevention of patient injuries will empower surgical team members to provide quality outcomes for patients undergoing laparoscopic procedures.

Adult↗
PubMed1995

Tissue actions of bipolar scissors compared with monopolar devices.

OBJECTIVES: To establish whether bipolar scissors offer equivalent cutting performance compared with monopolar scissors and to compare extent of thermal coagulation injury using two electrosurgical generators. DESIGN: Eighteen female rabbits' uterine horns were cut using controlled velocity at several different wattages with either bipolar or monopolar scissors. The specimens were examined microscopically and zones of thermal necrosis were measured using a stage micrometer against a 1 mm standard. RESULTS: Bipolar scissors cut equally well compared with monopolar scissors and showed significantly less thermal injury. When coupled to a constant voltage generator both the bipolar and monopolar scissors performed better. CONCLUSION: Bipolar scissors offer the surgeon significant safety advantages and equivalent or better performance compared with monopolar scissors when used for laparoscopic surgery.

Animals↗
PubMed1995

Laparoscopic electrosurgical injuries: survey results and their implications.

This article provides the results of a survey on electrosurgical complications and surgical techniques during laparoscopy from the American College of Surgeons. Of the respondents, 18% stated that they had personally experienced an electrosurgical burn to their patient during laparoscopy. The survey shows that the majority of surgeons, 74%, employ coagulation mode most commonly during surgery. Of the surgeons, more than one third routinely employ high-voltage coagulation and blend mode operation at power settings > 40 W. We discuss the possible complications that may occur from high-voltage-high-power settings, such as direct coupling, insulation failure, and capacitive coupling of unintended current into internal tissue such as bowel. We further describe techniques that may be employed to minimize the likelihood of unintended electrosurgical burns as well as technologies that can eliminate or greatly decrease the likelihood of electrosurgical complications.

Burns, Electric↗
PubMed1994

Unrecognized hazards of surgical electrodes passed through metal suction-irrigation devices.

Surgical electrodes, passed through metal suction-irrigation devices, pose significant risks for unrecognized visceral burns through capacitively coupled current using monopolar electrosurgery. Plastic cannulas (and reducers) should be avoided with the metal suction-irrigation electrode; an all-metal trocar cannula confers limited safety. With surgeon education and advances in engineering, the potential for unrecognized visceral injury with capacitive coupling can be eliminated.

Burns↗
PubMed1993

Effect of thermal treatment on heating characteristics of Ni-Cu alloy for hyperthermia: preliminary studies.

Ferromagnetic Ni-Cu alloy wires were characterized in order to obtain well-defined thermoseeds for application in interstitial hyperthermia of prostate cancer. Thermoseeds have been produced which possess Curie points in the therapeutic hyperthermia range, approximately 40 to 50 degrees C. The effect of thermal treatment and composition on the heating characteristics of the thermoseeds were investigated. The preliminary study shows that the recrystallization is crucial for altering thermoseeds' heating characteristics. Obtaining thermoseeds which behave as desired depends on changes in annealing times and temperatures. One may increase the maximum heating temperature (similar to Curie temperature) by increasing the annealing time and cooling time. Decreasing the lower annealing plateau temperature also increases the maximum seed heating temperature. Higher nickel content compositions did not affect rise time but increased the maximum heating temperature.

Alloys↗
PubMed1993

Heat shock protein response in a prostate tumor model to interstitial thermotherapy: implications for clinical treatment.

Hyperthermia is being utilized individually and in conjunction with other therapies in treating malignant and benign tumors, though few studies have examined cellular effects of elevated temperatures in the prostate model. Highly conserved proteins of the 70 kDa heat shock protein family (HSP 70) are produced in response to environmental stresses, including heat, and are found in all organisms. HSPs are an indicator of cell damage, are associated with thermotolerance, and provide cells with transient resistance to subsequent thermal challenges. Transient thermotolerance is important in the determination of temperature, duration, and sequencing for treatments. This preliminary study analyzes the HSP 70 response of the Dunning R3327 adenocarcinoma model to a single 50 degrees C 1 hr treatment. Elevated HSP levels were found between 10 and 16 hr, returning to baseline by 24 hr. As some fractions of the cells are able to produce HSP 70 following treatment, the data suggest that currently utilized clinical temperatures (42-46 degrees C) administered for 1 hr are inadequate. HSP levels in response to hyperthermia, radiation, and chemotherapy may be useful in finding optimal treatment regimens for prostate cancer.

Adenocarcinoma↗
PubMed1993

Bipolar electrosurgical devices.

The authors point out the safety benefits of bipolar electrosurgical devices as opposed to monopolar. They describe the working principles of bipolar endoscopic coagulators, polyp snares, biopsy probes and papillotomes and laparoscopic forceps, hooks and scissors and deal with their specific functional and safety requirements. The use of bipolar devices is advocated, particularly in view of the anticipated increase in litigation costs.

Electric Conductivity↗
PubMed1992

Education and engineering solutions for potential problems with laparoscopic monopolar electrosurgery.

The potential problems of monopolar electrosurgery relate to unrecognized energy transfer ("stray current") outside the view of the laparoscope. Mechanisms of stray current and unrecognized tissue injury include: (1) insulation breaks in electrodes; (2) capacitive coupling, or induced currents through the intact insulation of the active electrode to surrounding cannulas or other instruments; and (3) direct coupling (or unintended contact) between the active electrode and other metal instruments or cannulas within the abdomen. Capacitive coupling poses the greatest risk for injury when the outer conductor (trocar cannula or irrigation cannula) is electrically isolated from the abdominal wall by a plastic nonconductor. Capacitive coupling is increased by the coagulation mode (versus cut), open circuit (versus tissue contact with the electrode), 5-mm cannulas (versus 11 mm), and higher voltage generators. The safety of electrosurgery can be enhanced by surgical education regarding the biophysics of radio frequency electrical energy, technical choices in instruments using all-metal cannula systems, and engineering developments with a dynamically monitored system for insulation failure and capacitive coupling.

Electric Conductivity↗
PubMed1992

The effect of interstitial hyperthermia on the Dunning prostate tumor model.

The effect of hyperthermia was examined on the Dunning prostate tumor model in rats. Hyperthermia was created by heating self-regulating interstitial seeds with an external oscillating magnetic field. The seed alloy was comprised of 70% nickel and 30% copper. One treatment with 50C seeds for two hours did not provide significant delay in tumor growth compared to controls. However, regimens with two treatments separated by either 48 hours or one week did cause significant delay (p = 0.0013 and p = 0.0096, respectively). These results suggest that an interstitial hyperthermia seed may provide an efficacious outpatient therapy for prostate cancer. Further, interstitial hyperthermia may be readily combined with existing radiotherapy with interstitial gold coated seeds to provide additive or synergistic anti-tumor effects.

Adenocarcinoma↗
PubMed1992

The effect of bipolar electrosurgical coagulation waveform on a rat uterine model of fallopian tube sterilization.

Laparoscopic bipolar electrosurgical sterilization has been employed for nearly two decades. This bipolar procedure was intended to reduce the incidence of unintended complications, such as bowel burns. However, compared to the monopolar procedure, it produced a higher failure rate. This study examines the role of the low power-high voltage coagulation waveform on the effectiveness of electrosurgical desiccation on the rat uterine model of the fallopian tube. Desiccations were performed with both Kleppinger and Storz forceps using generator settings from 2 to 6. Desiccations performed to the visual endpoint (blanch, swell, and collapse) required from 23.8 to 30.0 joules, although procedures performed at a generator setting of 2 required long application times, an average 15.4 sec (Storz) and 28.2 (Kleppinger). All bipolar procedures led to a loss of tissue at the desiccation site at 12 weeks postsurgery. Therefore, the electrosurgical coagulation waveform proved to be effective in producing adequate in vivo tissue destruction even at very low generator settings.

Animals↗