Biomedical subjects

D N Buechler

Publications and source records attributed to D N Buechler.

5 recordsLinked to original sources

PubMed2001

Calculation of electric fields induced in the human knee by a coil applicator.

Calculations are presented of the induced electric fields and current densities in the cartilage of the knee produced by a coil applicator developed for applying pulsed magnetic fields to osteoarthritic knees. This applicator produces a sawtooth-like magnetic field waveform composed of a series of 260-micros pulses with a peak to peak magnitude of approximately 0.12 mT in the cartilage region. The simulations were performed using a recently developed 3 dimensional finite difference frequency domain technique for solving Maxwell's equations with an equivalent circuit model. The tissue model was obtained from the anatomically segmented human body model of Gandhi. The temporal peak electric field magnitude was found to be -153 mV/m, averaged within the medial cartilage of the knee for the typical dB/dt excitation levels of this coil. The technique can be extended to analyze other excitation waveforms and applicator designs.

Bone and Bones↗

PubMed1997

Calculation of electric fields induced near metal implants by magnetic resonance imaging switched-gradient magnetic fields.

Electric (E) fields induced near metal implants by MRI switched-gradient magnetic fields are calculated by a new equivalent-circuit numerical technique. Induced E-field results are found for a metallic spinal-fusion implant consisting of two thin wires connected to the metallic case of a current generator as well as for its subsections: a bare U-shaped wire, an insulated U-shaped wire, a cut insulated wire, and a generator. The presence of the metallic implants perturbs the E field significantly. Near the ends of the bare U-shaped wire, the E field is 89.7 times larger than in the absence of the wire. The greatest E field concentration occurs near the ends of the cut insulated wire, where the E field is 196.7 times greater than in the absence of the wire. In all cases, the perturbation of the induced E field by the implanted wire is highly localized within a few diameters of the wire.

Bone Wires↗

PubMed1989

The CDRH helix. A phase I clinical trial.

Seventeen patients have been given regional hyperthermia treatments using the Center for Devices and Radiologic Health (CDRH) Helix, a resonant helical coil unit. Most of these patients had large, clinically advanced tumors, whose mean volume exceeded 1000 cc. Mean maximum, minimum, and average temperatures were 40.6, 38.6, and 39.6 degrees C, respectively, for all sites combined. The pelvic heating capabilities of the CDRH Helix and the BSD-1000 annular phased array were compared, and generally were equivalent. Although the Helix could be used in a wider variety of locations, and was more comfortable and easier to use than the BSD-1000 annular phased array, neither device was particularly effective in generating clinically useful temperatures; the Helix is currently under investigation for use in regional-systemic hyperthermia in combination with antineoplastic drugs and biologic response modifiers.

Clinical Protocols↗

PubMedDate not supplied

Regional hyperthermia for deep-seated malignancies using the BSD annular array.

Forty-four patients were treated using the BSD-1000 Annular Phased Array between April 1983 and December 1986. There were 32 pelvic, nine abdominal, two extremity, and one thoracic sites treated. Mean tumour volume was 646 cc. Thirty-nine patients had concurrent radiation therapy, receiving a mean dose of 38 Gy. Mean average temperature was 41.0 +/- 1.4 degrees C. Most patients experienced local or systemic toxicity, requiring temporary treatment interruption in 33 patients, and termination of treatment in eight. Chronic complications were seen in four, but these were in patients receiving high total radiation doses as well. There were six complete and five partial responses. Among the 32 patients with pelvic tumours, mean tumour volume was 317 cc, mean radiation dose was 42 Gy, and mean average temperature was 41.3 +/- 1.2 degrees C. There were five complete and four partial responses. Achieving tumour temperatures greater than or equal to 42 degrees C with the annular array is difficult, due to both systemic and local toxicity. To improve clinical hyperthermia for thoracic, abdominal, and pelvic tumours, new technologies such as steerable phased array microwave systems; scanned, focused ultrasound; and permanently implantable thermoregulating ferromagnetic seeds, or new approaches such as using drugs to alter blood flow, or combining hyperthermia with antineoplastic drugs or biological agents, will be necessary.

Clinical Trials as Topic↗

PubMedDate not supplied

Finite element simulation of Sigma 60 heating in the Utah phantom: computed and measured data compared.

An initial series of comparisons are made between finite element computations and laboratory measurements obtained during heterogeneous phantom heating with the Sigma 60 applicator. The phantom is a relatively complex, though still idealized, rendering of the pelvic area which has been used to study the deep heating characteristics of the Sigma 60 in this anatomy. Direct electric field measurements as well as inferred SAR through transient temperature analysis are plotted against computed results along 11 one-dimensional tracks through the phantom. Quantitative comparisons provided through the track-by-track analysis show generally good agreement between computation and measurement. The finite element method is found to predict well the jumps in the electric field when polarized perpendicularly to a muscle/fat interface. Visualizations of the complete three-dimensional distributions are also highlighted and correlate well with physical reasoning about the expected behaviour of the fields produced. Some discrepancies in the data persist and are discussed and analysed in depth. They underscore the difficulties that can arise in performing comparisons between measured and computed results and stress the need for careful and thorough investigations when attempting these types of model validation studies.

Biophysical Phenomena↗