PubMed HealthSearch

PubMed · 8288286

Analysis and optimization of waveguide multiapplicator hyperthermia systems.

Abstract

A method is proposed for determining the excitation coefficients of an antenna array operating in a large rectangular waveguide and used as a hyperthermia system. The excitation coefficients of the array elements are optimized for attaining an improved specific absorption rate (SAR) distribution around a deep-seated tumor. The method is applied to a two-dimensional problem of a piecewise homogeneous post in a waveguide representing a section of the human torso. The array is operating below the cutoff frequency of the dominant mode of the waveguide. Numerical simulations have been performed to check the effectiveness of this approach. The results show that by using the proposed optimization method, SAR distributions can be improved.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

A Boag, Y Leviatan. 1993. Analysis and optimization of waveguide multiapplicator hyperthermia systems.. https://doi.org/10.1109/10.245616

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

Myc-mediated transactivation of HSP70 expression following exposure to magnetic fields.

We investigated c-myc protein-binding sites on the HSP70 promoter as modulators of the induction of HSP70 gene expression in response to magnetic field stimulation (8microT at 60Hz) and whether the presence of c-myc protein potentiates transactivation of HSP70 expression. A 320 base pair region in the HSP70 promoter (+1 to -320) was analyzed. This region contains two c-myc-protein binding sites with consensus sequences located at -230 and -160 nucleotide positions (relative to the transcription initiation site) and overlapping with the region reported for the regulation of HSP70 gene expression by c-myc protein. This promoter region is upstream of other regulatory sequences, including the heat shock element (HSE), AP-2, and serum response element (SRE). Transfectants containing both c-myc protein-binding sites, HSP-MYC A and HSP-MYC B, and exposed to magnetic fields showed a 3.0-fold increase in expression of CAT activity as compared with sham-exposed control transfectants. Transfectants containing one c-myc binding site, HSP-MYC A, and exposed to magnetic fields showed a 2.3-fold increase in CAT expression. Transfectants in which both HSP-MYC A and HSP-MYC B binding sites were deleted showed no magnetic field sensitivity; values were virtually identical with sham-exposed controls. If the c-myc expression vector was not co-transfected with the constructs containing myc-binding sites, there was no difference in the expression of CAT activity between magnetically stimulated and sham-exposed controls, although both responded to heat shock. These data suggest that endogenous elevated levels of myc protein contribute to the induction of HSP70 in response to magnetic field stimulation.

Electromagnetic Fields

Magnetic field exposure enhances mRNA expression of sigma 32 in E. coli.

The mechanism of interaction between weak electromagnetic fields and cells is not understood. As a result, the health effect(s) induced by exposure to these fields remains unclear. In addition to questions relating to the site of initial magnetic field (MF) interactions, the nature of the cell's response to these perturbations is also unclear. We examined the hypothesis that the cells respond to MFs in a manner similar to other environmental stressors such as heat. Using the bacterium Escherichia coli, we examined the mRNA levels of sigma 32, a protein that interacts with RNA polymerase to help it recognize a variety of stress promoters in the cell. Our data show that the intracellular level of sigma 32 mRNA is enhanced following a 15-min exposure to a 60 Hz, 1.1 mT magnetic field.

Electromagnetic Fields