Microwave radiation is one of the most useful techniques for creating thermal fields in tissue, but its use is limited because of the rapid attenuation of propagation through the body. Therefore, a superficial localized tumor is only the object of microwave hyperthermia.
This study was designed to perform fundamental experiments with localized hyperthermia induced by 2450 MHz microwave radiation. In order to improve the temperature distribution and heating efficiency produced by Microtizer (Minato Medical Science Co., Ltd), we used a cylindrical cardboad cone covered with alminum foil and a collimator with a hole in the alminum plate that were specially designed. The characteristics of temperature distribution patterns using these applicators were tested using a tissueequivalent agar phantom and an unhomogeneous phantom which contained a ham or animal muscle with fat.
The conclusions were drawn from our experimental results as follows;
1) By the use of specially desinged cone and collimator, focusing microwave radiation was improved, that is, both the homogeneity of temperature distribution patterns and the high elevation of temperature were achieved.
2) The relation between the distance from an antenna-tip to phantom surface and the heating efficiency depended on conditions of microwave radiation. With a single refrector, the heating effect decreased in inverse proportion to the distance. With the use of a cone and a collimator, however, the optimum distance of 13 cm exsisted, depending on a given frequency.
3) The hole diameter of collimators for obtaining effective temperature distribution patterns depended on a frequency employed. The heating efficiency was not achieved when the hole diameter was less than λ/4.
4) There was no relationship between VSWR (voltage standing wave ratio) and heating effect.
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