MULTI-CHANNEL SYSTEM FOR MICROWAVE-HEATING OF TISSUES

A four-channel microwave heating system, designed for the treatment of small animals, has been described. The temperature of each region treated may be maintained to within approximately ±0.15°C and thermal gradients in the tissues may be minimized by adjustment of microwave power and liquid-bolus temperature. It has been demonstrated that orientation of the tissue with respect to the microwave electric field does not affect significantly the absorption of microwaves by the tissue. The cooling effect of blood flow within tissue during microwave heating may be reduced from that observed when heating is by immersion in hot water. Although this system is designed for the treatment of experimental animals, the technique of controlled switching of microwave power to a number of applicators should also prove to be of use in the treatment of patients. The heating of deeply lying tissues relative to superficial ones could be increased by using a number of direct contact applicators. The heating patterns produced in tissues by such applicators can be calculated and, by proper choice of their relative positions and the duration and sequence in which they are energized, an optimum hyperthermia treatment can be envisaged. It is well known that many artefacts may appear in the measurement of temperature with thermocouples or thermistors in the presence of elctromagnetic fields. The control of microwave power, either by modulation of the microwave generator or by switching into a dummy load, would allow reliable temperature measurements in the tissue to be made in the absence of microwaves.