Heating patterns produced in humans by 433.92 MHz round field applicator and 915MHz contact applicator.

Temperature distributions produced by a round field applicator operating at a frequency of 433.92 megahertz (MHz) are comparable to those produced by a 915 MHz cooled contact applicator in human volunteers with less than or equal to 1 cm or greater than or equal to 2 cm of subcutaneous fat. The major difference between the two applicators is the temperatures produced on the skin surface and in the subcutaneous fat in humans. The circulating coolant of the 915 MHz contact applicator keeps skin surface temperatures much lower than those produced by the round field applicator in thick and thin subjects. It also tends to cool the superficial subcutaneous fat layer in thin subjects but doesn't affect the deeper subcutaneous fat layer in subjects with greater than or equal to 2 cm of subcutaneous fat. The 915 MHz contact applicator gives the ability to control by cooling the temperatures produced in the superifical tissues. By regulating the temperature of coolant and time of cooling, temperature gradients can be modified so the highest temperatures may be found in the muscle. However, the superficial tissue temperature cannot be regulated with the present application of the 433.92 MHz applicator. When the two applicators were compared, it was shown that the 433.92 MHz round field applicator did not surpass the heating ability of the 915 MHz contact applicator. Therefore, at this time, there is no reason to legalize the frequency of 433.92 MHz for diathermy use in the United States.