INFLUENCE OF WATER BOLUS TEMPERATURE ON MEASURED SKIN SURFACE AND INTRADERMAL TEMPERATURES

Temperature measurements utilizing thermometry probes placed on the sk in surface are often used clinically to assess temperatures for the pu rposes of power control and evaluating treatment efficacy. There is a question, however, as to what extent applicator temperature-controlled liquid coupling boluses can create temperature gradients which can ca use significant differences between measurements taken by sensors plac ed on the skin surface and the actual temperature of the tissue beneat h. To address this question, experiments were conducted with human sub jects instrumented with surface and shallowly implanted temperature se nsors. Microwave applicators with circulating bolus water set at 21 an d 41 -degrees-C were used to induce a temperature gradient in depth in the superficial tissue by thermal conduction. No microwave energy was applied. The average measurement offset at 41-degrees-C was 15 % of t he difference in temperature between the interstitially measured skin temperature and the coupling bolus temperature. towards the temperatur e of the coupling bolus. The corresponding offset with coupling boluse s set near 21-degrees-C was 32 %. Different water bolus types and volu mes were observed to induce different percentage offset errors.