Errors in temperature measurement by thermocouple probes during ultrasound induced hyperthermia

A major problem in the use of localised hyperthermia for treatment of malignant tumours is to obtain an accurate measurement of the temperature in the tissue being treated. Thermocouple probes have generally been employed for measuring temperature elevation during ultrasound irradiation. However, when small objects such as thermocouples are in an ultrasound field in a medium such as tissue, viscous forces acting between the object and the tissue will cause an additional local rise in temperature (Fry & Fry, 1954a, b; Dunn, 1962; Hynynen et al, 1982). This will produce an error in any measurement of tissue temperature with invasive probes. The magnitude of the temperature elevation resulting from shear viscosity has been measured for 50 μm thermocouples in tumour tissue.