Measurement of thermal diffusivity of biomaterials by focused ultrasonic beams (thermal pulse decay method by focused ultrasonic beams).

This study propose a new simple method of measuring the thermal diffusivity of living tissue by thermal pulse decay technique with focused ultrasonic beam, which does not require the accurate knowledge of Gaussian variance within the focal region. The measurement of temperatures at two different locations outside the focal region replaces the elaborate measurement of the size of the focal region and gives a thermal diffusivity with reasonable accuracy and automatically avoids the artifact due to beam-thermocouple interaction. The focused ultrasound was generated by the bowl-shaped ceramic piezoelectric transducer with the diameter of 30 mm. The focal lengths of transducer were 40 mm and 60 mm and the frequencies 1.7 and 3.6 MHz. The values of thermal diffusivity of biological tissues obtained in this method are fairly close to the previously published values and are also compared to the values obtained by heated thermistor method.