Estimation of the thermo-physical property of biological tissues from temperature rise due to ultrasound exposure

This study discusses the feasibility of a method for ultrasonic tissue characterization according to the thermo-physical properties of biological tissues. Since this method measures the ratio of sound velocity variation due to ultrasonic heating, it is significant to clarify the relationship between the ratio and thermo-physical properties. The ratio of sound velocity variation of a tissue sample was measured from phase shifts of echoes before and after the temperature rise by transmitting an ultrasonic pulsed wave. In the experiments the transducer used for heating was a resonance frequency of 5.0 MHz, concave ring shape, inner diameter of 5 mm, and outer diameter of 12 mm. It was arranged coaxially on the outer perimeter of the transducer used for the measurement. This transducer was a resonance frequency of 10 MHz, a focal distance of 15 mm, and a diameter of 4 mm. The exposure time of heating ultrasound is 100 ms. As a result of heating sound pressure of 1.0 MPa, 1.5 MPa and 2.0 MPa, the estimated values of temperature rise were 0.56 ˚C, 1.1 ˚C and 2.0 ˚C, respectively. [This study was supported by MEXT-Supported Program for the Strategic Research Foundation at Private Universities, 2013-2017.]