Change in acoustic impedance and sound speed of HIFU-exposed chicken breastmuscle

High-intensity focused ultrasound (HIFU) is used as a therapeutic method totreat non-superficial-tumors by inducing high temperature to coagulate them. Inthis study, we measured the acoustic impedance distribution and sound speed ofthe HIFU-exposed chicken breast muscle. HIFU exposure was at about 800 W/cm² for 60 s. Ultrasound B-mode images were taken at before and afterthe HIFU exposure for focal plane. The HIFU-exposed specimen was sliced asthickness of 3 mm to measure sound speed. Acoustic impedance was mapped for fivespecimens using an ultrasound impedance microscope at room temperature. Meanacoustic impedance of non-denatured region and thermally denatured region was(1.65 0.021) and (1.61 0.023) [10⁶ kgm² s ¹],respectively. Sound speed of the specimen was measured for four specimens by apulse-echo method at 26.5 0.5C in a thermostat bath. The mean sound speed ofthermally denatured and non-denatured specimens was (1603.8 8.0) and (1569.012.8) [m/s], respectively. The acoustic impedance and sound speed of thecoagulated specimen was similarly lower than that of the non- coagulatedspecimen. The decrease ratios of those were quantitatively consistent. A B-modeimage of the HIFU-exposed specimen shows a bright region at the HIFU focalpoint, corresponding to the thermally denatured region. In a B-mode image fromthe acoustic impedance map, a similar bright region was observed.