CHANGES IN ULTRASONIC PROPERTIES OF LIVER TISSUE IN VITRO DURING HEATING-COOLING CYCLE CONCOMITANT WITH THERMAL COAGULATION

The present work considers the ultrasonic properties of porcine liver tissue in vitro measured during heating concomitant with thermal coagulation followed by natural cooling, so as to provide information about changes in the ultrasonic properties of the tissue after thermal coagulation. The excised liver samples were heated in a degassed water bath up to 75 degrees C and naturally cooled down to 30 degrees C. The tissue was observed to begin thermally coagulating at temperatures lower than 75 degrees C. The ultrasonic parameters considered include the speed of sound, the attenuation coefficient, the backscatter coefficient and the nonlinear parameter of B/A. They were more sensitive to temperature when heating than during natural cooling. All of the parameters were shown to rise significantly on completion of the heating-cooling cycle. At 35 degrees C after thermal coagulation, the B/A value was increased by 96%, the attenuation and backscatter coefficients were increased by 50%similar to 68% and 33%similar to 37%, respectively, in the typical frequency ranges of 3 MHz similar to 5 MHz used for ultrasonic imaging and the speed of sound was increased by 1.4%. The results of this study added to the evidence that tissue characterization, in particular, based on the B/A could be valuable for ultrasonically imaging the thermal lesions following high-intensity focused ultrasound (HIFU) surgery. (E-mail: mjchoi@jejunu.ac.kr) (C) 2011 World Federation for Ultrasound in Medicine & Biology.