Temperature dependence of ultrasonic propagation speed and attenuation in canine tissue.

Previously reported data on the temperature dependence of propagation speed in tissues generally span only temperature ranges up to 60 degrees C. However, with the emerging use of thermal ablative therapies, information on variation in this parameter over higher temperature ranges is needed. Measurements of the ultrasonic propagation speed and attenuation in tissue in vitro at discrete temperatures ranging from 25 to 95 degrees C was performed for canine liver, muscle, kidney and prostate using 3 and 5 MHz center frequencies. The objective was to produce information for calibrating temperature-monitoring algorithms during ablative therapy. Resulting curves of the propagation speed vs. temperature for these tissues can be divided into three regions. In the 25-40 degrees C range, the speed of sound increase rapidly with temperature. It increases moderately with temperature in the 40-70 degrees C range, and it then decreases with increasing temperature from 70-95 degrees C. Attenuation coefficient behavior with temperature is different for the various tissues. For liver, the attenuation coefficient is nearly constant with temperature. For kidney, attenuation increases approximately linearly with temperature, while for muscle and prostate tissue, curves of attenuation vs. temperature are flat in the 25-50 degrees C range, slowly rise at medium temperatures (50-70 degrees C), and level off at higher temperatures (70-90 degrees C). Measurements were also conducted on a distilled degassed water sample and the results closely follow values from the literature.