Effect of gaseous inclusions on the frequency dependence of ultrasonic attenuation in liver.

The greatest variation in published data of the attenuation of ultrasound in mammalian liver in vitro occurs at the lower end of the 0.5 to 7 MHz frequency range and gives rise to some departure from a linear or simple power law dependence of attenuation on frequency. These effects do not appear to be highly dependent on the method of measurement. It is suggested that they are due to a varying presence of small gas bubbles distributed throughout the tissue--a suggestion based on calculated estimates of the attenuation due to microscopic bubbles and on the measured frequency dependence of attenuation in water loaded sponges containing varying amounts and distribution of gas. We now believe that preferred methods of tissue specimen preparation, for in vitro measurement of ultrasonic attenuation or scattering, should involve either pressurization as described elsewhere (Frizzell et al., 1979) or storage under refrigeration.