ESTIMATING THE ACOUSTIC ATTENUATION COEFFICIENT SLOPE FOR LIVER FROM REFLECTED ULTRASOUND SIGNALS

The acoustic attenuation coefficient measured in dB/cm is known to increase linearly with frequency for liver tissue. The slope of this linear function, denoted by β, has been shown by other investigators to be an indicator of tissue state. β is usually measured from the change in the log spectrum experienced by an acoustic pulse when it is transmitted through the tissue. Research is presented in estimatingβ from the reflected signals which are currently used in the clinical environment to generate diagnostic images. The reflected signals from internal tissue structures (in liver, the vascular and biliary system) are distorted by the irregular reflector shapes. By modeling the roughness of the typical acoustic reflector, the distribution of the values within each spectrum can be derived and the 95-percent confidence limits for the measured β can be calculated. The confidence limits are presented in terms of the tissue size and average reflector density. Experimental results using the reflected signals from in vitro refrigerated and formalinfixed liver sections are presented. It is predicted mathematically and verified experimentally that an uncertainty in the estimate exists due to the lack of knowing the exact reflector shapes within the liver. This uncertainty decreases as the amount of available data increases. For a large organ, such as liver, which provides large quantities of reflected data, our signal processing techniques may provide diagnostically valuable information. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.