Improvements in the spectral difference method for measuring ultrasonic attenuation.

The accuracy of the spectral difference method for measuring ultrasonic attenuation has been investigated using tissue-mimicking phantoms. Attenuation coefficients of the phantom materials were measured using a narrow-band substitution technique and compared with the results of the spectral difference method. Agreement within +/-10 percent was typical for measurements in homogeneous materials. The best agreement between the spectral difference and substitution techniques was obtained when effects due to transducer beam diffraction were taken into account in the analysis. This was found for two types of homogeneous tissue-mimicking materials, both having speed of sound and attenuation properties similar to human liver but each with different backscatter properties. The effects of inhomogeneous tissues interposed between the transducer and the interrogated volume were also studied by simulating these conditions in phantoms. Experimental techniques which minimize the effects of perturbations introduced by these inhomogeneities are suggested.