Nonlinearity parameter for tissue-mimicking materials

A finite amplitude insert-substitution method has been used to determine the ultrasonic nonlinearity parameter BIA of nine versions of water-based, macroscopically uniform ultrasonically tissue-mimicking (TM) nonfat and fat materials. In this method, the amplitude of the second harmonic following transmission through degassed distilled water with known B/A (B/A = 5.2) and the amplitude of the second harmonic following transmission through the unknown sample are measured. The ratio of these amplitudes allows calculation of the B/A of the sample. Measured B/A values of the nonfat materials range from 5.6 to 6.6, These values compare favorably with published values for nonfat soft tissues. In contrast, the measured B/A values for two tissue-mimicking fat materials are 9.8 and 11.1; these two values represent the low and high end of B/A for most fresh fatty tissues. For comparison, B/A was measured for two commonly available uniform materials, corn oil and ethylene glycol, and the results are in good agreement with published values. (C) 1999 World Federation for Ultrasound in Medicine & Biology.