Ultrasound Nonlinearity Parameter of Soft Biological Tissues

Ultrasound non-linearity parameter (B/A) is determined using finite amplitude method. Second harmonic was generated on account of non-linear propagation of ultrasonic wave through the biological tissues. Transmitting transducers of 1.0 and 2.0 MHz and receiving transducers at double of these frequencies at 2.0 and 4.0 MHz were used. The second harmonic was analyzed and recorded. Biological samples under investigation were liver, kidney and spleen obtained from freshly sacrificed goat. Another group of samples were placed in 10% formaldehyde for 48 hours. The values of B/A for fresh liver, kidney and spleen turns out to become 7.48±0.05, 6.75±0.03 and 9.8±0.06 successively. However, in case of formalin fixed tissues the values were found to increase in all the samples to 7.52±0.04, 6.82±0.05 and 9.91±0.04 respectively. It appears that the trend of increasing B/A value is related to the structural, composition and state of the specimen. These observations, therefore, suggest the use of the nonlinearity parameter B/A in tissue characterization, particularly since structural alteration often attends the pathological state of the tissues.