The development of harmonic distortion in pulsed finite-amplitude ultrasound passing through liver.

The progressive development of finite-amplitude distortion of ultrasonic pulses has been investigated in excised bovine liver using pulsed focused ultrasonic beams at nominal frequencies of 2.5 and 3.5 MHz. Both the transducers and the powers used were those which may be encountered with clinical imaging equipment. Significant distortion of the waveform was observed to occur, particularly at higher powers. For example, at 2.5 MHz, with a mean input pressure (p0) of 0.58 MPa, the second harmonic in the pulse spectrum showed a maximum value of 10.5 dB below the fundamental and the highest third harmonic component was 19 dB below the fundamental. These particular observations illustrate that finite-amplitude distortion may be of considerable significance in the transmission through tissue of ultrasonic pulses during diagnostic scanning.