ABSTRACT
In earlier years, for the sake of simplicity, ultrasound propagation in biological tissues was assumed to be a linear phenomenon because it was believed that the power imparted by a diagnostic instrument was so low that nonlinear effects could not occur. As the requirement for better sensitivity (signal-to-noise ratio) and image quality grew, the peak and the average intensity used in diagnostic instruments increased. At sufficiently high ultrasonic pressure levels and intensities, it is inevitable that nonlinear effects appear as well as new acoustic phenomena. Among the most important are heating, wave distortion, cavitation, radiation force, and streaming (NCRP, 1983; Hamilton and Blackstock, 1998). Table 10.1 lists typical acoustic output values for ultrasonic diagnostic instruments (AIUM, 1992a; Patton et al., 1994; Zagzebski, 1996).
