Study of ultrasonic contrast agents using a dual-frequency band technique

We have developed a dual-frequency band technique to study frequency-depend ent phenomena associated with ultrasonic contrast agents, Our technique use s a superimposed high-frequency (10 MHz) broad-band ultrasound (US) pulse t o investigate contrast agent interaction with a low-frequency (e.g., 0.5 MH z) ultrasonic field, Our digitally controlled system has the ability to pro duce two colinear, confocal US pulses at different center frequencies, to a djust the relative phasing and pulse repetition frequency of each pulse, an d to acquire digital backscatter data. A series of experimental studies dem onstrated that the high-frequency backscatter signal responded to several p henomena induced in contrast agent particles by the low-frequency beam. The se phenomena included radial pulsations, nonlinear oscillations and depleti on. Initial results also demonstrated a relative phase shift between the hi gh- and low-frequency signals; this shift is due to a difference in sound v elocity at these frequencies, and it may convey information about the contr ast agent concentration. (C) 2000 world Federation for Ultrasound in Medici ne & Biology.