Frequency modulated pulse for ultrasonic imaging in an attenuating medium

Abstract

It is argued that the probability that ultrasound used at the intensities employed clinically will cause bioeffects characteristic of transient cavitation is immensely greater above a threshold peak intensity of the interrogating ultrasound pulse. Simulations and experiments in nonattenuating media show that a factor of 16 to 50 reduction in peak intensity is possible without sacrificing the signal primarily used for imaging, or the resolution. This factor depends on the effective time-bandwidth product of the frequency modulated pulse. However, in a frequency-dependent attenuating medium, such as soft tissue, this advantage could diminish. A linear-frequency and linear-phase model for attenuation was incorporated in the simulation process. The time-bandwidth product was evaluated for reflectors at various depths and as a function of the center frequency and bandwidth of the frequency-modulated pulse.<>