Beschreibung:
<jats:p>The paper describes a method able to perform an ultrasonic study of a single UCA bubble immersed in a tank filled with a liquid (water) by means of ultrasonic equipment able to insonify and acquire RF echo signals coming from an isolated bubble with a high frame rate. The work was focused on the study of subharmonic emission from an isolated bubble of SonoVue. In particular, the acoustic pressure threshold for a subharmonic stable emission was evaluated for a subset of 50 microbubbles at 3.3 MHz and at 5 MHz of insonation frequencies. An unexpected second pressure threshold, which caused the standstill of the subharmonic emission, was detected at 3.3 MHz and 5 MHz. A transient subharmonic emission, which is hypothesized as being related to the formation of new free gas bubbles, was detected during the ultrasound-induced destruction of microbubbles. Several sequences of RF echo signals and the related spectra, acquired from a set of 400 isolated microbubbles, is investigated at different acoustic driving pressures and excitation frequencies. Specific bubble behaviors concerning the stable subharmonic emission, the inhibition of subharmonic generation, and the transient subharmonic emission were detected during experimentation and discussed in this paper.</jats:p>