Evaluation of a Three-Hydrophone Method for 2-D Cavitation Localization.

Cavitation is a critical parameter in various therapeutic applications involving ultrasound (US) such as histotripsy, lithotripsy, drug delivery, and cavitation-enhanced hyperthermia. A cavitation exposure outside the region of interest may lead to suboptimal treatment efficacy or in a worse case, to safety issues. Current methods of localizing cavitation are based on imaging approaches, such as beamforming the cavitation signals received passively by a US imager. These methods, although efficient, require expensive equipment, which may discourage potential future developments. We propose a three-hydrophone method to localize the cavitation cloud source. First, the delays between the three receptors are measured by detecting the maximum of their intercorrelations. Then, the position of the source is calculated by either minimizing a cost function or solving hyperbolic equations. After a numerical validation, the method was assessed experimentally. This method was able to track a source displacement with accuracy similar to the size of the cavitation cloud (2-4 mm). This light and versatile method provides interesting perspectives since localization can be executed in real time, and the extension to 3-D localization seems straightforward.

Determination of the acoustic pressure at and the reflection coefficient of a target through measurements of the absorbed power and the emitter voltage.

A harmonic acoustic wave, fed back by a reflecting target, modifies the electric impedance of the emitter. This effect is studied using a tightly focused beam and various flat targets with known reflection coefficients, which are placed at pressure maxima or minima of the standing wave in the focal zone. It is possible to establish relationships that allow one to determine, for flat targets with unknown acoustic properties, the acoustic impedance and reflection coefficient of the target as well as the acoustic pressure present at the target, only from measurements of the absorbed power and the emitter voltage.