[n40487171]

The wave would be focused by the transducer (analog of a lens) so that the energy flux is highest at the focal point and presumably low enough not to cavitate outside the focal area. I.e. magnifying glass and the sun kinda thing.

[ugh123]

Makes sense but what if there's another organ in the way?

[stubish]

I think the way it works is you have sound from multiple sources, and you time the sound waves so that the peaks and troughs all hit the targeted area at the same time. Each individual 'beam' is harmless, but at the point of intersection they add up and can do damage.