[fc417fc802]

Waves scatter off of everything so that's not of concern. Depending on the intensity, frequency, and tissue in question ultrasound can have an effect. Someone elsewhere linked to a couple academic papers on the topic.

I share your hesitation about using this on the brain, at least barring exhaustive long term animal model trials. Subject a mammal to this every day for 10 years and show that there are no negative effects relative to the control.