How HIFU Works
In order to understand the basic concept of how HIFU works an analogy can be drawn between HIFU burning prostate tissue and sun rays entering a magnifying glass to burn a leaf. When a magnifying glass is held above a leaf in the correct position on a sunny day the sun's rays intersect below the lens and cause the leaf to burn at the point of intersection.
If you insert your hand into the path of either one of the sun's rays individually, away from the point of intersection, there is no significant heat felt or harm caused. Alternatively, if you place your hand at the point of intersection you will be burned.
The scientific principles at work in this example are the same as those with HIFU. Instead of light as the energy source, HIFU utilizes sound. Instead of a magnifying glass, HIFU uses a transducer. Just as the individual ray does not burn the hand, the individual sound wave does not burn the tissue it travels through.