Ultrasound machines for home use versus those used by clinics?

How do the specs of ultrasound heating machines for home use compare to those used by clinics? (I'm talking about those used like "heat packs" on injuries, not the ones used for imaging.)

I don't know anything about the specs of the machines used in clinics. Most of the ones advertised for home use say 1 Mhz frequency but they don't specify a power rating.