What is the type of ultrasound used for deep tissue massages during physical therapy?

Therapeutic: It is quite literally called "therapeutic ultrasound". The frequency used is 0.7 to 3.3 MHz. Diagnostic (imaging) ultrasound uses frequencies 3 to 18 MHz. The theory is that the ultrasound waves warm the tissues and break up scars to hasten recovery. However, there is controversy on whether therapeutic ultrasound actually works, as scientific studies tend to contradict each other on the subject.