Therapeutic ultrasound is different than diagnostic ultrasound. Diagnostic ultrasound allows physicians to look at tissues and structures inside the body. Therapeutic ultrasound is a deep heating modality. It can be used to heat tissues 3 cm deep into the body. Theraputic ultrasound also uses a gel on the patient to help the ultrasound tool glide over the surface of the skin. The patient may feel warmth during the therapy. Therapeutic ultrasound is good at increasing collagen extensibility, increasing metabolism of edema, promoting cellular repair, decreasing joint stiffness, and decreasing muscle spasm.