Ultrasound therapy in a physical therapy clinic is different than ultrasound or sonograms in radiology. Although both utilize sound waves at a higher frequency than the human ear can detect, depending on the frequency of the sound waves we can achieve different treatment results. In radiology a very high frequency is selected which tends to reflect off different tissues differently and a machine generates an image. In physical therapy we select a frequency of sound wave that penetrates deeper into the tissues resulting in an increased tissue temperature (deep heat). Most people don't feel the heat since the sound waves bypass the temperature receptors in the skin, but the therapeutic benefits are taking place none the less. The advantage of ultrasound is the sound waves' ability to penetrate up to 2” deep compared to 1/2 to 2/3” with superficial hot packs. These deeper benefits are especially useful for tissue and joints of the spine that are too deep to be reached by hot packs. Ultrasound also has selective benefits at the (specialized portion of the muscle) tendon bone interface as in a tendinitis.