An ultrasound machine produces ultrasound waves by means of a piezoelectric transducer. The ultrasonic vibrations that are produced are then transmitted through soft tissue with the help of a conductive gel. This gel, also known as ultrasound gel, keeps air pockets from forming between the skin and the head of the transducer, helping the sound waves penetrate the skin evenly as the wand is moved around the treated area. Ultrasound procedures usually last between 5 to 10 minutes and the patient can feel a mild pulsating or slight warmth, but no discomfort should occur. Make sure you never use ultrasound machines or other electrotherapy devices over open wounds or near a pacemaker.