Ultrasound is a technique using pulsed high frequency sound waves to produce an image of a wide range of body parts and blood vessels.
A hand-held transducer and gel will be placed on the skin. The transducer sends a brief pulse of sound (a millionth of a second) into the body. The travelling pulse reaches different body structures and sends back echoes to a high speed computer which transforms them into images which are displayed on a monitor.
Your ultrasound will be performed by a sonographer or a radiology doctor. As far as medical research understands, diagnostic ultrasound is a safe procedure.