Ultrasound uses a sound wave with a frequency much higher than human hearing. Diagnostic Ultrasound, or Sonography, is similar in principle to sonar in a submarine whereby images are formed by detecting reflected sound waves or echoes. Most people are familiar with ultrasound examinations as they are routinely used during pregnancy. Gel is placed on the relevant body part and a small hand held ultrasound probe or transducer is applied. The transducer emits a high frequency sound wave, which then passes into the body. Some sound is reflected back to the transducer and this reflection is reconstructed as an image on a monitor. Ultrasound is used to image many soft tissue structures in the body including blood vessels, muscles and internal organs.