Ultrasound is a non-invasive imaging technique which utilizes high frequency sound waves beyond the range of human hearing to produce images. Sound waves are transmitted into the body by a probe, called a transducer. Some of the waves are reflected and these are processed by the ultrasound machine to form diagnostic images. Ultrasound can be used to image muscles, tendons, and many internal organs in real time. It can also be used to visualize an embryo or fetus during pregnancy. Ultrasound has been used to image the human body for at least 50 years and is one of the most widely used diagnostic tools in modern medicine. Diagnostic ultrasound poses no known risks and does not use ionizing radiation.