Ultrasound imaging is a common diagnostic procedure which uses high-frequency sound waves to produce dynamic images (sonograms) of organs, tissues, or blood flow within the body. Ultrasonography is a technical term for ultrasound imaging. It can be used to perform both diagnostic and therapeutic procedures such as when ultrasound is used as a guide in interventional procedures. During ultrasound imaging a hand-held probe (called a transducer) is placed directly on the region to be visualised and moved over it. A water-based gel is applied to the area to couple the ultrasound between the transducer and patient. Apart from musculoskeletal disorders, diagnostic ultrasonography is used in many other specialities including cardiology, endocrinology, gastroenterology, gynaecology, obstetrics, ophthalmology and urology.