Ultrasound (sonography) is a medical diagnostic technique which uses high frequency sound waves. When these sound waves meet interfaces (when one tissue meets another) between tissues, part of the wave is reflected back to receivers, making a "reflective pattern" which is then sent to a computer.

The computer processes the information and produces an image which can be used for diagnostic purposes. Ultrasound can be used for various foot conditions,  and is often used to help diagnose Achilles tendon injuries, ankle sprains, soft tissue masses and infections.