The practice of medicine has been revolutionised by imaging – the ability
to see inside the intact human body. Nowadays, the principal methods of
clinical imaging are X-ray, radionuclide, magnetic resonance and ultrasonic techniques. Ultrasonic imaging uses mechanical waves, usually with frequencies in the megahertz range. The method can provide two- and three-dimensional images, often in real time, as well as information about blood flow and tissue motion. Contrast agents are coming into clinical use, and research into elasticity and photoacoustic imaging is opening up new areas of application.