Ultrasound enables the rapid acquisition of high-resolution images of anatomic structures in real time. Medical ultrasound refers to the emission of sound waves at frequencies above the human audible range. The waves travel through tissues and are reflected at tissue interfaces before returning for processing. Using the speed of sound and the time taken to return, the distance from the transducer to the tissue edge is calculated and used to generate two-dimensional images.

The image obtained is dependent on the strength and quality of the emitted and returning signal. Attenuation of the signal is also determined by absorption, scattering, acoustic impedance, diffraction, and refraction. Higher frequencies using linear probes achieve greater spatial resolution but have low tissue penetration. These are better for superficial structures. For deeper structures curvilinear probes which use lower frequencies are required. However this limits spatial resolution. The sonographic appearance of structures will also vary according to the plane of the ultrasound beam e.g. transverse or longitudinal. Perioperative uses of ultrasound include guidance for regional anaesthesia and vascular cannulation, examination of pulmonary, gastric, and other abdominal structures and echocardiography of the heart and great vessels.