The earliest introduction of vascular ultrasound contrast agents (USCA) was by Gramiak and Shah in 1968, when they injected agitated saline into the ascending aorta and cardiac chambers during echocardiographic to opacify the left heart chamber. Strong echoes were produced within the heart, due to the acoustic mismatch between free air microbubbles in the saline and the surrounding blood.

Huygens principle states that an expanding sphere of waves behaves as if each point on the wave front were a new source of radiation of the same frequency and phase. The principle explains how a flat ultrasound transducer can transmit a narrow ultrasound beam, which in the near field is confined to the dimensions of the transducer surface.
Spherical wavelets are emitted from numerous point sources on the transducer surface. They interfere to form a narrow, slightly converging beam of ultrasound in the near field. The wavefronts in the beam are nearly parallel. A precondition for this interference is that the transducer surface is much larger than the ultrasound wavelength.

See also Interference Artifact.

'SonoSite, Inc. is the worldwide market and technology leader in high performance, hand-carried ultrasound. Through its expertise in ASIC design, SonoSite is able to offer imaging performance typically found in ultrasound systems weighing more than 300 pounds in a system architecture that is approximately the size and weight of a laptop computer and provides a significant price to performance advantage compared to conventional systems. This breakthrough is transforming and expanding the worldwide diagnostic ultrasound market by serving existing clinical markets more efficiently and creating new point-of-care applications where ultrasound was either too cumbersome or too expensive to be used before. With over 15,000 systems sold since 1999, SonoSite products are known for exceptional performance, ease of use and durability.'

'SonoSite began as a division of ATL Ultrasound in 1997 focused on the development of all-digital, handheld ultrasound devices. In February 1995, the U.S. Defense Advanced Research Project Administration (DARPA) had awarded to ATL a two-year matching grant to develop a highly portable ultrasound device for use on the battlefield or in natural or man-made disasters to diagnose victims of severe trauma. This program culminated with a prototype in October 1998. ATL spun off SonoSite as a public company on April 6, 1998.'

In March 2012 Fujifilm Holdings completes the acquisition of SonoSite.

Ultrasound Systems:

Ultrasound elastography is a specialized imaging technique that provides information about tissue elasticity or stiffness. It is used to assess the mechanical properties of tissues, helping to differentiate between normal and abnormal tissue conditions.
The basic principle behind ultrasound elastography involves the application of mechanical stress to the tissue and measuring its resulting deformation. This is typically achieved by using either external compression or shear waves generated by the ultrasound transducer.
There are two main types of ultrasound elastography:
Both strain elastography and shear wave elastography offer valuable insights into tissue characteristics and can assist in the diagnosis and characterization of various conditions. In clinical practice, ultrasound elastography is particularly useful for evaluating liver fibrosis, breast lesions, thyroid nodules, prostate abnormalities, and musculoskeletal conditions. By providing additional information about tissue stiffness, ultrasound elastography enhances the diagnostic capabilities of traditional ultrasound imaging. It allows for non-invasive assessment, improves the accuracy of tissue characterization, and aids in treatment planning and monitoring of various medical conditions.
See also Ultrasound Accessories and Supplies, Sonographer and Ultrasound Technology.

Christian Johann Doppler first described the effect of motion of sound sources and the frequency change of the sound to the observer.
Doppler ultrasound uses this effect to detect and measure blood flow, and the major reflector is the red blood cell. Doppler ultrasound depends on the fact that if the reflecting surface is moving in relation to the transducer (blood flowing in a vessel) the frequency of the received ultrasound wave will be different from that of the transmitted wave. If blood cells are moving towards the transducer, they increase the frequency of the returning signal. As cells move away from the transducer, the frequency of the returning signal decreases.

See also Quadrature Detection and Doppler Techniques.