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Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz". In air at atmospheric pressure, ultrasonic waves have wavelengths of 1.9 cm or less. Ultrasound can be generated at very high frequencies; ultrasound is used for sonochemistry at frequencies up to multiple hundreds of kilohertz.
Medical ultrasound includes diagnostic techniques (mainly imaging techniques) using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles, joints, blood vessels, and internal organs, to measure some characteristics (e.g., distances and velocities) or to generate an informative audible sound.
The transducer may be used in contact with the skin, as in fetal ultrasound imaging, or inserted into a body opening such as the rectum or vagina. Clinicians who perform ultrasound-guided procedures often use a probe positioning system to hold the ultrasonic transducer. [9] Compared to other medical imaging modalities, ultrasound has several ...
The disturbances caused by magnetostriction then propagate in the material as an ultrasound wave. In polycrystalline material, the magnetostriction response is very complicated. It is affected by the direction of the bias field, the direction of the field from the AC electric coil, the strength of the bias field, and the amplitude of the AC ...
Contrast in ultrasound imaging relies on the difference in acoustic impedance, a function of both the speed of the ultrasound wave and the density of the tissues, [12] between tissues or regions of interest. [5] As the sound waves induced by ultrasound interact with a tissue interface, some of the waves are reflected back to the transducer.
Synthetic aperture ultrasound (SAU) imaging is an advanced form of imaging technology used to form high-resolution images in biomedical ultrasound systems. Ultrasound imaging has become an important and popular medical imaging method, as it is safer and more economical than computer tomography (CT) and magnetic resonance imaging (MRI).
Weighing the Pros/Cons This article was reviewed by Craig Primack, MD, FACP, FAAP, FOMA. While weighing yourself every day certainly can help keep you on track, it can also lead to obsessive thoughts.
The notion of acoustic microscopy dates back to 1936 when S. Ya. Sokolov [1] proposed a device for producing magnified views of structure with 3-GHz sound waves. However, due to technological limitations at the time, no such instrument could be constructed, and it was not until 1959 that Dunn and Fry [2] performed the first acoustic microscopy experiments, though not at very high frequencies.