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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 ultrasound within tissue consists of very high frequency sound waves, between 800,000 Hz and 20,000,000 Hz, which cannot be heard by humans. Some of the advantages of ultrasound as a diagnostic and therapeutic tool include its safety profile, lack of radiation, portability, and low cost. [ 4 ]
Ultrasound energy, simply known as ultrasound, is a type of mechanical energy called sound characterized by vibrating or moving particles within a medium. Ultrasound is distinguished by vibrations with a frequency greater than 20,000 Hz, compared to audible sounds that humans typically hear with frequencies between 20 and 20,000 Hz.
For frequencies of ultrasound from 25 to 50 kHz, a guideline of 110 dB had been recommended by Canada, Japan, the USSR, and the International Radiation Protection Agency, and 115 dB by Sweden [24] in the late 1970s to early 1980s, but these were primarily based on subjective effects. The more recent OSHA guidelines above are based on ACGIH ...
Typical diagnostic ultrasound machines operate in the frequency range of 2-18 megahertz, whereas home ultrasound machines and therapeutic ultrasound machines operate in the frequency range of .7-3.3 megahertz. Diagnostic sonography is typically used to create an audio "image", such as during pregnancy to visualize the developing baby.
A curvilinear array ultrasonic transducer for use in medical ultrasonography Inside construction of a Philips C5-2 128 element curved array ultrasound sensor. Ultrasonic transducers and ultrasonic sensors are devices that generate or sense ultrasound energy. They can be divided into three broad categories: transmitters, receivers and transceivers.
Mechanical index (MI) is a unitless ultrasound metric. It is defined as [1] =, where P r is the peak rarefaction pressure of the ultrasound wave , derated by an attenuation factor to account for in-tissue acoustic attenuation; f c is the center frequency of the ultrasound pulse .