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Ultrasound is sound with frequencies greater than 20 kilohertz. [1] This frequency is the approximate upper audible limit of human hearing in healthy young adults. The physical principles of acoustic waves apply to any frequency range, including ultrasound. Ultrasonic devices operate with frequencies from 20 kHz up to several gigahertz.
Derivative of Heath Raftery's own creation. Rough diagram of sound frequency scale, showing ultrasound and some applications. Date: 28 June 2010, 23:30 (UTC) Source: Ultrasound_range_diagram.png; Ultrasound_range_diagram_png_(sk).svg; Author: Ultrasound_range_diagram.png: The original uploader was LightYear at English Wikipedia.
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.
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.
Medical ultrasound uses high frequency broadband sound waves in the megahertz range that are reflected by tissue to varying degrees to produce (up to 3D) images. This is commonly associated with imaging the fetus in pregnant women.
All modern ultrasound scanners use pulsed Doppler to measure velocity. Pulsed wave instruments transmit and receive series of pulses. The frequency shift of each pulse is ignored, however the relative phase changes of the pulses are used to obtain the frequency shift (since frequency is the rate of change of phase).
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 .
This article contains contradictory figures for the ranges of ultrasound used in medical ultrasonography. 15 MHz, 18 MHz, and 20 MHz are all listed as upper limits of the range of frequencies used. User:Madmonk325 —Preceding signed but undated comment was added at 03:28, 26 September 2007 (UTC) [ reply ]