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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.
This method of medical ultrasound therapy can be used for various types of pain relief and physical therapy. In physics, the term "ultrasound" [1] applies to all acoustic energy with a frequency above the audible range of human hearing. The audible range of sound is 20 hertz – 20 kilohertz. Ultrasound frequency is greater than 20 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.
These procedures generally use high frequency ultrasound (1–10 MHz) and a range of intensities (0–20 W/cm 2). The acoustic energy is focused on the tissue of interest to agitate the cellular matrix and make it more permeable for therapeutic drugs. [14]
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).