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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.
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 hearing is a recognised auditory effect which allows humans to perceive sounds of a much higher frequency than would ordinarily be audible using the inner ear, usually by stimulation of the base of the cochlea through bone conduction. Normal human hearing is recognised as having an upper bound of 15–28 kHz, [1] depending on the person.
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 ...
The ultrasonic devices achieve high directivity by modulating audible sound onto high frequency ultrasound. The higher frequency sound waves have a shorter wavelength and thus don't spread out as rapidly. For this reason, the resulting directivity of these devices is far higher than physically possible with any loudspeaker system. However, they ...
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 ultrasound probe emits a high-frequency sound wave (usually a multiple of 2 MHz) that bounces off various substances in the body. These echoes are detected by a sensor in the probe. In the case of blood in an artery, the echoes have different frequencies depending on the direction and speed of the blood because of the Doppler effect. [2]
These procedures generally use lower frequencies than medical diagnostic ultrasound (from 0.7 to 2 MHz), but higher the frequency means lower the focusing energy. HIFU treatment is often guided by MRI. Focused ultrasound may be used to dissolve kidney stones by lithotripsy. Ultrasound may be used for cataract treatment by phacoemulsification.