Ultrasound
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Wikipedia-Article "Ultrasound"
Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz. Some animals, such as dogs, dolphins, bats, and mice have an upper limit that is greater than that of the human ear and thus can hear ultrasound.
Ultrasound has industrial and medical applications. Medical Sonography (also called ultrasonography) can visualise muscle and soft tissue, making them useful for scanning the organs, and obstetric sonography is commonly used during pregnancy. The use of microbubble contrast media in medical sonography to improve ultrasound signal backscatter is known as contrast enhanced ultrasound. This technique is currently used in echocardiography, and may have future applications in molecular imaging and drug delivery.
Typical diagnostic sonography scanners operate in the frequency range of 2 to 13 megahertz. More powerful ultrasound sources may be used to generate local heating in biological tissue, with applications in physical therapy and cancer treatment. Focused ultrasound sources may be used to break up kidney stones or for cataract treatment by phacoemulsification.
Diagnostic Sonography is often incorrectly referred to as "ultrasound"; however, ultrasound is a term of physics meaning acoustic energy with a frequency above human hearing. To call a sonogram an “ultrasound” is analogous to calling a photograph a "light". There are other uses of ultrasound in medicine that are not imaging or sonography. These include heating tissue in physical therapy, cleaning teeth in dental hygiene. Ultrasound is also used by iron workers for nondestructive testing of metals and welds, and jewelers use ultrasound to clean rings and watches. These other uses are not included in the definition of Diagnostic Sonography.
Ultrasonic cleaners, sometimes mistakenly called supersonic cleaners, are used at frequencies from 20-40 kHz for jewellery, lenses and other optical parts, watches, dental instruments, surgical instruments and industrial parts. The main mechanism for cleaning action in an ultrasonic cleaner is actually the energy released from the collapse of millions of microscopic cavitation events occurring in the liquid of the cleaner. Home cleaners are available and costs range from approximately US $100.
Ultrasound when applied in specific configurations can produce exotic phenomena such as sonoluminescence. These phenomena are being investigated partly because of the possibility of bubble fusion.
Ultrasound generator/speaker systems are sold with claims that they frighten away rodents and insects, but there is no scientific evidence that the devices work; controlled tests have shown that rodents quickly learn that the speakers are harmless.
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Dangers of Ultrasound
There have been disputes whether ultrasound is safe. But since ultrasound is energy, there are questions such as, "What are the energy waves doing to my tissue?" There are some reports of low birth weight babies being born to mothers who had more than the recommended ultrasound examination.
There may be side-effects of the following:
- Heat development: Local tissue absorb the ultrasound energy and increases the temperature of those tissues
- Bubble formation: Gasses, that are dissolved, come out of the solution due to local heat increases
However, there are no substantiated side-effects documented in studies.
From sound to image
The creation of an image from sound is done in three steps - producing a soundwave, receiving echos, and interpreting those echos.
Producing a sound wave
In medical ultrasonography, a soundwave is produced by creating short, strong pulses of sound from a phased array of piezoelectric transducers (usually a type of ceramic). The electrical wiring and transducers are encased in a probe. The electrical pulses vibrate the ceramic to create a series of sound pulses from each. The frequencies present in this sound wave can be anywhere between 2 and 10 MHz; well above the capabilities of the human ear. Any frequency above the capabilities of the human ear is referred to as 'ultrasound'. The goal is to produce a single focused arc-shaped soundwave from the sum of all the individual pulses emitted by the transducer.
To make sure the sound is transmitted efficiently into the body (a form of impedance matching), the transducer is coated with rubber and a special gel.
The soundwave, which is able to penetrate bodily fluids, but not solids, bounces off the solid object and returns to the Transducer, this return is an echo.
Receiving the echos
The return of the soundwave to the Transducer results in the same process that it took to send the soundwave, just in reverse. The return soundwave vibrates the Transducer and turns that vibration into an electrical pulse that is sent through the probe and into sonographer's computer where it can be interpreted and transformed into a digital image.
Interpreting the echo
The computer must determine three things from each electrical impulse received: 1.) Which wire did the impulse come from (There are multiple receiving wires on a transducer). 2.) How strong was the impulse. 3.) How long did it take the impulse to be received from when it was sent. Once the computer determines these three things, it can locate which portion of the monitor to light up and what color. Transforming the electrical signal into a digital image can be best explained by using a blank Microsoft Excel Worksheet as an analogy. The wire receiving the impulse determines the 'Column' in our Excel Worksheet (A,B,C,etc.). The time that it took to receive the impulse determines the 'Row' (1,2,3,etc.), and the strength of the impulse determines the color that the cell should change too (white for a strong pulse, black for a weak pulse, and varying shades of grey for everything in between.)
See also
- Dog whistle
- Infrasound (sound at extremely low frequencies)
- Light
- Pelvic ultrasound
- Physics
- Ultrasound weapons
- Gravis Ultrasound
- SoundTechNarrative2
- From Sound to Image
- Ultrasound flow meter
- Medical ultrasonography
- Contrast enhanced ultrasound