Ultrasound

A picture of a fetus, aged 29 weeks, in a "3D ultrasound"

Ultrasound (also called ultrasonography, computer echotomography, echography (or echotomography), and ultrasonic imaging) is a type of using sound to make images of what is under the skin (such as in pregnancy) or the blood vessels. The images are made with a frequency higher than humans can hear. This frequency, the upper limit of human hearing, is approximately 20,000 hertz (20 kilohertz).

Another type of medical imaging, which unlike ultrasound, does come with risk, is computer tomography (CT). CT scans use X-rays to create the image.

Terms

Ultrasound is a tool used to make medical images in sonography. The images are called sonograms, sonography being a procedure.

It is a non-invasive procedure, which means it is relatively safe. It is safe because it does not require opening up the body or putting things in it. However it might be used to help other procedures, such as surgery, which is invasive. This type of sonography normally uses gel on the skin to make it slide around easier, which is easily wiped off after.

The computers which make the images use the echo of the sound waves. Ultrasonography creates what is called real-time imaging for doctors to see, and in pregnancy sometimes the mother and father too, in which case the heartbeat of the baby is there is one can be seen as a flicker on the monitor.

The echo is why echotomography starts with echo-. Tomo means slice in greek. -graphy means to graph or write down something (or in this case, show an image).

Echocardiography (the "cardio" in the middle) is ultrasonography used to look at, or operate on, the heart.

Obstetric ultrasonography is ultrasonography used during pregnancy

Hearing ultrasound

Some animals, such as dogs, dolphins, bats, and mice, are able to hear sounds which have a frequency higher than upper-limit of the human ear. This makes them able to hear ultrasounds. Children can hear some high-pitched sounds that older adults cannot hear, as in humans the upper limit pitch of hearing gets lower as a person gets older. This frequency limit is caused by the middle ear that acts as a low-pass filter. If ultrasound is fed directly into the skull bone and reaches the cochlea without passing through the middle ear, much higher frequencies (up to about 200 kHz) can be heard. This effect (sometimes called ultrasonic hearing) was first discovered by divers exposed to a high-frequency (ca. 50 kHz) sonar signal.

Medical ultrasonography is commonly used during pregnancy. Ultrasound is generally thought of as a "safe test" because it does not use destructive ionizing radiation like x-rays.

Ultrasonic cleaning

Ultrasonic cleaners are sometimes mistakenly called supersonic cleaners. They are used at frequencies from 20 to 40 kHz for jewellery, lenses and other optical parts, watches, dental instruments, surgical instruments and industrial parts. An ultrasonic cleaner works by the energy released from the collapse of millions of tiny (microscopic) bubbles near the dirty surface. The bubbles are formed by cavitation and collapse, forming small jets directed at the surface.

Related pages

• Obstetric ultrasonography
• Computed tomography (X-rays)