How fast does ultrasound travel

An ultrasound scan uses high-frequency sound waves to create images of the inside of the body. It is suitable for use during pregnancy. Ultrasound scans, or sonography, are safe because they use sound waves or echoes to make an image, instead of radiation. Ultrasound scans are used to evaluate fetal development, and they can detect problems in the liver, heart, kidney, or abdomen. They may also assist in performing certain types of biopsy.

The person who performs an ultrasound scan is called a sonographer, but the images are interpreted by radiologists, cardiologists, or other specialists. Ultrasound is sound that travels through soft tissue and fluids, but it bounces back, or echoes, off denser surfaces.

This is how it creates an image. For diagnostic uses, the ultrasound is usually between 2 and 18 megahertz MHz. Higher frequencies provide better quality images but are more readily absorbed by the skin and other tissue, so they cannot penetrate as deeply as lower frequencies.

Ultrasound will travel through blood in the heart chamber, for example, but if it hits a heart valve, it will echo, or bounce back. It will travel straight through the gallbladder if there are no gallstones , but if there are stones, it will bounce back from them.

This bouncing back, or echo, gives the ultrasound image its features. Varying shades of gray reflect different densities. Some very small transducers can be placed onto the end of a catheter and inserted into blood vessels to examine the walls of blood vessels. Ultrasound is commonly used for diagnosis, for treatment, and for guidance during procedures such as biopsies.

It can be used to examine internal organs such as the liver and kidneys, the pancreas, the thyroid gland, the testes and the ovaries, and others. Scientists can study sounds by measuring the size and energy of the waves that are created.

Wave frequency refers to the length of a wave and how fast it is traveling. Sound wave frequency is measured using a unit called Hertz Hz. Our ears can hear audible sound , which are sounds with frequencies that range between 20 and 20, Hz.

Any sound frequencies above or below that cannot be heard by our ears. Look at Figure 1 to learn about the different sound frequencies that were discussed here. If you stop reading this and let out a high-pitched scream, you can probably generate sound waves with frequencies of about 3, Hz. We can use special machines to generate ultrasound frequencies that are much greater than that.

The machines we use to generate ultrasounds can create sound waves with frequencies above 1,, Hz. These very high frequency sounds are especially useful in medicine because they can be used to safely look inside our bodies. Because sound has the ability to travel through air, liquids, and solids, we can point sound waves toward the heart, for example, and see what the naked eye cannot see through the skin.

Imagine yourself standing in a valley between two large mountains. If you scream loudly, you will hear an echo of your voice.

This is because the sound waves bounce back and forth between the mountains and return back to your ears. Similarly, an ultrasound machine produces sound waves and listens for the returning waves made by the sound bouncing back off the tissues that make up the different organs in your body. In Figure 2 , you can see an ultrasound probe that produces ultrasound waves. When it is pointed at your body, the sound waves can travel through your skin and into the organ that your doctor wants to look at for example, your liver.

Every time the waves hit a surface with different physical properties, they get reflected back to the probe [ 1 ]. The probe measures the amount of time it takes for each wave to return to it.

Using this information, a computer is able to calculate the distance to each surface the wave bounces into. The computer puts all this information together and creates an image of what is deep inside your body. Different tissues in your body appear differently on an ultrasound machine. This is because the amount of sound that is reflected back from the tissue and heard by the machine depends on the type of tissue that the sound waves are hitting and the speed of the waves coming back to the probe [ 1 ].

In medicine, ultrasound waves can be used to identify why someone is sick—this is referred to as a diagnostic use. An ultrasound can also be used to assess blood flow within the body. The ultrasound transducer that does this contains a Doppler probe, which evaluates the speed and direction of blood flow in vessels by making the sound waves easy to hear. The degree of loudness of the sound waves indicates the rate of blood flow within a blood vessel.

Absence or faintness of these sounds may mean there is a blockage of blood flow. Ultrasound may be used to assess the size and location of organs and structures in the body. It can also be used to check the body for conditions such as:. Ultrasound may be used to guide needles used to biopsy the removal of a piece of tissue for testing.

Ultrasound is also used to drain fluid from a cyst or abscess. There may be other reasons for your healthcare provider to recommend an ultrasound. There is no radiation used and generally no discomfort caused by moving the ultrasound transducer over the skin. Ultrasound may be safely used during pregnancy or in people with allergies to contrast dye, because no radiation or contrast dyes are used. There may be risks depending on your specific medical condition. Be sure to discuss any concerns with your healthcare provider before the procedure.

A 3D ultrasound image of a fetus. As well as for the detection of any abnormalities, such scans have also been shown to be useful for strengthening the emotional bonding between parents and their unborn child.

Indeed, current technology cannot do quite this well. In practice, 1-mm detail is attainable, which is sufficient for many purposes.

Higher-frequency ultrasound would allow greater detail, but it does not penetrate as well as lower frequencies do. Higher frequencies may be employed in smaller organs, such as the eye, but are not practical for looking deep into the body.

In addition to shape information, ultrasonic scans can produce density information superior to that found in X-rays, because the intensity of a reflected sound is related to changes in density. Sound is most strongly reflected at places where density changes are greatest.

Figure 6. This Doppler-shifted ultrasonic image of a partially occluded artery uses color to indicate velocity. The highest velocities are in red, while the lowest are blue. The blood must move faster through the constriction to carry the same flow.

Another major use of ultrasound in medical diagnostics is to detect motion and determine velocity through the Doppler shift of an echo, known as Doppler-shifted ultrasound. This technique is used to monitor fetal heartbeat, measure blood velocity, and detect occlusions in blood vessels, for example. See Figure 6. The magnitude of the Doppler shift in an echo is directly proportional to the velocity of whatever reflects the sound.

Because an echo is involved, there is actually a double shift. The first occurs because the reflector say a fetal heart is a moving observer and receives a Doppler-shifted frequency. The reflector then acts as a moving source, producing a second Doppler shift. A clever technique is used to measure the Doppler shift in an echo. The frequency of the echoed sound is superimposed on the broadcast frequency, producing beats. But measuring the beat frequency is easy, and it is not affected if the broadcast frequency varies somewhat.

Furthermore, the beat frequency is in the audible range and can be amplified for audio feedback to the medical observer. Doppler-shifted radar echoes are used to measure wind velocities in storms as well as aircraft and automobile speeds. The principle is the same as for Doppler-shifted ultrasound. There is evidence that bats and dolphins may also sense the velocity of an object such as prey reflecting their ultrasound signals by observing its Doppler shift.

Figure 7. Ultrasound is partly reflected by blood cells and plasma back toward the speaker-microphone. Because the cells are moving, two Doppler shifts are produced—one for blood as a moving observer, and the other for the reflected sound coming from a moving source. The magnitude of the shift is directly proportional to blood velocity. Ultrasound that has a frequency of 2.

Assume that the frequency of 2. The last question asks for beat frequency, which is the difference between the original and returning frequencies. Identify knowns. The beat frequency is simply the absolute value of the difference between f s and f obs , as stated in:. The Doppler shifts are quite small compared with the original frequency of 2. It is far easier to measure the beat frequency than it is to measure the echo frequency with an accuracy great enough to see shifts of a few hundred hertz out of a couple of megahertz.

Furthermore, variations in the source frequency do not greatly affect the beat frequency, because both f s and f obs would increase or decrease. Industrial, retail, and research applications of ultrasound are common. A few are discussed here. Ultrasonic cleaners have many uses. Jewelry, machined parts, and other objects that have odd shapes and crevices are immersed in a cleaning fluid that is agitated with ultrasound typically about 40 kHz in frequency.