How does ultrasound work?

Doctors use an ultrasound machine for the examination. It usually looks like a cabinet with a computer-like device and a screen. A hand-held device called a transducer is connected to it by a cable.

Ultrasound machine with a screen and transducer

The transducer has special crystals inside it. When the machine is switched on, the transducer acts like a loudspeaker and produces sound waves that the human ear can't hear. These sound waves pass into the body when the transducer is held against your skin. The sound waves then bounce back from the organs and tissues inside the body, like an echo.

Different types of tissue reflect the sound waves differently. A computer uses these echoes to determine the position, shape and structure of the organs. This is then displayed on the attached monitor as an ultrasound image. The results of the examination and individual images can be saved and printed.

Some ultrasound devices can also determine the direction and speed at which blood is flowing through blood vessels or the heart. That is known as Doppler ultrasound.

Do you need to prepare?

You usually don’t need to do anything to prepare for an ultrasound examination. If you do, your doctor will let you know: For instance, in order to see the urinary bladder better, it should be at least partially full. So you may be asked to not go to the toilet right before the examination. Air and partially digested food may cause problems with the ultrasound image when the bowel and nearby organs are examined more closely. So you may be asked to come to an ultrasound examination of the abdomen on an empty stomach.

What does the examination involve?

Typically, you will have to lie down on your back. Depending on what part of the body needs to be examined, you may be asked to move into a special position – like turning to your side so that doctors can get better images of your heart or kidneys, for example. When examining the neck, a small cushion is placed under your neck so that your head tilts back a little.

What parts of the body are examined?

Ultrasound can be used to examine almost all of the body:

• The most commonly examined structures in the head and neck area are the thyroid gland and the blood vessels.
• In the chest area, ultrasound is mostly used to look at the heart (also called an echocardiogram or “echo”). But ultrasound can be used to look at the edges of the lungs, too. Deeper inside the lungs, the air affects the quality of the images. Changes in the inner areas of the lungs can be seen clearly using x-rays, for example.
• Abdominal ultrasound is used to examine the organs in the abdomen, including the liver and gallbladder, pancreas and spleen. The abdominal aorta (the largest artery in the belly area) can also be seen clearly using ultrasound. It is easy to get a good view of the kidneys from the side. Ultrasound can be used to look at the stomach and bowel, too. But air and partially digested food often make it harder to see them properly. Doctors can look at these organs using examinations like gastroscopy or colonoscopy, though.
• In the lower part of the abdomen, ultrasound is most commonly used to examine the bladder or the sex organs.
• During pregnancy, ultrasound is used to see unborn babies.
• In the arms and legs, ultrasound is most commonly used to examine blood vessels. Muscles, tendons and joints can be seen with ultrasound, too.

An abdominal ultrasound can be used to examine the liver, for example

What can you find out using ultrasound?

In pregnancy, ultrasound can be used to check on the growth of the unborn baby: The doctor can measure the child’s height and see how all of the organs and limbs are developing. They can also examine the placenta and the umbilical cord supplying the baby with oxygen and nutrients.

Other than that, ultrasound can be used to diagnose medical conditions or see tissue damage, especially:

• Swelling of tissue or entire organs, such as the spleen or lymph nodes. That may be a sign of inflammation, for instance.
• Aneurysms or narrow passages in blood vessels or heart valves.
• Cysts (hollow spaces). These can develop in the kidneys or the ovaries, for example.
• Calcium deposits – for instance, in the pancreas – or other types of deposits like gallstones.
• The build-up of fluids – such as between the lungs and the chest wall (pleural effusion).
• Changes in tissue, like in fatty liver or liver cirrhosis.
• Changes in organ size, like in an enlarged thyroid (goiter) or kidney atrophy (shrunken kidneys).
• Growths like tumors or those that have spread from them (metastases).

What is endosonography?

Some organs can’t be seen very clearly using ultrasound through the skin. They are too far inside the body or covered by bones. Then an especially thin transducer can be inserted through a natural opening in the body to examine the particular area “from the inside” (in Greek: “endo”): For example, the female sex organs can be examined through the vagina, and in men the prostate can be examined through the anus. Endosonography can also be used to look at organs in the abdomen or the chest – like the heart. Then the transducer is attached to the end of a thin tube that is gently guided down the esophagus (food pipe), like in gastroscopy. It is easier to view the heart from there.

A thin catheter can be used to do an ultrasound of the blood vessels from the inside as well. Then a small incision (cut) is made to insert the catheter.

Anesthetics usually aren’t needed for endosonography. But you might be given a sedative so that you can sleep during the examination.

Sources

• Lambertz H, Lethen H. Transösophageale Echokardiographie. Lehrbuch und Atlas zur Untersuchungstechnik und Befundinterpretation. Stuttgart: Thieme; 2018.
• Loscalzo J, Kasper DL, Longo DL et al. Harrison's Principles of Internal Medicine (Vol. 1 & Vol. 2). New York: McGraw-Hill; 2022.
• Niehaus J. Praxishandbuch Sonografie. Munich: Urban und Fischer; 2018.
• Pschyrembel Online. 2024.

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