A Guide to Ultrasound Scans

Medically Reviewed By Meredith Goodwin, MD, FAAFP
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Ultrasound is an imaging device that uses sound waves to create many different types of images, including organs and body parts in motion. Ultrasound is safe, effective, and does not involve radiation. Moving a sound wave generator — or transducer — over your skin makes sound waves go through your body. When sound waves hit tissue, fluid, or bones, they bounce back to the transducer. It then converts them into images your doctor can see on a monitor.

From the patient’s point of view, ultrasound is pain-free and requires no special preparation.

Other names for ultrasound include sonogram, sonography, and ultrasonography.

A person undergoing an abdominal ultrasound scan
A person undergoing an abdominal ultrasound scan. Santi Nuñez/Stocksy United

This article explains how ultrasound works and the reasons doctors use it. The discussion also includes an explanation of various types of ultrasounds.

What is an ultrasound?

A person undergoing a thyroid ultrasound scan
A person undergoing a thyroid ultrasound scan. Cancer prevention Getty Images

An ultrasound is a noninvasive, painless imaging exam. It makes pictures of organs and structures inside the body using sound waves. This is the diagnostic or anatomical ultrasound. It lets doctors view internal tissues that may be the source of disease. Doctors use it to find the cause of symptoms, such as pain.

Ultrasound imaging can also capture body parts in motion as they work. This is the functional ultrasound.

In addition, there is a form of ultrasound that is not for imaging purposes. Instead, the sound waves interact with a body structure or tissue to change it. This is therapeutic ultrasound.

How does ultrasound work?

Ultrasound uses sound waves to make images. A transducer makes the sound waves. It works by employing piezoelectrics in the transducer. These ceramic crystals can produce and detect sound waves. In ultrasound, they send out sound waves into the body and receive the echo of them when they bounce back.

The transducer is a small hand-held device that makes contact with the skin. The sound waves it makes are higher pitched than humans can hear. A computer translates information from the transducer into visible images on a monitor.

Depending on the technology, the images can appear in 2D, 3D, or 4D, which is 3D in motion. 

Why is an ultrasound done?

Many people are familiar with this imaging technology from having it or seeing it during pregnancy. However, there are many uses of ultrasound.

For pregnancy

Ultrasound images can give your doctor lots of information about your pregnancy. This includes the age of your developing baby, the baby’s position, and the baby’s overall health. A prenatal ultrasound can tell the baby’s sex, too. 

For blood vessel problems

A Doppler ultrasound uses sound waves to provide images of blood passing through your veins or arteries. Your doctor may order this type of ultrasound to look for a blood clot or a blockage in your circulatory system.

If you have had surgery on a blood vessel, your doctor may use ultrasound to make sure the typical blood flow returns.

For abdominal problems

A person undergoing an abdominal ultrasound scan
A person undergoing an abdominal ultrasound scan. andresr/Getty Images

If you have swelling, bloating, or belly pain, an abdominal ultrasound can help your doctor determine the cause. The images it creates let your doctor see your kidneys, bladder, liver, gallbladder, pancreas, spleen, and the blood vessels in your abdomen.

It can also provide images of internal female sex organs, including the ovaries and uterus.

For children

Because ultrasound is painless and has no harmful radiation, it can be a good option for use with children. If your child has abdominal pain, an ultrasound may be the first test the child’s doctor orders. The doctor can also learn about blood flow through the abdomen, arms, legs, neck, and brain. 

For biopsies

Your doctor may rely on ultrasound for biopsies. A biopsy takes a tissue sample for examination under a microscope. Ultrasound can act as a guide. The ultrasound image tells your doctor exactly where to take the sample.

Biopsy is one way to diagnose cancer. A common example is a breast biopsy. The ultrasound image of a breast lump shows the doctor where to place a needle into the lump to remove cells. The doctor does not need to make an incision. Doctors also use ultrasound to guide biopsies for diagnosing thyroid lumps or nodules.

For your heart

If you have symptoms of heart disease, your doctor may order an ultrasound exam called an echocardiogram, or echo. Like other ultrasound exams, an echo is painless.

An echo can give your doctor information about the size of your heart and any problems with your heart valves. It can show how well your heart pumps blood. During pregnancy, an echo of the fetus can show if the baby has a heart defect.

What are some types of ultrasound?

There are two main types of ultrasound. The first is conventional ultrasound. It traditionally displays images in 2D, or a flat two dimensional picture.

Advances in this technology allow for 3D and 4D images. In a 4D ultrasound, a 3D image is in motion.

The other type of ultrasound is a Doppler ultrasound. This technology can show blood flow through vessels and organs. There are several types of Doppler ultrasound, including:

  • color Doppler, which converts the sound waves into colors that indicate the speed and direction of blood flow
  • power Doppler, which is a type of color Doppler that can show greater detail when there is limited blood flow
  • spectral Doppler, which shows blood flow as a graph and can convert it into a sound

How do you prepare for an ultrasound?

For most ultrasounds, there is no special preparation. It helps to wear loose, comfortable clothing. However, it may be necessary to change into a gown for the exam. 

In some cases, there may be instructions you need to follow before an ultrasound. For example, a pelvic ultrasound requires you to drink water to fill your bladder before the test. Other scans need you to fast from food and drink for a period beforehand.

What to expect during an ultrasound?

An ultrasound procedure generally involves these steps:

  1. You will lie on a table and expose the body part for examination.
  2. A healthcare professional will apply ultrasound gel to the area.
  3. The professional will place the transducer onto the skin where the gel is.
  4. The professional will move the transducer over the skin and may press it into the skin at times.
  5. The transducer will send images to view on a monitor.
  6. Once the test is complete, the professional will wipe off the water-soluble gel.

The procedure usually takes less than an hour.

For some types of ultrasound, a thin transducer goes into a body cavity. These include:

  • Transesophageal echocardiograms: This ultrasound involves inserting a transducer down the esophagus to view the heart.
  • Transrectal ultrasounds: This ultrasound involves inserting a transducer into the rectum to view the prostate gland.
  • Transvaginal ultrasounds: This ultrasound involves inserting a transducer into the vagina to view the uterus and ovaries.

Ultrasound exams are painless. However, there may be discomfort if a body part is already sore or painful. You can resume daily activities right afterward. You can generally expect the results within a few days.

Are there risks or limitations of ultrasound?

There are no known risks to standard diagnostic ultrasounds. However, there are limitations. 

Ultrasound cannot penetrate bone, and air disrupts the sound waves. So, it is not effective for viewing bones or air-filled organs, such as the lungs and bowel.

The sound waves can also weaken in people with excess weight, as the waves have farther to travel through the tissue.

Other imaging techniques, such as CT or MRI, may be more useful in all of these situations.

CT or MRI may also be necessary if an ultrasound shows a potential problem that needs more detailed imaging.

Summary

Ultrasound is a safe, painless imaging exam. Unlike X-rays, it does not use radiation. Instead, sound waves penetrate body tissues and bounce back to the machine to make the images.

There are several types of ultrasound and various uses for it. In most cases, it is a quick procedure with little to no preparation. 

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Medical Reviewer: Meredith Goodwin, MD, FAAFP
Last Review Date: 2022 Jun 14
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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