Ultrasound

Overview

Ultrasound uses sound waves at a higher frequency than what a human ear can pick up. It is used in medicine for imaging and treatment. Medical ultrasound includes diagnostic and therapeutic types.

Diagnostic ultrasound is used to image the inside of the body. Unlike X-rays, it doesn’t produce harmful ionizing radiation. Therapeutic ultrasound can also be used for treatment by interacting with the body’s tissues. It can change, destroy tissue or target target medicines to specific locations.

How Ultrasound Works

A transducer, or probe, transmits and detects ultrasound waves. The active elements in most ultrasound transducers are made of special ceramic crystal materials. These materials produce sound waves when an electric field is applied to them. They also work in reverse — producing an electric field when a sound wave hits them.

In a diagnostic scanner, a transducer sends a beam of sound waves into the body. The sound waves are reflected back to the transducer by boundaries between tissues in the path of the beam, for example boundaries between fluid and soft tissue or tissue and bone. When these echoes return to a transducer, they generate electrical signals that are sent to the ultrasound scanner. The scanner calculates the distance from the transducer to the tissue boundary and uses this information to generate two-dimensional images of tissues and organs.

During an ultrasound exam, the technician applies a gel to the skin to prevent air pockets from forming that would block the sound waves.

Types of Ultrasounds

Diagnostic Ultrasound

Diagnostic ultrasound non-invasively images internal organs but generally doesn’t provide good images of bones or tissues with air such as the lungs. Exceptions include imaging bones in a fetus or small baby or when lungs are filled or partly filled with fluid.

One common use of diagnostic ultrasound is to monitor the growth and development of a fetus.

Other uses include imaging the heart, blood vessels, eyes, thyroid, brain, breast, abdominal organs, skin, and muscles. Ultrasound images are displayed in either 2D, 3D, or 4D (which is 3D in motion).

A transducer is typically placed on the skin to take a diagnostic ultrasound scan, but for enhanced image quality it may be placed inside the body via the digestive tract, vagina, or blood vessels. Ultrasound can also be used during surgery by placing a sterile probe into the area being operated on.

Diagnostic ultrasound examples include the following:

Carotid Ultrasound

Carotid ultrasound is a painless technique to detect plaque buildup in the carotid arteries and determine if plaque is blocking blood flow to the brain. Combined with Doppler ultrasound, it also shows how blood moves through the arteries and can inform prevention and treatment strategies for health risks like stroke.

Echocardiography (Echo)

Echocardiography (Echo) is a painless test that uses sound waves to create moving pictures of the heart revealing its size, shape, and how well it pumps blood. It is used to detect blood clots inside the heart, fluid buildup in the sac around the heart, tumors, and can help identify the cause of abnormal heart sounds including heart murmurs. Echo is also used to detect congenital heart defects, coronary heart disease, heart attack, heart failure, and heart valve diseases. 

There are many types of echocardiography:

• Transthoracic echocardiography involves the placement of a transducer on the chest after gel is applied to the skin. Sound waves bounce off the heart and are converted to images on a screen.
• Stress echocardiography is part of a stress test that generates images before and after exercise or medicine-induced stress to create comparative images of the heart.
• Transesophageal echocardiography provides a more detailed view of the heart as a transducer attached to a flexible tube is carefully guided down the throat into the esophagus.
• Fetal echocardiography images an unborn baby’s heart to assess heart health and is commonly done around 18–22 weeks of pregnancy.
• Three-dimensional (3D) echocardiography creates 3D images of the heart and may be done as part of a transthoracic or transesophageal echo.

Functional Ultrasound

Functional ultrasound applications include Doppler and color Doppler ultrasound for measuring and visualizing blood flow in vessels within the body or in the heart. It can also measure the speed and direction of blood flow. Doppler imaging is commonly used to determine if plaque inside the carotid arteries is blocking blood flow to the brain.

Elastography is another type of functional ultrasound that measures and displays the relative stiffness of tissues and can be used to detect tumors or liver fibrosis. Liver fibrosis occurs when excessive scar tissue builds up from inflammation.

Ultrasound is also used for procedures inside the body:

• Ultrasound-guided needle biopsy helps doctors see the position of a needle as it is guided to a target, such as a mass or tumor in the breast.
• Ultrasound can guide catheter placement.
• Ultrasound provides surgeons with real-time images of the inside of the body supporting minimally invasive surgery.

Therapeutic Ultrasound

Therapeutic ultrasound can produce high intensity sound waves which can be targeted to heat or break up specific tissue. Other uses include dissolving blood clots and delivering drugs to specific locations in the body with the advantage that no incisions or cuts are necessary that would damage the skin.

Therapeutic High Intensity Focused Ultrasound (HIFU) uses high-intensity beams with precision targeting to treat diseased or abnormal tissues like tumors without damaging skin or surrounding tissue. Either ultrasound or MRI can be used to identify and target the tissue, guide and control the treatment in real time, and confirm treatment effectiveness.

HIFU is FDA approved for treating uterine fibroids, relieving pain of secondary bone cancer, and ablation of prostate tissue. HIFU is also being investigated for closing wounds and stopping bleeding, and researchers are also looking at temporarily opening the blood-brain barrier to allow drugs to pass through.

Related Health Effects

While diagnostic ultrasound is generally safe, if used improperly, it can produce negative health effects. This is why the U.S. Food and Drug Administration (FDA) requires that diagnostic ultrasound operates within defined limits. It is also why the FDA, and many professional societies discourage casual use of ultrasound such as keepsake videos and recommend its use only for medical needs.

Find Clinical Trials

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials on ultrasound.

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.

NIH supports research to enhance ultrasound technologies.

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.