An ultrasound test uses high-frequency, low-energy sound waves to create images of internal organs or tissues. Some waves sent by the ultrasound machine pass through tissues, and others bounce back. Different quantities of waves bounce back depending upon density of the tissue, thus helping to distinguish different tissues. As sound waves bounce back, they are recorded and displayed on a computer screen or television-type monitor.

The image created is considered to be less clear than those from other imaging tests such as a CAT scan or MRI. However, ultrasound is often used for a wide array of procedures because it is fast, generally noninvasive, relatively inexpensive and more specific than other tests for some conditions.

Ultrasound technology can help a physician find the source of chest pain, abdominal pain, pelvic pain and sexual pain. It can be used in diagnosing and monitoring the progress of numerous conditions, such as prostate enlargement (benign prostatic hyperplasia), tendon and muscle ruptures, kidney stones, lupus, osteoporosis, rheumatoid arthritis and some cancers.

Ultrasound can also be used to monitor fetal development, and to help guide needles and other instruments under the skin and to the target area.

In addition to diagnostic ultrasound, there is therapeutic ultrasound, which employs higher frequencies of sound to produce heat. This form of thermotherapy can help control muscle spasms, pain, inflammation and other problems.

Ultrasound, which is sometimes called ultrasonography or sonogram, uses high-frequency sound waves to create images of organs, blood vessels and tissues. The sound waves are too high for the human ear to hear, but they produce an image that allows physicians to view internal organs and to assess blood flow through various vessels. Ultrasound is often performed by a technician and then analyzed by a physician.

Inspired by sonar technology, which uses sound waves to detect objects underwater, ultrasound can help diagnose a wide range of diseases and conditions. It can be used alone or with other diagnostic procedures. Sonography is the medical term for the testing and recording of the ultrasound. Sound waves are sent by a device called a transducer into the body and their echo is recorded. The velocity of the waves is different when passing through tissues of different density and elasticity. This allows machines to read the echoed sound waves and display an image, or sonogram, on a monitor.

Ultrasound is considered the primary imaging study for soft tissue abnormalities. X-rays are more commonly used for images of bones and joint spaces, but they produce levels of radiation unsafe for certain people (e.g., pregnant women). Ultrasound is the first study of choice in obstetrics and cardiology and is one of the most common imaging studies used worldwide. CAT scan (computed axial tomography), MRI (magnetic resonance imaging),   radionuclide imaging, angiography, cystoscopy or other tests may be used after ultrasound if diagnosis is still unclear.

Contrast media (dyes) that help highlight internal structures have more often been used with other imaging tests but are also being used in ultrasound. For example, microscopic gas bubbles injected into a vein in the patient’s arm may enhance an echocardiogram, reveal blunt abdominal trauma or congregate in areas suspicious for cancer.

Because ultrasound does not expose the patient to any radiation or powerful magnetic waves known, it may be used as a substitute for x-rays and MRI when the use of these studies is not advised (e.g., patients who should not be exposed to radiation, patients with pacemakers, patients who cannot remain still for extended periods of time, pregnant women). Ultrasound is typically noninvasive and causes little or no discomfort, making it well tolerated by patients, including small children. Cost considerations also favor ultrasound over other imaging tests such as CAT scan or MRI.

The disadvantages of ultrasound are diminishing as technology improves and more technicians gain experience obtaining and evaluating sonograms. However, findings may not specify any particular condition and are highly dependent on the expertise of the technician. Ultrasound may be much less useful in obese patients because sound waves do not travel well through fat. In addition, ultrasound is not effective in examining the lining of the digestive tract.  It also becomes ineffective if there is too much gas present in the bowel.

The benefits of ultrasound include:

• Portability. Can be performed in a physician’s office, at a patient’s bedside in a hospital, or in a locker room immediately after an athletic injury.
  
  
• Real-time capability. Can provide information while the technician or patient moves the area under study, such as flexing and relaxing a muscle. This may yield information hidden by imaging studies requiring the patient to remain still.
  
  
• Wide availability. Ultrasound equipment is available in many locations. Hospitals and medical centers tend to have this equipment, even if they do not have the equipment necessary for other imaging studies (e.g., MRI, CAT scan).
  
  
• Relatively low cost. The cost of ultrasound is a great deal less than other imaging studies, such as MRI and CAT scan.
  
  
• Ability to record motion. Ultrasound can record internal structures in motion.

Ultrasound can be used to examine numerous internal structures, including:

• Abdominal and pelvic structures
• Heart and blood vessels
• Liver
• Gallbladder
• Spleen
• Pancreas
• Kidneys and ureters
• Thyroid gland
• Tendons and ligaments
• Joints, including hip, shoulder, elbow and knee

Within these structures, ultrasound can be used to detect many abnormalities and diagnose many conditions. It is more useful in detecting structural abnormalities (such as shapes or masses that appear suspicious) than abnormalities that tend to occur throughout the body (e.g., inflammation of several organs). Abnormalities and conditions that ultrasound may identify or monitor include:

• Tendon and muscle ruptures. Can differentiate between full and partial tears and lesions. This includes tears in the rotator cuff (structure that secures the arm to the shoulder), which may be difficult to detect by other means and may exhibit no symptoms. Ultrasound can demonstrate the full extent of a tear and does not exaggerate the dimensions of the injury like other imaging studies such as arthroscopy or arthrography.
  
  
• Tendinitis. Tendon inflammation that may be chronic or acute. In most cases, the tendon itself is thickened and there may be no increase in the surrounding joint fluid.
  
  
• Cause of jaundice. Can distinguish jaundice caused by bile duct obstruction from that caused by liver malfunction.
  
  
• Tumors, including some forms of cancer, such as pancreatic, stomach, colorectal, gallbladder, esophageal, prostate, ovarian and breast cancers. In breast cancer, ultrasound can distinguish between solid tumors and fluid-filled cysts and evaluate lumps that may be difficult to see on a mammogram.
  
  
• Other prostate disorders, including benign prostatic hyperplasia (BPH) and prostatitis.
  
  
• Kidney damage. Ultrasound can detect and monitor renal dysfunction caused by lupus, diabetes, stones and other conditions.
  
  
• Osteoporosis. The DEXA scan (dual-energy x-ray absorptiometry) is the standard method of measuring bone mineral density and is often used to screen for osteoporosis, especially in women after menopause. Most DEXA scans use X-rays, but some portable units use ultrasound instead.
  
  
• Rheumatoid arthritis. May be useful in early diagnosis when other imaging studies may not detect the disease. Even though ultrasound is usually not very useful in rheumatoid arthritis, it may be of importance because some rheumatoid arthritis patients cannot undergo invasive procedures. This may be because of an increased risk of causing injury and infection due to the medications used to treat the condition.

Other conditions and abnormalities that ultrasound may detect include:

• Cardiovascular conditions, including arterial plaque, a risk factor for heart attack
• Gallstones
• Myositis
• Loose bodies
• Cysts
• Hematoma (accumulation of blood)
• Effusions (accumulation of fluids)
• Bursitis
• Bile tract abnormalities
• Appendicitis
• Sarcoidosis 

In addition, ultrasound is commonly used during pregnancy to monitor fetal development. It can also be used to locate the placenta and assess the opening of the cervix.

Ultrasound may be used to guide procedures, such as amniocentesis, injections of corticosteroids or other medications, needle biopsy, joint fluid aspiration (removal of synovial fluid from a joint) and extracorporeal shock wave lithotripsy (ESWL, a treatment for kidney stones).

High-intensity focused ultrasound (HIFU) may be used surgically, such as ablation, a treatment to kill prostate cancer, uterine fibroids or certain other tumors. HIFU is also being studied as a treatment for BPH, brain disorders, vascular (blood vessel) disorders and other conditions.

Phonophoresis is the use of ultrasound to introduce medications below the skin. Ultrasound can also be used as a type of thermotherapy to relieve many painful conditions, ranging from herniated discs to carpal tunnel syndrome. For more information, see Therapeutic uses of ultrasound.

There are various techniques of ultrasound imaging, including:

• A-mode. Also called amplitude modulation. Recorded as a single line showing the time needed to reach the organ and return to the transducer, a small device that sends ultrasound waves through the body.
  
  
• B-mode. Also called brightness modulation. Recorded as variations in brightness and darkness.
  
  
• Gray scale. Demonstrates various organs in shades of white and gray. Shades vary according to the strength of the sound wave echoes. The strongest echoes are white and the weaker echoes are darkening shades of gray.
  
  
• Real-time imaging. Shows rapid multiple views of anatomical structures, simulating motion.
  
  
• Doppler imaging. Used to measure blood flow. A shift in frequency occurs when a sound wave is echoed from something that is moving. Using this, ultrasound can measure the velocity of what is being studied, such as blood flow in a blood vessel. Different rates of flow are displayed in different colors on the monitor. This may be used to diagnose and evaluate many conditions, including:
  
  
• Risk of stroke
• Blood clots
• Valve function and defects
• Blocked arteries
• Stenosis (narrowing) of an artery
  
  
• Echocardiogram. Shows heart anatomy and function.
  
  
• Internal ultrasound. These tests are minimally invasive. The transducer in inserted into the body to obtain more detailed images. Forms of internal ultrasound include:
  
  
• Transesophageal echocardiogram (TEE). Insertion of a flexible, tube-like probe into the esophagus to view the heart. The patient typically receives a sedative and anesthetic.  The heart chambers and valves can be visualized better with this minimally invasive procedure.
  
  
• Transrectal ultrasound (TRUS). Insertion of a probe into the rectum to view the prostate.
  
  
• Transvaginal ultrasound (TVUS). Insertion of a probe into the vagina to view the uterus and ovaries.
  
  
• Intravascular ultrasound (IVUS). Attachment of the ultrasound transducer to a catheter, which is threaded through a blood vessel to view the internal structure of the vessel or the heart.

In addition to diagnostic ultrasound, there is also therapeutic ultrasound, a form of thermotherapy. Ultrasound may be used in physical therapy and occupational therapy at higher frequencies because the thermal effects have been found to be helpful for treatment of musculoskeletal injuries, breaking down scar tissue and helping to stretch and warm tendons.

Therapeutic ultrasound may be used to treat many conditions, including osteoarthritis, rheumatoid arthritis, tendinitis, bursitis, fibromyalgia, herniated discs and carpal tunnel syndrome. It can be used to heal wounds such as diabetic foot ulcers and to introduce medication through the skin (phonophoresis).

Unlike diagnostic ultrasound, therapeutic ultrasound has some known risks. The higher frequency of sound may cause damage to a developing fetus and typically will not be used over the abdomen of a pregnant woman. It may also have negative effects on cancerous tissues or areas of bone overgrowth. Patients who cannot perceive pain and heat are also advised against therapeutic ultrasound because overuse can cause burns.

Preparations for an ultrasound test depend greatly on the type of ultrasound being performed. However, most ultrasound tests require little or no preparation. For ultrasounds being performed on internal organs, such as the gallbladder, patients may be asked to avoid eating or drinking for six to eight hours before the examination.

However, for other ultrasounds, such as pregnancy or bladder tests, the patient may be asked to drink up to six glasses of water one hour prior to the test to fill the area with extra fluid. The excess fluid in the bladder helps to move air–filled bowel loops away from the area of concern for a clearer view.

In preparation for an ultrasound, it may be helpful to ask a healthcare provider about:

• Eating or drinking restrictions prior to the test
• Taking any medications prior to the test
• Smoking or using nicotine products before the test
• Avoiding soda or other carbonated drinks before the test
• Wearing loose-fitting, comfortable clothing
• Leaving jewelry and valuables at home

Most often, ultrasounds are outpatient procedures, but these tests are also used in hospitals as part of diagnostic patient care. In general, most ultrasounds follow a similar routine:

1. Depending on the area being tested, the patient may lie on a padded examining table during the test, which normally takes only about 20 to 30 minutes. It may be necessary to change into a hospital gown, depending on the area to be examined.
   
   
2. A small amount of water-soluble gel, which acts as a conducer, is placed on the part of the body to be tested and/or directly on the transducer, a small device that sends ultrasound waves through the body. The gel does not harm the skin or stain clothing. The ultrasound transducer should not be placed over an open or draining wound.
   
   
3. The technician places the transducer on the part of the body to be scanned. In some tests, a probe transducer may be placed within an opening, such as the vagina or rectum.
   
   
4. The sound waves sent from the transducer bounce off the structures within the body and the information is deciphered by the computer to create the ultrasound images.
   
   
5. The ultrasound images then appear on the television monitor and the moving pictures can be recorded on videotape.

There is no pain associated with the ultrasound test. Minor discomfort may be caused by the pressure of the transducer against the skin or, in the case of transrectal or transvaginal ultrasound, probe in a body cavity.

After the test, the gel is wiped off. The test is then evaluated by a radiologist, and results are relayed to the patient’s primary healthcare provider. If the ultrasound shows a problem, additional diagnostic tests, such as an MRI (magnetic resonance imaging), may be recommended.

Researchers are working on improving the images produced by ultrasound to increase diagnostic accuracy. Three-dimensional ultrasound shows promise in helping to detect breast abnormalities in younger women, whose breast tissue tends to be denser. In addition, Doppler ultrasound techniques can help reveal enlarged blood vessels that may be associated with an abnormal mass.

Other advances include:

• A new device called a sonic flashlight uses a 2-inch ultrasound monitor to guide placement of catheters into blood vessels.
  
  
• Scientists are improving ultrasound contrast media to enhance detection of cancer and other conditions.
  
  
• High-intensity focused ultrasound (HIFU) is being developed as a treatment for tumors, prostate disorders, bleeding (due to trauma or surgery), blood clots, atrial fibrillation (a type of abnormal heartbeat), thyroid nodules and other conditions.
  
  
• Cardiologists are calling for adoption of a recently developed screening method for heart attacks. The test uses CAT scan (computed axial tomography) to measure calcium in the coronary arteries and ultrasound to reveal arterial plaque and thickness of arterial walls.
  
  
• Diabetes researchers are refining use of ultrasound to guide minimally invasive injections of insulin-producing pancreatic cells in people with type 1 diabetes..

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor (or ultrasound technician or therapist) the following questions about ultrasound:

1. How experienced are you with ultrasound?
   
   
2. What kind of ultrasound will I have?
   
   
3. What area will be examined?
   
   
4. What are you looking for with this ultrasound?
   
   
5. Do I need to make any preparations before undergoing this ultrasound?
   
   
6. Will I receive a contrast medium? What does this involve?
   
   
7. What will happen during my procedure?
   
   
8. What do my results indicate?
   
   
9. Will other tests follow my ultrasound if it is not conclusive?
   
   
10. How often should I have an ultrasound to monitor my condition?
    
    
11. Can ultrasound therapy help my condition?
    
    
12. Do I face any risks from the use of ultrasound?