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.