An ultrasound test, also known as a sonogram,  uses high-frequency sound waves to create images of internal organs or tissues. It works by sending low-energy sound waves against tissue. Some waves pass through the tissue and others bounce back. As sound waves bounce back, they are recorded and displayed on a computer screen or television-type monitor.

The image created by an ultrasound is considered to be less clear than those from computed axial tomography (CAT) scans or magnetic resonance imaging (MRI). However, ultrasound is often used for a wide array of procedures since it is fast, generally noninvasive and relatively inexpensive.

Ultrasound technology can help a physician diagnose and monitor the progress of numerous conditions associated with the digestive system, such as those that affect the gallbladder, liver, bile ducts, pancreas and kidneys.

Ultrasound can also be used to help guide needles and other instruments under the skin and to the proper organ or body area. For example, ultrasound might be used to guide the needle to the liver during a liver biopsy. Therapeutic ultrasound employs higher frequencies of sound to produce a thermal effect. This may be used as a type of heat therapy (thermotherapy) to help control muscle spasms, pain, inflammation and other problems.

Preparations for an ultrasound test depend greatly on the type of ultrasound being performed. Some may require changes in diet whereas others require little or no preparation. During the procedure, a small amount of water-soluble gel is placed on the part of the body to be tested. This helps transmit the sound waves. The technician then places places a transducer (small device that sends ultrasound waves through the body) on the part of the body to be scanned. 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. A radiologist analyzes the images and results are relayed to the patient’s primary health care provider.