A thyroid ultrasound is an imaging method used to see the thyroid -- a gland in the neck that regulates metabolism.

A thyroid ultrasound is usually done when you have a growth on your thyroid gland. The exam can help tell the difference between a sac containing fluid (cyst) and abnormal tissue that may or may not be cancerous (a tumor).

Ultrasound is a painless method that uses sound waves to create images of the inside of the body. The test is usually done in the ultrasound or radiology department.

You will lie with your neck extended beyond its usual limit (hyperextended). The ultrasound technician will place a lubricating gel onto your neck. Next, the technician will move a wand, called a transducer, over the area.

The transducer gives off sound waves. The sound waves go through the body and bounce off the area being studied (in this case, the thyroid gland). A computer looks at the pattern that the sound waves create when bouncing back, and creates an image.

No special preparation is necessary for this test.

You should feel very little discomfort with this test. The gel may be cold.