Rectal endoscopic ultrasound is a test that allows your doctor to look at the walls of your lower gastrointestinal tract. A rectal ultrasound does not use X-rays or other radiation.

The doctor uses a thin, lighted tube that bends. It's called an endoscope, or scope. The scope has an ultrasound probe and camera at the tip. The doctor gently inserts the scope into your rectum to the area to be examined. The scope can take pictures of organs and tissues to check for problems in the colon, liver, gallbladder, or pancreas.

The procedure can take up to an hour if a biopsy is done.