Ultrasound is mainly used to see if colon cancer has spread. Three types of ultrasound imaging may be used: Abdominal ultrasound can detect the spread of cancer to the liver, gallbladder, or pancreas (but not the presence of tumors in the colon or rectum). Endorectal ultrasound is performed by inserting the transducer (a thin instrument that picks up the sound waves) into the rectum to see if and how far cancer has infiltrated the walls of the rectum. It also can reveal if cancer has reached nearby organs or the lymph nodes. Intraoperative ultrasound, which is done during surgery, can detect if colon cancer has spread to the liver.