An endorectal ultrasound scan (ERUS) can show the size and location of a cancer in the rectum, using soundwaves to build up a picture.
Ultrasound scans use sound waves to build up a picture of body tissues. An endorectal ultrasound scan can show the size and where the cancer is in the rectum.
For the test, you lie on your left side with your knees bent up. A nurse or doctor gently passes a small, lubricated probe into the back passage. This produces an image of the rectum on a screen.
The scan takes about 10 minutes and you can usually go home as soon as it is over.