Ultrasound uses sound waves to look inside your body. The waves are sent out from a probe that's put into your rectum. The sound waves bounce off body parts and send back signals, like sonar on a submarine. A computer then receives the signals and makes an image of the inside of your body.

This test can help healthcare providers find out if the cancer has spread deep into the tissues around the anus or to nearby lymph nodes in your pelvis. It can also see how big the tumor is and how deep the cancer has grown into the wall of the anus.

A CT scanner takes many X-rays as you slide through it on a table. A computer combines these images to make detailed pictures of your insides. You will need to drink a special X-ray dye (contrast medium) just before the scan. Dye may also be injected right into your blood through a vein in your arm or hand. The dye helps get clearer images.

This test can help tell if the anal cancer has spread into your lymph nodes, liver, or other nearby organs. A CT scan is sometimes used to help guide the needle when doing a biopsy. A biopsy is when a small piece of tissue is taken out to check for cancer cells.

MRIs use radio waves and magnets to make detailed pictures that look like slices of the body. You lie on a narrow table that slides through the tube-like scanner. Some people have trouble with this test because they don't like being in tight spaces. Let your doctor know if this is a problem for you. A dye will be put into a vein on your hand or arm before this test. This helps get better pictures.

MRIs can help your healthcare provider figure out the location, size, and stage (extent) of the cancer. They can also show if it’s spread to nearby tissues. For instance, MRI can show enlarged lymph nodes. This may be a sign that cancer has spread to them.

You may have an X-ray done to see if the cancer has spread to your lungs. Many times a CT scan of the chest is used instead.

A PET scan shows tissues actively using glucose. Glucose use is a sign of increased metabolic activity. It’s seen in quickly dividing cells, such as anal cancer cells. For this test, your healthcare provider injects you with a small amount of radioactive glucose. Then you lie still on a table that's pushed into the PET scanner. It rotates around you, looking for the radioactivity. This is converted into a picture of your whole body, showing "hot spots" where a lot of radioactivity was found.

PET scans don't show a lot of detail, so they're often done along with a CT scan. This is called a PET/CT scan. The combination gives detailed pictures of where cancer may be anywhere in your body.