CT colonography (virtual colonoscopy) Diagnostic Imaging

CT colonography, also called virtual colonoscopy, uses a low-dose CT scanner and computer software to create images of the colon and rectum.

CT colonography (virtual colonoscopy) procedure illustration

Overview

CT colonography, also called virtual colonoscopy, uses a low-dose CT scanner and computer software to create images of the colon and rectum. A small tube is placed in the rectum to gently inflate the colon with air or carbon dioxide so the walls can be seen clearly. It is used to look for polyps, growths, or other changes. Many guidelines list it as one option for colorectal cancer screening, and it can also be used when a standard colonoscopy cannot be completed.

Overview Preparation Clinical Info Recovery FAQ References

Also known as: Virtual colonoscopy, CTC, Computed tomographic colonography

Recovery
0–1 days
Return to Work
0–1 days

Preparation & Next Steps

Everything you need to know before and after your procedure

Before Care

  • Follow the facility's bowel prep instructions, which often include a clear liquid diet and laxatives the day before.
  • Ask about stool tagging agents or enemas and how to use them as part of the prep.
  • Confirm arrival time, location, parking, and how long you will be at the facility.
  • Drink plenty of clear fluids during the prep unless told otherwise to reduce dehydration.
  • Tell the imaging center if you could be pregnant or have had recent bowel surgery or acute bowel illness.
  • Wear comfortable clothing and avoid bulky jewelry or metal near the abdomen.
  • Bring a list of your medicines, allergies, and any prior colonoscopy or imaging results.
  • Plan for possible follow-up testing if the exam finds polyps or other abnormalities.
  • Ask whether you can take your usual medicines on the day of the test and how to time them around the prep.
  • Review how results will be delivered and who will explain next steps.

After Care

  • You can usually return to normal eating and activities the same day unless your provider gives different instructions.
  • Expect gas, mild cramping, or bloating for several hours; walking and hydration can help.
  • Review your report and images if offered through a patient portal or from the imaging center.
  • If the exam found polyps or suspicious areas, a standard colonoscopy may be recommended to remove or biopsy them.
  • Keep track of any additional imaging suggested for findings outside the colon.
  • Resume your usual medicines unless told otherwise by your clinician.
  • Contact a clinician if you have severe or worsening belly pain, fever, persistent rectal bleeding, or increasing abdominal swelling.
  • Note when you are due for your next screening based on guideline intervals and your clinician's plan.

Clinical Information

Important medical details about this procedure

Indications

  • Screening for colorectal cancer in adults at average risk
  • Evaluation after an incomplete or difficult standard colonoscopy
  • Assessment of the colon when sedation or invasive endoscopy is not feasible
  • Imaging of the colon in certain symptoms when endoscopy is contraindicated

Alternatives

  • Standard colonoscopy
  • Fecal immunochemical test (FIT)
  • High-sensitivity guaiac fecal occult blood test (gFOBT)
  • Stool DNA test (FIT-DNA)
  • Flexible sigmoidoscopy

Risks

  • Exposure to low levels of ionizing radiation
  • Rare colon perforation from air or carbon dioxide inflation
  • Discomfort, cramping, or bloating during or after the exam
  • False positives or false negatives that may lead to more testing
  • Incidental findings outside the colon that may require follow-up imaging
  • Need for a standard colonoscopy if a polyp or abnormality is found

Contraindications

  • Known or suspected pregnancy due to radiation exposure
  • Active severe colitis or acute diverticulitis
  • Recent colorectal surgery with healing tissue
  • Known or suspected bowel obstruction or perforation

Recovery Timeline

What to expect during your recovery

Most people resume normal activities the same day. Temporary gas or bloating is common and usually improves within hours.

Typical Range

0–1 days

Return to Work

0–1 days

Recovery Milestones

Day 0

Resume light daily activities and regular eating

Day 0–1

Gas and bloating improve with walking and fluids

Day 1–7

Review results and plan any follow-up colonoscopy if needed

Frequently Asked Questions

Common questions and expert answers about this procedure

How is CT colonography different from standard colonoscopy?

It uses a CT scanner to make images of the colon without a scope inside the entire colon. No sedation is usually needed, but polyps cannot be removed during the test.

Do I still need bowel prep?

Yes. A clean colon is needed for clear images. Prep often includes a clear liquid diet, laxatives, and sometimes stool tagging agents.

Will I need sedation?

Sedation is not typically used. Most people can drive themselves home and return to normal activities after the exam.

How often is CT colonography used for screening?

Many guidelines list it as a screening option at set intervals, often every 5 years, for average-risk adults within the recommended screening ages.

What happens if a polyp is found?

You may be referred for a standard colonoscopy to remove or biopsy the polyp, sometimes on a separate day.

Is there radiation exposure?

Yes, it uses low-dose X-rays. The dose is generally lower than many diagnostic CT scans, but it is still ionizing radiation.

How long does the exam take?

The CT scanning itself usually takes minutes. The total visit is longer due to check-in, positioning, and post-exam review.

Are there risks of complications?

Serious complications are uncommon. Rarely, the colon can tear from the air or carbon dioxide used to inflate it. Some people feel cramping or bloating.