CT Colonoscopy

Exam Description

CT virtual colonoscopy is a new method to evaluate the large bowel (colon) for polyps and cancers.  Polyps are small growths in the colon that may become cancerous if not removed.  CT colonoscopy uses a CT scanner and computer virtual reality software to look inside the body without inserting a long tube (conventional optical colonoscopy) into the colon and without having to fill the colon with liquid barium (barium enema).  Research has shown that CT colonoscopy is better able to see polyps than barium enema and is nearly as accurate as conventional optical colonoscopy.

Why CT Colonoscopy?

Colorectal cancer is the third most common cancer found in men and women in the US.  Colon cancer can be prevented if polyps are discovered and removed early.  Tumors take years to develop.  Initially, a cell can multiply abnormally, resulting in a benign (non-cancerous) polyp, which can remain harmless for a long time before becoming an aggressive cancer.  Polyps, when detected, can be removed preventively before possible degeneration into a cancer.  Despite this, individuals at greatest risk for colorectal cancer remain largely under-screened.  This is due, in part, to poor public awareness and non-acceptance of current screening techniques.

Several tests are used to detect polyps.  Current recommendations by the American Cancer Society include an evaluation of the entire colon at the age of 50 and then every three to five years.  Currently, there are two accepted methods for seeing the entire colon: conventional optical colonoscopy and barium enema.  The sensitivity of barium enema is far from optimal and is uncomfortable for the patient.  Conventional optical colonoscopy is associated with increased risk and cost.  In addition, this test may cause injury to the colon in 1 out of 1500 patients and is unable to evaluate the entire colon in 1 out of 10 patients.  Medications given through the veins (intravenous sedation) is usually required for conventional optical colonoscopy to make the exam bearable.  Thus, patients cannot resume normal activities immediately after the test.

CT colonoscopy is a safe method to evaluate the entire colon without the need for intravenous sedation.  This test uses a standard CT scan performed with a low radiation dose protocol to generate 3D images of the colon.  Patients need to complete a cleansing preparation of the bowel before the test.  The CT colonoscopy procedure begins with a small flexible rubber tube being placed in the rectum through which air is introduced into the colon.  A CT scan is then performed while patients like comfortably on their backs.  A second scan is then performed while the patients lie on their stomach.  The total time required for the study is approximately 10-20 minutes.  Because sedation is not required, patients are free to leave the radiology department immediately without the need for observation or recovery and can resume normal activities immediately, including driving from the hospital.  A radiologist specially trained in CT colonoscopy then analyzes the CT data to detect polyps or cancer.