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Virtual Colonoscopy

What is Virtual Colonoscopy?

Virtual colonoscopy is a new method that allows radiologists to evaluate the lining of the colon (large bowel) to detect polyps and cancers. Polyps are growths in the colon that may become cancerous if they are not removed. Utilizing a high-speed multidetector CT scanner and specialized computer software images are obtained that “visualize” the surface contour of the colon. Images are evaluated in both two and three dimensional projections as well as endoscopic views similar to those seen during conventional colonoscopy.

How is it done?

The first and most important part of the Virtual Colonoscopy, as with conventional colonoscopy, is the proper preparation. In order to perform an accurate evaluation of the colon a thoroughly cleaned colon is necessary. To achieve this, a clear liquid diet, a bowel cleansing kit and use of a tagging agent (Tagitol), which is used in opacifying residual stool, are each required to be completed 24 hours prior to the exam. An inadequately cleaned colon can lead to a non-diagnostic study and even erroneous results.

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The day of the examination the patient comes to the office and Virtual Colonoscopy is performed with high-speed multidetector computed tomography (CT or CAT scan). The patient lies on the CT table and a small flexible enema tip is placed in the rectum so that air can be introduced to distend the colon.

A scan of the colon is performed with the patient lying on their back and then repeated with the patient lying flat on their stomach. Each scan takes about 20 seconds with the total time for the procedure approximating 15-20 minutes.

After reconstruction of the data the radiologist will evaluate the images to detect colon polyps or cancers. Since hundreds of images are generated careful review is time consuming and rapid analysis is not in the best interest of the patient. Pertinent images of the virtual colonoscopy are recorded on film and sent to your physician. Digital images are stored at our facility.

Is it painful?

The most difficult part of the procedure for most patients is the preparation the day before the examination. During the examination some patients experience “gas pains” or cramping with the introduction of air into the colon. This is usually temporary and rarely results in terminating the study. Proper distention is imperative to visualize the entire colon adequately. The introduction of air can be performed by the radiologist; however, it sometimes is more relaxing for the patient to insufflate the air themselves.

What are the Advantages over Conventional Colonoscopy?

  • No Sedation
  • Immediate Resumption of normal activities
  • Rapid, Safe, Accurate

What are the Disadvantages compared to Conventional Colonoscopy?

  • Mucosal detail and color is not visible which limits characterization of lesions
  • Detection of small polyps (less than 1 cm) is inferior
  • Polyps if detected cannot be removed and would require follow up colonoscopy and second preparation
  • Ionizing Radiation – Approximately 20% less than a Barium Enema

How Accurate is it?

Studies suggest a very high sensitivity for detection of polyps 1 centimeter or greater approaching that of conventional colonoscopy. These are the ones that have significant malignant potential. Smaller polyps are more difficult to detect. As with any procedure, including conventional colonoscopy, both polyps and cancers can be missed.

Is Virtual Colonoscopy covered by Insurance?

Virtual colonoscopy is not usually reimbursed by most insurance companies. The patient must therefore cover the cost of the procedure. Medicare patients will be required to sign a waiver stating it is a non-covered service and you will accept responsibility for payment. However, Medicare may pay for this procedure if your physician has documented that there was a failed attempt at conventional colonoscopy.

Why is screening important?

Colorectal cancer is a leading cause of cancer related death in the United States. Colon cancer can be prevented if polyps are discovered and removed early before they become cancerous. It is believed that tumors take years to develop and typically form from a benign non-cancerous polyp. If these are removed progression to malignant disease can be prevented. Nevertheless, individuals remain largely under screened, in part due to poor public awareness and reluctance to current screening procedures.

What are the options to detect polyps?

The American Cancer Society recommends that patients undergo a test that allows the entire colon to be visualized at the age of 50 and then every 3 to 5 years. The two currently accepted methods include Conventional Colonoscopy and Barium Enema. Although both visualize the entire colon, barium enema is a less sensitive examination and is considered an inferior test. Colonoscopy, which is more sensitive as a screening procedure, is more costly and requires sedation and anesthesia. The introduction of a safe, non-invasive, and affordable procedure for detecting polyps has appeal for the individual and society as a whole. Virtual Colonoscopy is felt by several institutions including Boston Medical Center and The Mayo Clinic to fulfill many of these requirements. Multi-institutional studies are being performed to compare these techniques.

What are your feelings as a radiologist?

The most important thing is that the patient be screened by some technique for colonic polyps and cancer. Since many deaths maybe prevented with early detection … no screening is the biggest mistake. The gold standard for detection and removal of polyps is still conventional colonoscopy. Not only is this the most sensitive procedure, in addition, if a polyp is found a therapeutic polypectomy can be performed during the same procedure. Since virtual colonoscopy is only a diagnostic procedure if an abnormality is detected another preparation and conventional colonoscopy will be needed. If conventional colonoscopy is contraindicated or you are unwilling to have the procedure than virtual colonoscopy would certainly be a viable and beneficial option. We would consider barium enema to be the last resort but still better than no evaluation at all.