Virtual Colonoscopy Screening: Procedure, Preparation, and Benefits

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• Virtual Colonoscopy Standards
• Bowel Preparation Process
• Fecal Tagging Technique
• CT Scan Analysis Methods
• Advantages Over Optical Colonoscopy
• Full Transcript

Virtual Colonoscopy Standards

Dr. Perry Pickhardt, MD, states that virtual colonoscopy, or CT colonography, is a highly effective screening tool. He confirms that any modern multi-detector CT scanner from major vendors can produce uniform, high-quality images. The key to a successful exam lies not in the scanner hardware but in the center's experience and protocols. Dr. Pickhardt advises patients to seek out clinics with a proven track record and published results in CT colonography.

Bowel Preparation Process

The bowel preparation for a virtual colonoscopy is a low-volume regimen designed for patient comfort. Dr. Perry Pickhardt, MD, explains that his protocol typically uses magnesium citrate as a gentle cathartic. Patients only need to drink a small, flavored bottle of this liquid. This mild preparation is a significant advantage over the more extensive cleansing often required for traditional optical colonoscopy, improving the overall patient experience.

Fecal Tagging Technique

A critical component of the virtual colonoscopy preparation is fecal tagging. Dr. Perry Pickhardt, MD, details that after the cathartic, patients drink an oral CT contrast agent. This contrast material "tags" or highlights any residual fluid and stool in the colon. On the CT scan images, radiologists can then digitally subtract these tagged materials. This process allows for a clearer view of the actual colon wall and any polyps, dramatically increasing the accuracy of the test.

CT Scan Analysis Methods

The analysis of a virtual colonoscopy is a sophisticated two-step process. Dr. Perry Pickhardt, MD, emphasizes that a robust 3D fly-through software, which simulates an endoscopic view, is essential. However, this must always be backed by a review of the original 2D CT scan source images. Any potential abnormality spotted in the 3D view must be confirmed as real soft tissue on the 2D cross-sectional images. This combined method ensures the robust and reliable results that define a high-quality exam.

Advantages Over Optical Colonoscopy

Virtual colonoscopy offers several distinct advantages over its optical counterpart. Dr. Perry Pickhardt, MD, highlights the creation of a permanent digital record. The CT scan data is saved forever, allowing for re-review if a patient later develops symptoms. This holds radiologists to a high standard of diligence. Furthermore, the procedure is less invasive, uses a gentler preparation, and does not typically require sedation. For cancer staging in diagnosed patients, CT colonography with IV contrast serves as a comprehensive one-stop shop.

Full Transcript

Dr. Anton Titov, MD: What is the best in virtual colonoscopy today from a technical standpoint? A patient may have a choice of CT scanner in his or her city somewhere in the world. What should they ask for when they call radiology centers for virtual colonoscopy? Is it a certain type of 64-slice multi-detector CT scanner? What are the best standards for virtual colonoscopy screening to be aware of?

Virtual colonoscopy progress has been remarkable. It is also called CT colonography. Virtual colonoscopy is now perhaps the best screening method to find colon cancer and precancerous colon polyps. It is important especially for those who use patient-driven healthcare systems outside the US.

Dr. Perry Pickhardt, MD: Almost 1.5 million people around the world are diagnosed with colon cancer every year. Colorectal cancer is the second most common cancer. But it is entirely preventable by screening.

The good news with CT colonography is that any multi-detector CT scanner by any of the major vendors are comparable in quality. CT colonography is really a forgiving test. It is a static CT scan basically of the gas-filled large bowel.

From the imaging standpoint, virtual colonoscopy test is really quite uniform. Anywhere you go, you should receive similar quality of CT scanning. The difference comes in what specific large bowel preparation is used. What distention technique is used.

What software is used to fly through the colon during analysis. Those are the nuances. You have to look to virtual colonoscopy clinics that have the most experience and that have published their testing results.

The software that we use is the Viatronix system. I have no relationship with this software company. Far and away, Viatronix has been the best software over the years. There have been some other vendors that have approached the quality of that particular software system.

But it is important to know. I don't expect patients to have that level of information available. That decision comes down to looking into what centers have the most experience with CT colonography.

Dr. Anton Titov, MD: Do they have a proven track record of performing many virtual colonoscopies?

Dr. Perry Pickhardt, MD: The good news being that it is very easy from a CT scanner perspective to offer very uniform quality of virtual colonoscopy. It is possible to record the CT scan done during the virtual colonoscopy on a CD. Preparation must be done properly and CT scan is done in good quality.

CT colonography data can be analyzed anywhere around the world. Is that correct?

That is true. Another advantage to CT colonography is that the information is always there, forever. We can go back and look at CT scan acquired during virtual colonoscopy. It holds us to a higher standard.

Because cancers can be missed at optical colonoscopy. Patient presents maybe several years later with symptomatic colon cancer. There is no method to go back and see what was missed during optical colonoscopy. Because there is no record of the optical colonoscopy examination.

With radiology, we are held to the higher standard of diligence. We can go back and look. We can see if something was missed. It tends to keep us a little more on our toes. We know that we must find a precancerous lesion or early cancer. It is our job to pick it up.

Dr. Anton Titov, MD: In the US it certainly increases the cost of the liability insurance for the radiologists!

Absolutely, yes!

Dr. Anton Titov, MD: What kind of large bowel preparation do you use for the CT colonography?

Dr. Perry Pickhardt, MD: The bowel preparation tends to be a low volume preparation. We typically are using magnesium citrate as our cathartic medication. It is a fairly gentle catharsis. It only requires ingesting a small bottle of flavored liquid.

We use lemon-flavored magnesium citrate. We follow that with oral CT contrast. This tags the fluid and residual materials in the feces. We can distinguish that from the bowel wall and soft tissues and polyps.

Dr. Anton Titov, MD: This is called "fecal tagging"?

Dr. Perry Pickhardt, MD: That is correct, yes. We have been employing fecal tagging. We first introduced fecal tagging with the clinical trial you mentioned earlier. It was published in our first New England Journal article about virtual colonoscopy.

At the time fecal tagging by oral CT contrast was not considered standard of care. But now over time fecal tagging is definitely the standard of care. But we use it in conjunction with the cathartic medication, magnesium citrate.

The benefit is that it leads to a higher accuracy virtual colonoscopy exam. Fecal tagging also allows the patient to undergo same day polyp removal, if there is the small chance that they have a large polyp seen.

Dr. Anton Titov, MD: Do you use intravenous contrast for CT colonography?

Dr. Perry Pickhardt, MD: No, for screening virtual colonoscopy intravenous contrast is not employed. We do use intravenous contrast for patients with a known colon cancer. If we are doing CT scan for cancer staging, or we are looking for cancer metastases.

For example, a patient may have an occlusive colon cancer at colonoscopy. Gastroenterologists often send the patient straight to us. We look for proximal cancer lesions in the colon. We also can stage the abdomen and pelvis.

This is the standard of care for newly discovered colorectal cancer. It serves as a one-stop shop for patients with known or proven colon cancers.

Dr. Anton Titov, MD: You have mentioned several times that you do a three-dimensional fly-through the large bowel. 3-D analysis by the software is the preferred method for virtual colonoscopy analysis?

Dr. Perry Pickhardt, MD: To be true, yes. You need a robust 3D fly-through the large bowel. This simulates endoscopic optical colonoscopy. This is why we call it virtual colonoscopy.

But it is very important to back that up with 2D analysis. We use 2D analysis as radiologists. Those are our source images for virtual colonoscopy. Anything seen on the 3D fly-through must be confirmed as a soft tissue abnormality on the 2D CT scan images.

That is part of the nuance of reading virtual colonoscopy data. It is probably too technical for the typical patient-level of information. But in truth it is a combined 2D and 3D data analysis. This method of virtual colonoscopy analysis results in the robust results that we get in our practice.

Thank you! This is very important to know. Because in many areas around the world patients take a much more proactive role. They often discuss certain topics with doctors. If they are aware of certain technicalities.

Dr. Perry Pickhardt, MD: Even without going into very deep details, it helps the discussion between patient and gastroenterologist, and possibly with a radiologist.

Dr. Anton Titov, MD: Yes, I agree. Virtual colonoscopy vs. regular optical colonoscopy – bowel preparation, procedure and analysis overview. Virtual colonoscopy is now perhaps the best screening method to find colon cancer and precancerous colon polyps.

Virtual Colonoscopy Procedure described by leading gastrointestinal radiologist. See short video About Procedure Preparation for virtual colonoscopy. Preparing for Virtual Colonoscopy takes drinking a mild bowel preparation of magnesium citrate. Patients also drink oral CT contrast for fecal tagging.

What distention technique is used for large bowel during the CT colonography. The key to successful analysis of virtual colonoscopy data is in software and experience of radiologist. CT colonography data can be analyzed anywhere around the world. CT colonography information is always recorded and available forever.