From virtual microscopy to virtual colonoscopy

Virtual microscopy (whole slide imaging) at current resolutions is nearly if not as good as glass slide microscopy.  With current technologies it may be better for some purposes, given all the deliverables of a digital image (image processing, image analysis, rare event detection, spectroscopy, archiving, etc…).

In our teaching conferences now using a digital camera and high-end projector, most attendings and residents prefer to look at the digital imagery as opposed to sitting at the microscope given the optics of that system compared with the projected digital image.

While you may miss certain findings on virtual microscopy or need additional information beyond what the slide shows, the same is certainly true of glass slides.  The same analogy can be drawn on virtual CT colonography compared with endoscopic evaluation.  It appears there may be a role for both technologies, with increased numbers of patients getting screened for colon cancer which is responsible for 52,000 deaths a year. 

And I think the same is true of virtual slides and glass slides.  While one may not entirely replace or be more sensitive/specific than the other for particular diagnoses, the two formats may be complimentary to one another with each having a specific role in terms of clinical utlity and public health.

Radiology and gastroenterology have been looking at virtual colonoscopy and studying results from a large multi-center trial recently published in the New England Journal of Medicine. 

It turns out gastroenterologists who perform colonoscopies should not be worried that they may lose business to virtual colonoscopies, despite reports that both approaches work equally well at detecting colon cancer, a gastroenterology expert recently said based on details of the study published this week.

Partial results had been presented at medical meetings. Dr. Daniel Johnson of the Mayo Clinic in Scottsdale, Arizona and colleagues did both virtual colonoscopies and standard colonoscopies on 2,500 volunteers. They found that the virtual technique, which uses an X-ray computed tomography or CT scanner, detected 90 percent of precancerous polyps 10 millimeters or larger.

Regular colonoscopies are done by gastroenterologists using a flexible lit tube passed through the bowel. A device on the end can remove polyps for testing right away.

But with a virtual colonoscopy, also known as CT colonography or CTC, there is no sedation, so patients can quickly go back to their normal activities, the cost is significantly lower than a colonoscopy, and there is less risk of the bowel being punctured.

Both require drinking strong laxatives, a major complaint among patients. And if lesions are spotted during a virtual colonoscopy, the patient will require a standard procedure to remove them.

Virtual colonoscopies can also be uncomfortable because they require briefly inflating the bowel with carbon dioxide while the patient lies on a scanner.

"Both techniques are going to miss some lesions, both polyps and cancers," Johnson said in a telephone interview with a news agency. 

"In our study, there was a patient with a 35 millimeter mass that was missed in colonoscopy but found in CT colonography. None of these tests are perfect."

Colorectal cancer kills 52,000 people in the United States each year, according to the American Cancer Society. Most Americans are advised to begin getting regular colonoscopies at age 50.

Only about half of the 70 million Americans at risk for colon cancer are getting screened now, and the choice of CTC may encourage more people to be tested, he said. Gastroenterologists "are nervous that a lot of business will be taken away from them," Johnson said.

But the availability of a noninvasive method "has actually increased our colonoscopy volume," said Dr. Brooks Cash of the American Gastroenterology Association and a gastroenterologist at the National Naval Medical Center in Bethesda, Maryland, where both techniques are used.

That means more people need a follow-up colonoscopy to remove any polyps that could grow into tumors.

Cash estimated that colonoscopies typically account for 50 to 60 percent of a gastroenterologist’s income.

"It appears to be a very reasonable, very accurate test for colon cancer screening," he said in a telephone interview. "It will get them (patients) into the store, if you will. Then they can use either test."

Johnson said CTC uses half the radiation of a standard CT scan.