Computed tomographic colonography with a computer-aided detection system for polyps is highly effective, according to a presentation at the annual meeting of the Radiological Society of North America.

The large-scale, multi-center study was conducted by the National Institutes of Health (NIH).

CT colonography, commonly called virtual colonoscopy, is desirable because there is no risk of bleeding or colon perforation and intravenous sedation is unnecessary. The procedure is less costly than conventional colonoscopy and more convenient, taking 15 minutes or less.

"The performance of virtual colonoscopy continues to improve, and the exam will become a colorectal cancer screening method more patients and doctors will find acceptable," said the study's senior investigator Ronald M. Summers, MD, PhD. Summers is staff radiologist, chief of the clinical image processing service, and chief of the virtual endoscopy and computer-aided diagnosis laboratory at the NIH clinical center in Bethesda, MD.

Summers and colleagues studied 792 patients at three medical centers using virtual colonoscopy with computer-aided detection to detect adenomatous colon polyps eight millimeters (mm) and larger.

CT colonography produces 600 to 1,000 images per patient. Summers likened the interpretation process to the "needle in a haystack problem." With computer-aided technology, after the radiologist interpreted the images, the computer acted as a second set of eyes, reviewing the images and marking abnormalities for the radiologist to review. Computer-aided detection systems have the potential to find polyps that a radiologist might miss.

"We think that Computer-aided detection will help improve the performance of virtual colonoscopy by reducing the perceptual error that can occur when radiologists have to read the large number of images in these studies," Summers said.

In the current study, researchers detected polyps in 89.3 percent of patients with polyps 10 mm or larger and 85.4 percent of patients with polyps 8 mm or larger. The computer system’s false positive rates were 2.1 per patient for polyps 10 mm and larger and 6.7 per patient for polyps 8 mm and larger, which fell within the researchers' acceptable limits.

Summers predicted that soon all physicians who are interpreting virtual colonoscopy will want to have computer-aided systems readily at hand. "I think CAD is soon to become a mainstream technology."