Duke study renews challenge of CT colonography

Joking that he had donned a Kevlar vest for protection, a Duke University investigator Thursday presented data at a virtual colonoscopy symposium suggesting the CT modality is far inferior to optical colonoscopy in sensitivity for 6-mm and 1-cm polyps.

The study found that the sensitivity for 1-cm polyps was 48% for air contrast barium enema, 59% for CT colonography, and 98% for optical colonoscopy. For polyps greater than 6 mm, sensitivity was 41% for barium enema, 55% for CT colonography, and 99% for optical colonoscopy, according to Dr. Erik K. Paulson, director of abdominal imaging division at Duke.

The preliminary data were presented at the Fifth International Symposium on Virtual Colonoscopy in Boston. Final data are expected to be reported at the RSNA meeting in November.

The preliminary sensitivity results, described as mediocre by several presenters at the symposium, joined low sensitivity numbers obtained in the Cotton study, which were published in the Journal of the American Medical Association earlier this year, and high sensitivity numbers obtained by the Pickhardt group, which were first presented at this symposium last year and published in the New England Journal of Medicine. (JAMA 2004;291[14]:1713-1719 and NEJM 2003;349(23):2191-2200).

Paulson said the prospective multicenter Duke study had been originally budgeted for 2400 patients but was halted at the recommendation of Duke's Data and Safety Monitoring Board after 614 patients from 14 sites had completed all three exams.

The preparations for all three studies were standard, Paulson said. He describe the protocol for CT colonography:

• 4-slice MDCT

• 2.5 mm thickness

• 7.5 mm/rotation

• reconstruction interval 1 mm

• supine/prone

Readers used 2D as their primary tool, with 3D images for problem solving.

The study was originally designed in 1999 and used what was at the time state of the art in terms of 3D software and imaging protocols, according to Paulson.

The issue of 2D versus 3D being used for primary reads was the sticking point that caused the most controversy during a question and answer period. Dr. Mark Klein, a radiologist in Washington, DC, said it is a disservice to patients to continue to discuss studies that use outdated protocols.

Dr. Judy Yee, chief of radiology at the San Francisco VA Medical Center, the session's moderator, said even the Pickhardt study, with its good results, was not specifically designed to compare 3D versus 2D primary reads.

Paulson said that he stood by the study's design as rigorously conceived with state-of-the-art protocols at the time of conception.

"In order to make decisions, we need well-controlled trials," Paulson said.

For more information from the online Diagnostic Imaging archives:

Radiologists enter round two of colonoscopy debate

3D virtual colonoscopy gets thumbs up

Virtual colonoscopy

Obstacles to virtual colonoscopy fall quickly