Use of filet view software simplifies CT colonography

Image reconstruction software that virtually unfolds the colon wall could shorten CT colonography's reading time without compromising diagnostic accuracy, according to researchers at the 2005 RSNA meeting.

The team, led by Dr. Patricia Carrascosa, director of research at the Diagnostico Maipu imaging center in Buenos Aires, evaluated the usefulness of unfolded haustra software (the filet view) and conventional CTC in the first study to compare the two.

The Argentine study involved 23 patients with suspected colon cancer who underwent conventional 2D/3D CTC, filet-view CTC, and gold standard colonoscopy one day after preparation. Investigators found that both interpretation techniques provided similar diagnostic yields that correlated to colonoscopy.

Colonoscopy detected 35 elevated-type lesions. Both conventional and filet-view CTC found 29 of these lesions and erroneously characterized six as false negatives. However, the unfolded haustra technique significantly reduced interpretation time from 15 to eight minutes.

The filet view allows simultaneous evaluation of supine and prone acquisitions. The software reconstructs the colon lumen in 3D, draws a centerline from cecum to rectum, and bisects the colon, spreading it flat along its longitudinal axis. The system displays the unfolded colonic haustra with a 10 degrees overlap at the edges and eliminates the need for bidirectional fly-throughs.

Diagnostico Maipu radiologists currently use the technique in all patients undergoing CTC. The strategy reduces postprocessing and reading time and allows patients to get results immediately after the exam.

The Argentine healthcare system currently covers virtual colonoscopy in patients with a personal or family history of colorectal cancer or polyps. It also covers CTC for related clinical conditions, such as rectal bleeding, or patients with positive fecal occult blood tests.

Nonsymptomatic patients must pay for screening studies themselves, Carrascosa said.

CT colonography experts had hoped the new technique would prove useful in reducing interpretation time for 3D primary reads. These study results are thus encouraging, but caveats exist, said Dr. Perry J. Pickhardt, an associate professor of radiology at the University of Wisconsin Medical School in Madison. The 3D rendering technique may distort polyps, even large ones, beyond recognition, undermining detection of significant lesions in screening populations.

"We should continue to test and improve this novel 3D view but must realize that it is not yet ready for routine clinical practice," he said.

Not everybody shares Pickhardt's view, however. Dr. William Glenn, a private practice radiologist in Manhattan Beach, CA, and an expert on image manipulation and postprocessing techniques, says a combined approach that uses the filet view and CAD is the best way to speed up colon cancer screening.

Glenn expressed satisfaction with the Argentine data. The filet view is the only rational approach to managing the massive volume of colon cancer screening, he said.