Dual-energy CT shows potential for colonography

Most of the potential associated with dual-beam CT scanning, a technology developed and being solely pioneered by Siemens Medical Solutions, has been in cardiology. The applicability of this technology to other disciplines is only beginning to be explored.

Researchers at Emory University School of Medicine have constructed a simulated model of the human colon in a natural state, then applied dual-energy scanning to differentiate polyps from fecal matter in a simulated CT colonography exam. The colon model included 17 lesions simulating polyps and six simulating fecal matter. Two abdominal radiologists who independently reviewed scans of the model found accuracy of polyp detection to be 73% and 69% at the routinely used settings of 120 kVp and 140 kVp - and 87% and 82% when data from the lower energy 80 kVp was factored in.

If this dual-energy approach is proven in clinical tests, it would free patients from the unappealing aspects of colonic preparation currently required before CT colonography, noted Dr. Sunit Sebastian, a research associate at Emory.

"CT colonography can be a valuable noninvasive tool to screen for polyps and precancerous lesions," Sebastian said. "However, every patient has to undergo a tedious and uncomfortable colonic preparation prior to the procedure. The recent introduction of dual-energy CT scanners provides an opportunity to explore the role of dual-energy CT to differentiate between polyps and fecal matter in an unprepped colon. Our study is the first step in this direction,"

Results of the study were presented May 7 during the American Roentgen Ray Society meeting in Orlando, FL. Also at the meeting, researchers from the University of Wisconsin Hospital and Clinics in Madison presented data indicating the overall potential of multislice CT for this application. They reported 90% agreement between CT colonoscopy and optical colonoscopy, as nearly 90% of colon polyps equal to or greater than 6 mm in size detected at CTC were demonstrated to represent true polyps at subsequent optical colonoscopy.

The researchers, led by Dr. Tyler Prout, a UW clinical assistant professor of radiology, analyzed the findings of 363 CTC-detected lesions in 244 patients who subsequently underwent optical colonoscopy. The presence of polyps was verified in 321 of the 363 CTC-detected instances, making for an overall positive predictive value of 88.4. In addition, the combined group of polyps with either sessile or pedunculated morphology yielded a matching lesion at optical colonoscopy 91.8% of the time.

"From a practical standpoint, this is very important, because if CTC is to be an effective screening tool, it must not only have a high sensitivity, but also a sufficiently high concordance rate at subsequent optical colonoscopy to avoid unnecessary colonoscopies," Prout said.

The relative comfort of CT versus optical colonoscopy might persuade more patients to be screened for the early signs of colon cancer. Dual-energy scanning could make CTC even more appealing.

The next step toward that goal is to test whether lower CT settings, identified in the simulated colon, would work with actual patients, a step the Emory researchers plan to take. They have obtained institutional review board approval from the university to perform CT colonography on patients using dual-energy CT.

"If favorable results are obtained in the patient population, it would mean that we could avoid or totally bypass uncomfortable colonic preparation, thereby making CT colonography more patient-friendly," Sebastian said. "This would further enhance patient compliance in screening for colon cancer."