Multi-energy CT differentiates polyps from fecal matter

An increasing number of institutions are conducting feasibility studies regarding the use of multi-energy imaging to differentiate one or more anatomic features based on their Hounsfield unit attenuation. Researchers at Emory University School of Medicine have taken this concept into the unprepped bowel.

Research associate Dr. Sunit Sebastian and colleagues aimed energies of 80, 100, 120, and 140 kVp at a custom-made phantom designed to simulate the unprepped colon, with fecal matter and polyps of varying size, morphology, and attenuation. They found that the lower kVp (80) allowed enhanced differentiation of fecal matter from polyps compared with the routinely used 120 or 140 kVp.

"There is a drop in Hounsfield unit attenuation in fecal matter compared with polyps," Sebastian told Diagnostic Imaging.

The study, which was presented at the 2007 American Roentgen Ray Society meeting, represents a preliminary and promising step for researchers. The next step, applying dual-energy CT colonography in humans, is slated to begin this summer. Favorable results would mean that patients could bypass colonic preparation, which could enhance compliance, Sebastian said.

The Emory researchers hope to validate this method as a means to help promote colon cancer screening, particularly among African Americans who, unlike their white counterparts, have not seen a decrease in the incidence of colon cancer in the last 20 years.

While the multi-energy technique may prove accurate, its effective dose of between 10 mSv and 12 mSv is three times the median effective dose for conventional single-energy CTC-much too high for screening. Sebastian cautioned that much work remains to be done to optimize visualization while reducing dose. It may be possible to scan subjects in one position with two energies, as opposed to the traditional two positions with one energy, he said.