The boundary between air in the colonic lumen and tagged fecal materials, known as the AT boundary, is a critical juncture in the science of electronic cleansing (EC). In this region, radiologists must determine the nature of findings -- e.g., do they represent fecal material or polyps?
Previously, the research team from Harvard Medical School measured significant attenuation differences between components of the colonic lumen scanned at virtual colonoscopy, paving the way for more accurate electronic cleansing of tagged fecal materials and, eventually, an easier exam for patients.
"One of the common EC artifacts is caused by the partial-volume effect at the boundary between air and tagged fecal materials (AT boundary), which may share a similar CT value and a gradient value as those of the soft tissue," presenter Wenli Cai, PhD, explained to AuntMinnie.com. "Conventional EC has no efficient solution for differentiation of the mixture of AT boundary from soft tissue."
In their phantom study, Cai and co-investigators used the concept of dual-energy index to investigate DEI values in different materials, including air, soft tissue, and tagged fecal materials. They found that the mean attenuation of air in voxels of interest was different in statistically significant levels in each group of low- and high-energy images in 10 separate scans (p < 0.001).
The scans showed that "both air and tagged fecal materials have substantially higher DEI value than soft tissue," Cai said. "Thus, it provides us an efficient solution for accurate and precise removal of the AT boundary in electronic cleansing."
Dual-energy CT offers a means of identifying the material mixtures in virtual colonoscopy images and, thus, can significantly reduce the artifacts in electronically cleansed images, Cai explained. As a result, dual-energy CT "provides a new technique for artifact-free visualization of the colonic mucosa in [VC] and thereby advances colon cancer screening by use of fecal-tagging [VC]."
