Surface coverage in CT colography studies

The early detection of colorectal polyps may reduce morbidity and mortality due to colon cancer(1-7). Reliable detection of polyps in CT colography requires presentation of the entire colonic surface to the radiologist(6-9). We have developed a simple technique for quantifying surface coverage of the colonic mucosa as shown on CT colography. The air in the colon is segmented. A shell surrounding the air volume is generated by successively growing surfaces continguous with previously grown voxels using thresholds of -900 HU and -100 HU. To evaluate techniques used for viewing the colon, shell voxels used in the presentation techniques are monitored, and a list of voxels missed by the technique is compiled. The missed voxels can be visually inspected and quantified using clustering methods that parameterize volumes of missed voxels, The usefulness of this method was investigated using a technique that displays reformatted views about a pre-calculated centerline. A modification of the presentation method in which additional images are generated by interpolation to improve surface sampling near regions of high centerline curvature was also evaluated. The surface coverage and neighborhood parameters were calculated for 15 clinical colography studies. The results indicate that an average of 99.68% of the shell voxels were included in the reformatted images prior to interpolation. Surface coverage was improved to 99.9% when additional interpolated planes were included. The average number of missed neighbors improved from 8.13 to 5.29 with interpolation. The dimensions of the missed volumes provided useful information for surface coverage.