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Development of a Cathartic-Free Colorectal Cancer Screening Test Using Virtual Colonoscopy: A Feasibility Study

¹ Department of Radiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905.
² Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN.
³ Facilities and Systems Support Services, Mayo Clinic, Rochester, MN.

View larger version (167K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —Study phantom. Colon phantom (A) constructed of Silastic (liquid silicone rubber C6-515, parts A and B, Dow Corning) walls containing multiple 6-mm flat polyps (B) are shown. Colonic flexure is created by placing soft phantom in curved Lucite tray.

View larger version (156K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —Study phantom. Colon phantom (A) constructed of Silastic (liquid silicone rubber C6-515, parts A and B, Dow Corning) walls containing multiple 6-mm flat polyps (B) are shown. Colonic flexure is created by placing soft phantom in curved Lucite tray.

View larger version (9K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2 —Attenuation of human stool. Tagged human stool density has highly variable attenuation (mean, 356-411 H) throughout colon.

View larger version (9K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3 —Heterogeneity of human stool. Wide variation exists in human stool heterogeneity. Homogeneity increases in distal colon. From left to right, bars indicate homogeneous, mildly heterogeneous, moderately heterogeneous, and severely heterogeneous.

View larger version (7K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4 —Effect of various thresholds on simulated polyps. No polyps were subtracted using a threshold value of 200 H. Severity index refers to severe (3) to no (0) subtraction.

View larger version (10K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A —Assessment of stool subtraction algorithms. Severity index refers to severe (3) to no (0) subtraction. From left to right, bars indicate homogeneous, moderately heterogeneous, and severely heterogeneous stool. Algorithm 1, threshold of 200 H. No polyp subtraction occurred, but multiple other severe subtraction artifacts were seen.

View larger version (9K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B —Assessment of stool subtraction algorithms. Severity index refers to severe (3) to no (0) subtraction. From left to right, bars indicate homogeneous, moderately heterogeneous, and severely heterogeneous stool. Algorithm 2, threshold of 200 H plus expansion. Halo artifacts were eliminated with this algorithm, and other artifacts were reduced to a moderate level. Mild polyp subtraction occurred.

View larger version (8K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5C —Assessment of stool subtraction algorithms. Severity index refers to severe (3) to no (0) subtraction. From left to right, bars indicate homogeneous, moderately heterogeneous, and severely heterogeneous stool. Algorithm 3, threshold of 200 H plus expansion and convolution. Nearly all artifacts were reduced to a mild degree without polyp subtraction.

View larger version (136K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6A —CT of colon phantom using algorithm 1. Scan shows polyp (arrow) submerged in stool.

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6B —CT of colon phantom using algorithm 1. Scan shows subtraction of most of labeled stool as well as severe residual halos and islands of retained stool. Polyp (arrow) is not subtracted.

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7A —CT of colon phantom using algorithm 2. Polyp (arrow) is submerged in labeled stool.

View larger version (103K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7B —CT of colon phantom using algorithm 2. After subtraction, polyp has been removed.

View larger version (180K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 8A —CT of human colon containing large polyp in 51-year-old woman. Algorithm 3 was used for these scans. Large polyp (arrow) is present in sigmoid colon adjacent to well-labeled stool.

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 8B —CT of human colon containing large polyp in 51-year-old woman. Algorithm 3 was used for these scans. After subtraction, labeled stool has been removed without affecting polyp.

View larger version (140K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 9A —CT of human colon containing small polyp in 59-year-old man. Algorithm 3 was used for these scans. Small polyp (arrow) is shown on unsubtracted scan.

View larger version (131K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 9B —CT of human colon containing small polyp in 59-year-old man. Algorithm 3 was used for these scans. After subtraction, polyp (arrow) is clearly visible without artifacts.

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