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Computer-Aided Detection of Colonic Polyps at CT Colonography Using a Hessian Matrix–Based Algorithm: Preliminary Study

¹ Department of Radiology, Seoul National University College of Medicine, 28, Yongon-dong, Chongno-gu, Seoul 110-744, Korea.
² Institute of Radiation Medicine, Seoul National University College of Medicine, Seoul, Korea.
³ Department of Medical Engineering, Seoul National University College of Medicine, Seoul, Korea.
⁴ Department of Radiology, Stedelijk Ziekenhuis, Roeselare, Belgium.

View larger version (17K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1 —Schematic diagram of our methods of detecting polyps in CT colonography.

View larger version (11K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2 —Schematic diagrams of measures of similarity to local structures and basic conditions of these local structures. For line structure, Eigen values 2 and 3 along directions of greater gray-level changes are larger than Eigen value 1, which corresponds to direction e1 of smaller gray-level change ( 0). For blob that represents polyp in colon, change of gray level is large in all three directions of blob. For sheetlike structure, Eigen value 3 along direction of greater gray-level change is larger than Eigen values 1 and 2, which correspond to directions e1 and e2 of smaller gray-level change ( 0).

View larger version (63K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A —45-year-old woman with 6-mm hyperplastic polyp in rectum. On CT colonographic images in supine (A) and prone (B) views, part of polyp (arrow) is colored red and detected with computer-aided detection scheme on both supine and prone data sets. Note endoluminal appearance of polyp on each data set (right lower corner).

View larger version (67K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B —45-year-old woman with 6-mm hyperplastic polyp in rectum. On CT colonographic images in supine (A) and prone (B) views, part of polyp (arrow) is colored red and detected with computer-aided detection scheme on both supine and prone data sets. Note endoluminal appearance of polyp on each data set (right lower corner).

View larger version (125K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C —45-year-old woman with 6-mm hyperplastic polyp in rectum. Colonoscopic image shows a sessile polyp.

View larger version (72K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A —41-year-old man with 20-mm pedunculated polyp in sigmoid colon. On axial and corresponding 3D endoluminal (right lower corner) CT colonographic images in supine view, color coding is based on shape likelihood, in which polyps, folds, and colonic wall are shown in red, blue, and green, respectively. As a result, polyp is clearly differentiated from folds and colonic wall. Pedunculated polyp is represented by red and is detected as a polyp candidate (arrow) by computer-aided detection (CAD).

View larger version (66K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B —41-year-old man with 20-mm pedunculated polyp in sigmoid colon. On axial and corresponding 3D endoluminal (right lower corner) CT colonographic images in prone view, head of pedunculated polyp is submerged in residual fluid and only part of stalk (arrow) of polyp is visualized. Therefore, polyp cannot be identified by CAD algorithm.

View larger version (105K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4C —41-year-old man with 20-mm pedunculated polyp in sigmoid colon. Colonoscopic image shows adenomatous polyp (arrow) having a long stalk (asterisk).

View larger version (65K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A —71-year-old man with 9-mm sessile polyp in ascending colon. On axial and corresponding 3D endoluminal (right lower corner) CT colonographic images in supine view, polyp (arrow) looks smaller than expected and appears to be flat. On this view, polyp does not contain adequate voxels with high likelihood of being a blob, making it not detectable by computer-aided detection (CAD) algorithm.

View larger version (71K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B —71-year-old man with 9-mm sessile polyp in ascending colon. On axial and corresponding 3D endoluminal (right lower corner) CT colonographic images in prone view, polyp (arrow) appears rounder and larger than its supine counterpart, so it was identified by CAD algorithm. Colonoscopic biopsy confirmed an adenomatous polyp (not shown).

View larger version (74K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6A —Examples of false-negative lesions by computer-aided detection (CAD). A 10-mm flat adenomatous polyp in sigmoid colon was missed by CAD. Axial 3D endoluminal (right lower corner) CT colonography images (supine, A; prone, B) show polyp (arrow) that is not tagged with red.

View larger version (69K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6B —Examples of false-negative lesions by computer-aided detection (CAD). A 10-mm flat adenomatous polyp in sigmoid colon was missed by CAD. Axial 3D endoluminal (right lower corner) CT colonography images (supine, A; prone, B) show polyp (arrow) that is not tagged with red.

View larger version (104K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6C —Examples of false-negative lesions by computer-aided detection (CAD). Colonoscopic image of polyp reveals flat nature of lesion.

View larger version (78K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6D —Examples of false-negative lesions by computer-aided detection (CAD). Note 7-mm pedunculated polyp in distal rectum. On axial 3D endoluminal (right lower corner) CT colonography image of prone view, polyp (arrow) was not identified by CAD algorithm. Polyp is located in narrow space where rectal wall and rectal tube are attached, so shape of polyp is seen as flat even though original shape of lesion is pedunculated. Colonoscopic biopsy confirmed adenomatous polyp (not shown).

View larger version (69K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7A —Examples of false-positive lesions by computer-aided detection (CAD). Axial and corresponding 3D endoluminal (lower corner) CT colonographic images of false-positive findings by computer-aided detection (CAD). Feces (arrow, A) and prominent or converging folds (arrow, B) tend to be major causes of false-positive findings, followed by residual fluid (arrow, C), ileocecal valve (arrow, D), and rectal tube (arrow, E). These lesions appear as blobs and were thus incorrectly identified by CAD as polyp. Various false-positive lesions are colored red, which indicates false-positive findings by CAD.

View larger version (71K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7B —Examples of false-positive lesions by computer-aided detection (CAD). Axial and corresponding 3D endoluminal (lower corner) CT colonographic images of false-positive findings by computer-aided detection (CAD). Feces (arrow, A) and prominent or converging folds (arrow, B) tend to be major causes of false-positive findings, followed by residual fluid (arrow, C), ileocecal valve (arrow, D), and rectal tube (arrow, E). These lesions appear as blobs and were thus incorrectly identified by CAD as polyp. Various false-positive lesions are colored red, which indicates false-positive findings by CAD.

View larger version (71K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7C —Examples of false-positive lesions by computer-aided detection (CAD). Axial and corresponding 3D endoluminal (lower corner) CT colonographic images of false-positive findings by computer-aided detection (CAD). Feces (arrow, A) and prominent or converging folds (arrow, B) tend to be major causes of false-positive findings, followed by residual fluid (arrow, C), ileocecal valve (arrow, D), and rectal tube (arrow, E). These lesions appear as blobs and were thus incorrectly identified by CAD as polyp. Various false-positive lesions are colored red, which indicates false-positive findings by CAD.

View larger version (71K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7D —Examples of false-positive lesions by computer-aided detection (CAD). Axial and corresponding 3D endoluminal (lower corner) CT colonographic images of false-positive findings by computer-aided detection (CAD). Feces (arrow, A) and prominent or converging folds (arrow, B) tend to be major causes of false-positive findings, followed by residual fluid (arrow, C), ileocecal valve (arrow, D), and rectal tube (arrow, E). These lesions appear as blobs and were thus incorrectly identified by CAD as polyp. Various false-positive lesions are colored red, which indicates false-positive findings by CAD.

View larger version (67K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7E —Examples of false-positive lesions by computer-aided detection (CAD). Axial and corresponding 3D endoluminal (lower corner) CT colonographic images of false-positive findings by computer-aided detection (CAD). Feces (arrow, A) and prominent or converging folds (arrow, B) tend to be major causes of false-positive findings, followed by residual fluid (arrow, C), ileocecal valve (arrow, D), and rectal tube (arrow, E). These lesions appear as blobs and were thus incorrectly identified by CAD as polyp. Various false-positive lesions are colored red, which indicates false-positive findings by CAD.

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