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CT Colonography with Computer-aided Detection: Automated Recognition of Ileocecal Valve to Reduce Number of False-Positive Detections¹

¹ From the Department of Diagnostic Radiology, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bldg 10, Rm 1C660, 10 Center Dr, MSC 1182, Bethesda, MD 20892-1182 (R.M.S., J.Y.); and Department of Radiology, Mayo Clinic, Rochester, Minn (C.D.J.). Received August 22, 2003; revision requested October 31; revision received December 16; accepted January 30, 2004. Supported by the intramural research programs of the Diagnostic Radiology Department, Warren G. Magnuson Clinical Center. Supported in part by NIH grant RO1CA75333. Address correspondence to R.M.S. (e-mail: rms@nih.gov).

View larger version (23K): [in a new window]   Figure 1a. Plots of mean CT attenuation versus volume of true polyps (TP) and ICVs. (a) Data set 2: a training set of 40 patients—20 of whom had normal colonoscopy results and 20 of whom were at high risk for colorectal cancer—with a total of 18 large polyps. Data for the 14 true polyps shown represent those for nine distinct large polyps identified with CAD. The five additional polyps represent multiple detected findings on these nine large polyps and/or findings detected at both supine and prone CT colonography. (b) Data set 1: a test set of 20 patients with 26 known large polyps. The 48 true polyps shown represent 21 distinct large polyps identified with CAD. The 27 additional polyps represent multiple detected findings on these 21 large polyps and/or findings detected at both supine and prone CT colonography. The ICVs are all of those in the data set—regardless of whether they were detected by the CAD system—that were manually identifiable and that could be segmented by the deformable contour segmentation algorithm. True polyps tend to have relatively low attenuation, which is attributable to the partial volume effect. The thick connecting horizontal and vertical lines in a and b show cutoffs for the mean lesion attenuation (less than –124 HU) and the lesion volume (>1.5 cm3) that were found to be optimal for detecting the ICV in this study. Findings in the left upper quadrant of the plot (above and to left of thick lines), which are those of lesions with low attenuation and large volume, are consistent with ICVs and are rejected from the list of polyp candidates reported by the CAD system.

View larger version (23K): [in a new window]   Figure 1b. Plots of mean CT attenuation versus volume of true polyps (TP) and ICVs. (a) Data set 2: a training set of 40 patients—20 of whom had normal colonoscopy results and 20 of whom were at high risk for colorectal cancer—with a total of 18 large polyps. Data for the 14 true polyps shown represent those for nine distinct large polyps identified with CAD. The five additional polyps represent multiple detected findings on these nine large polyps and/or findings detected at both supine and prone CT colonography. (b) Data set 1: a test set of 20 patients with 26 known large polyps. The 48 true polyps shown represent 21 distinct large polyps identified with CAD. The 27 additional polyps represent multiple detected findings on these 21 large polyps and/or findings detected at both supine and prone CT colonography. The ICVs are all of those in the data set—regardless of whether they were detected by the CAD system—that were manually identifiable and that could be segmented by the deformable contour segmentation algorithm. True polyps tend to have relatively low attenuation, which is attributable to the partial volume effect. The thick connecting horizontal and vertical lines in a and b show cutoffs for the mean lesion attenuation (less than –124 HU) and the lesion volume (>1.5 cm3) that were found to be optimal for detecting the ICV in this study. Findings in the left upper quadrant of the plot (above and to left of thick lines), which are those of lesions with low attenuation and large volume, are consistent with ICVs and are rejected from the list of polyp candidates reported by the CAD system.

View larger version (92K): [in a new window]   Figure 2a. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 51-year-old man from data set 2 group. The ICV, which was detected by using CAD and then eliminated by the ICV detector, has a mean attenuation of –131 HU and a volume of 2.7 cm3. The partial fat content of the ICV is evident in a. (c) Marked CT colonographic image shows computer-generated boundary (white outline) of the ICV. Attenuation measurements reflect the mean attenuation within the outline and were obtained in three dimensions, not just on the image shown.

View larger version (126K): [in a new window]   Figure 2b. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 51-year-old man from data set 2 group. The ICV, which was detected by using CAD and then eliminated by the ICV detector, has a mean attenuation of –131 HU and a volume of 2.7 cm3. The partial fat content of the ICV is evident in a. (c) Marked CT colonographic image shows computer-generated boundary (white outline) of the ICV. Attenuation measurements reflect the mean attenuation within the outline and were obtained in three dimensions, not just on the image shown.

View larger version (127K): [in a new window]   Figure 2c. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 51-year-old man from data set 2 group. The ICV, which was detected by using CAD and then eliminated by the ICV detector, has a mean attenuation of –131 HU and a volume of 2.7 cm3. The partial fat content of the ICV is evident in a. (c) Marked CT colonographic image shows computer-generated boundary (white outline) of the ICV. Attenuation measurements reflect the mean attenuation within the outline and were obtained in three dimensions, not just on the image shown.

View larger version (90K): [in a new window]   Figure 3a. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 51-year-old woman from data set 2 group. The ICV, which was detected by the CAD system and then eliminated by the ICV detector, has a mean attenuation of –147 HU and a volume of 2.5 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (131K): [in a new window]   Figure 3b. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 51-year-old woman from data set 2 group. The ICV, which was detected by the CAD system and then eliminated by the ICV detector, has a mean attenuation of –147 HU and a volume of 2.5 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (140K): [in a new window]   Figure 3c. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 51-year-old woman from data set 2 group. The ICV, which was detected by the CAD system and then eliminated by the ICV detector, has a mean attenuation of –147 HU and a volume of 2.5 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (127K): [in a new window]   Figure 4a. Transverse prone CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 59-year-old man from data set 2 group. The ICV, which was detected by the CAD system and then eliminated by the ICV detector, has a mean attenuation of –155 HU and a volume of 5.0 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (165K): [in a new window]   Figure 4b. Transverse prone CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 59-year-old man from data set 2 group. The ICV, which was detected by the CAD system and then eliminated by the ICV detector, has a mean attenuation of –155 HU and a volume of 5.0 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (165K): [in a new window]   Figure 4c. Transverse prone CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 59-year-old man from data set 2 group. The ICV, which was detected by the CAD system and then eliminated by the ICV detector, has a mean attenuation of –155 HU and a volume of 5.0 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (111K): [in a new window]   Figure 5a. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 53-year-old man from data set 2 group. The ICV, which was detected by the CAD system but not eliminated by the ICV detector because it was too high in attenuation, has a mean attenuation of –90 HU and a volume of 4.9 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (132K): [in a new window]   Figure 5b. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 53-year-old man from data set 2 group. The ICV, which was detected by the CAD system but not eliminated by the ICV detector because it was too high in attenuation, has a mean attenuation of –90 HU and a volume of 4.9 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (138K): [in a new window]   Figure 5c. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 53-year-old man from data set 2 group. The ICV, which was detected by the CAD system but not eliminated by the ICV detector because it was too high in attenuation, has a mean attenuation of –90 HU and a volume of 4.9 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (114K): [in a new window]   Figure 6a. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 56-year-old woman from data set 2 group. The ICV, which was detected by the CAD system but not eliminated by the ICV detector because it was too small, has a mean attenuation of –132 HU and a volume of 1.3 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (138K): [in a new window]   Figure 6b. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 56-year-old woman from data set 2 group. The ICV, which was detected by the CAD system but not eliminated by the ICV detector because it was too small, has a mean attenuation of –132 HU and a volume of 1.3 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (151K): [in a new window]   Figure 6c. Transverse supine CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 56-year-old woman from data set 2 group. The ICV, which was detected by the CAD system but not eliminated by the ICV detector because it was too small, has a mean attenuation of –132 HU and a volume of 1.3 cm3. (c) Marked CT colonographic image shows the computer-generated boundary (white outline) of the ICV.

View larger version (62K): [in a new window]   Figure 7a. Transverse prone CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 61-year-old woman from data set 1 group. The ICV, which was detected with CAD and then eliminated by the ICV detector, has a mean attenuation of –140 HU and a volume of 2.0 cm3. (c) Marked CT colonographic image shows computer-generated boundary (white outline) of the ICV.

View larger version (129K): [in a new window]   Figure 7b. Transverse prone CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 61-year-old woman from data set 1 group. The ICV, which was detected with CAD and then eliminated by the ICV detector, has a mean attenuation of –140 HU and a volume of 2.0 cm3. (c) Marked CT colonographic image shows computer-generated boundary (white outline) of the ICV.

View larger version (131K): [in a new window]   Figure 7c. Transverse prone CT colonographic images obtained by using (a) soft-tissue and (b, c) lung window settings show ICV (arrow) in 61-year-old woman from data set 1 group. The ICV, which was detected with CAD and then eliminated by the ICV detector, has a mean attenuation of –140 HU and a volume of 2.0 cm3. (c) Marked CT colonographic image shows computer-generated boundary (white outline) of the ICV.