Figure 6b. (a, b) Scatterplots depict the distribution of the shape index and curvedness values for possible polyps before (a) and after (b) the fuzzy clustering process (Fig 1). Gray dots depict true-positive findings and black squares depict false-positive findings. The number of false-positive findings in b is much smaller than that in a because of the effect of fuzzy clustering. As expected, polyps have higher shape index values and lower curvedness values than do a majority of the false-positive findings. The solid line in b was used in the CAD scheme to help discriminate true- from false-positive findings. A substantial number of false-positive findings can be eliminated by disregarding the possible polyps in the upper left region above the line. (c, d) Scatterplots depict the distribution of CT and gradient values (Hounsfield units) for possible polyps before (c) and after (d) fuzzy clustering. Black squares depict true-positive findings and gray dots depict false-positive findings. The number of false-positive findings in d is much smaller than that in c because of the effect of fuzzy clustering. However, a substantial overlap remains between the true- and false-positive findings in d. Although the minimum and maximum threshold values for CT and gradient values (dashed lines) were used to reduce false-positive findings in the CAD scheme, thresholding was effective only for the elimination of outliers located outside the central rectangular region.