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Automated Polyp Measurement with CT Colonography: Preliminary Observations in a Phantom Colon Model

Joel G. Fletcher1, Fargol Booya1, Zachary Melton1, Kristina Johnson1, Lutz Guendel2, Bernhard Schmidt2, Cynthia H. McCollough1, Brett Young1, Jeff L. Fidler1 and William S. Harmsen1

1 Department of Radiology, Mayo Clinic, 200 First St. SW, Mayo E-2, Rochester, MN 55905.
2 Siemens Medical Solutions, Malvern, PA.


Figure 1
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  		Fig. 1A —Colon phantom. Images show use of automated polyp measurement tool. Three-dimensional endoluminal view obtained with 50-mA data set shows 7-mm sessile polyp not on haustral fold. After activation of automated polyp measurement tool, single mouse click was made at tip of arrow. 3a = polyp number assigned as part of study.

 

Figure 2
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  		Fig. 1B —Colon phantom. Images show use of automated polyp measurement tool. Two-dimensional multiplanar reformation (MPR) corresponding to polyp in A shows how automated polyp measurement tool circumscribes polyp in box. Reported measurement is 0.63 cm. 3a = polyp number assigned as part of study.

 

Figure 3
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  		Fig. 1C —Colon phantom. Images show use of automated polyp measurement tool. Oblique 2D MPR image corresponding to polyp in A shows circumscribed polyp in plane perpendicular to B.

 

Figure 4
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  		Fig. 1D —Colon phantom. Images show use of automated polyp measurement tool. Three-dimensional endoluminal view of polyp in A shows polyp boundaries circumscribed with automated polyp measurement tool (box). 3a = polyp number assigned as part of study.

 

Figure 5
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  		Fig. 1E —Colon phantom. Images show use of automated polyp measurement tool. Three-dimensional endoluminal view of polyp in A with orientation changed. Automated polyp measurement tool is activated by clicking on another point (arrow) on polyp surface. 3a = polyp number assigned as part of study.

 

Figure 6
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  		Fig. 1F —Colon phantom. Images show use of automated polyp measurement tool. Two-dimensional MPR image corresponding to polyp measurement in E. Automated polyp measurement device shows diameter of 0.63 cm. 3a = polyp number assigned as part of study.

 

Figure 7
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  		Fig. 1G —Colon phantom. Images show use of automated polyp measurement tool. Three-dimensional endoluminal view of polyp in A-F obtained from 12-mA data set. Automated polyp measurement tool circumscribes borders of polyp (box). 2a = polyp number assigned as part of study.

 

Figure 8
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  		Fig. 1H —Colon phantom. Images show use of automated polyp measurement tool. Two-dimensional MPR image obtained from 12-mA data set corresponding to G shows polyp diameter is 0.65 cm.

 

Figure 9
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  		Fig. 2 —Chart shows experimental design. Each reviewer performed two automated measurements and one manual measurement for each polyp in each data set. Each data set contained 24 polyps of three morphologic types (pedunculated, sessile, or flat), four sizes (5, 7, 9, or 12 mm), and two locations (tip of fold or not). Brackets indicate how measurement data were pooled to address specific questions.

 

Figure 10
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  		Fig. 3A —Graphs show accuracy of automated polyp measurement tool. Mean absolute error represents pooling of data across all four reviewers and all CT data sets. When multiple polyp characteristics associated with measurement inaccuracy are combined (e.g., small size, flat morphologic type, location on tip of haustral fold), measurement errors can be large. Graph shows accuracy of measurement of polyps not on tip of fold.

 

Figure 11
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  		Fig. 3B —Graphs show accuracy of automated polyp measurement tool. Mean absolute error represents pooling of data across all four reviewers and all CT data sets. When multiple polyp characteristics associated with measurement inaccuracy are combined (e.g., small size, flat morphologic type, location on tip of haustral fold), measurement errors can be large. Graph shows accuracy of measurement of polyps on tip of fold.

 

Figure 12
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  		Fig. 4A —Colon phantom with 5-mm flat polyp (3a) on tip of fold. Example of inaccurate measurement with automated tool. Two-dimensional multiplanar reformation (MPR) image shows 5-mm flat polyp (arrow) obtained from 100-mA CT data set. Large arrow shows which polyp was measured.

 

Figure 13
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  		Fig. 4B —Colon phantom with 5-mm flat polyp (3a) on tip of fold. Example of inaccurate measurement with automated tool. Oblique 2D MPR image bisecting polyp (arrow) shows largest cross-sectional diameter and manual measurement of 4.8 mm.

 

Figure 14
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  		Fig. 4C —Colon phantom with 5-mm flat polyp (3a) on tip of fold. Example of inaccurate measurement with automated tool. Three-dimensional endoluminal view of polyp in B shows that automated polyp measurement tool has included underlying haustral fold in polyp, labeled 3a, boundary (box). 1a = another polyp.

 

Figure 15
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  		Fig. 4D —Colon phantom with 5-mm flat polyp (3a) on tip of fold. Example of inaccurate measurement with automated tool. Two-dimensional MPR image shows polyp and underlying haustral fold, both of which were circumscribed by automated polyp measurement tool, producing overestimate of polyp size at 7.3 mm.

 

Figure 16
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  		Fig. 5 —Graph shows precision of manual measurements versus automated measurements for two observers measuring 96 polyps. Precision is reported as difference between either two manual measurements or two automated measurements. Points above diagonal line represent polyps in which two automated measurements were closer. Points below diagonal line represent polyps in which two manual measurements were closer. For two observers, difference between automated measurements was smaller than difference between manual measurements for 82/96 (85%) of polyps (p < 0.01).

 

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