Rationale and Objectives
The purpose of this study was to assess (1) the agreement of two-dimensional (2D) and three-dimensional (3D) manual and automated polyp linear diameter measurements at CT colonography (CTC), with optical colonoscopic equivalents and (2) intraobserver and interobserver agreement of the CTC measurements.
Materials and Methods
Using the same CTC system, two radiologists independently measured the maximum linear diameter of 44 polyps (reference size 3–15 mm) matched on CTC and optical colonoscopy: manual 2D optimized multiplanar reformatted planes with standard window settings (level 1500 HU, width −200 HU), manual 3D measurement with software calipers and automated 3D measurement with software. After 2 weeks, polyps were measured again. Compatibility of CTC measurement with that of optical colonoscopy and measurement reproducibility was assessed statistically.
Results
In the manual measurement, 44 polyps were analyzed and 41 in automated measurement; three polyps could not be extracted. Although the measurement difference was noted for automated, manual 3D, and manual 2D measurements, statistically supported agreement with optical colonoscopic measurement was noted only with manual 2D measurement for both observers. However, 95% limits of agreement were wide for all the measurement methods. When categorized according to the optical colonoscopic measurement, manual 2D, 3D, and automated measurements showed “good” agreement. Although intraobserver and interobserver agreement was good with manual measurement, intraobserver and interobserver agreement was excellent with automated measurement.
Conclusion
Manual 2D measurements demonstrated trends of better approximation to optical colonoscopy measurements than manual 3D or automated measurements. And automated measurement eliminated intraobserver and interobserver variability. For noninvasive CTC surveillance, manual 2D measurements are expected to measure medium-sized polyps with sufficient agreement with optical colonoscopic measurements and excellent intraobserver and interobserver variability, especially if combined with automated measurement.
It is widely believed that the majority of colorectal cancers arise from precursor adenomatous polyps and that endoscopic polypectomy is preventive ( ). In the absence of histology, maximal polyp size is the most reliable predictor of developing malignancy ( ). For polyps ≥10 mm, the risk of high-grade dysplasia or cancer ranges from 10% to 25% ( ). While there is general consensus that large, ≥10-mm polyps are excised ( ), there is a more broad range of practice management of the medium-sized (6−9 mm) and small (<6 mm) polyps, ranging from surveillance to polypectomy ( ), depending on the clinical context of the patient.
Based on this evidence, a working group has developed patient management strategies predicated by the largest polyp found at CT colonography (CTC) ( ) that are now regarded as a sensitive screening tool for colonic adenomatous polyps ( ). For this management algorithm to be useful in daily clinical practice, accurate measurement of polyps (especially for medium-sized polyps), the clinical legitimacy and the replication with optical colonoscopic measurements are essential and critical for treatment choice ( ). Moreover, for noninvasive CTC surveillance of unresected medium-sized polyps, measurements from successive follow-up examinations must be so highly repeatable and reproducible that discernment of interval polyp growth or regression can allow appropriate clinical decision making ( ). This is important because polyps left in situ require reexamination and remeasurement, perhaps after an interval of several years, which makes it less likely that the subsequent measurement will be performed by the same observer who made the first measurement. However, with CTC, a degree of intraobserver and interobserver variability is inevitable during manual measurement, which can result in misclassification and errors in the management, computer-aided automated measurement is now coming to the front ( ).
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Materials and methods
Polyp Dataset
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CT Scanning
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Polyp Measurement
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Statistical Analysis
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Results
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Agreement With Optical Colonoscopic Measurement
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Table 1
Agreement Between Observer CT Measurement and Optical Colonoscopic Reference
Reader and Measurement Method Mean Measurement Difference Between Optical Colonoscopic and CTC Measurement (mm) ⁎ P Value † 95% Limits of Agreement ‡ Observer 1 Manual 2D ( n = 44) 0.39 (−0.19, 0.98) 0.182 −3.46, 4.25 Manual 3D ( n = 44) 1.15 (0.50, 1.81) 0.001 −3.18, 5.49 Automated ( n = 41) 2.21 (1.48, 2.94) 0.000 −2.41, 6.83 Observer 2 Manual 2D ( n = 44) 0.30 (−0.33, 0.93) 0.339 −3.85, 4.45 Manual 3D ( n = 44) 1.15 (0.42, 1.89) 0.003 −3.70, 6.00 Automated ( n = 41) 2.21 (1.48, 2.94) 0.000 −2.41, 6.83
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Polyp Categorization
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Table 2
Polyp Size Categorization According to Observer and the Measurement Method
A. Observer 1 Polyp Size (mm) † Manual 2D Measurement <6 6−9 ≥10 <6 ( n = 20) 12 (60) 8 (40) 0 (0) 6−9 ( n = 14) 2 (14) 12 (86) 0 (0) ≥10 ( n = 10) 0 (0) 3 (30) 7 (70) κ = 0.548.
B. Observer 1 Polyp Size (mm) † Manual 3D Measurement <6 6−9 ≥10 <6 ( n = 20) 8 (40) 12 (60) 0 (0) 6−9 ( n = 14) 1 (7) 11 (79) 2 (14) ≥10 ( n = 10) 0 (0) 2 (20) 8 (80) κ = 0.427.
C. Observer 2 Polyp Size (mm) † Manual 2D Measurement <6 6−9 ≥10 <6 ( n = 20) 12 (60) 8 (40) 0 (0) 6−9 ( n = 14) 2 (14) 11 (79) 1 (7) ≥10 ( n = 10) 0 (0) 4 (40) 6 (60) κ = 0.478.
D. Observer 2 Polyp Size (mm) † Manual 3D Measurement <6 6−9 ≥10 <6 ( n = 20) 8 (40) 11 (55) 1 (5) 6−9 ( n = 14) 1 (7) 9 (64) 4 (29) ≥10 ( n = 10) 0 (0) 3 (30) 7 (70) κ = 0.330.
E. Observers 1 and 2 Polyp Size (mm) † Automated Measurement <6 6−9 ≥10 <6 ( n = 19) 5 (26) 11 (58) 3 (16) 6−9 ( n = 14) 0 (0) 9 (64) 5 (36) ≥10 ( n = 8) 0 (0) 1 (13) 7 (87) κ = 0.300.
*Values are numbers of polyps. Numbers in parentheses are percentages.
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Intraobserver Agreement
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Table 3
Mean Difference and Bland-Altman 95% Limits of Agreement for Intraobserver Comparisons of Polyp Measurement According to Measurement Method
Observer and Measurement Method Mean Measurement Difference Between First and Second Measurement (mm) ⁎ P Value † 95% Limits of Agreement ‡ Observer 1 Manual 2D 0.07 (−0.03, 0.17) 0.19 −0.59, 0.72 Manual 3D −0.02 (−0.12, 0.07) 0.62 −0.63, 0.58 Automated 0.00 (0.00, 0.00) 1.00 0.00, 0.00 Observer 2 Manual 2D 0.25 (0.04, 0.45) 0.02 −1.08, 1.57 Manual 3D 0.30 (0.06, 0.54) 0.01 −1.27, 1.88 Automated 0.00 (0.00, 0.00) 1.00 0.00, 0.00
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Interobserver Agreement
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Table 4
Mean Difference and Bland-Altman 95% Limits of Agreement for Interobserver Comparisons of Polyp Measurement According to Measurement Method
Measurement Method Mean Measurement Difference Between Observer 1 and 2 (mm) ⁎ P Value † 95% Limits of Agreement ‡ Manual 2D 0.09 (−0.15, 0.34) 0.45 −1.52, 1.70 Manual 3D 0.00 (−0.33, 0.33) 0.99 −2.16, 2.16 Automated 0.00 (0.00, 0.00) 1.00 0.00, 0.00
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Discussion
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Appendix
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