Academic Radiology
Volume 16, Issue 1 , Pages 4-14, January 2009

Conspicuity of Colorectal Polyps at CT Colonography:1

Visual Assessment, CAD Performance, and the Important Role of Polyp Height

  • Ronald M. Summers, MD, PhD

      Affiliations

    • Diagnostic Radiology Department, National Institutes of Health Clinical Center, Bldg. 10, Room 1C368X, MSC 1182, Bethesda, MD 20892-1182
    • Corresponding Author InformationAddress correspondence to: R.M.S.
    • ,
  • Suzanne M. Frentz, BS

      Affiliations

    • Diagnostic Radiology Department, National Institutes of Health Clinical Center, Bldg. 10, Room 1C368X, MSC 1182, Bethesda, MD 20892-1182
    • ,
  • Jiamin Liu, PhD

      Affiliations

    • Diagnostic Radiology Department, National Institutes of Health Clinical Center, Bldg. 10, Room 1C368X, MSC 1182, Bethesda, MD 20892-1182
    • ,
  • Jianhua Yao, PhD

      Affiliations

    • Diagnostic Radiology Department, National Institutes of Health Clinical Center, Bldg. 10, Room 1C368X, MSC 1182, Bethesda, MD 20892-1182
    • ,
  • Linda Brown, MD

      Affiliations

    • Diagnostic Radiology Department, National Institutes of Health Clinical Center, Bldg. 10, Room 1C368X, MSC 1182, Bethesda, MD 20892-1182
    • ,
  • Adeline Louie, MD

      Affiliations

    • Diagnostic Radiology Department, National Institutes of Health Clinical Center, Bldg. 10, Room 1C368X, MSC 1182, Bethesda, MD 20892-1182
    • ,
  • Duncan S. Barlow, MD

      Affiliations

    • Colon Health Initiative, National Naval Medical Center, Bethesda, MD
    • ,
  • Donald W. Jensen, MD

      Affiliations

    • Colon Health Initiative, National Naval Medical Center, Bethesda, MD
    • ,
  • Andrew J. Dwyer, MD

      Affiliations

    • Diagnostic Radiology Department, National Institutes of Health Clinical Center, Bldg. 10, Room 1C368X, MSC 1182, Bethesda, MD 20892-1182
    • ,
  • Perry J. Pickhardt, MD

      Affiliations

    • Department of Radiology, University of Wisconsin School of Medicine, Madison, WI
    • ,
  • Nicholas Petrick, PhD

      Affiliations

    • LAMIS Image Analysis Laboratory, FDA/CDRH/OSEL, Silver Spring, MD

Received 8 April 2008; accepted 9 June 2008.

Rationale and Objectives

The factors that influence the conspicuity of polyps on computed tomographic (CT) colonography (CTC) are poorly understood. The aim of this study is to compare radiologists' visual assessment of polyp conspicuity to quantitative image features and show the relationship between visual conspicuity and the detection of colonic polyps by computer-aided detection (CAD) on CTC.

Methods

One polyp (size range 6—10 mm) was selected from the CTC examination of each of 29 patients from a larger cohort. All patients underwent oral contrast-enhanced CTC with same-day optical colonoscopy with segmental unblinding. The polyps were analyzed by a previously validated CAD system and placed into one of two groups (detected [n = 12] or not detected [n = 17] by CAD). The study population was intentionally enriched with polyps that were not detected by the CAD system. Four board-certified radiologists, blinded to the CAD results, reviewed two- and three-dimensional CTC images of the polyps and scored the conspicuity of the polyps using a 4-point scale (0 = least conspicuous, 3 = most conspicuous). Polyp height and width were measured by a trained observer. A t-test (two-tailed, unpaired equal variance) was done to determine statistical significance. Intra- and interobserver variabilities of the conspicuity scores were assessed using the weighted κ test. Regression analysis was used to investigate the relationship of conspicuity to polyp height and width.

Results

A statistically significant difference was found between the average conspicuity scores for polyps that were detected by CAD compared to those that were not (2.3 ± 0.6 vs. 1.4 ± 0.8) (P = .004). There was moderate intraobserver agreement of the conspicuity scores (weighted κ 0.57 ± 0.09). Interobserver agreement was fair (average weighted κ for six pair-wise comparisons, 0.38 ± 0.15). Conspicuity was correlated with manual measurement of polyp height (r2 = 0.38–0.56, P < .001).

Conclusions

This CAD system tends to detect 6—10 mm polyps that are more visually conspicuous. Polyp height is a major determinant of visual conspicuity. The generalizability of these findings to other CAD systems is currently unknown. Nevertheless, CAD developers may need to specifically target flatter and less conspicuous polyps for CAD to better assist the radiologist to find polyps in this clinically important size category.

Key Words: CT, colon, colon cancer, conspicuity

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1 This research was supported in part by the Intramural Research Programs of the NIH Clinical Center and the National Institute of Biomedical Imaging and Bioengineering. No FDA endorsement of any product or company mentioned in this manuscript should be inferred. This work was presented at the 2007 RSNA Scientific Meeting, Chicago, IL.

PII: S1076-6332(08)00408-X

doi:10.1016/j.acra.2008.06.007

Academic Radiology
Volume 16, Issue 1 , Pages 4-14, January 2009

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