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Diagnostic Accuracy of Laxative-Free Computed Tomographic Colonography for Detection of Adenomatous Polyps in Asymptomatic Adults: A Prospective Evaluation

Michael E. Zalis, MD; Michael A. Blake, MB BCh; Wenli Cai, PhD; Peter F. Hahn, MD, PhD; Elkan F. Halpern, PhD; Imrana G. Kazam, PhD; Myles Keroack, MD; Cordula Magee, PhD; Janne J. Näppi, PhD; Rocio Perez-Johnston, MD; John R. Saltzman, MD; Abhinav Vij, MD; Judy Yee, MD; and Hiroyuki Yoshida, PhD
[+] Article, Author, and Disclosure Information

From Massachusetts General Hospital, Brigham and Women's Hospital, Boston, Massachusetts, and University of California, San Francisco, San Francisco, California.

Disclaimer: Drs. Zalis, Cai, Näppi, and Yoshida are co-inventors of electronic cleansing and computer-aided detection software patents assigned to their home institution, without associated royalties.

Acknowledgment: The authors thank the clinical staff of the departments of gastroenterology, radiology, and pathology of the participating institutions for the excellent care provided during the performance of this study.

Grant Support: Dr. Zalis is supported by GE Healthcare (03-OPQ-001), the American Cancer Society (RSG-08-221-01-CCE), and the National Institutes of Health (1K22CA098422). Drs. Zalis, Cai, Näppi, and Yoshida are supported by the National Institutes of Health (1 RO1 CA095279). Dr. Yoshida is supported by the American Cancer Society (RSG-05-088-01-CCE).

Potential Conflicts of Interest: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M11-2437.

Reproducible Research Statement:Study protocol, statistical code, and data set: Not available.

Requests for Single Reprints: Michael E. Zalis, MD, Department of Imaging, Massachusetts General Hospital, Suite 400A, 25 New Chardon Street, Boston, MA 02114; e-mail, mailto:mzalis@mgh.harvard.edu.

Current Author Addresses: Drs. Zalis, Blake, Cai, Hahn, Kazam, Magee, Näppi, Perez-Johnston, Vij, and Yoshida: Department of Imaging, Massachusetts General Hospital, Suite 400A, 25 New Chardon Street, Boston, MA 02114.

Dr. Halpern: Institute for Technology Assessment, 101 Merrimac Street, Boston, MA 02114.

Dr. Keroack: Eau Claire Center, 2116 Craig Road, Eau Claire, WI 54701.

Dr. Saltzman: Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115.

Dr. Yee: Radiology and Biomedical Imaging, University of California, San Francisco, and Department of Radiology, San Francisco Veterans Affairs Medical Center, 4150 Clement Street, San Francisco, CA 94121.

Author Contributions: Conception and design: M.E. Zalis, W. Cai, E.F. Halpern, M. Keroack.

Analysis and interpretation of the data: M.A. Blake, P.F. Hahn, E.F. Halpern, I.G. Kazam, R. Perez-Johnston, A. Vij, J. Yee.

Drafting of the article: M.E. Zalis, M.A. Blake, P.F. Hahn.

Critical revision of the article for important intellectual content: M.E. Zalis, M.A. Blake, P.F. Hahn, J.J. Näppi, J.R. Saltzman, J. Yee, H. Yoshida.

Final approval of the article: M.E. Zalis, M.A. Blake, W. Cai, P.F. Hahn, E.F. Halpern, M. Keroack, J.R. Saltzman, J. Yee.

Provision of study materials or patients: M.E. Zalis, E.F. Halpern, I.G. Kazam, M. Keroack, J.R. Saltzman, J. Yee, H. Yoshida.

Statistical expertise: E.F. Halpern, A. Vij.

Obtaining of funding: M.E. Zalis, H. Yoshida.

Administrative, technical, or logistic support: M.E. Zalis, W. Cai, I.G. Kazam, M. Keroack, C. Magee, J.J. Näppi, J.R. Saltzman, H. Yoshida.

Collection and assembly of data: M.E. Zalis, P.F. Hahn, I.G. Kazam, M. Keroack, C. Magee, J.J. Näppi, J.R. Saltzman, A. Vij, J. Yee, H. Yoshida.

Ann Intern Med. 2012;156(10):692-702. doi:10.7326/0003-4819-156-10-201205150-00005
Text Size: A A A

Background: Colon screening by optical colonoscopy (OC) or computed tomographic colonography (CTC) requires a laxative bowel preparation, which inhibits screening participation.

Objective: To assess the performance of detecting adenomas 6 mm or larger and patient experience of laxative-free, computer-aided CTC.

Design: Prospective test comparison of laxative-free CTC and OC. The CTC included electronic cleansing and computer-aided detection. Optical colonoscopy examinations were initially blinded to CTC results, which were subsequently revealed during colonoscope withdrawal; this method permitted reexamination to resolve discrepant findings. Unblinded OC served as a reference standard. (ClinicalTrials.gov registration number: NCT01200303)

Setting: Multicenter ambulatory imaging and endoscopy centers.

Participants: 605 adults aged 50 to 85 years at average to moderate risk for colon cancer.

Measurements: Per-patient sensitivity and specificity of CTC and first-pass OC for detecting adenomas at thresholds of 10 mm or greater, 8 mm or greater, and 6 mm or greater; per-lesion sensitivity and survey data describing patient experience with preparations and examinations.

Results: For adenomas 10 mm or larger, per-patient sensitivity of CTC was 0.91 (95% CI, 0.71 to 0.99) and specificity was 0.85 (CI, 0.82 to 0.88); sensitivity of OC was 0.95 (CI, 0.77 to 1.00) and specificity was 0.89 (CI, 0.86 to 0.91). Sensitivity of CTC was 0.70 (CI, 0.53 to 0.83) for adenomas 8 mm or larger and 0.59 (CI, 0.47 to 0.70) for those 6 mm or larger; sensitivity of OC for adenomas 8 mm or larger was 0.88 (CI, 0.73 to 0.96) and 0.76 (CI, 0.64 to 0.85) for those 6 mm or larger. The specificity of OC at the threshold of 8 mm or larger was 0.91 and at 6 mm or larger was 0.94. Specificity for OC was greater than that for CTC, which was 0.86 at the threshold of 8 mm or larger and 0.88 at 6 mm or larger (P = 0.02). Reported participant experience for comfort and difficulty of examination preparation was better with CTC than OC.

Limitations: There were 3 CTC readers. The survey instrument was not independently validated.

Conclusion: Computed tomographic colonography was accurate in detecting adenomas 10 mm or larger but less so for smaller lesions. Patient experience was better with laxative-free CTC. These results suggest a possible role for laxative-free CTC as an alternate screening method.

Primary Funding Source: GE Healthcare and the American Cancer Society.


Grahic Jump Location
Figure 1.

Study flow diagram.

A total of 605 participants completed the study protocol and yielded complete data sets for interpretation and comparison: 76 were recruited from Brigham and Women's Hospital, 479 from Massachusetts General Hospital, 1 from North Shore Medical Center, and 49 from the University of California, San Francisco, Veterans Affairs Medical Center. CTC = computed tomographic colonography; GI = gastrointestinal; LFD = low-fiber diet; OC = optical colonoscopy; PCP = primary care provider.

Grahic Jump Location
Grahic Jump Location
Figure 2.

Colonic adenoma as seen on laxative-free CTC and OC.

CTC = computed tomographic colonography; OC = optical colonoscopy. A. Zoomed axial 2-dimensional CTC image before electronic cleansing. B. Zoomed axial 2-dimensional CTC image after electronic cleansing. C. Endoluminal 2-dimensional CTC image. Yellow arrow represents computer-aided detection marker placed automatically by the computer to assist the reader; computer-aided detection markers were available for both 2- and 3-dimensional views. The blue arrows in panels A and B indicate the point of view for 3-dimensional reconstruction (C). D. OC image of confirmed 12-mm adenoma prospectively identified by CTC colonography and OC in an asymptomatic 63-year-old male study participant. The yellow box is an annotation placed manually by the gastroenterologist to highlight the polyp for the colonoscopy report.

Grahic Jump Location




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Submit a Comment/Letter
Estimating Specificity of CTC
Posted on May 24, 2012
Paul F.Pinsky, Researcher
Conflict of Interest: None Declared

Zalis et al. report on the diagnostic accuracy of laxative-free computed tomographic colonography (CTC), as well as of optical colonoscopy (OC), for detection of various sized adenomas [1]. They report for CTC a specificity of 85% (or a false positive rate of 15%) for 10mm+ adenomas. Apparently, though, they define a false positive for 10mm+ adenomas as CTC identifying a lesion measured (by the observer) as at least 6mm in subjects without a 10mm+ adenoma. By this definition, however, if CTC correctly classified a subject as having, say, a 7mm lesion, and hence not having a 10mm+ adenoma, this result still was classified as a false positive for 10mm+ (and 8mm+) adenomas. Thus, the reported specificity seems to underestimate the true accuracy of CTC for identifying 10mm+ adenomas. It would be useful to know what the false positive rate would be if a positive test for 10mm adenomas was defined as identifying a lesion that was estimated (by the observer) to be 10mm+. In the presence of measurement error, this could also affect sensitivity, if for example, a true 10mm adenoma was measured as 9mm by the observer. In clinical practice, referral to OC could well take into account the measured lesion size in relation to a (say) 10mm threshold, not just whether the measured size was at least 6mm.

Paul F. Pinsky National Cancer Institute


1. Zalis ME, Blake MA, Cai W et al. Diagnostic accuracy of laxative- free computed tomographic colonography for detection of adenomatous polyps in asymptomatic adults: a prospective elaluation. Ann Intern Med 2012 156: 692-702.

Conflict of Interest:

None declared

Submit a Comment/Letter

Summary for Patients

Screening for Colon Cancer by Using a Computed Tomographic Scan Without a Laxative

The full report is titled “Diagnostic Accuracy of Laxative-Free Computed Tomographic Colonography for Detection of Adenomatous Polyps in Asymptomatic Adults. A Prospective Evaluation.” It is in the 15 May 2012 issue of Annals of Internal Medicine (volume 156, pages 692-702). The authors are M.E. Zalis, M.A. Blake, W. Cai, P.F. Hahn, E.F. Halpern, I.G. Kazam, M. Keroack, C. Magee, J.J. Näppi, R. Perez-Johnston, J.R. Saltzman, A. Vij, J. Yee, and H. Yoshida.


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