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Influence of Image Acquisition Parameters on CT Artifacts and Polyp Depiction in Spiral CT Colonography: In Vitro Evaluation¹

¹ From the Electronic Radiology Lab (B.R.W.) and Abdominal Imaging Section (E.G.M.), Mallinckrodt Institute of Radiology, 510 S Kingshighway Blvd, St Louis, MO 63110; and the Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Conn (J.A.B.). Received September 22, 1999; revision requested November 5; revision received February 1, 2000; accepted February 8. Supported in part by the National Cancer Institute, Prostate-Colon-Lung-Ovary Preventative Trial, grant N01-CN-25516; the Washington University Cancer Center; the GE Association of University Radiologists; and the Mallinckrodt Institute of Radiology Summer Research Program. Address correspondence to B.R.W. (e-mail: bwhiting@wuerl.wustl.edu).

PURPOSE: To quantify the effects of spiral computed tomographic (CT) acquisition parameters on the magnitude of three-dimensional (3D) rippling artifacts and polyp depiction.

MATERIALS AND METHODS: An in vitro colon phantom was constructed with air-filled acrylic cylinders that contained synthetic polyps of 3–13 mm. The phantom was submerged in fluid and positioned at four angles of inclination relative to the z axis. Image data were acquired at collimation and pitch combinations of 3 mm and 1.67 and 5 mm and 1.6, respectively. Rippling artifacts were quantified by measuring the longitudinal variation of in-plane phantom edge width, and the influence of these artifacts on the depiction of pedunculated and sessile polyps was assessed qualitatively.

RESULTS: The in-plane magnitude of the rippling artifact was a function of the angle of inclination relative to the longitudinal axis and the table increment. The through-plane periodicity of the artifact was equal to one-half the table increment.

CONCLUSION: The table increment and angle of inclination of the surface of the object relative to the z axis determine the periodicity and magnitude of the rippling artifact at 3D spiral CT colonography. Although the depiction of small pedunculated polyps was not compromised, some sessile polyps were degraded by the artifact.

Index terms: Colon, CT, 75.12115, 75.12117 • Colon neoplasms, 75.311 • Computed tomography (CT), artifact • Computed tomography (CT), image processing, 75.12115, 75.12117 • Computed tomography (CT), three-dimensional, 75.12115, 75.12117

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