title: Optimization of scanning parameters for CT colonography.
abstract: To determine the optimal collimation, pitch and reconstruction interval for CT colonography, 10 spherical polyps between 1 mm and 10 mm diameter and made of tissue equivalent material with a CT number of 40 Hounsfield units (HU) were placed in the colon of an anthropomorphic phantom. The phantom was scanned at slice thicknesses of 3 mm, 5 mm and 7 mm and pitches of 1.0, 1.3, 1.5, 1.7 and 2.0 on an IGE Hispeed advantage system. Images were reconstructed for each scanning parameter at the minimum intervals allowed along the z-axis. The optimum scanning protocol was assessed by measuring maximum contrast between the polyp and air, sensitivity for detection of each polyp along the z-axis, and relative radiation dose. In addition, images were reviewed separately by two radiologists who graded polyp conspicuity as: 0, not seen; 1, faintly seen; 2, well seen. It was found that varying the scanning parameters caused a marked alteration in the maximum contrast between each polyp and air. For example, for the 5 mm polyp, the range of contrasts from best to worst case was 910-490 HU. It was noted that with contrasts of less than 500 HU, polyps were only faintly seen. A slice thickness of 3 mm with a pitch of 2 offers optimal polyp conspicuity with a relatively low radiation dose, we conclude that scanning parameters can be optimized for threshold contrast, radiation dose and subjective conspicuity. We propose an optimal parameter of 3 mm slice thickness and pitch 2.
authors.affiliation: Department of Radiology, St. Bartholomew's Hospital, West Smithfield, London EC1A 7EB, UK.
authors.forename: N P
authors.initials: NP
authors.lastname: Power
authors.forename: M D
authors.initials: MD
authors.lastname: Pryor
authors.forename: A
authors.initials: A
authors.lastname: Martin
authors.forename: J
authors.initials: J
authors.lastname: Horrocks
authors.forename: A M
authors.initials: AM
authors.lastname: McLean
authors.forename: R H
authors.initials: RH
authors.lastname: Reznek
mesh_terms: D000886:Anthropometry; D003111:Colonic Polyps / Q000000981:diagnostic imaging*; D023881:Colonography, Computed Tomographic / Q000592:standards*; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage