title: Stair-step artifacts with single versus multiple detector-row helical CT.
abstract: OBJECTIVE
  To compare the effects of acquisition parameters on the magnitude and appearance of artifacts between single and multiple detector-row helical computed tomography (CT).
  
  
  METHODS
  A cylindric (12.7 x 305.0-mm) acrylic rod inclined 45 degrees relative to the z axis was scanned at the isocenter and 100 mm from the isocenter with single detector-row (single-channel) helical CT (beam width, 1-10 mm; pitch, 1.0, 2.0, or 3.0) and multiple detector-row (four-channel) helical CT (detector width, 1. 25, 2.5, 3.75, and 5 mm; pitch, 0.75 or 1.5). The SD of radius measurements along the rod (SD(r)) was used to quantify artifacts in all 72 data sets and to analyze their frequency patterns. Volume-rendered images of the data sets were ranked by six independent and blinded readers; findings were correlated with acquisition parameters and SD(r) measurements.
  
  
  RESULTS
  SD(r) was smaller in four- than in single-channel helical CT for any given table increment (TI). In single-channel helical CT, SD(r) increased linearly with beam width and geometrically with pitch. In four-channel helical CT, SD(r) measurements were directly proportional to the TI, regardless of the detector width and pitch combination used. Off-center object position on average increased SD(r) by a factor of 1.6 for single-channel helical CT and by a factor of 2.0 for four-channel helical CT. Subjective rankings of image quality correlated excellently with SD(r) (Spearman r = 0.94, P <.001).
  
  
  CONCLUSIONS
  Artifacts are quantitatively and subjectively smaller with four- compared with single-channel helical CT for any given TI.
authors.affiliation: Department of Radiology, Stanford University School of Medicine, 300 Pasteur Dr, S-072 Stanford, CA 94305-5105, USA.
authors.forename: D
authors.initials: D
authors.lastname: Fleischmann
authors.forename: G D
authors.initials: GD
authors.lastname: Rubin
authors.forename: D S
authors.initials: DS
authors.lastname: Paik
authors.forename: S Y
authors.initials: SY
authors.lastname: Yen
authors.forename: P R
authors.initials: PR
authors.lastname: Hilfiker
authors.forename: C F
authors.initials: CF
authors.lastname: Beaulieu
authors.forename: S
authors.initials: S
authors.lastname: Napel
mesh_terms: D016477:Artifacts; D019047:Phantoms, Imaging; D014057:Tomography, X-Ray Computed / Q000379:methods