Stair-step artifacts with single versus multiple detector-row helical CT

PURPOSE: To compare the effects of acquisition parameters on the magnitude and appearance of artifacts between single and multiple detector-row helical computed tomography (CT). MATERIALS AND 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,) 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, measurements. RESULTS: SD, was smaller in four- than in single-channel helical CT for any given table increment CTI). In single-channel helical CT,SD, increased linearly with beam width and geometrically with pitch. in four-channel helical CT, SD, measurements were directly proportional to the TI, regardless of the detector width and pitch combination used. Off-center object position on average increased SD, 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, (Spearman r = 0.94, P<.001). CONCLUSION: Artifacts are quantitatively and subjectively smaller with four-compared with single-channel helical CT for any given Tl.