title: Longitudinal aliasing in multislice helical computed tomography: sampling and cone-beam effects.
abstract: In this study, we examine longitudinal aliasing properties in multislice helical computed tomography (CT) volumes reconstructed under the multiple parallel fanbeam approximation by use of a 180LI-type algorithm. We focus on the differences between the multislice case and the single-slice case, which has been studied previously. Specifically, we examine longitudinal aliasing properties in four-slice scanners for helical pitches 3 and 6, which are sometimes called "preferred" in four-slice helical CT, because it is believed that the effective longitudinal sampling intervals at these pitches are equivalent to those in single-slice helical CT operating at pitches 1 and 2, respectively. While these equivalences have been supported by comparative studies of slice-sensitivity profiles in single- and multislice helical CT, artifacts have been observed in pitch-3 and pitch-6 multislice images that were not evident in their purported single-slice counterparts. We attribute these differences to aliasing arising in the multislice reconstructions that is not present in the single-slice counterparts. We find that the aliasing has two principal origins: sampling effects similar to those in the single-slice case and cone-beam effects. The difference between the multislice, pitch-3 and single-slice, pitch-1 results is attributed to the small cone angle in multislice helical CT, which introduces inconsistencies among the measurements of different detector rows. The difference between multislice, pitch-6 and single-slice, pitch-2 results is attributed to a combination of the cone angle and genuine differences in sampling patterns. It is argued, however, that the lack of strict equivalence with single-slice counterparts does not necessarily undermine the claim that pitches 3 and 6 are "preferred" relative to other pitches in multislice helical CT.
authors.affiliation: Department of Radiology, University of Chicago, 5841 S. Maryland Ave., MC-1037, Chicago, IL 60637, USA.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: La Rivière
authors.forename: Xiaochuan
authors.initials: X
authors.lastname: Pan
mesh_terms: D016477:Artifacts; D019544:Equipment Failure Analysis; D019047:Phantoms, Imaging; D011786:Quality Control; D015203:Reproducibility of Results; D018401:Sample Size; D012680:Sensitivity and Specificity; D036542:Tomography, Spiral Computed / Q000295:instrumentation*