Longitudinal aliasing in multislice helical computed tomography: sampling and cone-beam effects

Area of Science:

• Medical Imaging
• Computed Tomography
• Image Reconstruction

Background:

• Multislice helical CT (MSHCT) is widely used, but its aliasing properties require detailed examination.
• Previous studies focused on single-slice helical CT (SSHCCT), leaving MSHCT aliasing less understood.
• Specific helical pitches (3 and 6) in four-slice scanners are considered 'preferred' due to purported sampling equivalency with SSHCCT.

Purpose of the Study:

• To investigate and differentiate longitudinal aliasing properties in MSHCT compared to SSHCCT.
• To analyze aliasing artifacts at preferred pitches 3 and 6 in four-slice helical CT.
• To identify the origins of aliasing artifacts unique to MSHCT reconstructions.

Main Methods:

• Reconstruction of MSHCT volumes using a 180LI-type algorithm under the multiple parallel fanbeam approximation.
• Comparative analysis of aliasing properties between MSHCT and SSHCCT at specific helical pitches.
• Examination of artifacts in four-slice scanners at helical pitches 3 and 6.

Main Results:

• Longitudinal aliasing in MSHCT differs significantly from SSHCCT, even at preferred pitches.
• Observed artifacts in MSHCT (pitches 3 and 6) are not present in equivalent SSHCCT reconstructions (pitches 1 and 2).
• Aliasing in MSHCT originates from both sampling effects and cone-beam effects, with cone-beam effects causing inconsistencies across detector rows.

Conclusions:

• The 'preferred' pitches 3 and 6 in MSHCT do not achieve strict sampling equivalence with SSHCCT due to cone-beam effects.
• Cone-beam effects introduce unique aliasing artifacts in MSHCT, distinguishing it from SSHCCT.
• Despite differences, pitches 3 and 6 may still offer relative advantages in MSHCT compared to other pitches.