In multi-slice cone beam CT imaging, there are artifacts known as windmill artifacts. These artifacts are due
to not satisfying the Nyquist criteria in the patient longitudinal direction. This paper quantifies and compares
these artifacts as a function of the number of rows, pitch, collimation, and image thickness of the CT scanner.
Scanners with rows of 16, 64 and 128 are measured and compared with simulated data, using both Helical and
Axial scanning modes. In addition three focal spot switching modes are compared: the traditional within image
plane mode; diagonal mode; and quad mode. All images are compared via four criteria: artifacts, MTF, SSP
Results show that the frequency of the artifact, or number of blades on the windmill and magnitude of each
blade, is dependent on the rate at which the rows are crossed for an image. For example, for a given pitch,
doubling the rows doubles the frequency of the artifact, with each artifact approximately the magnitude. A
similar result can be obtained by keeping the number of rows constant and varying the pitch. The artifact
disappears as the Nyquist criteria is satisfied by either increasing the slice thickness or incorporating one of the
focal spot switching modes that switch in the patient longitudinal direction. For a given MTF and SSP, the
diagonal focal spot switching mode has slightly more noise while the other two are approximately equal. The
artifact varies with the quad mode being the best and traditional mode being the worse.