The pitch factor is a selectable CT parameter. The definition depending on the IEC standards is the ratio of the table speed per rotation and the total collimation.
The choice of pitch factor is determined on practical considerations and on the availability of the computed tomography algorithms and parameters for image reconstruction.

See Pitch.

(p) The pitch (in computed tomography) is the ratio of the patient table increment to the total nominal beam width for the CT scan. The pitch factor relates the volume coverage speed to the thinnest sections that can be reconstructed. In spiral CT, dose is always inversely proportional to pitch.
Among the different manufacturers, there are various definitions of pitch depending on whether a single-detector (single-slice) or multi-detector (multi-slice) CT scanner is used.