Pitch (P) is a term used in helical CT. It has two terminologies depending on whether single slice or multislice CT scanners are used 1-3.

Single slice CT (SSCT)

The term detector pitch is used and is defined as table distance traveled in one 360° gantry rotation divided by beam collimation 2.

For example, if the table traveled 5 mm in one rotation and the beam collimation was 5 mm then pitch equals 5 mm / 5 mm = 1.0. 

Choice of pitch affects both image quality and patient dose 2:

  • P = 1.0:  x-ray beams are contiguous for adjacent rotations
  • P >1.0: x-ray beams are not contiguous for adjacent rotations, i.e. there are gaps in between the x-ray beams and tissue is not irradiated
  • P <1.0:  there is x-ray beam overlap; i.e. a volume of tissue is irradiated more than once per scan

Thus a pitch >1.0 results in decreased patient dose but also decreased image quality (through fewer projections obtained, resulting in lower SNR). A pitch of <1.0 results in better image quality, but a higher patient dose. 

Multislice CT (MSCT) 

Beam pitch is defined as table distance traveled in one 360° gantry rotation divided by total thickness of all simultaneously acquired slices 3.


Share article

Article Information

rID: 18984
Section: Physics
Tags: ct, refs
Synonyms or Alternate Spellings:
  • CT pitch
  • Detector pitch
  • Beam pitch

Support Radiopaedia and see fewer ads

Updating… Please wait.
Loadinganimation

Alert accept

Error Unable to process the form. Check for errors and try again.

Alert accept Thank you for updating your details.