Pitch (CT)
Updates to Article Attributes
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 travelled in one 360° gantry rotation divided by beam collimation 2.
For example, if the table travelled 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;1.0: x-ray beams are not contiguous for adjacent rotations; i.e. there are gaps in the x-ray helix, but the full volume is still irradiated, only with fewer projections per rotation - P <
; 1;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;1.0 results in decreased patient dose but also decreased image quality (fewer projections are obtained, resulting in lower SNR). A pitch of < 1;1.0 results in better image quality, but a higher patient dose.
Multislice CT (MSCT)
Beam pitch is defined as table distance travelled in one 360° gantry rotation divided by the total thickness of all simultaneously acquired slices 3.
-<li>P > 1.0: x-ray beams are not contiguous for adjacent rotations; i.e. there are gaps in the x-ray helix, but the full volume is still irradiated, only with fewer projections per rotation</li>-<li>P < 1.0: there is x-ray beam overlap; i.e. a volume of tissue is irradiated more than once per scan</li>-</ul><p>Thus a pitch > 1.0 results in decreased patient dose but also decreased image quality (fewer projections are obtained, resulting in lower SNR). A pitch of < 1.0 results in better image quality, but a higher patient dose. </p><h5>Multislice CT (MSCT) </h5><p><strong>Beam pitch</strong> is defined as table distance travelled in one 360° gantry rotation divided by the total thickness of all simultaneously acquired slices <sup>3</sup>.</p>- +<li>P >1.0: x-ray beams are not contiguous for adjacent rotations; i.e. there are gaps in the x-ray helix, but the full volume is still irradiated, only with fewer projections per rotation</li>
- +<li>P <1.0: there is x-ray beam overlap; i.e. a volume of tissue is irradiated more than once per scan</li>
- +</ul><p>Thus a pitch >1.0 results in decreased patient dose but also decreased image quality (fewer projections are obtained, resulting in lower SNR). A pitch of <1.0 results in better image quality, but a higher patient dose. </p><h5>Multislice CT (MSCT) </h5><p><strong>Beam pitch</strong> is defined as table distance travelled in one 360° gantry rotation divided by the total thickness of all simultaneously acquired slices <sup>3</sup>.</p>
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