Pitch (CT)
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In helical CT, pitch (P) is 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 travelled 5mm in one rotation and the beam collimation was 5mm then pitch equals 5mm / 5mm = 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 less projections obtained resulting in lower SNR). A pitch of < 1.0 results in better image quality but at higher patient dose.
Multislice CT (MSCT)
Multislice CT (MSCT) - "beamBeam pitch" is is defined as table distance traveled in one 360 degree° gantry rotation divided by total thickness of all simultaneously acquired slices 3.
-</ul><p>Thus a pitch > 1.0 results in decreased patient dose but also decreased image quality (through less projections obtained resulting in lower SNR). A pitch of < 1.0 results in better image quality but at higher patient dose. </p><h5>Multislice CT (MSCT) </h5><p>Multislice CT (MSCT) - "<strong>beam pitch</strong>" is defined as table distance traveled in one 360 degree gantry rotation divided by total thickness of all simultaneously acquired slices <sup>3</sup>.</p>- +</ul><p>Thus a pitch > 1.0 results in decreased patient dose but also decreased image quality (through less projections obtained resulting in lower SNR). A pitch of < 1.0 results in better image quality but at higher patient dose. </p><h5>Multislice CT (MSCT) </h5><p><strong>Beam pitch</strong> is defined as table distance traveled in one 360° gantry rotation divided by total thickness of all simultaneously acquired slices <sup>3</sup>.</p>
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