pitch
In helical CT, the ratio of table travel per rotation to total detector z-axis coverage. Pitch > 1 spreads the helix thinner with gaps; pitch < 1 overlaps slices. Modern dual-source CT systems (SOMATOM Definition Flash, Force) can run high-pitch Flash mode at pitch > 3, covering chest in fractions of a second.
Why it matters to buyers: Higher pitch = faster scan, lower dose, potentially lower image quality at the spatial-resolution boundary. Protocols specify pitch per exam type — cardiac CTA at low pitch with retrospective gating, trauma pan-scan at moderate pitch, Flash-mode chest at very high pitch on dual-source.
Why it matters to engineers: Helical artifact (windmill, cone-beam) varies with pitch and reconstruction algorithm. Phantom QA at clinically used pitches catches reconstruction-side artifact issues before they show up on patient studies.