About this CT Pitch
In helical (spiral) CT scanning, 'Pitch' is a parameter that describes how fast the patient table moves relative to the X-ray beam width. It is a fundamental trade-off: higher pitch scans faster with less dose but lower resolution; lower pitch provides higher detail and overlapping data but increases dose.
Who this calculator is for
- CT technologists, protocol designers, and imaging trainees learning helical acquisition basics.
- People reviewing table feed and total collimation from a scanner protocol.
- Anyone comparing faster versus more overlapping CT acquisitions in an educational workflow.
When to use it
- Use this calculator when checking the pitch implied by a planned or completed CT protocol.
- Use it to explain how changing table feed alters overlap, speed, and dose efficiency.
- Use it when teaching the relationship between pitch and z-axis sampling in helical CT.
How to use this calculator
- Enter the Table Feed (mm traveled per rotation).
- Enter the Total Beam Width (Total Collimation).
- The result is the Pitch.
Key assumptions
- The calculation assumes a standard helical CT definition of table feed per rotation divided by total beam width.
- Dose and image-quality implications are directionally useful but simplified; modern scanner behavior also depends on modulation, reconstruction, and cardiac gating.
- This tool is best used for protocol understanding, not as the sole basis for changing a clinical technique.
Accuracy and testing
Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.
How this calculator works
Inputs explained
Table Feed
The distance the table moves during one full 360-degree rotation of the gantry.
Beam Width
The total width of the X-ray beam interacting with the detectors. Also called total collimation.
Understanding your results
Example scenarios
Standard Chest
Feed 40mm. Beam 40mm. Pitch = 1.0.
Trauma/Fast
Feed 60mm. Beam 40mm. Pitch = 1.5. (Fast scan, lower dose).
High Res Cardiac
Feed 10mm. Beam 40mm. Pitch = 0.25. (High overlap for gating).
Key Features
- Standard Formula
- Scan Type Classification
- Dose Implication
Tips & Best Practices
- Increasing pitch often lowers dose efficiency, but the real dose impact depends on scanner controls and protocol settings.
- Pitch > 2.0 is rarely used due to significant artifacts.
Glossary of Terms
- Helical CT
- Scanning geometry where the gantry rotates continuously while the table moves, tracing a spiral path.
- Collimation
- The width of the X-ray beam determined by lead shutters.