Resources/CT fundamentals
Protocol basics
A CT protocol is a chain of decisions: how much energy (kVp), how many photons (mAs), how fast to cover the anatomy (pitch), and how to turn raw data into images (kernel, slice thickness, window). Every choice trades image quality against dose or time.
The acquisition parameters
| Parameter | Typical (chest) | What it controls |
|---|---|---|
| kVp | 120 | Beam energy — penetration and contrast |
| mAs | 100–250 | Photon count — noise vs dose |
| Pitch | 0.9–1.4 | Table speed vs coverage overlap |
| Collimation | 64×0.6 mm | Detector configuration and slice capability |
| Rotation time | 0.5 s | Temporal resolution and scan speed |
The reconstruction parameters
The scan is only half the protocol. The same raw data can be reconstructed with a soft kernel for mediastinum, a sharp kernel for lung detail, in thin slices for detail or thick for low noise. That is why one chest acquisition routinely yields two or three reconstruction series.
- Kernel: soft (smooth, low noise) for soft tissue; sharp (edge-enhancing, noisier) for lung and bone.
- Slice thickness: thin for detail and reformats, thicker for noise control.
- Window/level: lung (W ~1500 / L ~−600), mediastinal (W ~350 / L ~40), bone (W ~1800 / L ~400).
Scout first, always
The scout (topogram) sets your scan range and drives automatic exposure control. Sloppy scout, sloppy protocol: excess range is pure unnecessary dose.
Try it in ScanFlo: Run the chest case and reconstruct the same acquisition twice: soft kernel with a mediastinal window, then sharp kernel with a lung window. Same photons, two different diagnostic worlds.