AP skull X-ray positioning
An extra skull view, used when a routine one is not enough. The patient lies on their back, the beam passes front to back (AP), tilted 20° towards the head, and the centring point is the nasion.
By the ScanFlo Editorial Team · Updated
In this section · X-ray positioning
- X-ray positioning guides
- Skull positioning
- Face & sinuses positioning
- Soft tissue neck positioning
- C-spine positioning
- Chest positioning
- Shoulder positioning
- Humerus positioning
- Elbow positioning
- Forearm positioning
- Wrist positioning
- Hand positioning
- T-spine positioning
- Abdomen positioning
- L-spine positioning
- Sacrum & SI joints positioning
- Pelvis positioning
- Hip positioning
- Femur positioning
- Knee positioning
- Tibia & fibula positioning
- Ankle positioning
- Foot positioning
Still being checked: a radiographer is reviewing this guide. If your department does it differently, follow your department.
Patient position
Supine. Remove dentures, earrings, hair clips and anything in the hair. Lay the patient supine, head flat on a thin radiolucent pad (no pillow), orbitomeatal line perpendicular to the table.
Centring & collimation
Central ray
APCentre: the nasion.
Beam: AP, angled 20° cephalad.
Collimate: the whole skull vault
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | |
| Receptor | 24 × 30 cm | portrait |
| Placement | Table bucky | Grid in |
| Angulation | 20° | cephalad |
Marker & breathing
- Marker: R or L marker on the side nearest the detector
- Breathing: No breathing instruction needed.
Exposure by patient size
Treat these as a starting point. Your detector, your generator and the patient in front of you will all move the numbers.
| Patient size | kV | mAs (chart) | mAs (DR default) |
|---|---|---|---|
| XS | 70 | 12.5 | 5 |
| S | 70 | 20 | 8 |
| M | 70 | 25 | 10 |
| L | 70 | 40 | 16 |
| Child | 70 | 20 | 8 |
These start from a classic film-screen chart (70 kV, 50 mAs at 140 cm) and are adjusted for a digital detector at 100 cm. The DR column is what ScanFlo's console suggests; each step up or down changes the mAs by about a quarter.
Image quality checklist
- No rotation.
- Petrous ridges in the lower orbits.
- Whole vault included.
- The anatomical side marker is visible, correct and clear of the anatomy.
- Collimation borders are visible on all sides, no wider than the area requested.
Faults & how to fix them
| Fault | Cause | Fix |
|---|---|---|
| Head tilted | Pillow under the head | Use a thin flat pad. |
Common questions
- Where do you centre for a skull AP X-ray?
- The centring point is the nasion.
- What distance and beam angle does a skull AP need?
- 100 cm from the tube to the receptor. The beam passes front to back (AP), tilted 20° towards the head.
- What size receptor, and do you need a grid?
- Use a 24 × 30 cm receptor, portrait, in the table bucky. A grid is needed.
- Where does the lead marker go?
- R or L marker on the side nearest the detector.
- What goes wrong most often on a skull AP?
- Head tilted. Usual cause: pillow under the head. The fix: use a thin flat pad.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a skull ap in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.