AP pelvis X-ray positioning
One of the routine pelvis views. The patient lies on their back, the beam passes front to back (AP), straight on to the receptor, and the centring point is 4 cm above the symphysis, midline.
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. Patient lies on the back. With no suspected fracture, rotate both legs inward so the big toes meet and the heels sit apart; with a suspected fracture, leave the legs exactly as found.
Centring & collimation
Central ray
APCentre: 4 cm above the symphysis, midline.
Beam: AP, perpendicular to the receptor.
Collimate: iliac crests to below the lesser trochanters
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | |
| Receptor | 35 × 43 cm | landscape |
| Placement | Table bucky | Grid in |
| Angulation | None | Perpendicular to the receptor |
Marker & breathing
- Marker: R marker
- Breathing: Suspend respiration.
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 |
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
- Iliac crests and both lesser trochanters shown.
- Obturator foramina symmetric.
- Femoral necks not foreshortened (feet turned in).
- 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 |
|---|---|---|
| Femoral necks foreshortened | Feet not rotated in | Turn the feet in 15° unless injured. |
Common questions
- Where do you centre for a pelvis AP X-ray?
- The centring point is 4 cm above the symphysis, midline.
- What distance and beam angle does a pelvis AP need?
- 100 cm from the tube to the receptor. The beam passes front to back (AP), straight on to the receptor.
- What size receptor, and do you need a grid?
- Use a 35 × 43 cm receptor, landscape, in the table bucky. A grid is needed.
- What should the patient do with their breathing?
- Ask them to stop breathing for the moment of the exposure.
- What goes wrong most often on a pelvis AP?
- Femoral necks foreshortened. Usual cause: feet not rotated in. The fix: turn the feet in 15° unless injured.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a pelvis ap in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.