AP chest X-ray positioning (supine)
An extra chest view, used when a routine one is not enough. The patient lies on their back, the beam passes front to back (AP), straight on to the receptor, and the centring point is the sternum at the level of T7.
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. Lay the patient supine with a small pillow under the head, arms by the sides and rotated away from the chest, shoulders level.
Centring & collimation
Central ray
APCentre: the sternum at the level of T7.
Beam: AP, perpendicular to the receptor.
Collimate: apices to costophrenic angles
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 110 cm | |
| Receptor | 35 × 43 cm | portrait |
| Placement | Table bucky | Grid in |
| Angulation | None | Perpendicular to the receptor |
Marker & breathing
- Marker: R marker, upper outer corner
- Breathing: Breathe in and hold.
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 | 120 | 0.5 | 0.5 |
| S | 120 | 0.8 | 0.8 |
| M | 120 | 1 | 1 |
| L | 120 | 1.6 | 1.6 |
| Child | 90 | 0.8 | 0.8 |
These start from a classic film-screen chart (120 kV, 2.5 mAs at 140 cm) and are adjusted for a digital detector at 110 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
- Apices and costophrenic angles included.
- No rotation: clavicles symmetric about the spine.
- Adequate inspiration.
- 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 |
|---|---|---|
| Free air or fluid levels not shown | Supine projection | Add an erect or decubitus view if the question is air or fluid. |
Common questions
- Where do you centre for a chest AP supine X-ray?
- The centring point is the sternum at the level of T7.
- What distance and beam angle does a chest AP supine need?
- 110 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, portrait, in the table bucky. A grid is needed.
- What should the patient do with their breathing?
- Ask them to breathe in and hold it while you expose.
- What goes wrong most often on a chest AP supine?
- Free air or fluid levels not shown. Usual cause: supine projection. The fix: add an erect or decubitus view if the question is air or fluid.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a chest ap supine in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.