AP chest X-ray positioning (sitting)
An extra chest view, used when a routine one is not enough. The patient sits, the beam passes front to back (AP), straight on to the receptor, and the centring point is the sternum, midway between the jugular notch and xiphoid.
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
Sitting. Sit the patient upright with the back against the bucky, shoulders down and rolled forward, chin raised. Use this only when the patient cannot stand.
Centring & collimation
Central ray
APCentre: the sternum, midway between the jugular notch and xiphoid.
Beam: AP, perpendicular to the receptor.
Collimate: apices to costophrenic angles, skin margin to skin margin
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 180 cm | |
| Receptor | 35 × 43 cm | portrait |
| Placement | Erect (wall) 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 | 1.25 | 1 |
| S | 120 | 2 | 1.6 |
| M | 120 | 2.5 | 2 |
| L | 120 | 4 | 3.2 |
| Child | 90 | 2 | 1.6 |
These start from a classic film-screen chart (120 kV, 2.5 mAs at 140 cm) and are adjusted for a digital detector at 180 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
- The patient is upright: no fluid level is distorted by a slumped posture.
- Both apices and costophrenic angles are included.
- Clavicles are symmetric about the spine.
- 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 |
|---|---|---|
| Heart looks enlarged | AP projection magnifies the heart | Note AP on the image; do not compare heart size with a PA. |
| Apices cut off | Patient slumped down the bucky | Sit the patient fully upright and recentre. |
Common questions
- Where do you centre for a chest AP sitting X-ray?
- The centring point is the sternum, midway between the jugular notch and xiphoid.
- What distance and beam angle does a chest AP sitting need?
- 180 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 wall 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 sitting?
- Heart looks enlarged. Usual cause: aP projection magnifies the heart. The fix: note AP on the image; do not compare heart size with a PA.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a chest ap sitting in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.