Ribs Posterior AP is a radiography positioning projection of the Thorax. AP posterior ribs, erect. SID 40". Breathing varies by location. The centering point is located above diaphragm: t7 on inspiration. below diaphragm: t11 (midway between xiphoid and lower rib margin) on expiration.. The central ray is perpendicular to ir, horizontal. t7 for ribs above the diaphragm; t11 for ribs below the diaphragm.. Image-quality criteria include all 12 ribs demonstrated from above diaphragm to below diaphragm., ribs projected parallel to each other without foreshortening.. Standard exposure ranges from 65 to 75 kVp, 12 to 20 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- All 12 pairs of ribs from apex to lowest rib.
- Costochondral junctions.
- Intercostal spaces.
- Thoracic vertebral bodies.
- Mediastinal structures.
- Diaphragm.
Patient preparation
- Verify patient identity using two identifiers.
- Remove all radiopaque objects from the chest and trunk.
- Position patient erect facing the tube.
- Instruct: For upper ribs above diaphragm, breath on inspiration and hold.
- For lower ribs below diaphragm, breath on full expiration and hold.
Position & centering point
Above diaphragm: T7 on inspiration. Below diaphragm: T11 (midway between xiphoid and lower rib margin) on expiration.
Central ray
Perpendicular to IR, horizontal. T7 for ribs above the diaphragm; T11 for ribs below the diaphragm.
Exposure / technique
- kVp
- 65–75
- mAs
- 12–20
- SID
- 40" (102 cm)
- Notes
- Grid required. For ribs above diaphragm: full inspiration. For ribs below diaphragm: full expiration.
Image-quality criteria
- All 12 ribs demonstrated from above diaphragm to below diaphragm.
- Ribs projected parallel to each other without foreshortening.
- Costochondral junctions clearly visible.
- Diaphragm clearly visible as a dividing line between upper and lower.
- No rotation of the thorax; symmetry of the ribs.
- Vertebral column superimposed by the sternum.
Common errors / ARRT traps
- 1 Rotation of the thorax foreshortens ribs on one side.
- 2 Inadequate inspiration flattens the upper ribs and diaphragm.
- 3 Inadequate expiration reduces the space between ribs below the diaphragm.
- 4 Breathing instructions not followed causes motion blur.
- 5 CR aimed above or below T7 clips ribs from the field.
Clinical indications
- Suspected rib fracture evaluation.
- Trauma assessment of the thoracic cage.
- Detection of rib metastases or lytic lesions.
- Post-operative follow-up after thoracic procedures.
Aligned to the 2025 ARRT Content Specifications.