Chest Lateral Decubitus is a radiography positioning projection of the Thorax. Patient on side with horizontal beam. SID 72". The centering point is located level of t7. patient recumbent on the affected side.. The central ray is horizontal, perpendicular to the vertical ir.. Image-quality criteria include free air or fluid visible, dependent and horizontal., affected lung field clearly visible without superimposition.. Standard exposure ranges from 110 to 125 kVp, 2 to 5 mAs, at an SID of 72 inches (180 cm).
Anatomy demonstrated
- Both lungs with the affected side partially dependent.
- Free air or fluid dependent and layered.
- Mediastinal structures in recumbent position.
- Thoracic vertebral bodies.
- Ribs and costophrenic angles.
- Heart and mediastinal contours.
Patient preparation
- Verify patient identity using two identifiers.
- Remove all radiopaque objects from the chest area.
- Position patient on the affected side (or supine per protocol).
- Place the IR vertical perpendicular to the table.
- Maintain the position for at least 5 minutes to allow layering.
Position & centering point
Level of T7. Patient recumbent on the affected side.
Central ray
Horizontal, perpendicular to the vertical IR.
Exposure / technique
- kVp
- 110–125
- mAs
- 2–5
- SID
- 72" (180 cm)
- Notes
- Horizontal beam. Best visualizes fluid or air dependent to the side down.
Image-quality criteria
- Free air or fluid visible, dependent and horizontal.
- Affected lung field clearly visible without superimposition.
- Mediastinal structures visible and not obscured.
- No rotation evident from bilateral symmetry of the field.
- Sharp visualization of the costophrenic angles.
Common errors / ARRT traps
- 1 Insufficient time supine allows fluid to settle but not fully layer.
- 2 Beam not horizontal misses the true dependent layering.
- 3 Rotation of the patient twists the mediastinum.
- 4 IR not truly vertical prevents clear visualization.
- 5 Patient not resting on the affected side when intended.
Clinical indications
- Detection of pleural effusion or hemothorax.
- Demonstration of free air (pneumothorax) dependent to the side down.
- Assessment of free fluid loculation or layering.
- Patients unable to sit or stand upright due to acute illness.
Aligned to the 2025 ARRT Content Specifications.