Chest Dorsal Decubitus is a radiography positioning projection of the Thorax. Supine chest with horizontal beam. SID 72". The centering point is located level of t7, mid-chest. patient supine on table.. The central ray is horizontal, perpendicular to the vertical ir.. Image-quality criteria include lungs visualized with horizontal air-fluid levels, if present., mediastinal structures visible in their supine configuration.. Standard exposure ranges from 110 to 125 kVp, 2 to 5 mAs, at an SID of 72 inches (180 cm).
Anatomy demonstrated
- Bilateral lungs in supine position.
- Heart and mediastinum in dependent configuration.
- Thoracic vertebral bodies.
- Ribs and intercostal spaces.
- Diaphragm in supine position.
- Free air or fluid if present.
Patient preparation
- Verify patient identity using two identifiers.
- Remove all radiopaque objects from the chest area.
- Position patient supine on the radiographic table.
- Place the IR vertical behind the patient (perpendicular to the table).
- Ensure patient is stable and comfortable; explain the position.
Position & centering point
Level of T7, mid-chest. Patient supine on table.
Central ray
Horizontal, perpendicular to the vertical IR.
Exposure / technique
- kVp
- 110–125
- mAs
- 2–5
- SID
- 72" (180 cm)
- Notes
- Horizontal beam decubitus technique. Allows visualization of horizontal fluid levels.
Image-quality criteria
- Lungs visualized with horizontal air-fluid levels, if present.
- Mediastinal structures visible in their supine configuration.
- Free air or fluid dependent in the supine position.
- No rotation of the mediastinum from the midline.
- Sharp visualization of the diaphragm and costophrenic angles.
Common errors / ARRT traps
- 1 Rotation of the patient twists the mediastinum and obscures symmetry.
- 2 Improper vertical IR position prevents horizontal beam projection.
- 3 Patient too close or far from the IR causes distortion.
- 4 Inadequate inspiration limits the lung field visualization.
- 5 Beam not truly horizontal misses air-fluid levels.
Clinical indications
- Detection of free air (pneumothorax) layering horizontally.
- Visualization of free fluid (hemothorax, pleural effusion).
- Assessment of horizontal fluid levels in the thorax.
- Patients unable to stand or sit upright due to trauma or illness.
Aligned to the 2025 ARRT Content Specifications.