Chest Dorsal Decubitus is a radiography positioning projection of the Thorax. Supine chest, horizontal beam across the thorax, giving a lateral image. SID 72". The centering point is located level of T7, 3-4 inches below the jugular notch, mid-coronal plane. 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, fluid layers posteriorly; free air rises anteriorly in the supine position. A sample technique is 120 kVp with DR 4.5 or CR 9 mAs, at an SID of 72 inches (183 cm).
Anatomy demonstrated
- Both lungs superimposed in a lateral projection.
- 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 against the side of the thorax, perpendicular to the table.
- Raise both arms above the head, out of the field.
- Ensure patient is stable and comfortable; explain the position.
Position & centering point
Level of T7, 3-4 inches below the jugular notch, mid-coronal plane. Patient supine on table.
Central ray
Horizontal, perpendicular to the vertical IR.
Exposure / technique
- kVp
- 120
- mAs
- DR 4.5 / CR 9
- SID
- 72" (183 cm)
- Notes
- Horizontal beam decubitus technique. ARRT's 2022 and 2027 outlines list dorsal decubitus under abdomen, not chest. Allows visualization of horizontal fluid levels. Sample technique: DR 4.5 / CR 9 mAs at 120 kVp, 72 in SID, for a 33 cm part (Merrill's sample chart). Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Lungs visualized with horizontal air-fluid levels, if present.
- Fluid layers posteriorly; free air rises anteriorly in the supine position.
- Body in a true supine position, with no rotation.
Common errors
- 1 Body not in a true supine position.
- 2 Exposure not made after the second full inspiration.
- 3 Beam not truly horizontal misses air-fluid levels.
Clinical indications
- Detection of free air rising to the anterior chest.
- Visualization of free fluid (hemothorax, pleural effusion).
- Patients unable to stand or sit upright due to trauma or illness.