Chest -Lateral Decubitus

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Radiographic Positioning

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Name of projection Chest - Lateral Decubitus (either AP or PA)
Area Covered Lung fields, apices, costophrenic angles, heart
Pathology shown This projection is used to detect any air and fluid levels present in the pleural cavity. Air in the case of a pneumothorax or fluid in the case of pleural effusions. It also shows changes in fluid position from PA/AP view and reveals any previously obscured pulmonary areas
Radiographic Anatomy Chest Radiographic Anatomy
IR Size & Orientation 35 x 43 cm
Usually portrait (the long axis of the IR is parallel to the long axis of the torso)
D.R. may cover 43 x 43 cm
Film / Screen Combination Regular
(CR and DR as recommended by manufacturer)
Bucky / Grid Moving or Stationary Grid, portable X-ray may be done without grid
Filter No
Exposure 85 kVp 2.5 mAs no grid
100 kv 4 mAs with grid
FFD / SID 180cm
Central Ray Directed to the midsaggital plane at the level of T7
Perpendicular to the IR
Collimation Centre: T7 or the inferior border of the scapula
Shutter A: Open to approximately 5cm above the shoulder to include upper airway
Shutter B: Open to the level of the acromioclavicular joints (AC joints) laterally. This will include the lung fields laterally.
Markers Superior and Lateral
Marker orientation either AP or PA, depending on the patient's positioning
Marker indicating the side which is up
Shielding Gonadal (check your department's policy guidelines)
Respiration On suspended deep inspiration
  • Position the patient in the lateral decubitus position
    • usually AP, as this is often easier for the patient
    • with either the left or right side up (see Special Notes below)
    • ensure that the side that is touching the bed or table is slightly raised, perhaps using a sponge, so that the entire lungs fields are included on the image and are not 'cut off'.
  • If possible, wait at least 5 minutes before taking the image to allow gas fluid levels to form
  • Bring the patient's arms above their head so they do not superimpose over the thorax
  • Check that the patient is in a true lateral position, and that the coronal plane is parallel to the IR

  • No rotation as evidenced by
    • the medial ends of the clavicles equidistant from the spine
    • the clavicles are in the same horizontal plane
  • The lungs fields are clear of the scapulae
  • The 10th posterior ribs will be visualised above the diaphragm on full inspiration

Area Covered
  • Lungs fields, apices, costophrenic angles, heart

  • Centre: T7 Thoracic vertebra
  • Shutter A: Open to show the lung apices superiorly and the costophrenic angles inferiorly
  • Shutter B: Open to show the lung fields laterally

  • There should be adequate exposure so that
    • the ribs and thoracic vertebrae are seen faintly through the heart
    • vascular lungs markings are shown
    • air and fluid levels are able to be seen
Special Notes Left vs Right Lateral Decubitus Chest
For possible fluid - put the suspected side down
For possible air - put the suspected side up

Indicate "Decubutis" on the image as well as the side up