Procedures · Positioning basics2 min read5-question check
Trauma and mobile adaptations
In trauma, move the tube and IR, not the patient, and still get two projections 90 degrees apart.
The rule
A trauma patient is positioned by moving the equipment. Leave the patient as found, then bring the tube and IR to the part. You still need at least two projections 90 degrees apart, because one view can hide a fracture or a dislocation. Joints usually need three views. A cervical collar stays on until a physician clears the spine from the images. Never remove it, turn the head or ask the patient to sit up on your own judgment.
Cross-table work
A cross-table lateral uses a horizontal beam with the IR held against the side of the part. For the cervical spine it is done first, at 72 inches, with the shoulders pulled down only if the physician approves; if C7 is not seen, a swimmer's lateral is the next step. For a suspected hip fracture, the inferosuperior axiolateral or Danelius-Miller method raises the unaffected leg and aims a horizontal beam perpendicular to the femoral neck, so the injured leg is never moved into a frog-leg position. A cross-table lateral knee can show a fat-fluid level in the joint, called a lipohemarthrosis, which suggests a fracture inside the joint.
Mobile chest
A mobile chest is an AP projection, supine or semierect. Sit the patient as upright as is safe; only a horizontal beam, erect or decubitus, will show air-fluid levels. Otherwise angle the CR caudad so it is perpendicular to the sternum, centered to T7, about 3 to 4 inches below the jugular notch. Use 72 inches when the room allows and the same SID every day, because changing the SID changes magnification, and the heart size and tubes can look different from day to day. With a grid, keep the CR centered and do not angle across the grid lines, to avoid grid cutoff.
Documenting it
Tell the radiologist what you had to change. Annotate the image with the projection, patient position, such as supine, semierect or cross-table, and the time for serial mobile images. Note any limitation on the requisition or in the exam notes, such as a patient who could not raise the arm. Place a lead side marker in the field during the exposure.
Clinical Example
A motor vehicle crash patient arrives on a backboard in a collar. You take the cross-table lateral C-spine first, without moving the head, and show it to the physician. The collar stays on until the physician clears the spine.
Common Mistakes
- Rolling a trauma patient into a lateral instead of using a horizontal beam.
- Sending only one projection because the patient is hard to move.
- Changing SID between daily mobile chests.
- Leaving out annotation of position or limitations.
Why It Matters
Moving an unstable spine or fractured hip can cause permanent injury. The registry tests cross-table lateral use, the two-projection rule and collar safety.
Key Relationships
- Move the tube and IR, not the patient
- Minimum two projections 90 degrees apart
- Air-fluid levels need a horizontal beam
- Same SID daily for mobile chest comparisons
- Collar stays on until a physician clears it