17.2 Trauma, Mobile, Surgical & Special Populations

Trauma, Mobile, Surgical, and Special Populations

Routine positioning assumes a cooperative, mobile patient in a controlled room. Trauma, portable, surgical, and special-population imaging remove those assumptions: the patient may be immobilized, unstable, sterile-draped, very small, or very large. The radiographer must adapt the geometry and technique while preserving the diagnostic goal and radiation safety. Routine projections themselves are taught in Chapters 13-16; this section teaches how to modify them safely.

Cardinal Trauma Principles

Trauma radiography follows a small set of rules that the ARRT tests repeatedly. First, do not rotate or move an injured part into a standard position; instead move the tube, the image receptor (IR), and the central ray (CR) around the patient. Rotating a fracture or an unstable spine can convert a stable injury into a displaced or neurologic one. Second, keep the CR perpendicular to the part and the part parallel to the IR to preserve the true anatomic relationship and minimize distortion; when anatomy cannot be repositioned, adapt the CR angle to open the joint or projection of interest. Third, obtain a minimum of two projections at right angles (90 degrees apart) so that displacement, angulation, and foreign bodies are seen in two planes; a fracture can appear undisplaced on one view yet grossly displaced on the orthogonal view. Fourth, image the entire anatomic structure, including both joints of a long bone, and demonstrate any suspected fracture in its entirety.

The cross-table (horizontal-beam) lateral is the workhorse of trauma because it produces a lateral projection without turning the patient. On the acute cervical-spine series it is taken first and must include C7-T1; an inadequate lateral that clips C7 misses the most commonly injured lower cervical segment. When the shoulders obscure C7, a swimmer's (Twining) lateral is added. Other trauma-specific projections replace prone positions with supine equivalents: the acanthioparietal (reverse Waters) is performed AP/supine when a facial-trauma patient cannot assume the prone Waters, and the axiolateral (Danelius-Miller) cross-table lateral of the hip replaces the frog-leg lateral because the frog-leg requires abduction and external rotation of a possibly fractured proximal femur.

Trauma Adaptation Checklist

• Never remove immobilization (backboard, cervical collar, splints) without physician clearance; image through it.
• Move the tube/IR, not the patient; the part-CR-IR relationship is preserved by geometry, not repositioning.
• Two projections 90 degrees apart for every fracture; include both adjacent joints of a long bone.
• Cross-table lateral first for cervical spine (must show C7-T1) and for suspected hip fracture (Danelius-Miller).
• Use the reverse Waters (acanthioparietal) and other AP/supine substitutes for the prone-averse trauma patient.
• Adjust the CR angle rather than forcing the part when the anatomy cannot be moved.
• Place markers in the field at the time of exposure; anatomic side errors are indefensible in trauma.

Mobile (Portable) Radiography

Mobile units bring imaging to the bedside for patients who cannot travel to the department. Image quality suffers from short and variable source-to-image distance (SID), patient motion, and uncontrolled scatter, so the radiographer compensates deliberately. Position the patient as upright as the condition allows and minimize rotation for the mobile chest; a semi-erect or upright projection improves aeration and reduces magnification of the heart. Use a consistent, measured SID (commonly 40-72 inches depending on protocol) because variable SID changes both density and magnification. A grid is used for thicker parts and higher kVp but demands careful alignment: mobile grids are prone to grid cutoff from off-center, off-level, off-focus, or upside-down errors, so keep the tube centered and the grid perpendicular to the CR. Anti-scatter grids also raise dose, so reserve them for parts over roughly 10-12 cm.

Radiation safety at the bedside is paramount because there are no fixed shielded barriers. Announce the exposure, clear or shield nearby staff and patients, and exploit the inverse-square law: the operator stands at least 6 feet (about 2 meters) from the tube, patient, and beam, ideally at a 90-degree angle to the primary beam where scatter is lowest. Wear a lead apron, use the shortest cord fully extended, and collimate tightly to reduce scatter and dose.

Surgical / C-arm Fluoroscopy

In the operating room the radiographer operates a mobile C-arm while maintaining the sterile field. Drape the C-arm with sterile covers, and coordinate and announce every movement with the surgical team so the sterile field is never breached. The standard orientation places the x-ray tube under the table and the image intensifier (or flat-panel detector) on top, close to the patient; this configuration reduces backscatter to the operator's head, eyes, and thyroid and improves image quality by shortening the object-to-image distance. Inverting the C-arm (tube on top) dramatically increases operator eye and face dose and is avoided except for specific lateral projections. Minimize fluoroscopy time, use last-image hold to review anatomy without additional exposure, and keep all non-essential personnel back. Everyone in the field wears lead; the radiographer maximizes distance and may step behind a mobile shield when clinically feasible.

Pediatric, Geriatric, and Bariatric Adaptations

Pediatric imaging emphasizes immobilization and communication: use age-appropriate explanation, allow a parent when appropriate (with shielding), and employ devices such as the Pigg-O-Stat, sandbags, and Velcro to reduce motion without restraint injury. Children are radiosensitive, so use higher mAs-lowering short exposure times, close collimation, and the lowest dose consistent with ALARA. Geriatric patients may have osteoporosis, kyphosis, tremor, and reduced hearing; reduce technique for demineralized bone, handle joints gently, allow extra time, and speak clearly. Bariatric patients require increased kVp and mAs to penetrate greater tissue thickness, a grid to control the larger scatter volume, tight collimation, and awareness of table weight limits and increased OID magnification. Across every special population the goals are unchanged: a diagnostic image, patient safety, and the lowest reasonable dose.