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Exam category: Procedures → all three (Head/Spine/Pelvis, Thorax/Abdomen, Extremity)
Why it matters: Every procedure module that follows uses this vocabulary without re-explaining it. Get "position" vs. "projection" vs. "view" and the body-plane/directional terms solid now, or every subsequent module is harder than it needs to be.
Three different words — position, projection, view — describe three different things, and the registry is precise about which one is correct in which context. Everything else in this module (planes, directional terms, oblique naming) exists to describe a patient's body accurately enough that any technologist reading the order knows exactly what to do.
| Term | Restricted to | Example |
|---|---|---|
| Position | The patient's physical position | Supine, prone, RAO, left lateral |
| Projection | The path/direction of the central ray | AP, PA, mediolateral, AP axial |
| View | Not a correct US positioning term — describes the anatomy as seen on the resulting image, not something you do | — |
Anatomic position (the universal reference): upright, arms slightly abducted, palms forward, head and feet forward. Every directional term below is defined relative to this position.
| General | Specific |
|---|---|
| Supine, prone, erect, recumbent, Trendelenburg, Sims, Fowler, lithotomy | R/L lateral; oblique (LPO, RPO, LAO, RAO); decubitus (left lateral, right lateral, ventral, dorsal); lordotic |
Oblique naming logic: the name states which side is rotated toward the IR and whether that's the anterior or posterior body surface. LAO = body rotated so the Left Anterior surface is closest to the IR. RPO = Right Posterior surface closest to the IR.
Named for the CR's entry point → exit point: AP = anterior entry, posterior exit (CR travels front-to-back). PA = posterior entry, anterior exit. Same logic extends to mediolateral/lateromedial, and the named axial/tangential projections used throughout the extremity and skull chapters.
A rotated limb is named differently from a rotated trunk — this catches people out. Section 4's LAO/RPO scheme is for the body: it names the side and surface nearest the IR. A limb oblique keeps its ordinary AP or PA label and adds a direction-of-rotation qualifier — medial rotation or lateral rotation — because "AP oblique" on its own doesn't say which way the limb was turned. So you get "AP oblique projection, medial rotation" for an elbow or a foot, and "RPO" for a trunk. Medial (internal) rotation turns the anterior aspect of the part toward the midline; lateral (external) rotation turns it away.
Memory cue — trunks get letters, limbs get a direction. A rotated trunk is named by which corner touches the IR (LAO, RPO). A rotated limb stays AP/PA oblique and tells you which way it turned (medial or lateral rotation).
The first general rule of diagnostic radiology: most procedures need at least two projections, and they should sit as close to 90° apart as the patient allows. Three reasons, and they are the reasons the exam tests:
The exceptions are a short, memorisable list, and they exist because one projection usually answers the clinical question on its own: an AP mobile (portable) chest, a single AP abdomen (KUB), and an AP pelvis.
Memory cue — two at 90°, and only three routine exceptions. Portable chest, KUB abdomen, AP pelvis. Anything else — and every suspected fracture or dislocation — gets two projections at right angles.
The exam tests procedure adaptation as its own topic: how a routine changes for trauma, body habitus, age, or limited mobility. Trauma is the version that shows up most, and it rests on one principle.
Adapt the equipment, not the patient. The two-projections-at-90° requirement does not relax for a trauma patient — what changes is how you achieve it. You keep true CR-to-part-to-IR alignment by angling the central ray and repositioning the IR, rather than by turning or straightening the injured part. A horizontal (cross-table) beam with the IR stood on edge is the standard way to get the second, orthogonal projection when the patient cannot be moved.
Do not move an injured limb. Image it in the position you find it. Don't straighten it, don't apply traction, and don't rotate it into a textbook position — forcing a fractured limb can damage the surrounding vessels and nerves. If a routine calls for internal rotation and the injury forbids it, you accept the resulting appearance rather than force a true projection. The same rule covers dislocations, which are imaged in two planes at 90° to show the degree of displacement, and which are painful to move.
Include both joints on a long bone. For an injured long bone, the image must take in the joint above and below the fracture site — a second, smaller receptor is used if one won't cover it.
Memory cue — move the beam, not the bone. Trauma still needs two projections at 90°. When the patient can't be turned, get the second one by angling the CR and standing the IR on edge (the horizontal-beam lateral). Image the limb as found, and include the joint above and below.
Students use "view," "position," and "projection" interchangeably in casual speech, which is fine day-to-day but wrong on the exam — the registry tests the precise, restricted meaning of each term, not the colloquial one.
Source: Bontrager, Textbook of Radiographic Positioning and Related Anatomy, 10th ed., Ch. 1. Cross-checked against the official current ARRT content spec's own terminology attachment (Attachment B) — the two agree on all core definitions. Sections 6 and 7 are Bontrager Ch. 1 for the minimum-two-projections rule, its three reasons and its named exceptions (AP mobile chest, AP abdomen/KUB, AP pelvis), and for limb-oblique naming by direction of rotation with the medial/lateral rotation definitions; and Bontrager Ch. 15 (Trauma, Mobile, and Surgical Radiography) for the trauma-adaptation principle — two projections 90° apart with true CR/part/IR alignment, achieved by adapting CR angle and IR placement rather than moving the patient — and for imaging dislocations in two planes. These map to the Procedures section of the current ARRT spec, whose four topics include 3. Procedure adaptation (which names trauma explicitly) and 4. Evaluation of displayed anatomical structures (tube-part-image receptor alignment).
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