Radiographic Positioning Terminology: 30 Key ARRT Terms
Every exam you'll ever perform starts with a shared language. When you say "PA chest" or "left lateral decubitus," a radiologist, another tech, and your clinical instructor all picture the exact same setup. Radiographic positioning terminology is that language — the projection and position terms, the four body habitus types, and the palpable landmarks that tell you where to center. Get these 30 terms down and every positioning guide on this site (and most of the positioning questions on the registry) starts to feel familiar.
This guide is your plain-English glossary. We'll cover projection and position terms first, then the four body habitus types that change where organs sit, then the surface landmarks that anchor your centering. If you are brand new, start with our introduction to radiography or the X-ray modality overview before you continue.
Why Terminology Matters on the ARRT Registry
The ARRT radiography exam tests positioning and procedures heavily, and it assumes you know this vocabulary cold. The exam won't ask you to spell "anteroposterior" — it will ask which projection places the anterior structures closest to the image receptor, or which position best demonstrates free air. Those are terminology questions wearing a clinical disguise.
Why This Topic Matters on Exams
Positioning terminology is the foundation for a large portion of the ARRT content specifications' positioning and procedures category. Master the 30 terms in this guide — especially body habitus and landmark-to-vertebral-level matching — and you'll turn a whole family of "which position / which projection / where do I center" questions into free points.
Anatomic Directions and Planes You Need First
Before projections make sense, you need the directions and planes they're built on. These come straight from standard anatomy teaching (StatPearls, NCBI):
- Anterior / posterior — front / back of a body part.
- Superior / inferior — top / bottom.
- Medial / lateral — toward / away from the midline.
- Proximal / distal — toward / away from the body's center (used for limbs).
- Cranial / caudal — toward the head / toward the feet.
- Anatomic position — the reference posture: standing, arms at the sides, palms forward (supinated), thumbs pointing away from the body.
Three planes describe how the body is divided and how the beam travels:
- Sagittal plane — a vertical plane parallel to the midsagittal (midline) plane.
- Coronal plane — a vertical plane perpendicular to the median plane (divides the body into front and back).
- Axial (transverse) plane — a horizontal plane crossing the body's long axis.
Keep these three planes in mind — every projection name describes how the central ray crosses them.
Projection Terms (10 Terms)
A projection describes the path of the central ray through the patient. Here are the projection terms you'll use constantly:
| # | Term | Definition |
|---|---|---|
| 1 | AP (anteroposterior) | Central ray enters the anterior surface and exits posteriorly; posterior structures sit closest to the detector. |
| 2 | PA (posteroanterior) | Central ray enters the posterior surface and exits anteriorly; anterior structures sit closest to the detector. |
| 3 | Lateral | Central ray travels across the body from one side to the other; the sagittal (median) plane is parallel to the image receptor. |
| 4 | Oblique | Body rotated at an angle (commonly about 45°, though bone-specific values vary) so the central ray passes through an angled plane. Named by the surface and side nearest the image receptor — RAO, LAO, RPO, LPO. |
| 5 | Axial | Central ray passes along the body's long axis (an angled CR, cephalad or caudad), as in AP axial views. |
| 6 | Tangential | Central ray is directed tangent to a curved body surface to profile a structure (e.g., tangential patella, zygomatic arch). |
| 7 | Decubitus | Patient is recumbent (lying down) and the beam is horizontal — used to detect free air (e.g., lateral decubitus abdomen). |
| 8 | Lordotic | An AP axial projection (patient leans back) used mainly on the chest to evaluate lung apices and clavicles. |
| 9 | Horizontal beam (cross-table) | The central ray travels parallel to the floor, allowing a lateral image of a patient who cannot be moved (e.g., cross-table lateral hip). |
| 10 | Axiolateral | An axial-lateral projection combining a lateral position with an angled central ray (e.g., axiolateral mandible). |
A chest exam is the classic example: an erect PA minimizes magnification of the cardiac silhouette, while a portable chest is shot AP because the patient can't stand — accepting some cardiac magnification. See our chest X-ray positioning guide for the full breakdown.
ARRT Exam Tip: Decubitus Means Horizontal Beam
A favorite registry question: "Which position is used to demonstrate free intraperitoneal air?" The answer is lateral decubitus with a horizontal beam. Air rises to the highest point, so the patient lies on one side and the horizontal beam profiles the air against the abdominal wall — a supine (vertical-beam) image would not show it.
Patient Position Terms (7 Terms)
A position describes how the patient's body is arranged on the table or upright receptor:
| # | Term | Definition |
|---|---|---|
| 11 | Anatomic position | The reference posture (standing, palms forward) all other positions are described from. |
| 12 | Supine | Lying on the back, face up. |
| 13 | Prone | Lying face-down on the abdomen. |
| 14 | Recumbent | Lying down in any posture (includes supine, prone, and lateral recumbent). |
| 15 | Erect (upright) | Standing or seated vertically — used for chests, free-air studies, and air–fluid levels. |
| 16 | Trendelenburg | Whole body inclined head-down, feet elevated (used for shock and some GI exams). |
| 17 | Fowler's | Semi-upright / semi-sitting with the backrest raised. |
Body Habitus: Four Types That Change Where Organs Live (4 Terms)
Body habitus is the physical build and constitution of the body, and it determines the size, shape, and position of internal organs. Standard radiography texts classify four types (Bontrager & Lampignano, 2014). The percentages are textbook approximations:
| # | Habitus | ~% | Diaphragm | Lungs | Heart | Stomach |
|---|---|---|---|---|---|---|
| 18 | Sthenic | 50% | Expected level | Moderate length | Moderately transverse | High, upper-left quadrant |
| 19 | Hypersthenic | 5% | High | Short & broad | Transverse | High & nearly horizontal |
| 20 | Hyposthenic | 35% | Slightly low | Slightly long/narrow | Slightly vertical | Slightly lower |
| 21 | Asthenic | 10% | Low | Long & narrow | Vertical | Low, vertical (J-shaped), near midline |
Why does this matter at the console? A hypersthenic patient has short, broad lungs — so the standard chest image receptor placement may clip the apices or bases, and the receptor is often rotated (landscape) to capture them. An asthenic patient has a low, J-shaped stomach that may extend further inferiorly than you expect, so centering for an upper GI still has to include it. Organ position can shift by several vertebral levels between the extreme habitus types — always palpate the landmarks and adapt your centering to the patient in front of you, not the one in the textbook.
ARRT Exam Tip: The Habitus Extremes
Two registry favorites: which habitus has the most transverse (horizontal, high) stomach? — hypersthenic. Which has the most vertical, low, J-shaped stomach? — asthenic. Remember: hyper = high and horizontal (a wide-set, heavy build); asthenic = low and elongated (a long, slender build).
Palpable Bony Landmarks for Centering (9 Terms)
Landmarks are the palpable surface structures you use to find centering points. The most exam-relevant are:
| # | Landmark | Approx. level | Where you use it |
|---|---|---|---|
| 22 | Vertebra prominens | C7 | Base of the posterior neck; locating the cervicothoracic junction and chest setups |
| 23 | Jugular (suprasternal) notch | T2–T3 | Level of the lung apices; AP chest, upper thoracic, and esophagus centering |
| 24 | Xiphoid process | T9–T10 | Lower sternum; lower GI / UGI stomach region, abdomen centering |
| 25 | Iliac crest | ~L4 (some references L4–L5) | Standard centering for AP abdomen and lumbar spine |
| 26 | ASIS (anterior superior iliac spine) | anterior end of the iliac crest | Assessing rotation and aligning the pelvis and hips |
| 27 | Pubic symphysis | midline pelvis | Lower border for pelvis/hip/abdomen; confirms bladder inclusion |
| 28 | Coracoid process | shoulder | AP shoulder centering point (Clark's) |
| 29 | Greater trochanter | proximal femur | Hip and femur centering and rotation |
| 30 | External auditory meatus (EAM) | skull | Skull and TMJ baseline (OML/IOML) and lateral skull positioning |
The spine article on this site uses the same landmarks — our thoracic & lumbar spine positioning guide centers on the vertebra prominens (C7), jugular notch (T2–T3), the inferior scapular angle (T7), and the xiphoid tip (T9–T10), all of which match the levels above. For the whole lower abdomen, the abdominal X-ray positioning guide shows how the iliac crest anchors your centering.
Clinical Pearl: Trust Your Palpation More Than the Protocol
Textbook centering points assume a sthenic patient. On a hypersthenic or asthenic patient, the same landmarks sit at different true levels, so a standard centering point can "clip" anatomy. Palpate the nearest landmark, adjust your centering by the patient's actual build, and double-check the collimation borders cover the anatomy — that habit prevents more retakes than any single technique number.
Clark's Pocket Handbook for Radiographers — the positioning reference this site is built on — is where these projection and position conventions come from. Two of the landmark-based centering points it establishes are the chest lateral centering at T7 (about 3–4 inches below the vertebra prominens) and the AP shoulder centered on the coracoid process. When a department's local protocol differs, the local order and validated department protocol take precedence.
Putting It Together: One Setup, Full Vocabulary
Imagine walking up to a left lateral decubitus abdomen projection. In one phrase you've used several of the 30 terms at once: lateral (side-to-side beam), decubitus (patient recumbent + horizontal beam), and the landmark-based centering from your iliac crest and ASIS. Your patient's body habitus then tells you whether the expected anatomy sits higher or lower than the text. That's the value of this vocabulary — it turns a room full of variables into a repeatable, communicable exam.
Key Takeaways
- Projection = path of the central ray (AP, PA, lateral, oblique, axial, tangential, decubitus, lordotic, horizontal beam, axiolateral).
- Position = how the patient lies (anatomic, supine, prone, recumbent, erect, Trendelenburg, Fowler's).
- Four habitus types: sthenic 50%, hyposthenic 35%, asthenic 10%, hypersthenic 5% — hypersthenic = high/transverse organs, asthenic = low/vertical organs.
- Decubitus always means horizontal beam with a recumbent patient — the free-air technique.
- Landmark levels: vertebra prominens C7, jugular notch T2–T3, xiphoid T9–T10, iliac crest ~L4, scapular angle T7.
Frequently Asked Questions
What is the difference between a projection and a position in radiography?
A projection describes the path of the central ray through the patient (AP, PA, lateral, oblique, axial), while a position describes how the patient's body is arranged (supine, prone, recumbent, erect, Trendelenburg). The two go together: for example, a "PA erect chest" describes both the beam path and the patient's posture.
Which body habitus has a transverse, high stomach?
Hypersthenic. The hypersthenic habitus has a massive, broad build with a high diaphragm, short and broad lungs, a transverse heart, and a high, nearly horizontal stomach.
Why is a portable chest radiograph obtained as AP instead of PA?
Because the patient usually cannot stand. An AP projection places the posterior structures closer to the detector, which magnifies the cardiac silhouette; it is the standard fallback when an erect PA is impossible.
What position demonstrates free air in the abdomen?
The lateral decubitus projection — a recumbent patient with a horizontal (cross-table) beam — lets free intraperitoneal air rise to the highest point and be profiled against the abdominal wall.
What vertebral level is the iliac crest?
Approximately L4 in most references (some texts cite L4–L5). It is the standard centering landmark for AP abdominal and lumbar spine projections.
Which habitus has the most vertical, J-shaped stomach?
Asthenic. The asthenic habitus is long and slender with a low diaphragm, vertical heart, and a low, vertical, J-shaped stomach near the midline.
Authoritative Sources
- StatPearls — "X-ray Radiographic Patient Positioning" (NCBI Bookshelf NBK565865, updated 2022): ncbi.nlm.nih.gov/books/NBK565865
- Bontrager's Textbook of Radiographic Positioning and Related Anatomy (Bontrager & Lampignano, 2014) — body habitus types and population percentages
- UMSystem Clinical Preceptor Reference Guide — Appendix C "Anatomy & Landmarks Reference" (C. Allen, ©2025): umsystem.pressbooks.pub
- Clark's Pocket Handbook for Radiographers (16th ed.) — positioning projection/position conventions and landmark centering points
- Radiology Key — "Radiographic Positioning" (oblique naming): radiologykey.com