Unit 1 Terminology & Positioning Principles: Comprehensive Notes

Levels of Human Structural Organization

  • Sequence of structural levels: Atoms → Molecules → Cell → Tissue → System → Organism (consists of 10 body systems) → Organ
  • Key idea: each level builds on the previous to form complex biological function

Body Systems (overview and essential roles)

  • Circulatory System
    • Distributes oxygen to cells
    • Transports waste products from cells
    • Composed of cardiovascular organs and lymphatic organs
  • Digestive System
    • Primary functions: Absorption and Elimination
  • Respiratory and Urinary Systems
    • Respiratory System: supplies oxygen and eliminates carbon dioxide
    • Urinary System: regulates blood and eliminates waste products
  • Reproductive System
    • Reproduces organism (Male and Female)
  • Nervous and Muscular Systems
    • Nervous System: regulates body activities
    • Muscular System: enables movement; includes skeletal, smooth, and cardiac muscle
  • Endocrine and Integumentary Systems
    • Endocrine System: ductless glands; regulates body via hormones
    • Integumentary System: protects body; eliminates waste through perspiration

Skeletal System and Bone Biology

  • Skeletal System features 206 separate bones
  • Osteology: study of bones
  • Arthrology: study of joints
  • Skeletal Anatomy divisions
    • Axial skeleton: 80 bones (central axis: skull, vertebral column, ribs, sternum)
    • Appendicular skeleton: 126 bones (limbs; shoulder and pelvic girdles)
  • Bone Classifications
    • Long Bones: shaft (diaphysis) with two ends; found in appendicular; contains compact bone and spongy bone; medullary cavity contains fatty yellow marrow; periosteum; articular cartilage covers ends
    • Short Bones: cuboidal; found in appendicular; mostly spongy bone with thin layer of compact bone
    • Flat Bones: two plates of compact bone with spongy bone between; found in axial and appendicular skeleton
    • Irregular Bones: various peculiar shapes; mix of compact and spongy bone
  • Sesamoid Bones
    • Small, oval bones embedded in tendons near joints
    • Act as a fulcrum for flexor tendons; protect surrounding tendons

Long Bone Development (ossification and growth)

  • Ossification processes
    • Intramembranous ossification: bone replaces membranes
    • Endochondral ossification: bone replaces cartilage
  • Developmental centers
    • Primary center (diaphysis): becomes the body of the bone
    • Secondary centers: Epiphysis (ends of bone) and Metaphysis (between epiphysis and diaphysis; growth in length occurs here)
  • Epiphyseal plate (growth plate)
    • Located between epiphysis and metaphysis
    • Growth in length occurs at this plate
    • Plate fuses (closes) at about 25 years of age

Joints (articulations)

  • Joint Classifications by structure
    • Fibrous
    • Cartilaginous
    • Synovial
  • Joint Classifications by function
    • Synarthrosis – immovable
    • Amphiarthrosis – limited movement
    • Diarthrosis – freely moveable
  • Fibrous Joints
    • Syndesmoses – interosseous ligaments and fibrous cords
    • Sutures – interlocking edges held by fibrous tissue/ligaments
    • Gomphoses – conical process fits into socket-like bone region
  • Cartilaginous Joints
    • Symphyses – broad fibrocartilage disk between bones
    • Synchondroses – temporary joints with hyaline cartilage ossifying into bone (epiphyseal plates on long bones)
  • Synovial Joints
    • Features: fibrous capsule enclosing a joint cavity with synovial fluid (viscous lubricant)
    • Movement types (7):
    • Plane (gliding)
    • Ginglymus (hinge)
    • Trochoid (pivot)
    • Ellipsoid (condyloid)
    • Sellar (saddle)
    • Spheroidal (ball-and-socket)
    • Bicondylar
    • Common examples (by movement type)
    • Plane: intercarpal, intermetacarpal, carpometacarpal joints
    • Ginglymus: interphalangeal joints, elbow
    • Trochoid: proximal and distal radioulnar joints; C1–C2; wrist joints
    • Ellipsoid: metacarpophalangeal joints (1st–5th)
    • Sellar: 1st carpometacarpal joint (thumb)
    • Spheroidal: hip, shoulder
    • Bicondylar: temporomandibular joint (TMJ), knee

General Radiography Terminology

  • Radiography: the practice/technique; Radiograph (image): the captured image or picture
  • Radiographic procedure (examination)
  • Image Receptor (IR): device that captures the radiographic image
  • Central Ray (CR): the central portion of the x-ray beam

Anatomic Position

  • Standard reference position for describing body orientation
  • Used to describe positioning terms accurately in radiography

Body Planes and Skull Planes

  • Body Planes
    • Sagittal (midsagittal): divides body into left and right; medial plane
    • Coronal (midcoronal): divides body into anterior and posterior
    • Oblique: angled plane
    • Horizontal (axial): divides body into superior and inferior portions
  • Planes of Skull
    • Base plane
    • Occlusal plane

Orientation Terms: Posterior vs Anterior; Dorsal vs Palmar

  • Posterior (dorsal): toward the back of the body
    • Dorsum: dorsum pedis (top of the foot)
    • Plantar surface: bottom of the foot
  • Anterior (ventral): toward the front of the body
  • Dorsal surface of hand: back of the hand
  • Palmar surface: palm of the hand

Body Surfaces and Parts (brief)

  • Dorsal surface (posterior side) vs Palmar surface (anterior/palm side)
  • Anterior surface (ventral) vs Posterior surface (dorsal)

Body Positions (in imaging practice)

  • Used to describe the patient’s general position and the part closest to the IR
  • Examples: supine, erect, recumbent; left lateral, right anterior oblique, external oblique
  • Common generic positions
    • Supine: patient lies on back
    • Prone: patient lies on abdomen
  • General Body Positions (definitions)
    • Erect: upright; standing or sitting
    • Recumbent: lying down in any position
    • Dorsal recumbent = supine (on back)
    • Ventral recumbent = prone (on abdomen)
    • Lateral recumbent = lying on side
  • Additional named positions (examples)
    • Trendelenburg
    • Fowler's position
    • Modified Sims' position
    • Lithotomy position
  • Lateral Position: side view; right/left lateral
  • Oblique Position: angled; closest part to IR described (e.g., thorax, abdomen, pelvis)
  • Decubitus Positions: lying on a horizontal surface; designated by surface on which patient rests (e.g., left lateral decub)
  • Projections: describe the path of the CR relative to the body; entrance and exit points; may include direction terms (e.g., axial, transthoracic)

Projections and View Terminology

  • Projections describe the path of the CR; examples include:
    • PA (posterior–anterior): CR enters from posterior and exits anterior
    • AP (anterior–posterior): CR enters from anterior and exits posterior
    • Oblique projections
    • Lateral projections
    • Axial projections: any CR angle of 10 degrees or more along the long axis
  • Lateral Projections
    • Lateromedial: CR enters medial side and exits lateral side
    • Mediolateral: CR enters lateral side and exits medial side
  • Axial Projections
    • AP Axial: long-axis CR alignment with part at an oblique angle
    • Inferosuperior (CR enters from below and exits above) vs Superoinferior (CR enters from above and exits below)
  • Tangential Projections
    • CR touches a curve or surface at only one point
  • Special named projections
    • AP Axial Projection – Lordotic: chest-position to exaggerate lumbar curvature
    • Transthoracic Lateral: lateral projection through the thorax
    • Foot projections:
    • Dorsoplantar: CR enters dorsal (anterior) surface; exits plantar surface
    • Plantodorsal: CR enters plantar surface; exits dorsal (anterior) surface
    • Parietoacanthial and Submentovertex: unique projection lines
  • Relationship Terms
    • Medial vs. Lateral: toward vs away from center
    • Proximal vs. Distal: toward the origin or closest to the source vs away from it
  • CR angle mnemonics
    • Caudal angle: toward the feet
    • Cephalad angle: toward the head
    • Mnemonic cue often used in teaching: “PHILLY LOW” and “CAPON COLLAR LOW” as reminders for angulation
  • Flexion/Extension
    • Flexion: decrease angle between parts
    • Extension: increase angle between parts
    • Hyperextension: extension beyond neutral
  • Movement terminology
    • Radial deviation vs Ulnar deviation
    • Dorsiflexion vs Plantar flexion
    • Medial rotation vs Lateral rotation
    • Abduction vs Adduction
    • Supination vs Pronation
    • Circumduction: moving around in a circle
    • Rotation vs Tilt
  • Radiographic View terminology
    • Radiographic View is not an accepted positioning term in the United States; “view” describes the body part as seen by the IR or other recording medium (e.g., fluoroscopic screen)

Evaluation Criteria and Image Quality (example)

  • Example: Lateral Forearm Evaluation Criteria
    • Pertinent anatomy demonstrated? Elbow and wrist joints included; proper collimation
    • Position quality? No rotation at wrist or elbow; CR alignment with part
    • Exposure quality? Optimal exposure factors (mAs and kV) achieved
    • Image markers? Correct marker placement (e.g., “R” marker visible)

Patient Identification and Anatomic Markers

  • Patient Identification on radiographs
    • Typical elements: patient’s name, date of birth, date and time of exam, case number, institution information
    • Entered electronically before or after exposure with digital systems (CR: bar-code; DR: computer)
  • Anatomic Side Markers
    • Must include R or L side; indicate which limb/body side was x-rayed
    • Markers must be radiopaque
    • Placement: directly on the IR or adjacent to the patient; inside the collimated border and not superimposed over anatomy
    • Orientation: placed correctly; should be placed at time of exam
    • Digital markers: possible after processing but discouraged due to legal/liability concerns
  • Marker Placement Examples (visual guides)
    • Correct placement (marker outside anatomy field, within border, labeled accurately)
    • Incorrect placement (marker overlapped with anatomy or off-resonance with the image)
  • Procedures Markers (example set)
    • Variables shown: LEFT, COMPARISON, SUPINE, WT. BEARING, ERECT, FLEXION, PRONE, EXTENSION, DECUB, STANDING, SCOUT, EXT. ROT, PRELIM, INT. ROT

Positioning Rules & Principles

  • Projections required
    • Minimum of two projections (per view) at 90° to each other
    • Rationale: some pathology not visualized on a single projection; aids localization of lesions/foreign bodies; helps determine alignment of fractures
  • Prime joint areas
    • Minimum of three projections when joints are in the prime interest area: AP or PA, Lateral, and Oblique
  • Long-bone localization
    • Must include both joints on long bones to assess alignment and length

Palpation and Landmarks for Positioning

  • Palpation: applying pressure with hands/fingers to locate positioning landmarks
  • Landmarks used for centering and positioning (common examples)
    • Iliac crest
    • Anterior superior iliac spine (ASIS)
    • Xiphoid process
    • Spinous processes
    • Inferior angle of scapula

Viewing Images and Orientation Guidelines

  • Torso projections (AP/PA) and obliques
    • Viewed in anatomic position
    • Example: PA chest – left side of the body on the viewer’s right
  • Lateral torso projections
    • Viewed in the position taken (as the tube sees the image)
    • Example: Left lateral chest
  • Decubitus torso projections
    • Viewed crosswise in the position taken
    • Example: Left lateral decub chest
  • Extremity images
    • Viewed in anatomic position with limbs hanging down
    • Exception: hands and feet viewed with digits up

Practical and Ethical Considerations

  • Proper patient identification and marking are critical for patient safety and legal accountability
  • Use of anatomic side markers must be accurate to prevent mislabeling and potential liability
  • When digital markers are used, facilities often discourage sole reliance on post-processed digital markings due to residual legal risk
  • Palpation landmarks must be used ethically and carefully to avoid patient discomfort or injury during positioning

Connections to Foundational Principles and Real-World Relevance

  • Anatomy and physiology underpin radiographic positioning (bone types, joints, body planes, and organ systems guide how projections are planned)
  • Understanding ossification and growth plates is essential for pediatric and adolescent imaging; awareness of fusion age helps interpret radiographs correctly
  • Knowledge of joint types and movement can inform choice of projection to visualize a joint’s true anatomy and pathology
  • Positioning rules (two projections minimum, three projections for joints, and inclusion of both joints on long bones) are foundational for diagnostic accuracy and standardization across exams
  • Ethical practice requires accurate labeling, proper marker placement, and patient-centered care during positioning procedures

Quick Reference: Key Numbers and Terms in this Unit

  • Number of body systems: 10
  • Age for epiphyseal plate fusion: approximately 25 years
  • Projections: minimum 2 projections; often 3 projections for prime joints
  • Planes and angles: typical CR angles include any angle of the CR of at least 10^ ext{ extdegree} along the long axis (Axial projections)
  • Common numbers associated with bone anatomy: 206 bones in the adult skeleton
  • Movement types: 7 distinct synovial joint movement types
  • Common directional terms: medial, lateral, proximal, distal, cranial (cephalad), caudal

Summary of Connections to Other Lectures

  • This unit lays the groundwork for radiographic technique and image interpretation taught in later chapters: positioning routines, landmarks, and projection selection connect directly to anatomy and clinical imaging for musculoskeletal and thoracic/pelvic regions
  • Ethical and legal considerations introduced here recur in modules on radiographic quality assurance, patient safety, and digital imaging workflows