Comprehensive Guide to Radiographic Terminology, Positioning Principles, Imaging Basics, and Radiation Protection

Introduction and Body Habitus

• Body Habitus Definition: Refers to the build, physique, and general shape of the human body. It impacts the positioning of specific regions.
• Sthenic:   - Represents about $50\%$ of the population.   - Considered the "average" body style for radiographic positioning purposes.
• Hyposthenic:   - Characterized as thin and more slender than the sthenic build.   - Represents about $35\%$ of the population.
• Asthenic:   - Characterized as thin, slender, with a long and narrow build.   - Represents about $10\%$ of the population.
• Hypersthenic:   - Characterized by a broad frame compared to the sthenic build.   - Bariatric Patient: Defined by abnormal or excessive fat accumulation that may impair health.   - Represents about $5\%$ of the population.
• Impact on Positioning:   - Centering of the central ray (CR) may need to be altered based on body habitus.   - Image receptor (IR) placement must be considered, specifically whether to use a lengthwise (portrait) or crosswise (landscape) orientation.

Fundamental Positioning Terminology

• Radiographic Positioning: The study of patient positioning performed for radiographic demonstration or visualization of specific body parts on image receptors.
• General ARRT Approved Terms:   - Radiograph: An image of a patient’s anatomic part(s) produced by the action of x-rays on an image receptor.   - Film-screen (analog): A technology where the image is captured and displayed on physical film.   - Digital Technology: Images are viewed and stored on digital display monitors.   - Radiography: The process and procedures involved in producing a radiograph.
• Image Receptor (IR): A device that responds to ionizing radiation to create the radiographic image after it exits the patient. This term applies to both analog cassettes and digital acquisition devices.
• Central Ray (CR): The center-most portion of the x-ray beam emitted from the x-ray tube; it is the portion of the beam with the least divergence.

Imaging Receptors and Technology

• Diagnostic Radiography IR Devices:   1. Imaging Plate (IP): Specifically the Photostimulable storage phosphor plate ($PSP\,IP$).   2. Solid-state Detectors: Built into the x-ray table/upright wall unit or housed in a cassette-like portable enclosure.   3. Fluoroscopic Image Receptor.
• Computed Radiography (CR):   - Uses the $PSP\,IP$ to store x-ray energy for later processing.   - After exposure, the cassette is inserted into a reader device.   - The reader scans the IP with a laser to release stored energy as light.   - The image is converted to a digital format and viewed on a computer monitor or printed on film (rare).
• Digital Radiography (DR):   - Uses solid-state digital detectors (flat panel IR) to convert x-ray energy directly into a digital signal.   - Detectors can be built-in or portable.   - Portable detectors may be "tethered" (wired) or connected wirelessly.
• Fluoroscopy IR:   - Designed for "real-time" imaging to guide procedures or capture motion video.   - Images are saved as static images, video recordings, or video files.

Radiographic Procedure Functions

• The Five General Functions of a Radiographic Exam:   1. Positioning of the body part and alignment with the IR and CR.   2. Application of radiation protection measures and devices.   3. Selection of exposure factors (radiographic technique) on the control panel.   4. Patient instructions related to respiration (breathing) and initiation of the exposure.   5. Processing of the IR.
• Diagnosis and Sample Patient Interaction:   - If a patient asks about results, the radiographer must tactfully advise them that the referring physician receives the report once interpreted by a radiologist.   - Image interpretation beyond quality assessment is outside the radiographer's scope of practice.

Body Planes, Sections, and Lines

• Anatomic Position: The body is viewed upright, arms down, palms and feet facing forward. Radiographs are generally displayed as if the patient is in this position facing the viewer.
• Sagittal Plane: Any longitudinal plane dividing the body into right and left segments.   - Midsagittal Plane (MSP): Also called the "median" plane; divides the body into equal right and left halves.
• Coronal Plane: Divides the body or part into anterior (front) and posterior (back) segments.   - Midcoronal Plane: Also called the "midaxillary" plane; divides the body into equal anterior and posterior halves.
• Horizontal (Axial) Plane: Passes crosswise at right angles to longitudinal planes, dividing the body into superior (upper) and inferior (lower) portions. Also known as the transverse plane.
• Oblique Plane: A longitudinal or transverse plane at an angle or slant, not parallel to sagittal, coronal, or horizontal planes.
• Application in Positioning:   - Planes are used to center parts to the IR or CR.   - In an AP projection, the CR passes parallel to the sagittal plane and perpendicular to the coronal plane.
• Special Skull Planes:   - Base of Skull (Frankfort horizontal plane): Transverse plane from the infraorbital margins to the superior margins of the External Auditory Meatus ($EAM$).   - Occlusal Plane: Horizontal plane formed by the biting surfaces of upper and lower teeth.

Body Surfaces and Relationship Terms

• General Surfaces:   - Posterior (Dorsal): Back half of the patient; includes the top of the feet and back of hands.   - Anterior (Ventral): Front half of the patient; includes the tops of feet and palms of hands.
• Hands and Feet Specifics:   - Foot: "Plantar" refers to the sole (posterior) surface; "Dorsum" refers to the top (anterior) surface.   - Hand: "Palmar" refers to the palm (anterior); "Dorsal" refers to the back (posterior) aspect.
• Relationship Terms:   - Cephalad: Toward the head.   - Caudad: Away from the head (toward the feet).   - Superior: Situatied above or nearer the head.   - Inferior: Situated below or nearer the feet.   - Medial: Toward the midline or "inside."   - Lateral: Away from the midline or toward the "outside."   - Proximal: Nearer the point of attachment, origin, or center.   - Distal: Farthest from the point of attachment or center.   - Ipsilateral: Parts on the same side of the body (e.g., right thumb and right great toe).   - Contralateral: Parts on the opposite side of the body (e.g., right knee and left hand).

Radiographic Projections

• Projection Definition: The path of the central ray as it exits the x-ray tube and passes through the patient to the IR.
• AP (Anteroposterior): CR enters the anterior surface and exits the posterior surface. For the foot, this is also called the "dorsoplantar" projection.
• PA (Posteroanterior): CR enters the posterior surface and exits the anterior surface.
• Axial Projection: Includes longitudinal angulation of the CR with the long axis of the body part (10^\\circ or more). Cephalad or caudad angles are used.
• Tangential Projection: The CR merely "skims" a body part to project it into profile and away from other structures (e.g., zygomatic arch).
• Lateral Projection: CR enters one side and passes transversely along the coronal plane to the opposite side. Named by the side closest to the IR.   - Lateromedial / Mediolateral: Terms used for limbs to specify entry/exit sides.
• Transthoracic Lateral: A unique projection used for shoulder radiography.
• Oblique Projection: CR enters from a side angle following an oblique plane. Resulting projections depend on position (e.g., LPO position results in an AP oblique projection; RAO results in a PA oblique projection).

Radiographic Body Positions

• Position Definition: Refers to the specific placement of the body part relative to the table/IR or the overall posture of the patient.
• General Body Positions:   - Supine: Lying on the back.   - Prone: Lying on the stomach.   - Erect: Upright.   - Recumbent: Lying down in any position (dorsal, ventral, or lateral).   - Trendelenburg: Head lower than the feet.   - Reverse Trendelenburg: Head higher than the feet.   - Lateral Recumbent: Lying on the side (left or right).   - Left Lateral Recumbent (Modified Sim's): For barium enema tip insertion; lying on the left anterior side with the right knee flexed.   - Lithotomy: Supine with knees and hips flexed, thighs abducted, and supported by stirrups.
• Specific Radiographic Positions:   - Oblique Positions: Named by the side closest to the IR (LPO, RPO, LAO, RAO).   - Decubitus Position: Patient is lying down and the CR is horizontal/parallel to the floor. Used for air-fluid levels.     - Lateral Decubitus: Lying on the side (Right or Left).     - Dorsal Decubitus: Lying on the back.     - Ventral Decubitus: Lying on the stomach.   - Lordotic Position: Patient leans backward so only shoulders touch the IR; used for pulmonary apices.

Body Movement Terminology

• Flexion vs. Extension:   - Flexion: Bending a joint; decreases the angle.   - Extension: Straightening a joint; increases the angle.   - Hyperextension: Extending a joint beyond the neutral position.
• Deviation: Turning away from standard; includes Ulnar deviation and Radial deviation of the wrist.
• Ankle Movements:   - Dorsiflexion: Moving foot/toes upward.   - Plantar Flexion: Extending the joint downward.   - Eversion: Outward turning of the foot at the ankle.   - Inversion: Inward turning of the foot at the ankle.   - Valgus: Bending a part outward/away from midline.   - Varus: Bending a part inward/towards midline.
• Rotational and Limb Movements:   - Abduction: Movement away from the central axis.   - Adduction: Movement toward the central axis.   - Pronation: Forearm rotation so palm is down.   - Supination: Forearm rotation so palm is up (anatomic position).   - Protraction: Forward movement.   - Retraction: Backward movement.   - Elevation: Lifting superiorly.   - Depression: Lowering inferiorly.   - Circumduction: Circular movement of a limb.   - Rotation: Turning a part on its axis.   - Tilt: Slanting the midsagittal plane.

Positioning Principles and Evaluation

• Evaluation Criteria Format:   1. Anatomy Demonstrated: Precise parts clearly visualized.   2. Position: Placement of part, correct centering, and collimation.   3. Exposure: Evaluating $kV$, $mA$, and time for optimum image quality. Note: Motion is assessed here as time is its controlling factor.
• Image Markers and Identification:   - Mandatory markers: Patient ID (name, date, case number) and Anatomic Side Markers (R or L).   - Markers must be radiopaque and placed within the collimated field. Post-processing digital annotation is legally unacceptable.
• Positioning Rules:   1. Minimum of Two Projections: Taken at 90^\\circ (right angles) to each other. Reasons: avoid superimposition, localize lesions/foreign bodies, and determine fracture alignment.   2. Minimum of Three Projections for Joints: (AP/PA, Lateral, Oblique). Required because small chip fractures or joint space abnormalities may be missed on only two views.
• Exceptions to Rules:   - Single projection: Pelvis study (unless hip injury suspected), AP abdomen ($KUB$), Portable chest.   - Two projections: Postreduction limb studies to check alignment; long bones (Forearm, Humerus, Femur, Tib-fib) generally require two.

Topographic Landmarks and IR Alignment

• Palpation: Applying light pressure with fingertips to locate bony structures (topographic landmarks).   - Procedures: Inform the patient of the purpose, obtain permission, and perform gently.   - Sensitive landmarks (e.g., pubic symphysis, ischial tuberosity) may have institutional restrictions; alternative landmarks should be used.
• IR Alignment: Long axis of anatomy is usually aligned to the long dimension of the IR.   - Sizes: Standard portrait or landscape orientations (typically $14 \times 17\,inches$).
• Viewing Radiographs:   - Standard: Patient facing viewer (Patient's Left is Viewer's Right).   - Lateral/Oblique: Viewer sees it from the perspective of the x-ray tube.   - Decubitus: Upside of the patient is at the top of the monitor.   - Digits: Hands and feet viewed with digits pointing up.   - CT/MRI: Patient’s Right is at the Viewer’s Left.

Imaging Principles: SID, OID, and CR

• X-ray Beam Divergence: Least amount of distortion is at the CR. Distortion increases as distance from CR increases.
• Source-to-Image Receptor Distance (SID):   - Greater SID = less magnification and better recorded detail.   - Traditional: $40\,inches$ ($102\,cm$).   - Current recommendations: $44$-$48\,inches$ ($112$-$122\,cm$).   - Chest radiography: Minimum $72\,inches$ ($183\,cm$) to reduce heart magnification.
• Object-to-Image Receptor Distance (OID):   - Smaller OID (closer to IR) = less magnification/distortion and better resolution.
• Distortion types: Elongation (part appears longer) and Foreshortening (part appears shorter).

Radiation Protection and ALARA

• ALARA: "As Low As Reasonably Achievable."
• Three Cardinal Principles: Time (minimize), Distance (maximize), Shielding (use lead).
• Units of Radiation:   - Roentgen (R) / Air kerma ($Gy_a$): Exposure in air.   - Rad / Gray (Gy): Absorbed dose.   - Rem / Sievert (Sv): Equivalent/Effective dose for worker protection.
• Dose Limits (DL):   - Occupational Workers: Annual $50\,mSv$ ($5\,rem$). Cumulative $10\,mSv \times \text{age}$.   - General Population: Annual $1\,mSv$ ($100\,mrem$).
• Personnel Monitoring: Dosimeters (Film badge, $TLD$, $OSL$, Digital) worn at chest level.
• Pregnancy:   - Technologist: "Voluntary declaration" required. Secondary monitor worn at waist under lead apron.   - Limit: $0.5\,mSv$ per month or $5.0\,mSv$ for entire pregnancy.
• Patient Protection:   - Minimize repeats (clear instructions).   - Use appropriate filtration and accurate collimation ($PBL$).   - Shielding: $1\,mm$ lead equivalent reduces primary dose by $95\%$ to $99\%$.   - Fetal Protection: If dose is expected above $10\,mGy$ ($1\,rad$), consult a radiologist. The "10-day rule" for LMP is now considered obsolete.

Communication and Ethical Standards

• ASRT ACE Campaign:   - A: Announce your name.   - C: Communicate your credentials.   - E: Explain the procedure.
• Patient Assessment checklist:   - Verify ID (two forms: name/armband).   - Verify the procedure ordered.   - Acquire clinical history and pregnancy status.   - Provide opportunity for questions.
• Institutional Programs:   - Image Wisely: Focuses on adult radiation safety and appropriateness.   - Image Gently: Focuses on pediatric imaging safety due to increased radiosensitivity.
• Clinical Rules for Students: Students must NEVER hold patients during exposure and must wear dosimeters at all times during labs and clinics.

Terminology and Practice Review

• Question: Hand—1, 2, or 3 projections? Answer: 3 (Joint involved).
• Question: Forearm—1, 2, or 3 projections? Answer: 2 (Long bone).
• Question: Femur—1, 2, or 3 projections? Answer: 2.
• Question: Knee—1, 2, or 3 projections? Answer: 3.
• Question: Humerus—1, 2, or 3 projections? Answer: 2.
• Question: Patient lying on abdomen with x-ray beam directed horizontally? Answer: Ventral Decubitus.
• Question: Body position where head is lower than feet? Answer: Trendelenburg.