- ALARA
- As Low As Reasonably Achievable — keep every radiation dose to patients, staff, and the public as low as possible while still getting a diagnostic image.
- Inverse square law
- Intensity is inversely proportional to the square of distance: I₁/I₂ = (D₂)²/(D₁)². Doubling distance cuts intensity to one quarter.
- Cardinal principles of protection
- Time, distance, and shielding. Distance is the most effective because of the inverse square law.
- Anode heel effect
- Beam is more intense on the cathode side, less on the anode side. Place the thicker body part toward the cathode.
- kVp controls…
- Beam quality (energy/penetration) and the scale of radiographic contrast. Higher kVp = more penetration, lower (longer-scale) contrast.
- mAs controls…
- Beam quantity (number of photons) and receptor exposure (density). Directly proportional: double mAs = double exposure.
- mAs formula
- mAs = mA × exposure time (seconds).
- 15% rule
- Increasing kVp by 15% has the same effect on receptor exposure as doubling the mAs. Raise kVp 15% and halve mAs to cut dose at constant exposure.
- Photoelectric effect
- Photon is totally absorbed by an inner-shell electron — no scatter. Builds image contrast, depends on Z³ and lower kVp, and increases patient dose.
- Compton scatter
- Photon ejects an outer-shell electron and continues deflected. The scatter fogs the image (lowers contrast) and is the main occupational dose hazard.
- Quantum mottle
- Grainy image noise from too few photons (mAs too low). Fix it with more mAs, not more kVp.
- Grid cutoff causes
- Off-level, off-center, off-focus (wrong SID range), and upside-down focused grid — all absorb useful primary beam.
- Line focus principle
- An angled anode makes the effective focal spot smaller than the actual focal spot — sharper detail while spreading heat.
- Occupational annual dose limit
- 50 mSv/yr whole-body effective dose; cumulative lifetime limit = 10 mSv × age in years (NCRP-116).
- Public annual dose limit
- 1 mSv/yr for continuous/frequent exposure (5 mSv/yr infrequent).
- Embryo/fetus dose limit
- 5 mSv total over the entire gestation, and no more than 0.5 mSv in any single month.
- Lens of eye annual limit (occupational)
- 150 mSv/yr (NCRP-116).
- Skin & extremities annual limit
- 500 mSv/yr (occupational, NCRP-116).
- Bremsstrahlung
- 'Braking' radiation — a high-speed electron is decelerated/deflected by the nucleus, emitting an x-ray. The dominant source of the diagnostic beam.
- Characteristic radiation
- An inner-shell electron is ejected, an outer electron fills the gap, and a photon of energy specific to the target element is released.
- ARRT
- American Registry of Radiologic Technologists — develops and administers the Radiography (R) exam and other radiologic credentials.
- ARRT Radiography exam: scored vs total questions
- 200 scored multiple-choice questions plus 30 unscored pilot questions = 230 total.
- ARRT Radiography passing score
- A scaled score of 75 on a 1–99 scale — not a percentage. Scaling equates difficulty across forms.
- ARRT Radiography test time
- 230 minutes (about 3 hours 50 minutes) of test time — roughly one minute per question.
- Four ARRT content categories (scored)
- Patient Care (33), Safety (50), Image Production (51), Procedures (66) = 200 scored.
- Informed consent — who obtains it?
- The physician obtains informed consent. The technologist verifies it is documented and that the patient understands the procedure.
- Negligence
- Failure to act as a reasonably prudent technologist would under the circumstances, resulting in harm.
- Assault vs battery
- Assault = threatening or attempting a procedure without consent. Battery = actually touching/performing it without consent.
- Four core ethical principles
- Autonomy (right to decide), beneficence (do good), nonmaleficence (do no harm), and justice (fairness).
- Two patient identifiers
- Verify a patient with two identifiers (e.g., name + date of birth) and confirm the correct exam and side before any exposure.
- Standard precautions
- The minimum infection-control practices used on every patient: hand hygiene, PPE as needed, respiratory hygiene, safe injection, and cleaning equipment.
- Medical vs surgical asepsis
- Medical asepsis = clean technique that reduces microorganisms. Surgical asepsis = sterile technique that eliminates them (for invasive procedures).
- Contact precautions
- Gown + gloves on entry. For MRSA, VRE, and C. difficile (use soap and water for C. diff — alcohol does not kill spores).
- Droplet precautions
- Surgical mask within ~6 ft. For influenza, pertussis, and mumps.
- Airborne precautions
- N95 respirator + negative-pressure room. For tuberculosis, measles, and varicella (chickenpox).
- Normal adult blood pressure
- About 120/80 mmHg (systolic <120, diastolic <80).
- Normal adult heart rate
- 60–100 beats per minute.
- Normal adult respiratory rate
- 12–20 breaths per minute.
- Normal adult temperature
- About 98.6°F (37°C).
- Normal oxygen saturation (SpO₂)
- 95–100%.
- Ionic vs nonionic contrast
- Ionic = high osmolality, more reactions. Nonionic = low osmolality, far better tolerated and standard for intravascular use.
- Positive vs negative contrast
- Positive contrast (iodine, barium) absorbs more x-rays and appears bright. Negative contrast (air/gas) is radiolucent and appears dark.
- Barium vs water-soluble contrast in the GI tract
- Use barium sulfate for routine GI studies, but switch to a water-soluble iodinated agent if perforation is suspected (leaked barium causes peritonitis).
- Grading contrast reactions
- Mild (nausea, hives → observe), moderate (marked urticaria, mild bronchospasm → treat), severe (laryngeal edema, anaphylaxis → emergency, epinephrine).
- Screen before iodinated contrast
- Ask about prior reaction, renal function, diabetes/metformin, and asthma/allergies; have emergency equipment ready.
- HIPAA
- Federal law protecting the privacy and security of patient health information; only share on a need-to-know basis.
- False imprisonment
- Unlawful restriction of a patient's freedom of movement (e.g., improper use of restraints).
- ASRT
- American Society of Radiologic Technologists — the professional society that publishes practice standards for the field.
- Patient holding during exposure
- Avoid having radiology staff hold patients. If a holder is needed, use a non-occupational person in a lead apron and gloves, out of the primary beam.
- Trendelenburg position
- Supine with the head lower than the feet; used for some procedures and to manage hypotension.
- X-rays on the EM spectrum
- High-energy, short-wavelength ionizing electromagnetic radiation; they travel in straight lines and cannot be focused by a lens.
- Efficiency of x-ray production
- Only about 1% of the electrons' kinetic energy becomes x-rays; ~99% becomes heat at the anode.
- Thermionic emission
- Boiling off of electrons from the heated cathode filament; these electrons are then driven across to the anode.
- Which interaction increases patient dose?
- The photoelectric effect — the photon's full energy is absorbed by the tissue.
- Which interaction predominates at diagnostic kVp?
- Compton scatter predominates at the higher kVp range used in diagnostic radiography.
- Absorbed dose — SI unit
- Gray (Gy); 1 Gy = 100 rad. Energy deposited per unit mass of tissue.
- Equivalent/effective dose — SI unit
- Sievert (Sv); 1 Sv = 100 rem. Absorbed dose weighted for biological harm; the unit used for dose limits.
- Radioactivity — SI unit
- Becquerel (Bq); 1 curie (Ci) = 3.7 × 10¹⁰ Bq.
- Roentgen (R)
- The traditional unit of exposure/air kerma; SI now uses the gray (air kerma). ≈ 1 R = 0.00876 Gy air kerma.
- Law of Bergonié and Tribondeau
- Cells are most radiosensitive when highly mitotic, undifferentiated, and have a long mitotic future.
- Most radiosensitive cells
- Embryo/fetus, bone marrow (blood-forming), intestinal crypt cells, and reproductive cells.
- Most radioresistant cells
- Nerve and muscle cells (highly differentiated, non-dividing).
- Deterministic effects
- Tissue reactions with a threshold dose; severity increases with dose (skin erythema, cataracts, sterility).
- Stochastic effects
- Effects with no threshold; probability (not severity) increases with dose (cancer, heritable genetic effects).
- Linear no-threshold (LNT) model
- The assumption that any dose, however small, carries some stochastic risk — the basis for minimizing all exposure.
- LET (linear energy transfer)
- The amount of energy a radiation deposits per unit path length; high-LET radiation causes more biological damage.
- RBE (relative biological effectiveness)
- A comparison of a radiation's biological damage to that of a reference radiation for the same dose; rises with LET.
- Direct vs indirect radiation action
- Direct: radiation hits DNA itself. Indirect: radiation ionizes water, forming free radicals that damage DNA (most common in tissue).
- Acute radiation syndrome — earliest system affected
- The hematopoietic (bone marrow) system, because blood-forming cells are highly radiosensitive.
- Atomic number and the photoelectric effect
- Photoelectric absorption increases roughly with the cube of atomic number (Z³), which is why bone and contrast media appear bright.
- ALARA — who is responsible?
- Every radiographer; it is the guiding philosophy for protecting patients, staff, and the public.
- Most effective cardinal principle
- Distance — by the inverse square law, doubling the distance cuts dose to one quarter.
- Time principle
- Dose is directly proportional to time in the radiation field; minimize exposure time.
- Shielding principle
- Use lead aprons, thyroid shields, gloves, and barriers to absorb radiation when distance cannot be increased.
- Exposure-maintenance (density) formula
- new mAs = old mAs × (new SID² / old SID²). Going 40→80 inch SID needs 4× the mAs.
- Cumulative occupational dose limit
- 10 mSv × the worker's age in years (NCRP-116).
- OSL dosimeter
- Optically stimulated luminescence badge — the current standard personnel monitor; accurate and re-readable.
- Film badge vs TLD vs pocket dosimeter
- Film badge (older), TLD (thermoluminescent), and pocket dosimeter (instant reading) are alternative personnel monitors; OSL is now standard.
- Where to wear the dosimeter in fluoroscopy
- At collar level on the outside of the lead apron.
- Fetal monitoring badge
- A declared-pregnant worker wears a second badge at waist level under the lead apron to monitor fetal dose.
- Collimation
- Restricting the beam to the area of interest; reduces patient dose and scatter and improves contrast.
- Filtration purpose
- Aluminum removes low-energy photons that would only add patient skin dose, hardening the beam.
- Minimum total filtration
- 2.5 mm aluminum equivalent for tubes operating above 70 kVp (21 CFR 1020.30).
- Lead apron thickness
- Typically 0.5 mm lead equivalent for protective aprons.
- Inherent vs added filtration
- Inherent = filtration built into the tube/housing. Added = the aluminum sheet plus the collimator mirror; the two sum to total filtration.
- Primary vs secondary (scatter) radiation
- Primary = the useful beam from the tube. Secondary/scatter = radiation deflected by the patient — the main staff hazard.
- Biggest source of operator dose
- Scatter radiation from the patient, especially during fluoroscopy and mobile/portable exams.
- Repeat exposures and dose
- Every repeat doubles patient dose; correct one cause at a time and avoid unnecessary repeats (ALARA).
- Gonadal/patient shielding (current stance)
- Contact/area shielding of patients is now applied per current facility and professional-society policy rather than routinely for every exam.
- Control booth barrier
- A fixed protective barrier (often leaded glass) behind which the operator stands to make the exposure.
- Radiographic contrast — primary control
- kVp. Higher kVp = lower (longer-scale) contrast with more shades of gray.
- Receptor exposure (density) — primary control
- mAs, which is directly proportional to receptor exposure.
- Short scale vs long scale contrast
- Short scale = high contrast, few densities (low kVp). Long scale = low contrast, many densities (high kVp).
- Spatial resolution
- The ability to image small, closely spaced structures (detail/sharpness). Best with a small focal spot, long SID, and short OID.
- Signal-to-noise ratio (SNR)
- The ratio of useful image signal to noise; raising mAs increases SNR (cleaner image) but adds dose.
- When is a grid used?
- For body parts thicker than about 10 cm or exposures above roughly 60 kVp, where scatter is significant.
- Grid ratio
- Height of the lead strips ÷ the distance between them. Higher ratios remove more scatter but need more exposure.
- Bucky factor
- The factor by which exposure must increase when a grid is used, to compensate for primary beam the grid absorbs.
- Air-gap technique
- Increasing OID so scatter misses the receptor — an alternative to a grid that reduces scatter (but increases magnification).
- Magnification factor
- MF = SID / SOD (also image size ÷ object size), where SOD = SID − OID.
- Minimize magnification
- Keep the part close to the receptor (low OID) and use a long SID.
- Size vs shape distortion
- Size distortion (magnification) comes from distance. Shape distortion (foreshortening/elongation) comes from tube–part–receptor alignment.
- Penumbra
- The blurred, unsharp edge of a structure; reduced by a small focal spot, long SID, and short OID.
- Computed radiography (CR)
- Uses a photostimulable phosphor imaging plate that is scanned by a separate reader after exposure.
- Digital radiography (DR)
- Uses a flat-panel detector that sends the image directly and immediately — no cassette to process.
- Exposure index (EI)
- A number reported by digital systems indicating the radiation exposure the receptor received.
- Deviation index (DI)
- How far the actual exposure deviated from target: near 0 = correct, positive = overexposed, negative = underexposed.
- Histogram (digital)
- A graph of the pixel-value distribution the system uses to apply the look-up table (LUT) and render the image.
- Why digital can mask exposure errors
- Processing rescales the image to look correct, so EI/DI — not appearance — is how you confirm an ALARA-appropriate dose.
- Detective quantum efficiency (DQE)
- How efficiently a detector converts incident x-rays into image signal; higher DQE = better image at lower dose.
- Common digital artifacts
- Ghosting/lag, dead pixels, grid-line (moiré) artifact, and dust/scratch artifacts on CR plates.
- Off-level grid cutoff
- Tube angled across the lead strips → uniform underexposure (overall light image).
- Off-center grid cutoff
- Central ray laterally off the grid midline → uniform underexposure.
- Off-focus grid cutoff
- SID outside the focused grid's focal range → cutoff toward the periphery (light edges).
- Upside-down focused grid
- Strips angle the wrong way → severe peripheral cutoff with a light band at the sides.
- X-ray tube cathode
- The negative side: filament + focusing cup; emits electrons by thermionic emission and focuses them at the anode.
- X-ray tube anode
- The positive side: the angled tungsten target the electrons strike, where x-rays (and heat) are produced.
- Effective vs actual focal spot
- By line focus, the effective (projected) focal spot is smaller than the actual focal spot where electrons land.
- Small vs large focal spot
- Small focal spot = sharper detail but limited heat loading. Large focal spot = higher techniques but less sharpness.
- Anode angle and the heel effect
- A steeper (smaller) anode angle gives a smaller effective focal spot but a more pronounced anode heel effect.
- Using the heel effect
- Place the thicker/denser anatomy toward the cathode (more intense) side — e.g., the thoracic spine with the abdomen at the cathode.
- Rectification
- Converting alternating current to the unidirectional current the x-ray tube requires.
- Voltage ripple by generator
- Single-phase = high ripple, three-phase = lower, high-frequency = lowest ripple (near-constant potential), most efficient output.
- High-frequency generator
- The current standard: lowest ripple, most consistent and efficient x-ray output, compact design.
- Automatic exposure control (AEC)
- Ion chambers behind the receptor that terminate the exposure once a preset receptor exposure is reached.
- AEC backup timer
- A safety limit on the maximum exposure time/mAs in case the AEC fails to terminate.
- AEC positioning rule
- Center the anatomy of interest over the active AEC cell(s); off-centering causes incorrect exposure.
- kVp accuracy test
- A QC test confirming the actual tube kVp matches the selected value within tolerance.
- Reproducibility (QC)
- The same exposure technique produces the same output every time.
- Linearity (QC)
- Output (mGy/mAs) stays proportional and consistent across the different mA stations.
- Half-value layer (HVL)
- The thickness of aluminum that reduces beam intensity to half; a measure of beam quality and adequate filtration.
- Beam–light field alignment
- A QC test ensuring the light field matches the actual x-ray field within tolerance (±2% of SID).
- Focusing cup
- The negatively charged cup around the filament that narrows the electron stream onto the focal spot.
- Tube heat units
- A measure of heat load on the anode; high-frequency generators produce more heat per technique, limited by the tube rating chart.
- Rotating anode purpose
- Spreads heat over a larger track so the tube can tolerate higher exposures than a stationary anode.
- Projection vs position
- Projection = the path of the central ray through the body (AP, PA, oblique). Position = the patient's body placement (lateral, decubitus).
- Central ray (CR)
- The most central, least divergent portion of the beam; centered and angled to the part and receptor to minimize distortion.
- AP vs PA projection
- AP: beam enters anterior, exits posterior. PA: beam enters posterior, exits anterior (used for the routine chest).
- Sthenic habitus
- The average body type (~50% of patients); the reference for standard positioning and technique.
- Hypersthenic habitus
- Massive, broad build (~5%); organs sit high and horizontal — wide thorax and abdomen.
- Asthenic habitus
- Very slender, frail build (~10%); organs sit low and very vertical (long and narrow).
- Hyposthenic habitus
- Slender, lighter build (~35%); organs slightly lower and more vertical than sthenic.
- PA chest SID
- 72 inches (180 cm) to minimize heart magnification.
- PA chest technique
- Upright, full inspiration (suspend on the 2nd breath), scapulae rolled off the lung fields, no rotation; CR to T7.
- Lateral chest
- Left lateral (left side to receptor) to minimize heart magnification; arms raised, CR to T7.
- Why upright chest on inspiration?
- Upright shows air–fluid levels and lets the diaphragm drop; full inspiration expands the lungs for maximal aeration.
- Abdomen KUB
- AP supine projection of kidneys, ureters, and bladder; CR perpendicular to the iliac crest, exposure on expiration.
- Upright abdomen
- Shows air–fluid levels and free air under the diaphragm; CR ~2 inches above the iliac crest to include the diaphragm.
- Routine extremity series
- Three projections: AP/PA, oblique, and lateral, with the part close to the receptor and a small focal spot.
- Ankle mortise
- AP oblique with the leg/foot internally rotated 15–20° to open the mortise joint evenly.
- Scaphoid (navicular) projection
- A special wrist view (ulnar deviation / Stecher method) to better demonstrate the scaphoid for suspected fracture.
- AP axial cervical spine
- Central ray angled 15–20° cephalad to open the intervertebral disk spaces.
- Open-mouth (odontoid) projection
- Shows C1–C2 (the dens); CR perpendicular between the upper and lower incisors with the mouth open.
- Cervical obliques
- 45° rotation; AP obliques (CR 15° cephalad) open the intervertebral foramina on the side farthest from the receptor.
- Lumbar obliques — 'Scottie dog'
- 45° rotation demonstrates the zygapophyseal joints; the 'Scottie dog' appearance — neck = pars interarticularis.
- AP pelvis foot position
- Internally rotate the feet/legs 15–20° to overcome femoral-neck anteversion and show the necks in profile.
- AP pelvis with suspected hip fracture
- Do NOT rotate the legs — rotation could displace the fracture; image as-is.
- Skull positioning lines OML & IOML
- Orbitomeatal line (outer canthus → EAM) and infraorbitomeatal line (inferior orbit → EAM); OML is ~7–8° steeper than IOML.
- Waters projection
- A PA axial facial-bone/sinus view that projects the petrous ridges below the maxillary sinuses.
- Towne projection
- An AP axial skull view (CR 30° caudad to OML) demonstrating the occipital bone and foramen magnum.
- Caldwell projection
- A PA axial skull/sinus view (CR 15° caudad) demonstrating the frontal bone and ethmoid sinuses.
- Lateral decubitus position
- Patient lies on their side with a horizontal beam; shows air–fluid levels and free air (e.g., left lateral decubitus abdomen).
- Knee AP routine
- AP with CR 0–5° cephalad (varies with the patient's pelvis-to-tabletop measurement) to open the joint.
- Shoulder external vs internal rotation
- External rotation = true AP (greater tubercle in profile). Internal rotation = lateral humerus (lesser tubercle in profile).
- Hand PA, oblique, lateral
- PA (CR to 3rd MCP), 45° oblique (fingers separated), and lateral 'fan' to assess fractures and foreign bodies.
- Foot AP axial
- Dorsoplantar with CR 10° toward the heel (posteriorly) to open the tarsometatarsal joints.
- Why mark images with R/L
- Anatomical side markers are a legal requirement and prevent wrong-side errors; place them within the collimated field.
- Lateral lumbar spine CR
- CR perpendicular to the level of interest (often L3 / iliac crest); a small caudal angle may be needed if the spine sags.
- Why PA (not AP) routine chest
- PA reduces heart magnification (heart is closer to the receptor) and reduces breast/thyroid dose.
- Decubitus marker rule
- Always mark which side is up and use a horizontal beam, so free air and air–fluid levels are demonstrated.
- Respondeat superior
- 'Let the master answer' — the employer can be held legally liable for the negligent acts of an employee performed within the scope of employment.
- Res ipsa loquitur
- 'The thing speaks for itself' — negligence is obvious from the circumstances (e.g., a retained foreign object).
- Implied vs informed consent
- Implied consent is assumed in an emergency when the patient can't respond. Informed consent requires the physician to explain risks, benefits, and alternatives.
- Patient Care Partnership
- The AHA document (formerly the Patients' Bill of Rights) outlining what patients should expect: privacy, information, involvement in care, and respect.
- Chain of infection
- Pathogen → reservoir → portal of exit → mode of transmission → portal of entry → susceptible host. Break any link to stop spread.
- Reverse (neutropenic) isolation
- Protective isolation that shields an immunocompromised patient FROM the environment, rather than protecting others from the patient.
- Hand hygiene — most important
- Hand hygiene is the single most effective way to prevent the spread of infection.
- Extravasation (contrast)
- Contrast leaking into the tissues around the IV instead of the vein; stop the injection, elevate, and apply cold/warm compresses per protocol.
- Document after contrast
- Record the contrast agent, dose/amount, route, site, time, and any reaction.
- Renal labs before iodinated contrast
- BUN, creatinine, and eGFR — to assess kidney function and the risk of contrast-induced nephropathy.
- Manipulating digital image data — ethics
- Improperly altering exposure indicators or cropping/masking anatomy to hide error is an ARRT ethics violation.
- Fowler's position
- Semi-sitting (head of bed elevated ~45–60°); eases breathing for patients in respiratory distress.
- Continuous vs discrete x-ray spectrum
- Bremsstrahlung gives a continuous spectrum (0 up to peak kVp); characteristic radiation gives discrete energies specific to the target.
- Tungsten target
- Tungsten (Z=74) is the standard anode target — high atomic number (efficient x-ray production) and high melting point (heat tolerance).
- kVp and characteristic radiation
- Tungsten K-characteristic x-rays only appear above about 70 kVp, because the K-shell binding energy is ~69.5 keV.
- Photoelectric probability
- Increases with the cube of atomic number and decreases sharply with photon energy (roughly Z³/E³); dominant at low diagnostic energies.
- Compton and atomic number
- Compton scatter is essentially independent of atomic number (it depends on electron/tissue density) and dominates across most of the diagnostic range.
- Coherent (classical) scatter
- A low-energy interaction in which the photon changes direction without losing energy; a minor contributor to image fog at low kVp.
- Air kerma
- Kinetic energy released per unit mass of air, measured in gray; the modern quantity that replaces the roentgen for exposure.
- Direct vs indirect DNA damage
- Direct: radiation ionizes DNA itself. Indirect: radiation ionizes water into free radicals that then damage DNA — the more common path in tissue.
- Most radiosensitive blood cell
- The lymphocyte — highly radiosensitive and an early indicator of radiation exposure, even though it is not actively dividing.
- Genetic vs somatic effects
- Genetic (heritable) effects occur in reproductive cells and affect offspring; somatic effects occur in the exposed individual's other body cells.
- Tissue weighting factor
- A factor applied to each organ's dose to reflect its relative radiosensitivity when calculating whole-body effective dose.
- Threshold dose
- The minimum dose required to produce a deterministic effect; below it, the effect does not occur.
- Dose limits are ceilings, not targets
- Regulatory dose limits are maximums; ALARA still requires keeping actual dose well below them.
- Primary protective barrier
- A barrier in the path of the useful (primary) beam (e.g., the wall the beam points at); thicker than a secondary barrier.
- Secondary protective barrier
- A barrier protecting against leakage and scatter radiation only (e.g., the control-booth barrier); thinner than a primary barrier.
- Leakage radiation limit
- Radiation escaping the tube housing must not exceed 100 mR/hr at 1 meter.
- Pregnant worker — declaration
- Declaration of pregnancy is voluntary and in writing; it activates the 0.5 mSv/month and 5 mSv gestational fetal limits and a second monitoring badge.
- 10-day rule (historical)
- An obsolete rule that elective abdominal/pelvic exams of childbearing-age women be done within 10 days of menses onset; replaced by pregnancy-status screening.
- Effective dose
- A whole-body dose estimate that weights each organ's dose by its radiosensitivity; used to compare risk across different exposures.
- Image gently / image wisely
- Campaigns promoting dose optimization — Image Gently for pediatrics and Image Wisely for adults.
- Why collimation improves contrast
- A smaller field produces less scatter radiation, and less scatter means higher image contrast — as well as lower patient dose.
- HVL and beam quality
- A higher half-value layer means a 'harder,' more penetrating beam and confirms adequate filtration.
- Gonadal shielding — why moved away
- Surface shields don't block internal scatter (the main out-of-field dose), can trigger the AEC to raise dose, and may obscure anatomy and cause repeats.
- Skin entrance dose and SID
- A longer source-to-skin distance lowers patient skin entrance dose, which is why a minimum SSD is enforced (e.g., for fluoroscopy and mobile units).
- Long-scale vs short-scale contrast factor
- kVp is the controlling factor: high kVp = long scale (low contrast, many grays); low kVp = short scale (high contrast).
- Dose creep
- Gradual overexposure on digital systems because images still look acceptable; the deviation index (DI) detects it.
- Spatial resolution factors
- Improved by a small focal spot, long SID, and short OID; degraded by motion, large focal spot, and increased OID.
- Motion — the enemy of detail
- Patient motion is the most common cause of unsharpness; reduce it with short exposure times, clear instructions, and immobilization.
- Reciprocity in mAs
- Different mA and time combinations that give the same mAs produce the same receptor exposure (e.g., 200 mA × 0.1 s = 100 mA × 0.2 s = 20 mAs).
- Grid frequency
- The number of grid lines per inch (or cm); higher frequency grids are less visible on the image.
- Air-gap technique trade-off
- Increasing OID lets scatter miss the receptor (an alternative to a grid) but increases magnification — so a longer SID is used to compensate.
- Window width and window level
- Post-processing controls: window width adjusts displayed contrast; window level adjusts displayed brightness.
- Look-up table (LUT)
- A processing map that converts raw detector values into the displayed brightness/contrast appropriate for the body part.
- Bit depth / contrast resolution
- The number of shades of gray a system can display; higher bit depth gives finer contrast resolution.
- Histogram-analysis error
- If the system mis-identifies the data of interest (wrong body part menu, collimation error), the image can be too dark or too light despite correct technique.
- Moiré artifact
- A wavy grid-line pattern from a stationary grid whose frequency interferes with the CR scanning frequency.
- Thermionic emission depends on
- Filament current (mA): more heating current boils off more electrons, raising the tube current and the quantity of x-rays.
- Space charge effect
- The cloud of electrons around the filament that limits how many more electrons can be emitted at low kVp.
- Rotating anode purpose
- Spreads the heat of the electron stream over a large focal track so the tube tolerates higher exposures without melting.
- Half-wave vs full-wave rectification
- Half-wave uses only the positive half of the AC cycle (wasteful); full-wave flips the negative half to also produce x-rays (more efficient).
- AEC density controls
- Buttons (e.g., −2 to +2) that adjust the preset receptor exposure up or down from the default to fine-tune image brightness.
- AEC minimum response time
- The shortest exposure the AEC can produce; very thin parts may overexpose if their needed exposure is below it.
- Exposure linearity test
- Confirms that output (mGy per mAs) stays consistent and proportional as you change between mA stations.
- Exposure reproducibility test
- Confirms that the same selected technique gives the same output every time it is repeated.
- Light-field / radiation-field alignment
- Must agree within ±2% of the SID; verifies the collimator light accurately shows where the beam will go.
- Monitor QC (GSDF)
- Display monitors are calibrated to the DICOM Grayscale Standard Display Function and checked for luminance and uniformity.
- Tube rating chart
- A chart showing the maximum safe combinations of kVp, mA, and time for a tube to prevent overheating/damage.
- LAO/RAO vs LPO/RPO
- Anterior obliques (LAO/RAO) place that anterior side closest to the IR; posterior obliques (LPO/RPO) place that posterior side closest to the IR.
- Radiographic view
- The body part as seen from the perspective of the image receptor (the opposite of the projection's entrance side).
- Recumbent / supine / prone
- Recumbent = lying down; supine = lying on the back (face up); prone = lying face down.
- Cervical obliques — foramina
- 45° obliques open the intervertebral foramina; posterior obliques (RPO/LPO) show the foramina farthest from the IR (CR 15° cephalad).
- Scottie dog parts
- On a lumbar oblique: ear = superior articular process, eye = pedicle, nose = transverse process, neck = pars interarticularis, front leg = inferior articular process.
- Lateral cervical SID
- A 60–72 inch (longer) SID is used for the lateral cervical spine to reduce magnification from the increased OID.
- AP open-mouth contraindication
- Defer the open-mouth (and any rotation) on a suspected unstable C-spine trauma; obtain a cross-table (horizontal-beam) lateral first.
- Frog-leg (modified Cleaves)
- A hip/pelvis projection with the knees flexed and abducted; shows the femoral heads/necks in a lateral profile (non-trauma only).
- Cross-table lateral hip
- A horizontal-beam lateral used for a suspected hip fracture, because the affected leg must not be moved.
- Grashey (AP oblique shoulder)
- Posterior oblique that opens the glenohumeral joint space, demonstrating it without bony overlap.
- Calcaneus axial (plantodorsal)
- CR angled 40° cephalad to the long axis of the foot to show the calcaneus without superimposition.
- Elbow lateral position
- Flex the elbow 90° with the humerus and forearm on the same plane; demonstrates the fat pads (a sign of effusion/fracture).
- PA chest rotation check
- The sternoclavicular joints should be symmetric and equidistant from the spine — asymmetry indicates rotation.
- Two-projection (90°) rule
- Most bony anatomy is imaged in at least two projections roughly 90° apart so fractures and alignment aren't missed.
- Why mark the image at exposure
- Anatomical R/L lead markers must be placed within the collimated field at the time of exposure — they are a legal record, not added later.
