Diagnostic Radiographer cheat sheet

ALARA: occupational dose limit 20 mSv/year averaged over 5 years (100 mSv per 5 years), with no single year exceeding 50 mSv.

Public dose limit: 1 mSv/year effective dose; lens of eye equivalent dose limit 15 mSv/year for workers (ICRP 2011).

Effective dose E = Σ w_T · H_T, where w_T is tissue weighting factor and H_T is equivalent dose; H_T = w_R · D_T.

Radiation weighting factors w_R: photons and electrons = 1; protons = 2; alpha particles = 20; neutrons = 2.5–20 depending on energy.

Linear energy transfer (LET) is the energy deposited per unit path length; high-LET radiation (alpha, neutrons) has greater relative biological effectiveness (RBE) and higher oxygen enhancement ratio.

Law of Bergonié and Tribondeau: cells are most radiosensitive when undifferentiated, rapidly dividing, and have a long mitotic future (e.g., basal cells, lymphocytes, intestinal crypt cells).

Acute radiation syndrome thresholds: prodromal syndrome ~1 Gy, hematopoietic syndrome ~2–5 Gy, gastrointestinal syndrome ~5–12 Gy, cerebrovascular syndrome >20 Gy.

Inverse square law: intensity I₁/I₂ = (d₂/d₁)²; doubling distance from a point source reduces exposure to one quarter.

Half-value layer (HVL): thickness of material that reduces beam intensity to 50%; for diagnostic X-rays, typical HVL is 2.5–4 mm Al at 70–80 kVp.

X-ray tube cathode: tungsten filament thermionic emission; anode: tungsten-rhenium target with focal spot sizes; stationary anode for low-power, rotating anode for high-power applications.

Heel effect: X-ray intensity is lower on the anode side of the beam; place thicker body parts toward the cathode side to compensate.

Automatic exposure control (AEC) uses ionization chambers or solid-state detectors to terminate exposure when a preset receptor dose is reached; density controls adjust the reference signal.

Quality control tests: kVp accuracy ±5% or ±5 kVp; timer accuracy ±5% for times >10 ms; mAs linearity ±10%; exposure reproducibility ±5%; HVL within manufacturer specification.

Collimator alignment: X-ray field must coincide with light field to within 2% of source-to-image distance (SID) on each side.

Focal spot size measured by pinhole camera or star pattern; nominal focal spot sizes 0.6 mm and 1.2 mm common; small focal spot improves spatial resolution.

Digital detector calibration: flat-field (gain) calibration corrects for detector nonuniformity; bad pixel maps are generated during QC.

Processor QC: sensitometry for film processors measures speed, contrast, and base-plus-fog; base-plus-fog should not exceed 0.20 optical density.

Photoelectric effect dominates at low kVp (below ~50 keV) and in high-Z materials; it provides high subject contrast but increases patient dose.

Compton scatter dominates at higher kVp and in low-Z materials (soft tissue); scatter reduces contrast and increases fog.

Beam attenuation: I = I₀ e^(−μx), where μ is linear attenuation coefficient and x is thickness; half-value layer HVL = 0.693/μ.

Spatial resolution is limited by focal spot size, detector element (del) size, and motion; modulation transfer function (MTF) quantifies resolution performance.

Contrast resolution (low-contrast detectability) depends on noise, which is inversely proportional to the square root of the number of photons (quantum mottle).

Grid ratio = height of lead strips / distance between strips; higher grid ratio removes more scatter but requires higher mAs and precise centering.

Grid cutoff occurs when the central ray is not perpendicular to the grid or when the grid is used outside its focal range; it appears as a uniform or bilateral density loss.

Deviation index (DI) = actual exposure index (EI) − target EI; DI within ±3 is generally acceptable, indicating exposure within ~30% of optimal.

AP projection: central ray enters anterior and exits posterior; PA projection: enters posterior and exits anterior; lateral: enters side and exits opposite side.

Oblique positions are named by the side closest to the image receptor (e.g., RAO = right anterior oblique).

Chest radiography: PA erect at 180 cm (72 in) SID, 110–125 kVp, high mA with short exposure time; lateral at 180 cm with arms elevated.

Abdomen: supine AP (KUB) at 100 cm SID, 70–80 kVp; upright abdomen to demonstrate air-fluid levels and free air.

Cervical spine lateral: 180 cm SID, patient upright, chin slightly elevated; ensure all seven cervical vertebrae and C7-T1 junction are visible.

Lumbar spine AP: 100 cm SID, 75–85 kVp; lateral: 100 cm SID, patient in lateral recumbent or standing position with knees flexed.

Skull: PA (Caldwell) at 100 cm SID with 15° caudal tube angle; lateral at 100 cm SID with interpupillary line perpendicular to IR.

Extremity radiography: SID 100 cm; use small focal spot; collimate to include joint above and below the area of interest.

Informed consent must include the nature of the procedure, risks, benefits, alternatives, and the patient's right to refuse.

Universal precautions: treat all blood and body fluids as potentially infectious; use gloves, gown, mask, and eye protection as indicated.

Contrast media reactions: mild (nausea, flushing, urticaria) managed supportively; moderate (vomiting, bronchospasm) require antihistamines and monitoring; severe (anaphylaxis, laryngeal edema) require epinephrine and emergency response.

Metformin and iodinated contrast: withhold metformin for 48 hours after contrast in patients with renal impairment or at risk of lactic acidosis.

Pregnancy screening: ask all patients of childbearing age about last menstrual period and possibility of pregnancy; use lead shielding and optimize exposure.

Patient identification: use at least two identifiers (name and date of birth or medical record number) before every procedure.

Immobilization devices: sandbags, sponges, and tape reduce motion; use for pediatric and uncooperative patients.

Vital signs: normal adult heart rate 60–100 bpm, respiratory rate 12–20/min, blood pressure <120/80 mmHg, temperature 36.5–37.5°C.

Standard anatomical position: body erect, face forward, arms at sides with palms forward, feet parallel.

Anatomical planes: sagittal (divides left and right), coronal (divides anterior and posterior), transverse/axial (divides superior and inferior).

Body cavities: thoracic (heart, lungs, mediastinum), abdominal (liver, spleen, kidneys, intestines), pelvic (bladder, reproductive organs, rectum).

Vertebral column regions: cervical (7), thoracic (12), lumbar (5), sacral (5 fused), coccygeal (3–4 fused); total 33 vertebrae in adults.

Liver occupies right upper quadrant, extends across midline; spleen lies in left upper quadrant posterior to stomach.

Kidneys are retroperitoneal at T12–L3 level; right kidney slightly lower due to liver.

Cross-sectional CT: Hounsfield units (HU) = 1000 × (μ_tissue − μ_water) / μ_water; water = 0 HU, air = −1000 HU, bone = +1000 HU or higher.

Chest CT: mediastinal window (W ~350, L ~50 HU) for soft tissue; lung window (W ~1500, L ~−600 HU) for parenchyma.

X-ray production: bremsstrahlung (continuous spectrum from electron deceleration) and characteristic X-rays (discrete energies from electron shell transitions).

Maximum X-ray energy (keV) equals the kVp applied across the tube; the continuous spectrum has a maximum at approximately one-third to one-half of kVp.

mAs controls the quantity of X-rays (exposure); kVp controls the quality (penetrating power) and also affects quantity approximately as kVp².

Filtration: inherent filtration (glass envelope, oil) equivalent to ~0.5–1.0 mm Al; added filtration brings total to at least 2.5 mm Al for tubes operating above 70 kVp.

Half-life of common radionuclides: Tc-99m 6 hours, I-131 8 days, F-18 110 minutes, Mo-99 66 hours.

Radioactive decay: N = N₀ e^(−λt); activity A = λN; half-life T½ = 0.693/λ.

Electromagnetic spectrum: X-rays have wavelengths 0.01–10 nm and frequencies 3×10^16–3×10^19 Hz; they travel at the speed of light in a vacuum.

Photoelectric absorption cross-section increases with atomic number (Z³) and decreases with photon energy (1/E³).

ARRT Standards of Ethics: Code of Ethics (aspirational) and Rules of Ethics (enforceable); violations may result in sanctions, suspension, or revocation of certification.

Patient confidentiality: HIPAA Privacy Rule protects individually identifiable health information; minimum necessary standard applies to disclosures.

Informed consent is required for invasive procedures and research; documentation must be in the patient's record.

Scope of practice: radiographers must perform only procedures for which they are educationally prepared and legally authorized; state licensure may add requirements.

Radiation protection regulations: 10 CFR Part 20 (occupational dose limits), 21 CFR Part 1020 (performance standards for diagnostic X-ray systems), and state radiation control programs.

Continuing education: ARRT requires 24 credits every 2 years, including at least 12 in the discipline of certification and 1 credit in ethics.

Medical error reporting: report errors and near misses through institutional incident reporting systems; disclosure to patients is an ethical obligation.

Professional boundaries: avoid dual relationships, maintain patient dignity, and obtain consent before any physical contact or exposure.