ARRT Radiography cheat sheet

Normal adult vital signs: heart rate 60–100 beats/min, respirations 12–20/min, oral temperature 36.1–37.8 °C (97–100 °F), blood pressure below 120/80 mmHg.

Oxygen delivery: nasal cannula 1–6 L/min (24–44% FiO2), simple face mask 6–10 L/min (35–55%), nonrebreather mask 10–15 L/min (60–95%).

Orthopnea is difficulty breathing when supine, so the patient is imaged upright or semi-upright; dyspnea is labored breathing in any position.

Informed consent requires capacity, disclosure of risks/benefits/alternatives, comprehension, and voluntariness; the radiographer witnesses the signature but does not obtain consent.

Contrast premedication for a prior reactor: prednisone 50 mg by mouth at 13, 7, and 1 hour before injection, plus diphenhydramine 50 mg by mouth 1 hour before.

Transmission-based precautions: contact (gown and gloves), droplet (surgical mask, private room), airborne (N95 respirator, negative-pressure room, closed door).

Over-the-needle catheter gauges are inverse to size: 14–18 G for rapid fluid or power-injected contrast, 22–24 G for routine small-volume injections.

Extravasation response: stop the injection, disconnect tubing, elevate the limb, apply a compress per department policy, then document and monitor the site.

Surgical asepsis: a sterile field is contaminated by contact with its 1-inch outer border, the table edge, non-sterile persons, or any item held below waist level.

mAs controls receptor exposure (photon quantity); kVp controls contrast and penetrability. A 15% increase in kVp doubles receptor exposure, so halve the mAs.

Density maintenance formula: mAs1/mAs2 = (SID2/SID1)²; inverse square law: intensity is proportional to 1 divided by distance squared.

Heat units: HU = kVp × mA × seconds × waveform factor, where factor is 1.0 for single-phase full-wave and high-frequency, 1.35 for three-phase 6-pulse, 1.41 for 12-pulse.

Grid conversion factors (mAs multiplier): no grid 1, 5:1 = 2, 6:1 = 3, 8:1 = 4, 12:1 = 5, 16:1 = 6.

Anode heel effect: intensity is lower on the anode side of the beam, so the thicker portion of the anatomy is placed toward the cathode side.

Magnification factor = SID ÷ SOD; increasing object-to-image distance or decreasing SID enlarges the image and reduces recorded detail.

Minimum total filtration is 2.5 mm aluminum equivalent for units operating above 70 kVp; 0.5–1.5 mm Al equivalent for units limited to 70 kVp or less.

AEC uses ionization chambers to terminate exposure at a preset receptor dose; minimum response time sets the shortest possible exposure, and density controls shift the calibration ±.

Detector metrics: fill factor and DQE describe conversion efficiency, MTF describes resolution; collimating to the anatomy lowers scatter, raises contrast, and reduces patient dose.

Deviation index: DI = 10 log10(EI ÷ target EI); a DI within ±3 is acceptable, while a larger magnitude indicates over- or underexposure requiring review or repeat.

Quantum mottle (noise) is caused by too few photons reaching the receptor: low mAs, high speed class, excessive filtration, or excessive distance.

Spatial resolution improves with a small focal spot, short object-to-image distance, long SID, small pixel pitch, and patient immobilization.

Size distortion is caused by magnification; shape distortion is caused by misalignment of tube, part, and receptor, producing elongation or foreshortening.

Subject contrast depends on tissue thickness, density, and atomic number plus kVp and contrast medium; displayed contrast can be altered by post-processing.

Rotation on a PA chest: equidistant clavicular heads and symmetric sternoclavicular joints indicate no rotation; asymmetry indicates rotation.

Scatter production increases with higher kVp, larger field size, greater patient thickness, and no grid; scatter adds fog and lowers image contrast.

Adequacy criteria: anatomy of interest fully included, collimation visible, no motion, correct centering and rotation, adequate inspiration (9–10 posterior ribs on chest), exposure indicator in range.

CR histogram error occurs when the beam is not collimated to the anatomy of interest or when unexpected material is on the plate, shifting the values of interest and the exposure indicator.

PA chest: 72-inch (183 cm) SID, upright, chin elevated, shoulders rolled forward, centering at T7, exposure at the end of the second full inspiration.

Positioning levels: jugular notch T2–T3, sternal angle (angle of Louis) T4–T5, xiphoid process T9–T10, iliac crest L4–L5, ASIS S1–S2.

Barium sulfate is contraindicated when perforation or obstruction is suspected; a water-soluble iodinated agent (Gastrografin) is used instead.

Double-contrast barium enema: barium coats the mucosa while air distends the colon, demonstrating small polyps; contraindicated in toxic megacolon and suspected perforation.

Skull lines: OML runs from the outer canthus to the external auditory meatus; IOML runs from the infraorbital margin to the EAM; GAL runs from glabella to alveolar process.

Nonionic low-osmolar iodinated contrast has lower osmolality and chemotoxicity, produces fewer adverse reactions, and costs more than ionic agents.

Arthrography injects contrast, sometimes with air for double contrast, into a joint capsule; most commonly performed on the shoulder and knee.

Esophagram evaluates swallowing and esophageal motility; an upper GI series with barium evaluates the stomach and duodenum, typically with the patient NPO for 8 hours beforehand.

Dose limits (NCRP): occupational effective dose 50 mSv/yr (5 rem); lens of eye 150 mSv/yr; skin and extremities 500 mSv/yr; general public 1 mSv/yr; embryo-fetus 0.5 mSv in any month.

ALARA: exposures are kept as low as reasonably achievable by weighing dose reduction against the image quality needed for diagnosis.

Cardinal principles: minimize time, maximize distance (dose falls with the square of distance), and use shielding such as lead aprons and barriers.

Personnel monitoring: the whole-body dosimeter is worn at collar level outside the lead apron; a second badge worn under the apron estimates dose to the protected tissues.

Fluoroscopy: the cumulative timer alarms at 5 minutes of fluoroscopic exposure; last-image hold and pulsed fluoroscopy reduce patient and staff dose.

Collimation and added filtration reduce patient dose, whereas grids, higher mAs, and repeat exposures increase it.

Protective aprons and thyroid shields must be at least 0.5 mm lead equivalent, attenuating roughly 90% of scattered radiation at diagnostic energies.

Entrance skin exposure is highest at the skin surface and decreases with depth, while dose area product reflects the total radiation energy delivered to the patient.