Quick Answers
Straight, sourced answers to the ARRT questions students search most.
Every answer here is checked against an authoritative source: Bushong, Bontrager, NRC 10 CFR 20, FDA 21 CFR 1020.30, the ARRT Content Specifications, IAEA, CDC, and NCBI. No competitor links. No marketing fluff. Just the canonical answer with a citation.
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Patient Care
2 answers
Adult vs Pediatric Vital Signs (ARRT): The Full Comparison
Adult pulse 60-100, respiration 12-20, BP 120/80. Pediatric runs much higher: infants 100-160 bpm, 30-60 respiration. Canonical ARRT ranges.
Often misunderstoodGeriatric Patient Definition (ARRT): 65 Years and Beyond
ARRT defines geriatric as 65 or older with physical or cognitive impairment. CDC and AGS use 65. Key radiography considerations.
Safety
5 answers
Do Grids Reduce Patient Dose? No, They Increase It
Grids increase patient dose, not reduce it. mAs must rise by the grid conversion factor: 5:1=2x, 8:1=4x, 12:1=5x, 16:1=6x. ARRT canonical.
Regulatory clarificationEffective Dose from Dual Dosimeter Readings: The NCRP 122 Formula
Effective dose from collar and waist dosimeter readings uses NCRP 122 formula: E = 0.04 x collar + 1.5 x waist. Per NCRP Report 122, U.S. regulatory standard.
Often misunderstoodLead Apron Attenuation: 0.5 mm Pb Gives 75-88% at 75-100 kVp
A 0.5 mm Pb apron attenuates 75-88% of scatter at 75-100 kVp, not 95-99%. Only 1.0 mm Pb reaches 95-99%. Energy-dependent protection.
Fact checkSkin Erythema Threshold Doses: Early Transient vs Main
Early transient erythema: 2 Gy (200 rem). Main erythema: 6 Gy (600 rem). Temporary epilation: 3 Gy. Deterministic effects explained for ARRT prep.
Regulatory clarificationIs a Thyroid Shield Required for Fluoroscopy? (ARRT Answer)
Per NRC 10 CFR 20 and 21 CFR 1020.32, thyroid shields are NOT federally required for fluoroscopy. They are strongly recommended and must be available.
Image Production
15 answers
Which AEC Cell for Chest PA? Outside Cells, Not Center
For chest PA, use the two outside AEC cells over the lungs, not the center cell. Center cell over mediastinum overexposes lungs. ARRT answer.
Often misunderstoodCan Window/Level Reveal Hidden Detail? No, Only Remap What's There
Window/level only re-displays stored pixel data with different brightness/contrast. It cannot recover detail from under or overexposed regions. ARRT answer.
Often misunderstoodFilm vs Digital Spatial Resolution: Film Significantly Higher
Film achieves up to 10 lp/mm spatial resolution. Digital (DR/CR) typically achieves 2.5-5 lp/mm. Film is significantly better, not slightly.
Fact checkHigh Frequency Generator Heat Unit Multiplier: 1.45, Not 1.41 (ARRT)
The high-frequency generator heat unit multiplier is 1.45, not 1.41. The 1.41 value belongs to 3-phase 12-pulse. ARRT canonical, per Bushong.
Fact checkInherent vs Added Filtration: What's What (Collimator Mirror is Added)
Inherent filtration is the glass envelope, tube oil, and seal. The collimator mirror is added filtration, not inherent. ARRT canonical.
Critical clarificationIs Breathing Voluntary or Involuntary Motion? (ARRT Answer)
Breathing is voluntary motion because patients can hold their breath. Involuntary motion is peristalsis, heartbeat, and tremors. The fix depends on which type.
Often misunderstoodMost Common Cause of Repeat Exposures: Positioning Errors
Positioning errors are the most common cause of repeat radiographs (51-85%). Motion artifact is secondary. ARRT-verified canonical answer.
Often misunderstoodmAs vs kVp: What Each Controls (ARRT Radiography)
mAs controls beam quantity (intensity). kVp controls beam quality (penetration). The 15% rule: 15% kVp increase equals doubling mAs.
Critical clarificationPediatric AEC: Why It Underexposes (Not Overexposes)
Pediatric AEC underexposes when a small body doesn't fully cover the photocells. Uncovered cells receive raw radiation and terminate the exposure early.
Fact checkExposure Index by Vendor: Philips EI vs Siemens EXI (ARRT)
Philips uses EI. Siemens uses EXI. Fuji uses S-number. Agfa uses lgM. IEC 62494 defines a unified EI standard. Vendor exposure indices explained.
Fact checkTungsten Anode Melting Point: 3410°C (Why X-Ray Tubes Use It)
Tungsten melts at 3410°C (some sources cite 3422°C). The highest melting point of any metal makes it the only practical choice for x-ray tube anodes.
Critical clarificationWindow Level Direction: Does Higher Level Mean Brighter or Darker?
Higher window level makes the image appear darker, not brighter. Window width sets contrast, window level sets brightness midpoint. ARRT-canonical answer.
Critical clarificationHow to Read a Tube Rating Chart (ARRT): kVp, mA, Time Axes
Tube rating charts show maximum safe exposure combinations. Y-axis = kVp, X-axis = time (seconds), each curve = mA value. Below the curve is safe.
Fact checkX-Ray Filament Burnout: Vacuum Failure, Not Tungsten Evaporation
X-ray tube filament burnout is caused by vacuum deterioration (gassy tube), not tungsten evaporation. Evaporation causes arcing instead. ARRT-canonical answer.
Often misunderstoodX-Ray Production Efficiency: 99.8% Heat, 0.2% X-Rays
99.8% of electron energy at the anode converts to heat. Only 0.2% becomes x-rays. Canonical value per Bushong. Drives anode design and tube life.
Procedures
6 answers
AP Pelvis CR Centering: Midway Between ASIS and Pubic Symphysis
AP pelvis CR is centered midway between the ASIS and pubic symphysis (or 2 inches above pubic symphysis), not ASIS to ASIS. Bontrager-canonical positioning.
Critical clarificationAxiolateral Hip (Danelius-Miller): CR Enters Medial, Cassette Lateral
Axiolateral hip (Danelius-Miller): CR enters medially from the groin; cassette is lateral against the hip. Used in hip trauma when leg cannot rotate.
Fact checkAnkle Joint Classification: Hinge (Ginglymus) Joint
The ankle (talocrural) joint is a synovial hinge (ginglymus) joint that forms the ankle mortise and allows dorsiflexion and plantar flexion.
Fact checkBest Projection for the Sphenoid Sinus: SMV (Not Lateral)
The SMV (submentovertex/full basal) projection best demonstrates the sphenoid sinus, not the lateral. Caldwell for frontal, Waters for maxillary. Per Bontrager.
Fact checkSmallest Facial Bone? Lacrimal Bones, Not Nasal Bones
The lacrimal bones are the smallest of the 14 facial bones, not nasal bones. Why study materials get this wrong and the ARRT tests it.
Fact checkSternal Angle Vertebral Level: T4-T5, Not T3
Sternal angle (angle of Louis) lies at T4-T5 disc, not T3. Key landmark for chest positioning, 2nd rib, tracheal carina, aortic arch start.
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