You've done the work. Tonight is not about learning new material — it's about locking in
easy points, resting your brain, and walking in tomorrow with a plan. Read this once tonight and once
tomorrow morning. That's it.
01
Know exactly what you're walking into
230
Total questions
200
Scored
30
Unscored pilot
230 min
Test time (~1 min/Q)
75
Scaled score to pass
The 30 pilot questions are mixed in and look identical to scored ones —
so if a question feels bizarre or impossible, it may not even count. Answer it, let it go, move on.
Your full appointment is about 4 hours 10 minutes (tutorial, NDA, and survey take up the rest).
Procedures + Image Production = over half the exam. Positioning and
technique-factor questions are where prepared people win.
02
Tonight & tomorrow morning
No new material tonight. Cramming new content the night before trades sleep (which you need) for facts you won't retain. Review this sheet, then close the books.
Pack now, not tomorrow:two valid, unexpired forms of ID — your primary must be government-issued with your photo and signature, the second must be signed as well, and the names must match your ARRT record exactly.
Plan the drive. Know the route and parking. Arrive at least 30 minutes early — arriving 15+ minutes late can forfeit your appointment.
Sleep beats studying. A rested brain retrieves; a fried one freezes. Aim for a full night.
Morning: eat something real, skim this sheet once, and stop. Confidence is a skill — act like someone who's about to pass, because you are.
At the center: lockers are provided for personal items; you'll get an erasable noteboard. First thing after you're allowed to write, brain-dump your formulas onto the noteboard — then they're free for the rest of the exam.
At the test center
Everything goes in the locker. Phone, smartwatch, calculator, study guides, jacket/hoodie — and empty your pockets. Nothing personal comes into the exam room, so don't plan to reference anything.
Check-in photographs you and your ID. Smartwatches and jewelry or hairclips wider than ¼ inch aren't allowed — leave them at home.
18-minute tutorial, then a 2-minute window to accept the NDA. Miss that window and you forfeit the attempt — accept promptly, and don't write on your noteboard until after you do.
Breaks are allowed, but the clock keeps running — and leaving for more than 10 minutes triggers an incident report. Use the restroom before you start.
Noteboard & marker only — no scratch paper and no calculator, so do every calculation on the board. Raise your hand for a fresh one if you fill it.
Answer every question. There's no penalty for guessing and an unanswered item is scored wrong; you need a scaled 75 to pass.
Dress in layers for unpredictable room temperature. Any ADA accommodation (earplugs, extra time) must be pre-approved by ARRT with your application — the center can't grant it on the spot.
03
The test-taking game plan
RADAR — the method for every question
R
Read the question line first. The last sentence tells you what's actually being asked — read it before the story.
A
Anticipate the answer before you look at the options. If your answer is there, that's strong evidence it's right.
D
Define the concept. Name the topic being tested ("this is a 15% rule question"). Hard questions are just well-disguised easy ones — same method, thicker disguise.
A
Attack the options. Eliminate. Watch qualifiers (most, least, except, not), absolute words (always, never — usually wrong), and opposite pairs (the answer is often one of the two).
R
Review. Did you answer the question that was asked? Units right? Direction right (increase vs. decrease)?
Pacing & strategy rules
You have ~1 minute per question. Most take 30 seconds; that banks time for the hard ones. Check the on-screen timer at question 60, 115, and 170.
Never leave a question unanswered. There's no penalty for guessing — your score is purely the number correct. If unsure: guess, flag it, and return at the end.
Don't change answers without a concrete reason. "It felt wrong on review" is not a reason. "I misread 'except'" is.
Two-pass elimination on hard questions: kill the two options you know are wrong, then pick between the remaining two using the concept — a coin flip you've weighted to ~50%+ beats a blank stare at four options.
Read "EXCEPT / NOT / LEAST" twice. Half the "trick" questions on this exam are just a missed qualifier.
A weird question ≠ you're failing. It may be one of the 30 pilots. Answer and move on — momentum is worth more than certainty.
04
The formula sheet — brain-dump these
Technique & exposure
mAs
mAs = mA × time (s)
400 mA × 0.05 s = 20 mAs. mAs controls quantity (receptor exposure) only.
To keep exposure the same: raise kVp 15% → cut mAs in half; lower kVp 15% → double mAs. Example: 80 kVp @ 20 mAs → 92 kVp @ 10 mAs.
Inverse square law (intensity)
I1 / I2 = (D2)² / (D1)²
Double the distance → ¼ the intensity. Halve the distance → 4× the intensity. (Your single best radiation-protection tool.)
Exposure-maintenance (direct square) law
mAs2 = mAs1 × (D2)² / (D1)²
Changing SID and keeping receptor exposure: 40″ → 72″ means mAs × (72/40)² ≈ mAs × 3.24. Note it's the opposite direction of the inverse square law — distance up, mAs up.
Height of the lead strips ÷ distance between them. Higher ratio → more scatter cleanup, more patient dose, less positioning latitude.
Geometry & image size
Magnification factor
MF = SID / SOD · SOD = SID − OID
Image size = object size × MF. Example: SID 40″, OID 4″ → MF = 40/36 ≈ 1.11 → a 10 cm object images at ~11.1 cm.
Less magnification / better detail
↑ SID · ↓ OID · small focal spot
The recipe for sharpness, every time it's asked.
Physics & equipment
Transformer law
Vs / Vp = Ns / Np
Voltage changes with the turns ratio; current changes inversely (step-up transformer: voltage ↑, current ↓).
Ohm's law & power
V = I × R · P = I × V
Volts = amps × ohms; watts = amps × volts.
Unit conversions
1 Gy = 100 rad · 1 Sv = 100 rem · 1 rad = 10 mGy · 1 rem = 10 mSv
Gray = absorbed dose (D) · Sievert = equivalent/effective dose (H/E) · air kerma (Gy in air) has largely replaced the roentgen.
05
Numbers they love to ask
Dose limits (NCRP)
Limit
Value
Occupational — annual effective dose
50 mSv (5 rem)
Occupational — cumulative lifetime
10 mSv × age (1 rem × age)
Occupational — lens of eye (annual)
150 mSv(NCRP/ARRT answer; ICRP has since lowered it to 20 mSv/yr)
Occupational — skin, hands & feet (annual)
500 mSv
Public — annual effective dose
1 mSv frequent exposure · 5 mSv infrequent
Embryo/fetus (declared pregnancy)
0.5 mSv per month · 5 mSv total gestation
Student under 18
1 mSv per year
TrickOccupational limits are in tens/hundreds of mSv; public and fetal limits are single digits. If an option mixes those scales, it's wrong.
Equipment & fluoro regulations
Item
Value
Total filtration (operating above 70 kVp)
≥ 2.5 mm Al equivalent
Fluoro tabletop exposure rate — standard max
10 R/min (88 mGya/min)
Fluoro tabletop — high-level control (HLC) max
20 R/min (176 mGya/min), audible signal required
Fluoro cumulative timer alarm
5 minutes
Source-to-skin distance — fixed fluoro
≥ 38 cm (15″)
Source-to-skin distance — mobile fluoro
≥ 30 cm (12″)
Protective apron (fluoro)
≥ 0.25 mm Pb minimum (0.5 mm common practice)
Protective curtain & Bucky slot cover
0.25 mm Pb each
Leakage radiation limit (tube housing, 1 m)
≤ 100 mR/hr (~0.88 mGya/hr)
Standard SIDs
40″ (100 cm) table · 72″ (180 cm) chest
Patient-care vitals (adult norms)
Vital
Normal adult range
Temperature
98.6 °F (37 °C) — normal range ~97–99 °F (36.1–37.2 °C)
Pulse
60–100 bpm
Respirations
12–20 breaths/min
Blood pressure
<120 and <80 mm Hg (Stage 1 HTN ≥130/80, Stage 2 ≥140/90 — normal needs both low; hypertension is either value high. Older texts still teach 140/90.)
CPR compressions
30:2 compressions:breaths · 100–120/min · 2–2.4 in (5–6 cm) deep
06
Positioning easy wins
Decode the projection name — free points
The projection name tells you the beam path: first word = where the beam ENTERS, second word = where it EXITS (the IR side).
Mediolateral = enters medial, exits lateral → the lateral surface is against the IR (the routine lateral ankle and lateral calcaneus are mediolateral; the axial calcaneus is plantodorsal).
AP = posterior surface against IR. PA = anterior surface against IR (palm down for the hand/wrist).
If a question names a projection you've never heard of — decode it. It's an easy question in a disguise.
The oblique rules (the #1 trap zone)
Structure
Rule
Example
Cervical intervertebral foramina
Posterior obliques (AP) show the side FARTHEST from the IR; anterior obliques (PA) show the side CLOSEST
LPO → right foramina · RAO → right foramina
Lumbar zygapophyseal (facet) joints
Posterior obliques show the side CLOSEST to the IR
LPO → left joints (look for the "Scottie dog")
Sacroiliac joints
Posterior obliques show the UP side (farthest from IR)
RPO → left SI joint
TrickCervical and lumbar obliques are opposites: cervical foramina = far side, lumbar facets = near side. Nail that one contrast and you've disarmed the most common inversion trap on the exam.
Classic CR angles
Projection
CR
AP axial cervical spine
15–20° cephalad
AP axial skull (Towne)
30° caudad to OML (37° to IOML)
PA axial skull (Caldwell)
15° caudad, exits nasion
AP axial clavicle
15–30° cephalad
AP axial sacrum
15° cephalad
AP axial coccyx
10° caudad
AP axial L5–S1 junction
30–35° cephalad
TrickSacrum vs. coccyx: the sacrum curves back (angle up 15°), the coccyx curves forward (angle down 10°) — the CR follows the curve. AP axial angles on the skull are caudad; on the spine below it, mostly cephalad.
TrickkVp is the only common factor that changes beam quality AND quantity. mAs is quantity only. Filtration raises quality but lowers quantity.
08
Radiation biology quick hits
Stochastic effects: probability rises with dose, no threshold, severity independent of dose — cancer and genetic effects. This is what radiation protection (ALARA) is built around.
Deterministic effects:threshold exists, severity increases with dose — skin erythema, epilation, cataracts, and fetal malformation & growth effects. (Childhood cancer from prenatal exposure, by contrast, is stochastic — no threshold.)
Most radiosensitive cells: lymphocytes. Law of Bergonié & Tribondeau: sensitivity is highest in cells that are immature, undifferentiated, and rapidly dividing.
Most radiosensitive cell-cycle phase: mitosis (M); most resistant: late S.
Indirect effect dominates with diagnostic x-rays: the photon ionizes water (radiolysis), creating free radicals that then damage DNA. Direct action (photon hits DNA itself) is the minority pathway at diagnostic energies.
Whole-body lethality: the human LD50/60 ≈ 3.5 Gy (350 rad) — the dose killing half of those exposed within 60 days without medical support.
Three cardinal principles of protection:time, distance, shielding — and distance is the most powerful (inverse square law).
09
How wrong answers give themselves away
Absolutes are usually wrong. "Always," "never," "all," "none," "only" — one exception kills them, and medicine rarely deals in absolutes.
Two opposite options → one is usually the answer. When two choices are direct opposites (AP vs. PA, increase vs. decrease, cephalad vs. caudad), the test is making you choose between them. Spend your focus there.
The longest, most-qualified answer is often correct — the right choice frequently needs the extra clause to be fully true. A tiebreaker, not a law.
A number that's an order of magnitude off is a giveaway. If three options cluster and one is wildly larger or smaller, it's usually the trap, not the answer.
Grammar that doesn't fit the stem (a/an, singular/plural) quietly rules an option out.
Last thing before you close this.
You already know this material — that's why the questions above read like review, not revelation. Tomorrow isn't a test of whether you learned enough; it's a test of staying calm and working your method on 200 questions you're ready for.
Guess-flag-move when you're stuck. Trust your first instinct. Breathe when your mind blanks — it's nerves, not a gap, and the answer surfaces on the second read. Go earn it.