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ARRT CT Cheat Sheet

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Patient Care

  • 13% of exam
  • Contrast Media Contrast Safety Reactions Injection Technique

Safety

  • 13% of exam
  • Radiation Physics Dose Metrics Dose Reduction Personnel Protection

Image Production

  • 32% of exam
  • CT Components Acquisition Parameters Reconstruction Artifacts Image Quality

Procedures

  • 43% of exam
  • Head & Spine Neck & Chest Abdomen & Pelvis Vascular & Interventional

Quick Facts

  • Exam ARRT CT
  • Pathway Postprimary
  • Total Questions 195 (165 scored)
  • Test Time 195 minutes
  • Pass Score Scaled 75
  • Pass Rate 74.7% (2025)
  • Fee $225 ARRT pathway
  • Content Spec Eff. Sep 1 2026
  • Provider Pearson VUE

Contrast Reaction Ladder PA

  • Mild -> Moderate -> Severe
  • Mild: hives, itching Moderate: bronchospasm, hypotension Severe: anaphylactoid, arrest

Bolus Tracking vs Test Bolus PA

Bolus tracking

  • Monitors live ROI
  • Auto-triggers diagnostic scan
  • Used during real injection

Test bolus

  • Small preview injection
  • Measures time to peak
  • Given before diagnostic bolus
  • Live trigger vs preview

Contrast Protocol Picker PA

  • Suspected pulmonary embolism → CTPA bolus tracking ( Pulmonary artery ROI )
  • Suspected acute stroke → Noncontrast head CT ( Rule out bleed first )
  • Suspected renal colic → Noncontrast stone protocol ( Avoid contrast mimicry )
  • Characterize liver lesion → Triple-phase liver CT ( Arterial, portal, delayed )
  • Suspected interstitial lung disease → Prone HRCT ( Fibrosis vs atelectasis )
  • High lung-cancer risk → Low-dose screening CT ( Lung-RADS scoring )

Contrast Media Types PA

  • Nonionic Standard low-osmolar contrast
  • Ionic Higher osmolality, older type
  • Barium sulfate GI tract contrast
  • Water-soluble IV or oral iodinated
  • Osmolarity Reaction-risk factor
  • Air Colonography bowel distension

Contrast Safety Checks PA

  • eGFR Renal function check
  • Metformin Hold if renal impaired
  • Prior reaction Triggers premedication protocol
  • Pregnancy Risk-benefit review
  • Lactation Feeding usually continues
  • hCG Pregnancy screening lab

Contrast Reaction Levels PA

  • Mild Hives, itching, nausea
  • Moderate Bronchospasm, hypotension
  • Severe Anaphylactoid, cardiac arrest
  • Nephrotoxicity Delayed kidney complication
  • Extravasation Contrast leaks into tissue
  • Treatment Steroids, antihistamine, epinephrine

Injection & Bolus Technique PA

  • Power injector Controlled flow rate
  • Single-phase One constant flow rate
  • Multiphase Variable flow rate
  • Bolus tracking Live ROI auto-trigger
  • Test bolus Small timing preview
  • Scan delay Fixed post-injection wait

Dose Metric Order SA

  • CTDIvol -> DLP -> SSDE
  • CTDIvol: per location DLP: total exam dose SSDE: size-adjusted estimate

CTDIvol vs DLP SA

CTDIvol

  • Dose at one location
  • Measured in mGy
  • Based on standard phantom

DLP

  • Total dose across exam
  • Measured in mGy·cm
  • CTDIvol times scan length
  • Point dose vs total dose

Dose Reduction Tool Picker SA

  • Variable patient thickness → Tube current modulation ( Auto mA adjustment )
  • Noisy low-dose images → Iterative reconstruction ( Reduces image noise )
  • Need faster coverage → Pitch above one ( Lower relative dose )
  • Cardiac motion control → ECG gating ( Prospective preferred )
  • Track cumulative exam dose → CTDIvol and DLP ( Location and total )
  • Adjust dose for size → SSDE calculation ( Uses patient diameter )

Radiation Physics Basics SA

  • Bremsstrahlung Braking radiation, most x-rays
  • Characteristic Electron shell interaction
  • Photoelectric Full photon absorption
  • Compton Partial scatter interaction
  • Inverse square law Intensity drops with distance
  • Attenuation Depends on tissue density

Photon Interaction Pair SA

  • Photoelectric absorbs, Compton scatters
  • Photoelectric: full absorption Compton: partial scatter Both shape image contrast

CTDIvol vs SSDE SA

CTDIvol

  • Uses standard phantom size
  • Same for all patients
  • Console-displayed value

SSDE

  • Uses patient's actual size
  • Adjusted per individual
  • More accurate estimate
  • Standard vs personalized dose

Dose Measurement Units SA

  • CTDIvol Dose at scan location mGy
  • DLP Total dose across exam mGy·cm
  • SSDE Size-adjusted dose estimate
  • Absorbed dose Measured in mGy
  • Effective dose Measured in mSv
  • SI units Primary CT dose units

Dose Reduction Techniques SA

  • Tube current modulation Auto-adjusts mA
  • Iterative reconstruction Lower noise, lower dose
  • Pitch above 1 Faster, lower dose
  • Collimation Matches beam to anatomy
  • Shielding Lead apron protection
  • Gating Times cardiac dose

HU Reference Points IM

  • Air -1000 | Water 0 | Bone +1000
  • Air: -1000 HU Water: 0 HU Fat: -50 to -100 Bone: +1000 HU+

kVp vs mAs IM

kVp

  • Controls beam energy
  • Affects penetration and contrast
  • Raise for larger patients

mAs

  • Controls photon quantity
  • Mainly affects image noise
  • Raise mainly reduces noise
  • Energy vs quantity

Artifact Fix Picker IM

  • Streaks between dense bones → Beam-hardening correction ( Or raise kVp )
  • Metal implant present → MAR algorithm ( Metal artifact reduction )
  • Patient movement blur → Faster scan or gating ( Not a kVp fix )
  • Circular pattern on image → Detector recalibration ( Equipment issue, not patient )
  • Small lesion looks blurred → Thinner slice thickness ( Trades noise for detail )

CT Unit Components IM

  • Gantry Houses tube and detectors
  • Slip rings Enable continuous rotation
  • DAS Digitizes detector signal
  • Generator Powers the x-ray tube
  • Detectors Convert photons to signal

Pitch Rule IM

  • Below 1 overlap, above 1 spacing
  • Below 1: higher dose At 1: contiguous data Above 1: faster, lower dose

Pitch Below vs Above 1 IM

Pitch below 1

  • Overlapping helical data
  • Higher patient dose
  • Better spatial resolution

Pitch above 1

  • Wider helical spacing
  • Lower relative dose
  • Faster table coverage
  • Overlap vs speed

Acquisition Parameters IM

  • kVp Beam energy, penetration
  • mAs Photon quantity, noise
  • Pitch Table feed per rotation
  • Collimation Total beam width
  • SFOV Scan field of view
  • Slice thickness Z-axis resolution

Beam Hardening vs Metal Artifact IM

Beam hardening

  • Caused by dense tissue
  • Dark streaks or cupping
  • Corrected with algorithms or kVp

Metal artifact

  • Caused by metal implants
  • Bright and dark streaking
  • Corrected with MAR algorithms
  • Tissue cause vs metal cause

Reconstruction & Postprocessing IM

  • Filtered back projection Traditional reconstruction method
  • Iterative Reduces noise per dose
  • Reconstruction interval Overlap spacing, no dose
  • MPR Multiplanar reformatted images
  • MIP Max intensity projection
  • Isotropic voxels Equal x, y, z size

Motion vs Ring Artifact IM

Motion artifact

  • Caused by patient movement
  • Blur or streak pattern
  • Fixed by speed or gating

Ring artifact

  • Caused by detector fault
  • Circular pattern on image
  • Fixed by recalibration
  • Patient cause vs equipment cause

Artifact Recognition IM

  • Beam hardening Dark streaks, cupping
  • Metal artifact Bright and dark streaking
  • Motion Blur from patient movement
  • Ring artifact Detector miscalibration circle
  • Partial volume Averaged mixed-tissue voxel

Reconstruction Interval vs Slice Thickness IM

Reconstruction interval

  • Spacing between displayed images
  • Can overlap freely
  • Adds no extra dose

Slice thickness

  • Set at acquisition time
  • Affects raw resolution
  • Affects noise per slice
  • Display spacing vs raw data

Image Quality Metrics IM

  • Spatial resolution Fine structural detail
  • Contrast resolution Density difference detection
  • Temporal resolution Freezes motion in time
  • Noise Grainy image appearance
  • HU Hounsfield unit scale
  • Window width Displayed contrast range

Prospective vs Retrospective Gating PR

Prospective gating

  • Triggers at one phase
  • Lower radiation dose
  • Less arrhythmia tolerance

Retrospective gating

  • Covers full cardiac cycle
  • Higher radiation dose
  • Allows functional data
  • Triggered vs continuous

Procedure Protocol Picker PR

  • Complex intra-articular fracture → Thin-slice CT with MPR ( Not first-line imaging )
  • Suspected aortic dissection → CTA root to femorals ( Full coverage required )
  • Peripheral arterial disease symptoms → Runoff CT angiography ( Bolus-timed table speed )
  • MRI unsafe with hardware → CT myelography ( Intrathecal contrast injection )
  • Deep bone or soft-tissue biopsy → CT-guided biopsy ( Real-time needle guidance )

Head, Spine & MSK PR

  • Noncontrast head CT Rules out hemorrhage first
  • Temporal bone CT Thin-slice bone kernel
  • C-spine trauma Thin axial, reformats
  • Postmyelogram Follows intrathecal injection
  • Postarthrogram Follows joint contrast injection

CTA vs CTV PR

CTA

  • Arterial-phase timing
  • Evaluates arteries
  • Earlier peak enhancement

CTV

  • Venous-phase timing
  • Evaluates veins
  • Later peak enhancement
  • Artery phase vs vein phase

Neck & Chest Procedures PR

  • CTPA Bolus-tracked pulmonary timing
  • HRCT Thin-slice, often prone
  • Coronary calcium score Prospective gated, noncontrast
  • Low-dose lung screening Lung-RADS classification
  • Cardiac CTA ECG-gated coronary study

Abdomen & Pelvis Procedures PR

  • Multiphase liver Arterial, portal, delayed
  • Renal stone protocol Noncontrast, low-dose
  • Urogram Excretory-phase kidney timing
  • CT colonography Insufflation, two positions
  • Appendicitis CT IV contrast standard

Vascular & Interventional PR

  • Aortic CTA Root through femoral arteries
  • Runoff CTA Bolus-timed leg coverage
  • CT-guided biopsy Real-time needle path
  • CT fluoroscopy Near real-time guidance
  • Percutaneous drainage Catheter to fluid collection

Common Traps

CTDIvol vs DLP

  • CTDIvol measures one location ≠ DLP measures total exam dose

Bolus Tracking vs Test Bolus

  • Tracking triggers the live scan ≠ Test bolus previews timing only

Beam Hardening vs Metal Artifact

  • Hardening comes from dense tissue ≠ Metal artifact comes from implants

Pitch Below vs Above One

  • Below one raises patient dose ≠ Above one lowers patient dose

Prospective vs Retrospective Gating

  • Prospective triggers a single phase ≠ Retrospective covers the full cycle

kVp vs mAs Effects

  • kVp mainly changes penetration ≠ mAs mainly changes image noise

CTA vs CTV Timing

  • CTA times the arterial phase ≠ CTV times the venous phase

Last Minute

  • 1. 195 total = 165 scored + 30 pilot
  • 2. Test time is 195 minutes
  • 3. Pass score = scaled 75 of 99
  • 4. Procedures = 43% of scored exam
  • 5. Image Production = 32% of exam
  • 6. Patient Care ties Safety at 13%
  • 7. CTDIvol = dose per scan location
  • 8. DLP = total dose for exam
  • 9. Pitch above one lowers dose
  • 10. Noncontrast head CT excludes hemorrhage first
  • 11. Renal stone CT skips IV contrast
  • 12. Three attempts allowed within three years
  • 13. Exam fee is $225 standard
  • 14. Supporting credential required before applying

ARRT Computed Tomography

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