Patient Care
13%of exam
Contrast MediaContrast SafetyReactionsInjection Technique
Safety
13%of exam
Radiation PhysicsDose MetricsDose ReductionPersonnel Protection
Image Production
32%of exam
Procedures
43%of exam
Quick Facts
- Exam
- ARRT CT
- Pathway
- Postprimary
- Total Questions
- 195 (165 scored)
- Test Time
- 195 minutes
- Pass Score
- Scaled 75
- Pass Rate
- 73.9% (2024)
- Fee
- $225 ARRT pathway
- Content Spec
- Eff. Sep 1 2026
- Provider
- Pearson VUE
Contrast Reaction Ladder
Mild -> Moderate -> Severe
Mild: hives, itchingModerate: bronchospasm, hypotensionSevere: anaphylactoid, arrest
Bolus Tracking vs Test Bolus
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
- 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
- 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
- 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
- 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
- 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
CTDIvol -> DLP -> SSDE
CTDIvol: per locationDLP: total exam doseSSDE: size-adjusted estimate
CTDIvol vs DLP
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
- 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
- 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
Photoelectric absorbs, Compton scatters
Photoelectric: full absorptionCompton: partial scatterBoth shape image contrast
CTDIvol vs SSDE
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
- CTDIvol
- Dose at scan locationmGy
- DLP
- Total dose across exammGy·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
- 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
Air -1000 | Water 0 | Bone +1000
Air: -1000 HUWater: 0 HUFat: -50 to -100Bone: +1000 HU+
kVp vs mAs
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
- 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
- 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
Below 1 overlap, above 1 spacing
Below 1: higher doseAt 1: contiguous dataAbove 1: faster, lower dose
Pitch Below vs Above 1
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
- 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
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
- 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
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
- 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
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
- 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
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
- 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
- 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
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
- 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
- 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
- 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
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