FREE CT Study Guide 2026: The Complete ARRT CT Walkthrough

This free CT study guide walks through the highest-yield content the ARRT Computed Tomography (CT) post-primary certification exam tests, organized by the four official ARRT CT content categories — Patient Care, Safety, Image Production, and Procedures.^[1]

It is interactive, not a wall of text: every category has worked clinical scenarios, exposure- and contrast-timing tables, labeled diagrams, and built-in flashcards — taught to the post-primary CT-technologist standard the exam actually measures.

Read it category by category, then round out your prep with our practice questions and flashcards. The exam has 165 scored questions (plus 30 unscored pilot items) and a passing scaled score of 75.^[1] If you are still earning your primary credential, see our ARRT Radiography study guide first — CT is a specialty layered on top of it.

ARRT CT Exam Snapshot

Procedures is the largest category at 71 scored questions, followed by Image Production; together they are about three-quarters of the exam, so weight your study there. Patient Care and Safety are smaller but rule-based, making them some of the easiest points to bank.^[1] The counts below reflect the current specifications in effect through August 31, 2026.

The percentages above are each category’s share of the 165 scored questions; the exam also includes 30 unscored pilot questions mixed in that do not count.^[1] SI units (gray, sievert; CTDIvol and DLP in mGy and mGy·cm) are the primary units of measurement on the exam.

How the ARRT CT Exam Is Built

The exam is built from ARRT’s published Computed Tomography Examination Content Specifications — the blueprint that lists exactly how many scored questions come from each category and sub-category. Every scored item maps to that outline, so studying by the blueprint is the most efficient path.^[1]

ARRT uses scaled scoring. Your raw number of correct answers is converted to a scaled score on a 1–99 range, where 75 is passing.

Scaling equates difficulty across the many exam versions, so two candidates who take slightly different forms are judged by the same standard. A 75 is therefore not “75% correct” — the raw correct needed varies by form, and there is no penalty for guessing.^[4]

This guide is organized into six study modules that map onto the four content categories: Patient Care; Safety (Radiation Safety & Dose); Image Production split into Image Formation and Image Evaluation & Quality (its two official sub-categories); and Procedures split into Head/Spine/Musculoskeletal and Neck/Chest/Abdomen/Pelvis (its three positioning sub-categories grouped into two teaching modules).^[1]

Patient Care

Patient Care is 21 scored questions (about 13% of the exam).^[1] For a CT technologist this category is dominated by iodinated contrast — screening, injecting, and recognizing and managing reactions — plus assessment, consent, time-out, and infection control.

Assessment, History & Lab Values

Before any contrast-enhanced CT, screen the patient. Confirm renal function with eGFR / creatinine, because impaired kidneys raise the risk of contrast-associated kidney injury.^[9]

Ask about a prior contrast reaction, asthma or allergies, and diabetes/metformin use. Metformin is renally cleared, so if contrast impairs kidney function it can accumulate and rarely cause lactic acidosis — manage it per ACR/FDA guidance.

Always verify pregnancy status before scanning a patient of childbearing potential. Other lab values (e.g., D-dimer, INR/PT/PTT, WBC, hCG) inform specific protocols and bleeding/biopsy risk.

Contrast Media & Injection

Iodinated contrast is positive (high-attenuation, bright) and is either ionic (high osmolality, more reactions) or nonionic (low osmolality, far better tolerated and standard for intravascular use).^[9] Barium sulfate is a separate positive oral/GI agent; neutral (water-density) oral contrast distends bowel for enterography; water-soluble iodinated oral contrast is used when GI perforation is suspected (never barium, which causes peritonitis if it leaks).

Contrast is usually delivered by a power injector. A single-head injector gives contrast only; a dual-head injector adds a saline flush to push the bolus and clear the line — tightening the bolus and reducing injection-site streak.

Set the flow rate and volume to the protocol, and match the IV gauge and placement to that flow rate (a high-flow CTA needs a larger-bore, well-seated antecubital IV) to limit extravasation risk. Bolus tracking and a timing bolus set the scan delay to peak enhancement.

Contrast Reactions & Emergencies

Grade reactions and respond. Mild (limited hives, nausea, flushing) → observe; moderate (diffuse urticaria, mild bronchospasm, vomiting) → treat and notify the physician; severe (laryngeal edema, anaphylaxis, cardiovascular collapse) → emergency response and epinephrine.^[9]

In every reaction the first action is the same: stop the injection, maintain IV access, assess airway-breathing-circulation, and call for help. Keep emergency equipment and a crash cart available wherever contrast is given.

Consent, Time-Out & Infection Control

Informed consent for contrast is obtained after the patient is told the risks, benefits, and alternatives; the technologist verifies it is documented. Perform a time-out to confirm the correct patient (two identifiers — e.g., name and date of birth, never room location), the correct procedure and protocol, and the correct site before scanning.^[10] Apply standard precautions to every patient (hand hygiene, PPE for body-fluid contact, aseptic IV technique, safe injection practice) and clean the table, gantry bore, and accessories between patients.

Safety & Radiation Protection

Safety (Radiation Safety & Dose) is 21 scored questions.^[1] CT delivers far more dose than radiography, so this category is about understanding the physics, measuring dose with the right metrics, and minimizing it for patients and staff.

Radiation Physics & Interactions

X-rays are produced in the tube by bremsstrahlung (an electron decelerated by the target nucleus — the dominant source) and characteristic radiation. Inside the patient, two interactions matter.^[6]

In the photoelectric effect the photon is totally absorbed (it builds contrast, depends on atomic number and lower energy, and adds patient dose), which is why iodine and bone appear bright. In Compton scatter the photon ejects an outer electron and continues deflected — this scatter degrades contrast and is the main occupational dose hazard to staff in the room.

The inverse square law governs distance: doubling your distance from the patient (the scatter source) cuts your dose to one quarter.

CT Dose Metrics: CTDIvol & DLP

Know the dose chain. CTDIvol (mGy) is the average dose within the scanned volume for one series, normalized for pitch — the per-scan value on the console. DLP (mGy·cm) = CTDIvol × scan length and reflects the total dose over the whole scan.

Effective dose (mSv) ≈ DLP × a region-specific k factor and estimates whole-body biological risk for comparing exams.^[6] Because DLP scales with scan length, scanning only the indicated anatomy lowers dose even at the same CTDIvol.

Dose-Reduction Techniques

ALARA drives CT technique.^[7] The biggest levers are tube current modulation (automatic mA by patient size/region), size-based protocols and appropriate kVp (lower kVp boosts iodine contrast and can lower dose), higher pitch, tight collimation, iterative reconstruction, limiting the scan range, and avoiding unnecessary multiphase scans.

Adaptive z-collimation reduces helical over-ranging dose. Dose notification/alert values warn the operator before a scan exceeds a facility limit.

Protecting Patients & Staff

Protect patients by justifying every exam, optimizing technique, shielding per current policy, and limiting repeats. Protect staff with the cardinal principles — time, distance (most effective), and shielding (lead aprons/barriers) — especially during CT-guided procedures and any in-room presence, where the patient is the scatter source.^[7]

Maintain controlled access to the scan room and keep occupational dose monitored. Adverse-event reporting (scanning errors, dose events, reactions) is part of the CT safety program and is emphasized in the updated content outline.^[5]

Image Production: Image Formation

Image Formation is the first half of Image Production — 30 scored questions, the single largest sub-category.^[1] It covers the CT machine, the parameters you set, how data are acquired and reconstructed, and how the data are post-processed.

Components of a CT Unit

In the gantry, the x-ray tube (cathode emits electrons; the rotating anode is the target) faces a detector array; a generator powers the tube, and slip rings transmit power/data to the continuously spinning gantry, enabling helical scanning.^[6] Multi-detector (MDCT) arrays acquire several slices per rotation.

The data acquisition system (DAS) digitizes the detector signal and passes projection data to the array processor and host computer. The bowtie filter equalizes beam intensity across the fan.

Imaging Parameters & Pitch

The operator sets kVp (beam energy/penetration; lower kVp raises iodine contrast), mAs (photon quantity — more mAs lowers noise but raises dose), collimation / beam width, acquisition slice thickness, the scan field of view (SFOV), and the pitch.^[1] Pitch is table travel per rotation ÷ total beam width: pitch > 1 spreads the beam (faster, lower dose, more noise); pitch < 1 overlaps it (more dose, lower noise).

Acquisition & Reconstruction

Data are acquired sequentially (axial step-and-shoot — the table is still during each rotation) or helically/volumetrically (continuous rotation while the table moves), with dual-energy / dual-source options.^[6] Reconstruction turns raw projection data into images: filtered back projection is fast but noisy at low dose, while iterative reconstruction lowers noise and enables lower-dose scanning. The reconstruction kernel (sharp vs. smooth), reconstruction slice thickness, and reconstruction interval (overlap) are chosen after acquisition — thin, overlapping slices improve reformations.

Post-Processing: MPR, MIP & 3D

Volumetric, ideally isotropic data can be reformatted without re-scanning. Multiplanar reformation (MPR) produces coronal, sagittal, or oblique planes; maximum intensity projection (MIP) highlights contrast-filled vessels for CT angiography; and 3D volume rendering (and the older shaded-surface display) shows surfaces and depth.^[6]

Quantitative tools measure distance, diameter, and calcium scoring. This is why CT routinely acquires thin, overlapping slices — it preserves the data for any reformation.

Image Production: Evaluation & Quality

Image Evaluation & Archiving is the second half of Image Production — 22 scored questions.^[1] It is about reading and judging the image: Hounsfield units and windowing, the components of image quality, recognizing artifacts, and quality assurance and informatics.

Hounsfield Units & Windowing

The Hounsfield unit is the standardized CT number for tissue attenuation, calibrated so water = 0 HU and air ≈ −1000 HU; dense bone is +1000 HU or more, fat about −100 to −50, and soft tissue +30 to +60.^[6] To display them, you choose a window: window width (WW) is the HU range shown as gray (it controls contrast), and window level (WL) is the window’s center HU (it controls brightness). The same data are re-windowed for lung, soft-tissue, and bone reading without re-scanning.

Image Quality: Resolution & Noise

Judge an image on four qualities. Spatial resolution (small high-contrast detail) improves with a smaller FOV, thinner slices, and sharp kernels.

Contrast resolution (distinguishing similar tissues) — CT’s strength — improves with higher mAs (less noise), smooth kernels, and lower kVp. Noise is mostly quantum mottle from too few photons (too low mAs); raising mAs or using iterative reconstruction reduces it.^[6]

Temporal resolution (speed) matters for cardiac imaging. A smaller display FOV spreads the same matrix over less anatomy, giving smaller pixels and higher displayed spatial resolution.

Artifact Recognition & Reduction

Recognize the common artifacts and their fixes.^[6] Beam hardening causes dark streaks/cupping (posterior fossa, around metal) — reduced by the bowtie filter, higher kVp, and iterative/MAR algorithms.

Metal artifact (streaks from implants) is reduced by higher kVp, MAR, and gantry angulation. Motion artifact (breathing, cardiac, peristalsis) is reduced by breath-hold, faster scans, gating, and immobilization.

Ring artifact signals a faulty/miscalibrated detector. Photon starvation streaks appear through thick regions (shoulders, hips). Partial volume averaging is reduced by thinner slices.

Quality Assurance & Informatics

Quality control keeps the scanner accurate: routine CT-number calibration (water must read 0 HU, air ≈ −1000 HU), noise/uniformity, slice-thickness, spatial/contrast-resolution, linearity, laser/alignment, and tube warm-up.^[6] On the informatics side, know PACS (image storage/distribution) and DICOM (the image standard), HIS/RIS/EMR/EHR information systems, security and confidentiality, teleradiology, and downtime procedures — the updated outline expands this section.^[5]

Procedures: Head, Spine & Musculoskeletal

Procedures is the largest category — 71 scored questions total across three sub-categories, of which Head, Spine & Musculoskeletal is 25.^[1] Every procedure question can probe cross-sectional anatomy, pathology, landmarks, vasculature, imaging planes, protocol/patient considerations, contrast, and post-processing — so learn each study’s indication, technique, and key anatomy.

Cross-Sectional Anatomy Basics

CT is read in the axial plane (plus MPR), so cross-sectional anatomy is the backbone of Procedures. Master the circle of Willis (the anterior/posterior cerebral, communicating, and internal carotid arteries; the two vertebral arteries join to form the basilar artery), the brain ventricles and lobes, the Couinaud liver segments, mediastinal great vessels, and abdominal vascular landmarks (e.g., the celiac trunk arises from the anterior aorta around T12–L1). Recognize structures on axial images and trace vessels across slices.

Head, Brain & Special Senses

For the head/brain, the first study in suspected acute stroke or headache with possible bleed is a non-contrast head CT — acute hemorrhage appears hyperdense (bright) (≈ 50–100 HU) and must be excluded before thrombolytics or any contrast study. CT perfusion then assesses ischemia: a markedly reduced cerebral blood volume marks the irreversible core, while prolonged transit time with preserved volume marks the salvageable penumbra.

Thin slices (≈ 1–2 mm) detect small intracranial lesions and reduce posterior-fossa beam hardening. Angle/reformat parallel to the orbitomeatal line to keep dose off the radiosensitive lenses. Sinuses are best shown on coronal reformats (ostiomeatal complex), and temporal bones need thin, high-resolution, bone-kernel imaging for the ossicles and inner ear.

Spine & Musculoskeletal

For the spine (cervical, thoracic, lumbosacral, post-myelogram), align the acquisition or reformations parallel to the intervertebral discs to optimize disc spaces and alignment; review with both a bone kernel (osseous detail) and a soft-tissue kernel/window (disc and thecal-sac detail).^[1] Musculoskeletal studies (upper/lower extremity, post-arthrogram, shoulder, bony pelvis, hip) use thin slices, bone kernels, and MPR/3D for complex fractures and joints. Dual-energy CT can differentiate uric acid from calcium crystals in gout.

Procedures: Neck, Chest, Abdomen & Pelvis

The other two Procedures sub-categories — Neck & Chest (22) and Abdomen & Pelvis (24) — together are 46 scored questions.^[1] These are contrast- and timing-heavy: the right phase at the right time is what makes the study diagnostic.

Neck & Chest (incl. Cardiac)

Neck CT (larynx/airway, soft tissue) uses contrast for masses and abscesses. Chest work spans a CT pulmonary angiogram timed to the pulmonary arterial phase for pulmonary embolism, HRCT (thin slices + sharp kernel) for interstitial lung disease and nodules, and low-dose lung cancer screening.^[6]

Cardiac CT requires ECG gating (usually diastole) to freeze heart motion; a beta-blocker lowers and steadies the rate (target ~<60 bpm) for coronary CTA, and a non-contrast gated scan gives the coronary calcium score. TAVR planning and TAVR/valve work also live here.

Abdomen & Multiphase Imaging

The abdomen is the home of multiphase imaging.^[6] Image in the arterial phase (~20–35 s) for hypervascular lesions and arteries, the portal-venous phase (~60–70 s) for liver and venous enhancement (the workhorse phase), and a delayed phase for washout.

Hepatocellular carcinoma classically shows arterial hyperenhancement with portal-venous/delayed washout — the reason for multiphase liver CT. Use oral contrast to opacify (positive) or distend (neutral, for enterography) the bowel; suspected appendicitis scans extend through the pelvis.

Lung-cancer staging includes the liver and adrenals (common metastatic sites), and adrenal washout protocols characterize adrenal lesions.

Pelvis & Additional Procedures

Pelvis studies include dedicated delayed bladder imaging, retrograde cystogram (catheter-instilled contrast for suspected bladder rupture), colorectal/rectal-contrast studies, CT colonography (“virtual” colonoscopy of the insufflated colon), and reproductive organs.^[1] CT urography adds an excretory phase to assess ureteral patency; suspected renal stones are scanned without contrast so the high-attenuation calculi are not obscured. Additional procedures across body regions include CT angiography (e.g., aorta, runoff), biopsy, drainage, aspiration, trauma pan-scans, and surgical planning.

How to Use This Study Guide

Work through the guide one category at a time. After each one, check it off in the contents to raise your exam-readiness score, then drill the same content in our free practice questions and flashcards — active recall and timed practice are what move knowledge into exam-day performance.

• Weight your time by the blueprint. Procedures (71) and Image Production (52) are about three-quarters of the exam — start there, then Patient Care and Safety.
• Learn contrast timing cold. Arterial vs. portal-venous vs. delayed, and which study uses which phase, is tested constantly.
• Master the numbers and units. HU anchors (water 0, air −1000), CTDIvol/DLP, and the kVp/mAs/pitch trade-offs return again and again.
• Know your cross-sectional anatomy. Recognizing structures and vessels on axial images is the foundation of every Procedures question.
• Then prove it. When a category feels solid, confirm with our practice questions — aim for a comfortable margin above 75 before exam day.

Common questions ARRT CT candidates search and get asked — each answered briefly and backed by an official source (ARRT, FDA, NCRP, the ACR–RSNA RadiologyInfo library, or CDC). Tap any card to test yourself.

ARRT CT Glossary

Key ARRT CT terms in one place. Hover any dotted term throughout the guide for its definition; the full list is below.

ARRT CT

The American Registry of Radiologic Technologists' post-primary Computed Tomography certification — earned by technologists already credentialed in radiography, nuclear medicine technology, or radiation therapy who specialize in CT imaging.

Hounsfield unit (HU)

The standardized CT number for tissue attenuation, calibrated so water = 0 HU and air ≈ −1000 HU; dense cortical bone is roughly +1000 HU or more, fat about −100 to −50, and soft tissue +30 to +60.

attenuation

The reduction of the x-ray beam's intensity as it passes through tissue (from absorption and scatter); the measured attenuation of each voxel is converted into a Hounsfield unit.

window width (WW)

The range of Hounsfield units displayed as shades of gray; it controls image contrast. A wide window (lung, bone) shows many HU values at low contrast; a narrow window (brain) shows few at high contrast.

window level (WL)

The center (midpoint) Hounsfield value of the displayed window; it controls brightness and should be set near the HU of the tissue of interest.

pitch

Table travel per gantry rotation ÷ total nominal beam width. Pitch > 1 spreads the beam (faster scan, less overlap, lower dose, more noise); pitch < 1 overlaps the beam (more dose, less noise).

CTDIvol

Volume CT Dose Index (mGy) — the average radiation dose within the scanned volume for one series, normalized for pitch; the primary per-scan dose value shown on the console.

DLP

Dose-Length Product (mGy·cm) = CTDIvol × scan length; it reflects the total radiation delivered over the whole scan and is used to estimate effective dose.

ALARA

As Low As Reasonably Achievable — keep every radiation dose to patients and staff as low as possible while still obtaining a diagnostic image.

tube current modulation

Automatic exposure control that adjusts mA based on patient size and attenuation along the scan, delivering uniform image quality at the lowest necessary dose; vendor names include CARE Dose4D, SmartmA, SURE Exposure.

MDCT

Multi-detector CT — a scanner with multiple rows of detectors along the z-axis that acquires several slices per gantry rotation, enabling fast coverage, thin slices, and isotropic volumetric data.

helical

Spiral CT acquisition in which the tube rotates continuously while the table moves through the gantry, collecting a volume of data (typically in one breath-hold) for overlapping, thin-slice reconstruction.

isotropic voxel

A voxel with equal dimensions in all three axes (x, y, z); isotropic data allow high-quality multiplanar and 3D reformations in any plane without loss of resolution.

MPR

Multiplanar reformation — reconstructing axial volumetric data into coronal, sagittal, or oblique planes without re-scanning the patient; best with thin, overlapping, isotropic slices.

MIP

Maximum intensity projection — a display that projects the highest-attenuation voxels along a ray, used to show contrast-filled vessels in CT angiography.

filtered back projection

The classic, fast CT reconstruction algorithm that back-projects filtered projection data into an image; noisier at low dose than iterative reconstruction.

iterative reconstruction

A reconstruction method that repeatedly refines the image against the raw projection data, reducing noise and enabling lower-dose scanning at greater computational cost.

reconstruction kernel

The mathematical filter applied during reconstruction; a sharp (bone) kernel boosts spatial resolution but adds noise, while a smooth (soft-tissue) kernel lowers noise but blurs fine detail.

spatial resolution

The ability to distinguish small, closely spaced high-contrast objects; improved by a smaller FOV, thinner slices, sharp kernels, and a smaller focal spot.

contrast resolution

The ability to distinguish tissues of similar attenuation (low-contrast detail); improved by higher mAs (less noise), smooth kernels, and lower kVp (more iodine contrast). CT's particular strength.

beam hardening

An artifact caused by the polychromatic beam: lower-energy photons are absorbed first in dense tissue, raising the mean beam energy and producing dark streaks or cupping (classically posterior fossa or around metal).

bowtie filter

A shaped filter that equalizes x-ray intensity across the fan beam — more attenuation peripherally, less centrally — reducing peripheral patient dose and beam-hardening artifact.

partial volume averaging

An artifact where a voxel spans more than one tissue type, so its HU is an average of them; reduced by using thinner slices.

bolus tracking

A technique that places an ROI in a target vessel and automatically triggers the scan when contrast reaches a set HU threshold, timing acquisition to peak vascular enhancement.

timing bolus

A small test injection scanned repeatedly at one level to measure time-to-peak enhancement, then used to set the optimal scan delay for the diagnostic acquisition.

nonionic contrast

Low-osmolality iodinated contrast that does not dissociate into ions; far better tolerated than ionic (high-osmolality) agents and the standard for intravascular CT injection.

extravasation

Leakage of injected contrast into the soft tissue around the IV instead of into the vein; stop the injection, assess the site, treat per policy, watch for compartment syndrome, and document.

eGFR

Estimated glomerular filtration rate — a measure of kidney function screened before iodinated IV contrast; a low value raises the risk of contrast-associated kidney injury.

ECG gating

Synchronizing CT acquisition (prospective) or reconstruction (retrospective) to the cardiac cycle (usually diastole) to freeze cardiac motion — essential for coronary CT angiography.

dual-energy CT

Acquiring data at two x-ray energies to differentiate materials by their energy-dependent attenuation — e.g., uric acid vs. calcium in gout, iodine maps, and virtual non-contrast images.

scout (topogram)

The preliminary low-dose projection image acquired first to plan scan range, centering, and the tube-current-modulation reference; it is not diagnostic.

Couinaud segments

A system dividing the liver into eight functionally independent segments based on portal and hepatic venous supply — used to localize lesions on CT.

circle of Willis

The arterial anastomotic ring at the base of the brain (anterior/posterior cerebral, communicating, and internal carotid arteries) — a key target of head/neck CT angiography.

CT Study Guide FAQ

References

1. 1.American Registry of Radiologic Technologists (ARRT). “Computed Tomography Examination Content Specifications (current through Aug 31, 2026; updated specs effective Sept 1, 2026).” ARRT. ↑
2. 2.American Registry of Radiologic Technologists (ARRT). “Postprimary Pathway: Computed Tomography (CT).” ARRT. ↑
3. 3.American Registry of Radiologic Technologists (ARRT). “Computed Tomography (CT) Credential Options.” ARRT. ↑
4. 4.American Registry of Radiologic Technologists (ARRT). “Exam Scoring.” ARRT. ↑
5. 5.American Registry of Radiologic Technologists (ARRT). “Updated CT Documents (Effective September 1, 2026).” ARRT. ↑
6. 6.U.S. Food and Drug Administration (FDA). “Computed Tomography (CT).” FDA. ↑
7. 7.National Council on Radiation Protection & Measurements (NCRP). “Limitation of Exposure to Ionizing Radiation (NCRP Report No. 116).” NCRP. ↑
8. 8.Radiological Society of North America & American College of Radiology. “Patient Safety — Radiation Dose in X-Ray and CT Exams.” RadiologyInfo.org. ↑
9. 9.Radiological Society of North America & American College of Radiology. “Patient Safety — Contrast Material.” RadiologyInfo.org. ↑
10. 10.Centers for Disease Control and Prevention (CDC). “Standard Precautions for All Patient Care.” CDC. ↑
11. 101.U.S. Food and Drug Administration (FDA). “Medical X-ray Imaging.” fda.gov, accessed 20 June 2026. ↑
12. 102.Radiological Society of North America & American College of Radiology (RadiologyInfo.org). “CT — Head.” radiologyinfo.org, accessed 20 June 2026. ↑
13. 103.Radiological Society of North America & American College of Radiology (RadiologyInfo.org). “CT — Abdomen and Pelvis.” radiologyinfo.org, accessed 20 June 2026. ↑
14. 104.Radiological Society of North America & American College of Radiology (RadiologyInfo.org). “CT — Heart (Coronary Arteries).” radiologyinfo.org, accessed 20 June 2026. ↑

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