Ready to conquer the CT registry? Our free ct registry practice test is designed to challenge your knowledge with realistic exam questions and boost your confidence on test day. Whether you're reviewing key concepts through our comprehensive CT Registry Practice Quiz or brushing up on fundamentals with a detailed cat scan registry review, you'll get hands-on practice with arrt ct practice test free questions and top practice ct registry questions. Perfect for aspiring radiologic technologists, this interactive session sharpens your skills and prepares you to dominate ct registry exam practice tests. Dive in now and see how high you can score!
What is the primary purpose of Hounsfield units (HU) in CT imaging?
Quantify tissue density relative to water
Adjust window and level settings
Measure patient radiation dose
Determine optimal kVp
Hounsfield units provide a standardized scale for measuring the attenuation of X-rays in various tissues relative to water. This scale allows radiologists to distinguish between materials like bone, soft tissue, and air based on their attenuation values. HU facilitates quantitative analysis and comparison across CT scanners. For more details see Hounsfield scale on Wikipedia.
The CT number of water is defined as:
0 Hounsfield units
-1000 Hounsfield units
+1000 Hounsfield units
-100 Hounsfield units
On the Hounsfield scale, water is assigned a CT number of zero to serve as the reference point for other tissues. Air is calibrated at approximately -1000 HU, while dense bone can exceed +1000 HU. Using water as a baseline ensures consistency in interpretation. For more information see CT Basics on RadiologyInfo.
In a CT scanner, what does the term 'pitch' refer to?
Field of view size
Table travel per rotation divided by slice thickness
Time per gantry rotation
Ratio of mA to kVp
Pitch is defined as the table movement distance per rotation divided by the total nominal slice thickness. A pitch of 1 means contiguous slices, while higher pitch reduces scan time but may increase noise. Proper pitch selection balances image quality and speed. More details at CT Image Quality on Wikipedia.
Increasing the kilovoltage peak (kVp) in CT imaging primarily results in:
Higher average photon energy
Narrower slice thickness
Lower patient dose
Faster gantry rotation
Raising the kVp increases the maximum and average photon energy of the X-ray beam, improving penetration through dense tissues. This can reduce contrast between soft tissues but may lower patient dose for similar image quality. Selecting kVp requires balancing contrast and penetration. See kVp on Radiopaedia.
Which artifact is commonly caused by metal objects in the CT scan field?
Partial volume artifact
Beam hardening artifact
Motion artifact
Ring artifact
Metal objects harden the X-ray beam by preferentially absorbing low-energy photons, creating streaks and dark bands known as beam hardening artifacts. These artifacts degrade image quality around metallic implants. Various correction algorithms attempt to mitigate this effect. More on this topic at Artifact Reduction in CT.
What is the standard reconstruction algorithm used for routine CT imaging?
Filtered back projection
Convolutional neural network
Iterative reconstruction
Fourier synthesis
Filtered back projection has been the traditional reconstruction algorithm in CT, using mathematical filters to reduce blur from simple back projection. While newer iterative methods exist, filtered back projection offers fast reconstruction suitable for routine exams. It remains widely used in many systems. For background see Filtered Back Projection.
What is the effect of increasing the tube current (mAs) in CT imaging?
Decreases photon energy
Reduces image noise
Shortens scan time
Improves temporal resolution
Increasing mAs raises the number of X-ray photons generated, resulting in lower quantum noise and improved image quality. However, higher mAs also increases patient radiation dose. Technologists balance mAs to achieve adequate image quality with acceptable dose. Learn more at AAPM CT Dose Documentation.
What is the typical matrix size used in standard CT images?
1024 x 1024
512 x 512
128 x 128
256 x 256
Most CT scanners reconstruct images on a 512 x 512 matrix, balancing spatial resolution with manageable image data size. Some high-resolution exams may use larger matrices, but 512² remains standard. The matrix size determines the number of pixels per image. See CT Image Quality Parameters.
Which slice thickness range is most commonly used in routine CT imaging?
5 - 10 cm
1 - 5 mm
0.1 - 0.3 mm
10 - 20 mm
Routine CT studies often employ slice thickness between 1 and 5 mm to balance resolution and noise. Thinner slices improve spatial resolution but increase noise and data volume. Thicker slices reduce noise but may obscure small structures. Additional info at CT Basics on RadiologyInfo.
The CT number for air is approximately:
-1000 HU
0 HU
-100 HU
+1000 HU
On the Hounsfield scale, air is assigned around -1000 HU because it attenuates X-rays much less than water. This stark contrast helps identify lung fields and free air. The scale ranges from -1000 HU for air to over +1000 HU for dense bone. See details at Hounsfield scale.
In multi-detector CT, which component directly converts X-ray photons into an electrical signal?
Slip ring
Pre-patient collimator
Scintillation detector with photodiode
Gantry cooling fan
Modern MDCT detectors use scintillator crystals that emit visible light when struck by X-rays, coupled with photodiodes that convert the light into electrical signals. This arrangement provides high efficiency and fast response. Slip rings enable continuous rotation but do not detect photons. More info at CT Detector.
What is the role of the bow-tie filter in CT imaging?
Reduce motion artifacts
Shape and attenuate the X-ray beam to match patient anatomy
Sharpen image edges
Control table movement
Bow-tie filters are placed between the X-ray tube and patient to shape the beam intensity, reducing peripheral dose and improving uniformity. They attenuate more photons at beam edges where the patient is thinner. This enhances image quality and reduces patient dose. Read more at AAPM CT Resources.
In CT image display, what does window width control?
Spatial resolution
Contrast range of the image
Temporal resolution
Overall image brightness
Window width determines the range of Hounsfield units mapped to the gray scale, effectively controlling image contrast. A narrow window width increases contrast, highlighting small density differences, while a wide width displays more gray shades. Adjusting window width is essential for optimal visualization of different tissues. For guidance see CT Windowing.
What does window level control in CT imaging?
Center of the Hounsfield scale, affecting image brightness
Range of displayed contrast
Patient dose
GANTRY rotation speed
Window level sets the midpoint HU value around which the window width spans. Changing the level shifts the gray scale range brighter or darker. Proper window level selection ensures that the tissues of interest are optimally displayed. Learn more at CT Windowing.
What is the primary function of the CT gantry?
House the patient table controls
Display reconstructed images
Automatically adjust scan parameters
Support and rotate the X-ray tube and detectors around the patient
The gantry is the rotating frame of the CT scanner that houses the X-ray tube and detector array. It rotates around the patient to acquire projection data at multiple angles. This rotation is essential for tomographic image reconstruction. More info at CT Equipment.
Which unit is commonly used to express CT radiation dose (CTDIvol)?
Becquerel (Bq)
Sievert (Sv)
Milligray (mGy)
Gray per centimeter (Gy/cm)
CTDIvol (Computed Tomography Dose Index volume) is expressed in mGy, reflecting the average dose within the scanned volume. Sieverts measure biological effect, while CTDI focuses on physical dose. Understanding CTDIvol helps manage patient radiation exposure. Refer to IAEA CT Dose Tracker.
In CT angiography, which phase is optimized to visualize the arterial system?
Portal venous phase
Equilibrium phase
Delayed phase
Arterial phase
The arterial phase occurs shortly after contrast injection when the arteries are maximally opacified. It is critical for evaluating vascular anatomy and identifying arterial lesions. Timing is typically 15 - 25 seconds post-injection. More details at CT Angiography.
What does AEC stand for in CT imaging?
Automatic Exposure Control
Adaptive Energy Calibration
Automated Electron Capture
Average Enhancement Contrast
Automatic Exposure Control adjusts the tube current in real-time based on patient attenuation, ensuring consistent image quality and optimized radiation dose. AEC systems modulate mA around the patient's anatomy. This technique reduces unnecessary exposure. For more, see AAPM CT Dose Reports.
Which premedication regimen is commonly used for patients with prior mild contrast reactions?
No premedication required
Prednisone and diphenhydramine prior to contrast
Ibuprofen alone
4 hours of IV fluids only
A typical premedication protocol for mild prior reactions includes corticosteroids like prednisone and antihistamines such as diphenhydramine. This reduces the risk of repeat contrast reactions. Protocols vary but often start 13 hours before injection. See guidelines at Contrast Reaction Guidelines.
Dual-energy CT differentiates materials primarily based on:
Temperature of structures
Electrical conductivity
Atomic number differences
Physical density only
Dual-energy CT acquires data at two distinct energy spectra, allowing differentiation of materials by their atomic number-dependent attenuation properties. This enables material decomposition such as calcium versus iodine. It enhances tissue characterization. More at Dual-Energy CT.
What is the typical contrast injection rate for CT angiography of the chest?
1 - 2 mL/s
3 - 5 mL/s
0.5 - 1 mL/s
5 - 7 mL/s
Chest CT angiography commonly uses injection rates of 3 - 5 mL/s to achieve adequate arterial enhancement. Faster rates provide sharp bolus peaks for optimal vessel opacification. Rates below 2 mL/s may be insufficient for arterial imaging. More details at Contrast Protocols.
Which reconstruction method is preferred for reducing dose while maintaining diagnostic image quality?
Direct Fourier reconstruction
Filtered back projection
Iterative reconstruction
Analytical back projection
Iterative reconstruction algorithms iteratively refine image data to reduce noise and artifacts, allowing lower radiation dose acquisitions. They outperform traditional filtered back projection in terms of dose efficiency. Many CT systems now offer iterative techniques. Learn more at AAPM CT Reports.
In dual-energy CT, what energy level (keV) is commonly used for virtual monochromatic imaging to enhance contrast?
70 keV
40 keV
140 keV
100 keV
Virtual monochromatic images around 70 keV often provide optimal balance between contrast and image noise. Lower keV images increase iodine contrast but also noise. Higher keV reduce noise but lower contrast. Specific keV selection may vary by application. See Virtual Monoenergetic Imaging.
Which artifact is primarily caused by patient movement during CT acquisition?
Partial volume artifact
Motion artifact
Beam hardening artifact
Ring artifact
Motion artifact results when the patient moves during data acquisition, leading to blurring or duplication of structures. It is especially noticeable in areas with stark density contrast. Strategies such as breath-hold instructions or faster scans help reduce this artifact. For techniques see Motion Correction in CT.
What is the main advantage of thin-slice imaging in CT?
Increased beam uniformity
Improved spatial resolution
Better temporal resolution
Reduced patient dose
Thin slices (e.g., ?1 mm) improve spatial resolution, allowing detection of small lesions and fine anatomical details. However, they can increase image noise and data volume. They are essential for high-resolution studies like lung nodule evaluation. See CT Image Quality Parameters.
In CT perfusion studies, which parameter measures the volume of blood within a given tissue volume?
Cerebral blood volume (CBV)
Time to peak (TTP)
Mean transit time (MTT)
Cerebral blood flow (CBF)
Cerebral blood volume represents the volume of blood in a given amount of brain tissue (mL/100 g). It is distinct from blood flow and transit times. CBV helps assess tissue viability in stroke. More at Perfusion Parameters.
Which statement best describes spiral (helical) CT acquisition?
Continuous rotation of the gantry with simultaneous table movement
Non-rotational fixed gantry imaging
Step-and-shoot acquisition without table movement
Acquisition using film X-ray detectors
Spiral or helical CT acquires data continuously as the gantry rotates and the patient moves through the scanner. This allows faster coverage and improved volume imaging. It became the standard for most CT applications. Further reading at Helical CT.
In CT dosimetry, what does DLP stand for?
Distributed Load Profile
Dose Linear Projection
Dose Length Product
Diagnostic Level Parameter
Dose Length Product (DLP) represents the total radiation dose along the scan length (mGy·cm). It is calculated by multiplying CTDIvol by scan length. DLP is used to estimate patient radiation exposure. More details at CT Dose on RadiologyInfo.
Which CT number would most likely represent a hyperdense intracranial lesion compared to normal brain parenchyma (~40 HU)?
+20 HU
+80 HU
-20 HU
0 HU
A hyperdense lesion has a higher attenuation than normal brain tissue (~30 - 45 HU). A measurement around +80 HU indicates increased density, as seen in acute hemorrhage or calcification. Lower values would be isodense or hypodense. For clinical context see CT of Hemorrhage.
Which post-processing technique is used to visualize vascular structures by removing bone from the image?
Maximum intensity projection
Multiplanar reconstruction
Bone-subtracted volume rendering
Surface shaded display
Bone-subtracted volume rendering uses dual-energy or specialized software to differentiate and subtract osseous structures, allowing clear visualization of vessels. This technique is valuable in CT angiography to assess vascular anatomy without bone interference. MIP displays high-density voxels but does not remove bone. Learn more at Bone Removal in CT Angio.
Automatic tube current modulation in CT adjusts mA based on:
Heart rate variability
Patient attenuation profile
Breath-hold duration
Gantry temperature
Automatic exposure control systems modulate the tube current in real time based on patient size and attenuation measured from scout images. This ensures uniform image quality while minimizing dose. It adapts mA both angularly and longitudinally. For systems details see AAPM Resources.
The effective atomic number (Zeff) in CT is most critical for characterizing:
Pitch value
Patient radiation dose
Material composition in dual-energy CT
Slice thickness
In dual-energy CT, Zeff helps differentiate materials by their atomic number-dependent X-ray attenuation characteristics. This enables identification of specific tissue types and contrast agents. It's not directly related to dose or geometric parameters. For more see Effective Atomic Number.
What does CTDIvol measure in CT dosimetry?
Entrance skin dose
Dose delivered to a specific organ
Average dose within the scanned volume
Maximum surface dose
CTDIvol (Computed Tomography Dose Index volume) represents the average radiation dose over the scan volume, normalized for beam width. It is not organ-specific but offers a standardized metric for comparing protocols. It helps in protocol optimization and dose monitoring. Details at CT Dose Tracker by IAEA.
Which modulation technique adjusts dose only along the z-axis?
Z-axis modulation
Angular modulation
Hybrid modulation
Adaptive statistical modulation
Z-axis (longitudinal) modulation changes tube current based on variations in patient attenuation along the length of the body. Angular modulation varies mA during rotation, while hybrid combines both. Longitudinal modulation helps maintain image quality across different body regions. See AAPM CT Dose Resources.
Photon starvation artifacts in CT most often appear as:
Mottled texture uniformly
Ring formations
Streaking in highly attenuating areas
Blurring across slices
Photon starvation occurs when insufficient photons reach the detector, especially behind dense objects, causing streaks and noise. Increasing mA or kVp and using proper filtration can mitigate it. It is different from ring artifacts from detector issues. More at Beam Hardening and Starvation.
Spectral CT imaging improves material separation by using:
Faster gantry rotation
Higher tube current only
More detector rows
Two distinct X-ray energy spectra
Spectral CT (dual-energy) uses two energy spectra to exploit different attenuation properties of materials at varying energies. This allows decomposition into specific substances like iodine or calcium. It goes beyond single-energy scans, enhancing tissue characterization. For more see Dual-Energy CT.
Which reconstruction method iteratively refines images to reduce noise?
Analytical back projection
Fourier transform reconstruction
Model-based iterative reconstruction
Filtered back projection
Model-based iterative reconstruction algorithms incorporate system physics and noise statistics to iteratively update image estimates, reducing noise and artifacts. They require more computation but allow lower dose exams. These methods are increasingly integrated into modern CT systems. Learn more at AAPM Reports.
Beam hardening correction algorithms primarily target which part of the spectrum?
Low-energy photons
Scattered photons
All photons equally
High-energy photons
Beam hardening arises when low-energy photons are preferentially absorbed, altering the beam spectrum. Correction algorithms compensate for this by modeling and removing effects of the hardened beam. This reduces streak artifacts near dense structures. Details at Beam Hardening.
In CT, the modulation transfer function (MTF) is used to describe:
Spatial resolution performance
Noise texture
Radiation dose distribution
Contrast sensitivity
MTF quantifies a CT system's ability to reproduce object details of varying spatial frequencies, effectively describing spatial resolution. A higher MTF at a given frequency indicates better ability to resolve fine structures. It is measured using specialized phantoms. See CT Quality Parameters.
What effect does a narrower focal spot have on CT image quality?
Increases temporal resolution
Improves spatial resolution
Decreases image contrast
Reduces patient dose
A smaller focal spot limits geometric unsharpness, improving spatial resolution and allowing finer detail visualization. However, it may restrict maximum tube current and increase heat load. Choice of focal spot balances resolution and tube heat capacity. Learn more at Focal Spot Size.
Metal artifact reduction in CT can be achieved using:
Reducing collimation width
Lowering mAs
Dual-energy acquisition
Decreasing rotation speed
Dual-energy CT helps separate and subtract metal-induced artifacts by acquiring data at different energies and applying material decomposition. Other methods include iterative metal artifact reduction algorithms. Simply lowering mAs may exacerbate noise. More at Metal Artifact Reduction.
What is the primary advantage of iterative reconstruction over filtered back projection?
Lower image noise at reduced dose
Faster reconstruction speed
Lower system cost
Eliminates beam hardening
Iterative reconstruction reduces image noise more effectively than filtered back projection, enabling lower radiation dose protocols. While computationally intensive, modern hardware has made these techniques practical. They also improve artifact suppression. Details at AAPM CT Reports.
In photon-counting CT detectors, what key benefit is realized compared to energy-integrating detectors?
Reduced system footprint
Lower detector cost
Energy discrimination per photon
Faster gantry rotation
Photon-counting detectors register individual X-ray photons and their energy, enabling true spectral imaging with higher spatial resolution and reduced electronic noise. Energy-integrating detectors sum all photon energies. This innovation enhances material decomposition and dose efficiency. Learn more at Photon-Counting CT.
Tin filtration in CT is used to:
Scatter the beam uniformly
Reduce kVp without changing spectrum
Remove low-energy photons from the beam
Increase the number of low-energy photons
Tin filters absorb low-energy photons that would contribute to patient dose without improving image quality. This spectral shaping hardens the beam, enhancing contrast-to-noise ratio at higher energies. It is used in modern CT dose reduction strategies. See Tin Filtration in CT.
In CT sampling theory, the Nyquist limit relates to:
Maximum resolvable spatial frequency
Maximum kVp setting
Minimum achievable dose
Tube current modulation limit
The Nyquist limit defines the highest spatial frequency that can be accurately represented given a sampling rate. Sampling below this leads to aliasing artifacts. In CT, it guides choice of focal spot, detector spacing, and reconstruction parameters. More at Sampling Theorem.
What is the purpose of a CT water phantom in quality control?
Measure table movement speed
Test motion artifact correction
Calibrate and verify Hounsfield unit accuracy
Evaluate detector heat capacity
A water phantom provides a uniform medium with known attenuation (0 HU) for verifying CT number accuracy and image uniformity. Regular scans ensure consistent performance. Deviations indicate calibration needs. For QC guidelines see AAPM Water Phantom Tests.
Which technique is most effective for reducing respiratory motion artifacts in chest CT?
Lower kVp
Breath-hold acquisition
Increased slice thickness
Use of tin filter
Instructing the patient to hold their breath during the scan eliminates respiratory motion, leading to sharp chest images. Alternative methods include respiratory gating but breath-hold is simple and widely used. Lower kVp or thicker slices do not mitigate motion. More at Chest CT Motion artifacts.
Which CT parameter most directly influences longitudinal spatial resolution?
mAs
Matrix size
Pitch
kVp
Pitch, the table movement per rotation relative to slice thickness, affects the overlap of data along the z-axis. A lower pitch (more overlap) improves longitudinal resolution but increases dose and scan time. It directly controls slice spacing. Reference at CT Pitch.
Monte Carlo simulation in CT is primarily used for:
Artifact suppression
Contrast media optimization
Accurate radiation dose estimation
Faster image reconstruction
Monte Carlo methods simulate the transport of individual photons through matter, providing highly accurate dose calculations in complex geometries. They are considered the gold standard for dose estimation but are computationally intensive. They aid in advanced dosimetry research. More info at Monte Carlo Dosimetry.
Photon starvation artifacts are best mitigated by:
Increasing tube voltage and current
Decreasing slice thickness
Adding tin filtration only
Lowering pitch
Photon starvation occurs where dense objects block X-rays, causing insufficient photons to reach detectors. Increasing kVp and mAs enhances photon flux and beam penetration, reducing starvation artifacts. Filters alone may not solve the issue. Read more at Beam Hardening.
Spectral shaping with tin filters in CT improves imaging by:
Reducing detector sensitivity
Hardening the X-ray beam
Increasing beam softening
Enhancing low-energy scatter
Tin filters preferentially remove low-energy photons that contribute to patient dose without enhancing image quality. This spectral shaping hardens the beam, improving contrast-to-noise ratio in high-energy ranges. It is used in protocols like lung screening. For details see Tin Filtration in CT.
Advanced model-based iterative reconstruction algorithms incorporate which components in their system model?
Only noise statistics
Only patient motion data
X-ray physics and detector response
Only geometric factors
Model-based iterative methods use comprehensive system models including X-ray source characteristics, beam spectrum, detector response, and noise statistics. This leads to superior image quality and artifact reduction. Simplified models lack this accuracy. More at AAPM CT Guidelines.
Dual-layer detector CT systems collect spectral data by:
Separating high- and low-energy photons in two detector layers
Time-interleaved energy switching
Alternating kVp values each rotation
Using two X-ray sources
Dual-layer detectors have two scintillator layers: the first absorbs lower-energy photons, and the second detects higher-energy photons that penetrate the first. This enables simultaneous collection of spectral data without changing acquisition parameters. It supports improved material decomposition. For more see Dual-Layer Detector CT.
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Study Outcomes
Understand CT Registry Exam Structure -
Learn about the format, question types, and scoring methods used in CT registry practice test to navigate the actual exam with confidence.
Apply Core CT Principles -
Reinforce your grasp of computed tomography fundamentals, including image acquisition, reconstruction, and contrast techniques through practice ct registry questions.
Analyze Diagnostic Images -
Develop skills in interpreting CT scans by identifying normal anatomy and common pathologies in a ct scan registry review context.
Evaluate Radiation Safety Protocols -
Assess best practices for radiation protection, dosage optimization, and patient safety procedures essential for ct registry exam practice tests and clinical application.
Identify Knowledge Gaps -
Use scored feedback from this arrt ct practice test free to pinpoint areas of weakness and focus your study efforts effectively.
Boost Exam Confidence -
Build test-taking strategies and timing skills that mirror the real exam experience, helping you approach your ct registry practice test with assurance.
Cheat Sheet
Hounsfield Unit Scale & Attenuation -
Review the formula HU = 1000 × (µ_material - µ_water) / µ_water to understand how tissue densities map on CT images. Remember the mnemonic "Air is - 1000, Water is 0, Bone is +1000" to quickly gauge structures during your ct scan registry review. These values form the foundation of CT image interpretation in any arrt ct practice test free scenario.
Acquisition Parameters: kVp, mA & Pitch -
Master how kVp influences beam penetration and contrast, mA controls photon quantity, and pitch (table movement per rotation) affects image quality versus scan speed. For a balanced ct registry practice test approach, recall "High kVp for dense structures, low pitch for finer detail." Adjusting these parameters correctly reduces noise and optimizes resolution.
Contrast Media Dynamics & Safety -
Understand iodine-based agents' wash-in/wash-out phases and tailor injection rates to the vascular territory, guided by protocols from the American College of Radiology. Always confirm renal function (eGFR >30 mL/min) before administration to minimize nephrotoxicity. In your ct registry exam practice tests, emphasize timing and patient screening to score high.
Radiation Dose Metrics: CTDIvol & DLP -
Know how CTDIvol (mGy) measures per-slice dose and DLP (mGy·cm) reflects total exam exposure. Apply the ALARA principle - "As Low As Reasonably Achievable" - to balance diagnostic quality and safety. Many practice ct registry questions focus on calculating DLP = CTDIvol × scan length, so practice this formula until it's second nature.
Common CT Artifacts & Troubleshooting -
Identify streaks (beam hardening), rings (detector calibration) and motion artifacts, then apply solutions like filtration, recalibration, or breath-hold coaching. For quick recall, use the phrase "STaR MoVe": Streaking, Rings, Motion - Verify equipment, Evaluate technique. Mastering artifact correction is crucial for acing the ct registry practice test.
