ARRT Computed Tomography (CT) Exam — Questions and Answers

Question 1: What is the role of the 'anti-scatter grid' in CT imaging?

It reduces scattered radiation reaching the detectors (Correct answer)
It filters out low-energy photons from the X-ray beam
It measures patient dose in real time
It collimates the primary beam before it reaches the patient

Correct answer: It reduces scattered radiation reaching the detectors

Anti-scatter grids are placed in front of detectors to absorb scattered photons that would otherwise degrade image contrast and quality.

Question 2: Which CT finding in the lung is most associated with malignancy in a solitary pulmonary nodule?

Smooth, well-defined margins
Satellite nodules
Spiculated (irregular/stellate) margins with pleural tethering (Correct answer)
Central calcification in a popcorn pattern

Correct answer: Spiculated (irregular/stellate) margins with pleural tethering

Spiculated margins reflect infiltrative tumor growth into adjacent lung parenchyma and are the strongest morphologic predictor of malignancy in a solitary pulmonary nodule.

Question 3: Which reconstruction algorithm produces sharper edges but increased image noise in CT?

Smooth/soft-tissue kernel
Standard kernel
Ultra-low-dose kernel
Bone/sharp kernel (Correct answer)

Correct answer: Bone/sharp kernel

Sharp (bone) kernels apply high-frequency enhancement to improve edge definition, which amplifies noise compared to smooth kernels.

Question 4: Which of the following signs may a patient in shock display? Which infection control measures are necessary at the site of an intravenous injection of iodinated contrast media?

Surgical asepsis (Correct answer)
Contact isolation
Medical asepsis
Enteric precautions

Correct answer: Surgical asepsis

An intravenous injection involves penetrating the skin barrier and directly accessing the bloodstream. To prevent the introduction of microorganisms and subsequent infection, a sterile technique is absolutely essential. Surgical asepsis, also known as sterile technique, aims to eliminate all microorganisms from an area and is the appropriate measure for any procedure that invades sterile body tissues or the circulatory system.

Question 5: A thyroid cancer patient requires radioiodine ablation therapy. Why must iodinated CT contrast be avoided before this treatment?

It permanently destroys the thyroid gland
It interferes with TSH levels only
It causes thyroid storm
Iodinated contrast saturates the sodium-iodide symporter, blocking therapeutic radioiodine uptake (Correct answer)

Correct answer: Iodinated contrast saturates the sodium-iodide symporter, blocking therapeutic radioiodine uptake

Excess stable iodine from contrast saturates thyroid transporters and competes with therapeutic I-131, significantly reducing radioiodine ablation efficacy for 2–8 weeks.

Question 6: What is the purpose of "windowing" in CT image display?

To adjust image brightness and contrast (Correct answer)
To enhance motion artifacts
To reduce radiation exposure
To add color to the image

Correct answer: To adjust image brightness and contrast

Windowing is a crucial post-processing technique in CT image display that allows for the adjustment of image brightness (window level) and contrast (window width). By manipulating these parameters, specific tissue types or pathologies can be optimally visualized. This enables radiologists to highlight structures with similar densities, improving diagnostic accuracy for various anatomical regions like bone, soft tissue, or lung.

Question 7: What does the term CTDI stand for in CT radiation dosimetry?

CT Dose Interval
Computed Tomography Dose Index (Correct answer)
CT Diagnostic Imaging
Computed Tomography Density Index

Correct answer: Computed Tomography Dose Index

CTDI (Computed Tomography Dose Index) is a standardized measure of radiation dose output from a CT scanner for a single rotation.

Question 8: During a CT scan, the technologist notices the patient's heart rate is 85 bpm for a cardiac CT. What is the most appropriate action?

Increase the kVp to compensate
Switch to a 64-slice scanner
Administer beta-blocker medication to lower heart rate below 60 bpm if not contraindicated (Correct answer)
Proceed without any intervention

Correct answer: Administer beta-blocker medication to lower heart rate below 60 bpm if not contraindicated

Heart rates above 65–70 bpm degrade cardiac CT image quality due to motion; beta-blockers are administered (when not contraindicated) to achieve a slower, steadier rate.

Question 9: Which structure is best evaluated using a 'brain window' setting (W:80, L:40)?

Gray-white matter differentiation in the brain (Correct answer)
Liver lesions
Pulmonary nodules
Cortical bone fractures

Correct answer: Gray-white matter differentiation in the brain

A narrow window width centered around 40 HU maximizes contrast between gray matter (~40 HU) and white matter (~30 HU), essential for evaluating brain parenchyma.

Question 10: X-rays of the body are captured from various angles during computed tomography (CT), which produces images that resemble 2- and 3-dimensional slices (cross-sections). All jewelry and metal objects, such as zippers and belt buckles close to the body portion being scanned, should be taken off by anyone getting a CT scan. Why are patients asked to remove metal before a CT scan?

The items may block the x-rays and blur the images (Correct answer)
The goods could burn the individual receiving the scan since they heat up in the machine.
The machine's rays could cause metallic items to release poisonous fumes.
The items can damage the CT machine

Correct answer: The items may block the x-rays and blur the images

Agile Methodology is characterized by its iterative and incremental approach, focusing on flexibility, collaboration, and rapid delivery. It breaks down projects into small, manageable iterations (sprints) to allow for quick progressions and faster releases of working software. This enables teams to adapt to changing requirements and deliver value continuously.

Question 11: CT angiography (CTA) of the brain is primarily used to evaluate:

Demyelinating lesions
Cortical atrophy
Intracranial aneurysms and vascular malformations (Correct answer)
Intraparenchymal calcifications

Correct answer: Intracranial aneurysms and vascular malformations

CTA uses rapidly acquired post-contrast images to visualize the cerebral vasculature, detecting aneurysms, AVM, and large-vessel occlusions.

Question 12: What is the primary purpose of a CT gantry tilt?

To improve contrast resolution
To reduce scan time
To increase patient comfort
To align the scan plane with anatomical structures while avoiding radiation-sensitive organs (Correct answer)

Correct answer: To align the scan plane with anatomical structures while avoiding radiation-sensitive organs

Gantry tilt allows the scan plane to be angled relative to the patient's body axis to align with anatomy or minimize dose to sensitive structures like the lens of the eye.

Question 13: What does the size-specific dose estimate (SSDE) correct for compared to CTDIvol?

Scan protocol complexity
Contrast agent type
Scanner manufacturer differences
Patient body size and diameter (Correct answer)

Correct answer: Patient body size and diameter

SSDE adjusts CTDIvol based on the patient's effective diameter to provide a more accurate estimate of actual patient dose.

Question 14: A CT scan shows an adrenal lesion with an unenhanced attenuation of 8 HU. What is the most likely diagnosis?

Adrenal adenoma (Correct answer)
Adrenal metastasis
Pheochromocytoma
Adrenal carcinoma

Correct answer: Adrenal adenoma

Adrenal lesions with unenhanced HU ≤10 are consistent with lipid-rich adenomas due to intracellular fat content.

Question 15: What does ALARA stand for in radiation protection?

As Low As Reasonably Achievable (Correct answer)
Automatic Level Adjustment for Radiation Areas
Allowable Limit for Any Radiation Application
Adjusted Limit of Acceptable Radiation Activity

Correct answer: As Low As Reasonably Achievable

ALARA is the guiding principle in radiation protection meaning doses should be kept as low as reasonably achievable while maintaining diagnostic image quality.

Question 16: What is the primary function of the high-voltage generator in a CT system?

To supply stable high voltage (kVp) to the X-ray tube for X-ray production (Correct answer)
To control the rotational speed of the gantry
To power the patient table movement mechanism
To process raw detector data into CT images

Correct answer: To supply stable high voltage (kVp) to the X-ray tube for X-ray production

The high-voltage generator converts standard AC power into the kilovoltage (80–140 kVp) required by the X-ray tube anode-cathode circuit to produce X-rays.

Question 17: What is the primary advantage of dual-energy CT (DECT) over single-energy CT?

Reduced contrast volume requirements in all body regions
Higher spatial resolution in the z-axis
Material decomposition enabling differentiation of tissues with similar HU values (Correct answer)
Faster gantry rotation speed

Correct answer: Material decomposition enabling differentiation of tissues with similar HU values

DECT acquires data at two kVp settings, enabling material decomposition algorithms that distinguish substances like iodine, uric acid, and calcium that may overlap in attenuation at single energy.

Question 18: What does 'window leveling' (adjusting the level/center) primarily affect in a CT image?

The spatial resolution of the image
The radiation dose delivered to the patient
The overall brightness or density of the displayed image (Correct answer)
The range of HU values displayed (contrast)

Correct answer: The overall brightness or density of the displayed image

The window level (center) sets the midpoint of the displayed HU range, shifting the image brighter or darker without changing the range of visible values.

Question 19: A patient experiences mild urticaria after CT contrast injection. What is the most appropriate immediate action?

Continue the scan without intervention
Immediately inject epinephrine
Administer diphenhydramine (Benadryl) and observe the patient (Correct answer)
Administer IV corticosteroids and discharge

Correct answer: Administer diphenhydramine (Benadryl) and observe the patient

Mild urticaria (hives only, no systemic symptoms) is treated with antihistamines and close observation while monitoring for progression to a more severe reaction.

Question 20: What type of CT artifact appears as dark streaks radiating from dense metallic objects such as hip prostheses?

Beam hardening and metal streak artifact (Correct answer)
Motion artifact
Partial volume artifact
Ring artifact

Correct answer: Beam hardening and metal streak artifact

Metal objects severely attenuate and preferentially absorb low-energy photons (beam hardening), causing dark streaks that obscure surrounding anatomy.

Question 21: What is the primary advantage of dual-energy CT (DECT) over single-energy CT?

Material decomposition and iodine quantification (Correct answer)
Faster gantry rotation
Wider detector coverage per rotation
Lower tube heat load

Correct answer: Material decomposition and iodine quantification

DECT acquires data at two different kVp levels, enabling material decomposition to identify and quantify iodine, calcium, uric acid, and other substances.

Question 22: What is the primary principle behind computed tomography imaging?

X-ray absorption (Correct answer)
Nuclear emission
Ultrasound reflection
Magnetic resonance

Correct answer: X-ray absorption

Computed tomography (CT) imaging works by sending multiple X-ray beams through the body from different angles. As these X-rays pass through tissues, they are absorbed to varying degrees depending on the tissue density. Detectors then measure the amount of X-rays that pass through, and this absorption data is used to reconstruct cross-sectional images.

Question 23: The 'salt and pepper' or 'stippled' calcification pattern seen within a brain tumor on CT is most characteristic of:

Metastasis
Ependymoma
Meningioma
Oligodendroglioma (Correct answer)

Correct answer: Oligodendroglioma

Oligodendrogliomas classically show fine stippled or 'salt and pepper' calcifications on CT in up to 90% of cases.

Question 24: Which component of a CT scanner rotates around the patient during image acquisition?

Console
Detector array
Gantry (Correct answer)
X-ray tube

Correct answer: Gantry

In CT imaging, 'slice thickness' refers to the width of the individual cross-sectional images acquired by the scanner. It essentially defines the dimension of the tissue volume represented by each image. While it can influence the detail within a single slice, it more accurately describes the spacing or thickness of the anatomical section being imaged.

Question 25: What is the primary radiation protection principle that requires justifying each CT examination?

Optimization
Dose constraint
ALARA
Justification (Correct answer)

Correct answer: Justification

Justification is the ICRP principle requiring that no examination be performed unless the expected benefit exceeds the radiation detriment to the individual.

Question 26: Which CT finding is most characteristic of a subdural hematoma compared to an epidural hematoma?

Midline hyperdense lesion
Rim-enhancing lesion after contrast
Biconvex lenticular hyperdense collection
Crescent-shaped collection that crosses suture lines (Correct answer)

Correct answer: Crescent-shaped collection that crosses suture lines

Subdural hematomas form a crescent shape and follow the brain contour, crossing suture lines, unlike the lenticular epidural hematoma.

Question 27: What is the primary advantage of iterative reconstruction over filtered back projection (FBP) in CT?

Faster reconstruction time
Elimination of metal artifacts
Better spatial resolution at high kVp
Significant noise reduction at equivalent or lower dose (Correct answer)

Correct answer: Significant noise reduction at equivalent or lower dose

Iterative reconstruction repeatedly refines the image estimate against raw data, reducing noise substantially, which allows lower dose acquisition without sacrificing image quality.

Question 28: Which post-processing technique in CT creates a three-dimensional display by showing only the highest attenuation voxel along each line of sight?

Volume rendering (VR)
Multiplanar reformation (MPR)
Minimum intensity projection (MinIP)
Maximum intensity projection (MIP) (Correct answer)

Correct answer: Maximum intensity projection (MIP)

Maximum intensity projection (MIP) projects the highest HU value along each ray through the data, making it ideal for visualizing contrast-enhanced vessels and calcifications.

Question 29: At what injection rate (mL/sec) is intravenous contrast typically administered for a CT pulmonary angiography (CTPA)?

0.5–1 mL/sec
Less than 0.5 mL/sec
3–5 mL/sec (Correct answer)
10–15 mL/sec

Correct answer: 3–5 mL/sec

CTPA requires a brisk injection rate of 3–5 mL/sec to achieve adequate pulmonary artery opacification during the brief arterial phase.

Question 30: What does 'temporal resolution' mean in cardiac CT?

The speed of the contrast bolus through the heart
The number of cardiac phases reconstructed
The minimum time interval the scanner needs to freeze cardiac motion (Correct answer)
The time required to reconstruct images after scanning

Correct answer: The minimum time interval the scanner needs to freeze cardiac motion

Temporal resolution in cardiac CT refers to the shortest acquisition time (typically half the gantry rotation time) needed to capture a sharp, motion-free image of the moving heart.

Question 31: In CT imaging, what does the term 'image noise' primarily refer to?

Artifacts caused by patient motion during scanning
Blurring caused by insufficient spatial resolution
Distortion caused by metallic implants in the patient
Random variation in CT numbers (HU) across a uniform object (Correct answer)

Correct answer: Random variation in CT numbers (HU) across a uniform object

CT image noise is the random fluctuation in Hounsfield units across a uniform region, primarily caused by quantum mottle from insufficient photon statistics.

Question 32: On a CT scan of the abdomen, what Hounsfield unit threshold is typically used to identify an acute hemorrhage?

20–40 HU
0–20 HU
55–80 HU (Correct answer)
40–60 HU

Correct answer: 55–80 HU

Acute hemorrhage typically measures 55–80 HU on non-contrast CT due to the high protein content of clotted blood, making it hyperdense relative to surrounding soft tissues.

Question 33: What is the purpose of the CT bowtie filter?

To reduce patient dose
To shape the X-ray beam (Correct answer)
To improve image contrast
To eliminate beam hardening

Correct answer: To shape the X-ray beam

A bowtie filter is a specialized filter used in CT scanners that is thicker at the edges and thinner in the center. Its primary purpose is to shape the X-ray beam, making it more intense at the center and less intense at the periphery. This design helps to reduce the dose to the patient's periphery while maintaining a more uniform signal reaching the detectors, which is crucial for image quality.

Question 34: What type of adverse reaction to iodinated contrast media involves an immune-mediated hypersensitivity response?

Anaphylactoid (allergy-like) reaction (Correct answer)
Contrast extravasation
Vasovagal syncope
Contrast nephropathy

Correct answer: Anaphylactoid (allergy-like) reaction

Anaphylactoid reactions mimic true anaphylaxis (urticaria, bronchospasm, hypotension) but do not require prior sensitization and are not IgE-mediated.

Question 35: A radiopaque contrast agent, a material that can be seen on X-rays to aid in identifying one tissue from another, may be administered to patients before a CT scan. Which of the following contrast agents is used with CT the most frequently?

Iodine (Correct answer)
Gadolinium
Barium
Microbubbles

Correct answer: Iodine

Metal objects, such as jewelry and zippers, are radiopaque, meaning they absorb X-rays. During a CT scan, these items can block the X-ray beam, creating artifacts or streaks on the images. These artifacts can obscure important anatomical structures, making it difficult for radiologists to accurately interpret the scan results and potentially leading to misdiagnosis.

Question 36: In CT, spatial resolution is most commonly measured using which parameter?

Modulation Transfer Function (MTF) or line pairs per centimeter (lp/cm) (Correct answer)
Contrast-to-noise ratio (CNR)
Signal-to-noise ratio (SNR)
Hounsfield Unit (HU) accuracy

Correct answer: Modulation Transfer Function (MTF) or line pairs per centimeter (lp/cm)

Spatial resolution in CT is quantified by the MTF or high-contrast resolution measured in line pairs per centimeter, describing the system's ability to resolve fine detail.

Question 37: Non-contrast CT brain: anticoagulated patient with right hemiparesis and abrupt onset of disorientation. What does the picture depict?

Intraventricular haemorrhage (Correct answer)
Subdural haemorrhage
Calcification of the choroid plexus
Enhancing mass
Epidural haemorrhage

Correct answer: Intraventricular haemorrhage

An anticoagulated patient experiencing abrupt neurological deficits like right hemiparesis and disorientation is at high risk for intracranial hemorrhage. On a non-contrast CT, acute blood appears hyperdense (bright white). Intraventricular hemorrhage (IVH) refers to bleeding into the ventricular system of the brain, which would appear as bright, dense material filling or layering within the ventricles on the CT scan.

Question 38: Which CT artifact appears as a star-burst pattern of dark and light streaks emanating from a dense object?

Metallic streak artifact (Correct answer)
Motion artifact
Ring artifact
Beam hardening artifact

Correct answer: Metallic streak artifact

Metallic streak artifacts are caused by extreme beam hardening and photon starvation from highly attenuating metal implants, producing characteristic streak patterns.

Question 39: What procedure results in a more monochromatic beam and lowers patient radiation exposure by reducing the longest wavelength photons?

Filtration (Correct answer)
Bean hardening
Slip rings
Detector collimation

Correct answer: Filtration

Detectors are the critical components within the CT gantry that measure the X-ray photons that have passed through the patient's body. These detectors convert the transmitted X-ray energy into electrical signals, which are then processed by a computer to reconstruct the cross-sectional images. The number and arrangement of detectors directly impact image quality and scan speed.

Question 40: What is the main disadvantage of increasing pitch in helical CT?

Reduced z-axis resolution (Correct answer)
Decreased detector coverage
Increased radiation dose
Longer scan time

Correct answer: Reduced z-axis resolution

Higher pitch values interpolate data across a wider z-axis distance, which degrades longitudinal (z-axis) spatial resolution and can increase image noise.

Question 41: What defines a 'dual-source' CT scanner?

A system with two X-ray tube and detector array pairs offset at approximately 90° (Correct answer)
A system using two different X-ray energies from a single tube
A scanner capable of imaging two patients simultaneously
A system with two separate patient tables

Correct answer: A system with two X-ray tube and detector array pairs offset at approximately 90°

Dual-source CT uses two X-ray tube/detector systems mounted approximately 90° apart, enabling ultra-fast acquisition and simultaneous dual-energy imaging.

Question 42: In CT fluoroscopy-guided procedures, which group is at highest risk for radiation injury?

Technologists monitoring from the control room
Other patients in adjacent rooms
The interventionalist's hands if placed in the beam (Correct answer)
The patient's eyes

Correct answer: The interventionalist's hands if placed in the beam

CT fluoroscopy uses continuous X-ray exposure, and the interventionalist's hands can receive very high doses if placed near or in the primary beam.

Question 43: Which term describes the ability of a CT system to distinguish between two objects with very similar attenuation values?

Low-contrast resolution (Correct answer)
Spatial resolution
Noise index
High-contrast resolution

Correct answer: Low-contrast resolution

Low-contrast resolution (contrast resolution) measures the system's ability to differentiate objects with nearly identical attenuation coefficients.

Question 44: What does the term 'pitch' refer to in helical CT scanning?

The speed of gantry rotation in RPM
The table distance traveled per gantry rotation divided by beam collimation (Correct answer)
The number of detector rows
The angle of the X-ray beam relative to the patient

Correct answer: The table distance traveled per gantry rotation divided by beam collimation

Pitch is calculated as table feed per rotation divided by total beam collimation width; a pitch of 1 means the table moves exactly one beam width per rotation.

Question 45: Using CT and a radiopaque contrast agent, CT angiography creates 2- and 3-dimensional pictures of blood vessels to look for anomalies. Which of the following statements most accurately describes why CT angiography is frequently employed instead of traditional angiography?

Takes more time
Is less invasive (Correct answer)
Detects blood clots in arteries
Is more accurate

Correct answer: Is less invasive

Iodine-based contrast agents are the most frequently used with CT scans due to their high atomic number, which allows them to effectively absorb X-rays and enhance the visibility of blood vessels and soft tissues. They are typically administered intravenously to highlight specific structures and differentiate them from surrounding tissues. Other agents like barium are used for gastrointestinal imaging, while gadolinium is primarily for MRI.

Question 46: What is the term for the minimum detectable difference in attenuation between two adjacent structures in CT?

Spatial resolution
Temporal resolution
Noise equivalent quanta
Contrast resolution (Correct answer)

Correct answer: Contrast resolution

Contrast resolution refers to the ability to distinguish between tissues with similar attenuation values, and it is primarily affected by noise and radiation dose.

Question 47: Increasing the mAs in CT by a factor of 4 will have what effect on image noise?

Reduce noise by 50% (Correct answer)
Double the noise
Quadruple the noise
Eliminate noise entirely

Correct answer: Reduce noise by 50%

Since noise is proportional to 1/√mAs, quadrupling mAs reduces noise by half (√4 = 2).

Question 48: The Nyquist theorem in CT states that to accurately represent a spatial frequency, the sampling rate must be at least:

Four times the frequency of interest
Twice the frequency of interest (Correct answer)
Equal to the frequency of interest
Half the frequency of interest

Correct answer: Twice the frequency of interest

The Nyquist criterion requires a sampling frequency at least twice the highest spatial frequency to avoid aliasing artifacts in the reconstructed image.

Question 49: Which factor contributes to the occurrence of motion artifacts in CT imaging?

High radiation dose
Slow heart rate
Fast scan times (Correct answer)
Sedation of the patient

Correct answer: Fast scan times

While fast scan times are primarily implemented to *reduce* the likelihood of motion artifacts by minimizing the time available for patient movement, they are often employed in imaging scenarios where involuntary motion (e.g., cardiac or respiratory motion) is inherently present. In these dynamic situations, even rapid data acquisition may not entirely eliminate the effects of motion, leading to residual artifacts. Thus, fast scan times are a response to, rather than a direct contributor to, the *occurrence* of motion, but motion can still be a challenge despite them.

Question 50: Which reconstruction algorithm provides the sharpest images but also the most noise in CT?

Iterative reconstruction
Lung kernel
Soft-tissue kernel
High-frequency (bone/edge) kernel (Correct answer)

Correct answer: High-frequency (bone/edge) kernel

High-frequency (bone/detail) kernels sharpen edges and fine structures but amplify image noise, making them ideal for bone but not soft tissue evaluation.

Question 51: What is the primary shielding material used in CT scanning room walls?

Aluminum
Fiberglass
Lead or lead-equivalent concrete (Correct answer)
Steel

Correct answer: Lead or lead-equivalent concrete

CT room walls are constructed with lead or high-density concrete to attenuate primary and scatter radiation to acceptable levels for adjacent areas.

Question 52: Which reconstruction algorithm uses a statistical model of the imaging process to minimize a cost function iteratively, achieving better noise properties than FBP?

Algebraic reconstruction without penalty
Maximum-likelihood expectation maximization (MLEM) (Correct answer)
Simple back-projection (SBP)
Filtered back-projection (FBP)

Correct answer: Maximum-likelihood expectation maximization (MLEM)

MLEM iteratively updates the image estimate to maximize the likelihood that the projection data would be observed given the current image, reducing noise and artifacts.

Question 53: In CT, which body region is most sensitive to radiation-induced cancer risk?

Extremities
Skin
Brain
Bone marrow and gonads (Correct answer)

Correct answer: Bone marrow and gonads

Bone marrow and gonads have the highest tissue weighting factors (wT), making them most sensitive to stochastic radiation-induced cancer risk.

Question 54: What is the primary component responsible for X-ray production in a CT scanner?

Gantry motor
Collimator
X-ray tube (Correct answer)
Detector array

Correct answer: X-ray tube

The X-ray tube generates the X-ray beam used for CT imaging through thermionic emission, converting electrical energy into X-ray photons.

Question 55: A CT brain ordered for a 70-year-old with progressive cognitive decline shows diffuse enlargement of sulci and ventricles proportional to each other. This pattern most likely represents:

Cerebral atrophy (ex vacuo ventriculomegaly) (Correct answer)
Communicating hydrocephalus
Bilateral subdural hygromas
Obstructive hydrocephalus

Correct answer: Cerebral atrophy (ex vacuo ventriculomegaly)

Proportional enlargement of both sulci and ventricles reflects volume loss (atrophy), distinguishing it from hydrocephalus where ventricles enlarge disproportionately.

Question 56: Which oral contrast agent is preferred in CT when bowel perforation is suspected?

No oral contrast is needed
Negative contrast (water only)
Water-soluble iodinated contrast (e.g., Gastrografin) (Correct answer)
Barium sulfate

Correct answer: Water-soluble iodinated contrast (e.g., Gastrografin)

Water-soluble iodinated agents are used when perforation is suspected because barium leaking into the peritoneum causes severe peritonitis.

Question 57: A patient presents with thunderclap headache. CT brain shows hyperdense material in the basal cisterns. The most likely diagnosis is:

Bilateral subdural hematomas
Cerebral venous thrombosis
Subarachnoid hemorrhage (Correct answer)
Basilar meningitis

Correct answer: Subarachnoid hemorrhage

Subarachnoid hemorrhage classically presents with thunderclap headache and appears as hyperdensity filling the basal cisterns on CT.

Question 58: What is the role of iterative reconstruction (IR) in modern CT imaging?

To increase spatial resolution beyond hardware limitations
To reduce image noise at lower radiation doses compared to filtered back projection (Correct answer)
To eliminate all metallic streak artifacts
To automatically segment anatomical structures

Correct answer: To reduce image noise at lower radiation doses compared to filtered back projection

Iterative reconstruction algorithms model the acquisition process and iteratively correct image data, enabling diagnostic image quality at significantly reduced radiation doses.

Question 59: In CT angiography, what timing method uses real-time monitoring of contrast arrival in a target vessel?

Saline flush technique
Fixed delay scanning
Bolus tracking (SmartPrep/Care Bolus) (Correct answer)
Test bolus technique

Correct answer: Bolus tracking (SmartPrep/Care Bolus)

Bolus tracking monitors a region of interest in real time and automatically triggers scanning when contrast attenuation reaches a preset threshold.

Question 60: What is the main advantage of using iterative reconstruction over filtered back projection (FBP)?

Elimination of all motion artifacts
Reduced image noise at lower radiation doses (Correct answer)
Improved temporal resolution
Faster reconstruction speed

Correct answer: Reduced image noise at lower radiation doses

Iterative reconstruction algorithms reduce noise more effectively than FBP, enabling diagnostic-quality images at significantly lower radiation doses.

Question 61: Which regulatory body in the United States sets occupational radiation dose limits for CT technologists?

Nuclear Regulatory Commission (NRC) (Correct answer)
ACR
Joint Commission
FDA

Correct answer: Nuclear Regulatory Commission (NRC)

The NRC sets the annual occupational whole-body dose limit of 50 mSv (5 rem) for radiation workers in the US, including CT technologists.

Question 62: What is the most appropriate CT protocol to evaluate a patient presenting with acute stroke within the therapeutic window?

Delayed post-contrast CT of the brain at 24 hours
Non-contrast CT brain followed by CT perfusion and CT angiography (Correct answer)
Contrast-enhanced CT brain only
CT of the chest and abdomen

Correct answer: Non-contrast CT brain followed by CT perfusion and CT angiography

The acute stroke CT protocol includes NCCT (to exclude hemorrhage), CT perfusion (to identify ischemic core and penumbra), and CTA (to identify vessel occlusion for thrombectomy planning).

Question 63: What is the typical kilovoltage peak (kVp) range used in routine clinical CT scanning?

200–300 kVp
80–140 kVp (Correct answer)
40–60 kVp
150–200 kVp

Correct answer: 80–140 kVp

Clinical CT scanners operate at 80–140 kVp, with lower values used for pediatric patients and iodinated contrast studies, and higher values for large patients.

Question 64: What is the primary use of saline flush immediately following IV contrast injection in CT?

To cool the injector tubing
To prevent extravasation
To dilute contrast in the kidneys and reduce nephrotoxicity
To push the contrast bolus forward and improve vascular opacification while reducing contrast volume (Correct answer)

Correct answer: To push the contrast bolus forward and improve vascular opacification while reducing contrast volume

A saline chase pushes residual contrast from the tubing and peripheral veins into circulation, extending the bolus and improving opacification with less total contrast.

Question 65: What is the primary purpose of using automatic exposure control (AEC) in CT?

Improve spatial resolution
Reduce contrast agent volume
Adapt tube current to patient size and anatomy (Correct answer)
Increase scan speed

Correct answer: Adapt tube current to patient size and anatomy

AEC (also called tube current modulation) automatically adjusts mA based on patient attenuation to optimize image quality while minimizing dose.

Question 66: What is the most common type of iodinated contrast media used for CT examinations?

Ionic high-osmolar contrast
Non-ionic, water-soluble iodinated contrast (Correct answer)
Gadolinium-based contrast
Barium sulfate suspension

Correct answer: Non-ionic, water-soluble iodinated contrast

Non-ionic, water-soluble iodinated contrast agents are preferred for CT because they have lower osmolality and fewer adverse reactions compared to ionic agents.

Question 67: Which unit is used to express the effective radiation dose received by a patient during a CT scan?

Rad
Milligray (mGy)
Millisievert (mSv) (Correct answer)
Roentgen (R)

Correct answer: Millisievert (mSv)

Millisievert (mSv) is the SI unit used to express effective dose, which accounts for the biological effect of radiation on different tissues.

Question 68: What is the purpose of a CT scout image?

To measure bone density (Correct answer)
To estimate patient size
To detect metallic implants
To preview the anatomy

Correct answer: To measure bone density

Cardiac CT is a specialized type of CT scan specifically designed to image the coronary arteries and assess heart health. It uses advanced technology to capture detailed images of the heart's anatomy, identify blockages or narrowing in the coronary arteries (coronary artery disease), and evaluate cardiac function. This non-invasive procedure is crucial for diagnosing and managing heart conditions.

Question 69: What is the primary advantage of using saline flush after contrast injection in CT?

Increases image noise
Pushes residual contrast into central circulation, improving vascular opacification and reducing dose (Correct answer)
Prevents nephrotoxicity
Reduces scan time

Correct answer: Pushes residual contrast into central circulation, improving vascular opacification and reducing dose

A 30–50 mL saline chaser propels contrast remaining in the IV tubing and peripheral vein into the bloodstream, maximizing the usable contrast bolus.

Question 70: Which imaging modality is typically combined with CT to provide functional and metabolic information?

Single Photon Emission Computed Tomography (SPECT)
Positron Emission Tomography (PET) (Correct answer)
Ultrasound
Magnetic Resonance Imaging (MRI)

Correct answer: Positron Emission Tomography (PET)

PET/CT is a hybrid imaging modality that combines the anatomical detail of CT with the functional and metabolic information from PET. PET uses radiotracers to detect metabolic activity, while CT provides precise anatomical localization of these active areas. This combination is particularly valuable in oncology for cancer staging, treatment planning, and monitoring response to therapy.

Question 71: In CT angiography, what is the bolus tracking technique used for?

Triggering the diagnostic scan when contrast reaches the target vessel (Correct answer)
Reducing the volume of contrast needed
Calculating vessel diameter automatically
Measuring blood flow velocity

Correct answer: Triggering the diagnostic scan when contrast reaches the target vessel

Bolus tracking monitors contrast enhancement in a target vessel using repeated low-dose images and automatically triggers the diagnostic scan when the preset HU threshold is reached.

Question 72: Which pre-medication regimen is typically used for patients with prior moderate contrast reactions undergoing non-emergent contrast CT?

IV methylprednisolone 30 minutes before only
Single dose of epinephrine before the scan
No premedication is effective
Oral prednisone 13 hours, 7 hours, and 1 hour before, plus diphenhydramine 1 hour before (Correct answer)

Correct answer: Oral prednisone 13 hours, 7 hours, and 1 hour before, plus diphenhydramine 1 hour before

The standard ACR-recommended steroid premedication protocol uses oral prednisone at three intervals before the scan combined with antihistamine to reduce breakthrough reaction risk.

Question 73: Which of the following best describes 'iterative reconstruction' in modern CT?

A post-processing filter applied only to bone windows
A computational algorithm that repeatedly refines the image to reduce noise while preserving spatial resolution (Correct answer)
A technique for synchronizing image acquisition with cardiac cycles
A method of acquiring projection data using multiple X-ray sources

Correct answer: A computational algorithm that repeatedly refines the image to reduce noise while preserving spatial resolution

Iterative reconstruction algorithms model the CT acquisition process and iteratively update the image estimate to reduce noise, allowing diagnostic quality at lower radiation doses.

Question 74: Iodinated contrast material is frequently injected intravenously at the following sites:

Antecubital vein
Cephalic vein
All of the above (Correct answer)
Basilic vein

Correct answer: All of the above

The antecubital, cephalic, and basilic veins are all commonly used and accessible sites for intravenous injections, including the administration of iodinated contrast material. The antecubital vein, located in the bend of the elbow, is often preferred due to its size and superficial location. The cephalic and basilic veins, running along the forearm, also provide suitable and frequently utilized access points for venipuncture.

Question 75: During a CT scan, tube current modulation (TCM) adjusts the mA based on:

Patient heart rate
Gantry rotation speed
Patient attenuation in real time (Correct answer)
Detector read-out speed

Correct answer: Patient attenuation in real time

TCM reduces mA in less-attenuating regions (e.g., lungs) and increases it in denser regions (e.g., shoulders), optimizing dose while maintaining image quality.

Question 76: What is the purpose of using a convolution kernel in CT image reconstruction?

To reduce patient motion
To enhance spatial resolution
To improve image quality (Correct answer)
To adjust radiation dose

Correct answer: To improve image quality

Convolution kernels, also known as reconstruction filters, are applied during the image reconstruction process to enhance specific aspects of image quality. Different kernels emphasize either spatial resolution (e.g., sharp or bone kernels) or contrast resolution and noise reduction (e.g., smooth or soft tissue kernels). Choosing the appropriate kernel is crucial for optimizing the image for the specific diagnostic task.

Question 77: What does the term 'partial volume averaging' refer to in CT imaging?

Reduction in FOV to improve spatial resolution
Use of partial rotation for faster data acquisition
Blending of attenuation values from different tissues within a single voxel (Correct answer)
Averaging of multiple scan acquisitions to reduce noise

Correct answer: Blending of attenuation values from different tissues within a single voxel

Partial volume averaging occurs when a voxel contains more than one tissue type, resulting in an averaged attenuation value that misrepresents both tissues.

Question 78: Which parameter directly controls the amount of radiation delivered per CT rotation?

Pitch
mAs (Correct answer)
Slice thickness
kVp

Correct answer: mAs

Milliampere-seconds (mAs) is the product of tube current and rotation time, directly determining the number of X-ray photons produced per rotation.

Question 79: Which CT scan view provides the best visualization of the interhemispheric fissure?

Sagittal
Coronal (Correct answer)
Oblique
Axial

Correct answer: Coronal

The interhemispheric fissure is the deep groove that separates the two cerebral hemispheres, running from the front to the back of the brain. A coronal CT scan view, which slices the brain from ear to ear (like looking at the face), provides an optimal cross-sectional image along the length of this fissure. This orientation allows for a clear and extensive visualization of its entire extent and any associated pathology.

Question 80: Which of the following is an advantage of CT over conventional X-ray imaging?

Better soft tissue contrast (Correct answer)
Lower radiation exposure
Portable equipment
Faster image acquisition

Correct answer: Better soft tissue contrast

The fundamental principle behind Computed Tomography (CT) imaging is X-ray absorption. A CT scanner uses an X-ray tube to generate X-rays that pass through the patient's body, and detectors measure the amount of X-rays absorbed by different tissues. The varying absorption rates, based on tissue density, allow a computer to reconstruct detailed cross-sectional images.

Question 81: What is the typical Hounsfield Unit (HU) value for simple (non-hemorrhagic) cerebrospinal fluid?

35–45 HU
0 HU (Correct answer)
80–100 HU
−100 HU

Correct answer: 0 HU

Simple CSF measures approximately 0–15 HU, close to the value of water, allowing differentiation from higher-density hemorrhage or proteinaceous fluid.

Question 82: What is the purpose of contrast bolus tracking in CT angiography?

To enhance the patient's comfort
To minimize patient motion
To monitor contrast agent injection (Correct answer)
To improve image resolution

Correct answer: To monitor contrast agent injection

Contrast bolus tracking is a technique used in CT angiography to optimize the timing of image acquisition relative to contrast agent injection. It involves monitoring the arrival of the contrast bolus in a target vessel or organ using real-time low-dose scans. This ensures that the diagnostic scan is performed precisely when the contrast enhancement is at its peak, maximizing vessel opacification and image quality.

Question 83: A patient having a history of an allergic reaction to iodinated contrast media may undergo the following procedures in advance of a contrast-enhanced CT scan:

Premedication with steroids and antihistamines (Correct answer)
Increase in fluids for 24 hours before the examination
Refraining from urination for 2 hours before the examination
Administration of a negative contrast agent

Correct answer: Premedication with steroids and antihistamines

For an adult, the normal range of respiration is typically 12-20 breaths per minute. This rate can vary slightly based on activity level, age, and individual health status. Monitoring respiration rate is a standard vital sign assessment, providing insight into a patient's respiratory function and overall physiological state.

Question 84: Which component of a CT scanner is responsible for rotating the X-ray tube and detector around the patient?

Collimator
Generato
Gantry (Correct answer)
Console

Correct answer: Gantry

The gantry is the large, donut-shaped component of a CT scanner that houses the X-ray tube and the detectors. It is responsible for rotating these components around the patient to acquire X-ray data from multiple angles. The patient lies on a table that slides through the opening of the gantry during the scan.

Question 85: In CT imaging, 'beam hardening artifact' in the posterior fossa is caused by:

Preferential absorption of low-energy X-ray photons by the dense temporal bones (Correct answer)
Patient motion during scanning
Excessive mAs settings
Metal implants in the cervical spine

Correct answer: Preferential absorption of low-energy X-ray photons by the dense temporal bones

Beam hardening occurs when dense bone absorbs low-energy photons, causing dark streaks between the temporal bones that obscure posterior fossa structures.

Question 86: On a CT abdomen, a lesion measures -120 HU. What does this attenuation value suggest?

Acute hemorrhage
Simple cyst
Fat-containing lesion (lipoma or angiomyolipoma) (Correct answer)
Calcified granuloma

Correct answer: Fat-containing lesion (lipoma or angiomyolipoma)

Fat has a characteristic negative attenuation of approximately -50 to -150 HU, so a value of -120 HU strongly indicates a fat-containing lesion.

Question 87: Which serum creatinine-based calculation is most commonly used to screen for contrast-induced nephropathy risk before CT?

Creatinine clearance via timed urine collection
BUN/creatinine ratio
Urine specific gravity
eGFR (estimated Glomerular Filtration Rate) (Correct answer)

Correct answer: eGFR (estimated Glomerular Filtration Rate)

eGFR calculated from serum creatinine is the standard screening tool; an eGFR <30 mL/min/1.73m² generally indicates high risk for contrast nephrotoxicity.

Question 88: What is the name of the CT artifact that appears as concentric rings centered on the isocenter?

Beam hardening artifact
Ring artifact (Correct answer)
Partial volume artifact
Aliasing artifact

Correct answer: Ring artifact

Ring artifacts are caused by defective or miscalibrated detector elements and manifest as circular bands centered on the gantry rotation axis.

Question 89: Which CT parameter, when increased, directly increases patient radiation dose?

FOV
Detector row width
Pitch (above 1.0)
mAs (Correct answer)

Correct answer: mAs

Increasing mAs increases the number of X-ray photons produced, directly increasing the radiation dose delivered to the patient.

Question 90: What is the primary advantage of using contrast enhancement in brain CT imaging?

Improved spatial resolution
Enhanced visualization of blood vessels (Correct answer)
Reduced radiation dose
Faster image acquisition

Correct answer: Enhanced visualization of blood vessels

Contrast agents, typically iodine-based, are injected intravenously and absorb X-rays more effectively than surrounding tissues. This differential absorption makes structures like blood vessels, tumors, and areas of inflammation appear brighter on the CT scan. This enhanced contrast allows for improved detection and characterization of vascular abnormalities, such as aneurysms or arteriovenous malformations, and helps differentiate pathological tissues from normal brain parenchyma.

Question 91: The DLP (Dose Length Product) in CT is calculated by multiplying CTDI_vol by which parameter?

Scan length (Correct answer)
Pitch factor
Rotation time
Slice thickness

Correct answer: Scan length

DLP = CTDIvol × scan length (in cm), providing an estimate of total energy deposited during the entire CT examination.

Question 92: Which scanning mode is most appropriate for imaging moving structures such as the heart in CT?

Prospective ECG-gated axial mode (Correct answer)
Sequential (axial) mode with wide detectors
High-pitch helical mode without gating
Low-pitch helical mode

Correct answer: Prospective ECG-gated axial mode

Prospective ECG-gated axial acquisition triggers the scan at a specific cardiac phase, freezing motion and substantially reducing radiation dose compared to retrospective gating.

Question 93: What is the recommended lead apron shielding thickness to protect gonads from scattered CT radiation?

0.5 mm lead equivalent (Correct answer)
No shielding is needed
0.1 mm lead equivalent
2.0 mm lead equivalent

Correct answer: 0.5 mm lead equivalent

A 0.5 mm lead equivalent apron is standard for gonadal shielding, though its effectiveness in CT is debated due to scatter from all directions.

Question 94: What kind of detector is used now that is both effective and popular?

Single detectors
Stationary detectors
Xenon gas detectors
Solid state crystalline detectors (Correct answer)

Correct answer: Solid state crystalline detectors

CT angiography is frequently preferred over traditional angiography because it is a significantly less invasive procedure. Traditional angiography involves inserting a catheter directly into an artery, which carries higher risks such as bleeding, infection, and arterial damage. CT angiography, on the other hand, only requires an intravenous injection of contrast material, making it safer and more comfortable for the patient.

Question 95: What effect does increasing CT tube voltage (kVp) have on patient dose?

Decreases dose by reducing scan time
Reduces dose by hardening the beam
Increases dose due to higher photon energy and greater beam penetration (Correct answer)
Has no effect on patient dose

Correct answer: Increases dose due to higher photon energy and greater beam penetration

Higher kVp increases photon energy and quantity (via space charge effect), generally increasing patient dose, though it may allow mAs reduction in large patients.

Question 96: A patient presents with an allergy to shellfish. What is the appropriate clinical management before administering iodinated contrast?

Shellfish allergy is an absolute contraindication; cancel the study
Double the contrast volume to overcome any allergic response
Shellfish allergy directly predicts iodinated contrast allergy; always premedicate
Shellfish allergy alone is not a reliable predictor; assess for prior contrast reactions specifically (Correct answer)

Correct answer: Shellfish allergy alone is not a reliable predictor; assess for prior contrast reactions specifically

Shellfish allergy is a common misconception as a predictor of contrast allergy; the true risk factor is a prior reaction to iodinated contrast media specifically.

Question 97: In CT, what is the 'matrix size' most commonly used in clinical scanners?

512 x 512 (Correct answer)
1024 x 1024
128 x 128
256 x 256

Correct answer: 512 x 512

Clinical CT scanners most commonly use a 512 x 512 matrix, balancing spatial resolution with acceptable processing time and storage requirements.

Question 98: What is the typical unit of measurement used for the density of tissues in CT scans?

X-ray Absorption Unit (XAU)
Hounsfield Unit (HU) (Correct answer)
Tissue Density Unit (TDU)
Tissue Attenuation Index (TAI)

Correct answer: Hounsfield Unit (HU)

The Hounsfield Unit (HU) is the standard quantitative scale used in CT imaging to measure and display the radiodensity of tissues. This scale is normalized, with water assigned a value of 0 HU and air approximately -1000 HU. Different tissues, such as bone, fat, and various organs, have characteristic HU values, allowing for their differentiation and analysis on CT images.

Question 99: What effect does increasing the pitch in helical CT have on patient dose?

Has no effect on dose
Decreases dose by reducing overlap (Correct answer)
Doubles the dose
Increases dose proportionally

Correct answer: Decreases dose by reducing overlap

Increasing pitch means the table moves faster per rotation, resulting in less beam overlap and a reduced effective dose to the patient.

Question 100: Which window setting is most appropriate for evaluating pulmonary nodules on chest CT?

Bone window (W:2000, L:500)
Brain window (W:80, L:35)
Soft tissue window (W:400, L:40)
Lung window (W:1500, L:-600) (Correct answer)

Correct answer: Lung window (W:1500, L:-600)

Lung window settings use a wide window width and low center level to display the full dynamic range of pulmonary parenchyma including subtle nodules and airways.

Question 101: What type of CT post-processing technique is most useful for evaluating complex vascular anatomy by removing bone from CT angiography data?

Maximum Intensity Projection (MIP) after bone subtraction (Correct answer)
Surface rendering
Volume averaging
Minimum Intensity Projection (MinIP)

Correct answer: Maximum Intensity Projection (MIP) after bone subtraction

MIP displays the brightest voxels along each ray, ideal for showing enhanced vessels; subtracting bone first prevents it from obscuring vascular structures.

Question 102: Which medication must be withheld 48 hours before and after iodinated contrast administration in patients with renal impairment?

Atorvastatin
Aspirin
Metformin (Correct answer)
Lisinopril

Correct answer: Metformin

Metformin must be withheld because contrast-induced nephropathy can impair its renal clearance, leading to toxic accumulation and risk of lactic acidosis.

Question 103: What is the purpose of 'prospective triggering' in cardiac CT?

To reconstruct multiple cardiac phases from one acquisition
To acquire data only during a specific, predetermined phase of the cardiac cycle (Correct answer)
To scan continuously throughout the cardiac cycle
To automatically adjust kVp based on heart rate

Correct answer: To acquire data only during a specific, predetermined phase of the cardiac cycle

Prospective triggering uses the ECG signal to trigger X-ray exposure only during a specific quiescent phase, significantly reducing radiation dose compared to retrospective gating.

Question 104: In CT imaging, what is a "Hounsfield Unit" (HU) a measure of?

Tissue density (Correct answer)
Pixel size
Image brightness
Radiation dose

Correct answer: Tissue density

The gantry is the large, donut-shaped component of a CT scanner that houses the X-ray tube and the detector array. During image acquisition, the gantry rotates rapidly around the patient, allowing the X-ray tube to emit radiation from multiple angles and the detectors to capture the transmitted X-rays. This rotation is essential for collecting the data needed to reconstruct cross-sectional images.

Question 105: What is the purpose of the CT couch indexing feature?

To move the patient through the gantry during scanning (Correct answer)
To adjust image contrast
To synchronize with the patient's breathing
To increase the tube current

Correct answer: To move the patient through the gantry during scanning

The CT couch indexing feature refers to the precise, controlled movement of the patient table (couch) through the gantry during a CT scan. In helical (spiral) CT, the couch moves continuously, while in axial (sequential) CT, it moves in discrete steps between slice acquisitions. This indexing ensures that the entire anatomical region of interest is systematically scanned.

Question 106: In CT scanner design, what is the 'focal spot' of the X-ray tube?

The center point of the reconstruction matrix
The small area on the anode where electrons strike and X-rays are produced (Correct answer)
The area of the detector that receives the highest X-ray intensity
The region of patient tissue receiving the highest dose

Correct answer: The small area on the anode where electrons strike and X-rays are produced

The focal spot is the small area on the rotating anode target where the electron beam strikes, causing X-ray emission; its size directly affects spatial resolution.

Question 107: Which organ is typically used as a reference when setting window level for abdominal CT?

Liver (Correct answer)
Spleen
Pancreas
Kidney

Correct answer: Liver

The liver is commonly used as the window level reference in abdominal CT because it has a consistent, predictable attenuation value of approximately 50-70 HU.

Question 108: The term 'isotropic voxel' in CT means the voxel dimensions are:

Larger in-plane than in the z-axis
Equal in all three dimensions (Correct answer)
Larger in the z-axis than in-plane
Variable depending on window settings

Correct answer: Equal in all three dimensions

Isotropic voxels have equal x, y, and z dimensions, enabling high-quality multiplanar reformations in any orientation.

Question 109: On CT brain, the normal Hounsfield unit (HU) range for white matter is approximately:

20–30 HU (Correct answer)
0–10 HU
80–100 HU
50–70 HU

Correct answer: 20–30 HU

White matter typically measures 20–30 HU, slightly lower than gray matter (30–40 HU) due to its higher myelin lipid content.

Question 110: What is meant by 'isotropic voxels' in CT imaging?

Voxels that contain only a single tissue type
Voxels with identical attenuation values in all directions
Voxels with equal dimensions in all three spatial planes (x, y, z) (Correct answer)
Voxels with zero noise contribution

Correct answer: Voxels with equal dimensions in all three spatial planes (x, y, z)

Isotropic voxels have equal length, width, and height, enabling high-quality multiplanar and 3D reconstructions without resolution loss in any plane.

Question 111: Which CT finding is the hallmark of carotid artery stenosis evaluation on CT angiography?

Calcification of the aortic arch
Presence of contralateral plaques
Wall thickening only
Percentage of luminal narrowing at the carotid bifurcation (Correct answer)

Correct answer: Percentage of luminal narrowing at the carotid bifurcation

Carotid CTA quantifies the degree of luminal stenosis (percent narrowing) at the bifurcation and proximal internal carotid artery, which determines treatment decisions for stroke risk reduction.

Question 112: What is the advantage of using a smaller CT field of view (FOV)?

Reduced patient dose
Improved spatial resolution for the targeted anatomy (Correct answer)
Faster scan time
Wider anatomical coverage

Correct answer: Improved spatial resolution for the targeted anatomy

A smaller FOV assigns more pixels per unit area, increasing spatial resolution and displaying finer anatomical detail in the region of interest.

Question 113: CT colonography (virtual colonoscopy) is performed with the patient in which position to evaluate both the colon positions?

Left lateral decubitus only
Both supine and prone positions (Correct answer)
Upright sitting position
Trendelenburg position

Correct answer: Both supine and prone positions

Both supine and prone acquisitions are standard for CT colonography; repositioning redistributes residual fluid and stool, allowing evaluation of dependent and non-dependent colonic segments.

Question 114: On non-contrast CT of the head, acute intraparenchymal hemorrhage typically appears as:

Hyperdense (bright white) relative to adjacent brain parenchyma (Correct answer)
Ring-enhancing
Isodense to brain
Hypodense (dark) relative to brain

Correct answer: Hyperdense (bright white) relative to adjacent brain parenchyma

Acute blood is hyperdense on NCCT due to the high protein content of clotted hemoglobin (55–75 HU), making it easily distinguishable from normal brain (~35 HU).

Question 115: A digital radiograph was produced while the patient bed was translated (moved) through the gantry, maintaining the X-ray tube and detector array in place.

What is a Scout Image in CT ? (Correct answer)
What Does a SSCT AND MSCT require?
What is the purpose of an scout image in CT ?
What is the purpose of Flying Focal Spot Technology ?

Correct answer: What is a Scout Image in CT ?

The description accurately defines the acquisition of a scout image in CT, also known as a topogram or surview. A scout image is a preliminary digital radiograph produced by translating the patient bed through the gantry while the X-ray tube and detector array remain stationary. This image is essential for planning the subsequent axial or helical CT scans, allowing the technologist to define the precise scan range and angle.

Question 116: Which type of contrast agent is commonly used in CT imaging to enhance blood vessels and soft tissue?

Ferumoxytol
Barium sulfate
Gadolinium-based contrast
Iodinated contrast (Correct answer)

Correct answer: Iodinated contrast

Iodinated contrast agents are commonly administered intravenously in CT imaging to enhance the visibility of blood vessels, organs, and soft tissues. Iodine, being a high-atomic-number element, strongly absorbs X-rays, making structures containing it appear brighter on the CT images. This allows for better differentiation of various anatomical structures and pathologies.

Question 117: Which type of brain imaging is most useful for assessing the presence of calcifications?

Magnetic Resonance Imaging (MRI)
Positron Emission Tomography (PET)
Computed Tomography (CT) (Correct answer)
Ultrasound

Correct answer: Computed Tomography (CT)

Computed Tomography (CT) scans are highly effective at detecting calcifications due to their principle of measuring X-ray attenuation. Calcium has a very high density and thus strongly attenuates X-rays, appearing very bright (hyperdense) on a CT image. This makes CT superior to other imaging modalities like MRI, which often struggles to visualize calcifications clearly, for this specific purpose.

Question 118: Which population group requires the most careful dose optimization in CT due to higher radiation sensitivity?

Athletic adults
Pediatric patients (Correct answer)
Male patients
Elderly patients

Correct answer: Pediatric patients

Children are more radiosensitive than adults and have more years of life remaining in which radiation-induced cancers could develop, requiring strict dose minimization.

Question 119: Which artifact occurs when an object is positioned partially in and partially out of the scan field of view?

Motion artifact
Metallic artifact
Partial volume artifact (Correct answer)
Beam-hardening artifact

Correct answer: Partial volume artifact

A partial volume artifact occurs when a voxel contains tissues or structures with significantly different attenuation values, such as bone and soft tissue, or when an object is only partially included in the slice thickness. The CT number assigned to that voxel represents an average of these different attenuations, leading to a misrepresentation of the true density and potentially blurring or obscuring small structures.

Question 120: Contrast extravasation during CT injection most commonly occurs at which site?

The renal pelvis
The IV catheter insertion site in the antecubital fossa (Correct answer)
The pulmonary veins
The aorta

Correct answer: The IV catheter insertion site in the antecubital fossa

Extravasation occurs when contrast leaks from a dislodged or infiltrated IV catheter into surrounding soft tissue, most often at the antecubital injection site.

Question 121: What technology allows modern helical CT scanners to rotate continuously without stopping?

Electromagnetic braking
Cable drive system
Slip ring technology (Correct answer)
Gear reduction transmission

Correct answer: Slip ring technology

Slip ring technology enables continuous electrical contact between the rotating gantry and stationary components, allowing uninterrupted 360° rotation.

Question 122: Which principle of radiation protection states that doses should be kept as low as reasonably achievable?

LNT
BERT
NCRP
ALARA (Correct answer)

Correct answer: ALARA

ALARA (As Low As Reasonably Achievable) is the guiding principle for minimizing radiation exposure to patients and staff.

Question 123: Which factor most significantly increases a patient's risk for a severe contrast reaction?

Asthma controlled with inhalers
Age over 65
History of a prior severe contrast reaction (Correct answer)
Mild shellfish allergy

Correct answer: History of a prior severe contrast reaction

A prior severe contrast reaction is the single strongest risk factor for a repeat severe reaction, increasing risk approximately 5-fold.

Question 124: What does 'window width' control in CT image display?

The brightness of the display
The range of HU values displayed as shades of gray (Correct answer)
The spatial resolution of the image
The slice thickness

Correct answer: The range of HU values displayed as shades of gray

Window width determines the range of Hounsfield units mapped to the grayscale display; a narrow width increases contrast, while a wide width shows a broader density range.

Question 125: What is the purpose of the bow-tie (wedge) filter in CT?

To remove high-energy photons from the beam
To reduce motion artifacts
To increase radiation dose to the center of the patient
To compensate for the varying thickness of the patient's body cross-section (Correct answer)

Correct answer: To compensate for the varying thickness of the patient's body cross-section

The bow-tie filter attenuates the beam more at the periphery (thinner patient edges) than at the center, equalizing detector signal and reducing skin dose.

Question 126: A pregnant patient requires abdominal CT for suspected appendicitis. Which statement about fetal radiation risk is most accurate?

Radiation risk is identical regardless of gestational age
The fetus is fully shielded by the uterus and receives no radiation dose
CT is absolutely contraindicated in all trimesters
Fetal risk is negligible at typical diagnostic doses below 50 mGy, but benefits must outweigh risks (Correct answer)

Correct answer: Fetal risk is negligible at typical diagnostic doses below 50 mGy, but benefits must outweigh risks

At diagnostic CT doses typically below 25 mGy, deterministic fetal effects are extremely unlikely; however, the ALARA principle still applies and clinical benefit must justify the exposure.

Question 127: During a dual-energy CT scan, what primary advantage does dual-energy provide over single-energy CT?

Lower radiation dose in all cases
Faster image acquisition
Improved temporal resolution
Material differentiation and virtual non-contrast imaging (Correct answer)

Correct answer: Material differentiation and virtual non-contrast imaging

Dual-energy CT acquires data at two different kVp settings, enabling material decomposition to distinguish iodine, calcium, and uric acid, and to create virtual non-contrast images.

Question 128: Which window level and window width settings are appropriate for evaluating brain parenchyma on CT?

Level 35 HU, Width 80 HU (Correct answer)
Level −600 HU, Width 1500 HU
Level 400 HU, Width 2000 HU
Level 60 HU, Width 350 HU

Correct answer: Level 35 HU, Width 80 HU

Brain window settings (level ~35 HU, width ~80 HU) optimize contrast between gray matter, white matter, and CSF within the narrow HU range of brain tissue.

Question 129: Which type of CT detector converts X-ray photons directly into electrical charge using amorphous selenium?

Scintillator-photodiode detector
Indirect-conversion flat-panel detector
Direct-conversion flat-panel detector (Correct answer)
Xenon ionization detector

Correct answer: Direct-conversion flat-panel detector

Direct-conversion detectors (e.g., amorphous selenium) convert X-rays directly to electrical charge without an intermediate light step, potentially improving spatial resolution.

Question 130: Dual-energy CT (DECT) can be used to create virtual non-contrast (VNC) images. What does this eliminate for the patient?

The use of a contrast injector
The need for a separate pre-contrast CT acquisition (Correct answer)
Post-processing time
The need for IV access

Correct answer: The need for a separate pre-contrast CT acquisition

VNC images derived from DECT data simulate non-contrast images by mathematically subtracting iodine signal, eliminating a dedicated unenhanced acquisition and reducing dose.

Question 131: Which intravenous catheter gauge is recommended for power injection during contrast-enhanced CT?

24–26 gauge
14 gauge or larger
Any gauge is acceptable
18–20 gauge (Correct answer)

Correct answer: 18–20 gauge

An 18–20 gauge IV catheter is recommended for power injection; smaller gauges risk rupture at high flow rates, while larger gauges are unnecessary.

Question 132: A ring artifact in CT is most commonly caused by:

Malfunction of one or more detector elements (Correct answer)
Patient motion during scanning
High-density metallic implants
Incorrect window/level settings

Correct answer: Malfunction of one or more detector elements

Ring artifacts result from a miscalibrated or malfunctioning detector element that consistently misreads attenuation values, creating a characteristic ring or arc pattern.

Question 133: On CT of the abdomen, the normal appendix should have a maximum diameter of:

Size is not diagnostically relevant
Less than 6 mm (Correct answer)
Less than 2 cm
Less than 1 cm

Correct answer: Less than 6 mm

A normal appendix is typically less than 6 mm in outer wall diameter; a distended appendix ≥6 mm with periappendiceal inflammation is diagnostic criteria for acute appendicitis.

Question 134: The term 'Z-axis dose profile' in CT refers to dose distribution along which direction?

Anterior-to-posterior axis
Left-to-right axis
Patient cranio-caudal (head-to-foot) axis (Correct answer)
Rotational axis of the gantry

Correct answer: Patient cranio-caudal (head-to-foot) axis

The Z-axis is the cranio-caudal axis along which the patient moves through the gantry, and the dose profile describes radiation distribution along this direction.

Question 135: Which CT acquisition mode collects data continuously as the table moves through the gantry?

Sequential (axial) mode
Scout (topogram) mode
Cine mode
Helical (spiral) mode (Correct answer)

Correct answer: Helical (spiral) mode

Helical CT rotates the X-ray tube continuously while the table advances, creating a spiral data set that allows retrospective reconstruction at any slice position.

Question 136: Which CT artifact is caused by two high-density objects lying in the same scan plane?

Ring artifact
Motion artifact
Partial volume artifact
Beam hardening artifact (Correct answer)

Correct answer: Beam hardening artifact

Beam hardening occurs when polychromatic X-rays are differentially absorbed, causing dark streaks between dense structures like metal implants or dense bone.

Question 137: What is the standard iodine concentration range (in mg I/mL) for contrast agents commonly used in diagnostic CT?

50–100 mg I/mL
300–370 mg I/mL (Correct answer)
500–600 mg I/mL
100–150 mg I/mL

Correct answer: 300–370 mg I/mL

Most CT contrast agents contain 300–370 mg I/mL; higher concentrations improve vascular opacification while lower volumes can be used to reduce total iodine load.

Question 138: What is the recommended fasting time before IV contrast-enhanced CT in non-emergency patients?

24-hour fast
No fasting required
12-hour fast
4 hours NPO for solids (Correct answer)

Correct answer: 4 hours NPO for solids

A 4-hour fast is recommended before contrast CT to reduce aspiration risk in the event of nausea or vomiting, while preventing dehydration.

Question 139: On a CT urogram, which phase of imaging is used to evaluate the collecting system, ureters, and bladder?

Portal venous phase at 70 seconds
Excretory (delayed) phase at 5–10 minutes (Correct answer)
Arterial phase at 25 seconds
Non-contrast phase

Correct answer: Excretory (delayed) phase at 5–10 minutes

The excretory phase captures opacified urine within the renal collecting system, ureters, and bladder after contrast is filtered and excreted by the kidneys.

Question 140: Which structure separates the right and left lobes of the liver and is identified by an imaginary line on CT?

Inferior vena cava
Main lobar fissure (Cantlie's line) from the gallbladder fossa to the middle hepatic vein (Correct answer)
Portal vein bifurcation
Falciform ligament

Correct answer: Main lobar fissure (Cantlie's line) from the gallbladder fossa to the middle hepatic vein

Cantlie's line is an imaginary line connecting the gallbladder fossa anteriorly to the middle hepatic vein posteriorly, dividing the liver into right and left functional lobes.

Question 141: What is the primary purpose of CT fluoroscopy?

To monitor needle guidance during procedures (Correct answer)
To enhance image resolution
To visualize blood vessels
To perform dynamic CT scans

Correct answer: To monitor needle guidance during procedures

CT fluoroscopy provides real-time CT images, similar to conventional fluoroscopy but with cross-sectional views. Its primary purpose is to guide interventional procedures, such as biopsies, drainages, and pain injections, by allowing the operator to continuously monitor the advancement of a needle or catheter. This real-time visualization significantly improves accuracy and safety during these procedures.

Question 142: On CT perfusion imaging of the brain, 'ischemic penumbra' refers to tissue with:

Reduced CBF but preserved CBV, representing salvageable tissue (Correct answer)
Elevated CBF and reduced MTT
Normal CBF and elevated CBV
Absent CBF and absent CBV, representing infarcted core

Correct answer: Reduced CBF but preserved CBV, representing salvageable tissue

The penumbra has reduced cerebral blood flow (CBF) but relatively preserved cerebral blood volume (CBV) due to autoregulatory vasodilation, representing at-risk but salvageable brain.

Question 143: What is the typical oral contrast agent used to opacify the GI tract during abdominal CT?

Gadolinium
Iohexol injection
Dilute barium or water-soluble iodinated contrast (Correct answer)
Normal saline

Correct answer: Dilute barium or water-soluble iodinated contrast

Dilute barium sulfate or water-soluble iodinated contrast is given orally to distend and opacify the bowel, distinguishing it from adjacent pathology.

Question 144: What technique is used to time the CT acquisition to arterial contrast peak in CT angiography?

Breathing command protocol
Bolus tracking (SmartPrep) or test bolus technique (Correct answer)
ECG gating
Fixed-delay scanning

Correct answer: Bolus tracking (SmartPrep) or test bolus technique

Bolus tracking uses real-time low-dose monitoring of a target vessel; when attenuation reaches a threshold, the diagnostic scan is automatically triggered.

Question 145: What does 'z-axis coverage' refer to in multi-detector CT?

The number of projection views acquired per rotation
The spatial resolution in the x-y image plane
The maximum tube voltage achievable
The total anatomical length imaged per gantry rotation (Correct answer)

Correct answer: The total anatomical length imaged per gantry rotation

Z-axis coverage is the total length along the patient's long axis covered per rotation, determined by the number of detector rows multiplied by individual detector width.

Question 146: Which type of CT scan is often used for imaging larger areas of the body with minimal patient movement?

Axial CT
ultidetector CT
Perfusion CT
Helical CT (Correct answer)

Correct answer: Helical CT

Helical CT, also known as spiral CT, involves continuous rotation of the X-ray tube and detectors while the patient table moves through the gantry. This allows for rapid, continuous acquisition of volumetric data over large anatomical areas. This method minimizes motion artifacts and reduces scan time, making it ideal for imaging extensive body regions with minimal patient movement.

Question 147: Which CT technique reduces dose by acquiring fewer projections and reconstructing with iterative algorithms?

Dual-energy CT
High-pitch spiral CT
Low-dose CT with iterative reconstruction (Correct answer)
Sequential CT

Correct answer: Low-dose CT with iterative reconstruction

Low-dose CT combined with iterative reconstruction algorithms can reduce dose by up to 80% compared to traditional filtered back projection while maintaining diagnostic quality.

Question 148: Quantum noise (mottle) in CT images is primarily caused by:

Patient motion during the scan
High tube voltage selection
Insufficient number of X-ray photons reaching the detectors (Correct answer)
Software reconstruction errors

Correct answer: Insufficient number of X-ray photons reaching the detectors

Quantum noise results from statistical fluctuations in photon detection; when too few photons reach the detector (low mAs or large patient), random variations appear as image noise.

Question 149: Who is credited with the invention of Computed Tomography (CT)?

Albert Einstein
Marie Curie
Godfrey Hounsfield (Correct answer)
Sir Isaac Newton

Correct answer: Godfrey Hounsfield

Sir Godfrey Hounsfield, an English electrical engineer, is widely recognized for his groundbreaking work in developing the first commercially viable Computed Tomography (CT) scanner. His invention in the early 1970s revolutionized medical diagnostics by providing detailed cross-sectional images of the body. For this achievement, he was awarded the Nobel Prize in Physiology or Medicine in 1979.

Question 150: In iterative reconstruction (IR), image quality is improved compared to FBP primarily by:

Increasing tube voltage
Modeling noise and system physics to suppress artifacts (Correct answer)
Speeding up gantry rotation
Reducing reconstruction matrix size

Correct answer: Modeling noise and system physics to suppress artifacts

Iterative reconstruction uses repeated cycles that model photon statistics and system geometry to reduce noise and artifacts, often permitting lower-dose acquisitions.

Question 151: Which phase of contrast enhancement is best for evaluating hypervascular liver tumors such as hepatocellular carcinoma (HCC)?

Arterial phase (25–35 seconds post-injection) (Correct answer)
Non-contrast phase
Portal venous phase (60–70 seconds)
Delayed phase (3–5 minutes)

Correct answer: Arterial phase (25–35 seconds post-injection)

HCC derives its blood supply primarily from the hepatic artery and enhances dramatically during the arterial phase, a hallmark feature used for diagnosis.

Question 152: Which intravenous contrast phase best demonstrates hepatocellular carcinoma (HCC)?

Non-contrast phase
Hepatic arterial phase (25–35 seconds) (Correct answer)
Delayed phase (3–5 minutes)
Portal venous phase (60–70 seconds)

Correct answer: Hepatic arterial phase (25–35 seconds)

HCC is hypervascular and receives arterial supply, causing peak enhancement during the hepatic arterial phase before the rest of the liver enhances via portal flow.

Question 153: Quantum noise in CT images is primarily a function of:

Detector element size
Reconstruction matrix size
The number of photons reaching the detector (Correct answer)
Table speed

Correct answer: The number of photons reaching the detector

Quantum (photon) noise arises from statistical fluctuations in photon counts; fewer photons (low mAs or high attenuation) result in increased noise.

Question 154: Which brain imaging technique is most sensitive for detecting acute ischemic strokes?

Positron Emission Tomography (PET)
Computed Tomography (CT)
Single-Photon Emission Computed Tomography (SPECT)
Magnetic Resonance Imaging (MRI) (Correct answer)

Correct answer: Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI), particularly with diffusion-weighted imaging (DWI) sequences, is the most sensitive technique for detecting acute ischemic strokes. DWI can detect changes in water movement within brain tissue that occur minutes after the onset of ischemia, often before any changes are visible on a standard CT scan. This early detection is crucial for timely intervention and treatment to minimize brain damage.

Question 155: What is the primary advantage of dual-energy CT (DECT) over single-energy CT?

Better spatial resolution
Lower radiation dose always
Faster scan acquisition
Material decomposition allowing tissue characterization (e.g., uric acid vs. calcium) (Correct answer)

Correct answer: Material decomposition allowing tissue characterization (e.g., uric acid vs. calcium)

DECT acquires data at two kVp levels and uses material decomposition algorithms to distinguish substances by their different attenuation characteristics at different energies.

Question 156: Which window setting is most appropriate for evaluating pulmonary nodules?

Bone window (WW 2000, WL 500)
Lung window (WW 1500, WL -600) (Correct answer)
Soft tissue window (WW 400, WL 40)
Brain window (WW 80, WL 40)

Correct answer: Lung window (WW 1500, WL -600)

The lung window uses a wide window width and low window level to optimize contrast between air-filled lung parenchyma and soft tissue nodules.

Question 157: Which type of contrast agent is commonly used in CT scans to enhance blood vessels and soft tissues?

Barium sulfate
Gadolinium
Iron oxide
Iodine-based (Correct answer)

Correct answer: Iodine-based

Iodine-based contrast agents are the most commonly used type in CT scans to enhance blood vessels and soft tissues. Iodine has a high atomic number, which allows it to effectively absorb X-rays, making structures where it accumulates (like blood vessels or highly vascularized lesions) appear brighter on the CT images. This enhancement is vital for detecting and characterizing various pathologies.

Question 158: What is the main clinical application of CT fluoroscopy?

Cardiac stress perfusion imaging
Whole-body oncologic staging
Real-time guidance for percutaneous biopsies and drainage procedures (Correct answer)
Dynamic assessment of swallowing disorders

Correct answer: Real-time guidance for percutaneous biopsies and drainage procedures

CT fluoroscopy provides continuous or near-continuous CT imaging to guide needle placement during interventional procedures such as lung biopsies or abscess drainage.

Question 159: In CT, what does 'z-axis resolution' refer to?

In-plane pixel size in the axial plane
Temporal resolution of the rotating gantry
Contrast resolution between adjacent soft tissue structures
Spatial resolution along the longitudinal (head-to-foot) axis of the patient (Correct answer)

Correct answer: Spatial resolution along the longitudinal (head-to-foot) axis of the patient

Z-axis (longitudinal) resolution determines the ability to distinguish structures stacked along the patient's long axis and improves with thinner collimation.

Question 160: Which contrast injection phase best visualizes hepatocellular carcinoma (HCC)?

Delayed phase
Portal venous phase
Non-contrast
Arterial phase (Correct answer)

Correct answer: Arterial phase

HCC is hypervascular and enhances avidly during the arterial phase (approximately 25-35 seconds after injection) when hepatic artery flow predominates.

ARRT Computed Tomography (CT) Exam

This exam certifies technologists in the specialized imaging modality of Computed Tomography, demonstrating competency in patient care, safety, and image acquisition.

160

Questions

210 min

Time Limit

75%

To Pass

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