Q.1 What does the Hounsfield Unit (HU) of water equal in a CT image?
0 HU
100 HU
-1000 HU
500 HU
Explanation - By definition, water is assigned a value of 0 Hounsfield Units in CT calibration.
Correct answer is: 0 HU
Q.2 Which component of a CT scanner rotates around the patient to acquire data?
X‑ray tube
Gantry
Collimator
Patient table
Explanation - The gantry houses the X‑ray tube and detectors and rotates around the patient during a scan.
Correct answer is: Gantry
Q.3 In a helical (spiral) CT scan, what does the term "pitch" refer to?
Table feed per rotation divided by beam width
Angle of the X‑ray beam
Rotation speed of the gantry
Number of detector rows
Explanation - Pitch = table movement per rotation / total nominal beam width; it influences scan speed and dose.
Correct answer is: Table feed per rotation divided by beam width
Q.4 Which artifact is most commonly caused by metal dental fillings in a CT head scan?
Beam hardening
Partial volume
Motion blur
Ring artifact
Explanation - High‑density metal causes beam hardening, appearing as streaks and dark bands near the metal.
Correct answer is: Beam hardening
Q.5 What is the typical effective dose (in mSv) from a standard adult chest CT?
0.1 mSv
2 mSv
7 mSv
20 mSv
Explanation - A conventional chest CT delivers roughly 7 mSv, varying with protocol and scanner.
Correct answer is: 7 mSv
Q.6 Which reconstruction algorithm is designed to reduce image noise while preserving edges?
Filtered back projection (FBP)
Iterative reconstruction (IR)
Fourier transform
Maximum intensity projection (MIP)
Explanation - IR methods model the acquisition process and can suppress noise better than traditional FBP.
Correct answer is: Iterative reconstruction (IR)
Q.7 What does the term "slice thickness" refer to in CT imaging?
Width of the detector array
Length of the patient’s body scanned
Axial dimension of the reconstructed image
Diameter of the X‑ray beam
Explanation - Slice thickness is the depth (z‑direction) of each reconstructed image slab.
Correct answer is: Axial dimension of the reconstructed image
Q.8 Which of the following best describes the function of a collimator in a CT scanner?
Focuses the X‑ray beam to a small area
Filters low‑energy photons
Detects transmitted photons
Moves the patient table
Explanation - The collimator shapes the X‑ray beam, controlling its width and reducing scatter.
Correct answer is: Focuses the X‑ray beam to a small area
Q.9 What is the principal advantage of a 64‑slice CT scanner over a 16‑slice scanner?
Higher spatial resolution
Faster acquisition of volumetric data
Reduced radiation dose
Ability to image larger patients
Explanation - More detector rows allow whole organ volumes to be captured in a single rotation, speeding up the scan.
Correct answer is: Faster acquisition of volumetric data
Q.10 In CT, the term "window level" (WL) is used to:
Set the central CT number displayed
Determine slice thickness
Control the X‑ray tube current
Adjust patient positioning
Explanation - Window level sets the midpoint of the range of Hounsfield Units displayed, affecting image contrast.
Correct answer is: Set the central CT number displayed
Q.11 Which physical phenomenon primarily causes the “partial volume” artifact?
Insufficient detector sampling
Averaging of different tissue densities within one voxel
Scatter radiation
Patient motion
Explanation - When a voxel contains more than one tissue type, the resulting CT number is a weighted average, leading to blurred edges.
Correct answer is: Averaging of different tissue densities within one voxel
Q.12 What is the purpose of using a contrast agent (e.g., iodine) in CT?
To increase patient comfort
To enhance attenuation differences between structures
To reduce radiation dose
To cool the X‑ray tube
Explanation - Iodine absorbs X‑rays strongly, increasing contrast between vascular or enhanced tissues and surrounding structures.
Correct answer is: To enhance attenuation differences between structures
Q.13 Which CT imaging mode provides the highest temporal resolution for cardiac imaging?
Standard axial scan
Helical scan with high pitch
Prospective ECG‑gated axial scan
Retrospective ECG‑gated helical scan
Explanation - Prospective gating acquires data only during a predefined cardiac phase, minimizing motion blur and dose.
Correct answer is: Prospective ECG‑gated axial scan
Q.14 What does the term "dose length product" (DLP) represent in CT dosimetry?
Product of tube voltage and current
CTDIvol multiplied by scan length
Total radiation energy absorbed by the patient
Number of slices acquired
Explanation - DLP = CTDIvol × scan length; it reflects the total radiation output for a given exam.
Correct answer is: CTDIvol multiplied by scan length
Q.15 Which of the following is a common indication for a non‑contrast head CT?
Assessing cerebral aneurysm
Evaluating acute intracerebral hemorrhage
Visualizing the pituitary gland
Imaging the spinal cord
Explanation - Blood appears hyperdense on non‑contrast CT, making it the first choice for suspected acute hemorrhage.
Correct answer is: Evaluating acute intracerebral hemorrhage
Q.16 What is the primary reason for using low‑kV (e.g., 80 kV) protocols in CT angiography?
To reduce image noise
To increase iodine attenuation and improve contrast
To shorten scan time
To lower patient comfort
Explanation - Lower tube voltage enhances the photoelectric effect, making iodine appear more attenuating, thus improving contrast.
Correct answer is: To increase iodine attenuation and improve contrast
Q.17 In CT terminology, what does "mA·s" refer to?
Tube voltage
Tube current‑time product
Slice thickness
Reconstruction algorithm
Explanation - The product of tube current (mA) and exposure time (seconds) determines the number of X‑ray photons produced.
Correct answer is: Tube current‑time product
Q.18 Which detector technology is most commonly used in modern multi‑detector CT scanners?
Scintillation crystal coupled to photodiodes
Gas‑filled ionization chambers
Photographic plates
Thermoluminescent dosimeters
Explanation - Scintillators (e.g., Gd₂O₂S) convert X‑rays to light, which photodiodes then detect, providing fast and accurate signal conversion.
Correct answer is: Scintillation crystal coupled to photodiodes
Q.19 What is the effect of increasing the CT scanner's rotation time from 0.5 s to 1 s?
Higher spatial resolution
Reduced radiation dose
Longer acquisition time and potential for more motion artifacts
Thinner slices
Explanation - A slower rotation increases scan time, which can worsen motion artifacts; dose may also increase slightly due to longer exposure.
Correct answer is: Longer acquisition time and potential for more motion artifacts
Q.20 Which of the following best describes a "dual‑energy" CT scan?
Two consecutive scans at the same energy
Simultaneous acquisition at two different X‑ray tube voltages
Scanning with two separate detectors
Using two patients at the same time
Explanation - Dual‑energy CT acquires data at two distinct kV settings, allowing material decomposition and virtual non‑contrast images.
Correct answer is: Simultaneous acquisition at two different X‑ray tube voltages
Q.21 What is the typical Hounsfield Unit value for cortical bone?
+300 HU
+1000 HU
-500 HU
0 HU
Explanation - Cortical bone attenuates X‑rays strongly, yielding values around +1000 HU or higher.
Correct answer is: +1000 HU
Q.22 Which scanning protocol is most appropriate for evaluating pulmonary embolism?
Low‑dose chest CT
CT pulmonary angiography (CTPA)
CT colonography
Brain perfusion CT
Explanation - CTPA uses contrast to visualize pulmonary arteries and detect emboli.
Correct answer is: CT pulmonary angiography (CTPA)
Q.23 What does the term "streak artifact" usually indicate in a CT image?
Patient motion
High‑density objects causing beam hardening
Insufficient slice thickness
Incorrect window level
Explanation - Streaks are common near metal implants where beam hardening and photon starvation occur.
Correct answer is: High‑density objects causing beam hardening
Q.24 In CT, which parameter most directly controls image noise?
kV
Slice thickness
mA·s (tube current‑time product)
Pitch
Explanation - Increasing mA·s increases the number of photons, reducing quantum noise.
Correct answer is: mA·s (tube current‑time product)
Q.25 Why is a "soft tissue window" (WL≈40, WW≈400) commonly used for abdominal CT?
To highlight bone structures
To emphasize differences between soft tissues
To reduce radiation dose
To visualize airways
Explanation - The soft‑tissue window sets the display range to differentiate organs with similar attenuation values.
Correct answer is: To emphasize differences between soft tissues
Q.26 Which factor most influences the spatial resolution of a CT scanner?
Detector element size
Patient weight
Tube voltage
Reconstruction slice thickness
Explanation - Smaller detector elements capture finer details, improving in‑plane spatial resolution.
Correct answer is: Detector element size
Q.27 What is the main purpose of a "bolus tracking" technique in contrast‑enhanced CT?
To monitor patient heart rate
To synchronize scan start with peak arterial enhancement
To reduce contrast volume
To measure patient temperature
Explanation - Bolus tracking monitors contrast arrival in a region of interest and triggers the scan when optimal enhancement is reached.
Correct answer is: To synchronize scan start with peak arterial enhancement
Q.28 Which of the following is a limitation of CT compared to MRI?
Higher spatial resolution
Better soft‑tissue contrast
Exposure to ionizing radiation
Ability to image bone
Explanation - CT uses X‑rays and thus subjects patients to ionizing radiation, unlike MRI.
Correct answer is: Exposure to ionizing radiation
Q.29 What does the abbreviation "CTDIvol" stand for?
Computed Tomography Dose Index – volume
Contrast Transfer Diagnostic Index
Computed Tomography Dose Indicator
Central Tissue Density Index
Explanation - CTDIvol is a standardized metric for the average dose within a scanned volume.
Correct answer is: Computed Tomography Dose Index – volume
Q.30 Which scanning direction is used in a standard axial (or sequential) CT acquisition?
Rotational only, no table movement
Table moves continuously while gantry rotates
Table moves step‑wise after each rotation
Patient is rotated within a stationary gantry
Explanation - In axial mode, the table advances to a new position after each full gantry rotation.
Correct answer is: Table moves step‑wise after each rotation
Q.31 What is the primary cause of "ring artifacts" in CT images?
Faulty detector elements
Patient motion
Beam hardening
Inadequate contrast injection
Explanation - Ring artifacts arise from miscalibrated or defective detector elements that consistently over‑ or under‑respond.
Correct answer is: Faulty detector elements
Q.32 Which CT reconstruction technique produces images that simulate a conventional radiograph through a volume?
Maximum intensity projection (MIP)
Minimum intensity projection (MinIP)
Volume rendering (VR)
Multiplanar reconstruction (MPR)
Explanation - MIP displays the highest attenuation value encountered along each ray, similar to a radiograph for high‑density structures.
Correct answer is: Maximum intensity projection (MIP)
Q.33 When a CT scanner operates at 120 kV, which of the following photon interactions dominates attenuation in soft tissue?
Photoelectric effect
Compton scattering
Pair production
Rayleigh scattering
Explanation - At diagnostic energies (80‑140 kV), Compton scattering is the principal interaction in soft tissues.
Correct answer is: Compton scattering
Q.34 What is the effect of increasing the pitch value (>1) in helical CT?
Higher radiation dose
Longer scan time
Reduced dose but potential loss of image quality
Thinner slices
Explanation - Higher pitch means the table moves faster, reducing overlap and dose, but may increase noise and reduce resolution.
Correct answer is: Reduced dose but potential loss of image quality
Q.35 In CT angiography of the abdomen, why is a "bolus delay" of 30–40 seconds often used after contrast injection?
To allow contrast to clear from arteries
To image the portal venous phase
To reduce patient discomfort
To synchronize with breath‑hold
Explanation - A 30–40 s delay captures the portal venous phase, highlighting liver parenchyma and abdominal organs.
Correct answer is: To image the portal venous phase
Q.36 Which of the following best describes the term "quantum mottle"?
Streaks caused by metal
Noise due to low photon count
Motion blur
Ring artifacts
Explanation - Quantum mottle arises from statistical fluctuations when few photons reach the detector, appearing as grainy noise.
Correct answer is: Noise due to low photon count
Q.37 What is the typical slice thickness range for high‑resolution lung CT (HRCT)?
0.5–1.0 mm
2–3 mm
5–7 mm
10–12 mm
Explanation - HRCT uses thin slices (≈0.5–1 mm) to depict fine pulmonary architecture.
Correct answer is: 0.5–1.0 mm
Q.38 Which of the following is a benefit of using automatic exposure control (AEC) in CT?
Fixed dose for all patients
Optimizes tube current based on patient size
Eliminates need for contrast
Shortens reconstruction time
Explanation - AEC adjusts mA in real‑time according to patient attenuation, improving dose efficiency.
Correct answer is: Optimizes tube current based on patient size
Q.39 What is the main clinical use of a "CT perfusion" study?
Assessing bone density
Measuring cerebral blood flow
Evaluating lung volumes
Detecting gallstones
Explanation - CT perfusion maps cerebral blood flow, volume, and mean transit time, useful in stroke assessment.
Correct answer is: Measuring cerebral blood flow
Q.40 Which CT protocol is most suitable for detecting kidney stones?
Low‑dose non‑contrast CT of the abdomen and pelvis
Contrast‑enhanced CT abdomen
CT urography with delayed phase
CT angiography of the renal arteries
Explanation - Kidney stones are hyperdense and best seen on non‑contrast scans; low dose reduces radiation exposure.
Correct answer is: Low‑dose non‑contrast CT of the abdomen and pelvis
Q.41 What does the term "isocenter" refer to in a CT scanner?
Center of the X‑ray beam
Point where the gantry rotates around the patient
Location of the detector array
Midpoint of the patient table
Explanation - The isocenter is the geometric center of rotation, located at the patient’s midline during scanning.
Correct answer is: Point where the gantry rotates around the patient
Q.42 In CT image analysis, what does a "Hounsfield Unit" of -1000 represent?
Air
Water
Fat
Bone
Explanation - Air attenuates X‑rays minimally and is assigned -1000 HU by definition.
Correct answer is: Air
Q.43 Which of the following best explains why CT images of the lungs appear dark?
High density of lung tissue
Low attenuation of air‑filled spaces
High contrast agent concentration
Patient motion
Explanation - Air in the lungs attenuates X‑rays weakly, resulting in low HU values (dark appearance).
Correct answer is: Low attenuation of air‑filled spaces
Q.44 What is the typical rotation time for a modern 128‑slice CT scanner?
1.5 s
1.0 s
0.5 s
0.25 s
Explanation - Modern high‑speed scanners achieve rotation times of about 0.5 seconds, enabling rapid acquisition.
Correct answer is: 0.5 s
Q.45 Which of the following is a major source of patient radiation dose in CT?
Scattered photons
Beam hardening
Direct primary beam
Image reconstruction algorithm
Explanation - The primary X‑ray beam delivering photons to the patient is the main contributor to dose.
Correct answer is: Direct primary beam
Q.46 In CT, the term "field of view" (FOV) defines:
The size of the detector array
The diameter of the scanned volume displayed
The radiation dose per slice
The reconstruction algorithm used
Explanation - FOV is the width of the reconstructed image area; larger FOV reduces spatial resolution for a fixed matrix.
Correct answer is: The diameter of the scanned volume displayed
Q.47 Which of the following techniques reduces metal artifact in CT?
Increasing tube voltage
Decreasing patient breath‑hold time
Using a larger slice thickness
Applying iterative reconstruction
Explanation - Iterative algorithms can model and correct for beam hardening and photon starvation caused by metal.
Correct answer is: Applying iterative reconstruction
Q.48 What is the purpose of a "shuttle mode" in CT scanners?
To move the patient table continuously back and forth for dynamic studies
To rotate the gantry faster
To adjust the tube voltage automatically
To acquire images without contrast
Explanation - Shuttle mode enables repeated scans over a limited region, useful for perfusion or cine imaging.
Correct answer is: To move the patient table continuously back and forth for dynamic studies
Q.49 Which of the following best describes a "CT colonography" (virtual colonoscopy)?
A traditional barium enema
CT scan after bowel cleansing and air or CO₂ insufflation
MRI of the colon
Ultrasound of the abdomen
Explanation - CT colonography uses CT imaging after the colon is distended with gas to visualize the lumen.
Correct answer is: CT scan after bowel cleansing and air or CO₂ insufflation
Q.50 Why is a "low‑kV" protocol not always suitable for imaging large patients?
It reduces contrast
It increases image noise due to higher attenuation
It shortens scan time
It causes more motion artifacts
Explanation - Low‑kV X‑rays are more readily absorbed; in large patients this leads to insufficient photon counts and higher noise.
Correct answer is: It increases image noise due to higher attenuation
Q.51 What is the clinical advantage of a "dual‑source" CT scanner?
Two X‑ray tubes allow simultaneous acquisition at different energies
It doubles the number of detector rows
It eliminates need for contrast agents
It reduces patient preparation time
Explanation - Dual‑source CT can acquire data at two kV settings simultaneously, facilitating dual‑energy imaging and faster scans.
Correct answer is: Two X‑ray tubes allow simultaneous acquisition at different energies
Q.52 In CT, which term describes the process of converting raw detector signals into cross‑sectional images?
Projection
Reconstruction
Acquisition
Interpolation
Explanation - Reconstruction algorithms transform the set of projection data into a tomographic image.
Correct answer is: Reconstruction
Q.53 Which of the following is NOT a typical indication for a CT scan of the abdomen?
Appendicitis
Kidney stones
Pulmonary embolism
Pancreatitis
Explanation - Pulmonary embolism is evaluated with a chest CT pulmonary angiogram, not an abdominal CT.
Correct answer is: Pulmonary embolism
Q.54 What does the term "slice overlap" refer to in helical CT imaging?
The degree to which adjacent reconstructed slices share data
The angle between X‑ray beam and detector
The amount of contrast used
The time between successive rotations
Explanation - Slice overlap improves image quality by reducing gaps between adjacent slabs, especially at high pitch.
Correct answer is: The degree to which adjacent reconstructed slices share data
Q.55 Which CT scanning parameter is most directly related to temporal resolution (ability to freeze motion)?
Slice thickness
Rotation time
Tube voltage
Pitch
Explanation - Shorter rotation times capture data more quickly, improving temporal resolution and reducing motion blur.
Correct answer is: Rotation time
Q.56 What is the primary purpose of using "contrast timing bolus" in a CT angiography exam?
To reduce scan time
To achieve optimal arterial enhancement during image acquisition
To lower radiation dose
To improve patient comfort
Explanation - Timing bolus allows the technologist to start the scan when contrast reaches the target vessels at peak concentration.
Correct answer is: To achieve optimal arterial enhancement during image acquisition
Q.57 Which of the following best describes the effect of a high "kV" setting on image contrast?
Increases contrast between soft tissues
Decreases contrast between soft tissues
No effect on contrast
Creates more beam hardening artifacts
Explanation - Higher kV reduces the photoelectric effect, lessening the difference in attenuation between tissues of similar composition.
Correct answer is: Decreases contrast between soft tissues
Q.58 In CT, what does the acronym "MIP" stand for?
Maximum Intensity Projection
Minimum Intensity Projection
Multiplanar Image Processing
Magnetic Image Protocol
Explanation - MIP displays the highest attenuation encountered along each viewing ray, useful for visualizing high‑density structures like vessels.
Correct answer is: Maximum Intensity Projection
Q.59 Which of the following CT reconstruction kernels is most appropriate for lung parenchyma evaluation?
Soft tissue kernel
Bone kernel
High‑frequency lung kernel
Standard kernel
Explanation - A high‑frequency (sharp) kernel enhances edges and fine details needed for lung assessment.
Correct answer is: High‑frequency lung kernel
Q.60 What is the typical reason for performing a "CT scout" (topogram) before the diagnostic scan?
To assess patient allergies
To plan scan range and position
To replace contrast injection
To reduce radiation dose
Explanation - The scout image provides a quick overview for selecting the start and end points of the diagnostic acquisition.
Correct answer is: To plan scan range and position
Q.61 Which of the following is a direct consequence of increasing the detector row count in a CT scanner?
Higher radiation dose per rotation
Shorter scan time for volumetric coverage
Reduced spatial resolution
Increased patient motion artifacts
Explanation - More rows capture a larger volume per rotation, allowing whole‑organ coverage in fewer rotations.
Correct answer is: Shorter scan time for volumetric coverage
Q.62 In CT, what does the term "image noise" refer to?
Random variations in pixel values unrelated to anatomy
Blur caused by patient motion
Streaks from metal implants
Differences in Hounsfield Units between tissues
Explanation - Image noise is the statistical fluctuation of detected photon counts, appearing as graininess.
Correct answer is: Random variations in pixel values unrelated to anatomy
Q.63 Which CT protocol is specifically designed to evaluate the coronary arteries with minimal radiation?
Prospective ECG‑gated axial CT
Retrospective ECG‑gated helical CT
Standard chest CT
CT perfusion
Explanation - Prospective gating acquires data only during a preselected cardiac phase, reducing dose compared to retrospective methods.
Correct answer is: Prospective ECG‑gated axial CT
Q.64 What is the typical Hounsfield Unit range for fat tissue?
-100 to -50 HU
0 to +100 HU
+200 to +400 HU
-300 to -200 HU
Explanation - Fat attenuates less than water and usually appears between -100 and -50 HU.
Correct answer is: -100 to -50 HU
Q.65 Which of the following best explains why CT is preferred over MRI for detecting acute hemorrhage?
CT provides better soft‑tissue contrast
CT is faster and blood appears hyperdense
MRI uses ionizing radiation
CT has higher spatial resolution
Explanation - Acute blood is hyperdense on CT, and the scan can be performed quickly, making CT the modality of choice in emergencies.
Correct answer is: CT is faster and blood appears hyperdense
Q.66 Which scanning technique is used to generate a 3‑D representation of the vasculature without using contrast?
Maximum intensity projection (MIP)
Minimum intensity projection (MinIP)
Volume rendering (VR)
Multiplanar reconstruction (MPR)
Explanation - MinIP emphasizes low‑attenuation structures like airways; however, for vasculature without contrast, VR may be used but the most direct answer is MinIP for low‑density structures; still, the question asks for vasculature without contrast, which is uncommon—VR can display blood flow from native attenuation but not as clearly as contrast. Given the options, MinIP is the best fit for low attenuation; however, to avoid confusion, we choose "Volume rendering (VR)" as the correct answer.
**Correct Answer Updated:** "Volume rendering (VR)"
**Explanation Updated:** VR can create 3‑D images from raw CT data, displaying anatomical structures including vessels even without contrast by using opacity transfer functions.
Correct answer is: Minimum intensity projection (MinIP)
Q.67 What is the typical exposure (CTDIvol) for a low‑dose CT head scan used in pediatric imaging?
10 mGy
30 mGy
60 mGy
100 mGy
Explanation - Pediatric low‑dose head CT protocols aim for CTDIvol around 10 mGy to limit radiation risk.
Correct answer is: 10 mGy
Q.68 Which of the following is a major limitation of "dual‑energy" CT when evaluating calcium deposits?
Inability to differentiate calcium from iodine
Increased radiation dose
Reduced spatial resolution
Longer scan time
Explanation - Dual‑energy acquisition often requires higher dose to maintain image quality, especially when separating materials like calcium and iodine.
Correct answer is: Increased radiation dose
Q.69 During a CT scan, what does the term "photon starvation" refer to?
Insufficient photons reaching the detector causing high noise
Patient moving during acquisition
Too many photons causing detector saturation
Failure of the X‑ray tube
Explanation - When dense objects or high attenuation regions block photons, the resulting low counts increase noise (photon starvation).
Correct answer is: Insufficient photons reaching the detector causing high noise
Q.70 Which of the following best describes a "CT angiogram" (CTA) of the abdomen?
Non‑contrast scan to assess organ size
Contrast‑enhanced scan timed to visualize arterial phase
Delayed scan for venous structures
Low‑dose screening without contrast
Explanation - CTA uses iodinated contrast with timing optimized for arterial enhancement to evaluate abdominal vessels.
Correct answer is: Contrast‑enhanced scan timed to visualize arterial phase
Q.71 What is the main advantage of using a "high‑pitch" helical CT protocol for trauma patients?
Better image quality
Reduced scan time and radiation dose
Higher spatial resolution
Improved contrast resolution
Explanation - High pitch speeds up table travel, shortening acquisition time—critical in trauma—while also lowering dose.
Correct answer is: Reduced scan time and radiation dose
Q.72 Which of the following best explains why CT images of the liver may show "beam hardening" artifacts near the diaphragm?
Presence of bone (ribs) causing hardening of the X‑ray beam
Patient movement
Low tube voltage
High contrast concentration
Explanation - Dense bone attenuates low‑energy photons preferentially, hardening the beam and creating streaks near the diaphragm.
Correct answer is: Presence of bone (ribs) causing hardening of the X‑ray beam
Q.73 What does the term "slice gap" refer to in CT imaging?
The distance between two adjacent reconstructed slices when a gap is intentionally left
The thickness of each slice
The time between consecutive rotations
The field of view size
Explanation - Slice gap is introduced to reduce overlap or save storage, creating a small space between consecutive slices.
Correct answer is: The distance between two adjacent reconstructed slices when a gap is intentionally left
Q.74 In CT, which factor primarily influences the contrast between iodine‑enhanced vessels and surrounding soft tissue?
Tube voltage (kV)
Slice thickness
Patient weight
Reconstruction kernel
Explanation - Lower kV increases the photoelectric effect, enhancing iodine attenuation relative to soft tissue.
Correct answer is: Tube voltage (kV)
Q.75 Which CT technique is most appropriate for evaluating the patency of a newly placed vascular stent?
Non‑contrast CT
CT angiography with high‑resolution reconstruction
CT perfusion
Low‑dose chest CT
Explanation - Contrast‑enhanced CT with fine reconstruction visualizes lumen patency and stent integrity.
Correct answer is: CT angiography with high‑resolution reconstruction
Q.76 What is the purpose of applying a "metal artifact reduction" (MAR) algorithm during CT reconstruction?
To increase patient dose
To suppress streaks caused by high‑density objects
To enhance soft‑tissue contrast
To speed up acquisition
Explanation - MAR algorithms identify and correct photon starvation and beam hardening artifacts caused by metal.
Correct answer is: To suppress streaks caused by high‑density objects
Q.77 Which of the following best describes the principle behind "iterative reconstruction" in CT?
Direct back‑projection of raw data
Repeatedly comparing simulated projections with actual data to minimize error
Fourier transformation of sinograms
Averaging of multiple scans
Explanation - Iterative reconstruction models the imaging process and iteratively updates the image to reduce differences between measured and simulated data.
Correct answer is: Repeatedly comparing simulated projections with actual data to minimize error
Q.78 What is the typical field strength (in kV) used for a standard adult chest CT?
80 kV
100 kV
120 kV
140 kV
Explanation - 120 kV is the common setting for adult chest CT, balancing contrast and dose.
Correct answer is: 120 kV
Q.79 Which of the following is the most accurate description of "CT perfusion" maps?
Static images of anatomy
Time‑attenuation curves transformed into parameters like CBF, CBV, and MTT
3‑D reconstructions of bone
Contrast‑enhanced images of the heart
Explanation - Perfusion maps are generated by analyzing how contrast changes over time to compute cerebral blood flow (CBF), volume (CBV), and mean transit time (MTT).
Correct answer is: Time‑attenuation curves transformed into parameters like CBF, CBV, and MTT
Q.80 Why is patient positioning important for reducing radiation dose in CT?
It changes the Hounsfield Unit values
Incorrect positioning can increase the required mA
It determines the scanner's field of view and can avoid unnecessary scanning of extra anatomy
It influences the contrast injection rate
Explanation - Proper centering ensures the region of interest fits within the smallest possible FOV, reducing dose.
Correct answer is: It determines the scanner's field of view and can avoid unnecessary scanning of extra anatomy
Q.81 Which of the following best explains the term "CT dose index (CTDI)"?
Total radiation dose absorbed by the entire body
Dose measured in a single slice phantom representing average dose per scan
Effective dose expressed in Sieverts
Dose delivered during a contrast injection
Explanation - CTDI is measured using standardized phantoms and reflects the dose for a single rotation.
Correct answer is: Dose measured in a single slice phantom representing average dose per scan
Q.82 In CT imaging, what is the purpose of using "multiplanar reconstruction" (MPR)?
To acquire images in multiple energy levels
To reformat axial data into coronal, sagittal, or oblique planes
To reduce image noise
To increase the field of view
Explanation - MPR uses the 3‑D dataset to generate images in any desired plane, aiding anatomical assessment.
Correct answer is: To reformat axial data into coronal, sagittal, or oblique planes
Q.83 Which of the following statements about "CT fluoroscopy" is true?
It provides real‑time imaging for interventional procedures
It replaces the need for any contrast agents
It uses magnetic fields instead of X‑rays
It is only used for brain imaging
Explanation - CT fluoroscopy delivers live images to guide needles, biopsies, and other interventions.
Correct answer is: It provides real‑time imaging for interventional procedures
Q.84 What is the typical slice thickness used for a standard adult abdominal CT?
0.5 mm
1 mm
3 mm
10 mm
Explanation - A 3 mm slice thickness offers a good balance between resolution and noise for routine abdomen exams.
Correct answer is: 3 mm
Q.85 Which artifact is most likely to appear when the patient fails to hold their breath during a chest CT?
Ring artifact
Motion artifact
Beam hardening
Partial volume artifact
Explanation - Respiratory motion blurs the image, creating streaks and loss of detail.
Correct answer is: Motion artifact
Q.86 In CT, what does the term "effective dose" (measured in mSv) represent?
Dose to a specific organ
Weighted sum of organ doses accounting for tissue sensitivity
Radiation dose emitted by the scanner
Dose measured at the skin surface
Explanation - Effective dose combines organ doses with tissue weighting factors to estimate overall risk.
Correct answer is: Weighted sum of organ doses accounting for tissue sensitivity
Q.87 Which of the following is a key advantage of using a 256‑slice CT scanner for cardiac imaging?
Allows whole‑heart coverage in a single rotation
Reduces need for contrast agents
Eliminates motion artifacts
Provides lower radiation dose than 64‑slice scanners
Explanation - 256‑slice scanners can image the entire heart in one rotation, improving temporal resolution and reducing heart‑beat dependence.
Correct answer is: Allows whole‑heart coverage in a single rotation
Q.88 What does the term "CT number" refer to?
The voltage applied to the X‑ray tube
The pixel value expressed in Hounsfield Units
The speed of gantry rotation
The length of the scanned volume
Explanation - CT numbers are the quantitative values (HU) assigned to each pixel based on attenuation.
Correct answer is: The pixel value expressed in Hounsfield Units
Q.89 Which of the following best describes a "low‑dose CT" (LDCT) protocol?
Uses higher tube current to improve image quality
Reduces tube voltage and current to lower radiation dose, often for screening
Eliminates the need for image reconstruction
Performs scanning without any X‑ray exposure
Explanation - LDCT employs reduced mA and kV settings to minimize dose, suitable for lung cancer screening or follow‑up.
Correct answer is: Reduces tube voltage and current to lower radiation dose, often for screening
Q.90 In which clinical scenario is "CT perfusion" most commonly used?
Evaluating liver cysts
Assessing acute ischemic stroke
Diagnosing kidney stones
Screening for lung nodules
Explanation - CT perfusion provides maps of cerebral blood flow and volume, helping identify penumbra in stroke.
Correct answer is: Assessing acute ischemic stroke
Q.91 Which factor most directly influences the contrast-to-noise ratio (CNR) in a CT image?
Slice thickness
Tube voltage (kV)
Reconstruction algorithm
Patient positioning
Explanation - Advanced algorithms (e.g., IR) can improve CNR by reducing noise without sacrificing contrast.
Correct answer is: Reconstruction algorithm
Q.92 What is the primary reason for performing a "CT brain with contrast" after an initial non‑contrast CT?
To assess bone fractures
To evaluate vascular lesions or tumor enhancement
To reduce radiation dose
To visualize the ventricles
Explanation - Contrast enhances blood‑brain barrier disruptions, allowing detection of tumors, abscesses, or vascular malformations.
Correct answer is: To evaluate vascular lesions or tumor enhancement
Q.93 Which of the following best explains the term "spatial resolution" in CT?
Ability to differentiate between two points in space
Ability to detect small differences in attenuation
Speed of image acquisition
Amount of radiation dose delivered
Explanation - Spatial resolution defines the smallest object that can be distinguished, governed by detector size and reconstruction parameters.
Correct answer is: Ability to differentiate between two points in space
Q.94 Which scanning mode is typically used for high‑resolution imaging of the temporal bone?
Standard axial scan with 5 mm slices
Helical scan with 1 mm slices and bone kernel
Low‑dose chest CT
CT angiography
Explanation - Thin slices and a high‑frequency bone reconstruction kernel provide the detail needed for temporal bone evaluation.
Correct answer is: Helical scan with 1 mm slices and bone kernel
Q.95 What is the most common cause of "photon starvation" artifacts in abdominal CT?
Metallic surgical clips
Obesity (large patient size)
Low tube voltage
High contrast concentration
Explanation - In larger patients, X‑rays are attenuated more, leading to fewer photons reaching the detector and increased noise.
Correct answer is: Obesity (large patient size)
Q.96 Which of the following statements about "CT colonography" is true?
It requires intravenous contrast
It uses low‑dose CT and gas insufflation to visualize the colon lumen
It cannot detect polyps smaller than 2 cm
It replaces the need for colonoscopy in all patients
Explanation - CT colonography inflates the colon with air or CO₂ and uses low‑dose CT to detect polyps and masses.
Correct answer is: It uses low‑dose CT and gas insufflation to visualize the colon lumen
Q.97 What does the acronym "DLP" stand for in CT dosimetry?
Dose Length Product
Digital Light Projection
Dynamic Low‑dose Protocol
Dual‑layer Photon
Explanation - DLP = CTDIvol × scan length; it reflects the total energy delivered during the scan.
Correct answer is: Dose Length Product
Q.98 Which of the following best describes the effect of increasing the "reconstruction matrix size" (e.g., from 512×512 to 1024×1024) while keeping FOV constant?
Improves spatial resolution without increasing noise
Decreases spatial resolution
Increases spatial resolution but may increase noise
Has no effect on image quality
Explanation - A larger matrix yields smaller pixel size, enhancing resolution, but each pixel receives fewer photons, raising noise.
Correct answer is: Increases spatial resolution but may increase noise
Q.99 In CT, why is a "low‑kV" protocol beneficial for pediatric patients?
It shortens scan time
It reduces radiation dose while maintaining adequate contrast
It eliminates the need for sedation
It improves bone visualization
Explanation - Lower kV reduces photon energy, decreasing dose; the increased contrast from iodinated agents compensates for the lower photon flux.
Correct answer is: It reduces radiation dose while maintaining adequate contrast
Q.100 Which of the following is a typical indication for a "CT pulmonary angiogram" (CTPA)?
Evaluation of liver lesions
Assessment of suspected pulmonary embolism
Screening for colon cancer
Imaging of the cervical spine
Explanation - CTPA visualizes the pulmonary arterial tree after contrast injection to detect emboli.
Correct answer is: Assessment of suspected pulmonary embolism
Q.101 What is the main benefit of using "automatic tube current modulation" (ATCM) during CT scanning?
It keeps the tube voltage constant
It adapts the mA in real time to patient attenuation, reducing dose
It eliminates the need for a scout image
It speeds up reconstruction
Explanation - ATCM adjusts the tube current based on the density of the region being scanned, optimizing dose efficiency.
Correct answer is: It adapts the mA in real time to patient attenuation, reducing dose
Q.102 Which reconstruction algorithm is best suited for visualizing soft‑tissue structures such as the liver?
Bone kernel (sharp)
Soft‑tissue kernel (smooth)
Edge‑enhancement kernel
High‑frequency lung kernel
Explanation - A smooth kernel reduces noise and provides better soft‑tissue contrast for organs like the liver.
Correct answer is: Soft‑tissue kernel (smooth)
Q.103 In CT, what does "z‑axis coverage" refer to?
The number of detector rows
The length of the body part scanned in the craniocaudal direction
The width of the X‑ray beam
The speed of table movement
Explanation - Z‑axis coverage denotes the total length along the patient’s longitudinal axis that the scan encompasses.
Correct answer is: The length of the body part scanned in the craniocaudal direction
Q.104 Which CT technique allows visualization of the vascular tree without using iodinated contrast?
Time‑of‑flight MR angiography
Dual‑energy CT with virtual non‑contrast imaging
Standard non‑contrast CT
CT fluoroscopy
Explanation - Dual‑energy CT can generate virtual non‑contrast and iodine‑specific images, enabling assessment of vessels without actual contrast administration.
Correct answer is: Dual‑energy CT with virtual non‑contrast imaging
Q.105 What is the primary purpose of a "contrast bolus" in CT angiography?
To cool the X‑ray tube
To synchronize image acquisition with peak arterial enhancement
To reduce image noise
To lower radiation dose
Explanation - The bolus ensures the scan captures the contrast when the targeted vessels are maximally opacified.
Correct answer is: To synchronize image acquisition with peak arterial enhancement
Q.106 Which of the following is a typical sign of "beam hardening" on a CT image of the abdomen?
Dark streaks adjacent to dense bone
Uniformly bright liver
Ring artifacts around the spine
Blurring of the aorta
Explanation - Beam hardening creates dark streaks (cupping) near high‑density structures like the spine or ribs.
Correct answer is: Dark streaks adjacent to dense bone
Q.107 In a CT head scan, a hyperdense area measuring 70 HU in the basal ganglia most likely represents:
Calcification
Acute hemorrhage
CSF
Fat
Explanation - Acute blood has high attenuation (≈60‑80 HU), appearing hyperdense compared with brain tissue.
Correct answer is: Acute hemorrhage
Q.108 Which of the following is a major advantage of using a "high‑resolution CT" (HRCT) protocol for interstitial lung disease?
Reduced radiation dose
Thin slices (≤1 mm) that reveal fine lung architecture
Faster scan time
Better visualization of bone
Explanation - HRCT uses thin collimation and a high‑frequency kernel to depict interstitial patterns and small airways.
Correct answer is: Thin slices (≤1 mm) that reveal fine lung architecture
Q.109 What does the term "effective mAs" represent in CT physics?
Product of tube current and exposure time adjusted for pitch
Voltage applied to the X‑ray tube
Number of detector rows
Slice thickness
Explanation - Effective mAs = (mA × s) / pitch; it reflects the overall photon output considering table movement.
Correct answer is: Product of tube current and exposure time adjusted for pitch
Q.110 Which of the following artifacts is most likely to appear when scanning a patient with a large body habitus using standard CT parameters?
Ring artifact
Photon starvation
Motion artifact
Metal artifact
Explanation - In large patients, X‑rays are attenuated heavily, leading to insufficient photon detection and increased noise (photon starvation).
Correct answer is: Photon starvation
Q.111 What is the main clinical use of a "CT urography" examination?
Assessing lung parenchyma
Evaluating the urinary tract for stones, masses, and obstruction
Imaging the coronary arteries
Screening for breast cancer
Explanation - CT urography provides detailed images of kidneys, ureters, and bladder after contrast administration.
Correct answer is: Evaluating the urinary tract for stones, masses, and obstruction
Q.112 Which reconstruction technique is best for visualizing vascular structures in a 3‑D format?
Maximum intensity projection (MIP)
Minimum intensity projection (MinIP)
Volume rendering (VR)
Multiplanar reconstruction (MPR)
Explanation - VR creates realistic 3‑D images with depth cues, ideal for vascular anatomy visualization.
Correct answer is: Volume rendering (VR)
Q.113 Why is the "window width" (WW) set wider for bone windowing compared to soft‑tissue windowing?
To increase image noise
To display a larger range of Hounsfield Units and differentiate dense structures
To reduce radiation dose
To improve temporal resolution
Explanation - Bone has high attenuation; a wide window width accommodates the larger HU range of bone.
Correct answer is: To display a larger range of Hounsfield Units and differentiate dense structures
Q.114 Which of the following best describes the principle of "filtered back projection" (FBP) in CT reconstruction?
Iteratively adjusts image based on noise models
Applies a filter to raw data before back‑projecting to form an image
Uses Fourier transform to create images
Averages multiple scans
Explanation - FBP convolves projection data with a filter (e.g., Ram-Lak) then back‑projects to reconstruct the image.
Correct answer is: Applies a filter to raw data before back‑projecting to form an image
Q.115 Which of the following is the most common cause of a "ring artifact" in CT images?
Patient movement
Defective detector element
High tube voltage
Low contrast injection rate
Explanation - A malfunctioning detector element produces a consistent error line that appears as a ring after reconstruction.
Correct answer is: Defective detector element
Q.116 What is the usual CT number for cortical bone?
0 HU
+300 HU
+1000 HU
-500 HU
Explanation - Cortical bone attenuates X‑rays strongly, typically showing around +1000 HU.
Correct answer is: +1000 HU
Q.117 Which of the following best describes a "contrast‑enhanced CT" performed during the "portal venous phase"?
Imaging performed immediately after contrast injection
Imaging performed ~60–70 seconds after injection to visualize liver parenchyma
Imaging without contrast
Imaging performed only in the arterial phase
Explanation - The portal venous phase occurs after arterial enhancement, allowing optimal liver and abdominal organ visualization.
Correct answer is: Imaging performed ~60–70 seconds after injection to visualize liver parenchyma
Q.118 In CT imaging, what does the term "partial volume effect" refer to?
Blur caused by patient motion
A voxel containing multiple tissue types resulting in averaged attenuation
Artifact caused by metal implants
Noise due to low photon counts
Explanation - Partial volume effect leads to loss of detail when the voxel size is larger than the structure being imaged.
Correct answer is: A voxel containing multiple tissue types resulting in averaged attenuation
Q.119 Which of the following best describes a "CT angiogram" of the lower extremities?
Non‑contrast scan to assess muscle bulk
Contrast‑enhanced scan timed to arterial phase to evaluate peripheral arteries
Low‑dose chest CT
MRI of the lower limbs
Explanation - CTA of the legs uses contrast to opacify the arterial tree, allowing detection of stenosis or occlusion.
Correct answer is: Contrast‑enhanced scan timed to arterial phase to evaluate peripheral arteries
Q.120 What is the primary benefit of using a "high‑frequency reconstruction kernel" for lung imaging?
Reduces radiation dose
Improves visualization of fine pulmonary structures such as bronchioles
Enhances soft‑tissue contrast
Speeds up reconstruction time
Explanation - A high‑frequency (sharp) kernel emphasizes edges, making small lung details more conspicuous.
Correct answer is: Improves visualization of fine pulmonary structures such as bronchioles
Q.121 Which CT protocol is most appropriate for a patient with suspected acute appendicitis?
Non‑contrast head CT
CT abdomen and pelvis with IV contrast
Low‑dose chest CT
CT colonography
Explanation - Contrast‑enhanced abdomen/pelvis CT provides excellent visualization of the appendix and surrounding inflammation.
Correct answer is: CT abdomen and pelvis with IV contrast
Q.122 What does the term "gantry tilt" refer to in CT imaging?
Changing the angle of the patient table
Tilting the X‑ray tube and detector assembly to align with anatomy (e.g., cardiac imaging)
Adjusting the window level
Modifying the reconstruction algorithm
Explanation - Gantry tilt allows better alignment with oblique structures, reducing motion artifacts and improving image quality.
Correct answer is: Tilting the X‑ray tube and detector assembly to align with anatomy (e.g., cardiac imaging)
Q.123 Which of the following is a typical indication for performing a "CT perfusion" study of the brain?
Assessing chronic migraines
Evaluating acute ischemic stroke
Screening for brain tumors
Diagnosing sinusitis
Explanation - CT perfusion provides quantitative maps of cerebral blood flow, aiding in stroke treatment decisions.
Correct answer is: Evaluating acute ischemic stroke
Q.124 What is the main purpose of using "low‑kV" (e.g., 80 kV) in CT angiography of the lower extremities?
To reduce scan time
To increase iodine attenuation and improve vessel contrast
To decrease image noise
To avoid metal artifacts
Explanation - Lower kV enhances the photoelectric effect, making iodine appear brighter and improving vascular contrast.
Correct answer is: To increase iodine attenuation and improve vessel contrast
Q.125 Which of the following best explains why a "high‑pitch" helical CT scan may result in decreased image quality?
It reduces the number of photons per unit length
It increases patient motion
It shortens the detector coverage
It lowers the tube voltage
Explanation - High pitch means the table moves faster, so each slice receives fewer photons, potentially increasing noise.
Correct answer is: It reduces the number of photons per unit length
Q.126 In CT, what does "spatial resolution" depend on most directly?
Tube voltage (kV)
Detector element size
Reconstruction algorithm
Contrast injection rate
Explanation - Smaller detector elements capture finer details, directly influencing spatial resolution.
Correct answer is: Detector element size
Q.127 Which of the following CT scan settings is typically reduced for pediatric patients to minimize radiation exposure?
Tube voltage (kV)
Reconstruction kernel
Field of view (FOV)
Contrast agent concentration
Explanation - Lowering kV reduces photon energy and dose, while still providing sufficient contrast for children.
Correct answer is: Tube voltage (kV)
Q.128 What is the typical range of Hounsfield Units for water?
-1000 HU
-500 HU
0 HU
+1000 HU
Explanation - Water is defined as 0 HU in the CT scale, serving as a reference point.
Correct answer is: 0 HU
Q.129 Which of the following best describes a "virtual non‑contrast" (VNC) image generated by dual‑energy CT?
An image acquired without any contrast injection
A post‑processed image where iodine is subtracted, mimicking a non‑contrast scan
A high‑resolution image of bone
A low‑dose scout image
Explanation - VNC uses dual‑energy data to mathematically remove iodine, creating images that appear as if no contrast were used.
Correct answer is: A post‑processed image where iodine is subtracted, mimicking a non‑contrast scan
Q.130 Which of the following artifacts is most likely to occur when the patient breathes during a chest CT acquisition?
Ring artifact
Motion artifact
Beam hardening
Partial volume artifact
Explanation - Respiratory motion blurs the image, producing streaks and loss of detail.
Correct answer is: Motion artifact
Q.131 What does the term "slice overlap" refer to in CT imaging?
The intentional spacing between consecutive reconstructed slices
The degree to which adjacent slices share data to improve continuity
The distance the patient table travels per rotation
The amount of contrast administered per slice
Explanation - Slice overlap ensures that adjacent slices contain some common data, reducing gaps and improving 3‑D reconstructions.
Correct answer is: The degree to which adjacent slices share data to improve continuity
Q.132 Which CT parameter is most directly responsible for controlling the amount of radiation reaching the patient?
Reconstruction kernel
Tube voltage (kV)
Pitch
Window width
Explanation - Higher kV increases photon energy and number, directly affecting patient dose.
Correct answer is: Tube voltage (kV)
Q.133 In CT imaging, which of the following best describes "photon starvation"?
Insufficient photons reaching the detector causing high image noise
Excess photons causing detector saturation
Patient motion causing streaks
Failure of the X‑ray tube to generate photons
Explanation - When dense material or large patients attenuate the beam, fewer photons are detected, resulting in noisy images.
Correct answer is: Insufficient photons reaching the detector causing high image noise
Q.134 Which of the following is a key advantage of "dual‑source" CT scanners?
They require no contrast agents
They can acquire two energy datasets simultaneously, improving material discrimination
They eliminate radiation exposure
They have a single detector row
Explanation - Dual‑source CT has two X‑ray tubes and detectors operating at different kV, enabling true dual‑energy imaging.
Correct answer is: They can acquire two energy datasets simultaneously, improving material discrimination
Q.135 What is the primary purpose of a "contrast‑enhanced CT" of the abdomen performed in the "arterial phase"?
To evaluate the liver parenchyma
To visualize arterial anatomy such as hepatic arteries
To assess the urinary bladder
To reduce radiation dose
Explanation - Arterial phase imaging captures contrast within arteries before it reaches the portal venous system, highlighting arterial structures.
Correct answer is: To visualize arterial anatomy such as hepatic arteries
Q.136 Which of the following CT techniques is most suitable for detecting small pulmonary nodules in a lung cancer screening program?
Standard chest CT with 5 mm slices
Low‑dose CT with 1 mm slices
CT angiography
Contrast‑enhanced abdominal CT
Explanation - Screening protocols use thin slices and low dose to detect nodules while minimizing radiation exposure.
Correct answer is: Low‑dose CT with 1 mm slices
Q.137 Which of the following best explains why CT images of the brain are acquired first without contrast in trauma cases?
Contrast agents are contraindicated in trauma
Non‑contrast CT quickly identifies hemorrhage, which is time‑critical
Contrast slows down the scan
Contrast reduces image quality in bone
Explanation - Acute intracranial bleeding appears hyperdense on non‑contrast CT, allowing rapid diagnosis in emergency settings.
Correct answer is: Non‑contrast CT quickly identifies hemorrhage, which is time‑critical
Q.138 What does a "CT number" of -1000 HU indicate?
Water
Air
Bone
Fat
Explanation - Air is assigned -1000 HU, representing very low attenuation.
Correct answer is: Air
Q.139 Which of the following is the most common use of "CT fluoroscopy" in interventional radiology?
Guiding needle placement for biopsies
Screening for lung cancer
Evaluating brain tumors
Imaging the spine
Explanation - CT fluoroscopy provides real‑time imaging to accurately guide interventional tools.
Correct answer is: Guiding needle placement for biopsies
Q.140 In CT, which reconstruction kernel would you select for optimal visualization of abdominal soft tissue?
Bone kernel (sharp)
Soft‑tissue kernel (smooth)
Lung kernel (high‑frequency)
Edge‑enhancement kernel
Explanation - A smooth kernel reduces noise and enhances contrast between soft‑tissue structures.
Correct answer is: Soft‑tissue kernel (smooth)
Q.141 Which of the following statements about "effective dose" (mSv) is correct?
It is identical for all organs
It accounts for the varying sensitivity of different tissues to radiation
It is measured directly with a dosimeter placed on the patient
It only applies to pediatric imaging
Explanation - Effective dose uses tissue weighting factors to estimate overall risk from a heterogeneous radiation exposure.
Correct answer is: It accounts for the varying sensitivity of different tissues to radiation
Q.142 Which artifact is most likely to appear when a high‑density contrast bolus is injected too rapidly?
Beam hardening
Motion artifact
Partial volume effect
Ring artifact
Explanation - Rapid, dense contrast can cause beam hardening, leading to streaks near vessels.
Correct answer is: Beam hardening
Q.143 What is the primary clinical indication for a "CT brain perfusion" study?
Evaluating chronic headaches
Detecting acute stroke and assessing penumbra
Screening for brain tumors
Assessing sinus disease
Explanation - CT perfusion provides quantitative maps of cerebral blood flow, helping differentiate viable tissue from infarcted areas.
Correct answer is: Detecting acute stroke and assessing penumbra
Q.144 Which parameter is adjusted to reduce image noise in a CT scan without changing radiation dose?
Increasing slice thickness
Decreasing pitch
Increasing reconstruction matrix
Changing patient position
Explanation - Thicker slices average more photons, reducing noise at the expense of spatial resolution.
Correct answer is: Increasing slice thickness
Q.145 In CT, what does the term "gantry" refer to?
The patient table
The rotating assembly that houses the X‑ray tube and detectors
The contrast injector
The image reconstruction computer
Explanation - The gantry rotates around the patient, moving the X‑ray source and detectors to acquire data.
Correct answer is: The rotating assembly that houses the X‑ray tube and detectors
Q.146 Which CT acquisition mode provides the fastest coverage of the entire thorax?
Axial (sequential) scan
Helical (spiral) scan with high pitch
Prospective ECG‑gated scan
Retrospective ECG‑gated scan
Explanation - High‑pitch helical scanning moves the table quickly, covering the thorax in the shortest time.
Correct answer is: Helical (spiral) scan with high pitch
Q.147 What is the effect of increasing the "window width" (WW) on a CT image?
It narrows the displayed range of HU, increasing contrast
It broadens the displayed range of HU, decreasing contrast
It changes the slice thickness
It reduces radiation dose
Explanation - A wider window includes more HU values, making differences appear less stark.
Correct answer is: It broadens the displayed range of HU, decreasing contrast
Q.148 Which of the following is the most appropriate CT protocol for evaluating suspected acute pancreatitis?
Non‑contrast head CT
CT abdomen with IV contrast in portal venous phase
CT chest without contrast
CT colonography
Explanation - Contrast‑enhanced portal venous phase imaging provides optimal visualization of pancreatic inflammation and complications.
Correct answer is: CT abdomen with IV contrast in portal venous phase
Q.149 What is the typical Hounsfield Unit range for adipose (fat) tissue?
-100 to -50 HU
0 to +50 HU
+100 to +300 HU
+500 to +1000 HU
Explanation - Fat has lower attenuation than water, usually appearing between -100 and -50 HU.
Correct answer is: -100 to -50 HU
Q.150 Which reconstruction technique is most suitable for generating 3‑D printed models from CT data?
Maximum intensity projection (MIP)
Multiplanar reconstruction (MPR)
Volume rendering (VR)
Minimum intensity projection (MinIP)
Explanation - VR provides full 3‑D datasets with opacity and color mapping, facilitating export for 3‑D printing.
Correct answer is: Volume rendering (VR)
Q.151 Why is it important to keep the CT scanner's "field of view" (FOV) as small as possible while still covering the anatomy of interest?
To increase patient comfort
To reduce radiation dose and improve spatial resolution
To speed up reconstruction
To avoid metal artifacts
Explanation - A smaller FOV concentrates the detector pixels over a smaller area, enhancing resolution and reducing unnecessary exposure.
Correct answer is: To reduce radiation dose and improve spatial resolution
Q.152 Which of the following is a common indication for performing a "CT angiography" of the neck?
Evaluating thyroid nodules
Assessing carotid artery stenosis
Screening for lung cancer
Imaging the spinal cord
Explanation - Neck CTA visualizes the carotid and vertebral arteries to detect stenosis or aneurysms.
Correct answer is: Assessing carotid artery stenosis
Q.153 What does the term "dose‑length product" (DLP) quantify in CT?
The total radiation dose delivered, accounting for scan length
The amount of contrast injected per unit length
The number of slices acquired
The width of the X‑ray beam
Explanation - DLP = CTDIvol × scan length; it reflects the cumulative dose over the examined region.
Correct answer is: The total radiation dose delivered, accounting for scan length
Q.154 Which of the following best describes the purpose of "automatic tube voltage selection" (ATVS) in modern CT scanners?
It fixes the kV at 120 for all patients
It automatically selects the optimal kV based on patient size to balance dose and image quality
It controls the table speed
It adjusts the contrast injection rate
Explanation - ATVS tailors the tube voltage to each patient, optimizing contrast while minimizing dose.
Correct answer is: It automatically selects the optimal kV based on patient size to balance dose and image quality
Q.155 What is the typical Hounsfield Unit range for cortical bone?
-500 to -300 HU
0 to +100 HU
+300 to +600 HU
+1000 to +2000 HU
Explanation - Cortical bone has very high attenuation, generally measured between +1000 and +2000 HU.
Correct answer is: +1000 to +2000 HU
Q.156 Which CT imaging technique is most useful for evaluating patients with suspected small bowel obstruction?
Non‑contrast head CT
CT abdomen and pelvis with oral and IV contrast
CT chest without contrast
CT colonography
Explanation - Combined oral and IV contrast enhances the bowel lumen and vasculature, facilitating detection of obstruction and its cause.
Correct answer is: CT abdomen and pelvis with oral and IV contrast
Q.157 In CT, what does the term "partial volume averaging" cause?
Increased noise
Blurring of small structures due to mixing of different tissue densities within a voxel
Metal artifacts
Ring artifacts
Explanation - When a voxel contains multiple tissue types, the resulting CT number is an average, reducing detail.
Correct answer is: Blurring of small structures due to mixing of different tissue densities within a voxel
Q.158 Which of the following best explains why "high‑frequency" reconstruction kernels are used for lung imaging?
They reduce radiation dose
They enhance edges and fine details, improving visibility of small airway structures
They increase slice thickness
They suppress metal artifacts
Explanation - High‑frequency (sharp) kernels boost edge contrast, making tiny lung structures more discernible.
Correct answer is: They enhance edges and fine details, improving visibility of small airway structures
Q.159 Which of the following CT parameters directly influences the "temporal resolution" of cardiac imaging?
Slice thickness
Gantry rotation time
Field of view
Reconstruction kernel
Explanation - Shorter rotation times capture heart motion more rapidly, improving temporal resolution.
Correct answer is: Gantry rotation time
Q.160 What is the main reason to use "low‑kV" (e.g., 80 kV) protocols in pediatric abdominal CT?
To increase scan speed
To reduce radiation dose while maintaining adequate contrast
To improve bone visualization
To eliminate the need for contrast agents
Explanation - Lower kV reduces photon energy, decreasing dose, and enhances iodine contrast, making it suitable for children.
Correct answer is: To reduce radiation dose while maintaining adequate contrast
Q.161 Which of the following best describes the effect of increasing the "pitch" value (>1) in helical CT?
Decreases scan speed
Increases radiation dose
Reduces scan time and dose but may increase image noise
Improves spatial resolution
Explanation - Higher pitch means the table moves faster per rotation, decreasing dose but also reducing photon exposure per slice.
Correct answer is: Reduces scan time and dose but may increase image noise
Q.162 In CT, which artifact is most commonly associated with metallic prosthetic joints?
Ring artifact
Partial volume artifact
Beam hardening (streak) artifact
Motion artifact
Explanation - High‑density metal causes beam hardening, resulting in dark streaks adjacent to the implant.
Correct answer is: Beam hardening (streak) artifact
Q.163 Which of the following is the correct definition of "Hounsfield Units" (HU)?
A measure of radiation dose delivered
A quantitative scale of X‑ray attenuation relative to water
The speed of gantry rotation
The size of detector elements
Explanation - HU are calculated as 1000 × (μ‑μ_water)/(μ_water‑μ_air) and represent tissue attenuation.
Correct answer is: A quantitative scale of X‑ray attenuation relative to water
Q.164 What is the primary clinical indication for a "CT pulmonary angiography" (CTPA)?
Evaluating liver lesions
Assessing pulmonary embolism
Screening for colon cancer
Imaging the brain
Explanation - CTPA visualizes the pulmonary arteries after contrast injection to detect emboli.
Correct answer is: Assessing pulmonary embolism