Computed Tomography Test Computed Tomography Knowledge Questions and An 3 — Questions and Answers
Question 1: Which parameter directly controls the amount of radiation delivered per CT rotation?
- kVp
- mAs (Correct answer)
- Pitch
- Slice thickness
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 2: A patient's CT scan demonstrates a hyperdense lesion in the basal ganglia on non-contrast CT. What is the most common cause?
- Ischemic infarction
- Acute hemorrhage (Correct answer)
- Air embolism
- Calcified granuloma
Correct answer: Acute hemorrhage
Fresh blood is hyperdense on non-contrast CT (55–80 HU) due to the protein content of clotted hemoglobin, making acute hemorrhage the most common cause of basal ganglia hyperdensity.
Question 3: What is the primary purpose of automatic exposure control (AEC) in CT?
- Increase image sharpness automatically based on organ type
- Modulate tube current to maintain consistent image quality while minimizing dose (Correct answer)
- Adjust kVp based on patient size
- Control injection rate of IV contrast automatically
Correct answer: Modulate tube current to maintain consistent image quality while minimizing dose
AEC (also called tube current modulation) adjusts mA in real time based on patient attenuation, maintaining target noise levels while reducing unnecessary radiation.
Question 4: Which CT artifact appears as a star-burst pattern of dark and light streaks emanating from a dense object?
- Ring artifact
- Beam hardening artifact
- Metallic streak artifact (Correct answer)
- Motion 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 5: What is the purpose of the 'scout' or 'topogram' image acquired before a CT scan?
- To measure patient radiation sensitivity
- To plan scan range, angulation, and protocol parameters (Correct answer)
- To assess contrast injection site patency
- To perform automatic patient weight calculation
Correct answer: To plan scan range, angulation, and protocol parameters
The scout (localizer) image is a low-dose 2D projection used to define the scan range, check patient positioning, and confirm the correct anatomical area.
Question 6: In multidetector CT (MDCT), what does the term 'detector configuration' refer to?
- The arrangement of X-ray tubes within the gantry
- The number of active detector rows and their width used during acquisition (Correct answer)
- The geometric shape of the detector array
- The software algorithm used to reconstruct images
Correct answer: The number of active detector rows and their width used during acquisition
Detector configuration describes how many detector rows are activated and the width of each row, determining the acquired slice thickness per rotation.
Question 7: Which intravenous contrast phase best demonstrates hepatocellular carcinoma (HCC)?
- Non-contrast phase
- Hepatic arterial phase (25–35 seconds) (Correct answer)
- Portal venous phase (60–70 seconds)
- Delayed phase (3–5 minutes)
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.
Computed Tomography Test Computed Tomography Knowledge Questions and An 3
Which parameter directly controls the amount of radiation delivered per CT rotation?