CAMRT Computed Tomography and Advanced Imaging Questions and Answers 1 — Questions and Answers
Question 1: In CT imaging, what does the term 'Hounsfield unit (HU)' measure?
- Radiation dose to the patient
- The attenuation value of tissue relative to water (Correct answer)
- The speed of image reconstruction
- The collimator aperture width
Correct answer: The attenuation value of tissue relative to water
Hounsfield units quantify the x-ray attenuation of a tissue relative to water (0 HU), with air at −1000 HU and dense bone at +1000 HU.
Question 2: Which CT windowing setting would best display pulmonary parenchyma?
- Window width 400, level 40 (soft tissue)
- Window width 1500, level −600 (lung window) (Correct answer)
- Window width 80, level 35 (brain window)
- Window width 2000, level 500 (bone window)
Correct answer: Window width 1500, level −600 (lung window)
A wide window width (~1500 HU) centered at a low level (~−600 HU) is used for lung windows to display the air-filled parenchyma with adequate contrast.
Question 3: What is the primary advantage of helical (spiral) CT over conventional axial CT?
- Lower radiation dose per slice
- Continuous data acquisition allowing volume imaging and multiplanar reconstruction (Correct answer)
- Better spatial resolution
- Elimination of beam-hardening artifacts
Correct answer: Continuous data acquisition allowing volume imaging and multiplanar reconstruction
Helical CT acquires a continuous volume of data during one breath-hold, enabling multiplanar reconstructions and reducing motion artifacts.
Question 4: In CT, pitch is defined as:
- The thickness of a single CT slice
- Table distance traveled per gantry rotation divided by beam collimation (Correct answer)
- The number of detector rows
- The tube current in milliamperes
Correct answer: Table distance traveled per gantry rotation divided by beam collimation
Pitch = table feed per rotation ÷ total beam collimation; a pitch >1 means faster coverage but can reduce dose and slice overlap.
Question 5: Which artifact in CT is caused by very dense structures (such as metal implants) and appears as dark and light streaks radiating from the object?
- Partial volume artifact
- Ring artifact
- Beam-hardening/metal artifact (Correct answer)
- Motion artifact
Correct answer: Beam-hardening/metal artifact
Metal implants absorb x-rays so strongly that insufficient photons reach the detector, causing beam-hardening and photon starvation, producing characteristic streak artifacts.
Question 6: What does CTDI (CT Dose Index) measure?
- Total effective dose to the patient
- Radiation dose profile along the z-axis for a single CT scan rotation (Correct answer)
- Image noise level
- Detector efficiency
Correct answer: Radiation dose profile along the z-axis for a single CT scan rotation
CTDI measures the absorbed dose along the z-axis (scan direction) for a single axial rotation and is a standardized CT dose descriptor.
CAMRT Computed Tomography and Advanced Imaging Questions and Answers 1
In CT imaging, what does the term 'Hounsfield unit (HU)' measure?