Computed Tomography Test CT Equipment and Technology 2 — Questions and Answers
Question 1: What is the function of the analog-to-digital converter (ADC) in a CT system?
- To amplify the X-ray signal from the tube
- To convert the electrical detector signal into digital data for processing (Correct answer)
- To control the rotation speed of the gantry
- To modulate the tube current based on patient size
Correct answer: To convert the electrical detector signal into digital data for processing
The ADC converts the analog electrical signal from the detector into a digital format that can be processed by the reconstruction computer.
Question 2: In multi-detector CT, pitch is defined as:
- Table feed per rotation divided by total beam collimation (Correct answer)
- Number of detector rows times the rotation speed
- X-ray tube current times rotation time
- Detector width divided by reconstruction matrix size
Correct answer: Table feed per rotation divided by total beam collimation
Pitch = table feed per rotation ÷ total beam collimation (detector rows × single detector width), directly affecting dose and image overlap.
Question 3: What is the role of the post-patient anti-scatter grid in CT?
- To define slice thickness before the beam enters the patient
- To block scattered radiation from reaching the detectors (Correct answer)
- To filter low-energy X-rays from the primary beam
- To align the X-ray beam with the detector array
Correct answer: To block scattered radiation from reaching the detectors
The anti-scatter grid blocks off-axis scattered radiation produced within the patient from reaching the detectors, improving image contrast.
Question 4: What type of anode is used in modern CT X-ray tubes to manage heat load?
- Stationary tungsten anode
- Rotating tungsten-rhenium alloy anode (Correct answer)
- Stationary molybdenum anode
- Copper-tungsten composite anode
Correct answer: Rotating tungsten-rhenium alloy anode
Modern CT tubes use rotating anodes made of tungsten-rhenium alloy to distribute heat over a larger focal track area, allowing sustained high-output scanning.
Question 5: What does 'z-axis coverage' refer to in multi-detector CT?
- The spatial resolution in the x-y image plane
- The total anatomical length imaged per gantry rotation (Correct answer)
- The number of projection views acquired per rotation
- The maximum tube voltage achievable
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 6: What is the purpose of using a 'sharp' (bone) reconstruction kernel in CT?
- To reduce image noise and smooth soft tissue details
- To enhance edge detail and spatial resolution at the cost of increased noise (Correct answer)
- To reduce radiation dose while maintaining image quality
- To eliminate metal artifacts from the image
Correct answer: To enhance edge detail and spatial resolution at the cost of increased noise
Sharp kernels apply high-pass filtering that enhances edge detail and spatial resolution, making them ideal for bone and lung imaging despite increased noise.
Question 7: What is the primary goal of automatic tube current modulation (ATCM) in CT?
- To increase image sharpness uniformly across the scan
- To maintain consistent image noise while minimizing radiation dose (Correct answer)
- To speed up gantry rotation during scanning
- To reduce scan time by increasing tube voltage
Correct answer: To maintain consistent image noise while minimizing radiation dose
ATCM automatically adjusts tube current based on real-time patient attenuation, delivering consistent noise levels while reducing dose in less-attenuating regions.
Computed Tomography Test CT Equipment and Technology 2
What is the function of the analog-to-digital converter (ADC) in a CT system?