CBET Diagnostic Imaging Equipment 4 — Questions and Answers
Question 1: In a CT scanner, what is the primary purpose of the anti-scatter grid?
- Reduce patient radiation dose
- Improve image contrast by blocking scattered X-rays (Correct answer)
- Increase detector sensitivity
- Collimate the primary X-ray beam
Correct answer: Improve image contrast by blocking scattered X-rays
Anti-scatter grids block scattered radiation from reaching the detector, improving image contrast and reducing noise.
Question 2: A fluoroscopy unit displays an 'image intensifier dose rate' alarm. Which parameter should the BMET check first?
- kVp calibration
- Automatic brightness control (ABC) circuit operation (Correct answer)
- Collimator alignment
- Film processor chemistry
Correct answer: Automatic brightness control (ABC) circuit operation
The ABC circuit regulates dose rate automatically; a malfunction can cause unexpectedly high or low dose rates.
Question 3: What does 'spatial resolution' measure in diagnostic imaging?
- The ability to distinguish two adjacent high-contrast objects as separate (Correct answer)
- The range of densities visible in a single image
- The speed of image acquisition
- The amount of noise present in the image
Correct answer: The ability to distinguish two adjacent high-contrast objects as separate
Spatial resolution describes the smallest separation at which two objects can be distinguished as distinct structures.
Question 4: During MRI QA, the BMET measures a phantom image and finds the signal-to-noise ratio (SNR) has dropped 20% from baseline. The most likely cause is:
- Incorrect slice thickness setting
- RF coil damage or poor coupling (Correct answer)
- Gradient amplifier overheating
- Incorrect TR parameter
Correct answer: RF coil damage or poor coupling
A damaged or poorly coupled RF coil reduces the received signal strength, directly decreasing SNR.
Question 5: Which unit describes the absorbed radiation dose in diagnostic imaging?
- Roentgen (R)
- Gray (Gy) (Correct answer)
- Sievert (Sv)
- Becquerel (Bq)
Correct answer: Gray (Gy)
The Gray (Gy) is the SI unit of absorbed dose, equal to 1 joule of energy deposited per kilogram of tissue.
Question 6: In ultrasound imaging, the term 'acoustic shadowing' occurs when:
- Sound waves are reflected entirely by a highly attenuating structure (Correct answer)
- Gain is set too high causing saturation
- The transducer frequency is below the tissue resonant frequency
- Time-gain compensation is disabled
Correct answer: Sound waves are reflected entirely by a highly attenuating structure
Dense structures such as bone or gallstones reflect or absorb nearly all incident sound, creating a dark shadow distal to the structure.
Question 7: A portable X-ray unit fails to produce an exposure when triggered. The BMET confirms the battery is fully charged. What should be checked next?
- High-voltage transformer primary winding
- Handswitch and exposure control circuitry (Correct answer)
- Focal spot size
- Collimator lamp
Correct answer: Handswitch and exposure control circuitry
The handswitch and exposure control circuit initiate the exposure sequence; a fault here will prevent triggering even with adequate power.
CBET Diagnostic Imaging Equipment 4
In a CT scanner, what is the primary purpose of the anti-scatter grid?