ARRT Equipment Operation and QA 3 — Questions and Answers
Question 1: A radiograph displays increased quantum mottle. Which of the following changes would most directly reduce this artifact?
- Decrease kVp
- Increase mAs (Correct answer)
- Use a higher grid ratio
- Decrease SID
Correct answer: Increase mAs
Quantum mottle results from insufficient photon flux reaching the detector; increasing mAs produces more photons and reduces statistical noise (mottle).
Question 2: Which digital detector type uses a direct conversion process where x-rays are converted directly into electrical charge?
- Computed radiography (CR) with BaFBr phosphor
- Indirect flat-panel detector using CsI and amorphous silicon
- Direct flat-panel detector using amorphous selenium (Correct answer)
- Charge-coupled device (CCD) with fiber-optic coupling
Correct answer: Direct flat-panel detector using amorphous selenium
Direct flat-panel detectors use amorphous selenium (a-Se), which converts x-ray photons directly into electrical charge without an intermediate light conversion step.
Question 3: What is the primary function of a grid in radiography?
- To reduce patient motion blur
- To absorb scattered radiation before it reaches the image receptor (Correct answer)
- To increase the primary beam intensity
- To filter low-energy photons from the primary beam
Correct answer: To absorb scattered radiation before it reaches the image receptor
Grids are composed of alternating radiopaque lead strips and radiolucent interspacing material that absorb obliquely traveling scattered photons while transmitting the primary beam.
Question 4: On a sensitometric curve (H&D curve), the region where the curve is steepest represents:
- The toe — underexposure region
- The shoulder — overexposure region
- The straight-line portion — optimal diagnostic range (Correct answer)
- The D-max — maximum density achievable
Correct answer: The straight-line portion — optimal diagnostic range
The steepest portion (straight-line region) represents the optimal exposure range where small changes in exposure produce proportional and maximum changes in density, yielding best contrast.
Question 5: A timer accuracy test reveals that the actual exposure time is 20% longer than the set time. This most likely indicates:
- A failing x-ray tube filament
- A malfunctioning timer circuit requiring calibration (Correct answer)
- Incorrect kVp setting on the control panel
- An off-focus radiation problem in the x-ray tube
Correct answer: A malfunctioning timer circuit requiring calibration
Timer inaccuracy — where actual exposure time deviates more than ±5% from the set value — indicates the timer circuit is out of calibration and needs servicing.
Question 6: Which of the following best describes the purpose of automatic exposure control (AEC) in radiography?
- To automatically adjust kVp based on patient thickness
- To terminate the exposure when a predetermined amount of radiation reaches the detector (Correct answer)
- To compensate for grid cutoff during oblique exposures
- To adjust the focal spot size based on required mAs
Correct answer: To terminate the exposure when a predetermined amount of radiation reaches the detector
AEC (phototiming) uses ionization chambers or solid-state detectors to monitor radiation reaching the image receptor and terminates the exposure when a preset dose has been received.
Question 7: In fluoroscopy, which component limits the maximum entrance skin exposure rate under normal operating mode per federal regulations?
- The image intensifier automatic brightness control
- The 10 R/min (2.58 mC/kg/min) dose rate limit enforced by the equipment (Correct answer)
- The collimator minimum field size setting
- The fluoroscopic timer 5-minute audible alarm
Correct answer: The 10 R/min (2.58 mC/kg/min) dose rate limit enforced by the equipment
Federal regulations (21 CFR 1020.32) limit fluoroscopic entrance skin exposure rate to a maximum of 10 R/min (88 mGy/min) in normal operating mode.
ARRT Equipment Operation and QA 3
A radiograph displays increased quantum mottle.
Which of the following changes would most directly reduce this artifact?