ARRT Equipment Operation and QA 5 — Questions and Answers
Question 1: In digital radiography, which exposure indicator value system uses a scale where the target value is approximately 300, with acceptable range of 200-800?
- Fuji S-number system
- Kodak EI system (Correct answer)
- Agfa lgM system
- Carestream REX system
Correct answer: Kodak EI system
The Kodak/Carestream Exposure Index (EI) system targets approximately 300 (with acceptable range 200-800), where higher numbers indicate higher detector exposure.
Question 2: A radiographer notices that images from a CR system appear consistently overexposed despite using correct technique. The most likely cause is:
- The CR plate is being stored in a bright room before use
- The CR reader laser is malfunctioning
- The exposure indicator shows values consistently higher than the target (Correct answer)
- The CR plate has not been erased and retains a previous latent image
Correct answer: The exposure indicator shows values consistently higher than the target
Consistently high exposure indicator values confirm that the detector is receiving excess radiation; this indicates a technique or AEC calibration issue causing overexposure.
Question 3: Which of the following describes the detective quantum efficiency (DQE) of an imaging system?
- The percentage of x-ray photons absorbed by the detector compared to those incident upon it
- A measure of how efficiently a detector converts absorbed x-ray signal into useful image information relative to an ideal detector (Correct answer)
- The ratio of scatter to primary radiation reaching the detector
- The maximum spatial frequency that a detector can resolve
Correct answer: A measure of how efficiently a detector converts absorbed x-ray signal into useful image information relative to an ideal detector
DQE expresses how well a detector uses the incident x-ray signal; it combines quantum detection efficiency and noise performance, with a perfect detector having DQE = 1.0.
Question 4: During fluoroscopy, the image intensifier converts x-ray photons into a visible image through which sequence?
- X-ray → photocathode electrons → electron lens acceleration → output phosphor light
- X-ray → output phosphor light → photocathode electrons → input phosphor
- X-ray → cesium iodide input phosphor light → photocathode electrons → output phosphor (Correct answer)
- X-ray → amorphous selenium charge → TFT array → CCD camera
Correct answer: X-ray → cesium iodide input phosphor light → photocathode electrons → output phosphor
In an image intensifier, x-rays strike the cesium iodide (CsI) input phosphor producing light, which ejects electrons from the photocathode; electrons are accelerated and focused onto the output phosphor.
Question 5: What is the purpose of the daily sensitometric (sensitometry) QC test in a film-based department?
- To measure the half-value layer of the x-ray beam
- To monitor processor performance by evaluating base plus fog, speed, and contrast index on a processed strip (Correct answer)
- To verify collimator light field alignment with the x-ray field
- To test the accuracy of the kVp selector on the x-ray generator
Correct answer: To monitor processor performance by evaluating base plus fog, speed, and contrast index on a processed strip
Daily sensitometry tracks film processor consistency by comparing base plus fog, speed index, and contrast index to established control values, detecting processor drift before it affects diagnostic images.
Question 6: A radiograph exhibits increased optical density on the anode side compared to the cathode side. This finding is most consistent with:
- Correct use of the heel effect with patient positioned appropriately
- The patient being positioned with the thick end toward the anode side (Correct answer)
- Tube angulation artifact causing differential attenuation
- Incorrect grid alignment causing grid cutoff on the cathode side
Correct answer: The patient being positioned with the thick end toward the anode side
The anode side has lower x-ray intensity due to the heel effect; if the thick part of the patient is placed under the anode, the reduced beam intensity is further attenuated, producing lower (not higher) density — thus finding higher density on the anode side indicates the thin end is under the anode, which is the incorrect positioning.
Question 7: Which of the following is the recommended frequency for performing a flat-panel detector (FDR) uniformity/flat-field calibration?
- Every 5 years as part of a major service contract
- Annually by a medical physicist only
- As recommended by the manufacturer, typically daily or when detector performance changes are noted (Correct answer)
- Only when image artifacts are visually apparent on clinical images
Correct answer: As recommended by the manufacturer, typically daily or when detector performance changes are noted
Manufacturers typically recommend flat-field (gain) calibration daily or when detector sensitivity changes, ensuring uniform response across the detector surface and minimizing fixed-pattern noise.
