ARRT Image Acquisition and Evaluation 4 — Questions and Answers
Question 1: A lateral knee radiograph shows the femoral condyles are not superimposed. Which positioning correction is needed?
- Flex the knee more
- Rotate the patient's foot internally or externally to align the condyles (Correct answer)
- Increase the SID
- Angle the tube caudally
Correct answer: Rotate the patient's foot internally or externally to align the condyles
Failure to superimpose the femoral condyles on a lateral knee indicates the leg is rotated; adjusting internal or external rotation corrects this.
Question 2: In digital radiography, what is the purpose of the exposure index (EI) deviation index (DI)?
- To set the kVp automatically
- To indicate how far the actual exposure deviates from the target exposure (Correct answer)
- To calculate patient dose in mGy
- To calibrate the antiscatter grid
Correct answer: To indicate how far the actual exposure deviates from the target exposure
The deviation index (DI) compares the actual EI to the target EI, indicating over- or underexposure so the technologist can adjust technique.
Question 3: Which technical factor change reduces patient dose while maintaining adequate image quality on a chest radiograph?
- Decrease kVp and increase mAs proportionally
- Increase kVp and decrease mAs proportionally (Correct answer)
- Decrease both kVp and mAs
- Increase both kVp and mAs
Correct answer: Increase kVp and decrease mAs proportionally
Increasing kVp and reducing mAs (high-kVp technique) maintains exposure to the detector while lowering patient dose due to increased beam penetration.
Question 4: A PA hand radiograph shows significant motion blur. Which receptor/technique change would most improve sharpness?
- Increase SID
- Use a smaller focal spot and immobilize the hand (Correct answer)
- Increase mAs
- Use a grid
Correct answer: Use a smaller focal spot and immobilize the hand
A smaller focal spot reduces geometric unsharpness, and immobilization eliminates motion unsharpness, both improving recorded detail.
Question 5: Which term describes the minimum detectable difference in tissue density that can be distinguished on a radiograph?
- Spatial resolution
- Contrast resolution (Correct answer)
- Dynamic range
- Modulation transfer function
Correct answer: Contrast resolution
Contrast resolution is the ability to distinguish between tissues of similar attenuation — the minimum density difference that can be detected.
Question 6: On an AP pelvis, which criterion confirms the patient is not rotated?
- The femoral necks are equal in length and the obturator foramina are symmetric (Correct answer)
- The iliac crests are at the same height
- The greater trochanters are both visible
- The ischial spines project symmetrically
Correct answer: The femoral necks are equal in length and the obturator foramina are symmetric
Symmetrical obturator foramina and equal femoral neck lengths on both sides confirm the pelvis is not rotated on an AP projection.
Question 7: Which artifact in computed radiography (CR) is caused by previous exposure data remaining on the phosphor plate?
- Moiré pattern
- Ghost image (latent image artifact) (Correct answer)
- Dropout lines
- Quantum noise
Correct answer: Ghost image (latent image artifact)
Ghost images occur when a CR plate is not fully erased before reuse, leaving residual signal from a previous exposure.
ARRT Image Acquisition and Evaluation 4
A lateral knee radiograph shows the femoral condyles are not superimposed.
Which positioning correction is needed?