ARRT Image Acquisition and Evaluation 5 — Questions and Answers
Question 1: What does a high MTF (modulation transfer function) value indicate about an imaging system?
- High patient dose is being delivered
- The system accurately reproduces fine detail (Correct answer)
- There is significant scatter in the image
- The detector is overexposed
Correct answer: The system accurately reproduces fine detail
MTF measures how faithfully an imaging system reproduces spatial frequencies; a high MTF indicates excellent spatial resolution and detail reproduction.
Question 2: Which condition would cause a foreshortened appearance of a long bone on a radiograph?
- Central ray angled along the long axis of the bone (Correct answer)
- Central ray perpendicular to the long axis
- Excessive OID
- High kVp technique
Correct answer: Central ray angled along the long axis of the bone
Angling the central ray along (parallel to) the long axis of a bone causes it to appear foreshortened on the image.
Question 3: A radiograph of the abdomen shows a faint diagonal line pattern overlying the image. What is the most likely cause?
- Quantum mottle
- Moiré pattern from grid-detector frequency mismatch (Correct answer)
- Patient motion
- Safelight fog
Correct answer: Moiré pattern from grid-detector frequency mismatch
A moiré pattern appears as a diagonal or wavy line artifact when the grid frequency and detector sampling frequency interact destructively.
Question 4: For an AP shoulder radiograph, which criterion indicates the glenohumeral joint space is adequately demonstrated?
- The humeral head overlaps the glenoid completely
- A clear space is visible between the humeral head and glenoid fossa (Correct answer)
- The coracoid process is not visible
- The clavicle is horizontal
Correct answer: A clear space is visible between the humeral head and glenoid fossa
Proper positioning demonstrates an open joint space between the humeral head and glenoid fossa, confirming adequate internal rotation and centering.
Question 5: Which factor has the greatest effect on reducing the amount of scatter radiation produced in the patient?
- Increasing SID
- Collimating to the smallest field size necessary (Correct answer)
- Using a faster image receptor
- Increasing mAs
Correct answer: Collimating to the smallest field size necessary
Tighter collimation reduces the volume of irradiated tissue, which is the primary determinant of scatter production.
Question 6: During evaluation of a lateral cervical spine, all seven vertebrae must be visualized. If C7 is not seen, what corrective action should the technologist take?
- Angle the tube 15 degrees caudally
- Have the patient depress the shoulders while taking a deep breath or use a swimmer's lateral (Correct answer)
- Increase kVp by 20
- Use a smaller focal spot
Correct answer: Have the patient depress the shoulders while taking a deep breath or use a swimmer's lateral
Depressing the shoulders or using the swimmer's lateral (Twining method) allows C7 and the cervicothoracic junction to be visualized when obscured by the shoulders.
Question 7: Which window setting in digital imaging is adjusted to control the range of densities displayed, effectively changing the image contrast?
- Window level
- Window width (Correct answer)
- Lookup table gamma
- Pixel pitch
Correct answer: Window width
Window width determines how many Hounsfield units (or gray levels) are mapped to the display range; a narrow width increases contrast while a wide width decreases it.
ARRT Image Acquisition and Evaluation 5
What does a high MTF (modulation transfer function) value indicate about an imaging system?