GXMO Image Quality and Interpretation 3 — Questions and Answers
Question 1: Which of the following describes the relationship between OID (object-to-image distance) and magnification?
- Increasing OID increases magnification (Correct answer)
- Decreasing OID increases magnification
- OID has no effect on magnification
- Increasing OID decreases penumbra
Correct answer: Increasing OID increases magnification
As OID increases, the object is farther from the image receptor and closer to the source, causing greater divergence of X-rays and increased magnification.
Question 2: On an AP pelvis radiograph, the obturator foramina appear unequal in size. What does this indicate?
- Patient rotation (Correct answer)
- Overexposure of the film
- Incorrect central ray angulation
- Grid cutoff artifact
Correct answer: Patient rotation
Unequal obturator foramina on an AP pelvis indicate patient rotation, as both foramina should appear symmetric when properly positioned.
Question 3: What does a step-wedge (penetrometer) image primarily evaluate?
- The exposure latitude and contrast scale of the imaging system (Correct answer)
- The focal spot size of the X-ray tube
- The accuracy of the collimator light field
- The grid alignment and ratio
Correct answer: The exposure latitude and contrast scale of the imaging system
A step-wedge produces a range of densities that allows evaluation of the system's exposure latitude, contrast, and density response across different exposure levels.
Question 4: Which radiographic finding is most characteristic of free air (pneumoperitoneum) on an upright abdominal radiograph?
- Air under the diaphragm (Correct answer)
- Air-fluid levels in the bowel
- Soft tissue calcifications
- Loss of psoas muscle shadow
Correct answer: Air under the diaphragm
Free intraperitoneal air rises to the highest point in the abdomen and appears as a radiolucent crescent under the diaphragm on an upright view.
Question 5: What effect does increasing the source-to-image distance (SID) have on image sharpness, assuming all other factors remain constant?
- Sharpness increases because geometric unsharpness decreases (Correct answer)
- Sharpness decreases because beam divergence increases
- Sharpness is unchanged because SID does not affect penumbra
- Sharpness decreases because mAs must be increased
Correct answer: Sharpness increases because geometric unsharpness decreases
At greater SID, the X-ray beam approaches parallel rays more closely, reducing geometric unsharpness (penumbra) and improving recorded detail.
Question 6: Which type of grid is designed to be used at a specific SID range and will produce grid cutoff if used outside that range?
- Focused grid (Correct answer)
- Parallel grid
- Cross-hatch grid
- Moving (Bucky) grid
Correct answer: Focused grid
A focused grid has grid lines angled to align with the divergence of the X-ray beam at a specific SID, causing cutoff artifacts if used at incorrect distances.
Question 7: When reviewing an image for diagnostic quality, which criterion confirms adequate penetration on a lateral thoracic spine radiograph?
- Intervertebral disc spaces are visible through the superimposed shoulders (Correct answer)
- The spinous processes are clearly visualized
- The lung fields appear uniformly radiolucent
- The ribs are visible without overexposure
Correct answer: Intervertebral disc spaces are visible through the superimposed shoulders
On a lateral thoracic spine, the intervertebral disc spaces must be visible through the shoulders to confirm sufficient penetration of all superimposed structures.
GXMO Image Quality and Interpretation 3
Which of the following describes the relationship between OID (object-to-image distance) and magnification?