GXMO Radiographic Exposure Techniques 2 — Questions and Answers
Question 1: A technique of 200 mA and 0.1 sec produces an acceptable image. Which combination produces the SAME density?
- 100 mA and 0.1 sec
- 400 mA and 0.05 sec (Correct answer)
- 200 mA and 0.2 sec
- 100 mA and 0.3 sec
Correct answer: 400 mA and 0.05 sec
Original mAs = 200 × 0.1 = 20 mAs; 400 mA × 0.05 sec = 20 mAs, maintaining identical density.
Question 2: If SID is decreased from 40 inches to 20 inches with all other factors constant, radiographic density will:
- Decrease by half
- Increase fourfold (Correct answer)
- Remain the same
- Double
Correct answer: Increase fourfold
Halving the SID increases beam intensity by a factor of 4 per the inverse square law, quadrupling radiographic density.
Question 3: To maintain the same density when SID is decreased from 40 inches to 20 inches, mAs should be:
- Doubled
- Halved
- Reduced to one-quarter (Correct answer)
- Kept the same
Correct answer: Reduced to one-quarter
Since halving SID quadruples intensity, mAs must be reduced to 1/4 to compensate using the exposure maintenance formula (mAs₂/mAs₁ = SID₂²/SID₁²).
Question 4: High-kVp techniques (above 100 kVp) produce images characterized by:
- High contrast with short gray scale
- Low contrast with long gray scale (Correct answer)
- Increased patient dose
- Decreased scatter radiation
Correct answer: Low contrast with long gray scale
High kVp causes more Compton scatter and less differential photoelectric absorption, producing a long gray scale (low contrast) image.
Question 5: Which body part typically requires the LOWEST kVp setting?
- Abdomen
- Chest (PA)
- Hand or wrist (Correct answer)
- Lumbar spine
Correct answer: Hand or wrist
Extremities like the hand and wrist require low kVp (50–65 kVp) to produce adequate contrast between fine bony detail and soft tissue.
Question 6: What is the PRIMARY purpose of using a radiographic grid?
- Increase image receptor exposure speed
- Reduce scatter radiation reaching the receptor (Correct answer)
- Decrease patient dose
- Improve focal spot performance
Correct answer: Reduce scatter radiation reaching the receptor
A grid is placed between the patient and image receptor to absorb off-angle scatter radiation and improve radiographic contrast.
Question 7: Grid ratio is defined as the ratio of:
- Grid strip height to lead strip width
- Lead strip height to inter-space width (Correct answer)
- Number of lead strips per cm
- Primary to scatter radiation
Correct answer: Lead strip height to inter-space width
Grid ratio = h/D, where h is the height (depth) of the lead strips and D is the width of the radiolucent interspaces between them.
GXMO Radiographic Exposure Techniques 2
A technique of 200 mA and 0.1 sec produces an acceptable image.
Which combination produces the SAME density?