GXMO Radiographic Exposure Techniques 1 — Questions and Answers
Question 1: Which exposure factor primarily controls the quality (penetrating power) of the x-ray beam?
- mAs
- kVp (Correct answer)
- Exposure time
- Focal spot size
Correct answer: kVp
kVp (kilovoltage peak) determines the energy of x-ray photons, directly controlling the beam's ability to penetrate tissue.
Question 2: Doubling the mAs while keeping all other factors constant will:
- Halve patient dose
- Double radiographic density (Correct answer)
- Increase image contrast
- Reduce scatter radiation
Correct answer: Double radiographic density
mAs controls x-ray quantity; doubling mAs doubles the number of photons reaching the image receptor, doubling radiographic density.
Question 3: The '15% rule' states that increasing kVp by 15% requires what mAs adjustment to maintain the same density?
- Double the mAs
- Halve the mAs (Correct answer)
- Increase mAs by 15%
- No mAs change needed
Correct answer: Halve the mAs
Increasing kVp by 15% doubles the effect on density, so mAs must be halved to maintain the original exposure level.
Question 4: What is the standard source-to-image distance (SID) used for PA chest radiographs?
- 40 inches
- 72 inches (Correct answer)
- 48 inches
- 56 inches
Correct answer: 72 inches
72 inches (180 cm) is the standard SID for PA chest radiographs to minimize magnification and accurately represent cardiac size.
Question 5: According to the inverse square law, if SID is doubled, x-ray beam intensity at the image receptor:
- Doubles
- Quadruples
- Decreases to one-quarter (Correct answer)
- Decreases by half
Correct answer: Decreases to one-quarter
The inverse square law states intensity is inversely proportional to the square of distance; doubling SID reduces intensity to 1/4.
Question 6: Which exposure factor has the GREATEST effect on radiographic contrast?
- mAs
- Focal spot size
- kVp (Correct answer)
- SID
Correct answer: kVp
kVp controls the differential absorption of x-rays between tissues, making it the primary determinant of radiographic contrast.
Question 7: Using a small focal spot instead of a large focal spot will primarily result in:
- Increased radiographic density
- Improved recorded detail/sharpness (Correct answer)
- Increased image contrast
- Reduced patient dose
Correct answer: Improved recorded detail/sharpness
A smaller focal spot reduces geometric unsharpness (penumbra effect), improving spatial resolution and recorded detail.
GXMO Radiographic Exposure Techniques 1
Which exposure factor primarily controls the quality (penetrating power) of the x-ray beam?