ARRT Digital Imaging and Exposure Factors 2 — Questions and Answers
Question 1: How does increasing the source-to-image receptor distance (SID) affect image magnification?
- Increases magnification
- Decreases magnification (Correct answer)
- Has no effect on magnification
- Only affects density, not magnification
Correct answer: Decreases magnification
Increasing SID moves the X-ray source farther from the image receptor, reducing the divergence of the beam at the IR and decreasing magnification.
Question 2: What is the relationship between mAs and receptor exposure in digital radiography?
- Inverse relationship — doubling mAs halves exposure
- Direct relationship — doubling mAs doubles receptor exposure (Correct answer)
- No relationship — mAs only affects contrast
- Doubling mAs quadruples exposure
Correct answer: Direct relationship — doubling mAs doubles receptor exposure
mAs directly controls the quantity of X-ray photons produced; doubling mAs doubles the number of photons reaching the receptor and doubles exposure.
Question 3: Which factor primarily controls quantum noise (quantum mottle) in a digital radiographic image?
- kVp setting
- mAs (number of photons reaching the detector) (Correct answer)
- SID
- Collimation size
Correct answer: mAs (number of photons reaching the detector)
Quantum mottle is caused by insufficient photons reaching the detector; increasing mAs increases photon fluence and reduces this noise.
Question 4: What is the 15% rule in radiographic technique adjustment?
- Increasing SID by 15% doubles exposure
- Increasing kVp by 15% has the same effect on exposure as doubling mAs (Correct answer)
- Decreasing mAs by 15% halves patient dose
- Increasing field size by 15% increases scatter by 15%
Correct answer: Increasing kVp by 15% has the same effect on exposure as doubling mAs
The 15% rule states that increasing kVp by 15% approximately doubles receptor exposure, equivalent to doubling the mAs.
Question 5: In digital imaging, what processing function allows the radiologist to adjust image brightness and contrast after acquisition?
- Spatial frequency filtering
- Window level and window width adjustment (Correct answer)
- Histogram equalization only
- Matrix size selection
Correct answer: Window level and window width adjustment
Window level controls the center of the displayed density range (brightness) and window width controls the range of densities displayed (contrast) in digital images.
Question 6: Which type of image receptor requires a laser scanner to read the stored image?
- Flat-panel direct conversion detector
- Computed radiography (CR) phosphor plate (Correct answer)
- Indirect flat-panel detector
- Film-screen cassette
Correct answer: Computed radiography (CR) phosphor plate
CR imaging plates store a latent image in photostimulable phosphors that must be released and detected by scanning with a helium-neon or diode laser.
ARRT Digital Imaging and Exposure Factors 2
How does increasing the source-to-image receptor distance (SID) affect image magnification?