ARRT Digital Imaging and Exposure Factors 1 — Questions and Answers
Question 1: In digital radiography, which exposure indicator value signifies optimal exposure on most current CR/DR systems?
- EI of 50
- EI of 300 (system-dependent target near 300) (Correct answer)
- EI of 1200
- EI of 25
Correct answer: EI of 300 (system-dependent target near 300)
Most systems target an Exposure Index around 300 (±30%), though exact targets are vendor-specific and defined by the manufacturer.
Question 2: What does a deviation index (DI) of 0 indicate in a digital imaging system?
- Severe underexposure
- Exposure is exactly at the target exposure index (Correct answer)
- Severe overexposure
- Equipment malfunction
Correct answer: Exposure is exactly at the target exposure index
A deviation index of 0 means the actual exposure exactly matched the target exposure index, indicating optimal exposure.
Question 3: Which primary exposure factor has the greatest effect on subject contrast in digital radiography?
- mA (milliamperage)
- kVp (kilovoltage peak) (Correct answer)
- Exposure time
- Source-to-image distance
Correct answer: kVp (kilovoltage peak)
kVp controls the energy and penetrating power of the X-ray beam, directly determining the differential absorption that creates subject contrast.
Question 4: In computed radiography (CR), what component captures the latent image?
- Flat-panel detector with amorphous silicon
- Photostimulable phosphor (PSP) imaging plate (Correct answer)
- Charge-coupled device (CCD)
- Direct conversion selenium detector
Correct answer: Photostimulable phosphor (PSP) imaging plate
CR uses a photostimulable phosphor imaging plate that stores a latent image as trapped electrons until scanned by a laser reader.
Question 5: What is the primary advantage of direct conversion flat-panel detectors (FPD) over indirect conversion FPDs?
- Lower cost
- Superior spatial resolution due to no light-spreading step (Correct answer)
- Higher radiation dose to patient
- Faster read time only
Correct answer: Superior spatial resolution due to no light-spreading step
Direct conversion detectors convert X-rays directly to electrical signals without an intermediate light step, eliminating blur from light spread and improving spatial resolution.
Question 6: Which artifact in digital radiography results from a CR imaging plate not being completely erased before reuse?
- Moiré artifact
- Ghost image (ghosting) (Correct answer)
- Grid cutoff
- Quantum mottle
Correct answer: Ghost image (ghosting)
Ghosting occurs when residual signal from a prior exam remains on the phosphor plate because erasure was incomplete, superimposing an old image onto the new one.
ARRT Digital Imaging and Exposure Factors 1
In digital radiography, which exposure indicator value signifies optimal exposure on most current CR/DR systems?