CRI Image Quality & Artifacts 2 — Questions and Answers
Question 1: Which artifact appears as a bright linear streak on a radiograph when a high-density object is present in the beam path of a CT scanner?
- Motion artifact
- Beam hardening streak (Correct answer)
- Ring artifact
- Partial volume artifact
Correct answer: Beam hardening streak
Beam hardening streaks occur when polychromatic X-rays pass through dense objects like metal implants, causing low-energy photons to be preferentially absorbed and producing bright linear artifacts.
Question 2: What term describes the minimum detectable flaw size in a radiographic inspection, often expressed as a percentage of material thickness?
- Sensitivity (Correct answer)
- Contrast
- Unsharpness
- Density
Correct answer: Sensitivity
Radiographic sensitivity is the smallest detectable discontinuity size, commonly expressed as 2% of material thickness for acceptable industrial inspections.
Question 3: A radiograph shows a diffuse, foggy appearance across the entire image without exposure to the primary beam. What is the most likely cause?
- Overdevelopment
- Radiation fog from scatter or secondary exposure (Correct answer)
- Underexposure
- Chemical fog from improper fixer
Correct answer: Radiation fog from scatter or secondary exposure
Background or radiation fog results from stray scatter radiation, leaky cassettes, or film exposed to secondary radiation before or after primary exposure.
Question 4: In digital radiography, what is the primary purpose of a flat-field correction?
- To increase image contrast
- To compensate for non-uniform detector response and sensitivity (Correct answer)
- To reduce image noise
- To sharpen edge definition
Correct answer: To compensate for non-uniform detector response and sensitivity
Flat-field correction normalizes pixel response across the detector panel, compensating for variations in detector element sensitivity and beam intensity distribution.
Question 5: Which factor has the GREATEST influence on reducing geometric unsharpness in radiography?
- Increasing film speed
- Increasing source-to-object distance (SOD) (Correct answer)
- Decreasing source-to-film distance
- Using a larger focal spot
Correct answer: Increasing source-to-object distance (SOD)
Increasing SOD reduces geometric unsharpness (Ug) because Ug = f × OFD/SOD, so a larger SOD directly decreases the penumbra effect.
Question 6: What type of artifact in computed radiography (CR) is caused by incomplete erasure of a previous image?
- Moiré pattern
- Ghost image (ghosting) (Correct answer)
- Quantum mottle
- Fixed-pattern noise
Correct answer: Ghost image (ghosting)
Ghosting or ghost images in CR occur when a previously exposed phosphor plate is not fully erased, leaving remnants of the prior image superimposed on the new one.
Question 7: On a radiograph of a weld, an elongated dark indication running parallel to the weld axis most likely represents which discontinuity?
- Porosity
- Lack of fusion
- Longitudinal crack or incomplete penetration (Correct answer)
- Tungsten inclusion
Correct answer: Longitudinal crack or incomplete penetration
Elongated dark indications parallel to the weld axis are characteristic of longitudinal cracks or incomplete root penetration, which create planar voids aligned with the weld direction.
CRI Image Quality & Artifacts 2
Which artifact appears as a bright linear streak on a radiograph when a high-density object is present in the beam path of a CT scanner?