CRI Advanced Imaging Techniques 2 — Questions and Answers
Question 1: In computed radiography (CR), the imaging plate stores a latent image as trapped electrons in which material?
- Barium sulfate crystals
- Photostimulable phosphor (BaFBr:Eu) (Correct answer)
- Silver halide emulsion
- Calcium tungstate screens
Correct answer: Photostimulable phosphor (BaFBr:Eu)
CR imaging plates use photostimulable phosphor (typically europium-doped barium fluorobromide) to store the latent radiographic image as excited electrons.
Question 2: Which tomographic reconstruction algorithm is most commonly used in industrial CT scanning due to its computational efficiency?
- Iterative reconstruction
- Filtered back projection (FBP) (Correct answer)
- Maximum likelihood expectation maximization
- Algebraic reconstruction technique (ART)
Correct answer: Filtered back projection (FBP)
Filtered back projection is the dominant algorithm in industrial CT because it offers fast reconstruction with well-understood artifacts and adequate image quality.
Question 3: When performing real-time radioscopy, the image intensifier tube converts X-ray photons first into:
- Visible light, then electrons, then amplified light (Correct answer)
- Electrons directly, then amplified light
- Visible light only, then amplification
- X-ray photons are directly amplified without conversion
Correct answer: Visible light, then electrons, then amplified light
In an image intensifier, X-rays strike the input phosphor producing light, which ejects photoelectrons from the photocathode, and these are accelerated and focused onto the output phosphor to produce a brighter image.
Question 4: In digital detector array (DDA) systems, fill factor refers to:
- The percentage of detector area actually sensitive to radiation (Correct answer)
- The ratio of detected photons to incident photons
- The number of active pixels per square centimeter
- The dynamic range of the detector
Correct answer: The percentage of detector area actually sensitive to radiation
Fill factor is the proportion of each pixel's total area that is actually photosensitive; higher fill factor means more efficient photon capture.
Question 5: A flat panel detector exhibiting 'lag' artifacts will show which characteristic defect?
- Random salt-and-pepper noise
- Ghost images from previous exposures overlaid on current images (Correct answer)
- Geometric distortion at image edges
- Loss of high-frequency spatial resolution
Correct answer: Ghost images from previous exposures overlaid on current images
Lag occurs when charge from a previous exposure is not fully cleared, creating ghost images superimposed on subsequent radiographs.
Question 6: In neutron radiography, the contrast between aluminum and steel components is primarily due to:
- Density differences between the metals
- Neutron cross-section differences independent of atomic number (Correct answer)
- Photoelectric absorption differences
- Compton scatter differences
Correct answer: Neutron cross-section differences independent of atomic number
Neutron attenuation depends on nuclear cross-sections, not atomic number or density, allowing neutron radiography to distinguish materials that appear similar on X-ray.
Question 7: The modulation transfer function (MTF) of an imaging system describes:
- The detector's ability to convert X-rays to signal
- How faithfully the system reproduces spatial frequencies (Correct answer)
- The ratio of signal to electronic noise
- The geometric magnification across the field of view
Correct answer: How faithfully the system reproduces spatial frequencies
MTF quantifies how well an imaging system transfers contrast from the object to the image as a function of spatial frequency, effectively measuring sharpness.
CRI Advanced Imaging Techniques 2
In computed radiography (CR), the imaging plate stores a latent image as trapped electrons in which material?