Computed Radiography (CR) and Photostimulable Luminescence
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Questions and Answers

What is the primary function of the photostimulable phosphors (PSP) in Computed Radiography?

  • To reflect infrared light for better imaging
  • To hold the X-ray energy as a latent image (correct)
  • To minimize static electricity buildup
  • To protect the imaging plate from damage

    • Which layer in a PSP screen is responsible for reflecting light towards the imaging plate?

  • Binder layer
  • Protective overcoat
  • Reflective layer (correct)
  • Antistatic layer

    • How do electrons in the phosphor crystals of a PSP screen return to their ground state?

  • When stimulated by focused infrared light (correct)
  • By cooling to room temperature
  • Through a chemical reaction
  • By exposure to X-ray energy

    • What is the purpose of the antistatic layer in a PSP screen?

    <p>To prevent static electricity buildup</p> Signup and view all the answers

    What is a metastable state in the context of photostimulable phosphors?

    <p>A temporary state where electrons can be easily released</p> Signup and view all the answers

    What is the purpose of lead backing on the Imaging Plate (IP) in Computed Radiography?

    <p>To reduce x-ray backscatter</p> Signup and view all the answers

    Which factor primarily affects the emitted signal during the stimulation of the Storage Phosphor Screens (PSPs)?

    <p>Intensity of the infrared laser beam</p> Signup and view all the answers

    What happens to the latent image created in a Storage Phosphor Screen (PSP) after approximately 8 hours?

    <p>It fades and becomes indistinguishable</p> Signup and view all the answers

    During the stimulation process in Computed Radiography, what is the primary region of the visible spectrum where the stimulated emission is detected?

    <p>Blue region</p> Signup and view all the answers

    What is the role of photodiodes (PDs) in Computed Radiography?

    <p>To detect stimulated emission</p> Signup and view all the answers

    What describes the initial reaction of electrons when exposed to an x-ray beam in the PSP?

    <p>Electrons are excited into a metastable state</p> Signup and view all the answers

    How does the diameter of the laser beam affect the Computed Radiography system?

    <p>It affects the resolution of the system</p> Signup and view all the answers

    In the light stimulation process of Computed Radiography, what is a common cause of signal loss during detection?

    <p>Light scattering</p> Signup and view all the answers

    What are Storage Phosphor Screens (PSPs) primarily composed of?

    <p>Small particles that are electrostatically protected</p> Signup and view all the answers

    In Computed Radiography, which component functions similarly to a screen-film cassette?

    <p>Imaging Plate</p> Signup and view all the answers

    What is the primary purpose of the precision drive mechanism in the CR reader?

    <p>To ensure accurate movement of the image plate</p> Signup and view all the answers

    Why is laser blanking necessary during the retrace in a CR reader?

    <p>To avoid errors in image capture</p> Signup and view all the answers

    What characteristic of solid-state lasers makes them advantageous in CR systems?

    <p>They emit longer wavelength light</p> Signup and view all the answers

    What is the consequence of exceeding the error tolerance during scanning in a CR reader?

    <p>Appearance of wavy edges in the image</p> Signup and view all the answers

    How do optical filters function in the optical subsystem of a CR reader?

    <p>They allow only the emitted light to reach the photodetector</p> Signup and view all the answers

    What is a potential issue caused by incorrect grid alignment during scanning?

    <p>Increased likelihood of aliasing artifacts</p> Signup and view all the answers

    What role do beam-shaping optics play in the CR reader’s optical subsystem?

    <p>They focus the laser beam to maximize interaction with electrons</p> Signup and view all the answers

    What is the likely effect of having a polychromatic emission from the image plate?

    <p>It decreases the amount of light reaching the photodetector</p> Signup and view all the answers

    What is the primary process involved in digitization within a CR system?

    <p>Sampling and quantization of signals</p> Signup and view all the answers

    What characteristic of the CR imaging process differs from screen-film imaging?

    <p>The presence of artifacts</p> Signup and view all the answers

    Which component is responsible for filtering light to improve signal quality in a CR reader?

    <p>Optical filters</p> Signup and view all the answers

    How does the clock speed of a computer influence the CR scanning process?

    <p>It manages both slow and fast scanning operations.</p> Signup and view all the answers

    Which of the following best describes the output of the photodetector in a CR system?

    <p>A time-varying analog signal</p> Signup and view all the answers

    What describes the image receptor response function for CR compared to screen-film receptors?

    <p>The CR function shows a characteristic curve.</p> Signup and view all the answers

    What is the effect of using a high-speed drive mechanism in a CR reader?

    <p>It enhances the scanning efficiency.</p> Signup and view all the answers

    What happens to the emitted light from the imaging plate before it reaches the photodetector?

    <p>It is filtered to improve resolution.</p> Signup and view all the answers

    What is the main source of noise in computed radiography images?

    <p>Scatter radiation</p> Signup and view all the answers

    What characteristic curve is associated with the value of each pixel in a computed radiography image?

    <p>Linear</p> Signup and view all the answers

    What allows for potentially reduced radiation dose in computed radiography compared to screen-film radiography?

    <p>Wider latitude of exposure</p> Signup and view all the answers

    Which of the following components in computed radiography is responsible for recording the latent image?

    <p>Imaging plate</p> Signup and view all the answers

    How many gray levels does a 14-bit computed radiography image have?

    <p>16,384</p> Signup and view all the answers

    What is the role of metastable electrons in computed radiography?

    <p>They emit light to create the visible image</p> Signup and view all the answers

    Which factor does NOT apply to control the imaging process in computed radiography?

    <p>Energy levels of the laser</p> Signup and view all the answers

    Which of the following is a common cause of signal loss in computed radiography?

    <p>Inadequate sampling</p> Signup and view all the answers

    What describes the effect of scatter radiation in computed radiography?

    <p>It creates image noise</p> Signup and view all the answers

    What is the primary mechanism through which the latent image is made visible in computed radiography?

    <p>Stimulating laser beam</p> Signup and view all the answers

    What is the primary function of the coupling element in digital radiography?

    <p>To transfer the x-ray-generated signal</p> Signup and view all the answers

    Which of the following materials can be used as a capture element in digital radiography?

    <p>Sodium iodide</p> Signup and view all the answers

    What advantage does scanned projection radiography (SPR) offer compared to other imaging techniques?

    <p>Reduced scatter radiation</p> Signup and view all the answers

    Which characteristic is NOT associated with charge-coupled devices (CCDs)?

    <p>Large physical size</p> Signup and view all the answers

    In the digital radiography process, what is the role of the collection element?

    <p>To collect light photons from the coupling element</p> Signup and view all the answers

    What is an advantage of using charge-coupled devices (CCDs) in medical imaging?

    <p>They have high sensitivity to low light levels.</p> Signup and view all the answers

    How do cesium iodide and amorphous silicon work together in digital radiography?

    <p>CsI converts x-rays into light, which is then captured by a-Si.</p> Signup and view all the answers

    What does the fill factor in an active matrix array-thin film transistor (AMA-TFT) refer to?

    <p>The percentage of the pixel sensitive to x-rays.</p> Signup and view all the answers

    What is the role of fiber optics in the CsI/CCD configuration?

    <p>To transmit light efficiently from the scintillator to the CCD.</p> Signup and view all the answers

    What is a characteristic feature of the response of charge-coupled devices (CCDs)?

    <p>Their response to x-ray exposure is linear.</p> Signup and view all the answers

    Which property of cesium iodide contributes to a lower radiation dose for patients?

    <p>High photoelectric capture efficiency.</p> Signup and view all the answers

    What is the primary benefit of using tiled CCDs in digital radiography?

    <p>They allow for the use of larger area x-ray beams.</p> Signup and view all the answers

    What does the term 'dynamic range' imply regarding CCDs?

    <p>The range of x-ray exposure levels that can be detected.</p> Signup and view all the answers

    What is the primary function of amorphous selenium (a-Se) in digital radiography?

    <p>To convert X-rays directly into electronic signals</p> Signup and view all the answers

    What does the term 'spatial resolution' refer to in digital radiography?

    <p>The ability to distinguish small details</p> Signup and view all the answers

    Which of the following accurately describes scanned projection radiography (SPR)?

    <p>It improves contrast resolution but may have limited spatial resolution</p> Signup and view all the answers

    What is the role of the active matrix array (AMA) in digital radiography?

    <p>To serve as an array of thin-film transistors (TFTs) for signal collection</p> Signup and view all the answers

    How does the thickness of amorphous selenium (a-Se) impact its function in digital radiography?

    <p>A thickness of 200 µm is optimal for direct ionization</p> Signup and view all the answers

    What element serves as a coupling element in direct digital radiography?

    <p>Amorphous selenium (a-Se)</p> Signup and view all the answers

    Which of the following describes the consequence of using smaller pixels in digital radiography?

    <p>Higher spatial resolution</p> Signup and view all the answers

    What is the main reason for collecting the created charge in the amorphous selenium (a-Se) layer?

    <p>To trigger the readout process via TFTs</p> Signup and view all the answers

    What is the significance of the fill factor in an active matrix array?

    <p>It determines the efficiency of photon collection</p> Signup and view all the answers

    Study Notes

    Computed Radiography (CR)

    • CR is a form of digital radiography
    • Unlike screen-film radiography, CR uses a scintillator that emits light in response to x-ray interaction
    • In CR, electrons are trapped temporarily in a metastable state in the image receptor
    • The responses to x-ray interaction in CR are electrons temporarily trapped in a higher energy, metastable state.

    Photostimulable Luminescence (PSL)

    • Some materials (e.g., barium fluorohalide) emit light initially and also emit light later when exposed to differing light sources, a process called PSL
    • The light-emitting component is called an activator, and it plays a similar role to the sensitivity center of a film emulsion.
    • Without the activator, there is no latent image.

    Photostimulable Phosphor (PSP) Screen

    • PSP (barium fluorohalide) is similar in structure to a radiographic intensifying screen, and the cross-section is shown in Figure 12.4
    • The PSP crystal is layered, encompassing a phosphor layer, binder, and protective overcoat
    • Phosphor layer thickness is between 100-250 mm

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    Description

    This quiz covers the principles of computed radiography (CR) and photostimulable luminescence (PSL). Learn how these technologies utilize scintillators, electrons, and activators to capture and emit images effectively. Test your understanding of the innovations in digital radiography.

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