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Radiation Physics
<ul><li>There are three key parts of the Image Receptor for Conventional Radiography: </li></ul><ul><ul><li>Film to record...
<ul><li>Less than 1% of the incident x-rays interact with the film to contribute to the latent image. </li></ul><ul><li>Th...
<ul><li>About 30% of the x-rays striking the screens interact with the screens producing a large number of visible light p...
<ul><li>Most conventional radiographic cassettes have a pair of screens that sandwich the film. This design used double em...
<ul><li>Four Distinct Layers </li></ul><ul><ul><li>Protective Coating </li></ul></ul><ul><ul><li>Phosphor </li></ul></ul><...
<ul><li>Coating is transparent to light. </li></ul><ul><li>Resistant to abrasion and damage from handling. </li></ul><ul><...
<ul><li>The active layer of the screen is the phosphors. </li></ul><ul><li>The phosphors emit light when stimulated by x-r...
<ul><li>Modern screens use rare earth elements such as: </li></ul><ul><ul><li>Gadolinium </li></ul></ul><ul><ul><li>Lantha...
<ul><li>High atomic number so x-ray absorption will be high.  Quantum Detective Efficiency (DQE) </li></ul><ul><li>Emit a ...
<ul><li>Phosphor Afterglow should be minimal. </li></ul><ul><li>Phosphor should not be affected by heat humidity or other ...
<ul><li>Thickness of the phosphor Layer </li></ul><ul><li>Concentration of the crystals </li></ul><ul><li>Size of the crys...
<ul><li>The light from the phosphors  is emitted isotropically. </li></ul><ul><li>Without a reflective layer, only half of...
<ul><li>Some screens have special dyes that absorb the light photons coming at a large angles. </li></ul><ul><li>These pho...
<ul><li>The base is the layer farthest from the film. </li></ul><ul><li>It is usually made of polyester. The base </li></u...
<ul><li>The x-ray photon is absorbed by the target atom.  </li></ul><ul><li>The outer shell electron is raised to an excit...
<ul><li>Any material that gives of light in response to a stimulus is a luminescent material. </li></ul><ul><li>Two types ...
<ul><li>Phosphor composition:  Rare earth screens are very efficient in conversion of x-ray to light. </li></ul>
<ul><li>Phosphor thickness:  The thicker the phosphor layer, the higher the number of x-rays converted to light. </li></ul...
<ul><li>Dye:  Light controlling dyes are added to control the light spread to improve spatial resolution. </li></ul><ul><l...
<ul><li>Concentration of crystals:  </li></ul><ul><ul><li>The higher the concentration of crystals, the higher the speed. ...
<ul><li>Rare earth screens have increased speed for two reasons: </li></ul><ul><ul><li>Detective Quantum Efficiency  (DQE)...
<ul><li>Conversion Efficiency:  High conversion efficiency results in increases image noise. </li></ul><ul><li>Noise (any ...
<ul><li>Image detail is the result of  spatial resolution  and  contrast resolution . </li></ul><ul><li>Generally the cond...
<ul><li>When screen phosphors reacts with x-rays a larger area of the film is exposed than what would be exposed by radiat...
<ul><li>Direct exposure can resolve 50 lp/mm with a very small focal spot. </li></ul><ul><li>High speed screens can resolv...
<ul><li>High speed screens have thick layers of crystal and /or large crystals. </li></ul><ul><li>High detail screens have...
<ul><li>Screens in pairs and double emulsion film is the standard of the industry. Less than 1% of the image is produced b...
<ul><li>The cassette is a rigid holder for the film and screens. </li></ul><ul><li>It will contain some form of compressio...
<ul><li>The back of the cassette may contain some form of metal that can absorb x-rays that are not absorbed by the screen...
<ul><li>For the screen to work at maximum efficiency, the light absorption characteristics of the film must be matched to ...
<ul><li>Calcium Tungstate emits a broad blue spectrum. </li></ul><ul><li>Rare earth emits a green spectrum. </li></ul><ul>...
<ul><li>Screens in the cassette can be of two types or speeds. Some people use two different speeds in cassette for full s...
<ul><li>High quality radiography requires that the screens be clean and free of artifacts. </li></ul><ul><li>Avoid touchin...
<ul><li>Keeping the dark room clean will help reduce dirt or dust getting into the cassette. </li></ul><ul><li>Don’t stack...
<ul><li>Clean the screens at least quarterly </li></ul><ul><li>Use only specially formulated screen cleaner with anti stat...
<ul><li>The hinge of the cassette has failed, resulting in a light leak. </li></ul>
<ul><li>Card inside cassette </li></ul>
<ul><li>This cassette popped partly open.  </li></ul><ul><li>With cassette artifacts, think about how the cassette opens. ...
<ul><li>Dirty screens will appear as white spots on the film. </li></ul><ul><li>This film also has some static electricity...
<ul><li>Dirty or damaged screens will cause white spots on the image . </li></ul>
<ul><li>Dirty or damaged screen will cause white spots on the image. </li></ul>
<ul><li>The white spots on this film are the result of damaged or worn out screens. </li></ul><ul><li>Never use alcohol or...
<ul><li>Poor screen contact will cause an area of the image to appear cloudy and blurry.  </li></ul><ul><li>Common reasons...
<ul><li>Common reasons for poor contact include: </li></ul><ul><ul><li>Warped cassette front or frame. </li></ul></ul><ul>...
<ul><li>A radiograph is taken and the film processed. </li></ul><ul><li>The image is viewed from 2 to 3 meters from the vi...
<ul><li>Test the cassette when they are purchased and then twice yearly. </li></ul>
<ul><li>Procedure: </li></ul><ul><li>Clean screens and let them dry. Use screen cleaner design for the screen used. </li><...
<ul><li>Procedure: </li></ul><ul><li>Set SID to 40” Table Top </li></ul><ul><li>Place  cassette on table. </li></ul><ul><l...
<ul><li>Procedure: </li></ul><ul><li>Hang film on view box. </li></ul><ul><li>Step back 72” from view box and view film. <...
<ul><li>There is a loss of detail in the thoracic and lumbar spine due to poor screen contact. </li></ul><ul><li>This was ...
<ul><li>Note the blurry image in the spine but sharp image of the ribs. </li></ul><ul><li>The screens were not in proper c...
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Intensifying screens

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Intensifying screens

  1. 1. Radiation Physics
  2. 2. <ul><li>There are three key parts of the Image Receptor for Conventional Radiography: </li></ul><ul><ul><li>Film to record the image </li></ul></ul><ul><ul><li>Intensifying Screens to expose the film </li></ul></ul><ul><ul><li>Cassette to protect the screens and film </li></ul></ul>
  3. 3. <ul><li>Less than 1% of the incident x-rays interact with the film to contribute to the latent image. </li></ul><ul><li>The intensifying screens converts the remnant radiation to light than produces the latent image. They act as an amplifier of the remnant radiation. </li></ul>
  4. 4. <ul><li>About 30% of the x-rays striking the screens interact with the screens producing a large number of visible light photons. </li></ul><ul><li>The use of intensifying screens results in considerable lower radiation dose to the patient but has the disadvantage of causing a slight blurring of the image. </li></ul>
  5. 5. <ul><li>Most conventional radiographic cassettes have a pair of screens that sandwich the film. This design used double emulsion film. </li></ul>
  6. 6. <ul><li>Four Distinct Layers </li></ul><ul><ul><li>Protective Coating </li></ul></ul><ul><ul><li>Phosphor </li></ul></ul><ul><ul><li>Reflective layer </li></ul></ul><ul><ul><li>Base </li></ul></ul>
  7. 7. <ul><li>Coating is transparent to light. </li></ul><ul><li>Resistant to abrasion and damage from handling. </li></ul><ul><li>Resistant to static electricity </li></ul><ul><li>Provide a surface for cleaning while protecting the phosphors. </li></ul>
  8. 8. <ul><li>The active layer of the screen is the phosphors. </li></ul><ul><li>The phosphors emit light when stimulated by x-rays. </li></ul><ul><li>Prior to 1970 the most common phosphor was a crystalline form of Calcium Tungstate. </li></ul>
  9. 9. <ul><li>Modern screens use rare earth elements such as: </li></ul><ul><ul><li>Gadolinium </li></ul></ul><ul><ul><li>Lanthanum </li></ul></ul><ul><ul><li>Yttrium </li></ul></ul>
  10. 10. <ul><li>High atomic number so x-ray absorption will be high. Quantum Detective Efficiency (DQE) </li></ul><ul><li>Emit a large amount of light per x-ray absorption. Conversion Efficiency </li></ul><ul><li>Light must be of proper wavelength to match the sensitivity of the film Spectral Matching </li></ul>
  11. 11. <ul><li>Phosphor Afterglow should be minimal. </li></ul><ul><li>Phosphor should not be affected by heat humidity or other environmental conditions </li></ul>
  12. 12. <ul><li>Thickness of the phosphor Layer </li></ul><ul><li>Concentration of the crystals </li></ul><ul><li>Size of the crystals. </li></ul>
  13. 13. <ul><li>The light from the phosphors is emitted isotropically. </li></ul><ul><li>Without a reflective layer, only half of the light would interact with the film. </li></ul><ul><li>The reflective layer redirects the light to the film. </li></ul>
  14. 14. <ul><li>Some screens have special dyes that absorb the light photons coming at a large angles. </li></ul><ul><li>These photons would increase the image blur. </li></ul><ul><li>Only the photons perpendicular to the film are emitted. The dye increases spatial resolution but reduce speed. </li></ul>
  15. 15. <ul><li>The base is the layer farthest from the film. </li></ul><ul><li>It is usually made of polyester. The base </li></ul><ul><li>should be: </li></ul><ul><ul><li>Rugged and moisture resistant </li></ul></ul><ul><ul><li>Can not be damaged by radiation or discoloration </li></ul></ul><ul><ul><li>Chemically inert, flexible and free of impurities. </li></ul></ul>
  16. 16. <ul><li>The x-ray photon is absorbed by the target atom. </li></ul><ul><li>The outer shell electron is raised to an excited state. </li></ul><ul><li>It returns to a ground state with emission of a light photon. </li></ul>
  17. 17. <ul><li>Any material that gives of light in response to a stimulus is a luminescent material. </li></ul><ul><li>Two types of luminescent material. </li></ul><ul><li>Fluorescent: gives off light only during stimulus. Good for screens </li></ul><ul><li>Phosphorescence: continues to give off light after stimulus. Bad for screens called Lag or Afterglow . </li></ul>
  18. 18. <ul><li>Phosphor composition: Rare earth screens are very efficient in conversion of x-ray to light. </li></ul>
  19. 19. <ul><li>Phosphor thickness: The thicker the phosphor layer, the higher the number of x-rays converted to light. </li></ul><ul><li>High speed screens have thick layer. Detail screens have a thin layer. </li></ul><ul><li>Reflective layer will increase speed and blur </li></ul>
  20. 20. <ul><li>Dye: Light controlling dyes are added to control the light spread to improve spatial resolution. </li></ul><ul><li>Crystal size: Larger crystal produce more light per interaction. Detail screens have small crystals. </li></ul>
  21. 21. <ul><li>Concentration of crystals: </li></ul><ul><ul><li>The higher the concentration of crystals, the higher the speed. </li></ul></ul>
  22. 22. <ul><li>Rare earth screens have increased speed for two reasons: </li></ul><ul><ul><li>Detective Quantum Efficiency (DQE) or the ability to absorb the photons ( High Z number) </li></ul></ul><ul><ul><li>Conversion Efficiency: Amount of light emitted per x-ray. </li></ul></ul>
  23. 23. <ul><li>Conversion Efficiency: High conversion efficiency results in increases image noise. </li></ul><ul><li>Noise (any unwanted information) can be speckled appearance or grainy </li></ul><ul><ul><li>It occurs with fast screens and use of high kVp. </li></ul></ul><ul><li>The factors that make rare earth screens have greater speed also contribute to increased noise. </li></ul><ul><li>Increased conversion efficiency results in lower exposure. Less x-rays results in an increased quantum mottle. </li></ul>
  24. 24. <ul><li>Image detail is the result of spatial resolution and contrast resolution . </li></ul><ul><li>Generally the conditions that increase speed reduce spatial resolution. </li></ul>
  25. 25. <ul><li>When screen phosphors reacts with x-rays a larger area of the film is exposed than what would be exposed by radiation alone. </li></ul><ul><li>This results in reduced spatial resolution and more blur. </li></ul>
  26. 26. <ul><li>Direct exposure can resolve 50 lp/mm with a very small focal spot. </li></ul><ul><li>High speed screens can resolve 7 lp/mm. </li></ul><ul><li>Detail screens can resolve 15 lp/mm </li></ul><ul><li>The unaided eye can resolve 10 lp/mm. </li></ul>
  27. 27. <ul><li>High speed screens have thick layers of crystal and /or large crystals. </li></ul><ul><li>High detail screens have a thin layer of small crystals. </li></ul>
  28. 28. <ul><li>Screens in pairs and double emulsion film is the standard of the industry. Less than 1% of the image is produced by the x-ray photons. </li></ul><ul><li>Each screen contributes relatively evenly in the production of the image. </li></ul>
  29. 29. <ul><li>The cassette is a rigid holder for the film and screens. </li></ul><ul><li>It will contain some form of compression to push the film in close contact with the screens. </li></ul><ul><li>The front of the cassette is made of a radiolucent material with low absorption characteristics. </li></ul>
  30. 30. <ul><li>The back of the cassette may contain some form of metal that can absorb x-rays that are not absorbed by the screens. </li></ul><ul><li>Sometime with cassettes that do not adequately absorb the rays, back scatter will result from scatter radiation from the cassette holder or near by wall. </li></ul>
  31. 31. <ul><li>For the screen to work at maximum efficiency, the light absorption characteristics of the film must be matched to the light emitted from the screens. </li></ul><ul><li>This is called spectrum matching. </li></ul>
  32. 32. <ul><li>Calcium Tungstate emits a broad blue spectrum. </li></ul><ul><li>Rare earth emits a green spectrum. </li></ul><ul><li>The film, screens and safelight must match. </li></ul>
  33. 33. <ul><li>Screens in the cassette can be of two types or speeds. Some people use two different speeds in cassette for full spine radiography. </li></ul><ul><li>When types of screens are different, they are referred to as Asymmetric screens. One side may be high contrast and the other side wide latitude. The combined image is superior. </li></ul>
  34. 34. <ul><li>High quality radiography requires that the screens be clean and free of artifacts. </li></ul><ul><li>Avoid touching the screens with your hands. </li></ul><ul><li>Clean the screens with screen cleaner. </li></ul><ul><li>Do not slide the film in or out when loading the cassette. </li></ul>
  35. 35. <ul><li>Keeping the dark room clean will help reduce dirt or dust getting into the cassette. </li></ul><ul><li>Don’t stack the cassette on top of each other as the weight can damage the cassette. </li></ul><ul><li>Load the film completely in the cassette. </li></ul>
  36. 36. <ul><li>Clean the screens at least quarterly </li></ul><ul><li>Use only specially formulated screen cleaner with anti static properties </li></ul><ul><li>Never use alcohol to clean screens </li></ul><ul><li>Make sure they are dry before reloading with film. </li></ul>
  37. 37. <ul><li>The hinge of the cassette has failed, resulting in a light leak. </li></ul>
  38. 38. <ul><li>Card inside cassette </li></ul>
  39. 39. <ul><li>This cassette popped partly open. </li></ul><ul><li>With cassette artifacts, think about how the cassette opens. </li></ul><ul><li>If the cassette pops open do not use the film. </li></ul>
  40. 40. <ul><li>Dirty screens will appear as white spots on the film. </li></ul><ul><li>This film also has some static electricity artifacts. </li></ul>
  41. 41. <ul><li>Dirty or damaged screens will cause white spots on the image . </li></ul>
  42. 42. <ul><li>Dirty or damaged screen will cause white spots on the image. </li></ul>
  43. 43. <ul><li>The white spots on this film are the result of damaged or worn out screens. </li></ul><ul><li>Never use alcohol or detergents to clean screens. </li></ul>
  44. 44. <ul><li>Poor screen contact will cause an area of the image to appear cloudy and blurry. </li></ul><ul><li>Common reasons for poor contact include: </li></ul><ul><ul><li>Worn contact felt </li></ul></ul><ul><ul><li>Loose, bent or broken hinges </li></ul></ul><ul><ul><li>Loose bent or broken latches </li></ul></ul><ul><ul><li>Warped screen </li></ul></ul>
  45. 45. <ul><li>Common reasons for poor contact include: </li></ul><ul><ul><li>Warped cassette front or frame. </li></ul></ul><ul><ul><li>Sprung or cracked cassette frame. </li></ul></ul><ul><ul><li>Foreign matter in the cassette. </li></ul></ul><ul><li>Screen contact is tested using a wire mesh test tool. </li></ul><ul><li>The wire mesh is placed on top of the cassette. </li></ul>
  46. 46. <ul><li>A radiograph is taken and the film processed. </li></ul><ul><li>The image is viewed from 2 to 3 meters from the view box. </li></ul><ul><li>Poor contact will appear as a cloudy and blurry area on the film. </li></ul>
  47. 47. <ul><li>Test the cassette when they are purchased and then twice yearly. </li></ul>
  48. 48. <ul><li>Procedure: </li></ul><ul><li>Clean screens and let them dry. Use screen cleaner design for the screen used. </li></ul><ul><li>With a felt tip pen, write an identification number on the screen next to the I.D. and on the back of the cassette. </li></ul><ul><li>Load cassettes. </li></ul>
  49. 49. <ul><li>Procedure: </li></ul><ul><li>Set SID to 40” Table Top </li></ul><ul><li>Place cassette on table. </li></ul><ul><li>Place wire mesh tool on cassette. </li></ul><ul><li>Set collimation to film size. </li></ul><ul><li>Make exposure and process film. </li></ul>
  50. 50. <ul><li>Procedure: </li></ul><ul><li>Hang film on view box. </li></ul><ul><li>Step back 72” from view box and view film. </li></ul><ul><li>Areas of increased density or loss of resolution indicates poor contact or stained screens. </li></ul>
  51. 51. <ul><li>There is a loss of detail in the thoracic and lumbar spine due to poor screen contact. </li></ul><ul><li>This was a new cassette. </li></ul>
  52. 52. <ul><li>Note the blurry image in the spine but sharp image of the ribs. </li></ul><ul><li>The screens were not in proper contact in the middle of the cassette due to a bow in the cassette back. </li></ul>

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