Card Set Information

2013-12-04 16:06:56

Show Answers:

  1. if we are using a grid we must increase what technical factor
  2. what is the purpose of a grid
    improves radiographic contrast in the image by absorbing scatter radiation before it reaches the image receptor
  3. penetration or transmission are the _____ spots and aborption are the _____ spots
    dark light
  4. what does scatter do to our image
    creates fog and lowers contrast makes it murky
  5. Scatter increases as what 3 things increase
    • kvp increases
    • field size increases
    • thickeness of part increases
  6. so when should use a grid
    • when the part thickness is greater than 10cm
    • and if the kvp is greater than 60 kvp
  7. what is the basic grid contrsuction definition
    a series of radiopaque lead strips separated by radiolucent interspace matter which can be aluminum or plastic
  8. who created the grid
    radiologist Dr.Gustav Bucky 1913
  9. why could we not use a crosshatched grid with a tube angle
    it will cause tube cut off which is undesirable absorption of the primary beam
  10. Grids allow what type of radiaition to reach the IR and absorbs most ofg what radiation
    • primary radiation
    • scatter radiaition
  11. what are the diasdvantages to grid use
    • increased patient dose
    • grid lines on film
  12. what are the grid ratio dimensions
    • h=the height of the radiopaque strips (divided by)
    • d=distance between the strips (thickness of the interspace material)
  13. List all the grid exposure factors
    • no grid = 1
    • 5:1 = 2
    • 6:1 = 3
    • 8:1 = 4
    • 10:1 = 5
    • 12:1 = 5
    • 16:1 = 6
  14. the higher the grid ratio the higher the removal of ______
  15. what is grid frequency
    what is the frequency range of the grid
    higher frequency have what type of lead strips
    • the number of lead strips per inch or cm
    • 60-200 lines/in
    • 25-80 lines/cm
    • thinner lead strips
  16. what is the average very high frequency grids in digital imaging systems
    103-200 lines/in
  17. high ratio, low frequency grids tend to have the ______ lead content
  18. what is the most important factor in grid efficiency
    lead content
  19. as lead content increases _______ increases and ______ increases
    scatter and contrast
  20. what are the two linear grid patterns
    parallel and focused
  21. criss crossed or cross hatched grids have what two lead strips
    on this grid the primary beam must be centered where
    what is the position of the grid
    • horizontal and vertical
    • perpendicular to the grid
    • grid must be flat
  22. what is the purpose of a linear grid
    allows primary beam to be angled along the long axis of grid without obtaining cut off
  23. what is the important factor about the focused linear grid
    • the lead strips are angled to match the divergence of the beam
    • -the primary beam will align with interspace material
    • -scatter absorbed by lead strips
  24. improper centering when using a focused linear grid results in what?
    when using a high ratio grid it requres what?
    • peripheral cut off
    • careful alignment with the tube
  25. what is the difference in a parallel linear grid
    so what does this do to our primary beam
    which results in what?
    • all lead strips are parallel to one another no divergence
    • abrosbs large amts of the primary beam
    • which results in some cut off
  26. what are stationary grids
    grids that can be attached to a cassette for use
  27. what grid moves during exposure
    potter bucky diaphragm
  28. what are the two movements of grids
    what is the difference
    • reciprocating and oscillating
    • reciprocating happens when the motor drives grid back and forth during exposre
    • oscillating electromagnets pulls grid to one side and releases it during exposure
  29. whenever a grid is placed om a beam to remove scatter we must do what and why
    increase exposure factors b/c density of the radiograph will go down
  30. what is the grid conversion factor
    m2 = m1 x grid (g2) over G1
  31. the ICRU evaluates grid performance by what 2 criteria
    • selectivity
    • contrast improvement ability
  32. what is selectivity
    which grids are more selective
    • describes grids ability to allow primary radiation to reach image receptor and prevent scatter
    • high lead content grids
  33. what is the k factor in contrast improvement ability
    what is the range
    • compares radiographic contrast of an image with a grid to radiographic contrast of an image w/o a grid
    • 1.5-3.5
  34. which radiography is the moire effect taken place
    Improper alignment between xray tube and grid is called what?
    what does this result in
    • digital radiography
    • grid error
    • grid cut off
  35. list all the grid errors and describe
    • off level - cut off across entire image light image
    • off center - cut off  across entire image light image
    • off focus -cut off toward the edge of the image
    • upside down - severe cut off toward the edge of the image
    • moire effect
  36. what is the off level grid error
    • tube is angled across lead strips
    • film is angled
    • causes overall grid cutoff
  37. what is off center grid
    • tube not centered to the grid
    • causes ovverall grid cut off
  38. what grid error causes grid cut off on the periphery but still perfect in the mdidle
    off focus grid error
  39. using the incorrect SID for a focused grid causes what grid error
    off focus grid error - dark center lighter periphery
  40. what grid error has a perfect middle but causes severe cut off on the edges
    upside down grid
  41. what causes cauderoy lines parallel to the scan lines and what can stop this phenomenon
    • moire effect
    • high frequency grids
  42. air gap technique is good for what and bad for what
    • good for contrast
    • bad for magnification which causes a loss of detail
  43. explain the air gap method to control scatter
    when the body part is far away from the film the scatter radiation disperses in the air before it can act with the film
  44. what is benefit of not using a grid when using the air gap technique
    it reduces the radiation exposure five fold with no loss of image quality