Card Set Information

2010-02-25 23:39:53
ch 18

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  1. Scatter is caused by what type of introduction?
  2. Scatter does what 2 things to the film?
    • Adds unwanted density
    • decrease contrast
  3. T or F: Fog always decreases Contrast
  4. Patient thickness and large open field size increase what?
  5. Where is the Grid located?
    between the patient and the film
  6. When should you use a grid? 2 things
    • parts greater that 10 cm
    • Kvp above 60
  7. Describe a grid..
    • thing flat rectangular device
    • contains lead strips separated by radiolucent enter space material
  8. Who invented the Bucky and Explain it?
    • Dr. Gustav Bucky
    • Lead strips in checker board appearance
  9. Describe Hollis Potters improvement to the Bucky?
    • Lead strip run in the 1 direction
    • strips move to blur during exposure
  10. What are Strips like located with the grid?
    Converted in foil, making them absorb more scatter because of high atomic number
  11. interspace material allows_______photons to pass through?
  12. The ratio of height of lead strips to the distance b/w them is_______
    grid ratio
  13. high grid ration= more or less scatter clean up?
  14. How does the beam have to be for it to get through a grid with high ratio?
    pretty darn straight
  15. With a longer distance you want low grid ratio? T or F
  16. Number of lead strips per inch is?
    Grid frequency
  17. the higher the frequency the thicker the lead strips? T or F
    F * Thinner
  18. The most common Grid frequency used is?
    85 - 103
  19. what is total lead content? and how is it measured?
    • amount of lead in grid
    • mAs per unit area= g/cm2
  20. what is the most important factor in determining scatter clean up?
    Lead content
  21. General Rules
    • Grids with high grid ration (close strips)
    • Grids with lower frequency (thicker)
  22. what are the two types of grid ratio?
    • linear
    • criss cross/cross hatched
  23. linear is the most common grid pattern? T or F
    True.. can never angle against strips
  24. can you angle the tube with a criss cross grid?
    No, will = grid cut off
  25. what is grid cut off
    loss of density with in the film
  26. Describe a parallel grid
    • strips that run up and down will never touch
    • longer SIDS= angle never strikes strips
  27. Where do the angled strips meet in a focused grid in space ?
    convergence line
  28. with a focused grid, is there more/less room for error and why?
    less, bc less latitude (less space b/w)
  29. The Bucky is a _______Grid?
  30. the bucky moves the lead strips perpendicular to the way they run? T or F
  31. in the table and upright Bucky do the strips run lengthwise or crosswise?
  32. when using a grid, higher kvp or mAs?
  33. what is GCF and what is the formula?
    • Grid Conversion factor
    • GCF= mAs1/mAs2 = GCF1/GCF2
  34. What are the four Rules of Grids?
    • 1) tube properly aligned to tube
    • 2) correct focal range
    • 3) correct angle with strips
    • 4) tube side of Grid, facing the grid
  35. What are 4 types of Grid errors and with what type of grid do they occur?
    • off level- focused and parallel
    • off center- focused
    • off focus-focused
    • upside down-focused