Density (Ch.28)

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Anonymous
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97642
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Density (Ch.28)
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2011-08-20 03:22:40
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Imaging Principles
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Imaging Principles, Chapter 28: Density
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  1. In film, it is called density. On the computer, it is called __________.
    Brightness
  2. Two photographic factors that allow detail to be seen:
    • Density
    • Contrast
  3. Typical OD range
    .25 - 2.5

    .25 is lower density; whiter

    2.5 is higher density, darker
  4. Instrument used to measure density.
    Densotometer
  5. What is density?
    variations of darkness; the black and white
  6. What is the main controlling factor of density?
    mAs (mass)
  7. 3 Lightening techniques:
    Bright "hot" lights - higher intensity; higher amps (higher numbers) means more light penetrating

    • Digital optical scanner - adjust the settings
    • Duplication (copying) - an older machine reprints the film lighter/darker
  8. main elements of the body that the x-ray interacts with:
    hydrogen (water component, body tissue, low atomic #)

    oxygen (water component, body tissue, low atomic #)

    calcium (bone, high atomic #)
  9. Does increasing mAs increase or decrease density?
    Increasing mAs increases density.

    Decreasing mAs decreases density.
  10. What is the "rule of thumb" when increasing mAs to change density?
    Double it to increase, Half it to decrease
  11. How much of a change is needed, in mAs, before a change in density is discernible to the naked eye?
    a 30% change.
  12. What type of radiation are we using? What is special about it?
    We use x-ray radiation. It is an ionizing radiation.
  13. What is the main influencing factor of density?
    kVp
  14. To change the density by changing the kVp, what is the generalized rule?
    Change in 15% increments...the 15% rule
  15. generators, listed from weakest energy to strongest energy:
    • single phase
    • 3-phase, 6-pulse
    • 3-phase, 12-pulse
    • high frequency
  16. Changing the kVp changes the:
    energy of the beam
  17. If you have good technique on a high frequency machine, what would you have to do if you changed to a single phase machine?
    You would have to increase your technique since it's a weaker beam. It would need increased power to show the same image as well as a stronger machine.
  18. Define Blooming.
    causing pixel size to become larger than the nominal or state size; a distortion
  19. Describe the expected influence of the focal spot on density when the unit has been properly calibrated.
    There should be no difference between large and small focal spots.
  20. What is the anode heel affect?
    An effect that alters the intensity of radiation (and therefore the density) between the anode and cathode ends of the x-ray tube.

    up to 45% difference depending on the angle of the anode
  21. When your patient is laying on the table, his/her head is always to your ________ (direction).
    left
  22. The patient's head is located on the ______ side, and the feel are located on the _______ side.
    head: cathode

    feet: anode
  23. Towards the cathode side, the density is ________.
    Greater (up to 45%)
  24. SID is short for:
    Source-to-image receptor distance
  25. Inverse Square Law
    • I1 D22
    • __ = _____
    • I2 D12


    • The law affects exposure in inverse proportions to the square of the distance.
    • Simply, if you step ****
  26. In this class...what will we always do with distance when it comes to formulas?
    Square anything to do with distance!!
  27. When distance increases, density ____________.
    decreases
  28. When collimation increases, density __________.
    decreases
  29. When field size increases, density __________.
    increases
  30. When beam restriction increases, density __________.
    decreases
  31. Increased filtration will ____________ density.
    decrease
  32. Filtration ___________ overall average energy of the beam.
    increases
  33. As tissue thickness increases, film density __________.
    decreases
  34. What happens as the atomic number of tissue gets higher?
    The tissue absorbs more of the x-ray, allowing less x-ray to pass through to the film. Therefore, the film density is less where there is tissue with high atomic number. Bone is an example of tissue with a high atomic number.
  35. Where is the highest atomic number in the body?
    the teeth (because of the enamel)
  36. Tissue type is affected by which 2 main factors?
    • the average atomic number
    • the density of the tissue
  37. You may have to __________the density when making large tube angles.
    increase
  38. In pathology, an additive __________ density and creates an effect called __________.
    additive: decreases density and is radiopaque.
  39. In pathology, a destructive _________ density and creates an effect called _________.
    destructive: increases density and is radiolucent.
  40. Example of an Additive:
    Fluid in the lungs (pneumonia)
  41. Example of a Destructive:
    Emphysema
  42. When grid ratio increases, density ___________.
    decreases
  43. Grid advantage/disadvantage
    • advantage: absorbs scatter; less reaches film
    • disadvantage: increases exposure to patient
  44. Grid Conversion Formula
    • GCF1 mAs1
    • ____ = ____
    • GCF2 mAs2
  45. Consider using a grid once the part being x-rayed reaches _______ in size.
    10cm
  46. When Relative Speed (RS) increases, density ________.
    increases
  47. RS conversion formula:
    • mAs1 RS2
    • _____= ___
    • mAs2 RS1
  48. When film processing time increases, density __________.
    increases
  49. When film processing temperature increases, density __________.
    increases
  50. When chemical activity increases, density __________.
    increases

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