Card Set Information

2010-03-02 11:01:32

test 2
Show Answers:

  1. How the eye works?
    The human eye gathers light, focuses the light, converts it to nervous impulse and transits it to the brain for processing
  2. Fovea centralis?
    gathers light to nerve impulse
  3. Optic nerve?
    Transmits nerve impulses to the brain
  4. Parts of the eye-
    • Aqueous humor
    • Cornea
    • Iris
    • Lens
  5. Phototopic
    • daylight vision- vision is controlled by the CONES they require relatively bright light to function they can see long=yellow
    • Medium= green
    • Short= violet
    • -good focus-good contrast perception
  6. Scotopic
    -night vision- vision is controlled by the RODS very sensitive to low levels and unable to see bring lights

    Can not seen colors—but come best see green if any

    -good peripheral vision
  7. What is perception?
    recognition and interpretation of what we see
  8. Threshold detection?
    • Perception of extremely small or faint detail
    • Is affected by background noise
    • Noise= fog(Compton scatter)
    • Artifacts=jewelry
  9. What is boundary effect?
    • Hard to see the difference in colors with colors are not close together
    • The longer the boundary the easier to tell the difference between shades
  10. Mach Effect?
    Nerve impulse and what our brain perceives with bright light or a big change
  11. Edge enhancement?
    • See a thin white strip b4 a big change in contrast
    • Scanning motions can help to reduce this or when gradually change contrast
  12. Veil glare?
    • Bright light shining out sides of view box
    • Can’t judge contrast
  13. How does change in distance effect light? And what goes on?
    Distance makes light diverge. It also changes blind spots. Humans have a blind spot at 9 inches. It also changes the cell so you don’t overuse a cell
  14. Patter recognition
    Faster when techs hang radiographs correct
  15. Localization process
    2 radiographs 90 degrees apart from one another
  16. How projection tells what is superimposed?
    the name tells what is being superimposed
  17. What type of interactions produce scatter
    • Incedent photons and outer shell electrons
    • compton interactions (high kvp)
  18. What happens to film when scatter strikes?
    Density increase and Contrast decrease
  19. Increase kvp? Interactions? Affects on contrast and scatter?
    As kvp increase there is more comptons interactions which increase scatter and decrease contrast.
  20. Changes in volume affecting scatter?
    As volume increases scatter increases
  21. What affects volume? Patient / tube?
    • Field size
    • Patient thickness
  22. How does atomic number affect scatter
    • The higher the atomic number the less scatter
    • Bones. Contrast media
  23. Field size
    • Large field size= more scatter produced
    • Small field size= less scatter produced
  24. 3 beam restricters
    • - Aperature diaphragms
    • - Cones and cylinders
    • - Collimaters
  25. Aperature Diaphrams Reduce penumbra, off focus, or stem?
    • they increase penumbra
    • dont decrease off focus
    • dont decrease stem
  26. What do cones and cylinders reduce
    • Reduce penumbra
    • Reduce off focus
  27. PBL?
    Senses size and orientation of the cassette
  28. What is penumbra? Off focus?
    • Penumbra- fuzzy borders-reduces detail -
    • Off focus- xray photons being created at tube and not at focal spot
  29. Purpose of grid
    Keep the scatter from hitting the cassette
  30. What components control scatter
    • Kvp
    • Irradiated material
    • beam restrictors
  31. Attenuation?
    Reduction in the total number of x-ray photons and the lower energy of the beam
  32. Types of attenuation
    • Absorption
    • scatter
  33. 3 possibilites at x-rays pass through matter
    • Continue on their way
    • Be absorbed
    • Change direction
  34. How do x-rays attenuate
  35. Beam that exits the patient
    Through transmission
  36. How thickness affects attenuation
    Thicker the patient the more attenuation
  37. How atomic number affects attenuation
    higher the atomic number the more attenuation *photoelectric absorbtion
  38. How density affects attenuation
    • More dense the more the attenuation
    • More tissue density the less radiographic density
  39. Number of electrons affect attenuation
    • Higher the electrons the more attenuation
    • Calcium-bones=more attenuation
  40. 4 substances that account for variations of absorption
    • air
    • fat
    • muscle
    • bone
  41. Air, fat,muscle and bones? How they compare in attenuation
    • Air- least
    • Fat-second least
    • Muscle-second most
    • Bone-most attenuation
  42. Define subject density and how it works?
    • More subject density less radiograph density
    • less subject density more radiograph density
  43. Subject contrast
    Amount of differential absorption

    • Chest- high subject contrast
    • Mammography- low subject contrast

    Age and size is what affects contrast
  44. Subject detail (resolution)
    • How patient affects Sharpness of structure as it appears on film
    • Highest detail when have the part is closest to film
    • We rely on where part lies on body and where patient is to the film
    • Less detail larger patients
  45. Subject distortion
    • Misrepresentation of size and shape of structure
    • Magnification-size
    • Angle-sharp
    • Larger the patient-less detail- more distortion – has to do with subject size
  46. Greatest variable?
  47. Additive condition?
    • Kvp- 5- 15 %
    • A place where there used to be or is supposed to be air turns into something more dense
    • As additive disease gets worse radiographic density gets less (whiter)
  48. Destrictive condition
    • mAs- 25- 50 %
    • a place that used to be a dense tissue turns to air or a less dense tissue
    • as destructive disease gets worse radiograph density gets greater (blacker)
  49. Patient history
    • good patient history
    • observe patient
    • clinical assessment
    • luenectomy
    • old exams
  50. How does kvp affect scatter
    higher the kvp the more scatter= contrast then decrease
  51. basic construction of grid and when to use a grid?
    • Thin flat rectangular device- in contains radiopaque (absorb) lead strips sepaorated by radiolucent( pass through) space material
    • Used body part greater than 10 cm
    • Used when kvp higher than 60 =kvp penetrating power
  52. Grid ratio
    • Higher the grid ratio= closer the strips = more scatter clean up= higher the contrast
    • Beam has to be pretty straight
  53. Grid frequency
    • Number of grids lines per inch
    • Higher grid frequency the thinner the strips= less scatter cleanup= lower contrast
  54. what do you want when dealing with grid ratio and frequency
    high grid ratio (close) – and less grid frequency (thick)
  55. Grid patterns
    • linear- can angle longitudinal
    • Criss cross (cross hatched)- can not angle
  56. Grid types
    Parallel- all grids run up and down = will never touch Use with longer SID

    • Focused-lead strips angle to match the beam Tube is supposed to be aligned to the convergence line o Have to be in the correct focal range
    • Not too much room for error
  57. high or low grid ratio makes more room for error?
    Lower grid ratio makes more room for error
  58. How does bucky work (reciprocating grid)
    • Grid strips move perpendicular to the way they run
    • Strips run length of bucky and table
  59. GCF compared to Ratio and mAs
    • When use grid you have to increase mAs
    • Higher the grid ratio the higher the GCF
    • Higher ratio higher the mAs
  60. Grid errors
    • Off level- one but not the other is angled—parallel and focused
    • Off center- tube is not aligned to grid -- focused
    • Off focus- center good the rest bad-- focused
    • Upside down- center good the rest bad -- focused