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Slockett's Rad Exposures > Grids Part II > Flashcards

Grids Part II Flashcards

1
Q

As grid ratio goes up…

A

Density goes down

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2
Q

What is another name for the GCF (Grid Conversion Factor?)

A

Bucky Factor

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3
Q

What is the GCF used for?

A

When changing from one grid ratio to another

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4
Q

What is the Grid Conversion Factor formula?

A

mAs w/o grid

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5
Q

What is the Grid Ratio & GCF chart?

A

Grid Ratio GCF

5: 1 2
6: 1 3
8: 1 4
12: 1 5
16: 1 6

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6
Q

What is the formula for increasing the grid ratio?

A

mAs1 = GCF1
—— ——-
mAs2 GCF2

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7
Q

If you increase grid ratio, will mAs go up or down?

A

Up

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8
Q

It is important to remember that patient dose is increased when…

A
  • Using a grid compared with not using a grid

- Using a higher grid ratio

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9
Q

What is the biggest problem when using grids?

A

Misalignment (increased OID as well)

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10
Q

Define

Grid Errors: Off Level

A
  • Grid is tilted
  • Could be because of detent

Results in:

  • Cutoff across entire image
  • Light image
  • Halo effect
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11
Q

Grid Errors:

Off Center

A

-Out of Lateral

Results in:
-Decreased density across entire image

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12
Q

Grid Errors:

Off Focus

A

-Improper SID

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13
Q

Grid Errors:

Upside Down Grid

A

Results in:

Cut off edges of film

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14
Q

Grid Errors:

Off center & Off focus

A

-Seen in portables

Results in:

  • Uneven exposure
  • Dark on one side, light on the other
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15
Q

What are some factors that increase scatter radiation?

A
  • Improper technique (low)
  • Poor position
  • Collimation
  • Cassette size
  • Lack of lead strips
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16
Q

A higher quality grid can attenuate how much scatter radiation?

A

80-90%

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17
Q

What are (3) factors that contribute to an increase in scatter?

A

Increased:

  • kVp
  • x-ray field size
  • patient thickness
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18
Q

Proper collimation has the primary effect of reducing…

A

Patient dose by reducing scatter

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19
Q

What is the Air Gap Technique?

A
  • Compensating for not using a grid

- Creating a gap where scatter can escape

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20
Q

What are disadvantages of using an Air Gap Technique?

A
  • Magnification
  • Image blur from OID
  • Patient dose
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21
Q

How much gap do you use in an Air Gap Technique

A
  • Receptor is 10-15 cm from patient
  • By doing this, ideally scatter is not detected
  • Contrast is enhanced
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22
Q

How much increase in technique do you need for an Air Gap Technique?

A

10% increase per cm

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23
Q

Using an Air Gap Technique, the 10cm is equivalent to what ratio grid…

A

15:1

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24
Q

A grid has the following characteristics: grid ratio = 10:1, grid height = 4.5mm; grid strip width = 40 um; interspace width = 450 um. What is the grid frequency

A

20 lines/cm

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25
Q

Statement:

All of the following are true about scattered radiation:

A
  • Puts density on the film
  • Travels in a different direction from primary radiation
  • Has less energy that primary radiation
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26
Q

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 14 Original Grid = 5:1 New Grid 16:1

A

14 2
___ = ___ x= 42
x 6

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27
Q

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 40 Original Grid = 6:1 New Grid 12:1

A

66.6

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28
Q

The spaces between the lead strips of a grid are called:

A

Interspaces

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29
Q

A grid that has strips that are .120 inch high and interspaces that are .010 inch wide has a grid ratio of:

A

12:1

30
Q

The use of a grid on a radiograph has what effect on contrast?

A

It increases it

31
Q

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 12 Original Grid = 8:1 New Grid = None

A

3 mAs

32
Q

The most common type of grid pattern is crossed?

A

True

33
Q

The purpose of moving the grid with the Bucky is:

A

Blur the grid lines

34
Q

Which grid ratio will absorb the most scattered radiation 8:1 or 12:1?

A

12:1

35
Q

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 40 Original Grid = 5:1 New Grid = 8:1

A

80

36
Q

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 15 Original Grid = 16:1 New Grid = 6:1

A

7.5

37
Q

The presence of a large amount of scattered radiation on the radiograph has what effect on contrast?

A

Decreases it

38
Q

As the grid ratio increases, there is also an increase in what?

A

Contrast improvement factor

39
Q

The name of the man who invented the grid is:

A

Gustave Bucky

40
Q

Unwanted absorption of primary radiation by the grid is the definition of:

A

Grid cut-off

41
Q

The minimum kVp that requires the use of a grid is:

A

60

42
Q

The number of grid lines per inch is the definition of:

A

Grid frequency

43
Q

The height of the lead strips compared to the distance between the lead strips is the definition of:

A

Grid ratio

44
Q

What is the purpose of a grid?

A

Absorb scatter and allow primary radiation to pass through

45
Q

Which of the following is not a grid positioning error?

  • Air gap grid
  • Lateral decentering
  • Off-center grid
  • Off-focus grid
  • Off-level grid
A

Air Gap Grid

46
Q

The focused grid pattern most closely matches the way the xray beam emerges from the tube?

A

True

47
Q

Which grid pattern will clean up the most scattered radiation?

A

Crossed

48
Q

What percentage of change in kVp is roughly equal to doubling the mAs?

A

15

49
Q

What happens to density as SID increases?

A

Decreases

50
Q

All other factors remaining constant, a switch to a slower screen will have what effect on density?

A

Decrease

51
Q

What happens to density when a grid is introduced into the system?

A

Decreases

52
Q

What happens to density with increases in filtration?

A

Decreases

53
Q

What happens to density with decreases in tissue thickness?

A

Increases

54
Q

A grid should be used if the body part measures more than:

A

10 cm

55
Q

What is contrast controlled by?

A

kVp

56
Q

A grid will decrease scatter production?

A

False

Scatter production takes place in the patient. A grid will reduce the amount that reaches the receptor.

57
Q

Collimation has what effect on image contrast?

A

Increases contrast

58
Q

What is density controlled by?

A

mAs

59
Q

What is the result in density after collimating?

A

Density will decrease

60
Q

mA and Density are _____ proportional

A

Directly

61
Q

Time and Density are _____ proportional

A

Directly

62
Q

mAs controls _____.

A

Density

63
Q

SID and Density are _____ proportional

A

Inversely

64
Q

OID and Density are ____ proportional because of the air gap

A

Inversely

65
Q

Focal spot size only effects _____ _____.

A

Recorded Detail

66
Q

A grid with a higher ratio contains more lead and reduces _____.

A

Density

67
Q

A larger collimation field size produces more scatter radiation and therefore more _____.

A

Density

68
Q

An increase in filtration _____ the amount of radiation in the beam

A

Reduces

69
Q

A higher speed screen will produce more light and more _____.

A

Density

70
Q

Developer temperature and Density are _____ proportional.

A

Directly

Slockett's Rad Exposures (8 decks)

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