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Slockett's Rad Exposures > Grids > Flashcards

Grids Flashcards

1
Q

Who built the 1st grid?

A

Dr. Gustav Bucky (1913)

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2
Q

What was Dr. Bucky’s original principle?

A

Lead foil strips standing on edge separated by x-ray transparent interspacers

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3
Q

What is responsible for dark areas?

A

Transmission

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4
Q

What is responsible for light areas?

A

Absorption

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5
Q

Who came up with the moving grid?

A

Hollis Potter (1915-1917)

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6
Q

What is another name for a moving grid?

A

Wire Grid

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7
Q

What was the idea behind the moving/ wire grid?

A

To get rid of grid lines

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8
Q

What was the problem with Potters grid?

A
  • It was filtering out radiation before it got to the patient
  • Required high technique to get through the grid
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9
Q

What was the Potter Bucky Diaphragm?

A

Moving grid

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10
Q

What determines when to use a grid?

A
  1. When body part thickness exceeds 10cm
    Ex: shoulders, knees
  2. kVp is above 60
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11
Q

What is a grid composed of?

A

Alternating strips of radiopaque and radiolucent material

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12
Q

What type of material absorbs scatter?

A

Radiopaque

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13
Q

What are the reasons lead is used as the typical radiopaque material?

A
  • Inexpensive
  • Shapes easily
  • High atomic #
  • Dense
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14
Q

What material are the interspaces, radiolucent or radiopaque?

A

Radiolucent

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15
Q

Is the interspace material typically thicker or thinner than lead?

A

Thicker

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16
Q

What is often used as the interspace material?

A

Aluminum

*Plastic fiber can also be used

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17
Q

Why is aluminum often used as the interspace material?

A
  • Durable

- Absorbs low energy scatter

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18
Q

Why is aluminum used more frequently than plastic fiber as the interspace material?

A

Aluminum has a higher atomic number

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19
Q

What is grid ratio?

A

The ratio between the lead content and the aluminum content

Height of grid strip (h)
_________________

Interspace width (d)

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20
Q

If the height of the lead strips stays the same and the distance between them decreases, what is the result of the grid ratio?

A

It increases

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21
Q

What is the grid ratio when the lead strips are 3.2mm high and separated by 0.2mm?

A
  1. 2
    - —- = 16:1
  2. 2
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22
Q

If a grid ratio has an interspace of 0.5mm and lead strips that are 3mm high, what is it’s grid ratio?

A

3

  • – = 6:1
    0. 5
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23
Q

What is the grid ratio range?

A

4: 1 - 16:1

* Mammo can go lower

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24
Q

Would a high grid ratio clean up more scatter radiation than a low grid ratio?

A

Yes

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25
Q

What would clean up scatter radiation better, a high or low grid ratio?

A

High

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26
Q

What type of grid ratio would improve contrast?

A

High

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27
Q

How does a high grid ratio clean up more scatter radiation?

A

It has more lead strips

28
Q

What type of relationship exists between the distance between the lead strips and the grid ratio when the height of the grid strips stays the same?

A

Inverse

29
Q

The higher the ratio the ______ room you have before grid cut off?

A

Less

30
Q

When angling against a grid, do you have more room to play with on a 16:1 or an 8:1 grid ratio before you get grid cutoff?

A

8:1

31
Q

How do you determine grid frequency?

A

By the number of lead strips per inch or cm

32
Q

Do you have to be more accurate on a low or high grid ratio?

A

High

33
Q

What is the most often seen grid frequency range?

A

60-110

34
Q

Typically higher frequency grids have ________ lead strips.

A

Thinner

35
Q

Which one has a higher frequency, a 10 line grid or an 8 line grid?

A

10 line grid

36
Q

Higher frequency with the same interspace distance reduces what?

A

The grid effectiveness

37
Q

What are the most common grid ratio’s?

A

8:1- 10:1

38
Q

How much cleanup will a 5:1 grid ratio give?

A

85%

39
Q

How much cleanup will a 16:1 grid ratio give?

A

97%

40
Q

The higher the grid ratio the _______ cleanup.

A

Better

41
Q

What material is the most important in determining grid efficiency?

A

Lead

42
Q

Lead content is greater in a grid with a…

A

High grid ratio

43
Q

As lead increases what happens?

A

Contrast increases and scatter decreases

44
Q

Parallel grids clean up scatter in how many directions?

A

One

45
Q

What cleans up scatter better, a parallel grid or a crossed grid?

A

Crossed grid

46
Q

Which grid has more potential for grid cutoff, parallel or cross?

A

Cross

47
Q

To be most effective, where must the CR be placed on a Crossed grid?

A

In the center

48
Q

How many directions does a cross grid clean up scatter?

A

All directions

49
Q

What kind of grid has lead strips that are angled to match the divergence of the beam?

A

Focused grids

50
Q

What type of grid requires a specific SID to minimize grid cut off or absorption?

A

Focused grid

51
Q

What type of grids are more difficult to manufacture?

A

Focused grid

52
Q

What are the (3) things to remember with focused grids?

A
  1. Centering
  2. Alignment
  3. SID
53
Q

Do grids move during exposure?

A

Yes

In a reciprocating or oscillating pattern

54
Q

What type of grid movement is described as; motor driven back and forth movement (@2cm)?

A

Reciprocating

55
Q

What type of grid movement is described as; circular movement?

A

Oscillating (like a pinball)

56
Q

What are the two types of grid movement?

A

Reciprocating & Oscillating

57
Q

What is the down side of a moving grid?

A

Creates image blur

Creating more OID

58
Q

What is Selectivity or the “K” factor?

A

The ability to allow primary radiation to reach the image receptor and prevent scatter

59
Q

Grids are designed to absorb scatter radiation, but they sometimes…

A

Absorb primary radiation

60
Q

Typically “K” factor ranges between…

A

1.5- 3.5 (1.5- 3.5 times better when grids are used)

61
Q

What does the “K” factor compare?

A

Contrast of an image with a grid to one without a grid

62
Q

What is the Contrast Improvement Factor?

A

Contrast w/o grid

63
Q

What are factors when selecting a grid?

A
  • Patient dose
  • Exam
  • Detail required
  • Part thickness
  • Desired technique
  • Equipment availability
64
Q

As grid ratio increases, radigraphic density decreases; as grid ratio decreases…

A

radiographic density increases

65
Q

Below 90 kVp, you can use grid ratio’s up to…

A

8:1

66
Q

Above 90 kVp you often use grid ratio’s of…

A

10:1 or higher

Slockett's Rad Exposures (8 decks)

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