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Slockett's Rad Exposures > Grids > Flashcards

Flashcards in Grids Deck (66):
1

Who built the 1st grid?

Dr. Gustav Bucky (1913)

2

What was Dr. Bucky's original principle?

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

3

What is responsible for dark areas?

Transmission

4

What is responsible for light areas?

Absorption

5

Who came up with the moving grid?

Hollis Potter (1915-1917)

6

What is another name for a moving grid?

Wire Grid

7

What was the idea behind the moving/ wire grid?

To get rid of grid lines

8

What was the problem with Potters grid?

-It was filtering out radiation before it got to the patient
-Required high technique to get through the grid

9

What was the Potter Bucky Diaphragm?

Moving grid

10

What determines when to use a grid?

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

11

What is a grid composed of?

Alternating strips of radiopaque and radiolucent material

12

What type of material absorbs scatter?

Radiopaque

13

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

-Inexpensive
-Shapes easily
-High atomic #
-Dense

14

What material are the interspaces, radiolucent or radiopaque?

Radiolucent

15

Is the interspace material typically thicker or thinner than lead?

Thicker

16

What is often used as the interspace material?

Aluminum

*Plastic fiber can also be used

17

Why is aluminum often used as the interspace material?

-Durable
- Absorbs low energy scatter

18

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

Aluminum has a higher atomic number

19

What is grid ratio?

The ratio between the lead content and the aluminum content

Height of grid strip (h)
_________________

Interspace width (d)

20

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

It increases

21

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

3.2
----- = 16:1
0.2

22

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

3
--- = 6:1
0.5

23

What is the grid ratio range?

4:1 - 16:1

*Mammo can go lower

24

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

Yes

25

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

High

26

What type of grid ratio would improve contrast?

High

27

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

It has more lead strips

28

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?

Inverse

29

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

Less

30

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?

8:1

31

How do you determine grid frequency?

By the number of lead strips per inch or cm

32

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

High

33

What is the most often seen grid frequency range?

60-110

34

Typically higher frequency grids have ________ lead strips.

Thinner

35

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

10 line grid

36

Higher frequency with the same interspace distance reduces what?

The grid effectiveness

37

What are the most common grid ratio's?

8:1- 10:1

38

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

85%

39

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

97%

40

The higher the grid ratio the _______ cleanup.

Better

41

What material is the most important in determining grid efficiency?

Lead

42

Lead content is greater in a grid with a...

High grid ratio

43

As lead increases what happens?

Contrast increases and scatter decreases

44

Parallel grids clean up scatter in how many directions?

One

45

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

Crossed grid

46

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

Cross

47

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

In the center

48

How many directions does a cross grid clean up scatter?

All directions

49

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

Focused grids

50

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

Focused grid

51

What type of grids are more difficult to manufacture?

Focused grid

52

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

1. Centering
2. Alignment
3. SID

53

Do grids move during exposure?

Yes

In a reciprocating or oscillating pattern

54

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

Reciprocating

55

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

Oscillating (like a pinball)

56

What are the two types of grid movement?

Reciprocating & Oscillating

57

What is the down side of a moving grid?

Creates image blur

Creating more OID

58

What is Selectivity or the "K" factor?

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

59

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

Absorb primary radiation

60

Typically "K" factor ranges between...

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

61

What does the "K" factor compare?

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

62

What is the Contrast Improvement Factor?

Contrast w/ grid
--------------------
Contrast w/o grid

63

What are factors when selecting a grid?

-Patient dose
-Exam
-Detail required
-Part thickness
-Desired technique
-Equipment availability

64

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

radiographic density increases

65

Below 90 kVp, you can use grid ratio's up to...

8:1

66

Above 90 kVp you often use grid ratio's of...

10:1 or higher