Grids Part II Flashcards Preview

Slockett's Rad Exposures > Grids Part II > Flashcards

Flashcards in Grids Part II Deck (70):
1

As grid ratio goes up...

Density goes down

2

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

Bucky Factor

3

What is the GCF used for?

When changing from one grid ratio to another

4

What is the Grid Conversion Factor formula?

mAs w/grid
---------------
mAs w/o grid

5

What is the Grid Ratio & GCF chart?

Grid Ratio GCF
5:1 2
6:1 3
8:1 4
12:1 5
16:1 6

6

What is the formula for increasing the grid ratio?

mAs1 = GCF1
------ -------
mAs2 GCF2

7

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

Up

8

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

-Using a grid compared with not using a grid
-Using a higher grid ratio

9

What is the biggest problem when using grids?

Misalignment (increased OID as well)

10

Define
Grid Errors: Off Level

-Grid is tilted
-Could be because of detent

Results in:
-Cutoff across entire image
-Light image
-Halo effect

11

Grid Errors:
Off Center

-Out of Lateral

Results in:
-Decreased density across entire image

12

Grid Errors:
Off Focus

-Improper SID

13

Grid Errors:
Upside Down Grid

Results in:
Cut off edges of film

14

Grid Errors:
Off center & Off focus

-Seen in portables

Results in:
-Uneven exposure
-Dark on one side, light on the other

15

What are some factors that increase scatter radiation?

-Improper technique (low)
-Poor position
-Collimation
-Cassette size
-Lack of lead strips

16

A higher quality grid can attenuate how much scatter radiation?

80-90%

17

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

Increased:
-kVp
-x-ray field size
-patient thickness

18

Proper collimation has the primary effect of reducing...

Patient dose by reducing scatter

19

What is the Air Gap Technique?

-Compensating for not using a grid
-Creating a gap where scatter can escape

20

What are disadvantages of using an Air Gap Technique?

-Magnification
-Image blur from OID
-Patient dose

21

How much gap do you use in an Air Gap Technique

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

22

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

10% increase per cm

23

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

15:1

24

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

20 lines/cm

25

Statement:
All of the following are true about scattered radiation:

-Puts density on the film
-Travels in a different direction from primary radiation
-Has less energy that primary radiation

26

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

14 2
___ = ___ x= 42
x 6

27

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

66.6

28

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

Interspaces

29

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

12:1

30


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


It increases it

31

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

3 mAs

32

The most common type of grid pattern is crossed?

True

33

The purpose of moving the grid with the Bucky is:

Blur the grid lines

34

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

12:1

35

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

80

36

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

7.5

37

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

Decreases it

38

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

Contrast improvement factor

39

The name of the man who invented the grid is:

Gustave Bucky

40

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

Grid cut-off

41

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

60

42

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

Grid frequency

43

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

Grid ratio

44

What is the purpose of a grid?

Absorb scatter and allow primary radiation to pass through

45

Which of the following is not a grid positioning error?
-Air gap grid
-Lateral decentering
-Off-center grid
-Off-focus grid
-Off-level grid

Air Gap Grid

46

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

True

47

Which grid pattern will clean up the most scattered radiation?

Crossed

48

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

15

49

What happens to density as SID increases?

Decreases

50

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

Decrease

51

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

Decreases

52

What happens to density with increases in filtration?

Decreases

53

What happens to density with decreases in tissue thickness?

Increases

54

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

10 cm

55

What is contrast controlled by?

kVp

56

A grid will decrease scatter production?

False

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

57

Collimation has what effect on image contrast?

Increases contrast

58

What is density controlled by?

mAs

59

What is the result in density after collimating?

Density will decrease

60

mA and Density are _____ proportional

Directly

61

Time and Density are _____ proportional

Directly

62

mAs controls _____.

Density

63

SID and Density are _____ proportional

Inversely

64

OID and Density are ____ proportional because of the air gap

Inversely

65

Focal spot size only effects _____ _____.

Recorded Detail

66

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

Density

67

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

Density

68

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

Reduces

69

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

Density

70

Developer temperature and Density are _____ proportional.

Directly