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RT 204 > 8. Grid > Flashcards

8. Grid Flashcards

1
Q

is a device used to improve the contrast of the

radiographic image

A

Grid

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2
Q

When an x-ray beam passes through the
body, one of three things will occur with the primary photons that originated at the target. They
will:

A
  1. ) Pass through the body unaffected
  2. ) Be absorbed by the body
  3. ) Interact and change direction
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3
Q

The photons that pass through the body ______ will

interact with the image receptor to create the image

A

unaffected

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4
Q

These differences exist because some photons pass through the body while others are

A

absorbed

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5
Q

Primary radiation that interacts and as a result of this interaction, changes direction is known as

A

scatter radiation

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6
Q

Since these photons _____ direction, they are no longer able to record exposures on the image receptor that
relate to the patient’s anatomy

A

change

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7
Q

add an overall density to the receptor
and as a result of this overall graying of the image,
contrast is lowered.

A

Scattered photons

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8
Q

Scatter increases with ______ in the volume of the tissue irradiated and decreases with ______ atomic number of the tissue

A

increases,

increased

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9
Q

The volume of tissue irradiated that is controlled by the ______ of the patient and the exposure field size

A

thickness

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10
Q

The amount of scatter radiation increases:

A
  1. Increases in patient thickness
  2. Larger field size
  3. Decrease atomic number of the tissue
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11
Q

General rule (Grid is employed):

A
  1. body part thickness exceeds 10 cm (6 in)

2. kVp is above 60

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12
Q

is a thin, flat, rectangular device made by placing
a series of radiopaque lead strips side by side and
separating the strips by an interspace material.

A

Grid

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13
Q

The very first grid was made in ____ by the

A

1913,

American Radiologist Gustav Bucky (1880-1963)

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14
Q

consisted of wide strips of lead spaced 2 cm apart and running in 2 directions, along the
the length of the image and across the image

A

Dr. Bucky’s first grid

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15
Q

In ______, ______ ,a Chicago radiologist

improved Dr. Bucky’s grid design

A

1920, Hollis Potter (1880-1963)

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16
Q

He realigned the lead strips so they would run in only 1 direction, made the lead strips thinner and therefore less obvious on the image, and then designed a new device (now known as the Potter-Bucky diaphragm) which allowed the grid to move during the exposure.

A

Hollis Potter (1880-1963)

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17
Q

Involves the selection of materials, grid ratio and grid frequency

A

Grid Construction

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18
Q

a grid is a series of _______ strips

which alternate with ______ interspace strips

A

radiopaque,

radiolucent

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19
Q

radiolucent

A

Interspace material

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20
Q 
Interspace material 
Either \_\_\_\_\_\_ (commonly used since it easier to manufacture, durable & has a high atomic) and fiber
A

aluminum

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21
Q

higher atomic number than fiber, it can provide additional absorption of low-energy scatter

A

Aluminum

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22
Q

(higher atomic number) increases the
absorption of the primary photons & this is a
disadvantage especially with low kVp techniques where this absorption would be greater

A

Aluminum

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23
Q

is the ratio of the height of the lead strips to the distance between the strips

A

Grid Ratio

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24
Q

If the height is grid is constant, _______ the distance between the lead strips would result in an increase in the grid ratio

A

decreasing

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25
Q

If the height of the grid is a constant, ______ the

distance between the lead strips would result in a decrease grid ratio

A

increasing

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26
Q

An ______ relationship exists between the distance of the lead strips and grid ratio when the height of the grid strips remain the same

A

inverse

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27
Q

allow less scatter radiation to pass through their interspace material to reach the image receptor

A

Higher grid ratios

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28
Q

are more effective at removing

scatter

A

Higher grid ratios

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29
Q

defined as the number of grid lines per inch or centimetre

A

Grid Frequency

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30
Q

Grids are made with a range in frequency from

A

60-200 lines/inch (25-80 lines/cm)

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31
Q

Most commonly used grids have a frequency of

A

85-103 lines/inch (33-41 lines/cm)

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32
Q

Very high frequency grids of approximately ________ are recommended for
stationary grids used with digital image receptor systems to minimize the possibility of seeing the grid lines on the image

A

103-300 lines/inch (41-80 lines/cm)

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33
Q

In general, lead content is greater in a grid that has a ______ grid ratio and _____ grid frequency

A

higher,

lower

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34
Q

As the lead content of a grid increases, the ability of the grid to remove scatter and improve contrast ______

A

increases

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35
Q

Grid with lead strips running in only one direction are called

A

linear grids

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36
Q

Grid Patterns

A

Linear Parallel,
Linear Focused,
Criss-Cross

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37
Q

Grids are also made by placing 2 linear grids on top of

one another so the grid lines are running at right angles

A

Criss-cross or cross-hatched

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38
Q

are more commonly used in clinical practice because they can be used when performing procedures that require tube angulation

A

Linear grids

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39
Q

Angulation across the long axis would result in the

primary beam being directed into the

A

lead strips

40
Q

Results If the primary beam is angled into the lead and the lead will absorb an undesirable amount of primary radiation

A

Grid cut-off

41
Q

GRID TYPES

A

Parallel Grids,

Focused Grids

42
Q

are made with the lead and interspace

strips running parallel to one another

A

Parallel Grids

43
Q

are designed so that the central grid strips are parallel and as the strips move away from the central axis they become more and more inclined

A

Focused Grids

44
Q

If these lead strips were extended, the strips would

intersect along a line in space known as the

A

convergence line

45
Q

The distance from the face of the grid to the points of

convergence of the lead strips is called the

A

grid radius

46
Q

For the grid to be _______, the x-ray tube must be located along the convergence line

A

properly focused

47
Q

Focused grids with _____ grid ratios allow for _____ latitude in the alignment of the tube with the grid.

A

lower,

greater

48
Q

With _____ grid ratio, proper alignment of the grid with the tube is more critical

A

higher

49
Q

are less commonly employed than focused because the strips do not try to coincide with the divergence of
the x-ray beam, some grid cut off will occur along the lateral edges, especially when the grid is employed at the short SIDs

A

Parallel grids

50
Q

A grid is used either in a _______ or _______
in a Potter-Bucky diaphragm to move it during
exposure

A

stationary position,

mounted

51
Q

are used primarily in portable procedures or for upright or horizontal beam views

A

Stationary grids

52
Q

Stationary grids are used primarily in portable
procedures or for upright or horizontal beam views.
• This design is called as the

A

Grid cassette

53
Q

The most common use of the grid is for procedures using the

A

Potter-Bucky diaphragm

54
Q

Potter-Bucky diaphragm usually called the

A

Bucky

55
Q

Device is mounted below the tabletop of radiographic and

radiographic/fluoroscopic tables and holds the cassette in place below the grid

A

Potter-Bucky diaphragm

56
Q

These grids are approximately ________,
large enough to cover a _______ cassette
placed either lengthwise or crosswise in the cassette tray

A

17” x 19” (43 x 48 cm),
14” x 17” (35 x 43 cm)

Potter-Bucky diaphragm

57
Q

The lead strips of the grid run along the ____ axis of the table

A

long

58
Q

To blur the head lines, the grid must move at a ______ to the direction of the lines

A

right angle

59
Q

There are 2 movement mechanisms used today : the movements are described as

A

reciprocating and oscillating

60
Q

a motor drives the grid back and forth during the exposure for a total distance of no more
than 2-3 cm

A

Reciprocating grid

61
Q

an electromagnet pulls the grid to one

side and then releases it during exposure

A

Oscillating grid

62
Q

Once a grid is selected and mounted in the Potter-Bucky Diaphragm, it is

A

not easily changed

63
Q

are generally made by the
department administrator in collaboration with the
radiologist.

A

Purchase decisions

64
Q

The more efficient a grid is at absorbing scatter, the _____ exposure will be received by the image receptor

A

less

65
Q

Increasing ____ to compensate but will result in greater patient dose

A

mAs

66
Q

The better the grid cleans up scatter, the _____ will be the dose given to the patient to achieve an adequate
exposure

A

greater

67
Q

The ______ of a grid in cleaning up or removing

scatter can be quantitatively measured

A

efficiency

68
Q

defines 2 criteria for
measuring a grid’s performance: Selectivity and Contrast
Improvement Ability

A

International Commission on Radiologic Units and

Measurements (ICRU) Handbook 89

69
Q

ICRU

A

International Commission on Radiologic Units and

Measurements

70
Q

Although grids designed to absorb

scatter, they also absorb some primary radiation

A

Selectivity

71
Q

Grids that absorb a greater percentage of scatter than

primary radiation are described as having a _____ degree of selectivity

A

greater

72
Q

The greater the grid is at removing scatter, the greater
will be the selectivity of the grid. This means that a grid with a higher lead content would have a ______
selectivity

A

greater

73
Q

The best measure
of how well a grid functions is its ability to improve
contrast in the clinical setting

A

Contrast Improvement Factor

74
Q

It is dependent on the amount of scatter produced,
which is controlled by kVp and volume of tissue
irradiated

A

Contrast Improvement Factor

75
Q

As the amount of scatter radiation increases, the ______ will be the contrast and the _____ the contrast
improvement factor

A

lower,

lower

76
Q

Poor images can result from ______ use of the grid

A

improper

77
Q

occurs when the tube is angled across the

long axis of the grid strips

A

Off-level

78
Q

can occur with a focused grid and it is the only positioning error possible with a parallel grid

A

Off-level grid error

79
Q

The x-ray tube must be centered along

the central axis of a focused grid to prevent an

A

off-center (off-axis or lateral decentering) grid error

80
Q

The result is a decrease in exposure across the entire image

A

Off-center

81
Q

The greater the degree of lateral decentering, the _____ the grid cut-off

A

greater

82
Q

is made to be used at very

specific distances as identified as the focal range labelled on the front of the grid

A

focus grid

83
Q

If the SID is not within the focus range of the grid, _____ will happen with the focused grids

A

grid cut off

84
Q

result in grid cut-off along the peripheral edges of the image

A

Off-focus errors

85
Q

a focused grid has an identified tube side

based o the way the grid strips are angled

A

Upside-down

86
Q

If the grid is used ______, severe peripheral grid cut-off will occur

A

Upside-down

87
Q

is a grid error that occurs with digital
image receptor systems when the grid lines are captured and
scanned parallel to the scan lines in the imaging plate readers

A

Moire Effect

88
Q

AN ALTERNATE SCATTER REDUCTION METHOD

A

AIR-GAP TECHNIQUE

89
Q

This is best done by restricting the primary beam

A

AIR-GAP TECHNIQUE

90
Q

Collimating to the size of the are being examined is

_____ to image quality.

A

critical

91
Q

is an alternative to the use of a grid

A

AIR-GAP TECHNIQUE

92
Q

It has primary applications in magnification

radiography and to a lesser extent, in chest radiography

A

AIR-GAP TECHNIQUE

93
Q

The technique involves placing the patient at a ______ object image receptor distance (OID), thus creating an air gap between the patient and the image receptor

A

greater

94
Q

While the same amount of scatter will be created during the exposure, less of the scatter will reach the image receptor if the patient is moved

A

farther away

95
Q

The primary disadvantage of the air-gap technique: _______ that results from the OID

A

loss of sharpness

RT 204 (11 decks)

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