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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
If the height of the grid is a constant, ______ the | distance between the lead strips would result in a decrease grid ratio
increasing
26
An ______ relationship exists between the distance of the lead strips and grid ratio when the height of the grid strips remain the same
inverse
27
allow less scatter radiation to pass through their interspace material to reach the image receptor
Higher grid ratios
28
are more effective at removing | scatter
Higher grid ratios
29
defined as the number of grid lines per inch or centimetre
Grid Frequency
30
Grids are made with a range in frequency from
60-200 lines/inch (25-80 lines/cm)
31
Most commonly used grids have a frequency of
85-103 lines/inch (33-41 lines/cm)
32
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
103-300 lines/inch (41-80 lines/cm)
33
In general, lead content is greater in a grid that has a ______ grid ratio and _____ grid frequency
higher, | lower
34
As the lead content of a grid increases, the ability of the grid to remove scatter and improve contrast ______
increases
35
Grid with lead strips running in only one direction are called
linear grids
36
Grid Patterns
Linear Parallel, Linear Focused, Criss-Cross
37
Grids are also made by placing 2 linear grids on top of | one another so the grid lines are running at right angles
Criss-cross or cross-hatched
38
are more commonly used in clinical practice because they can be used when performing procedures that require tube angulation
Linear grids
39
Angulation across the long axis would result in the | primary beam being directed into the
lead strips
40
Results If the primary beam is angled into the lead and the lead will absorb an undesirable amount of primary radiation
Grid cut-off
41
GRID TYPES
Parallel Grids, | Focused Grids
42
are made with the lead and interspace | strips running parallel to one another
Parallel Grids
43
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
Focused Grids
44
If these lead strips were extended, the strips would | intersect along a line in space known as the
convergence line
45
The distance from the face of the grid to the points of | convergence of the lead strips is called the
grid radius
46
For the grid to be _______, the x-ray tube must be located along the convergence line
properly focused
47
Focused grids with _____ grid ratios allow for _____ latitude in the alignment of the tube with the grid.
lower, | greater
48
With _____ grid ratio, proper alignment of the grid with the tube is more critical
higher
49
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
Parallel grids
50
A grid is used either in a _______ or _______ in a Potter-Bucky diaphragm to move it during exposure
stationary position, | mounted
51
are used primarily in portable procedures or for upright or horizontal beam views
Stationary grids
52
Stationary grids are used primarily in portable procedures or for upright or horizontal beam views. • This design is called as the
Grid cassette
53
The most common use of the grid is for procedures using the
Potter-Bucky diaphragm
54
Potter-Bucky diaphragm usually called the
Bucky
55
Device is mounted below the tabletop of radiographic and | radiographic/fluoroscopic tables and holds the cassette in place below the grid
Potter-Bucky diaphragm
56
These grids are approximately ________, large enough to cover a _______ cassette placed either lengthwise or crosswise in the cassette tray
17” x 19” (43 x 48 cm), 14” x 17” (35 x 43 cm) Potter-Bucky diaphragm
57
The lead strips of the grid run along the ____ axis of the table
long
58
To blur the head lines, the grid must move at a ______ to the direction of the lines
right angle
59
There are 2 movement mechanisms used today : the movements are described as
reciprocating and oscillating
60
a motor drives the grid back and forth during the exposure for a total distance of no more than 2-3 cm
Reciprocating grid
61
an electromagnet pulls the grid to one | side and then releases it during exposure
Oscillating grid
62
Once a grid is selected and mounted in the Potter-Bucky Diaphragm, it is
not easily changed
63
are generally made by the department administrator in collaboration with the radiologist.
Purchase decisions
64
The more efficient a grid is at absorbing scatter, the _____ exposure will be received by the image receptor
less
65
Increasing ____ to compensate but will result in greater patient dose
mAs
66
The better the grid cleans up scatter, the _____ will be the dose given to the patient to achieve an adequate exposure
greater
67
The ______ of a grid in cleaning up or removing | scatter can be quantitatively measured
efficiency
68
defines 2 criteria for measuring a grid’s performance: Selectivity and Contrast Improvement Ability
International Commission on Radiologic Units and | Measurements (ICRU) Handbook 89
69
ICRU
International Commission on Radiologic Units and | Measurements
70
Although grids designed to absorb | scatter, they also absorb some primary radiation
Selectivity
71
Grids that absorb a greater percentage of scatter than | primary radiation are described as having a _____ degree of selectivity
greater
72
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
greater
73
The best measure of how well a grid functions is its ability to improve contrast in the clinical setting
Contrast Improvement Factor
74
It is dependent on the amount of scatter produced, which is controlled by kVp and volume of tissue irradiated
Contrast Improvement Factor
75
As the amount of scatter radiation increases, the ______ will be the contrast and the _____ the contrast improvement factor
lower, | lower
76
Poor images can result from ______ use of the grid
improper
77
occurs when the tube is angled across the | long axis of the grid strips
Off-level
78
can occur with a focused grid and it is the only positioning error possible with a parallel grid
Off-level grid error
79
The x-ray tube must be centered along | the central axis of a focused grid to prevent an
off-center (off-axis or lateral decentering) grid error
80
The result is a decrease in exposure across the entire image
Off-center
81
The greater the degree of lateral decentering, the _____ the grid cut-off
greater
82
is made to be used at very | specific distances as identified as the focal range labelled on the front of the grid
focus grid
83
If the SID is not within the focus range of the grid, _____ will happen with the focused grids
grid cut off
84
result in grid cut-off along the peripheral edges of the image
Off-focus errors
85
a focused grid has an identified tube side | based o the way the grid strips are angled
Upside-down
86
If the grid is used ______, severe peripheral grid cut-off will occur
Upside-down
87
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
Moire Effect
88
AN ALTERNATE SCATTER REDUCTION METHOD
AIR-GAP TECHNIQUE
89
This is best done by restricting the primary beam
AIR-GAP TECHNIQUE
90
Collimating to the size of the are being examined is | _____ to image quality.
critical
91
is an alternative to the use of a grid
AIR-GAP TECHNIQUE
92
It has primary applications in magnification | radiography and to a lesser extent, in chest radiography
AIR-GAP TECHNIQUE
93
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
greater
94
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
farther away
95
The primary disadvantage of the air-gap technique: _______ that results from the OID
loss of sharpness

RT 204 (11 decks)

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