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image production and evaluation Semester 2 > Test 3 > Flashcards

Test 3 Flashcards

1
Q

beam restricting devices

A

tools an RT can use to limit the amount of scatter radiation reaching the IR

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2
Q

scatter

A

x ray photons that have changed direction after interacting with matter

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3
Q

factors contributing to scatter

A

increase kvp
increased xray field size
increased pt. thickness

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4
Q

beam restricting devices reduce scatter by:

A

decreasing xray beam size

decreasing amount of tissue radiated

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5
Q

fog

A

an unintended optical density on a radiograph that reduces contrast because of light or chemical contamination

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6
Q

effects of scatter

A

degrades visibility or image detail
degrades contrast resolution
degrades spacial resolution

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7
Q

spatial resolution

A

controlled by focal spot size

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8
Q

contrast resolution

A

affected by scatter radiation

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9
Q

increased kvp =

A

increased scatter and decreased contrast

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10
Q

high kvp is preferred to:

A

low kvp

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11
Q

as field size increases:

A

scatter radiation is increased

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12
Q

collimation reduces

A

scatter

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13
Q

we must raise our technique when we collimate

A

TRUE

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14
Q

thick parts of the body results in more scatter

A

TRUE

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15
Q

Compression devices

A

improve spatial resolution by reducing the thickness bringing the object closer to the IR

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16
Q

types of beam restricting devices

A

aperture diaphragm
cones
cylinders
collimators

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17
Q

aperture diaphragm

A

simplest
makes beam a bit smaller
low in cost
easy to use

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18
Q

aperture diaphragm disadvantages

A

field size is not adjustable

edges of image blurry aka penumbra

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19
Q

penumbra/image blur/edge gradient

A

area of unsharpness surrounding the image

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20
Q

penumbra is reduced when beam restrictor is further away from the tube port

A

TRUE

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21
Q

cones and cylinders

A

modifications of the aperture diaphragm
extended metal structure
distal end determines field size
has a circular field

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22
Q

cones

A

attach to bottom of collimator

limit the penumbra better than appertures

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23
Q

disadvantages of cones

A

if angle of cone is greater than divergent angle of primary beam tehn beam is not being restricted
cone cutting can occur

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24
Q

formula to determine field size

A

SID*diameter of lower opening / distance from focal spot to bottom of aperture or cone

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25
most common beam restricting device
collimator box
26
off focus radiation
when xrays are produced at a spot on the anode other than the focal spot collimators control this
27
off focus radiation results in
images similar to shadows of the pt.
28
PBL
positive beam limiting devices
29
Positive beam limiting devices
manual collimation is still necessary with these in order to more tightly cone down image and reduce pt. exposure mandated in 1974 removed in 1994
30
the xray beam should never exceed the size of the IR
TRUE
31
ancillary devices
lead blocker | lead mask
32
cone cutting
when the cone and IR are not aligned one side of the radiograph may not be exposed
33
when was the grid invented and by who
Gustave bucky 1913
34
grids
consist of sections of radiopaque material AKA the grid strips and sections of radiolucent material AKA interspace
35
the material used in the interspace can be
plastic or aluminum | plastic is preferred
36
the surface of the grid is called
the face
37
information about the grids construction consists of
type of interspace material grid frequency and ratio grid size and range of SID's that can be used
38
grids can attenuate
80-90% of scatter radiation
39
Grid ratio
relationship between the height of the lead strips and the distance between the strips h/d
40
high ratio grids are more effective in cleaning up scatter
TRUE
41
as grid ratio increases
radiographic density decreases
42
as grid ratio decreases
radiographic density increases
43
as grid ratio increases patient dose
increases
44
the higher the grid ratio the more spot on you have to be with
positioning
45
the lower the grid ratio the less accurate you have to be with
positioning
46
grid frequency
the number of grid strips or grid lines per inch
47
the higher the grid frequency the thinner
the led strips
48
contrast improvement factor
the ratio of radiographic contrast with a grid to that without a grid
49
contrast is approximately doubled when using a grid
TRUE
50
bucky factor
a number that can be used to determine the adjustment in mAs when changing from one grid to another or not using a grid at all
51
bucky factor =
mAs with grid / mAs without grid
52
no grid
bucky factor = 1
53
5:1 GRID
BUCKY FACTOR = 2
54
6:1 GRID
BUCKY FACTOR = 3
55
8:1 GRID
BUCKY FACTOR = 4
56
12:1 GRID
BUCKY FACTOR = 5
57
16:1 GRID
BUCKY FACTOR = 6
58
GRID CONVERSION FORMULA
mAs1/mAs2 = bucky factor 1/bucky factor 2
59
selectivity
the ratio of primary radiation transmitted through the grid to the amount of scatter radiation transmitted through the grid
60
the higher the selectivity the more efficient the grid is at cleaning up radiation
TRUE
61
types of grids
``` linear crossed focused parallel moving stationary short/long dimension ```
62
1st grid made was what pattern
criss cross
63
focused grid
lead strips are angled to work with the diverging beam
64
parallel grid
lead strips not angled and doesnt work as well with the shape of the beam cutoff is more pronounced
65
linear grid
most popular | allow angulation of xray tube
66
grid cutoff
undesirable absorption of primary xrays by the grid
67
convergent point
imaginary point in space above the grid where the focused lead lines would meet or converge if they were extended
68
focal distance
the distance between the grid and the convergent line | how you determine SID
69
focal range
the recommended range of SIDs that can be used with a focused grid
70
the higher the grid ratio the more the grid cutoff
TRUE
71
four types of grid cutoff errors
upside down focused grid off level grid off center grid off focus
72
upside down focused grid
happens when a focused grid is placed upside down on the IR which results in the grid lines going opposite the angle of the diverging xray beam appears as a loss of density along edges of image
73
off level grid
occurs when the xray beam is angled across the lead strips most common type of cutoff happens a lot with portables entire image turns out lighter
74
off center grid
occurs when the CR is not aligned from side to side with the center of the focused grid appears as an overall loss of density
75
off focus grid
occurs when the SID is outside of the recommended focal range if the SID is less than or greater than the focal range loss of density in the outer edges
76
off focus/off center grids
appears dark on one side and light on the other
77
stationary grid
ppossible to see the grid lines when using this type
78
wafer
matches size of cassette
79
grid cassette
IR that has a grid permanently mounted to its front surface
80
grid cap
contains permanently mounted grid | IR slides in behind it
81
moving grids
blurs out the grid lines | part of the potter-bucky diaphragm AKA bucky
82
2 kinds of moving grids
reciprocating - moves side to side | oscillating - moves in a circular motion
83
disadvantages of moving grid
increased OID motion pronounced grid lines minimum exposure time
84
RTs should select a grid according to
size of body part kvp being used grid pattern pt. dose
85
grids should be used when the kvp is set above
70
86
Long dimension grid
Lead strips run parallel to long axis horizontal
87
Short dimension grids
Lead strips run vertical/ perpendicular
88
Air gap technique
By increasing distance between the pt and the IR the scatter will miss the IR mAs must be increased Greater the gap greater reduction of scatter
89
Moire effect
Creates a wavy pattern on the image

image production and evaluation Semester 2 (4 decks)

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