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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
Q

most common beam restricting device

A

collimator box

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26
Q

off focus radiation

A

when xrays are produced at a spot on the anode other than the focal spot
collimators control this

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27
Q

off focus radiation results in

A

images similar to shadows of the pt.

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28
Q

PBL

A

positive beam limiting devices

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29
Q

Positive beam limiting devices

A

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

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30
Q

the xray beam should never exceed the size of the IR

A

TRUE

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31
Q

ancillary devices

A

lead blocker

lead mask

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32
Q

cone cutting

A

when the cone and IR are not aligned one side of the radiograph may not be exposed

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33
Q

when was the grid invented and by who

A

Gustave bucky 1913

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34
Q

grids

A

consist of sections of radiopaque material AKA the grid strips and sections of radiolucent material AKA interspace

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35
Q

the material used in the interspace can be

A

plastic or aluminum

plastic is preferred

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36
Q

the surface of the grid is called

A

the face

37
Q

information about the grids construction consists of

A

type of interspace material
grid frequency and ratio
grid size and range of SID’s that can be used

38
Q

grids can attenuate

A

80-90% of scatter radiation

39
Q

Grid ratio

A

relationship between the height of the lead strips and the distance between the strips
h/d

40
Q

high ratio grids are more effective in cleaning up scatter

A

TRUE

41
Q

as grid ratio increases

A

radiographic density decreases

42
Q

as grid ratio decreases

A

radiographic density increases

43
Q

as grid ratio increases patient dose

A

increases

44
Q

the higher the grid ratio the more spot on you have to be with

A

positioning

45
Q

the lower the grid ratio the less accurate you have to be with

A

positioning

46
Q

grid frequency

A

the number of grid strips or grid lines per inch

47
Q

the higher the grid frequency the thinner

A

the led strips

48
Q

contrast improvement factor

A

the ratio of radiographic contrast with a grid to that without a grid

49
Q

contrast is approximately doubled when using a grid

A

TRUE

50
Q

bucky factor

A

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
Q

bucky factor =

A

mAs with grid / mAs without grid

52
Q

no grid

A

bucky factor = 1

53
Q

5:1 GRID

A

BUCKY FACTOR = 2

54
Q

6:1 GRID

A

BUCKY FACTOR = 3

55
Q

8:1 GRID

A

BUCKY FACTOR = 4

56
Q

12:1 GRID

A

BUCKY FACTOR = 5

57
Q

16:1 GRID

A

BUCKY FACTOR = 6

58
Q

GRID CONVERSION FORMULA

A

mAs1/mAs2 = bucky factor 1/bucky factor 2

59
Q

selectivity

A

the ratio of primary radiation transmitted through the grid to the amount of scatter radiation transmitted through the grid

60
Q

the higher the selectivity the more efficient the grid is at cleaning up radiation

A

TRUE

61
Q

types of grids

A 
linear
crossed
focused
parallel
moving
stationary 
short/long dimension
62
Q

1st grid made was what pattern

A

criss cross

63
Q

focused grid

A

lead strips are angled to work with the diverging beam

64
Q

parallel grid

A

lead strips not angled and doesnt work as well with the shape of the beam
cutoff is more pronounced

65
Q

linear grid

A

most popular

allow angulation of xray tube

66
Q

grid cutoff

A

undesirable absorption of primary xrays by the grid

67
Q

convergent point

A

imaginary point in space above the grid where the focused lead lines would meet or converge if they were extended

68
Q

focal distance

A

the distance between the grid and the convergent line

how you determine SID

69
Q

focal range

A

the recommended range of SIDs that can be used with a focused grid

70
Q

the higher the grid ratio the more the grid cutoff

A

TRUE

71
Q

four types of grid cutoff errors

A

upside down focused grid
off level grid
off center grid
off focus

72
Q

upside down focused grid

A

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
Q

off level grid

A

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
Q

off center grid

A

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
Q

off focus grid

A

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
Q

off focus/off center grids

A

appears dark on one side and light on the other

77
Q

stationary grid

A

ppossible to see the grid lines when using this type

78
Q

wafer

A

matches size of cassette

79
Q

grid cassette

A

IR that has a grid permanently mounted to its front surface

80
Q

grid cap

A

contains permanently mounted grid

IR slides in behind it

81
Q

moving grids

A

blurs out the grid lines

part of the potter-bucky diaphragm AKA bucky

82
Q

2 kinds of moving grids

A

reciprocating - moves side to side

oscillating - moves in a circular motion

83
Q

disadvantages of moving grid

A

increased OID
motion
pronounced grid lines
minimum exposure time

84
Q

RTs should select a grid according to

A

size of body part
kvp being used
grid pattern
pt. dose

85
Q

grids should be used when the kvp is set above

A

70

86
Q

Long dimension grid

A

Lead strips run parallel to long axis horizontal

87
Q

Short dimension grids

A

Lead strips run vertical/ perpendicular

88
Q

Air gap technique

A

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
Q

Moire effect

A

Creates a wavy pattern on the image

image production and evaluation Semester 2 (4 decks)

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