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C2 > RADIOGRAPHIC IS > Flashcards

RADIOGRAPHIC IS Flashcards

1
Q

What is the purpose of a radiographic intensifying screen?

A

It amplifies the effect of image-forming x-rays that reach the screen-film cassette.

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2
Q

What does the phosphor in an intensifying screen do?

A

Converts the x-ray beam into light.

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3
Q

Radiation emitted with equal intensity in all directions.

A

isotropic emission

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4
Q

Name one advantage of using an intensifying screen.

A

Lower patient dose.

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5
Q

Name one disadvantage of using an intensifying screen.

A

Slightly blurred image.

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6
Q

How many layers does an intensifying screen have?

A

Four: protective coating, phosphor, reflective layer, and base.

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7
Q

What is the purpose of the protective coating in an intensifying screen?

A

Makes the screen resistant to abrasion and allows for routine cleaning.

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8
Q

What is the thickness range of the protective coating?

A

10-20 μm.

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9
Q

Which layer is closest to the film in an intensifying screen?

A

Protective coating.

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10
Q

What material was used historically for the phosphor in intensifying screens?

A

Calcium Tungstate (CaWO4).

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11
Q

What materials are now used in the phosphor layer?

A

Rare earth elements:
Gadolinium (Gd)
Lanthanum (La)
Yttrium (Y).

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12
Q

Why are rare earth elements preferred over calcium tungstate in intensifying screens?

A

They reduce patient dose and provide other benefits like less thermal stress on the x-ray tube.

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13
Q

Name two properties that are favorable in a phosphor material.

A

High atomic number
high detective quantum efficiency (DQE).

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14
Q

The percentage of x-rays absorbed by the image receptor.

A

detective quantum efficiency (DQE)

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15
Q

The rate at which x-ray energy is transformed into light in an intensifying screen.

A

conversion efficiency (CE).

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16
Q

What is afterglow in the context of intensifying screens?

A

The continuing emission of light after exposure to x-rays.

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17
Q

Who developed calcium tungstate for use in radiographic screens?

A

Thomas Edison.

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18
Q

What is the role of the reflective layer in an intensifying screen?

A

Redirects light to the film, increasing screen efficiency.

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19
Q

What is a disadvantage of adding dye to the reflective layer?

A

reduces screen speed.

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20
Q

What is the purpose of the base layer in an intensifying screen?

A

Provides mechanical support for the phosphor layer.

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21
Q

What material is the base layer typically made of?

A

Polyester.

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22
Q

Define luminescence.

A

emission of visible light in response to outside stimulation.

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23
Q

Name the two types of luminescence.

A

Fluorescence and phosphorescence.

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24
Q

What is fluorescence?

A

emission of visible light only during stimulation.

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25
Q

What is phosphorescence?

A

The emission of visible light during and after stimulation.

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26
Q

What are the three primary characteristics of a radiographic intensifying screen?

A

Screen speed
image noise
spatial resolution.

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27
Q

How does screen speed relate to patient dose?

A

Increased screen speed reduces patient dose.

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28
Q

A speckled appearance on images caused by factors like fast screens.

A

image noise

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29
Q

A measure of the screen’s speed, comparing exposure with and without a screen.

A

intensification factor

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30
Q

What does spatial resolution describe?

A

The ability to produce a clear image with defined details.

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31
Q

In what unit is spatial resolution typically expressed?

A

Line pairs per millimeter (lp/mm).

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32
Q

What is the speed range for intensifying screens?

A

100 (slow) to 1200 (very fast).

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33
Q

What color emission does a calcium tungstate screen produce?

A

blue

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34
Q

What is the typical speed range for a calcium tungstate screen?

A

50-200

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35
Q

How is rare earth screen speed typically classified?

A

80-1200, with high DQE.

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36
Q

Name a property that a radiologic technologist cannot control regarding an intensifying screen.

A

Phosphor composition.

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37
Q

What effect does a thicker phosphor layer have on screen characteristics?

A

Increases detective quantum efficiency (DQE) but decreases spatial resolution.

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38
Q

What is the purpose of adding dye to the screen?

A

To control light spread and improve spatial resolution.

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39
Q

What effect do larger phosphor crystals have?

A

Produce more light per x-ray interaction, increasing speed but decreasing detail.

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40
Q

How does increased kVp affect screen speed?

A

Increases intensification factor (IF).

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41
Q

A type of image noise resulting from high conversion efficiency.

A

quantum mottle

42
Q

Define conversion efficiency (CE) in a formula.

A

CE = (emitted light / x-rays absorbed) x 100.

43
Q

What is spatial resolution influenced by in intensifying screens?

A

Phosphor thickness and crystal size.

44
Q

The ability to distinguish between similar tissues in an image.

A

contrast resolution

45
Q

What are the benefits of proper screen-film combinations?

A

Decreased patient dose and occupational exposure, and flexibility in kVp selection.

46
Q

Holds the film and intensifying screen securely.

A

cassette

47
Q

Why is the front cover of a cassette made of low atomic number material?

A

To reduce x-ray attenuation.

48
Q

What material is typically used for the back cover of a cassette?

A

Heavy metal, to reduce backscatter.

49
Q

X-rays deflected backward after interacting with an object.

A

backscatter radiation

50
Q

What is the main cause of backscatter radiation?

A

High kVp techniques.

51
Q

How does carbon fiber in cassettes benefit radiography?

A

Reduces patient exposure and extends x-ray tube life.

52
Q

Compare direct film exposure to screen-film exposure in terms of x-rays absorbed.

A

Screen-film absorbs fewer x-rays, but produces more light photons.

53
Q

What is the advantage of rare earth screens?

A

Faster speed with lower patient dose.

54
Q

Name a disadvantage of rare earth screens.

A

Increased quantum mottle (noise).

55
Q

Name a rare earth element commonly used in screens.

A

terbium

56
Q

What is the purpose of spectral matching in screen-film combinations?

A

Ensures compatibility between the screen emission color and film sensitivity.

57
Q

What color light does calcium tungstate emit?

A

blue

58
Q

What color light does rare earth phosphors like gadolinium emit?

A

green

59
Q

Why is a red safelight used in darkrooms with rare earth screens?

A

It does not affect green-sensitive film.

60
Q

What element in the periodic table is a common rare earth material in screens?

A

lanthanum

61
Q

What is the atomic number of gadolinium?

A

64

62
Q

What is the primary use of asymmetric screens?

A

Chest, pediatric, and mobile radiography.

63
Q

What is the benefit of using a finer screen for mammography?

A

Higher spatial resolution.

64
Q

What is a major component of image noise?

A

quantum mottle

65
Q

Name a common cause of poor screen-film contact.

A

Worn or damaged cassette components.

66
Q

How often should screens be cleaned?

A

Periodically, using mild soap and water.

67
Q

Name a substance used in commercial screen cleaning materials.

A

Antistatic compounds.

68
Q

What is the effect of a bent hinge on screen-film contact?

A

Causes poor contact, affecting image quality.

69
Q

Why is it recommended to avoid leaving cassettes open?

A

Prevents dust and debris from damaging screens.

70
Q

What is the main purpose of the compression device in a cassette?

A

Ensures close contact between screen and film.

71
Q

What happens when kVp is too high in imaging?

A

Increases image noise due to backscatter.

72
Q

How is the spatial resolution of direct exposure film compared to intensifying screens?

A

Direct exposure film has higher spatial resolution.

73
Q

Why should films not be slid into cassettes?

A

To prevent scratching and damaging the screen.

74
Q

What material is preferred for cassette front covers in fluoroscopy?

A

Carbon fiber.

75
Q

How should film be removed from a cassette?

A

By rocking the cassette on its hinge.

76
Q

What is the K-shell binding energy of tungsten?

A

69 keV.

77
Q

What material can be used to reduce patient exposure in CT tables?

A

Carbon fiber.

78
Q

Why is yttrium used in radiographic intensifying screens?

A

It has a high atomic number, enhancing x-ray absorption.

79
Q

Matching film sensitivity to the color of light emitted by the screen.

A

spectral matching

80
Q

What effect does high-speed screen have on image quality?

A

Increases noise and reduces spatial resolution.

81
Q

How should screens be cleaned?

A

With mild soap and water, avoiding abrasives.

82
Q

What is the consequence of a warped cassette?

A

Poor screen-film contact and image quality loss.

83
Q

What material in screens emits yellow-green light?

A

Zinc cadmium sulfide.

84
Q

What is the benefit of using thulium-activated phosphors?

A

Blue light emission.

85
Q

Why is gadolinium commonly used in screens?

A

High atomic number and efficient light emission.

86
Q

What is the primary purpose of radiographic intensifying screens?

A

What is the primary purpose of radiographic intensifying screens?

87
Q

What is the advantage of rare earth screens over calcium tungstate?

A

Higher conversion efficiency.

88
Q

What is the advantage of rare earth screens over calcium tungstate?

A

Higher conversion efficiency.

89
Q

How does a thicker phosphor layer affect screen speed?

A

Increases screen speed.

90
Q

What property of screens is generally unaltered by temperature?

A

Detective quantum efficiency.

91
Q

How does high temperature affect intensifying screens?

A

Decreases intensification factor (IF).

92
Q

What phosphor layer thickness is used for fine-detail screens?

A

Thin layers for higher spatial resolution.

93
Q

What is quantum mottle influenced by?

A

Higher conversion efficiency and fast screens.

94
Q

What is the purpose of a cassette back cover’s high atomic number?

A

Reduces backscatter.

95
Q

How does a thicker reflective layer affect screen performance?

A

Increases efficiency but blurs images.

96
Q

What effect does large crystal size have on resolution?

A

Decreases spatial resolution.

97
Q

Why are lanthanum and gadolinium used in intensifying screens?

A

High atomic numbers for better x-ray absorption.

98
Q

What is the typical spatial resolution of a very fast screen?

A

Around 7 lp/mm.

99
Q

How is image detail related to screen speed?

A

Higher screen speed reduces detail.

100
Q

What is the relationship between intensification factor and spatial resolution?

A

Higher IF generally reduces spatial resolution.

C2 (7 decks)

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