5. Intensifying Screens Flashcards
1
Q
device found in radiographic cassettes that contains phosphors to convert x-ray energy into light, which then exposes the radiographic film
A
Intensifying Screen
2
Q
Intensifying Screen layers
A
- Protective layer
- Phosphor layer
- Reflecting or Absorbing layer
- Base
3
Q
10-20 micrometer thick
A
Protective Coating
4
Q
protects the screen from abrasion, helps eliminate static, and provides surface for cleaning
A
Protective Coating
5
Q
active layer
A
Phosphor layer
6
Q
50-300 micrometer
A
Phosphor layer
7
Q
Phosphor materials
A
calcium tungstate, zinc sulfide, barium lead sulfate, and rare earth oxysulfides such as gadolinium, lanthanum, and yttrium
8
Q
approx. 25 micrometer thick made of magnesium oxide or titanium dioxide
A
Reflective layer
9
Q
furthest from the film
A
Base
10
Q
approx. 1 mm thick, made of polyester
A
Base
11
Q
serves as mechanical support for active phosphor layer
A
Base
12
Q
intensifies x-rays reducing radiation dose
A
Intensifying screen
13
Q
emission of visible light
A
Luminescence
14
Q
emission of light during stimulation
A
Fluorescence
15
Q
afterglow
A
Phosphorescence
16
Q
emission of light after stimulation
A
Phosphorescence
17
Q
identified by relative speed ranging from 50 (slow, detail) to 1200 (very fast)
A
Screen speed
18
Q
Characteristic Type of Phosphor
A
- Color of emission
- Approximate speed
- Intensification factor
- Spatial resolution (lp/mm)
19
Q
Typical Radiographic Intensifying Screens
A
- Calcium Tungstate
- Oxysulfides and Oxybromides of Y, La, Gd
20
Q
La
A
Lanthanum (57)
21
Q
Y
A
Yttrium (39)
22
Q
Gd
A
Gadolinium (64)
23
Q
Color of emission (Calcium Tungstate)
A
Blue
24
Q
Color of emission (Oxysulfides and Oxybromides of Y, La, Gd)
A
Green or blue
25
Approximate speed (Calcium Tungstate)
50-200
26
Approximate speed (Oxysulfides and Oxybromides of Y, La, Gd)
80-1200
27
Intensification factor (Calcium Tungstate)
20-100
28
Intensification factor (Oxysulfides and Oxybromides of Y, La, Gd)
40-400
29
Spatial resolution in lp/mm (Calcium Tungstate)
8-15
30
Spatial resolution in lp/mm (Oxysulfides and Oxybromides of Y, La, Gd)
8-15
31
Intensification Factor
IF = Exposure required without screen/ Exposure required with screens
32
ratio of the exposure required to produce the same OD with a screen to the exposure required to produce and OD without a screen
Intensification Factor
33
the relationship between intensification factor and entrance skin exposure
inversely proportional
34
the _____ the ESE (patient dose), the ____ IF
larger ESE,
| smaller IF
35
uncontrollable factors affecting speed
- Phosphor Composition
- Phosphor Thickness
- Reflective Layer
- Dye
- Crystal Size
- Concentration of Phosphor Crystals
36
controllable factors affecting speed
- Radiation Quality
- Image Processing
- Temperature
37
rare earth phosphors efficiently convert x-rays into usable light
Phosphor Composition
38
the thicker the phosphor layer, the _____ is the detective quantum effiecient
higher
39
have thick phosphor layers
High-speed screens
40
have thin phosphor layers
Fine-detailed screens
41
increases screen speed but also increases image blur
Reflective layer
42
control the spread of light
Dye
43
improve spatial resolution but reduce speed
Dye
44
the larger the phosphor (crystal), the _____ the light produced
greater
45
are approx. 1/2 of the crystals of high-speed screens
crystals of detail screens
46
results in higher screen speed
higher crystal concentration
47
as x-ray tube potential is increased the IF _____
increase
48
excessive developing time for screen-film results in ____ IF
lower
49
IF is ____ at high temperatures
lower
50
deterioration of the radiographic image; speckled background that reduces image contrast
Image noise
51
is a measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to quality radiographic image
Detective Quantum Efficiency
52
refers to the ability of the screen to absorb the incident x-ray photons
Absorption Efficiency
53
describes how well the screen phosphor takes these x-ray photons and converts them to visible light
Conversion Efficiency
54
term used to evaluate the accuracy of the recorded anatomic structural lines
Spatial Resolution
55
refers to the smallest object that can be detected in an image
Spatial Resolution
56
the ability of a radiographic image to demonstrate sharp lines
Spatial Resolution
57
limiter by focal spot size
Spatial Resolution
58
measured through line-pair test pattern, expressed by the number of lp/mm
Spatial Resolution
59
using intensifying screens results to a _____ picture
blurry
60
lp/mm of Direct exposure
50 lp/mm
61
Increase IF, _____ Spatial resolution
decreases
62
term used to describe the ability of an imaging receptor to distinguish between objects having similar subject contrast
Contrast Resolution
63
rigid holder that contains the film and radiographic intensifying screens
Cassette
64
Cassette layers
1. Front cover (with low atomic number)
2. Front and Back Screens
3. Compression Device
4. Back cover (with high atomic number)
65
absorbs approx. half the number of x-rays
Carbon Fiber
66
reduces patient exposure, longer x-ray tube life
Carbon Fiber
67
emits light in the violet-to-blue region
Calcium Tungstate Screen (CaWO4)
68
principally gadolinium, lanthanum, yttrium
Rare Earth Screens
69
have the advantage of speed
Rare Earth Screens
70
increased DQE and CE (Conversion Efficiency)
Rare Earth Screens
71
refers to the color of light produced by a particular intensifying screen
Spectral Emission
72
refers to correctly matching the color sensitivity of the film to the color emission of the intensifying screen
Spectral Matching
73
Care of Screens
1. Do not slide film into a cassette
2. Do not dig the film out of the cassette
3. Do not leave the cassette open
4. Clean screens periodically
5. Check and maintain good screen-film contact
74
plastic that protects the phosphor
Protective layer
75
absorbs radiation and converts it to light
Phosphor layer
76
reflects light toward the film
Reflecting layer
77
absorbs light directed toward it
Absorbing layer
78
provides support and stability for the phosphor layer
Base
79
The desired type of luminescence
| in imaging is
Fluorescence
80
refers to the ability of phosphors to emit visible light
| only while exposed to x-rays (with little or no afterglow)
Fluorescence
81
An undesired type of luminescence is
Phosphorescence
82
is the emission of light after x-ray exposure has terminated
Phosphorescence
83
causes unwanted exposure to the film
Phosphorescence or afterglow
84
As screen speed ______, recorded detail ______
increases (s),
| decreases (r)
85
the capability of a screen to produce visible light is called
Screen speed
86
increase screen speed and decrease recorded detail
Reflective layer
87
decrease screen speed and increase recorded
| detail
Light-absorbing layer or Light-absorbing
| dyes
88
light-absorbing layer or light-absorbing
| dyes
Isotropic emission
89
Any material that emits light in response to some outside stimulation is called a
Phosphor
90
Higher conversion efficiency results in _______
| noise
increased
91
Image Detail =
Image Detail = Spatial Resolution + Contrast
| Resolution
92
The unaided eye can resolve about ____ lp/mm
10
93
Spatial resolution improves with _____ phosphor crystals and _____ phosphor layers
smaller,
| thinner
94
Increase phosphor thickness, ______ spatial resolution
decrease
95
Increase crystal size, ______ spatial resolution
decrease
96
Increase speed screen, ______ patient dose
decrease
97
The term rare earth describes those elements of group ____ in the periodic table
IIIa
98
These elements are transitional metals that are scarce in nature.
Rare earth
99
One advantage of the use of these commercial
| preparations is that they often contain ______ compounds, which can be helpful
antistatic
