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Physics > Physics Test 1 > Flashcards

Physics Test 1 Flashcards

1
Q

Decreasing scatter radiation reaching the film, does what to pt. exposure and image resolution/detail/quality?

A

Decreases pt. exposure

increases image resolution/detail/quality

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2
Q

what type of patient increases scatter

A

thicker

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3
Q

before scatter reaches the patient, what factors reduce scatter reaching the image receptor?

A

collimation, cones & cylinders, grid, decrease kvp.

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4
Q

as kvp increases, the likelihood of a photoelectric effect…

A

decreases

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5
Q

what are some important components of film?

A

base
adhesive layer
emulsion
protective layer

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6
Q

what is the purpose of the base layer in film?

A

-support
dimensional stability
lucent
often polyester

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7
Q

emulsion is considered what type of layer?

A

active

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8
Q

what are the different layers of alternative image receptors?

A 
backing
base
reflective layer
photostimulable phosphor
protective layer
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9
Q

what does the photostimulable phosphor consist of?

A

barium fluorohalide crystals coated with europium.

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10
Q

gelatin and silver halides in film emulsion are made of what?

A

silver bromide and silver iodide.

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11
Q

what formation are halides typically in today?

A

tabular grain

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12
Q

what is the sensitivity speck?

A

(silver sulfide) introduced near surface of crystal structure. It attracts photoelectrons and silver ions during exposure.

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13
Q

What is the reciprocity law?

A

Image density remains the same as long as you use the same mAs, regardless of combination of mA and time.

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14
Q

what type of exposure does the reciprocity law ALWAYS hold true?

A

direct exposure

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15
Q

when does the reciprocity law fail?

A

for exposure of film from screens at time extremes. Very long or very short exposures.

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16
Q

What are some specialty films?

A

mammo
laser
duplicating film
cine film

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17
Q

mammo

A

single emulsion, designed for use with single screen (load cassette with emulsion in contact with screen)

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18
Q

laser

A

use in laser printers, now with many modalities

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19
Q

duplicating film

A

designed for exposure by white light, for copying traditional images- single emulsion

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20
Q

cine film

A

like movie camera film

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21
Q

Direct or screen exposure, which is the slowest system?

A

Direct exposure.

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22
Q

Direct exposure results in:

A

best image quality (recorded detail) at highest patient dose.

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23
Q

Screen exposure does what to patient dose, recorded detail and scale of contrast?

A

less patient dose with less recorded detail and shorter scale of contrast.

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24
Q

as screen systems get faster, what happens to patient dose and image quality?

A

pt. dose continues to decline along with image quality

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25
Q

Within inherent speed, Large grain emulsion is:

A

typically “faster” thus thicker emulsion

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26
Q

Within inherent speed, small grain emulsion is:

A

typically “slower” thus thinner emulsion

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27
Q

For inherent contrast, how is film designed to produce shorter scale contrast?

A

Smaller halide grains of more uniform size

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28
Q

For inherent contrast, how is film designed to produce longer scale contrast?

A

larger halide grains of more variation.

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29
Q

What are some potential problems with film contrast and speed?

A

Crossover

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30
Q

what is crossover?

A

undesirable image blur caused when light from the screen on one side goes through the emulsion and base to expose the emulsion on the other side.

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31
Q

how is crossover reduced?

A

with tabular grain emulsion since you have a larger surface area, intercepting more of the light photons on the same side as they are produced.

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32
Q

for spectral matching, how does the film emulsion need to be designed?

A

to be sensitive to the light wavelengths produced by the intensifying screen in use.

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33
Q

how do tungsten screens produce light?

A

blue/violet region-use blue sensitive film

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34
Q

how do the rare earth screens produce light?

A

green region- use a film sensitive to these wavelengths- orthochromatic

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35
Q

what does improperly matched screen/film result in?

A

reduced image density

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36
Q

the darkroom safe light needs what color filter?

A

red to be safe with green or blue sensitive film

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37
Q

how do you test a safe light of a dark room?

A

putting film out on darkroom cabinet for periods and then processing

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38
Q

exposed or unexposed film is more sensitive to subsequent fog?

A

exposed

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39
Q

what type of device is used to test film resolution?

A

lp/mm test device (most can record more then the human eye can detect unaided)

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40
Q

what are the layers of the intensifying screen?

A

base
reflective layer
phosphor layer
protective coating

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41
Q

what does the base do in an intensifying screen?

A

support-rugged yet flexible

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42
Q

what does the reflective layer do in an intensifying screen?

A

bounce light back toward film

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43
Q

what are some phosphor characteristics?

A

high atomic number
high conversion efficiency
proper spectral match
minimal afterglow

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44
Q

high atomic number (phosphor characteristic)

A

absorbs more x-rays- creating environment for max PE

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45
Q

high conversion efficiency (phosphor characteristic)

A

lots of light emitted per x-ray absorbed

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46
Q

proper spectral match (phosphor characteristic)

A

emits light in a wavelength range that matches the emulsion sensitivity

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47
Q

minimal afterglow (phosphor characteristic)

A

light emission stops promptly when exposure is terminated.

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48
Q

what are two screen phosphors?

A 
calcium tungstate
rare earths (gadolinium, lanthanum, yttrium)
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49
Q

What does the lower atomic number of the elements gadolinium, lanthanum, and yttrium provide?

A

light absorption advantage for rare earth screens in the energy range between the k-shell binding energies.

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50
Q

You get the k-edge jump in the frequency of PE interactions at a what type of energy?

A

lower- which encompasses lots of dx range- since e’ binding energy is lower.

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51
Q

which screen phosphor absorbs 5x’s more photons and emits more light per photon than the other?

A

rare earth over calcium tungstate.

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52
Q

what two types are luminescence?

A

fluorescence

phosphorescence

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53
Q

fluorescence

A

light emitted only during stimulation by x-rays

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54
Q

phosphorescence

A

light continues to be emitted when stimulus has quit

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55
Q

how is screen speed expressed?

A

numerically. higher number, faster screen

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56
Q

as screens get faster, do they get thicker or thinner?

A

thicker

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57
Q

with a thick screen some interactions occur farther from the film emulsion, there fore there is more…

A

blur.

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58
Q

image resolution (recorded detail) declines with what type of screen speed?

A

increasing screen speed.

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59
Q

what is a screen intensification factor?

A

lets you know how patient dose is impacted by that particular screen

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60
Q

A screen IF “without” screen

A

is ALWAYS going to be greater than with screen. So resulting comparison is >1 (greater than 1)

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61
Q

the higher the IF, what happens to patient dose?

A

greater patient dose reduction

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62
Q

screens have a higher atomic number than film emulsion so absorption is..

A

.

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63
Q

where are screens mounted on the cassette?

A

both sides

64
Q

screens must provide good contact and be

A

light tight

65
Q

quality control for screens

A

wire mesh test instrument

66
Q

latent image

A

invisible

67
Q

manifest image

A

visible

68
Q

where does the latent image convert to manifest in image processing?

A

chemistry in the processor

69
Q

how does latent become manifest?

A

electrons released during Compton and photoelectric interactions in the emulsion congregate at the sensitivity speck- causing a region of “negativity”- which then attracts positive silver ions, combining to form metallic silver.

70
Q

what are the screen/film processing steps?

A

develop
fix
dry

71
Q

develop

A

convert latent image to manifest (change silver ions to metallic silver)

72
Q

fix

A

remove unexposed silver halide and harden gelatin (establish archival quality

73
Q

what are the steps in automatic processing?

A 
transport
temperature control
circulation
replenishment
dryer
74
Q

what is the transport phase in automatic processing?

A

rollers (controls time and agitates solutions) & microswitch (controls replenishment)

75
Q

for screen/film technique, is it better to use the shortest or longest time possible?

A

shortest

76
Q

for screen/film technique, use kvp for desired…

A

contrast level

77
Q

for film/screen technique, use mAs that gives..

A

desired quantity of photons

78
Q

for film/screen, what interaction dominates at high kvp?

A

Compton, there is less absorption/reduced subject contrast- resulting longer scales!

79
Q

for film/screen, mAs chosen should result in densities:

A

in useful range

80
Q

for film/screen, you should use the longest or shortest SID possible?

A

longest acceptable.

81
Q

kvp controls what?

A

quality (penatribility)

influences quantity

82
Q

Increasing kvp does what?

A

increases scatter production and forward direction. more likely to strike image receptor. (longer scale of contrast)

83
Q

mA is directly proportional to what?

A

quantity of x-rays produced. (number of electrons available at cathode)

84
Q

what is the major controlling factor of the number of electrons that flow cathode to anode?

A

mA

85
Q

time should be short to minimize

A

motion

86
Q

time combined with mA impacts:

A

quantity

87
Q

mAs

A

quantity, can use time & mA to compensate for one another

88
Q

Falling Load Generator

A

tech sets mAs

Machine automatically picks high mA & short time

89
Q

what potential problems exist with a falling load generator

A

when mA and focal spot size are automatically linked

90
Q

SID affects what about an image?

A

density

91
Q

density maintenance

A

allows you to determine new mAs necessary to produce same density at new distance.

92
Q

for equal image density, higher mAs is needed at ? distance

A

higher distance

93
Q

on an imaging system- Focal spot size

A

special microfocus tubes image very small objects at short SIDs (mammo)

94
Q

to stay within the heat loading capacity, what size focal spot would you use?

A

large focal spot to allow desired mAs with short time.

95
Q

high mA uses what size focal spot

A

large unless detail is primary concern.

96
Q

what are three patient factors?

A

part thickness

body composition

97
Q

part thickness

A

measure, takes more photons to get through a thick abdomen than a thin one

98
Q

body composition

A

consider range of anatomic mass densities involved

99
Q

select kvp depending on

A

subject contrast and part thickness

100
Q

which pathologies require an increase in technique?

A

additive

101
Q

which pathologies require a reduction in technique?

A

destructive

102
Q

high kv technique chart does what to patient dose?

A

reduces patient dose even more

103
Q

wide latitude has what scale of contrast?

A

long scale

104
Q

what is most important when dealing with AEC

A

positioning in front of aec

105
Q

what are some options for AEC

A

phototimers or ionization chambers

106
Q

what do phototimers or ionization chambers do?

A

detect radiation exiting the patient and reaching image receptor, between patient and IR or behind IR

107
Q

there are often 3 cells, exposure time safety limit. how long is the back up timer?

A

typically 2 sec. or maybe 600 mAs.

108
Q

there are a variety of densities to choose from on the aec….T or F?

A

true

109
Q

For the AEC what are four things to make sure you do?

A

set kvp
select density preset
set back up time
position precisely

110
Q

what is a programmed automated system?

A

lets you choose some factors while automatically combining with short time

111
Q

what is anatomically programmed?

A

pick body part, may need to put in measurement. (bone and joint)

112
Q

tomography

A
  • intentional/controlled motion unsharpness of objects anterior and posterior to the plane of interest.
  • contrast enhancement by adjacent blurring
  • the more the tube head moves and the more irregular the pattern of motion, increased image enhancement
113
Q

as the tomo angle increases, what happens to the object plane?

A

it gets thinner

114
Q

what is a fulcrum?

A

focal point/plain in tomo

115
Q

SID is _____ throughout

A

constant

116
Q

tomographic angle

A

angle of movement determines thickness of cut/object plane (larger angle, thinner cut) (larger angle, objects outside plane more blurred)

117
Q

what does tomography do to patient dose?

A

increase it

118
Q

simultaneous multi-image tomography

A

book cassette (image receptor speed must be varied to stabilize density while obtaining several cut levels with one exposure)

119
Q

Magnification

A

SID

SOD

120
Q

Magnification Factor

A

Image

Object

121
Q

Intentional Magnification

A

requires small focal spot

may not need grid if large OID creates air gap

122
Q

with magnification, what happens to patient dose

A

it increases (the patient is closer to the source, inverse square law)

123
Q

what is a triode on a grid controlled x-ray tube

A

has a third electrode (in additional to cathode and anode)

124
Q

how does a grid controlled x-ray tube work

A

several crisscrossed wires bridging the cathode’s focusing cup. when small negative potential is placed on the grid, it prevents capacitors from discharging through the x-ray tube. allowing the precision exposure switch.

125
Q

what is a grid bias

A

when small (-2 kV) negative potential is placed on a grid

126
Q

Why is grid bias reduced to near zero

A

to allow electrons to flow cathode to anode

127
Q

when does exposure stop on a grid controlled x-ray tube?

A

when the preselected mAs or density is reached, grid bias is automatically reapplied and exposure is stopped.

128
Q

what is a grid controlled x-ray tube mainly used for.

A

to stop discharge of capacitor discharge units (mobile units which store mAs when charged)

129
Q

what are screen/film artifacts

A

irregular/undesireable densities that do not represent accurate exit radiation shadowing

130
Q

exposure artifacts

A

grid/screen film/cassette errors. (interferes with collection of info)

131
Q

processor artifacts

A

in processing, guide-shoe marks, pi lines, emulsion pickoff/gelatin buildup, chemical fog, wet pressure sensitization (in developer tank)

132
Q

handling and storage artifacts

A

kinks/scratches, white light fog, static, safe light fog

133
Q

guide-shoe marks

A

improper position of springing of guide shoes in turnaround assembly

134
Q

pi lines

A

dirt or chemical stains on rollers

135
Q

sharp increase or decrease in OD

A

dirty or warped rollers, which can leave sludge deposits on film

136
Q

uniform dull, gray fog

A

improper or inadequate processing chemistry

137
Q

dichroic stain or “curtain effect”

A

improper squeezing of processing chemicals from film

138
Q

small circular patterns of increased OD

A

pressure caused by irregular or dirty rollers

139
Q

yellow-brown drops on film

A

oxidized developer

140
Q

milky appearance

A

underreplenished fixer

141
Q

greasy appearance

A

inadequate washing

142
Q

brittle appearance

A

improper dryer temperature or hardening in the fixer

143
Q

moire effect/pattern

A

a wavy artifact pattern which occurs when the grid lines and the scanning laser are parallel

144
Q

digital radiographic artifacts

A

on image receptor, software, object

145
Q

image receptor artifacts

A

dust, dirt, scratches, pixel malfunction, ghost images

146
Q

ssoftware artifacts

A

histograms, range/scaling, image compression

147
Q

object artifacts

A

patient positioning, collimator/partition, backscatter.

148
Q

histogram

A

graphic representation of frequency of digital value

149
Q

what does histogram selection determine

A

the reconstruction algorithm applied to the final image

150
Q

how does collimation influence histogram analysis

A

areas of max or absence of radiation detection

151
Q

histogram partitioning

A

must have clear margins between multiple fields on same IP to avoid histogram errors

152
Q

alignment of part and IP ALSO INFLUENCES HISTOGRAM ALALYSIS

A

.

153
Q

window width

A

adjust contrast

154
Q

window level

A

adjust brightness

155
Q

narrow (decreased) window width displays what type of contrast?

A

shorter scale

156
Q

wider (increased) window width displays what type of contrast?

A

longer scale

Physics (3 decks)

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