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Physics > Test 4-Ch.'s 10-11 > Flashcards

Test 4-Ch.'s 10-11 Flashcards

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1
Q

Spatial resolution is the ability to image ____ objects?

A

Small

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2
Q

As screen blur decreases, spacial resolution ___

A

improves

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3
Q

As motion blur decreases, spatial resolution ____

A

improves

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4
Q

As geometric blur decreases, spatial resolution ____

A

improves

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5
Q

What is contrast resolution?

A

ability to distinguish anatomy with similar subject contrast

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6
Q

random fluctuations in optical density of image

A

Noise

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7
Q

Noise is the overal _____

A

fuzz; graininess

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8
Q

What are the four components of radiographic noise?

A

film graininess
structure mottle
quantum mottle
scatter

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9
Q

Which 2 components (of noise) are inherent?

A

film graininess
structure mottle
(Contribute very little to radiographic niose)

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10
Q

What is quantum mottle controlled by?

A

mAs

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11
Q

Quantum mottle is less of an issue with (higher or lower) mAs techniques?

A

higher

only comes into play when using small amount of mAs

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12
Q

The use of high mAs and low kVp ____ quantum mottle

A

reduces

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13
Q

The use of very fast intensifying screens results in ____ quantum mottle?

A

increased

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14
Q

with fewer photons (low mAs), ___ likely to evenly cover the field.
result on the image??

A

less likely

image appears blotchy, ‘mottled’

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15
Q

quantum is = to the amount of insufficient # of ____

A

protons

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16
Q

as system speed increases, ____ mAs is needed

A

less

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17
Q

as system speed increases, pt. exp. ___

A

decreases

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18
Q

system speed increases= _____ noise
____ spatial resolution
____ contrast resolution

A

increased noise
decreased spatial resolution
decreased contrast resolution

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19
Q

system speed decreases= ____ noise
____ spatial resolution
____ contrast resolution

A

decreased noise
increased spatial resolution
increased contrast resolution

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20
Q

system speeds and image quality are ___ related?

A

inversely

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21
Q

study of the relationship between intensities and image density

A

Sensitometry

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22
Q

% of light transmitted

A

optical density

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23
Q

relationship between the OD and radiation exposure

A

Characteristic Curve

H & D Curve

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24
Q

device used to measure OD

A

densitometer

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25
Q

an increase of LRE of 0.3 results from ___ the radiation exposure.

A

doubling

doubling the mAs

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26
Q

log= ?/?

A

incident light/light transmitted

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27
Q

the bottom part of the H&D curve is known as the ____?
top part??
(body part)

A

bottom=TOE

top=SHOULDER

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28
Q

base + fog OD has a range of _____

A

0.1 - 0.3

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29
Q

What is the most useful range of radiographic densities? (AVERAGE GRADIENT)

A

0.25 - 2.5

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30
Q

Reciprocity Law states that image density is ____ related to total exposure

A

directly

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31
Q

When does the reciprocity law fail?

A

with screen/film systems using very short or very long times

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32
Q

What is the shortest and longest times that reciprocity law will fail (w/ screen/film)

A

shortest 2 s

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33
Q

Screen/Film or Digital Systems always have ____ scale than Direct Exposure

A

shorter

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34
Q

Contrast scale get ___ the faster the system?

A

shorter

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35
Q

What does increasing system speed to do detail, scale, and pt. exp.?

A

decreased detail
shorter scale
decreased pt. exp.

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36
Q

Film contrast is related to the ____ of the straight line portion of the characteristic curve?

A

slope

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37
Q

What is subject contrast determined by?

A

size, shape, and attenuating characteristics of subject

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38
Q

A more vertical H&D curve has a ____ scale of contrast?

A

short

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39
Q

as average gradient increases, you have a more ____ line, w/ a ___ scale of contrast

A

more vertical line, w/ a shorter scale

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40
Q

the higher the slope, the more ____ the line

A

vertical

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41
Q

a more horizontal line produces a ____ scale of contrast

A

longer

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42
Q

latitude is the range of acceptable _____

A

exposures

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43
Q

the line furthest to the left is the (fastest or slowest) out of the 2?

A

fastest

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44
Q

systems with a more vertical curve === _____ latitude

A

NARROW latitude

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45
Q

more horizontal curve == ____ latitude

A

WIDE latitude

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46
Q

latitude and contrast are ____ related

A

INVERSELY

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47
Q

slower systems produce ____ latitude

A

wider

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48
Q

faster systems produce ____ latitude

A

narrow

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49
Q

a wider latitude, produces _____ scale of contrast

A

longer

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50
Q

narrow latitude, produces ____ scale of contrast

A

shorter

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51
Q

What are the four factors that may affect the finished image in film screen?

A

concentration (strength)
agitation (stirred up)
time
temperature

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52
Q

longer time in processor means ____ speed and fog

A

increased

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53
Q

increasing temp. of processor ____ fog, which results in ____ scale of contrast

A

increased fog, longer scale

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54
Q

How long does a typical film take to completely process?

A

90 sec.

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55
Q

If the temperature in processor is too hot, converted to (light or dark) quicker

A

dark

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56
Q

faster film means (light or dark) quicker

A

dark

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57
Q

When development time extends far beyond the recommended period, the IR contrast (increases or decreases)

A

decreases

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58
Q

What does the developer do?

A

converts exposed silver halide crystals

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59
Q

What does the fixer do?

A

stops everything; removes unexposed crystals

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60
Q

What does the dryer do?

A

the permanents of the image

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61
Q

is magnification inherent or added?

A

inherent (there is always some distance between the object and IR)

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62
Q

MF= ?/? OR ?/?

A

image/object OR SID/SOD

since they both equal MF, they equal each other!

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63
Q

things that increase magnification also _____ recorded detail

A

reduce

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64
Q

object size will always be (smaller or bigger) than image size

A

smaller

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65
Q

what are the three geometric factors that radiographic quality?

A

magnification
distortion
focal-spot blur

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66
Q

to minimize magnification, you should use the (largest or smallest) SID and the (largest or smallest) OID?

A

largest SID

smallest OID

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67
Q

What is the unequal magnification of an object?

A

shape distortion

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68
Q

What are the 3 conditions that distortion depends on?

A

object thickness, position, and shape

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69
Q

thick objects are (more or less) distorted than thin objects?

A

more

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70
Q

CR must be (parallel or perpendicular) to both the object and IR.

A

perpendicular

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71
Q

to minimize distortion, CR should remain on area of ____

A

interest

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72
Q

The anatomy of interest should be placed where on IR to reduce distortion?

A

in the middle!

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73
Q

inclination of an object results in ______ (type of shape distortion)

A

foreshortening

74
Q

inclined object that is placed lateral to the CR may be _______ or _________

A

foreshortened or elongated

75
Q

foreshortening and elongation can occur if the object is not (parallel or perpendicular) to the IR

A

parallel

76
Q

what can occur if objects of the same size are positioned at different OIDs from the IR

A

spatial distortion

77
Q

when would you use a small focal spot?

A

most concerned about detail; bone work

78
Q

when would you use a large focal spot?

A

when heat loading capacity is of greatest concern

79
Q

focal spot blur causes “unsharpness of recorded detail”, which side of tube is this worse on? Why?

A

Cathode Side; effective focal spot size is largest on this side

80
Q

less magnification (decreases or increases) focal spot blur

A

decreases

81
Q

formula for calculating Focal Spot Blur=

A

(Effective focal spot) x OID/SOD

82
Q

focal spot blur is smaller with _____ OID and ____ SOD

A

decreased OID, increased SOD

83
Q

radiographic contrast = ________ x _______

A

IR contrast x subject contrast

84
Q

atomic number and subject contrast are ____ related

A

directly;

high atomic # = high subject contrast

85
Q

what is the most important influence on subject contrast

A

kVp

86
Q

low kVp = ___ scale of contrast, ____ pt. dose, ____ latitude

A

short scale (high contrast), increase pt. exp., decreased latitude

87
Q

high effective atomic number=___ photoelectric absorption

A

increased

88
Q

low atomic # = (radiopaque or radiolucent)

A

radiolucent (air, black)

89
Q

high atomic # = (radiopaque or radiolucent)

A

radiopaque (white)

90
Q

low kVp= ____ subject contrast

A

high subject contrast

this means short gray scale

91
Q

high kVp= ____ subject contrast

A

low subject contrast

this means long gray scale

92
Q

most common cause of motion blur

A

patient motion

93
Q

to reduce motion blur, you should use ____ exposure times, ____ SID, and ___ OID

A

short exp. times, long SID, and short OID

94
Q

you should position the area of interest (parallel or perpendicular) to the IR

A

parallel

95
Q

with increased kVp, noise is ____

A

increased

96
Q

high kVp = ____ pt. dose, ____ latitude

A

decreased pt. dose, wide latitude

97
Q

the primary control of Optical Density is ____

A

mAs

98
Q

increasing mAs= ____ pt. dose, ____ OD, ____ noise

A

higher pt. dose, increased OD, decreased noise

99
Q

direct exposure always has a _____ scale than screen/film; but ____ pt. exp.

A

longer scale; high (unacceptable) pt. dose

100
Q

image density is ____ proportional to mAs

A

directly

101
Q

What is the least amount of change in mAs needed to see a change in optical density? (in screen film)

A

30%

102
Q

doubling density = _______ darkness

A

doubling

103
Q

more density= more _____ that hit that spot

A

radiation

104
Q

contrast is controlled by ___

A

kVp

105
Q

latitude and contrast are _____ related

A

inversely

106
Q

high contrast (short scale) = _____ latitude

A

narrow

107
Q

imagiing systems (screen/film) have _____ scale than direct exp.

A

shorter

108
Q

reduction in scatter = ____ scale

A

shorter

109
Q

What does collimation do to pt. exp.? What does it do to contrast resolution?

A

decreases pt. exp.

imporves contrast resolution

110
Q

to decrease blur: use _____ focal spot size, ____ OID, ___ SID, the (slowest or fastest) imaging system

A

small focal spot, short OID, long SID, slowest system

111
Q

cones reduce (more or less) scatter than collimation

A

more

112
Q

When you remove scatter, you _____ image density

A

decrease

113
Q

What does collimating do to patient exposure?

A

decreases

114
Q

when kVp is increased, scatter is _____

A

increased

115
Q

increasing scatter=____ image contrast

A

reduced

116
Q

scatter increases as beam field size ______

A

increases

117
Q

you want to use the _____ field size

A

smallest

118
Q

when you collimate, you increase mAs to compensate for image density; what happens to pt. dose?

A

exp. to tissue would go up BUT overall pt. exp. is reduced since less tissue is irradiated

119
Q

thicker pt. parts produce ____ scatter

A

more

120
Q

compression of anatomy does what to pt. exp.? scatter? spatial and contrast resolution?

A

reduces pt. exp.
reduces scatter
improves spatial and contrast resolution

121
Q

three types of beam restrictors

A

collimator
cylinder (cones)
diaphragm

122
Q

What is PBL?

A

positive beam limitation

detects IR size and automatically collimates to that size

123
Q

Never have collimators _____ that IR size

A

larger

124
Q

at ____ kV= more photoelectric than Compton

A

lower

125
Q

In soft tissue: (keV, photoelectric, Compton)

A

20 keV photoelectric = Compton
< 20 keV mostly photoelectric
> 20 keV mostly Compton

126
Q

in Bone: (keV, photoelectric, Compton)

A

40 keV Compton = Photoelectric
< 40 keV mostly photoelectric
> 40 keV mostly Compton

127
Q

at Compton, (more or less) Scatter

A

More scatter with Compton

128
Q

What does the use of grids to do pt. exposure? Why?

A

increases it

b/c you had to increase mAs

129
Q

everything used under pt. to reduce scatter does what to pt. exp.?

A

increases

130
Q

What is the grid strip made of?

A

radiopaque material

131
Q

What is the interspace material made of?

A

radiolucent material

132
Q

What is absorbed in the grid?

A

Scatter radiation

133
Q

What are the four types of grids?

A

focused
moving
parallel
crossed

134
Q

as grid ratio increases, you must ____ technical factors

A

increase

135
Q

what is the number of grid strips per centimeter called?

A

grid frequency

136
Q

high-ratio grids ____ patient dose

A

increase

137
Q

The use of high frequency grids require higher techniques, which results in ____ patient dose

A

increased

138
Q

What does the interspace material of most grids consist of?

A

aluminum or plastic fiber

139
Q

What are most grid strips made of? Why?

A

lead

inexpensive, high atomic #, high mass density

140
Q

Scatter can get through grid at the right ____.

A

angle

141
Q

What is the principal function of a grid?

A

to improve contrast

142
Q

What is the Bucky Factor?

A

(the grid factor)

when a grid is used, the tech. factors must be increased to maintain IR signal

143
Q

the higher the grid ratio, the ____ the Bucky Factor

A

higher

144
Q

The Bucky Factor ____ with increasing kVp.

A

increases

145
Q

as Bucky Factor increases, radiographic technique and patient radiation dose _____ proportionately

A

increase

146
Q

as the lead gets skinnier the likelihood for absorbing scatter ____

A

decreases

147
Q

grid ratio = ?/?

A

height (of the grid strip) / distance (thickness of the interspace material)

148
Q

patient dose at high kVp is ____ than that at low kVp

A

less

149
Q

The higher the grid ratio, the ___ the scale of contrast

A

shorter

ex. 16:1 has shorter scale of contrast that 10:1

150
Q

What is focal distance?

A

distance at which a focused grid is designed to be used

151
Q

What happens if a focused grid is not at the focal distance?

A

grid cutoff

152
Q

How are the lead strips in a parallel grid lined up?

A

all lead grid strips are parallel

153
Q

What is grid cutoff?

A

the undesirable absorption of primary x-rays by the grid

cut off from reaching IR

154
Q

Which grid is cutoff most common with?

A

parallel

155
Q

Grid cutoff in parallel grids is most pronounced when the grid is used at a ___ SID

A

short

156
Q

when a grid is used, you get a ____ scale of contrast

A

shorter

157
Q

How are the strips in a crossed grid lined up?

A

lead grid strips run parallel to the long and short axes of the grid

158
Q

How is the crossed grid fabricated?

A

putting two parallel grids together, perpendicular

159
Q

Why aren’t crossed grids used much?

A

positioning challenges

160
Q

What is the focused grid designed to do?

A

minimize grid cutoff

161
Q

How are strips in a focused grid lined up?

A

the lead strips coincide with the divergence fo the x-ray beam

162
Q

What can cause focused grids to have grid cutoff?

A

off centered-cutoff everywhere

wrong distance or placed upside down-cutoff on outside

163
Q

What is contrast improvement factor?

A

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

164
Q

how to calculate contrast improvement factor =

A

image contrast with grid / image contrast without grid

165
Q

what is the range of contrast improvement factors for most grids?

A

1.5 - 2.5

166
Q

how much is contrast improved when grids are used?

A

they are approximately doubled

167
Q

what happens to grid lines when using a moving grid?

A

they disappear

168
Q

Where are moving grids usually found?

A

in the department

169
Q

extra distance with moving grids may cause an increase in what?

A

magnification and image blur

170
Q

the use of ____ kVp and ____ ratio grids results in lower pt. exp. and equal image quality

A

high kVp and low ratio grids

171
Q

when using a grid. technical factors must be increased; more common to increase mAs or kVp?

A

increase mAs

172
Q

What is the air gap technique?

A

scatter escapes between the patient and the IR

173
Q

When using the air gap technique, how far is the IR moved from the patient?

A

10-15 cm

174
Q

What is the one disadvantage with air gap technique?

A

magnification

175
Q

mAs used for air gap ends up being ____ to grid mAs

A

similar

176
Q

air gap ____ magnification

A

increases

177
Q

____ quantity of scatter reaching the IR w/ air gap (b/c of the space)

A

decreased

178
Q

keep SOD and SID as ____ as possible

A

long

179
Q

keep OID as ____ as possible

A

short

180
Q

faster systems require (more or less) exposures to get to optical density

A

less

181
Q

if you increase SID, magnification is ___

A

reduced

182
Q

increasing system speed, _____ detail

A

decreases

Physics (1 decks)

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