Test 4-Ch.'s 10-11 Flashcards
(182 cards)
1
Q
Spatial resolution is the ability to image ____ objects?
A
Small
2
Q
As screen blur decreases, spacial resolution ___
A
improves
3
Q
As motion blur decreases, spatial resolution ____
A
improves
4
Q
As geometric blur decreases, spatial resolution ____
A
improves
5
Q
What is contrast resolution?
A
ability to distinguish anatomy with similar subject contrast
6
Q
random fluctuations in optical density of image
A
Noise
7
Q
Noise is the overal _____
A
fuzz; graininess
8
Q
What are the four components of radiographic noise?
A
film graininess
structure mottle
quantum mottle
scatter
9
Q
Which 2 components (of noise) are inherent?
A
film graininess
structure mottle
(Contribute very little to radiographic niose)
10
Q
What is quantum mottle controlled by?
A
mAs
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
12
Q
The use of high mAs and low kVp ____ quantum mottle
A
reduces
13
Q
The use of very fast intensifying screens results in ____ quantum mottle?
A
increased
14
Q
with fewer photons (low mAs), ___ likely to evenly cover the field.
result on the image??
A
less likely
image appears blotchy, ‘mottled’
15
Q
quantum is = to the amount of insufficient # of ____
A
protons
16
Q
as system speed increases, ____ mAs is needed
A
less
17
Q
as system speed increases, pt. exp. ___
A
decreases
18
Q
system speed increases= _____ noise
____ spatial resolution
____ contrast resolution
A
increased noise
decreased spatial resolution
decreased contrast resolution
19
Q
system speed decreases= ____ noise
____ spatial resolution
____ contrast resolution
A
decreased noise
increased spatial resolution
increased contrast resolution
20
Q
system speeds and image quality are ___ related?
A
inversely
21
Q
study of the relationship between intensities and image density
A
Sensitometry
22
Q
% of light transmitted
A
optical density
23
Q
relationship between the OD and radiation exposure
A
Characteristic Curve
H & D Curve
24
Q
device used to measure OD
A
densitometer
25
an increase of LRE of 0.3 results from ___ the radiation exposure.
doubling
| doubling the mAs
26
log= ?/?
incident light/light transmitted
27
the bottom part of the H&D curve is known as the ____?
top part??
(body part)
bottom=TOE
| top=SHOULDER
28
base + fog OD has a range of _____
0.1 - 0.3
29
What is the most useful range of radiographic densities? (AVERAGE GRADIENT)
0.25 - 2.5
30
Reciprocity Law states that image density is ____ related to total exposure
directly
31
When does the reciprocity law fail?
with screen/film systems using very short or very long times
32
What is the shortest and longest times that reciprocity law will fail (w/ screen/film)
shortest 2 s
33
Screen/Film or Digital Systems always have ____ scale than Direct Exposure
shorter
34
Contrast scale get ___ the faster the system?
shorter
35
What does increasing system speed to do detail, scale, and pt. exp.?
decreased detail
shorter scale
decreased pt. exp.
36
Film contrast is related to the ____ of the straight line portion of the characteristic curve?
slope
37
What is subject contrast determined by?
size, shape, and attenuating characteristics of subject
38
A more vertical H&D curve has a ____ scale of contrast?
short
39
as average gradient increases, you have a more ____ line, w/ a ___ scale of contrast
more vertical line, w/ a shorter scale
40
the higher the slope, the more ____ the line
vertical
41
a more horizontal line produces a ____ scale of contrast
longer
42
latitude is the range of acceptable _____
exposures
43
the line furthest to the left is the (fastest or slowest) out of the 2?
fastest
44
systems with a more vertical curve === _____ latitude
NARROW latitude
45
more horizontal curve == ____ latitude
WIDE latitude
46
latitude and contrast are ____ related
INVERSELY
47
slower systems produce ____ latitude
wider
48
faster systems produce ____ latitude
narrow
49
a wider latitude, produces _____ scale of contrast
longer
50
narrow latitude, produces ____ scale of contrast
shorter
51
What are the four factors that may affect the finished image in film screen?
concentration (strength)
agitation (stirred up)
time
temperature
52
longer time in processor means ____ speed and fog
increased
53
increasing temp. of processor ____ fog, which results in ____ scale of contrast
increased fog, longer scale
54
How long does a typical film take to completely process?
90 sec.
55
If the temperature in processor is too hot, converted to (light or dark) quicker
dark
56
faster film means (light or dark) quicker
dark
57
When development time extends far beyond the recommended period, the IR contrast (increases or decreases)
decreases
58
What does the developer do?
converts exposed silver halide crystals
59
What does the fixer do?
stops everything; removes unexposed crystals
60
What does the dryer do?
the permanents of the image
61
is magnification inherent or added?
inherent (there is always some distance between the object and IR)
62
MF= ?/? OR ?/?
image/object OR SID/SOD
| since they both equal MF, they equal each other!
63
things that increase magnification also _____ recorded detail
reduce
64
object size will always be (smaller or bigger) than image size
smaller
65
what are the three geometric factors that radiographic quality?
magnification
distortion
focal-spot blur
66
to minimize magnification, you should use the (largest or smallest) SID and the (largest or smallest) OID?
largest SID
| smallest OID
67
What is the unequal magnification of an object?
shape distortion
68
What are the 3 conditions that distortion depends on?
object thickness, position, and shape
69
thick objects are (more or less) distorted than thin objects?
more
70
CR must be (parallel or perpendicular) to both the object and IR.
perpendicular
71
to minimize distortion, CR should remain on area of ____
interest
72
The anatomy of interest should be placed where on IR to reduce distortion?
in the middle!
73
inclination of an object results in ______ (type of shape distortion)
foreshortening
74
inclined object that is placed lateral to the CR may be _______ or _________
foreshortened or elongated
75
foreshortening and elongation can occur if the object is not (parallel or perpendicular) to the IR
parallel
76
what can occur if objects of the same size are positioned at different OIDs from the IR
spatial distortion
77
when would you use a small focal spot?
most concerned about detail; bone work
78
when would you use a large focal spot?
when heat loading capacity is of greatest concern
79
focal spot blur causes "unsharpness of recorded detail", which side of tube is this worse on? Why?
Cathode Side; effective focal spot size is largest on this side
80
less magnification (decreases or increases) focal spot blur
decreases
81
formula for calculating Focal Spot Blur=
(Effective focal spot) x OID/SOD
82
focal spot blur is smaller with _____ OID and ____ SOD
decreased OID, increased SOD
83
radiographic contrast = ________ x _______
IR contrast x subject contrast
84
atomic number and subject contrast are ____ related
directly;
| high atomic # = high subject contrast
85
what is the most important influence on subject contrast
kVp
86
low kVp = ___ scale of contrast, ____ pt. dose, ____ latitude
short scale (high contrast), increase pt. exp., decreased latitude
87
high effective atomic number=___ photoelectric absorption
increased
88
low atomic # = (radiopaque or radiolucent)
radiolucent (air, black)
89
high atomic # = (radiopaque or radiolucent)
radiopaque (white)
90
low kVp= ____ subject contrast
high subject contrast
| this means short gray scale
91
high kVp= ____ subject contrast
low subject contrast
| this means long gray scale
92
most common cause of motion blur
patient motion
93
to reduce motion blur, you should use ____ exposure times, ____ SID, and ___ OID
short exp. times, long SID, and short OID
94
you should position the area of interest (parallel or perpendicular) to the IR
parallel
95
with increased kVp, noise is ____
increased
96
high kVp = ____ pt. dose, ____ latitude
decreased pt. dose, wide latitude
97
the primary control of Optical Density is ____
mAs
98
increasing mAs= ____ pt. dose, ____ OD, ____ noise
higher pt. dose, increased OD, decreased noise
99
direct exposure always has a _____ scale than screen/film; but ____ pt. exp.
longer scale; high (unacceptable) pt. dose
100
image density is ____ proportional to mAs
directly
101
What is the least amount of change in mAs needed to see a change in optical density? (in screen film)
30%
102
doubling density = _______ darkness
doubling
103
more density= more _____ that hit that spot
radiation
104
contrast is controlled by ___
kVp
105
latitude and contrast are _____ related
inversely
106
high contrast (short scale) = _____ latitude
narrow
107
imagiing systems (screen/film) have _____ scale than direct exp.
shorter
108
reduction in scatter = ____ scale
shorter
109
What does collimation do to pt. exp.? What does it do to contrast resolution?
decreases pt. exp.
| imporves contrast resolution
110
to decrease blur: use _____ focal spot size, ____ OID, ___ SID, the (slowest or fastest) imaging system
small focal spot, short OID, long SID, slowest system
111
cones reduce (more or less) scatter than collimation
more
112
When you remove scatter, you _____ image density
decrease
113
What does collimating do to patient exposure?
decreases
114
when kVp is increased, scatter is _____
increased
115
increasing scatter=____ image contrast
reduced
116
scatter increases as beam field size ______
increases
117
you want to use the _____ field size
smallest
118
when you collimate, you increase mAs to compensate for image density; what happens to pt. dose?
exp. to tissue would go up BUT overall pt. exp. is reduced since less tissue is irradiated
119
thicker pt. parts produce ____ scatter
more
120
compression of anatomy does what to pt. exp.? scatter? spatial and contrast resolution?
reduces pt. exp.
reduces scatter
improves spatial and contrast resolution
121
three types of beam restrictors
collimator
cylinder (cones)
diaphragm
122
What is PBL?
positive beam limitation
| detects IR size and automatically collimates to that size
123
Never have collimators _____ that IR size
larger
124
at ____ kV= more photoelectric than Compton
lower
125
In soft tissue: (keV, photoelectric, Compton)
20 keV photoelectric = Compton
< 20 keV mostly photoelectric
> 20 keV mostly Compton
126
in Bone: (keV, photoelectric, Compton)
40 keV Compton = Photoelectric
< 40 keV mostly photoelectric
> 40 keV mostly Compton
127
at Compton, (more or less) Scatter
More scatter with Compton
128
What does the use of grids to do pt. exposure? Why?
increases it
| b/c you had to increase mAs
129
everything used under pt. to reduce scatter does what to pt. exp.?
increases
130
What is the grid strip made of?
radiopaque material
131
What is the interspace material made of?
radiolucent material
132
What is absorbed in the grid?
Scatter radiation
133
What are the four types of grids?
focused
moving
parallel
crossed
134
as grid ratio increases, you must ____ technical factors
increase
135
what is the number of grid strips per centimeter called?
grid frequency
136
high-ratio grids ____ patient dose
increase
137
The use of high frequency grids require higher techniques, which results in ____ patient dose
increased
138
What does the interspace material of most grids consist of?
aluminum or plastic fiber
139
What are most grid strips made of? Why?
lead
| inexpensive, high atomic #, high mass density
140
Scatter can get through grid at the right ____.
angle
141
What is the principal function of a grid?
to improve contrast
142
What is the Bucky Factor?
(the grid factor)
| when a grid is used, the tech. factors must be increased to maintain IR signal
143
the higher the grid ratio, the ____ the Bucky Factor
higher
144
The Bucky Factor ____ with increasing kVp.
increases
145
as Bucky Factor increases, radiographic technique and patient radiation dose _____ proportionately
increase
146
as the lead gets skinnier the likelihood for absorbing scatter ____
decreases
147
grid ratio = ?/?
height (of the grid strip) / distance (thickness of the interspace material)
148
patient dose at high kVp is ____ than that at low kVp
less
149
The higher the grid ratio, the ___ the scale of contrast
shorter
| ex. 16:1 has shorter scale of contrast that 10:1
150
What is focal distance?
distance at which a focused grid is designed to be used
151
What happens if a focused grid is not at the focal distance?
grid cutoff
152
How are the lead strips in a parallel grid lined up?
all lead grid strips are parallel
153
What is grid cutoff?
the undesirable absorption of primary x-rays by the grid
| cut off from reaching IR
154
Which grid is cutoff most common with?
parallel
155
Grid cutoff in parallel grids is most pronounced when the grid is used at a ___ SID
short
156
when a grid is used, you get a ____ scale of contrast
shorter
157
How are the strips in a crossed grid lined up?
lead grid strips run parallel to the long and short axes of the grid
158
How is the crossed grid fabricated?
putting two parallel grids together, perpendicular
159
Why aren't crossed grids used much?
positioning challenges
160
What is the focused grid designed to do?
minimize grid cutoff
161
How are strips in a focused grid lined up?
the lead strips coincide with the divergence fo the x-ray beam
162
What can cause focused grids to have grid cutoff?
off centered-cutoff everywhere
| wrong distance or placed upside down-cutoff on outside
163
What is contrast improvement factor?
ratio of radiographic contrast with a grid to that without a grid
164
how to calculate contrast improvement factor =
image contrast with grid / image contrast without grid
165
what is the range of contrast improvement factors for most grids?
1.5 - 2.5
166
how much is contrast improved when grids are used?
they are approximately doubled
167
what happens to grid lines when using a moving grid?
they disappear
168
Where are moving grids usually found?
in the department
169
extra distance with moving grids may cause an increase in what?
magnification and image blur
170
the use of ____ kVp and ____ ratio grids results in lower pt. exp. and equal image quality
high kVp and low ratio grids
171
when using a grid. technical factors must be increased; more common to increase mAs or kVp?
increase mAs
172
What is the air gap technique?
scatter escapes between the patient and the IR
173
When using the air gap technique, how far is the IR moved from the patient?
10-15 cm
174
What is the one disadvantage with air gap technique?
magnification
175
mAs used for air gap ends up being ____ to grid mAs
similar
176
air gap ____ magnification
increases
177
____ quantity of scatter reaching the IR w/ air gap (b/c of the space)
decreased
178
keep SOD and SID as ____ as possible
long
179
keep OID as ____ as possible
short
180
faster systems require (more or less) exposures to get to optical density
less
181
if you increase SID, magnification is ___
reduced
182
increasing system speed, _____ detail
decreases
