Unit 5 Flashcards
(121 cards)
1
Q
3 definition of spatial resolution:
A
- the smallest structures that may be seen in an image measured in LP/mm.
- the ability to image adjacent objects as being separate.
- refers to the distinctness or sharpness of structural lines that represent an image.
2
Q
What is spatial resolution expressed/measured in?
A
LP/mm
3
Q
The ____ the number of LP/mm, the _____ the object that can be imaged, and the ____ the spatial resolution.
A
The higher the number of LP/mm, the smaller the object that can be imaged, and the better the spatial resolution.
4
Q
What does LP/mm represent?
A
The smallest size object that the imaging system is capable of representing.
5
Q
Penumbra:
A
term that describes the areas of unsharpness around the periphery of the radiographic image
6
Q
Umbra:
A
term that describes a lack of unsharpness around the periphery of a radiographic image.
7
Q
Factors that Affect Spatial Resolution: 8
A
- OID
- SID
- Filament Size
- Anode Angle Size
- Pt. Motion
- Shape distortion
- Size distortion
- Imaging System/Display
8
Q
OID:
A
the distance from the IR to the object being imaged
9
Q
Increasing OID results in the object being ____
A
magnified
10
Q
Decreasing OID =
A
less mag
11
Q
What has the largest impact on object mag?
A
OID
12
Q
To double the size of a body part (2x mag), move the part 1/2 way between the ______ and the _____
A
IR and Source
13
Q
SID:
A
the distance from the IR to the anode target
14
Q
When you increase SID, mag ___
A
decreases
15
Q
When you decrease SID, Mag _____
A
increases
16
Q
Size distortion only alters ___ not shape
A
size
17
Q
Size distortion is influenced by ___, ____, and ___.
A
SID, OID, and SOD
18
Q
Longer SID = ____ size distortion
A
less
19
Q
Shorter SID = ___ size distortion
A
more
20
Q
more mag = ___ SR
A
less
21
Q
less mag = ___ SR
A
more
22
Q
SOD:
A
source to object distance
distance between the anode target and the object
23
Q
the source of x-rays:
A
the target
24
Q
Actual Focal Spot:
A
the area of the anode target struck by electrons from the cathode
25
AFS size is determined by
1. Filament size
2. Anode Target Angle
26
The larger the AFS, the ___ the SR
less
27
The smaller the AFS, the ____ the SR
better
28
Larger filament size = ____ AFS
larger
29
Smaller filament size = _____ AFS
smaller
30
Larger filament size = ____ SR
less
31
Smaller filament size = ____ SR
better
32
Smaller the filament = ___ EFS = ___ SR
smaller EFS = better SR
33
larger the filament = ____ EFS = ____ SR
larger EFS = less SR
34
smaller AA = ____ EFS= ___ SR
Smaller EFS = better SR
35
An increase in kVP results in which of the following?
1) Increased photon quantity
2) Increased photon quality
3) increased percentage of photoelectric effect
1 and 2
36
An increase in kVp will increase photon quality and quantity, but will ____ the percentage of the photoelectric effect.
An increase in kVp will increase photon quality and quantity, but will REDUCE the percentage of the photoelectric effect.
37
A 15% increase in kVp will double exposure to the ____
IR
38
A high contrast radiographic image has few shades of gray. It is also known as an image with an ____
Short gray scale
39
In order to maintain IR exposure, which of the following would be done if kVp was reduced by 15%?
Increase mAs by 100%.
40
While performing a portable abdominal radiograph, the technologist is satisfied with the IR exposure but would like to increase the subject contrast. What adjustments should be made to their exposure technique in order to improve subject contrast and maintain image receptor exposure?
Decrease kVp 15% and double mAs
41
Shorter OID = ___ MAG
less
42
Longer OID = ____ MAG
more
43
Larger AA = ____ EFS = ____ SR
greater EFS and less SR
44
EFS:
the area projected onto the pt.
45
Smaller filament = ___ SR
better
46
Focal spot blur:
blurred region of a radiograph that tech has little control over
47
Focal Spot Blur origin:
due to geometric quality of the beam
48
____ OID helps reduce effects of focal spot blur
reduced
49
Line Focus Principle:
states that by angling the face of the anode target, a large AFS can be maintained and a small EFS size can be created.
50
On an angled anode with an angle that is _________, EFS is always smaller than FSS
<45 degrees
51
a larger AA = ____ EFS size
larger AA = smaller EFS size
52
Why do we want to make the AFS larger than the filament size?
Heat dissipation.
The larger the angle, the greater ability of the anode to dissipate heat.
53
What is the line focus principle purpose?
to create a desired small EFS after creating a larger AFS
54
____ target angles = sharper images
less
55
____ AA = better heat disspiation
Greater
56
____ AA = less heat dissipation
Less
57
Larger filament = ____ AFS
larger
58
Smaller filament = ___ AFS
smaller
59
Greater EFS = ____ divergence = _____ SR
Greater EFS = more divergence = less SR
60
Smaller EFS = _____ divergence = _____ SR
Smaller EFS = less divergence = more SR
61
Pt. motion always ____ SR
Lowers
62
Shape distortion:
distortion of object shape
63
"True distortion"
Shape Distortion
64
Types of shape distortion:
Foreshortening
Elongation
65
Shape distortion results from ____
Anatomy, CR, and IR alignment
66
Which shape distortion is worse, and why?
Foreshortening. Can superimpose anatomy, and miss pathology.
67
Elongation cause:
Cr angled to anatomy.
- Angle of the CR will project the anatomy.
IR angled but CR and anatomy are perpendicular.
68
Foreshortening cause:
Anatomy not parallel with the IR
69
Examples of using shape distortion:
1) AP Axial Towne Skull
- better images occipital and parietal bones
2) PA Axial Projection (Tunnel View)
- elongation of intercondyloid fossa
3) PA Projection of OS Calcis
- elongation of calcaneous
70
Image distortion types:
Size and Shape
71
Size distortion causes:
Increased OID
Decreased SID
Increased Mag = more penumbra = less SR
72
Shape distortion causes:
Elongation from angling CR or IR
Foreshortening from angling the anatomy
73
3 primary geometric factors affecting image quality:
1) Magnification
2) Distortion (shape and size)
3) Focal spot blur: has to do w/ divergence
* all cause blur
74
Prime exposure factor and Pt. dose:
1) kVp
2) mA
3) Time
4) SID (distance)
75
Increasing kVp increases the quality and penetrability of the beam.
The creation of a _____ # of photons is created at the target when kVp increases.
Greater
76
X-ray quantity varies _______ w/ changes in kVp
Exponentially
77
Changes in x-ray quantity is _____ to the square of the ratio of the kVp
Proportional
78
When kVp is doubled, the beam quality increases by ______
a factor of 4
79
kVp x2 = Quantity x
4
80
Increasing kVp = increasing beam quantity along the entire spectrum of the x-ray beam = _____ pt. dose
increased
81
Bigger beam = ____ dose
more
82
There are more lower energy photons created that will be absorbed as dose, along with a greater number of higher energy photons that pass through the pt.
Increased dose = ____ transmission
increased
83
There is a greater proportional increase in the # of high energy photons that will pass through the pt., therefore there is a ____ in image contrast
Decrease
84
15% rule:
creates a 30% increase of photons hitting the pt.
85
Increasing kVp by 15% is equivalent to the mAs being ____
doubled
86
a 15% increase in kVp does not double ______
X-ray intensity
87
a 15% increase in kVp is equivalent to ______ ____ to the IR
doubling mAs
88
Radiographically, only a 15% increase in kVp is necessary to double IR exposure for two reasons:
1) increased # of photons created
2) increased # of photons penetrating the pt. and reaching the IR (other 70%)
89
Increasing kVp is better than increasing ____
Increasing mAs
90
kVp increased 15% = _x photons hitting the IR = _x mAs
kVp increased by 15% = 2x photons hitting the IR = 2x mAs
91
Decreasing kVp by 15% is equivalent to _____ the mAs
halving
92
a 15% decrease of kVp does not half the ____ ____
x-ray intensity
93
a 15% decrease in kVp is the equivalent to halving the ____ to the IR.
mAs
94
Radiographically, only a 15% decrease in kVp is necessary to half IR exposure for two reasons:
1) decreased # of photons created
2) decreased # of photons penetrating the pt. and reaching the IR
95
Quantum Noise
Umbrella term?
96
Underexposed means:
kVp or mAs is insufficient
97
If you increase kVp 15%, but don't touch mAs = _x photons will strike the IR and fix the image
2x
98
To increase the exposure to the IR, ____ kVp by 15%
increase
99
To decrease the exposure to the IR, ____ kVp by 15%
decrease
100
Decrease contrast and maintain exposure by ___ kVp 15% and ___ mAs
increase kVp 15% and 1/2 mAs
101
Increase contrast and maintain exposure by ____ kVp 15% and ___ mAs
decrease kVp 15% and double mAs
102
15% rule can ____ pt. dose
decrease
103
Increasing kVp 15% and 1/2 mAs 50% = _____ less dose
20%
104
Increasing kVp 15% without adjusting mAs will increase pt. dose by ____
30%
105
mAs and dose relationship:
proportional
106
As mA increases, so does the # ________ crossing the tube to reach the anode
Electrons
107
2x mA = 2x electrons = 2x xrays emitted
1/2 mA = 1/2 electrons = 1/2 xrays emitted
108
Time (S):
the amount of time that potential difference (voltage) is applied to the tube.
109
Changes in the length of time a tube is energized will effect the total # of ____ flowing from C to A
electrons
110
exposure time is directly proportional to the # of electrons crossing the tube, and is also directly proportional to the # of ____
x-rays generated
111
2x time = 2x # of electrons = 2x xrays generated
2x time = 2x dose
1/2 time = 1/2 dose
2x time = 2x # of electrons = 2x xrays generated
2x time = 2x dose
1/2 time = 1/2 dose
112
Beam Intensity:
the measurement of the concentration of photons in the primary beam measured at a single point.
113
Factors affecting beam intensity:
1) mA
2) exposure time
3) kVp
4) distance:
5) target material
6) target angle
7) generator type
8) filtration
114
Intensity of the beam and exposure to the IR varies greatly w/ changes in distance because:
the beam diverges as it travels from the anode target.
115
X-ray intensity and exposure to the IR will decrease as distance ___
increases
116
X-ray intensity and exposure to the IR will increase as distance ____
decrease
117
What illustrates the relationship between distance and beam intensity?
Inverse Square Law
118
If you double distance = Dose _____ x4
decreases
119
If you half distance = dose ____ x4
increases
120
A ____ SID requires mAs to increase to maintain exposure to the IR
Increased
121
A _____ SID requires mAs to decrease to maintain exposure to the IR
decreased
