Unit Two Flashcards
(113 cards)
1
Q
Attenuation
A
Removal of any photons from the primary beam before striking the IR.
A reduction in x-ray beam intensity as it passes through matter
2
Q
What causes attenuation
A
1) Pt. absorption (DA)
2) Compton scatter that doesn’t strike IR.
3
Q
Differential Absorption
A
the difference between the xray photons that are absorbed and those that penetrate the body
4
Q
Why is it called DA?
A
different body structures absorb xray photons to different extents
5
Q
Differential Attenuation
A
a form of primary beam attenuation specific to pt. absorption and transmission.
6
Q
Absorption
A
refers to xray photons that are attenuated by the body and don’t reach the IR
7
Q
Transmission
A
refers to xray photons that pass through the body and reach the IR
8
Q
Primary Beam
A
the xray beam as it is upon exiting the collimator and exposing the pt
9
Q
Remnant Beam
A
the xray beam that remains after interaction with the pt. and that is exiting the pt to expose the IR
10
Q
What is the remnant beam composed of?
A
Transmitted photons and scattered photons
11
Q
Radiopaque
A
body structures that readily absorb xray photons (bones)
12
Q
Radiolucent
A
less dense body structures that have a much lower probability of absorption (air-filled lungs)
13
Q
Factors that affect Radiographic Contrast
A
- kVp
- Differential absorption
- computer processing and display
- filtration
- compton scatter
- radiographic grids
- OID
- beam restriction
14
Q
Increased levels of DA = _____ b/w on radiograph
A
Increased
15
Q
Radiograph with increased DA = _____ subject contrast = _____ gray scale
A
High
Short
16
Q
Decreased DA = ____ gray on radiograph
A
more
17
Q
Radiograph with decreased DA = ____ subject contrast = _____ gray scale
A
low
long
18
Q
a uniform exposure on the IR that causes a loss of visible image contrast
A
noise
19
Q
What causes noise
A
Compton Scatter
20
Q
Most common beam restriction?
A
Collimation
21
Q
Increased field size = ____ scattered xrays (scattered radiation)
A
increased
22
Q
5 types of interaction with matter
A
- coherent (classical) scatter
- compton scatter
- photoelectric effect
- pair production
- photodisintigration
23
Q
Other names for coherent scatter
A
Classical
Thompson
24
Q
Coherent scatter energy
A
less than 10 kev
25
Coherent scatter steps
1. X-ray with energy less than 10 kev interacts with a target atom = atom excited
2. target atom releases energy as a scattered photon w/ a wavelength = to the incident xray
3. Result = change of direction of xray w/out a change in energy
26
Scatter with no ionization and no energy transfer
coherent scatter
27
Coherent scatter's contribution to medical image
very little
28
At ___ kVp, a small % of xrays undergo coherent scattering
70
29
Xrays undergoing an interaction w/ an outershell electron that change direction, reduces photon energy, and ionizes the atom.
Compton scatter
30
Compton scatter steps
1. incident xray interacts w/ outershell electron and ejects it from the atom = ionization
2. xray photon contributes to different direction w/ a reduction in energy
31
Name of electron ejected during a compton (outershell) scatter reaction
Recoil electron
Compton electron
32
Energy of comton scattered xray
Energy of incident xray - energy of ejected electron
33
Energy of ejected electron
binding energy + kinetic energy
34
during compton scattering, most energy is divided between ______ and _____
scattered xray and compton electron
35
During compton scattering, the scattered xray retains ____ of energy
most of
36
The amount of energy that ionizing radiation imparts to a given mass of matter.
The amount of radiation absorbed by an object
Dose or Absorbed Dose
37
Compton scatter contributes to
1. Decreased image contrast
2. Pt dose
3. Occupational dose
38
3 types of compton scatter
1) Back scatter
2) Side scatter
3) Forward scatter
39
Back scatter
photon scatters 180 degrees perpendicular to the primary beam, strikes the IR, and travels back in direction of the incident xray beam
- can contribute to pt dose
40
Type of scatter when the photon strikes the outershell electron head-on
Back scatter
41
Type of scatter when the photon strikes the outershell electron on the outer edge
Side scatter
42
Main source of occupational dose (specifically in Fluro)
Side scatter
43
Type of scatter when the photon grazes the orbital electron, barely gives up its energy, and travels forward to strike the IR
Forward scatter
44
Increased xray energies increased probability of _____ scatter
forward
45
Factors affecting production of compton scatter
1. field size (collimation)
2. body part thickness
3. body part density
4. body part electron density
5. photon energy
6. kVp
46
Increased field size = ____ intensity of scattered xrays
increased
47
Increased field size = _____ noise = _____ in overall image contrast
Increased
Decreased
48
Decreased field size = ____ compton scatter production in pt.
Decreased
49
Most effective way of decreasing dose
Decreasing field size (collimation)
50
Thicker part = ____ compton scatter than thinner part
More
51
Compression Results in:
Thinner part
Reduction in Compton scatter
Increased image contrast
52
Increased part density = ____ production of compton scatter
Increased
53
Why does a body part with a large volume of matter produce more scattered xrays?
Due to increased presence of hydrogen atoms and water rich tissues being more electron dense
54
Does atomic number of a tissue affect the likelihood of compton scatter?
NO
55
An ____ in the presence of water in soft tissue makes it to where compton is more likely
Increase
56
Hydrogen atom composition
No neutrons
Nucleus only has one proton and one electron
57
_____ amount of water present in a type of tissue = _____ amount of compton
Increase
57
57
Hydrogen atoms have _____ the amount (density) of electrons per cubit cm.
2x
58
As kVp increases, the likelihood of compton decreases because
Transmission increases as kVp increases
59
An increase in kVp makes a larger beam, which leads to more compton events but, _____- average compton events
decreased
60
Ways to reduce compton scatter
1. Lowest possible kVp
2. Grids
3. Collimation
4. Air gap technique
5. Part compression
61
Photoelectric effect =
Absorption
(photoelectric absorption)
62
Photoelectric effect happens when
xrays have ionizing interactions with inner-shell electrons
63
In photoelectric effect, the xrays are not scattered, but
totally absorbed
64
An electron removed from an atom during photoelectron effect is called
Photoelectron
65
Photoelectron kinetic energy
energy of the incident xray - the binding enrgy of electron
66
Photoelectric Effect:
The incident photon is absorbed by what shell?
K
67
Photoelectric Effect steps
1. Incident xray is absorbed by inner (K) electron
2. K-shell electron enters an excited state and is ejected from the shell.
3. Photoelectric effect produces secondary radiation through the cascading effect.
68
A photoelectric interaction cannot occur unless
The incident xray has energy equal to or slightly greater than the electron binding energy
69
Barium K-shell binding energy
37kev
70
Factors affecting Photoelectric Effect
1. kVp
2. Body part thickness
3. Body part density
4. Atomoic number of tissue
71
Photoelectric Effect relation with kVp
Indirect
(kVp up = PE down)
72
Photoelectric Effect relation with body part thickness
Direct
(thicker = more PE)
73
Photoelectric Effect relation with body part density
Direct
(more dense = more PE)
74
Photoelectric Effect relation with atomic number of tissue
Direct
(higher atomic# = more PE)
75
As kVp increases, the overall photoelectric effect increases, due to an increase in quantity of the polyenergetic beam. But, compared to transmission, the average PE events
decrease
(decrease in DA)
76
A higher atomic number increases the likelihood of PE ____
Greatly
77
Penetration from easy to hard
1. Air
2. Fat
3. Water
4. Muscle
5. Bone
6. Barium Sulfate
7. Lead
78
An increase in xray beam intensity = an overall ____ in ALL interactions.
Increase
79
An increase in xray beam intensity = an overall increase in ALL interactions, a _____ in average compton interactions.
Decrease
80
An increase in xray beam intensity = an overall increase in ALL interactions, a decrease in average compton interactions, a great ____ in average photoelectric interactions
Decrease
81
An increase in xray beam intensity = an overall increase in ALL interactions, a decrease in average compton interactions, a great decrease in average photoelectric interactions, and an _____ in transmission through the pt.
Increase
82
What modality is pair production used in?
Nuc med
83
Does pair production occur in the diagnostic range of x-radiation?
no
84
Pair production is important for
Positron Emission Tomography (PET)
85
Pair production requires an xray photon energy of
>1.02 mev
86
Pair production steps
1. photon escapes influence of orbital electrons, and interacts directly with the nucleus
2. photon disappears, and 2 electrons appear in its place (one is positive/positron, and one in negative/negatron)
87
What modality is photodisintegration used in?
Therapeutic Radiation Therapy
88
Photodisintegration requires photon energy of
>10 mev
89
Photodisintegration steps:
1. photon escapes interactions with orbital electrons and is absorbed by the nucleus
2. nucleus emits nucleon or neclear fragments
90
Does photodisentegration occur in the diagnostic range?
no
91
Define Image Contrast
The degree of difference between the light and dark areas of a radiograph.
92
Define Differential Absorption
The difference between the x-ray photons absorbed, and those that penetrate the body.
93
What makes blacks, whites, and grays on a radiograph?
differential absorption
94
What is subject contrast
The component of image contrast that is determined by the size, shape, and x-ray attenuating characteristics of the subject who is being examined and the energy of the beam.
95
Factors affecting Subject Contrast
Low kvp
High z-number anatomy
Thicker part
Denser part
96
What is attenuation?
The removal of any photons from the primary beam before striking the IR.
97
What causes attenuation
Pt absorption
Compton Scatter that does not strike IR
98
What is the technical term for photon aborption within the patient?
Differential Attenuation
99
What is another way of describing "high contrast"?
Short Gray Scale
100
What is another way of describing low contrast?
long gray scale
101
What is the controlling factor of subject contrast?
kVp
102
What is the controlling factor of image contrast?
LUT
103
Describes the effects of kVp on the xray beam
Determines quality/penetrability
Influences contrast (increase kVp = decreased contrast)
104
Describe the effects of kVp on differential absorption
Increasing kVp decreases the percentage of Differential Absorption
105
Describe the effects of kVp on patient dose/absorption
Direct relationship
Size of beam has direct relationship to dose
106
Briefly describe coherant scatter
An incident x-ray interacts with a target atom, the atom becomes excited then releases its excess energy as a scattered x-ray photon. The x-ray has a change in direction but not a change in energy.
107
Briefly describe compton scatter
An incident x-ray interacts with an outer-shell electron, ejects it, and then ionizes the atom. This results in a Compton electron or recoil electron. The photon changes direction and has a reduction in energy.
108
Briefly decribe photoelectric effect
The incident photon is absorbed by an inner (K-shell) electron, the electron gets ejected due to being in an excited state. Secondary radiation is produced from the cascading effect.
109
Three types of compton scatter
back
Forward
side
110
What determines the direction of a compton scattered photon?
where the photon interacts with the atom
111
Uniform overall reduction of image contrast, due to compton, is called?
Noise
