Chapter 3: Interaction of X-Radiation with Matter Flashcards
(163 cards)
1
Q
The processes of interaction between radiation and matter are emphasized because a basic understanding of the subject is necessary for radiographers to optimally select the following technical exposure factors:
A
- milliampere-seconds (mAs)
- peak kilovoltage (kVp)
2
Q
no dose is a
A
safe dose
3
Q
the highest energy level of photons in the x-ray beam, equal to the highest voltage established across the x-ray tube
A
peak kilovoltage (kVp)
4
Q
controls the quality, or penetrating power, of the photons in the x-ray beam and to some degree also affects the quantity, or number of photons, in the beam.
A
peak kilovoltage (kVp)
5
Q
is your penetration and quality
A
kvp
6
Q
polygenetic heterogenous beam
A
kvp
7
Q
90 kvp average energy is
A
1/3 so is 30
8
Q
is the product of milliamperes (mA) which is electron tube current and the amount of time in seconds that the x-ray tube is activated
A
Milliampere-seconds (mAs)
9
Q
is considered pt dose
A
mAs
10
Q
decrease pt dose
What technical factors?
A
increase kvp and decrease mAs
11
Q
if mAs is decrease too much
A
an grainy image will appear called quantum mottle
12
Q
is your current and quantity
A
mAs
13
Q
Selects technical exposure factors that control beam quality and quantity
- is actually responsible for the dose the patient receives during an imaging procedure
A
radiographer
13
Q
what are carriers of manmade electromagnetic energy
A
x-rays
13
Q
With a suitable understanding of these factors, radiographers will be able to select appropriate so they can
A
that can minimize that dose to the patient while producing optimal-quality images.
14
Q
If x-rays enter a material such as human tissue, they may:
A
- Interact with the atoms of the biologic material in the patient and be absorbed
- Interact with the atoms in the biologic material and be scattered, causing some indirect transmission
- Pass through without interaction
15
Q
If an interaction occurs, electromagnetic energy is transferred from the x-rays to the atoms of the patient’s biologic tissue. This process is called
A
absorption
16
Q
the amount of energy absorbed per unit mass is referred to as
A
absorbed dose
17
Q
The more electromagnetic energy that is received by the atoms of the patient’s body,
A
the greater is the possibility of biologic damage in the patient
18
Q
without absorption and the differences in the absorption properties of various body structures,
A
it would not be possible to produce diagnostically useful images, that is, images in which different anatomic structures could be perceived and distinguished
18
Q
gives you the different shades of gray black / white
A
absorption
19
Q
photoelectric is
A
absorption
20
Q
deposited into patient body
A
absorption
21
Q
absorbed dose is measured in
A
milligray (mGY)
22
A diagnostic x-ray beam is produced
when a stream of very energetic electrons bombards a positively charged target in a highly evacuated glass tube.
22
atomic number of tungsten
74
23
the target known as the anode is made up of
tungsten rhenium
23
why is tungsten used
High melting points
* High atomic numbers
24
atomic number of rhenium
75
25
As the electrons interact with the atoms of the tube target
x-ray photons are produced
26
Photons are particles associated with electromagnetic radiation that have neither mass nor electric charge and travel at the speed of light. X-ray photons exit from the tube target with a broad range, or spectrum, of energies and leave the x-ray tube through a glass window. The glass window permits passage of all but the lowest-energy components of the x-ray spectrum. It therefore acts as a filter by removing diagnostically useless, very-low-energy x-rays.
important
27
is the x-ray photon beam that emerges from the x-ray tube and is directed toward the image receptor
primary radiation
28
are particles associated with electromagnetic radiation that have neither mass nor electric charge and travel at the speed of light
photons
28
exit from the tube target with a broad range, or spectrum, of energies and leave the x-ray tube through a glass window.
xray photons
29
permits passage of all but the lowest-energy components of the x-ray spectrum. It therefore acts as a filter by removing diagnostically useless, very-low-energy x-rays. In addition to this, a certain thickness of added aluminum is placed within the collimator assembly to intercept the emerging x-rays before they reach the patient.
glass window
29
what is the average energy
1/3 of the kvp
30
whole voltage on the x-ray tube
kvp
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individual energy of specific x-rays
kev
32
In diagnostic radiology, the voltage is expressed in thousands of volts, or:
kilovolts (kv)
33
because the voltage across the tube fluctuates, it is usually charcterized by
kilovolt peak value (kvp)
34
True or False:
Not all photons in a diagnostic xray bean have the same energy
true
35
True or False :
The most energetic photons in the beam can have no more energy than the electrons that bombard the target
true
36
Photons that strike the image receptor are called
Transmitted photons
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are the photons that have undergone either absorption or scatter and do not strike the image receptor
attenuated photons
38
X-rays sometimes interact with atoms of a patient such that they give up all of their energy and cease to exist. These photons are said to be
absorbed
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Other photons interact with atoms of the patient, but only surrender part of their energy. They will continue to exist but will emerge from the interaction at a different angle (somewhat like a billiard ball colliding with another billiard ball). These photons are said to be
scattered
40
Some primary photons will traverse the patient without interacting. These noninteracting x-ray photons reach the radiographic image receptor (e.g., phosphor plate or digital radiography receptor).
what kind of transmission
direct transmission
41
Decrease in amount of photons reaching IR
attenuation
42
Direct and indirect transmission of x-ray photons
When an x-ray beam passes through a patient, it goes through a process called
attenuation
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If they interacted but still happened to strike the image receptor, they are termed
- as a result of scattered
indirect transmission of photons
42
If photons pass through the patient without interacting with the atoms of the patient, they are referred to as
direct transmission photons
42
Other primary photons can undergo Compton and/or coherent interactions and as a result may be scattered or deflected with a potential loss of energy. Such photons may still traverse the patient and strike the image receptor
indirect transmission
43
Primary, exit, and attenuated photons are photons that emerge
from the x-ray source
44
are photons that pass through the patient being radiographed and reach the radiographic image receptor
exit or image formation photons
45
are photons that have interacted with atoms of the patient’s biologic tissue and have been scattered or absorbed such that they do not reach the radiographic image receptor.
attenuated photons
46
interaction of photon is random or normal
random with biological matter
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primary beam going into
patient
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photoelectric
- absorbed in the body
absorption
49
not diagnostic what type of interaction
coherent interaction
50
diagnostic what types of interaction
photoelectric and compton
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scattered
compton
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When x-rays interact with human tissue electromagnetic energy is transferred from the x-rays to the atoms of the patient’s biologic material (absorption), and the amount of energy absorbed per unit mass
is the absorbed dose
53
Keep the amount of electromagnetic energy transferred to the patient’s body as small as possible to
minimize the possibility of biological damage
54
Diagnostic radiology
photoelectric absorption
54
Not significant in any energy range
Coherent scattering
55
diagnostic radiology and therapeutic radiology
Compton scattering
56
interactions that interact with tube
Bremsstrahlung and characteristics
56
interactions that interact with matter
photoelectric absorption, Compton scattering and coherent
57
Coherent scattering is sometimes also called by the following names:
- classical scattering
- elastic scattering
- unmodified scattering
- Thomson scattering
- Rayleigh scattering
57
A relatively simple process that results in no loss of energy as x-rays scatter
coherent scattering
58
It occurs with low-energy photons, typically less than 10 keV.Because the wavelengths of both incident and scattered waves are the same, no net energy has been absorbed by the atom (see Appendix E in textbook).Rayleigh and Thompson scattering play essentially no role in radiography
coherent scattering
59
scattering comes in with the same energy and leaves with the same energy
- no ionization
- decrease contrast b/c of scattered occurs
coherent scattering
60
. The incoming low-energy x-ray photon interacts with an atom and transfers its energy by causing some or all of the electrons of the atom to momentarily vibrate. The electrons then radiate energy in the form of electromagnetic waves. These waves nondestructively combine with one another to form a scattered wave, which represents the scattered photon. Its wavelength and energy, or penetrating power, are the same as those of the incident photon. Generally, the emitted photon may change in direction less than 20 degrees with respect to the direction of the original photon
coherent scattering
60
one coming in and one coming out
- photon coming in and photon coming out
coherent scattering
61
Diagnostic radiology energy range: 23 to 150 kVp
This is the most important mode of interaction between x-ray photons and the atoms of the patient’s body for producing useful images
photoelectric absorption
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inner shell (k-shell)
photoelectric absorption
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one incoming and one leaving
photoelectric absorption
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cascade effect
- without it no shades of gray
photoelectric absorption
65
To dislodge an inner-shell electron from its atomic orbit, the incoming x-ray photon must be able to transfer a quantity of energy as large as or larger than the amount of energy that holds the electron in its orbit. On interacting with an inner-shell electron, the x-ray photon surrenders all its energy to the orbital electron and ceases to exist. The electron escapes from its inner shell, thus creating a vacancy. The now unbound orbital electron, called a photoelectron, possesses energy equal to the energy of the incident photon minus the binding energy of its electron shell. This photoelectron may interact with other atoms in the vicinity, thereby causing excitation (promotion of electrons from lower energy shells to higher energy shells) or ionization (complete ejection of the electron from an atom), until all of its energy has been spent.
photoelectric absorption
66
On encountering an inner-shell electron in the K or L shells, the incoming x-ray photon surrenders all its energy to the electron, and the photon ceases to exist. (B) The atom responds by ejecting the electron, called a photoelectron,from its inner shell, thus creating a vacancy in that shell. (C) To fill the opening, an electron from an outer shell drops down to the vacated inner shell by releasing energy in the form of a characteristic photon. Then, to fill the new vacancy in the outer shell, another electron from the shell next farthest out drops down and another characteristic photon is emitted, and so on until the atom regains electrical equilibrium. There is also some probability that instead of a characteristic photon, an Auger electron will be ejected.
photoelectric absorption
67
come in with same energy, leave with same energy
coherent scattering
68
photon coming in and photoelectron leaving
photoelectric absorption
69
a vacancy is created in an inner shell of the target atom. For the ionized atom, this represents an unstable energy situation. The instability is alleviated by filling the vacancy in the inner shell with an electron from an outer shell, which spontaneously “falls down” into this opening. To do this, the descending electron must lose energy, that is, must pass from a less tightly bound atomic state (farther from the nucleus) to a more tightly held status (closer to the nucleus). The amount of energy loss involved is simply equal to the difference in the binding, or “holding,” energies associated with each electron shell. For a large atom such as an atom of the element lead, this energy can be in the kiloelectron volt range, whereas for the small or low atomic number atoms that make up most of the human body, the energy is on the order of 10 eV. The “released” energy is carried off in the form of a photon that is called a characteristic photon, or characteristic x-ray, because its energy is directly related to the shell structure of the atom from which it was emitted. Those photons generated from photoelectric interactions within human tissue are low enough in energy that they are predominantly absorbed within the body. In general, ensuing vacancies in other electron shells are successively filled, and associated characteristic photons are emitted until the atom achieves an electronic equilibrium.
photoelectric absorption
70
discovered by Pierre Victor Auger in 1925
- Produces an Auger electronIs - a radiationless effect
Auger effect (pronounced awzhay)
70
When an inner electron is removed from an atom in a photoelectric interaction, thus causing an inner-shell vacancy, the energy liberated when this vacancy is filled can be transferred to another electron of the atom, thereby ejecting that electron, instead of emerging from the atom as characteristic radiation. Such an emitted electron is called an Auger electron. Its energy is equal to the difference between that released by an outer electron in filling the initial created vacancy and the binding energy of the emitted or Auger electron. Because this process does not include any x-ray emission, it is called a radiationless effect. It reduces the total amount of characteristic radiation produced by photoelectric interactions.
Auger effect
71
refers to the number of x-rays emitted per inner-shell vacancy
fluorescent yield
72
the by-products of photoelectric absorption include the following:
1. Photoelectrons (those induced by interaction with external radiation and the internally generated Auger electrons)
2. Characteristic x-ray photons (fluorescent radiation)
73
is the most important mode of interaction between x-radiation and the atoms of the patient’s body in the energy range used in diagnostic radiology because this interaction is responsible for both the patient’s dose and contrast in the image. During the process of photoelectric absorption, the total energy of the incident photon is completely absorbed as it interacts with and ejects an inner-shell electron of an atom within human tissue or bone from its orbit. The newly ejected photoelectron has appreciable energy and thus can subsequently ionize other atoms it encounters until its energy is sufficiently depleted. After losing an electron, the original ionized atom is unstable and attempts to re-stabilize. This occurs as an electron from a higher shell drops down and fills the vacancy in the inner shell by releasing energy as a characteristic photon. This cascading effect of electrons dropping down to fill existing shell vacancies continues until the original atom regains its stability.
Photoelectric absorption
74
The probability of occurrence of photoelectric absorption per atom within a particular material depends on
- the energy (E) of the incident x-ray photons
- the atomic number (Z) of the atoms comprising the irradiated object
75
Probability of occurrence of photoelectric absorption increases
as the energy of the incident photon decreases and the atomic number of the irradiated atoms increases.
76
Aluminum atomic number and symbol
13 and Al
77
copper atomic number and symbol
29 and Cu
78
lead atomic number and symbol
Pb 82
79
(mass density measured in grams per cubic centimeter) of different body structures influence
attenuation
79
brighter
more absorption, less transmission
bone
80
less absorption
- more transmission
soft tissue
81
tightly packed they are
density
82
least to most attenuated
air, muscle, fat, organ, bone, metal
1. air
2. fat
3. muscle
4. organs
5. bone
6. metal
82
higher atomic number
higher absorption
83
considered positively charge
protons
83
tungsten binding energy
69.5 in k -shell or 70
84
electrons in outer shell possess
kinetic energy
84
electrons in inner shell ( k, l, m) have
lower kinetic energy but higher binding energy
84
contrast, window depth, dynamic range
photoelectric absorption
85
higher atomic number higher absorption less transmission
more white
86
fat atomic number
6.3
87
muscle atomic number
7.4
88
bone atomic number
13.8
89
air atomic number
7.6
90
iodine atomic numbr
53
91
barium atomic number
56
92
lead atomic number
82
93
radiation that originates from irradiated material outside tube
secondary radiation
94
Occupational dose is measured in
Sievert
95
The amount of radiation on object
Exposure
95
Amount of energy per unit mass absorbed
Absorbed dose
96
Measurement of overall risk of exposure to humans
Effective dose
96
Body part thickness
The thickness factor is approximately
Linear
96
If two structures have the same density and atomic number but one is twice as thick as the other
The thicker structure will absorb twice as many photons
97
As absorption increases
So does the potential for biological damage
98
The greater the difference in the amount of photoelectric absorption,
The greater the contrast in the radiographic image will be between adjacent structures of differing atomic numbers
99
To ensure both radiographic image quality and patient safety
Choose the highest-energy x-ray beam that permits adequate radiographic contrast for computed radiography, digital radiography, or conventional radiography
100
Use of positive contrast medium (barium or iodine)
Containing elements having a higher atomic number than surrounding soft tissue. Appear lighter higher absorbed dose
100
Use of a negative contrast medium (air or gas)
Are easier to penetrate result in areas of decreased brightness on the radiographic image
101
# 1 contrast agent
Air
102
Less attenuation
The darker the image
103
Compton scattering is also known as
- incoherent scattering
- inelastic scattering
- modified scattering
- occupational dose
103
Responsible for most of the scattered radiation produced during radiographic procedures
Compton scattering
104
Best place to stand is at
A 90 degree angle
105
You should stand
6 feet away
106
Don’t Point Tube at
Console
106
Outer shell, modified, scattered
Photon coming in interacting with outer shell electron
Compton scatter
107
One coming 2 leaving
Compton scatter
107
Degrading your image because of the fog
Compton scatter
108
Fog on image
Decreases contrast
108
How many times can it scattered before loosing its energy
2 times
108
Everytime x-ray photon scatters it leaves with
. 1% original intensity. One one thousand
109
On encountering the electron, the incoming x-ray photon surrendes a portion of its energy in dislodging the electron from its outer - shell orbit, thereby ionizing the biological atom. The freed electron called a Compton scattered electron or secondary or recoil, electron, possesses excess energy and thus is potentially capable of ionizing other biological atoms
Compton scatter
110
Annihilation radiation is used in an imaging modality employed in Nuclear Medicine called
positron emission tomography (PET)
111
Attenuation (loss of photons) , absorption, transmission
Increased thickness
^ attenuation ^ absorption decrease transmission
112
Attenuation (loss of photons) , absorption, transmission
Decreased thickness
decreased attenuation, decreased absorption, ^ transmission
113
Attenuation (loss of photons) , absorption, transmission
Increased atomic number
^ attenuation ^ absorption decrease transmission
114
Attenuation (loss of photons) , absorption, transmission
Decrease atomic number
Decrease attenuation, decrease absorption ^ transmission
115
Attenuation (loss of photons) , absorption, transmission
Increased tissue density
^ attenuation ^ absorption decrease transmission
116
Attenuation (loss of photons) , absorption, transmission
Decreased tissue density
Decrease attenuation, decrease absorption ^ transmission
117
Attenuation (loss of photons) , absorption, transmission
Increased beam quality
Decrease attenuation, decrease absorption ^ transmission
118
Attenuation (loss of photons) , absorption, transmission
Decreased beam quality
^ attenuation ^ absorption Decrease transmission
119
are emitted from nuclei of very heavy elements, such as uranium and plutonium, during their radioactive decay.
Alpha particles,
120
Each contains two protons and two neutrons.
Are simply helium nuclei (i.e., helium atoms minus their electrons)
Have a large mass (approximately four times the mass of a hydrogen atom) and a positive charge twice that of an electron
Alpha Particles
121
are less penetrating than beta particles
- They lose energy quickly as they travel a short distance in biologic matter
- Considered virtually harmless
- As an internal source of radiation, they can be very damaging
- If emitted from a radioisotope deposited in the body, such as in the lungs, alpha particles can be absorbed in the relatively radiosensitive epithelial tissue and are very damaging to that tissue
- superficial of skin
- more biological damage
alpha particles
122
emitted from nuclei/ nucleus
- if you ingest it is very damaging to your internal organs
Alpha particles
123
Identical to high-speed electrons except for their origin
8000 times lighter than alpha particles and have only one unit of electric charge (−1)
negative charge
beta particles
124
two units of electric charge (+2)
alpha particles
125
Number of protons in the nucleus of an atom constitutes its
atomic number
126
make up the nucleus of an atom
positively charge
proton
127
the lesser a structure attenuates
the darker the image will be
128
the more a structure attenuates
the brighter the image will be
129
what is remaining in the beam after it passes through matter
remnant beam
130
electron in
tube interactions
131
photon in
matter interactions
132
are photons that emerge from the x-ray source
Primary, exit, and attenuated photons
133
what comes in and what leaves in a photoelectric absorption
photon coming in, photoelectron leaving
134
is a composite Z value by weight for a material that is composed of multiple chemical elements.
Effective atomic number [Zeff]
