X-ray Production and Target Interactions
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1
Over what distance does the electron cloud accelerate from zero to half the speed of light?
2 cm
2
The greater the speed of the incident electrons, the greater the ______ and ______ of the x-ray photons produced.
quality | quantity
3
Incoming electrons that interact with the anode target are called ______ electrons.
incident
4
Less than ______ of incident electrons are converted to x-ray photons at the target.
1%
5
What percentage of incident electron kinetic energy is converted to heat at the anode target?
Over 99.8%
6
What are the two types of target interactions that produce diagnostic-range x-ray photons?
Bremsstrahlung interactions and characteristic interactions
7
The German word "Bremsstrahlung" translates to ______ or ______.
braking | slowing
8
What target structure does an incident electron interact with to cause a Bremsstrahlung interaction?
The force field of the target material's nucleus
9
List all important Brems STATs.
1. Incident electron interacts with the force field of the target nucleus, 2. Electron is slowed (German for braking or slowing), 3. Produces 80% to 90% of the primary beam, 4. Photon energies are not predictable
10
A characteristic interaction occurs only when an incident electron interacts with an ______ electron.
inner shell
11
True or False: A characteristic interaction can occur when an incident electron interacts with an outer shell electron.
False. A characteristic interaction occurs only when an incident electron interacts with an inner shell electron.
12
What happens to the target atom when an incident electron knocks an inner shell electron from orbit?
It is ionized, becoming unstable with a vacancy (hole) in the inner shell
13
The sequential process in which outer shell electrons drop down to fill inner shell vacancies (L to K, M to L, and so on) is called the ______.
characteristic cascade
14
In a characteristic interaction, what directly causes the emission of an x-ray photon?
An outer shell electron dropping down to fill an inner shell vacancy
15
During a characteristic cascade, outer shell electrons fill vacancies until shell ______ is left missing an electron.
Q
16
During a characteristic cascade, when an electron drops from shell L into shell K, the vacancy in shell L is filled by an electron from shell ______.
M
17
What is the difference between Bremsstrahlung and characteristic photon energies?
Characteristic photon energies are highly predictable, whereas Bremsstrahlung photon energies are not predictable.
18
Characteristic photon energies are predictable enough to be measured to determine the elemental composition of the sun, stars, and other ______ bodies.
celestial
19
Only characteristic photons from the ______ shell have enough energy to be part of the useful x-ray beam.
K
20
What is the minimum energy an x-ray photon must have to be considered "useful" in the diagnostic beam?
59.0 keV
21
What percentage of the primary diagnostic x-ray beam is produced by Bremsstrahlung interactions?
80% to 90%
22
Characteristic interactions account for ______ to ______ of the primary diagnostic x-ray beam.
10% | 20%
23
List all important Characteristic STATs.
1. Incident electron interacts with an inner shell electron, 2. Target atom is ionized, leaving a vacancy, 3. Outer shell electrons fill vacancies in a characteristic cascade (down to shell Q), 4. Photon energies are highly predictable, 5. Only K shell photons (at least 59.0 keV) are useful, 6. Accounts for 10% to 20% of the primary beam
24
What is the process called of eliminating undesirable low-energy x-ray photons by inserting absorbing materials into the primary beam?
Filtration
25
What is meant by hardening the beam?
Filtration removes low-energy photons from the primary beam, which increases the average energy of the beam
26
Why is the removal of low-energy x-ray photons by filtration necessary?
They do not contribute to the image and they increase radiation dose to the patient
27
Removing low-energy photons from the primary beam causes the average beam energy to ______.
increase
28
Soft tissue penetration requires photons with energies of approximately ______ to ______ keV.
30 | 40
29
What is the smallest photon energy considered high energy or useful?
59 keV
30
In diagnostic radiology, filtration is typically added between the ______ and the ______.
x-ray source | patient
31
What is the standard filter material used in diagnostic radiography?
Aluminum
32
Standard filtration is expressed in units of ______.
aluminum equivalency (Al/Eq)
33
Besides aluminum, what four other materials can be used for filtration?
Glass, oil, tin, and copper
34
What term describes the thickness of absorbing material that reduces the intensity of the primary beam to half of its original value?
Half-value layer (HVL)
35
How is a low half-value layer (HVL) corrected?
By inserting more absorbing material into the primary beam
36
What are the five types of filtration?
Inherent, added, compound, compensating, and total filtration
37
Inherent filtration refers to filtration found ______ the tube and tube housing.
within
38
The three components of inherent filtration are the glass envelope, the dielectric oil bath, and the ______.
glass window of the housing
39
From which component does most inherent filtration originate?
The window of the glass envelope
40
What material is used for the tube window of a mammography unit to allow more low-energy photons to escape?
- Beryllium
- Aluminum
- Glass
- Tin
41
The inherent filtration of a mammography unit is ______ than that of a standard diagnostic unit.
less
42
Tube aging causes inherent filtration to ______ because of vaporized tungsten coating the tube window and anode pitting.
increase
43
______ filtration is any filtration located outside the tube and housing before the beam reaches the image receptor.
Added
44
What is the difference between inherent and added filtration?
Inherent filtration is found within the tube and housing, whereas added filtration is located outside the tube and housing before the image receptor.
45
How much added filtration does a collimator typically provide because of the silver on its mirror?
1 mm Al/Eq
46
Compound filters, which use two or more materials to balance their absorbing abilities, are also called ______ filters.
K-edge
47
In a compound filter, which atomic number material is placed toward the tube and which toward the patient?
Highest atomic number toward the tube | lowest atomic number toward the patient
48
In a compound filter, each layer is designed to absorb the ______ photons created in the preceding layer.
characteristic
49
What three metals make up a Thoraeus filter used in radiation therapy?
Tin, copper, and aluminum
50
In a Thoraeus filter, ______ is placed closest to the tube and ______ is placed closest to the patient.
tin | aluminum
51
What is the purpose of a compensating filter?
To even out radiographic density caused by unequal subject densities
52
Which compensating filter is commonly used for radiography of the foot?
- Wedge filter
- Trough filter
- Thoraeus filter
- K-edge filter
53
A ______ filter has a double wedge design and is used for AP projections of the thorax.
trough
54
What is the equation for total filtration?
Total Filtration = Inherent Filtration + Added Filtration
55
Total filtration calculations exclude compound filtration and ______ filtration.
compensating
56
What undesirable effect does filtration have on overall radiographic density?
It decreases radiographic density
57
Why does adding filtration decrease overall radiographic density?
Some useful, high-energy photons are absorbed along with the low-energy photons
58
As photon energy increases, the percentage of photons attenuated by a filter ______.
decreases
59
True or False: Tube aging decreases inherent filtration.
False. Tube aging increases inherent filtration.
60
During which type of interaction is scatter radiation produced?
Compton interaction
61
What device is used by the radiographer to minimize the amount of scatter radiation reaching the image receptor?
A grid
62
The primary function of a grid in radiography is to improve ______.
contrast
63
What are the 2 principal factors that affect the amount of scatter produced?
kVp and the amount/type of irradiated material (volume of tissue)
64
Increasing beam restriction results in ______ primary photons emitted from the tube and collimator.
fewer
65
Increasing beam restriction results in ______ scattered photons being created.
fewer
66
How does restricting the beam improve image quality?
It reduces the volume of irradiated tissue so fewer scattered photons are created, which improves contrast
67
How does restricting the beam reduce patient dose?
Fewer primary photons are emitted from the tube and collimator, so less tissue is irradiated
68
Increasing beam restriction is also referred to as increasing ______.
collimation
69
______ interactions are absorbing interactions that result in less scatter radiation.
Photoelectric
70
As kVp increases, the percentage of x-rays undergoing Compton interactions ______ and the percentage undergoing photoelectric absorption ______.
increases | decreases
71
There is a ______ relationship between kVp and the percentage of Compton interactions.
direct
72
As kVp increases, ______ (fewer or more) total photons undergo interactions with matter because of their higher energy.
fewer
73
Increasing kVp, causes an increase in? (List all things that would apply)
Beam penetrability, scatter radiation produced (if mAs is not decreased), and the percentage of Compton interactions
74
True or False: Increasing kVp alone decreases the amount of scatter radiation produced.
False. Increasing kVp alone increases the amount of scatter radiation produced.
75
When kVp is increased but mAs is decreased, ______ scatter radiation is produced.
less
76
What beam characteristic is directly affected by kilovoltage (kVp)?
Penetrability
77
What two factors control the volume of irradiated material?
Field size and patient thickness
78
As field size and patient thickness increase, the amount of scatter radiation ______.
increases
79
In radiography, ______ devices are used to decrease patient thickness, bring tissue closer to the film, lower patient dose, and improve resolution and contrast.
compression
80
In which imaging modality are compression devices most commonly used?
Mammography
81
What effect does compression have on scatter production?
It decreases patient thickness, which decreases scatter production
82
As the atomic number of the irradiated material increases, scatter production ______.
decreases
83
Compared to soft tissue, bone absorbs ______ radiation and scatters ______ radiation.
more | less
84
What relationship exists between Compton scatter and atomic number of tissue? Between photoelectric interactions and atomic number of tissue?
Compton scatter decreases as atomic number increases (inverse), whereas photoelectric absorption increases as atomic number increases (higher atomic number materials absorb more radiation)
85
Compton scattering involves the interaction of an incident photon with what type of atomic electron?
A free or loosely bound outer-shell electron
86
The electron ejected from an atom as a result of a Compton interaction is called a ______ electron.
recoil (or Compton)
87
Compton interactions are most commonly seen at ______ kVp and higher.
80
88
Diagnostic x-ray interactions at ______ kVp and lower are most commonly photoelectric.
70
89
For x-ray photons that interact within the diagnostic energy range, what are the two primary types of interactions?
Compton interaction and photoelectric interaction
90
What are the three possible fates of an x-ray photon entering matter?
1. Travel all the way through without interaction, 2. Be completely absorbed, 3. Interact and change direction (scatter)
91
What is the primary purpose of a radiographic grid?
To improve contrast by absorbing scatter radiation
92
Photoelectric interactions in the patient's body result in photon ______.
absorption
93
Photons that pass through the body unaffected interact with the image receptor to create image ______.
contrast
94
An increase in kVp causes scatter radiation to ______ and overall contrast to ______.
increase | decrease
95
The amount of scatter radiation increases with what three things?
Increased patient thickness, larger field sizes, and decreased atomic number of irradiated tissues
96
As a general rule, a grid is used when the body part is greater than ______ cm or when kVp is above ______.
10 | 60
97
Who invented the original radiographic grid in 1913?
Dr. Gustav Bucky
98
What major flaw did Gustav Bucky's original grid, with lead strips running in two directions, produce on the image?
A visible checkerboard pattern
99
Who was Hollis Potter? And why is he significant?
A doctor who improved the grid in 1920 by running the lead strips in one direction, making them thinner, and making the grid move during exposure (Potter-Bucky diaphragm)
100
Radiopaque grid strips are typically made of ______.
lead
101
What are the two common radiolucent interspace materials used in grids?
Aluminum and plastic fiber
102
Which radiolucent interspace material is preferred for lower kVp techniques such as mammography?
Plastic fiber
103
What is the formula for grid ratio?
Grid Ratio = h / d, where h is the lead strip height and d is the interspace width
104
If lead strips are 2 mm high and separated by an interspace of 0.25 mm, the grid ratio is ______.
8:1
105
What is the most common grid ratio used in radiography?
10:1
106
When the height of the lead strips stays constant, what relationship exists between the distance between lead strips and the grid ratio?
An inverse relationship
107
What is the term for the number of grid lines per inch or per centimeter?
Grid frequency
108
What is the most common grid frequency range?
85 to 103 lines/inch
109
Compared to high-frequency grids, grids with a lower frequency have ______ lead strips.
thicker
110
Lead content is greatest in a grid that has a ______ grid ratio and a ______ grid frequency.
high | low
111
In a linear grid, tube angulation is permitted only along the ______ axis of the lead strips.
long
112
Which grid pattern consists of lead strips running in two directions and does not permit tube angulation?
Criss-cross (cross-hatched) grid
113
Linear grid vs parallel grid
A linear grid has lead strips running in one direction and allows tube angulation only along their long axis, whereas a parallel grid does not match beam divergence like a focused grid and is best employed at long source-to-image distances (SIDs)
114
A criss-cross grid is made by sandwiching two linear grids whose strips run ______ to each other.
perpendicular
115
Which grid type has lead strips angled to match the divergence of the primary x-ray beam?
- Focused grid
- Parallel grid
- Linear grid
- Criss-cross grid
116
What is the term for the distance from the face of a focused grid to the convergence line of the lead strips?
Grid radius (focal distance)
117
Parallel grids are best employed at ______ source-to-image distances (SIDs).
long
118
What is the difference between a reciprocating and an oscillating grid mechanism?
A reciprocating grid is driven back and forth 2 to 3 cm by a motor, whereas an oscillating grid is pulled to one side by an electromagnet and released.
119
What is the term for the undesired absorption of primary radiation when the primary beam is angled into the lead strips?
Grid cutoff
120
What is the formula for the Grid Conversion Factor (GCF)?
GCF = mAs with the grid / mAs without the grid
121
How does using a grid with a higher cleanup ability affect patient dose?
It increases patient dose, because technical factors such as mAs must be increased
122
What two criteria established by the ICRU measure a grid's performance?
Selectivity and contrast improvement ability (K)
123
ICRU means?
International Commission on Radiation Units and Measurements
124
What is the formula for grid selectivity?
Selectivity = % primary radiation transmitted / % scatter radiation transmitted
125
What is contrast improvement ability (K)?
A measure of grid performance equal to radiographic contrast with the grid divided by radiographic contrast without the grid
126
A contrast improvement factor of K = 1 indicates that ______.
no improvement in contrast has been made
127
Which grid error occurs when the tube is angled across the long axis of the grid strips, causing overall underexposure?
- Off-level grid error
- Off-center grid error
- Upside-down focused grid
- Moire effect
128
Which grid error occurs when the central ray is not aligned to the center of the grid?
Off-center grid error
129
What radiographic appearance results from an off-level or off-center grid error?
A uniform decrease in exposure across the entire image
130
What appears on the radiograph when a focused grid is placed upside down?
Severe peripheral grid cutoff (underexposure at the edges)
131
The ______ effect is a digital imaging grid error that occurs when grid lines are scanned parallel to the laser scan lines in the image reader.
Moiré
132
What is the primary disadvantage of using the air gap technique instead of a grid?
Loss of recorded detail (spatial resolution) due to increased object-to-image receptor distance (OID)
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