1
Q
4 requirements necessary for production of xrays
A
- source of free electrons
- acceleration of electrons
- focusing of electrons
- deceleration of electrons
2
Q
Thermionic emission
A
Heating of the filament to the point that electrons boil off its surface
3
Q
What determines the amount of current that will be sent to the filament
A
mA settings
4
Q
Where does current come from
A
From the step down transformer to produce thermionic emission
5
Q
Acceleration of electrons
A
High electrical potential (voltage) is applied to the cathode end of the xray tube
6
Q
How is x-radiation produced
A
By high speed electrons bombarding target area or anode
7
Q
What is target area made out of
A
Tungsten w/ rhenium
8
Q
Focusing cup
A
Surrounds the filament and maintains a concentrated stream of electrons from filament to target area on anode
9
Q
What is the focusing cup made out of
A
Molybdenum or nickel
10
Q
What are two components of the cathode
A
Focusing cup and filament wire
11
Q
What is the filament wire made up of
A
Tungsten w/ thorium
12
Q
Deceleration of electrons
A
- high speed electrons will strike tungsten target on anode and will get converted to xray
- produce heat 99%
- 1% converted to xray
13
Q
Atom
A
Smallest subdivision of an element that maintains all the physical and chemical properties of an element
14
Q
What is the atomic mass of protons and neutrons
A
1
15
Q
Atomic number (Z)
A
of protons in nucleus
16
Q
Atomic mass (A)
A
Sum of protons and neutrons in nucleus
17
Q
Electrons
A
Negatively charged and have no mass
18
Q
Electrons held in their orbital shells by what
A
Electron binding energy (K shell= 69.53/70)
19
Q
Tungsten atom Z #
A
74
20
Q
Valence number
A
- Number of electrons in last orbital shell (outermost max shell=8)
- 2n^2
21
Q
Ionization
A
- When an energy source contains sufficient energy to remove an electron from one of the orbital shells
- previously uncharged atom will now have an electrical charge (positive)
22
Q
What is the Brem photon energy equal to
A
- The amount of energy lost by the projectile electron
- greater the direction change, greater energy loss, and brem xray photon will have more energy
- anything before 70 is all Brems
23
Q
Characteristic (k-char.) radiation
A
High speed electrons interact with tungsten target atom by ejecting an inner shell electron and ionizing atom
24
Q
Process of filling the k-shell vacancy results in what
A
The emission of a characteristic xray photon
25
In k-char, energy of the xray photon is equal to what
Difference between the EBE of the orbital shell that contained the vacancy (k shell) and the orbital shell that filler the vacancy (70 minus L, M, N..)
26
When producing K char rad, what must the tube potential be
70
27
As a tech, when selecting 60 kV, how much of kV will be Brem?
100?
28
X-radiation if one form of what
Electromagnetic energy on the electromagnetic spectrum
29
Photon
Smallest bit of electromagnetic energy
30
Particulate radiation
Beta and alpha radiation- travel in particles
31
Frequency
Rate of rise and fall (oscillation) of the electromagnetic photon and is measured in hertz (Hz)
32
Wavelength
Distance between two successive peaks of an electromagnetic photon
33
Frequent and wavelength
Inversely related
34
Xray moves at speed of light
3 x 10^8 meters/sec (186,000 miles/sec)
35
Quality of beam
kVp, energy, penetrability, wavelength
36
Quantity of beam
- mAs, rate of exposure, intensity, pt dose
- measured in roentgen, mR, or mGy
- xray quantity directly proportional to mAs
37
xray quantity indirectly related to what
Filtration and distance
38
Technical factors that affect half value layer
kVp and filtration
39
What is the difference between xray and gamma
The source of radiation
40
Inverse square law
Used to calculate a change in beam intensity with changes in SID
41
Direct square law
Determine the change in mAs required if radiographic density is to remain constant and SID is changed
42
Image forming beam
Remnant xray beam
43
Attenuation
Progressive absorption of xray beam as it passes through matter
44
If distance gets doubled or cut in half, intensity will change how much
By factor of 4
| (Double= 4 x less) ?
45
Properties of xrays
1) travel in wave form
2) highly penetrating visible rays that are a form of electromagnetic radiation
3) heterogeneous (0-60) and polyenergetic
4) travel in straight lines
5) can ionize matter and release small amounts of energy upon passing through matter
6) can produce chemical and biological changes in matter through ionization and excitation of atoms and molecules
7) produce secondary and scattered radiation
8) travel at speed of light
9) no mass or electrical charge
10) high frequency and short wavelength- interact with matter on atomic and molecular level
46
Compton scatter
- Partial absorption of the incident xray photon
| - incident xray photon interacts with an outer shell electron of a target atom and removes the electron
47
Compton interaction can be
- forward scattering: degradation of image contrast
- side scatter: result in occupational exposure
- backscatter: resulting in pt exposure
48
Biggest source of scatter
Patient
49
During fluoro, what is a techs largest source of occupational exposure
Compton scatter
50
What is the maximum number of times an xray photon can be scattered before it loses all of its energy
2 times
51
During fluoro, 90 degree angle, right angle, perpendicular
Least amount of radiation (or close to 90)
52
During fluoro, 180 degree, head of foot
Most scatter
53
Photoelectric absorption
- total absorption of xray photon
- incident xray photon interacts with an inner K shell electron and remove electron
- all of remaining energy of incident photon is transferred to the ejected electron (photoelectron)
54
What is the primary source of patient radiation exposure
Photoelectric interaction
55
Every time an xray photon gets scattered, it will leave with how much of its original intensity
1/1000- 0.001
| Or 0.1%
56
Coherent (classical) scatter
- incident xray photon interacts with a target atom and excited the atom
- no orbital electrons and ejected, no ionization takes place
- no energy is exchanged b/w incident photon and target atom
- incident xray photon undergoes a change in direction with no energy loss
57
Contribute to patient skin exposure or degeneration of image quality
Classical coherent scattering
58
Absorbed dose
Gray (Gy) 0.01 multiplication factor
1 Gy= 100 rads
1 cGy= 1 rad
59
Dose equivalent
Sievert (Sv) 0.01 multiplication factor
| 1 Sv= 100 rems or 1 cSv= 1 rem
60
Quality factor of xrays, gamma rays, and beta particles
1
61
Quality factor of protons
5
62
Quality factor of fast neutrons
10
63
Quality factor of alpha particles
20
64
Exposure
Coulombs per kilogram of air (C/kg)
| 2.58 x 10^ -4
65
Effective dose
Sv
66
Air kerma
Gy
67
Curie (Ci)
Measurement of radioactivity
Standard equivalent: Becquerel (Bq)
3.7 x 10^10
68
Which trimester is the least resistant?
First
69
Non-threshold dose effect relationship
- any given dose of rad will yield some measurable effects
| - no amount of radiation, regardless of dose, is safe
70
Threshold dose effect relationship
Some amount of radiation is required before a measurable effect can be detected
71
Law of Bergonié and tribondeau
Cell radio sensitivity is affected by
Mitotic activity: radio sensitivity increases with increased maturity
Maturity
Degree of specificity
72
Linear energy transfer: LET
- the rate of energy deposited per unit track length through an absorber
- amount of radiation that is transferred to the body as the xray beam travels through the body
- diagnostic xrays are considered low LET radiation
73
What happens to the quality factor for a given form of radiation as LET increases
It will increase
74
Oxygen effect
The ability of aerobic conditions to enhance the effectiveness of radiation
75
Increasing the oxygenation of a cell does what to the cell’s sensitivity to radiation?
Increases it
76
Oxygen enhancement ratio (OER)
- numeric description of the oxygen effect
| - the effectiveness of radiation in an aerobic environment is 3x greater than an anoxic environment
77
Relative biologic effectiveness (RBE)
-ability to produce biologic damage
78
Increasing the LET of radiation will result in what effect to biologic damage?
- Increase in biologic damage
| - LET and RBE and directly related
79
What is the most radiosensitive cell in the body?
Lymphocytes
80
Least sensitive to greatest sensitive
1) nerve
2) muscle
3) stem/intestinal crypt
4) lymphocytes
81
Cell survival and recovery (LD 50)
Lethal dose to 50% of pop. over ___ number of days
82
Factors influencing survival
LET and oxygen
83
Fractionation
- Equal doses of radiation that are delivered with time interval separations
- offers cell the greatest ability to survive and recover from radiation exposure
84
Protraction
Radiation dose that is delivered continuously but at a lower dose rate
85
Radiolysis
- Radiation interaction with water
- photon-water interaction results in ionization of water (HOH+ & e-)
- positive water molecule can split into a free radical (highly reactive and unstable substance)
86
Free radicals can combine to form toxic substances such as
hydrogen peroxide (H2O2)
87
Radiation in directly or indirectly the cause of biologic damage?
Indirectly
-majority of rad damage of body is caused by the indirect action of radiation interacting with water due to large amount of water in cell
88
Interphase death
- Apoptosis
- cell dies without attempting to divide
- Amount of rad to cause interphase death depends on radio sensitivity of cell
89
Metaphase
Cell most sensitive
90
Mitosis
Cell division
91
Meiosis
Germ (sex) cell division
92
Mitotic delay
Mitotic activity resumes after a short delay
| Usually 10 mGy or 0.01 Gy
93
Reproductive failure
Cell does not die as a result of radiation exposure but loses the ability to procreate
1000 to 10,000 mGy
94
Somatic effects
Those limited to the exposed population (individual cell of body)
95
Short term somatic effects
- occur soon after exposure seconds, minutes, hrs, days, weeks
- epilation, nausea, vomiting, erythema, fatigue, epistaxis
96
Long term somatic effects
- occur years after exposure
- development of disease or the causes of mortality of an exposed pop are the same as unexposed pop
- cancer (leukemia) cataractogenesis, life span shortening
97
Acute (short term) exposure
- large dose over short time
| - more life span shortening than chronic rad exposure
98
Chronic (long term) exposure
- rad in small increments over long period of time (ex. occupational)
- 1 rad (0.01 Gy or 10 mGy)= 10 days of life span shortening
99
What is the most radiosensitive part of eye
Lens
100
What are the results of opacity in the lens of the eye due to radiation exposure?
Cataracts
101
Eye
Nonlinear, threshold dose (non-stochastic)
102
Thyroid
Linear, non threshold dose (stochastic)
103
Breast
Linear, non threshold dose (stochastic)
104
Bone marrow
Linear, threshold dose response
105
Skin
Threshold (non-stochastic)
106
Female gonad
- immature ova very radiosensitive
| - mature ova not radiosensitive and can carry damaged chromosomes
107
Male gonad
- doses from 500-600 rads (5-6 Gy) can cause permanent sterility
- doses of 10 rads (100 mGy) can result in genetic mutations
108
Carcinogenesis
- long term somatic effect of radiation
- cancer formation long after exposure to radiation
- where cancer may occur depends on rad dose and organ sensitivity
109
Local somatic effects
Effects that are limited to the exposed individual and the specific area of exposure only
110
General somatic effects
Effects that are limited to the exposed individual but the response to the radiation effects the entire body, not just the site of exposure
111
Stochastic (probabilistic) effects
- all or nothing effects (non threshold)
- probability of effects increase in frequency with increasing doses of radiation
- magnitude of response does not increase with increasing dose
112
Non stochastic (deterministic) effects
- existence of threshold
- occurs at higher radiation doses
- biologic effects increase in frequency and magnitude with increases in rad dose
- ex: cataracts, erythema, fibrosis, and hematopoietic damage
113
Ten day rule
Rad exposure to female in child bearing age should be limited to 10 days following the onset of menstruation
114
Why are pediatric pts more radiosensitive?
Cells reproduce frequently
115
Components of electromagnetic spectrum
- visible light
- ultraviolet light
- gamma radiation
- radio waves
116
Becquerel (unit of radioactivity) describes what
Disintegrations per second
117
Air kerma (unit of exposure) measures what
Quantity of ionization in air
118
Gray measures what
Energy deposited in any material
119
Sievert measures what
Dose to biologic material
120
Effective dose formula
```
EfD= equivalent dose (EqD) x Wt (tissue weighing factor)
EfD= radiation weighting factor x tissue weighting factor x absorbed dose
```
121
Effective dose refers to what
Whole body dose
122
What produces a potential difference within the xray tube during an exposure?
kVp
ARRT
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