Ch 1-3 Flashcards
(181 cards)
1
Q
Who discovered x-rays and when?
A
Wilhelm Conrad Roentgen on November 8, 1895
2
Q
X-rays are a form of what kind of radiation?
A
Electromagnetic/ionizing
3
Q
Radiation that produces positively and negatively charged particles (ions) when passing through matter; the production of these ions is the event that may cause injury to normal biologic tissue
If electromagnetic radiation is of high enough frequency, it can transfer sufficient energy to some orbital electrons to remove them from the atoms to which they were attached; foundation of the interactions of x-rays with human tissue
Conversion of atoms to ions; makes tissues valuable for creating images but has the undesirable result of potentially producing some damage in the biologic material
Adding or losing an electron X-rays knock electrons out of orbit and change things on a cellular level that can hurt us or offspring
A
Ionization
4
Q
6 consequences of ionization in human cells
A
- Creation of unstable atoms
- Production of free electrons (Compton scatter produces recoil electrons)
- Production of low energy x-ray photons
- Creation of reactive free radicals capable of producing substances poisonous to the living cell
- Creation of new biologic molecules detrimental to the living cell
- Injury to the cell that may manifest itself as abnormal function or loss of function
5
Q
4 ways humans can safely control the use of “radiant energy”
A
- Use knowledge of radiation-induced hazards that have been gained over many years
- Employ effective methods to eliminate those hazards
- Control radiation produced from an x-ray tube and ensure safety during all medical radiation procedures
- Limiting the energy deposited in living tissue by radiation can reduce the potential for adverse effects
6
Q
2 ways radiant energy emitted from the x-ray tube in the form of waves/particles can be controlled
A
- By the selection of equipment components and devices made for this purpose
- By the selection of appropriate technical exposure factors
7
Q
4 good practices of radiologic technologists and radiologists
A
- Are educated in the safe operation of radiation-producing equipment
- Use protective devices whenever possible (shield)
- Follow established procedures (ex: PA or AP, greater distance = less radiation)
- Select technical exposure factors that significantly reduce radiation exposure to patients and to themselves (low mAs, high kV)
8
Q
What is the benefit to the good practices radiologic technologists and radiologists follow?
A
Minimizing the possibility of causing damage to healthy biologic tissue
9
Q
Effective measures employed by radiation workers to safeguard patients, personnel and the general public from unnecessary exposure to ionizing radiation
A
Radiation protection
10
Q
Any radiation exposure that does not benefit a person in terms of diagnostic information obtained for the clinical management or any exposure that does not enhance the quality of the study
A
Unnecessary radiation exposure
11
Q
What is an example of unnecessary radiation?
A
Repeat exposures
12
Q
3 things effective protective measures take into consideration
A
- Both human and environmental physical determinants
- Technical elements
- Procedural factors
13
Q
Internation System (SI) Units of:
- Length
- Force (weight)
- Mass
- Energy
- Power
- Pressure
- Time
- Electric charge
- Temperature
- Absorbed dose
- Equivalent dose
A
- Meter (m)
- Newton (1 N = 1 kg-m/sec^2)
- Kilogram (kg)
- Joule (1 J = 1 kg-m/sec^2)
- Watt (1 W = 1 joule/sec)
- N/m^2
- Second
- Coulomb (C)
- Degrees Centigrade (Celsius), degrees Kelvin
- (Gray (Gy) (1 Gy = 1 J/kg)
- Sievert (Sv)
14
Q
English System units of:
- Length
- Force (weight)
- Mass
- Energy
- Power
- Pressure
- Time
- Electric charge
- Temperature
- Absorbed dose
A
- Foot, inch
- Pound (lb)
- Slug (an object of mass 1 slug weighs 32 lb)
- Foot-pound
- Horsepower (hp)
- lb/in^2
- Second
- Coulomb
- Degrees Fahrenheit (°F)
- No specified unit
15
Q
Damage to a living tissue of animals and humans exposed to radiation
A
Harmful biologic effects
16
Q
A patient can elect to assume the relatively small risk of exposure to ionizing radiation to obtain essential diagnostic medical information when illness or injury occurs when a specific imaging procedure for health screening purposes is prudent
Ex: mammography
A
Benefit versus risk
17
Q
The degree to which the diagnostic study accurately reveals the presence or absence of disease in the patient
Maximized when essential images are produced under recommended radiation protection guidelines
Provides the basis for determining whether an imaging procedure or practice is justified
A
Diagnostic efficacy
18
Q
Who carries the responsibility for determining the medical necessity of a procedure for the patient?
A
The referring physician accepts basic responsibility for protecting the patient from radiation exposure that is not useful and relies on qualified imaging personnel who accept a portion of the responsibility for the patient’s welfare by providing the high-quality imaging services
19
Q
Who shares with the referring physician in keeping the patient’s medical radiation exposure at the lowest possible level?
A
The radiographer and participating radiologist help ensure both occupational and nonoccupational doses remain well below allowable level (the upper boundary doses of ionizing radiation for which there is a negligible risk of bodily injury or genetic damage)
20
Q
3 ways occupational and nonoccupational doses can be kept well below the maximum allowable levels
A
- Use the smallest radiation exposure that will produce useful images
- Produce optimal images with the first exposure
- Avoid repeat examinations made necessary by technical error or carelessness
21
Q
The intention behind these concepts of radiologic practice is to keep radiation exposure and consequent dose to the lowest possible level
Because no dose limits have been established for the amount of radiation that patients may receive for individual imaging procedures, this philosophy should be established and maintained and must show that we have considered reasonable actions that will reduce doses to patients and personnel below required limits
Radiation-induced cancer does not have a fixed threshold (a dose level below which individuals would have no chance of developing this disease); therefore, because it appears that no safe dose levels exist for radiation-induced malignant disease, radiation exposure should be kept low for all medical imaging procedures and this should serve as a guide to radiographers and radiologists for the selection of technical exposure factors
A
As low as reasonably achievable (ALARA)
Optimization for radiation protection (ORP)
22
Q
3 basic principles/cardinal rules of radiation protection
A
- Time
- Distance
- Shielding
23
Q
3 principles that can be applied to reduce the exposure to the patient
A
- Reduce the amount of the x-ray “beam-on” time
- Use as much distance as warranted between the x-ray tube and the patient for the examination
- Always shield the patient with the appropriate gonadal and/or specific area shielding devices
24
Q
3 cardinal principles that can be used to minimize the occupation radiation exposure of imaging personnel
A
- Shortening the length of time spent in a room where x-radiation is produced
- Standing at the greatest distance possible from an energized x-ray beam
- Interposing a radiation-absorbent shielding material between the radiographer and the source of radiation
25
3 things the Radiation Safety Officer (RSO) is expressly charged by the hospital administration to be directly responsible for in the ALARA program
1. Execution
2. Enforcement
3. Maintenance
26
3 responsibilities of the employer for an effective radiation safety program
1. Implement and maintain an effective radiation safety program in which to execute ALARA by providing necessary resources and an appropriate environment for ALARA program
2. Make a written policy statement describing the ALARA program and identifying the commitment of management to keep all radiation exposure ALARA available to all employees in the workplace
3. Perform periodic exposure audits to determine how to lower radiation exposure in the workplace
27
2 responsibilities of the radiation worker for an effective radiation safety program
1. Be aware of rules governing the workplace
2. Perform duties consistent with ALARA
28
3 ways the radiographer can educate patients about imaging procedures to help ensure the highest quality of service
1. Use appropriate and effective communication
2. Answer questions about the potential risk of radiation exposure honestly
3. Inform patients of what needs to be done, if anything, as a follow-up to their examination
29
The probability of injury, ailment, or death resulting from an activity
Risk (general)
30
The possibility of inducing a radiogenic cancer or genetic defect after irradiation
Risk (medical with reference to the radiation sciences)
31
Perception that the potential benefit to be obtained is greater than the risk involved
Willingness to accept risk
32
A method that can be used to improve understanding and reduce fear and anxiety for the patient that compares the amount of radiation received over a given period of time based on an annual US population exposure of approximately 3 millisieverts per year
Background equivalent radiation time (BERT)
33
3 advantages of the BERT method when it is used appropriately
1. BERT does not imply radiation risk; it is simply a means for comparison
2. BERT emphasizes that radiation is an innate part of our environment
3. The answer given in terms of BERT is easy for the patient to comprehend
34
A subunit of the sievert (Sv) equal to 1/1000 of a sievert
Millisievert (mSv)
35
International System of Units (SI) unit of measure for the radiation quantity "equivalent dose"
Sievert (Sv)
36
A two phase radiation dose awareness and dose reduction program for patients through the process of education for these individuals, for the community, for health care workers employed in the medical imaging profession, and for physicians
Tools for Radiation Awareness and Community Education (TRACE) Program
37
2 phases of the TRACE program
1. Formulating new policies and procedures to promote radiation safety and the implementation of patient and community education
2. Technological enhancements
38
4 main components (technologic enhancements) of the TRACE program
1. Embedded software capable of recording and reporting dose
2. Timely notification of the patient and the referring physician when the radiation dose is greater than 3 Gy
3. The substantial lowering of computed tomography (CT) doses
4. Alterations to existing protocols
39
Can lead to a reduction in dose for the patient
Radiation dose to the patient for individual procedures, such as those involving general fluoroscopy, CT, and interventional procedures, needs to be dictated into every radiologic report
The benefit to the referring physician having direct access to a patient's radiation dose history is the option of knowing whether ordering an additional radiologic procedure is advisable
Standardized dose reporting
40
In what form is radiant energy emitted from the tube?
Waves or particles
41
2 sources of radiation (both contribute a percentage of the total amount of radiation that humans receive during their lifetime)
1. Natural
2. Manmade
42
Radiation that is always present in the environment
Natural
43
Radiation created by humans for specific purposes
Manmade
44
The ability to do work- that is, to move an object against resistance
Energy
45
Kinetic energy that passes from one location to another and can have many manifestations (many types of this exist)
Radiation
46
The full range of frequencies and wavelengths of electromagnetic waves
Each frequency within this has a characteristic wavelength and energy Higher frequencies are associated with shorter wavelengths and higher energies; therefore, as the wavelength ranges from largest to smallest, frequencies and energy cover the corresponding smallest to largest ranges
Electromagnetic spectrum
47
The number of crests of a wave that move past a given point in a given unit of time; hertz (Hz), cycles per second
Frequency
48
The distance between successive crests of a wave (meters)
Wavelength
49
A unit of energy equal to the quantity of kinetic energy an electron acquires as it moves through a potential difference of 1 volt
Electron volts (eV)
50
2 examples of different types of radiation
1. Mechanical vibrations of materials
2. The electromagnetic wave (radiation)
51
Such mechanical vibrations can travel through the air or other materials to interact with structures in the human ear and produce the sensation sound
Ultrasound is the mechanical vibration of a material in which the rate of vibration does not stimulate the human ear sensors and therefore is beyond the range of human hearing
Mechanical vibrations of materials
52
Electric and magnetic fields fluctuate rapidly as they travel through space
Characterized by their frequency (Hz) and wavelength (meters)
Electromagnetic waves (radiation)
53
This form of radiation can travel through space in the form of a wave but can interact with matter as a particle of energy
Dual nature
Photons moving in waves and interactive with matter
Wave-particle duality
54
Bundles of energy
Photons
55
7 types of electromagnetic waves (longer wavelength, lower frequency, lower energy to shorter wavelength, higher frequency, higher energy)
1. Radio waves
2. Microwaves
3. Infrared
4. Visible light
5. Ultraviolet (low and high energy)
6. X-rays
7. Gamma rays
56
2 parts the electromagnetic spectrum can be divided into
1. Ionizing
2. Nonionizing
57
3 forms of ionizing radiation
1. X-rays
2. Gamma rays
3. High-energy ultraviolet radiation (energy higher than10 eV)
58
5 forms of non-ionizing radiation
1. Low-energy ultraviolet
2. Visible light
3. Infrared rays
4. Microwaves
5. Radio waves
59
The amount of energy transferred to electrons by ionizing radiation
Radiation dose
60
Does not have the sufficient kinetic energy to eject electrons from the atom
Non-ionizing radiation
61
A radiation quantity used for radiation protection purposes when a person receives exposure from various types of ionizing radiation
Attempts to specify numerically the differences in transferred energy and therefore biologic harm produced by different types of radiation
Enables the calculation of effective dose (EfD)
SI unit: Sievert
Correlates the absorbed dose in biologic tissue with the type of energy of the radiation to which the human has been subjected (x-rays, gamma rays, etc.), applies only to ionizing types of radiation
Equivalent dose (EqD)
62
4 forms of particulate radiation
1. Alpha particles
2. Beta particles
3. Neutrons
4. Protons
63
Subatomic particles that are ejected from atoms at very high speeds
They possess sufficient kinetic energy to be capable of causing ionization by direct atomic collision
No ionization occurs when the subatomic particles are at rest
Particulate radiation
64
What is the weighting factor for x-radiation?
1
65
Emitted from nuclei of very heavy elements such as uranium and plutonium during the process of radioactive decay
Each contain two protons and two neutrons
Are simply helium nuclei (e.i., helium atoms minus their electrons)
Have a large mass (approximately 4 times the mass of a hydrogen atom) and a positive charge twice that of an electron
Weighting factor is 20 times higher than x-rays
Less penetrating than beta particles (fast electrons)
They lose energy quickly as they travel a short distance in biologic matter (i.e., into the superficial layers of the skin), so they are considered virtually harmless as an external source of radiation (a piece of ordinary paper can absorb them or function as a shield)
Can be very damaging as an internal source of radiation if emitted from a radioisotope deposited in the body (ex: in the lungs, they can be absorbed in the relatively radiosensitive epithelial tissue and are very damaging to that tissue)
Alpha particles/rays
66
Identical to high speed electrons except for their origin (emitted from within the nucleus of radioactive atoms that relieve their instability through the process of beta decay)
8,000 times lighter than alpha particles and have only one unit of electrical charge (-1) as compared with the alpha's two units of electrical charge (+2); will not interact as strongly with their surroundings as alpha particles and are therefore capable of penetrating biologic matter to a greater depth than alpha particles with far less ionization along their paths
With a lesser probability of interaction: can penetrate matter more deeply and therefore cannot be stopped by an ordinary piece of paper like an external alpha particle
For energies less than 2 millielectron volts, either a 1-cm thick block of wood or a 1-mm thick lead shield would be sufficient for absorption
Beta particles
67
Produced in a radiation oncology treatment machine (linear accelerator)
Used to treat superficial skin lesions in small areas and deliver radiation boost treatments to breast tumors at tissue depths typically not exceeding 5-6 cm
Require either millimeters of lead or multicentimeter thick slabs of wood to absorb them
High-speed electrons that are not beta radiation
68
Positively charged components of an atom
Have a relatively small mass that, however, exceeds the mass of an electron by a factor of 2800
Decide the type of element
Protons
69
Number of the protons in the nucleus of an atom constitutes this number
Atomic/Z number
70
The electrically neutral components of an atom and have approximately the same mass as a proton
Neutrons
71
Two atoms that have the same number of protons but a different number of neutrons in their nuclei (same element)
Isotopes
72
If one of these combinations of Z protons and so many neutrons leads to an unstable nucleus, gives off radiation
Radioisotopes
73
Wavelength formula
λ = c / v
λ = wavelength (m)
c = speed of light (3 x 10^8 m/sec)
v = frequency (Hz)
74
Takes into account the dose for all types of ionizing radiation (ex: alpha, beta, gamma, x-ray) to various irradiated organs or tissues in the human body (ex: skin, gonadal tissue, thyroid)
By including specific weighting factors for each of those body parts mentioned, this takes into account the chance or risk that each of those body parts will develop a radiation-induced cancer (somatic); in the case of the reproductive organs, the risk of genetic damage is considered
Because this includes all of the organ weighting factors, it represents the uniform whole-body dose that would give an equivalent biologic response or chance of cancer
Effective dose (EfD)
75
Produced when ionizing radiation penetrates body tissue and ejects electrons from the atoms composing the tissues
Biologic damage
76
Result of destructive radiation at the atomic level
Molecular change
77
Caused by molecular changes which leads to abnormal cell function or even entire loss of cell function
If excessive cellular damage occurs, the living organism will have a significant possibility of exhibiting genetic or somatic changes such as mutations, cataracts, leukemia, etc.
Cellular damage
78
Changes in the blood count that results from non-negligible exposure to ionizing radiation
Organic damage
79
_Occupational exposures_
Effective dose limits: *annual* and *cumulative*
Dose equivalent annual limits for tissues and organs: *lens of eye* and *skin, hands, and feet*
* Annual*: 50 mSv (5 rem)
* Cumulative*: 10 mSv x age (1 rem x age)
* Lens of eye*: 150 mSv (15 rem)
* Skin, hands, and feet*: 500 mSv (50 rem)
80
_Public exposures (annual)_
Effective dose limit: *continuous or frequent exposure* and *infrequent exposure*
Effective dose limits for tissues and organs: *lens of eye* and *skin, hands, and feet*
Continuous or frequent exposure: 1 mSv (0.1 rem)
Infrequent exposure: 5 mSv (0.5 rem)
Lens of eye: 15 mSv (1.5 rem)
Skin, hands, and feet: 50 mSv (5 rem)
81
Embryo-fetus exposures (monthly): equivalent dose limit
0.5 mSv (0.05 rem)
82
_Education and training exposures (annual)_
*Effective dose limit*
Dose equivalent limit for tissues and organs: *lens of eye* and *skin, hands, and feet*
Effective dose limit: 1 mSv (0.1 rem)
Lens of eye: 15 mSv (1.5 rem)
Skin, hands, and feet: 50 mSv (5 rem)
83
Radiation EqD (Sv) and subsequent biologic effects resulting from acute whole-body exposures (radiation exposures delivered to the entire body over a time period of less than a few hours)
* 0.25
* 1.5
* 2.0
* 2.5
* 3.0
* 6.0
* 0.25 = blood changes (e.g., measurable hematologic depression, decreases in the number of lymphocytes present in the circulating blood)
* 1.5 = nausea, diarrhea
* 2.0 = erythema (diffuse redness over an area of skin after irradiation)
* 2.5 = if dose is to gonads, temporary sterility
* 3.0 = 50% chance of death; lethal dose for 50% of population over 30 days (LD 50/30)
* 6.0 = death
84
2 sources of ionizing radiation that humans are exposed to
1. Natural
2. Manmade
85
Environmental sources of ionizing radiation
Natural (background) radiation
86
3 components of natural radiation
* Terrestrial radiation (e.g., radon, thoron)
* Cosmic radiation (solar and galactic, intensity increases with altitude)
* Internal radiation from radioactive atoms (radionuclides)
87
Earth gives off this terrestrial radiation; 37% of natural background radiation exposure comes from this
Largest contributor to background radiation
In homes: crawl spaces, floor drains, sump pumps, and porous cement block foundations
The Environmental Protection Agency (EPA) considers this to be the second leading cause of lung cancer in the US
Radon
88
Type of natural radiation in foods or inhaled particles in air
Main radioactive nuclide in body is Potassium-40 (40K)
Internal radiation from radioactive atoms (radionuclides)
89
7 forms of manmade radiation
1. Consumer products containing radioactive material
2. Air travel
3. Nuclear fuel for generation of power
4. Atmospheric fallout from nuclear weapons testing
5. Nuclear power plant accidents (TMI-2 and Chernobyl)
6. Nuclear power plant accidents as a consequence of natural disasters (Fukushima Daiichi)
7. Medical radiation
90
How much radiation did manmade radiation contribute to the average annual radiation exposure of the US population?
3.2 mSv
Medical radiographic procedures: 0.6 mSv
Nuclear medicine imaging: 0.7 mSv
CT scanning: 1.5 mSv
Interventional procedures: 0.4
Other manmade radiation sources: 0.1 mSv
91
Results from the use of diagnostic x-ray machines and radiopharmaceuticals in medicine
Medical radiation
92
2 largest sources of artificial radiation
1. Diagnostic medical x-ray (CT, interventional, conventional radiography or fluoroscopy)
2. Nuclear medicine procedures
93
4 ways to indicate the amount of radiation received by a patient from diagnostic x-ray procedures
1. Entrance skin exposures (including skin and glandular dose; greatest amount of radiation and why you don't want SOD to be small)
2. Bone marrow dose
3. Gonadal dose
4. Fetal dose in pregnant women
94
The current National Council on Radiation Protection and Measurements (NCRP) report that deals with medical radiation exposure of the US population (released March 3, 2009) reflects usage patterns through 2006
The number of medical procedures involving ionizing radiation has increased dramatically since the 1980's when the previous NCRP report (No. 93) was published
Resulted from increased use of imaging modalities such as CT and cardiac nuclear medicine examinations
Ionizing radiation exposure of the population of the US "Estimates the total amount of radiation delivered in 2006 and compares those amounts to the estimates published in 1987"
NCRP Report No. 160
95
What percentage of total background radiation does medical use now make up?
48%
96
2 ways to reduce the possibility of occurrence of genetic damage in future generations
1. Through efficient application of radiation protection measures on the part of the radiographer, radiologist, and physicians performing interventional procedures requiring the use of fluoroscopy
2. By limiting the widespread substitution of unnecessary CT scans by many emergency departments for convenience in place of using other, less costly diagnostic procedures
97
4 ways to decrease patient dose
1. Increase distance
2. Shield
3. Beam restriction
4. High kVp, low mAs
98
2 technical factors
1. Peak kilovoltage (kVp)
2. Milliampere-seconds (mAs)
99
Controls the quality/penetrating power of the photons in the x-ray beam, and to some degree also affects the quantity or number of photons in the x-ray beam
Highest energy level of photons in the x-ray beam, determines what kind of interaction will occur (high or low energy)
Although all photons in a diagnostic x-ray beam don't have the same energy, the most energetic photons in the beam can have no more energy than the electrons that bombard the target
Peak kilovoltage (kVp)
100
Controls the quantity of radiation that is directed toward a patient during a selected x-ray exposure
Milliampere-seconds (mAs)
mA x s = mAs
101
2 things x-rays (carriers of manmade electromagnetic energy) can do if they enter a material such as human tissue
1. Interact with the atoms of the biologic material in the patient and cause problems
2. Pass through without interaction (a lot of scatter will have enough energy to reach the IR and will fog/gray the image)
102
If an interaction occurs, electromagnetic energy is transferred from the x-rays to the atoms of the patient's biologic material
A total loss of radiation energy
Absorption
103
The amount of energy absorbed per unit mass
Absorbed dose (D)
104
3 factors affecting absorption
1. Atomic number
2. How tightly bound the atom's electrons are
3. Thickness of part (ex: femur vs finger)
105
2 benefits for the radiographer when the patient's dose is minimal
Less radiation is scattered from the patient
Reduces the occupational hazard for the radiographer
106
What reaction is the biggest concern for a technologist (occupational)?
Compton reactions produce scatter
107
How is a diagnostic x-ray beam produced?
A diagnostic x-ray beam is produced when a stream of high speed electrons bombards a positively charged target in a highly evacuated glass tube
108
What is the anode (target) made of?
Tungsten/tungsten rhenium alloy
109
2 reasons tungsten and tungsten rhenium alloy are used as target materials
1. High melting points
2. High atomic numbers (tungsten [74] and rhenium [75])
110
Why does the anode (target) need to have a high melting point?
99% of x-ray production is heat
111
Particles associate with electromagnetic radiation that have neither mass nor electric charge and travel at the speed of light
X-ray photons
112
Built-in filtration that results from the composition of the tube and housing
Inherent filtration
113
3 examples of inherent filtration
* The thickness of the glass envelope of the tube
* The dielectric oil that surrounds the tube
* The glass window of the housing
114
Any filtration that occurs outside the tube and housing and before the image receptor
Added filtration
115
3 examples of added filtration
1. A certain thickness of added aluminum in the collimator
2. The collimator device
3. The mirror is designed to reflect the collimator light to simulate the primary beam field size for positioning purpose
116
How does the glass window act as a filter?
As the electrons interact with the atoms of the target, x-ray photons emerge from the target with a broad range 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
117
How does aluminum in the collimator act as a filter?
A certain thickness of added aluminum is placed within the collimator assembly to intercept the emerging x-rays before they reach the patient
This aluminum "hardens" the x-ray beam (i.e., raises its effective energy) by removing low-energy components that would serve only to increase patient dose
118
Removes low-energy x-ray photons, thereby decreasing patient dose; equal to the sum of inherent and added filtration that does not include any compound or compensating filters that may be added later
The percentage of photons attenuated decreases as photon energy increases, even when filtration is increased
Total filtration (permanent)
119
What is the amount of total filtration at 70 kVp?`
2.5 mm aluminum (Al) equivalence
120
The combination of the x-ray tube glass wall and the added aluminum placed within the collimator
Permanent inherent filtration
121
The x-ray photon beam that emerges from the x-ray tube (source) and is directed toward the image receptor before they run into anything
Primary radiation/photons
122
Do all photons in a diagnostic x-ray beam have the same energy?
No, the most energetic photons in the beam can have no more energy than the electrons that bombard the target
123
In what terms is the energy of the electrons inside the x-ray tube expressed in?
Electrical voltage applied across the tube
In diagnostic radiology the energy of the electrons is expressed in volts or kilovolts (kV)
Because the voltage across the tube fluctuates, it is usually expressed in kVp
124
For a typical diagnostic x-ray unit, the energy of the average photon in the x-ray beam is about what the energy of the most energetic photon?
One third, 33%
125
If an electron is drawn across an electrical potential of 1 volt, it has acquired energy of 1 electron volt (eV)
00 kVp means that the electrons bombarding the target have maximum energy of 100,000 eV or 100 keV
Therefore, a 100-kVp beam contains photons having energies of 100 keV or less with an average energy of what?
33 keV
126
The reduction in the number of primary photons in the x-ray beam through absorption and scatter as a beam passes through the patient in its path (matter)
Any process decreasing the intensity of the primary photon beam that was directed toward a destination
Attenuation
127
A change of direction that may also involve a partial loss of radiation energy
Scatter
128
Some primary photons will traverse the patient without interacting and reach the radiographic image receptor (IR)
Direct transmission
129
3 types of IR's
1. Phosphor plate
2. Digital radiography receptor
3. Radiographic film
130
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 IR
Indirect transmission
131
Formed only when direct transmission x-ray photons reach the IR In clinical situations, scattered photons do reach the IR and degrade image quality (fog)
Optimal x-ray image
132
2 most common methods used to limit the effects of indirectly transmitted x-ray photons
1. Air gaps
2. Radiographic grids
133
What is the result of the IR covering a broad enough area in conventional or digital radiography that x-ray photons are scattered from one part of the beam may still strike the IR in another area?
The radiographic image is formed from both directly transmitted x-ray photons and indirectly transmitted (i.e., scattered) x-ray photons
134
Photons that pass through the patient being radiographed and reach the IR
Exit/image-formation photons
135
Photon's path was bent, but not so much that the photon missed its target
Because it reaches the IR it is part of the exit/image-formation radiation but its path was bent
Scattered photons in this category have essentially the same energy as the incident photons
Degrades the appearance of a completed radiographic image by blurring the sharp outlines of dense structures
Small-angle scatter
136
When obtaining a radiographic image, because many billions of small-angle scatter events occur, a greater overall exposure of the IR occurs, producing this
Undesirable additional exposure
Interferes with the radiologist's ability to distinguish different structures in the image
Radiographic fog
137
What does adequately collimating the x-ray beam do?
Reducing the amount of tissue irradiated decreases the amount of fog produced by small-angle scatter
Therefore, adequately collimating the x-ray beam is one way to reduce fog
138
What is the typical interaction that occurs at an x-ray photon energy range of 1-50 kVp?
Coherent scattering and/or photoelectric absorption
139
What is the typical interaction that occurs at an x-ray photon energy range of 60 kVp-2 meV?
Compton scattering
140
5 types of interactions between x-radiation and matter
1. Coherent
2. Photoelectric absorption
3. Compton scattering
4. Pair production
5. Photodisintegration
141
2 interactions important in diagnostic radiology
1. Compton scattering
2. Photoelectric absorption
142
3 other names for coherent scattering
1. Classical scattering
2. Elastic scattering
3. Unmodified scattering
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No ionization
A relatively simple process that results in no loss of energy as x-rays scatters
Occurs with low-energy photons
Because the wavelengths of both incident and scattered waves are the same, no net energy has been absorbed by the atom
Incoming and scattered photons have same energy; vibrates the atom and causes the photon to change direction with no loss of energy
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 vibrate momentarily
The electrons then radiate energy in the form of electromagnetic waves
These wave nondestructively combine with one another to form a scattered wave, which represents the scattered photon
Its wavelength and energy/penetrating power are the same as those as 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 (classical, elastic, or unmodified)
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2 processes of coherent scattering (classical, elastic, or unmodified)
1. Thompson
2. Rayleigh
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With what energy photons does coherent scattering (classical, elastic, or unmodified) occur?
Typically less than 10 keV
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The most important mode of interaction between x-ray photons and the atoms of the patient's body for producing useful images; have to have this to have a picture
Makes image more black and white and responsible for patient dose
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
The atom responds by ejecting the electron from its inner shell, thus creating a vacancy in that shell
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
Have to give off energy when moving into the inner shell in the form of x-rays; don't go very far and are absorbed
Initial electrons and low energy x-rays are absorbed
Photoelectric absorption
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An electron ejected from its inner shell during photoelectric absorption
Possesses kinetic energy equal to the energy of the incident photon less the binding energy of the electron shell
May interact with other atoms thereby causing excitation or ionization, until all its kinetic energy has been spent
Usually absorbed within a few micrometers of the medium through which it travels; in the human body, this energy transfer results in increased patient dose and contributes to biologic damage of tissues
Photoelectron
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An x-ray photon created by the electron transfer from one shell to another
As a result of the photoelectric interaction, a vacancy has been created in the 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 (further from the nucleus) to a more tightly held state (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
The "released" energy is carried off in the form of a photon
For a large atom such as those in lead, this energy can be in the kiloelectron volt range, whereas for the small or low atomic number atoms that are associated with the human body, the energy is on the order of 10 eV In general, ensuing vacancies in other electron shells are successively filled and associated characteristic photons are emitted until the atom achieves an electronic equilibrium
Low energy x-rays given off after a characteristic cascade
Characteristic photon/x-ray Fluorescent radiation
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2 by-products of photoelectric absorption
1. Photoelectrons (those induced by interaction with external radiation)
2. Characteristic x-ray photons (fluorescent radiation)
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When the energy of photoelectrons and characteristic x-ray photons is locally absorbed in human tissue, both the dose to the patient and the potential for biologic damage increases, decreases or remains the same?
Increases
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2 things the probability of the occurrence of photoelectric absorption depends on
1. Energy (E) of the incident x-ray photons
2. Atomic (Z) number of the atoms comprising the irradiated object
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2 reasons the probability of the occurrence of photoelectric absorption increases markedly
1. E of the incident photon decreases
2. Z of the irradiated atom increases
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How does the mass density of different body structures influence attenuation?
Even if the body structures have the same thickness, the different masses influence attenuation; more x-rays can go through soft tissue than bone because the atoms aren't as tightly bound and bone attenuates the beam more
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How does body part thickness influence attenuation?
The thickness factor is approximately linear
If two structures gave the same density and atomic number but one is twice as thick as the other, the thicker structure will absorb twice as many photons
Consequently, if soft tissue is twice as thick as the bone, the thickness difference approximately cancels out the density difference between the bone and soft tissue
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What does the ability to perceive and distinguish among different body structures in an image depend on?
The presence of differences in the amount of x-radiation these structures permit to pass through them to reach the radiographic IR
Such differences in absorption properties among different body structures makes diagnostically useful images possible
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The less a given structure attenuates radiation, the _______ will be its radiographic density on a radiographic film
Greater (less radiation get through since more gets absorbed/scattered)
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The more a given structure attenuates radiation, the _______ will be its radiographic density on a radiographic film
Lesser
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Degree of overall blackening on a radiographic film
Radiographic density
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Used in the digital environment to replace density (film)
The quantity of ionizing radiation received by a radiologic device and used to produce a viewable image
Image receptor (IR) exposure
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A monitor function that can change the lightness or darkness of the image on a display monitor; the intensity of the display monitor's light emission controlled by the radiographer
Has no affiliation with the controlling factors of density (mA and exposure time [mAs])
Not interchangeable with density
Brightness
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Sets the midpoint of the range of densities visible on the image, controls computer screen brightness
Window level
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Adjusting the window level, changing the brightness either to be increased or decreased throughout the entire range of densities
Windowing
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Increasing the window level on the displayed image (increased brightness) _______ the density on the hard copy image, whereas decreasing the window level on the monitor image (decreased brightness) _______ density on the hard copy
Decreases, increases
164
The greater the difference in the amount of photoelectric absorption, the ________ the contrast in the radiographic image will be between adjacent structures of differing atomic numbers
Greater
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As absorption increases, the potential for biologic damage \_\_\_\_\_\_\_
Increases
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How can you ensure both radiographic image quality and patient safety?
Choose the highest-energy x-ray beam that permits adequate radiographic contrast for computed, digital, or conventional radiography
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The difference between adjacent densities; one of the properties that comprise visibility of detail
Radiographic contrast
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The digital processing that produces changes in the range of density/brightness, which can be used to control contrast
Window width
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What is the diagnostic radiology energy range of photoelectric absorption?
23-150 kVp
170
Use of this may be needed to ensure visualization of tissues or structures that are similar in Z when mass density must be distinguished
Contrast media
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Consists of solutions containing elements having a higher atomic number than surrounding soft tissue (e.g., barium or iodine based) that are either ingested or injected into the tissues or structures to be visualized
The high atomic number of the contrast media (barium = 56, iodine = 53) significantly enhances the occurrence of photoelectric interaction relative to similar adjacent structures that don't have contrast media
The inner-shell electrons of barium and iodine have a binding energy that is in the energy range of the x-ray photons that is most commonly used in general-purpose radiography (30 to 40 keV) meaning photoelectric absorption of the photons in the x-ray beam is greatly increased
Structures enhanced by this contrast appear lighter than adjacent structures that didn't receive the contrast (white)
Also leads to an increase in absorbed dose in the body structures that contain it
Positive contrast medium
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Contrast mediums such as air or gas is also used for some radiologic examinations and result in areas of increased density on the completed image (black)
Negative contrast medium
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3 other names for Compton scattering
1. Incoherent scattering
2. Inelastic scattering
3. Modified scattering
174
What interaction is responsible for most of the scattered radiation produced during a radiographic procedure?
Compton (incoherent, inelastic, modified) scattering
175
An incoming x-ray photon interacts with a loosely bound outer electron of an atom of the irradiated object
On encountering the electron, the incoming x-ray photon surrenders a portion of its kinetic energy to dislodge the electron from its outer-shell orbit, thereby ionizing the biologic atom
The freed electron possesses excess kinetic energy and is capable of ionizing other atoms
It loses its kinetic energy by a series of collisions with nearby atoms and finally recombines with an atom that needs another electron; this usually occurs within a few micrometers of the site of the original interaction
The incident x-ray photon that surrendered some of its kinetic energy to free the loosely bound outer-shell electron from its orbit continues on its way but in a new direction has the potential to interact with other atoms either by the process of photoelectric absorption or scattering; it may also emerge from the patient, in which case it may contribute to degradation of the radiographic image by creating an additional, unwanted exposure (radiographic fog), or in fluoroscopy, it may exposure personnel who are present in the room to scattered radiation
onizing, occurs in the body
X-ray photon has more energy going in than when it leaves the atom
Increases as kVp increases
Produces scatter, no diagnostic value
Compton (incoherent, inelastic, modified) scattering
176
The dislodged electron resulting from Compton scattering
Compton scattered, secondary, or recoil electron
177
The incident x-ray photon that surrendered some of its kinetic energy to free the loosely bound outer-shell electron from its orbit continues on its way but in a new direction
Compton scattered photon
178
What is the probability of occurrence of Compton interaction dependent on?
Has no explicit dependence on atomic number; does no differentiate between equal amounts of bone and soft tissue and thus does not serve as a useful contrast mechanism for radiographic imaging
Instead, it shows something of an energy and density dependence
179
The more targets per unit volume, the greater is the likelihood of an interaction to occur
Density dependence
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In diagnostic radiology, the probability of occurrence of Compton scattering relative to that of the photoelectric interaction __________ as the energy of the x-ray photon increases
Increases
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Compton scattering a photoelectric absorption in tissue are equally probable at approximately what keV?
35 keV; therefore, in a 100 kVp x-ray beam when the photons have an average energy in the range of 30 to 40 keV, significant number of Compton events occur
