Safety Flashcards
4 requirements necessary for production of xrays
- source of free electrons
- acceleration of electrons
- focusing of electrons
- deceleration of electrons
Thermionic emission
Heating of the filament to the point that electrons boil off its surface
What determines the amount of current that will be sent to the filament
mA settings
Where does current come from
From the step down transformer to produce thermionic emission
Acceleration of electrons
High electrical potential (voltage) is applied to the cathode end of the xray tube
How is x-radiation produced
By high speed electrons bombarding target area or anode
What is target area made out of
Tungsten w/ rhenium
Focusing cup
Surrounds the filament and maintains a concentrated stream of electrons from filament to target area on anode
What is the focusing cup made out of
Molybdenum or nickel
What are two components of the cathode
Focusing cup and filament wire
What is the filament wire made up of
Tungsten w/ thorium
Deceleration of electrons
- high speed electrons will strike tungsten target on anode and will get converted to xray
- produce heat 99%
- 1% converted to xray
Atom
Smallest subdivision of an element that maintains all the physical and chemical properties of an element
What is the atomic mass of protons and neutrons
1
Atomic number (Z)
of protons in nucleus
Atomic mass (A)
Sum of protons and neutrons in nucleus
Electrons
Negatively charged and have no mass
Electrons held in their orbital shells by what
Electron binding energy (K shell= 69.53/70)
Tungsten atom Z #
74
Valence number
- Number of electrons in last orbital shell (outermost max shell=8)
- 2n^2
Ionization
- 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)
What is the Brem photon energy equal to
- 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
Characteristic (k-char.) radiation
High speed electrons interact with tungsten target atom by ejecting an inner shell electron and ionizing atom
Process of filling the k-shell vacancy results in what
The emission of a characteristic xray photon
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..)
When producing K char rad, what must the tube potential be
70
As a tech, when selecting 60 kV, how much of kV will be Brem?
100?
X-radiation if one form of what
Electromagnetic energy on the electromagnetic spectrum
Photon
Smallest bit of electromagnetic energy
Particulate radiation
Beta and alpha radiation- travel in particles
Frequency
Rate of rise and fall (oscillation) of the electromagnetic photon and is measured in hertz (Hz)
Wavelength
Distance between two successive peaks of an electromagnetic photon
Frequent and wavelength
Inversely related
Xray moves at speed of light
3 x 10^8 meters/sec (186,000 miles/sec)
Quality of beam
kVp, energy, penetrability, wavelength
Quantity of beam
- mAs, rate of exposure, intensity, pt dose
- measured in roentgen, mR, or mGy
- xray quantity directly proportional to mAs
xray quantity indirectly related to what
Filtration and distance
Technical factors that affect half value layer
kVp and filtration
What is the difference between xray and gamma
The source of radiation
Inverse square law
Used to calculate a change in beam intensity with changes in SID
Direct square law
Determine the change in mAs required if radiographic density is to remain constant and SID is changed
Image forming beam
Remnant xray beam
Attenuation
Progressive absorption of xray beam as it passes through matter
If distance gets doubled or cut in half, intensity will change how much
By factor of 4
(Double= 4 x less) ?
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
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
Compton interaction can be
- forward scattering: degradation of image contrast
- side scatter: result in occupational exposure
- backscatter: resulting in pt exposure
Biggest source of scatter
Patient
During fluoro, what is a techs largest source of occupational exposure
Compton scatter
What is the maximum number of times an xray photon can be scattered before it loses all of its energy
2 times
During fluoro, 90 degree angle, right angle, perpendicular
Least amount of radiation (or close to 90)
During fluoro, 180 degree, head of foot
Most scatter
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)
What is the primary source of patient radiation exposure
Photoelectric interaction
Every time an xray photon gets scattered, it will leave with how much of its original intensity
1/1000- 0.001
Or 0.1%
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
Contribute to patient skin exposure or degeneration of image quality
Classical coherent scattering
Absorbed dose
Gray (Gy) 0.01 multiplication factor
1 Gy= 100 rads
1 cGy= 1 rad
Dose equivalent
Sievert (Sv) 0.01 multiplication factor
1 Sv= 100 rems or 1 cSv= 1 rem
Quality factor of xrays, gamma rays, and beta particles
1
Quality factor of protons
5
Quality factor of fast neutrons
10
Quality factor of alpha particles
20
Exposure
Coulombs per kilogram of air (C/kg)
2.58 x 10^ -4
Effective dose
Sv
Air kerma
Gy
Curie (Ci)
Measurement of radioactivity
Standard equivalent: Becquerel (Bq)
3.7 x 10^10
Which trimester is the least resistant?
First
Non-threshold dose effect relationship
- any given dose of rad will yield some measurable effects
- no amount of radiation, regardless of dose, is safe
Threshold dose effect relationship
Some amount of radiation is required before a measurable effect can be detected
Law of Bergonié and tribondeau
Cell radio sensitivity is affected by
Mitotic activity: radio sensitivity increases with increased maturity
Maturity
Degree of specificity
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
What happens to the quality factor for a given form of radiation as LET increases
It will increase
Oxygen effect
The ability of aerobic conditions to enhance the effectiveness of radiation
Increasing the oxygenation of a cell does what to the cell’s sensitivity to radiation?
Increases it
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
Relative biologic effectiveness (RBE)
-ability to produce biologic damage
Increasing the LET of radiation will result in what effect to biologic damage?
- Increase in biologic damage
- LET and RBE and directly related
What is the most radiosensitive cell in the body?
Lymphocytes
Least sensitive to greatest sensitive
1) nerve
2) muscle
3) stem/intestinal crypt
4) lymphocytes
Cell survival and recovery (LD 50)
Lethal dose to 50% of pop. over ___ number of days
Factors influencing survival
LET and oxygen
Fractionation
- Equal doses of radiation that are delivered with time interval separations
- offers cell the greatest ability to survive and recover from radiation exposure
Protraction
Radiation dose that is delivered continuously but at a lower dose rate
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)
Free radicals can combine to form toxic substances such as
hydrogen peroxide (H2O2)
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
Interphase death
- Apoptosis
- cell dies without attempting to divide
- Amount of rad to cause interphase death depends on radio sensitivity of cell
Metaphase
Cell most sensitive
Mitosis
Cell division
Meiosis
Germ (sex) cell division
Mitotic delay
Mitotic activity resumes after a short delay
Usually 10 mGy or 0.01 Gy
Reproductive failure
Cell does not die as a result of radiation exposure but loses the ability to procreate
1000 to 10,000 mGy
Somatic effects
Those limited to the exposed population (individual cell of body)
Short term somatic effects
- occur soon after exposure seconds, minutes, hrs, days, weeks
- epilation, nausea, vomiting, erythema, fatigue, epistaxis
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
Acute (short term) exposure
- large dose over short time
- more life span shortening than chronic rad exposure
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
What is the most radiosensitive part of eye
Lens
What are the results of opacity in the lens of the eye due to radiation exposure?
Cataracts
Eye
Nonlinear, threshold dose (non-stochastic)
Thyroid
Linear, non threshold dose (stochastic)
Breast
Linear, non threshold dose (stochastic)
Bone marrow
Linear, threshold dose response
Skin
Threshold (non-stochastic)
Female gonad
- immature ova very radiosensitive
- mature ova not radiosensitive and can carry damaged chromosomes
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
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
Local somatic effects
Effects that are limited to the exposed individual and the specific area of exposure only
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
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
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
Ten day rule
Rad exposure to female in child bearing age should be limited to 10 days following the onset of menstruation
Why are pediatric pts more radiosensitive?
Cells reproduce frequently
Components of electromagnetic spectrum
- visible light
- ultraviolet light
- gamma radiation
- radio waves
Becquerel (unit of radioactivity) describes what
Disintegrations per second
Air kerma (unit of exposure) measures what
Quantity of ionization in air
Gray measures what
Energy deposited in any material
Sievert measures what
Dose to biologic material
Effective dose formula
EfD= equivalent dose (EqD) x Wt (tissue weighing factor) EfD= radiation weighting factor x tissue weighting factor x absorbed dose
Effective dose refers to what
Whole body dose
What produces a potential difference within the xray tube during an exposure?
kVp
