Ch. 3-4 Flashcards
What does kVp control
QUALITY, or penetrating power
Name 3 ways X-Rays interact with human tissue
- Interact with the atoms of the patient and become ABSORBED
- Intersect with the atoms of the patient and become SCATTERED
- Pass through the patient WITHOUT interaction
More Absorption =
Greater possibility of biological damage
Primary Radiation
What exits the tube
Anode
Target
Reasons tungsten/rhenium are used as target materials
High melting points
High atomic numbers
Inherent Filtration
Built-In
Added Filtration
A certain thickness of added ALUMINUM to “harden” the beam within the collimator
Combo of X-Ray tube glass wall and added aluminum placed within the collimator may be called
Permanent Inherent Filtration
Primary Radiation happens (before/after) it has gone through filtration
AFTER
SINGLE PHASE
100% voltage ripple
3 phase (6 pulse)
13% voltage ripple
3 phase (12 pulse)
4% voltage ripple
High Frequency
1% voltage ripple
Do all photons in a X-Ray beam have the same energy
No
The energy of the average photon is about 1/3 of the energy of the most energetic photon
Example:
100 kVp beam contains photons having energies of 100 KeV or less, with an average energy of approximately 33 KeV
100 divided by 1/3=33
Can the most energetic X-Ray photon have more energy than the set kVp
No, the photons can have no more energy than the set kVp
Photons that travel through the patient without interacting & reach the image receptor
Direct Transmission
(Possible/Impossible) to predict with certainty what will happen to a single photon when it enters human tissue
IMPOSSIBLE
(Possible/Impossible) to predict what will happen on the average when a large number of photons enter the human body
POSSIBLE
Absorbed Dose
D
Coherent Scattering
Occurs with low-energy photons, less than 10 KeV (kVp’s 1-50)
Wavelengths of incident and scattered are the same, so no new energy is absorbed by the atom, because no kinetic energy is lost
Small angle scatter
May result in small amounts of fog
Photoelectric Absorption
Interaction of a X-Ray PHOTON and an INNER SHELL ELECTRON
Involves ejection of an inner shell electron
Vacancy of inner shell is filled by an outer orbital shell electron
A difference in binding energies between the two electron shells forms a second photon
Photoelectron created ^
IMPORTANT MODE OF INTERACTION FOR PRODUCING USEFUL IMAGES
PHOTOELECTRIC ABSORPTION/Auger Effect
When an inner electron is removed (inner-shell vacancy) the energy given off by another electron filling his void can go on to eject another electron in the same atom
Instead of filling the “hole” , it ejects another electron
Probability of photoelectric absorption depends on
Energy (E) of the incident photons
Atomic number (Z) of the atoms comprising the body part
Energy of the incident photon decreases as
kVp decreases
Bone Atomic #
13.8
Soft Tissue Atomic #
7.4
Air Atomic #
7.6
Absorption vs kVp
As kVp decreases
Absorption increases
The whiter areas on radiographs
The higher the absorption
(Bone, Lead, Medal, Barium, ETC)
(Darker/Whiter) Less attenuation by the body part
Darker
(Darker/Whiter) More attenuation by the body part
Whiter
Ex: Knee replacements show up really bright because they absorb more
Increase window level =
Brighter, white, increased brightness
Decreased window level =
Darker, black, decreased brightness
Use of positive contrast medium- Iodine/Barium
Appears lighter because it increases photoelectric effect
Use of negative contrast medium-Air
Appears darker
Compton Scattering
Interaction with a loosely bound outer shell electron
X-Ray photon dislodges the electron from its outer shell, ionizing the atom
The freed electron is able to ionize other atoms and bounces around unit it finds an atom in need of another electron
The incident X-Ray photon that kicked out the electron continues on its way but in a new direction
Very Bad- Degrades image ‼️
Compton scattering scatter type
All-Directional scatter
Pair Production
Occurs when a high-energy photon interacts with the NUCLEUS of an atom
The photon disappears and the energy is converted into a NEGATRON (ordinary electron) and a POSITRON (positively charged electron)
Positron and electron will annihilate each other
Examples of unstable nucleus in PET
Fluorine-18
Carbon-11
Nitrogen-13
WHAT DOES PET SCANNING DO
Ibuprofen
Reveals how tissues and organs are functioning
Utilizes a radioactive drug
Used a radioactive drug- may be injected, swallowed, inhaled depending on study
Collects in areas of body that have higher levels of chemical activity , showing up as “bright spots”
Photodisintegration
Interaction that occurs at more than 10 MeV (3,000 kVp)
High energy photon is absorbed by a nucleus; completely destroying nucleus
Higher mA=
Higher number of electrons being produced
<5 rad
No immediate observable effects
~5 to 50 rad
Slight blood changes
~50 to 150 rad
Slight blood changes
Symptoms of nausea, fatigue, vomiting, etc..
~150 to 1,110 rad
Severe blood changes
Could die within two weeks
Infection likely
May need a bone marrow transplant
~1,100 to 2,000 rad
The probability of death increases 100% within one to two weeks
Symptoms are immediate
Gastrointestinal system is destroyed
Once GI System ceases to function, nothing can be done, care for comfort only
> 2,000 rad
Death
Central Nervous System can no longer control anything including breathing and blood circulation
Nothing can be done, care for comfort only
When were X-Rays discovered
November 8, 1895
Somatic Damage
Result of excessive occupational radiation exposure for early pioneers and excessive exposure of patients
Cancer
Blood Disorders
Unit used from 1900 to 1930 to measure radiation exposure
Skin Erythema Dose
Was the Skin Erythema Dose accurate?
No
Tammy; “It’s like being out in the sun until you get a sunburn and then determining that you shouldn’t be in the sun that long or you will burn”
Everybody’s different
SECOND INTERNATIONAL CONGRESS OF RADIOLOGY 1928
(The first was unable to make any decisions about the measuring effects of radiation) 1925
Acceptance of Roentgen (R)
Early Tissue Radiation Reactions
Nausea
Fatigue
Loss of hair
Fever
Blood disorders
Late Tissue Radiation Reactions
Cataracts
Reduced fertility
Sterility
Organ Atrophy (decrease in size due to cell shrinkage)
Stochastic-Probabilistic
Mutational or randomly occurring biological changes, INDEPENDENT OF DOSE
Stochastic effects
Cancer
Genetic effects
When does ROENTGEN become internationally accepted
1937
1934- committee recommendations of what daily limit dose
.2 roentgen
83x higher than what it is today‼️
1936-committee recommendations of what daily limit dose
.1 roentgen
40x higher than what it is today
Max permissible dose (MPD) replaces tolerance dose for radiation protection purposes
When?
Early 1950s
When is (R) redefined to increase accuracy and acceptability
1962
Is tolerance dose still accepted
No
NO DOSE IS SAFE‼️
INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASURES (ICRU)
What did they adopt and when?
Adopted SI units for use with ionizing radiation in 1980
National Council on Radiation Protection (NCRP)
What did they adopt and when?
Adopted SI units for use in 1985
International Commission on Radiological Protection
What did they adopt and when?
Adopted the term EFFECTIVE DOSE in 1991
✅
Exposure
Radiation quantity that expresses the concentration of radiation delivered to a specific area, such as the surface of the human body
Precise Measurements of Radiation Exposure
Total amount of ionization a X-Ray beam produces in a known mass of air
Accomplished in a lab by using an ionization chamber
Ampere
SI unit of electrical charge
Air Kerma
SI quantity used to express how energy is transferred from a beam of radiation to a material (patient’s skin)
Can be used to express X-Ray tube output and inputs to image receptors
❗️K❗️inetic
❗️E❗️nergy
❗️R❗️eleased
PER
UNIT
❗️MA❗️ss
Unit used to measure the quantity of air kerma
Gray (Gy)
Air Kerma
Metric units of JOULE (energy) per kilogram
(J/kg)
May be stated in Gy
When Gy is used to indication kinetic radiation energy absorbed in a MASS OF AIR, it is written as
(X-Ray Tube Output)
GYa
AIR-a
When the Gy is used to indicate kinetic radiation energy absorbed in a MASS OF TISSUE, it is written as
(Transmitted X-Rays absorbed)
GYt
Tissue-t
Dose Area Product (DAP)
Sum total of air kerma over the exposed area of the patients surface or, a measure of the amount of radiant energy that has been thrust into a portion of the patients body surface
Specified in units of nagy-cm2
Example:
Air kerma dose of 20mGy
Surface area exposed is 100cm2
DAP; 20mGy X 100cm2=2,000mGy/cm2
What’s Absorbed Dose responsible for
Any biological damage resulting from exposure of the tissues to radiation
X-Ray Photon, Beta, Gamma quality factor
1
Thermal Neutron Quality Factor
5
Fast neutron quality factor
20
Low energy internal protons, Alpha particles, Multiple charged particles of unknown energy quality factor
20
High energy external protons quality factor
1
EqD
Product of the average absorbed dose in a tissue or organ in the body and it’s associated with awe chosen for the type and energy of the radiation in question
Biological effects may be determined and expressed in..
Sv
EqD=
D X Wr
Sv=
Gy X Wr
Radiation Weighting Factor (Wr)
Must be used when determining EqD
Used for radiation protection purposes to account for differences in biological impact among various types of ionizing radiation
Places risks associated with biological effects on a common scale
Annual Whole Dose Limits
General Public
1mSv
EfD
Measure of the overall risk of exposure to humans from ionizing radiation
Both the effect of type of radiation and the variability in radio-sensitivity of the part
EfD=
D X Wr X Wt
mSv to mrem
X100
Collective EfD
Used in radiation protection to describe internal and external dose measurements
Quantity used to describe exposure of a POPULATION OR GROUP
Person-Sievert
Total Effective Dose Equivalent (TEDE)
Radiation dosimetry quantity that was defined by the NRC to monitor and control human exposure to ionizing radiation
TEDE
Designed to take in account ALL possible sources of radiation exposure
