Chapters 6-7 Flashcards
what are 2 interactions that create x-rays?
- bremsstrahlung and characteristic
How much of electrons turn into x-ray photons?
1%
how much of electrons turn into heat?
99% (infrared radiation)
what part of the atom do the electrons collide with once they reach the Anode?
- they hit the outer shell of an atom
define exitation
- raise the atom to a higher energy level
How are characteristics released?
- ionization of target atoms
how is bremsstrahlung released?
- interactions with target nuclei
what’s involved in characteristics?
- filament electrons
- orbital electron of a target atom
define cascade reaction
- process of outer-shell electrons filling inner-shell vacancies continues down the line, creating a cascading effect
- happens with characteristic and photoelectric
define characteristic interactions
- when orbital electrons of target atoms are removed from their shell
- outer-shell electrons fill inner-shell vacancies
Why are characteristics given the term “characteristic”?
- difference in binding energy between the shells involved
define binding energy
- how strong the fore holds the nucleus of an atom
What shell holds the most energy?
- k shell
- since its closer to the nucleus, it has a stronger force
define k-shell
- innermost shell in an atom
- highest energy
- useful for imaging purposes
what is the binding energy of the k-shell in Tungsten?
69-69.5
What happens if the technique is lower than 70kVp?
- no photons will be produced in the k-shell interaction
in the k shell, what is the binding energy in the tungsten?
69.5 keV
in the L shell, what is the binding energy in the tungsten?
12.1 keV
in the M shell, what is the binding energy in the tungsten?
2.82 keV
in the N shell, what is the binding energy in the tungsten?
0.6 keV
in the O shell, what is the binding energy in the tungsten?
0.08 keV
in the P shell, what is the binding energy in the tungsten?
0.008 keV
how do you find the photon energy of a shell?
- the difference in binding energy
- subtract the shell with the vacancy from the farther shell that’s filling up the shell
- the radiographer subtracts the binding energy of the farther shell (shell providing electron) from the closer shell (shell with vacancy) ??????
how are characteristics photons named?
- named for the shell being filled in each case.
- Ex.) If an outer-shell electron is filling a K shell, regardless of where that filling electron is coming from, the photon produced is called K characteristic.
how to find an energy of a characteristic photons?
- one must know the shell-binding energies of the element and the shells involved
what is an example of finding a photon energy?
A filament electron removes a K-shell electron, and an L-shell electron fills the vacancy:
K-shell binding energy = 69.5 keV
L-shell binding energy = 12.1 keV
69.5 − 12.1 = 57.4 keV
The energy of the K-characteristic photon produced is 57.4 keV.
define bremstrahlung
- means breaking radiation
- the filament electron misses all of the orbital electrons and interacts with the nucleus of the target atom
- The attraction causes the filament electron to slow down and change direction and, in doing so, lose kinetic energy.
- The closer the filament electron passes to the nucleus, the stronger the attraction.
- the stronger the resultant brems photon
how to find the energy of a Brems photon?
- subtracting the energy that the filament electron leaves the atom with from the energy it had upon entering.
- Ex.) a filament electron enters an atom with 100 keV of energy, passes very close to the nucleus, and leaves with 30 keV of energy.
The brems photon produced is 70 keV
100 keV − 30 keV = 70 keV
what are the 2 reasons why most of the photons are Brems?
- he filament electron is more likely to miss the orbital electrons of the target atom, because they are in constant motion and the atom is mostly empty space
- All lower settings (below a kVp of 70) result in a beam made up entirely of brems
define filtration
- the use of material to absorb x-ray photons from the x-ray beam
- can be used in inherent, added, or compensating filter
define inherent filtraton
- inheret to the tube assembly (tube and housing)
what is the primary contributor to the inherent filter?
- the target window
- equals to 0.5mm Al equivalent
what happens when the filament electron passes nearby the nucleus of an atom?
- there is a very strong attraction
- the nucleus has a strong binding energy, therefore, the attraction will be greater with the net charge difference
What is a result from a strong attraction between an atom and an electron?
- the more energy the filament electron loses and the stronger the resultant brems photon.
how are bremsstrahlung interactions produced?
- when filament electrons miss all of the orbital electrons of the target atom and interact with the nucleus
what are other ways to avoid radiation exposure?
- time
- distance
- shielding
define electron stream
- where the cloud travels
define actual focal spot
- portion where the electrons hit the anode angle
define effective focal spot
- the principle
- where all the photons go after the clash with the anode
what are the focus spots?
- filaments
how many focus spots do we have?
- 2
- small filament
- large filament
what are the factors of a small focus spot?
- we’ll get better resolution
- heat is increased
what are the factors of a large focus spot?
- less resolution (lack of detail)
- heat will decrease
What happens when we increase the anode angle?
- the effective focal spot will decrease
- indirect
what happens when we decrease the anode angle?
- the effective focal spot will increase
- indirect
what happens when we increase the actual focal spot?
- effective focal spot will increase
- direct
what happens when the actual focal spot decreases?
- effective focal spot will decrease
- direct
what does LFS stand for?
- Large focal spot
what does SFS stand for?
- small focal spot
what does FSS stand for?
- focal spot size
what is the focal spot size for LFS
-1.2mm
what is the focal spot size for SFS
- 0.6mm
What are the factors of a large filament?
- large focal spot
- decrease in resolution
- used in large body parts
- Ex.) Abdomen
what are the factors of a small filament?
- small focal spot
- an increase in resolution (more details)
- used for smaller body parts
Can small body parts be set up for LFS?
- yes
- small body parts are acceptable for LFS as long as the technique makes sense
- if the technique is unreasonable, or reaches its limit, an error will occur
define anode heel
- portion of the anode that absorbs the photons after the clash
- this results in less intensity on the anode side
- photons go through the metal of the anode
- attenuation occurs
- leads to the photons being weaker
because the cathode side has more intensity, what should be place in that area?
- body parts that are more dense
- Ex.) in a recumbent supine position, the pelvis will be facing the cathode side
- this works out because there are lots of dense tissue in the pelvis, meaning it will need a higher density so the photons can penetrate through
what are the factors when Anode Heel Effect increase?
- anode angle decreases
- SID decreases
- Field size increases
- vice versa
What happens when there is an increase in SID?
- the gradient of the blackness will be evenly spaced out
- one side wont have a higher intensity
- the intensity spreads out evenly
what happens when there is a decrease in SID?
- there will be more intensity on one side
- more photons are facing one way more
What does kVp stand for?
- kilovoltage peak
- penetration
what are the factors of a high kVp?
- more shades of gray
- more details
What does it mean when there is a short wavelength?
- higher frequency
- higher power
- more detailed
What does it mean when there is a long wavelength?
- lower frequency
- lower power
- less detail
true or false: the amount of photons reaching the receptor will be the same
true
true or false: receptor exposure will be the same
true
what is the average energy of brems?
-1/3 of the kVp
define added filtration
- to remove low-energy x-ray photons from the beam before they can expose the patient and contribute unnecessarily to radiation dose
- removing low-energy photons that would not contribute anything useful to the imaging process
define total filtration
- The combination of inherent and added filtration
define compensation filters
- are used to adjust or “compensate” for variations in patient thickness or density and create a more uniform exposure to the image receptor (IR)
- compensating filter designs are some variation of a wedge shape
- requires an increase in mAs to maintain overall exposure to the IR and is a trade-off of increasing patient dose slightly to improve image quality
what does added and inherent filtration have in common?
- they both remove low-energy photons before they expose the patient and add to radiation dose unnecessarily
define beam quantity
- the total number of x-ray photons in a beam.
what factors affect beam quantity?
- affected by mAs, kVp, distance, and filtration
what is the relationship between beam quantity and mAs?
- Beam quantity is directly proportional to mAs
- an increase in quantity increases the radiation dose delivered to the patient
true or false: Beam quantity is strongly affected by changes in kVp
- true
- kVp gives kinetic energy to the filament electrons.
- the greater the kinetic energy, the greater the chances for x-ray production.
define inverse square law
- the intensity of a beam is inversely proportional to the square of the distance from the source
how is the beam quantity affected when there is an increase of mAs?
- quantity increases
how is the beam quantity affected when there is an increase of kVp?
- quantity increases
how is the beam quantity affected when there is an increase of distance?
- quantity decreases
how is the beam quantity affected when there is an increase of filtration?
- quantity decreases
define beam quality
- the penetrating power of the x-ray beam.
define penetration
- those x-ray photons that are transmitted through the body and reach the image receptor
who affects beam quality?
- kVp and filtration
- controlled mainly by adjusting the kVp
define high quality/ hard beams
- X-ray beams with high energy (from high kVp settings)
define low quality/ soft beams
- X-ray beams with low energy (from low kVp settings)
how does filtration affect beam quality?
- serves to remove the lower-energy photons, making the average energy (quality) higher
how is the beam quality affected when there is an increase of kVp?
- quality increases
how is the beam quality affected when there is an increase of filtration?
- quality increases
how is beam quality measure?
- half-value layer (HVL).
define HVL
- half-value layer
- the thickness of absorbing material (aluminum [Al] or aluminum equivalent filtration) necessary to reduce the energy of the beam to one-half its original intensity.
define primary beam
- the x-ray beam as it is upon exiting the collimator and exposing the patient
- the photon that is released from the tube
define remnant beam
- the x-ray beam that remains after interaction with the patient and is exiting the patient to expose the image receptor
- the photon that has exited the patient
- leaves its black dot in the IR
- weaker than the primary beam
- composed of transmitted and scatter photons
define emission spectrum
- a graph that illustrates the x-ray beam
what type of graph does characteristic photons have?
- discreet emission spectrum
- called discrete because the photon energies are limited to just a few exact values.
- The x-axis is the x-ray energy, and the y-axis is the number of each type of x-ray photon.
what type of graph does brems photons have?
- continuous emission spectrum
define x-ray emission spectrum
- the combination of direct and continuous emission spectrum
true or false: K-characteristic x-rays are of the greatest importance in tungsten targets
- true
- they contribute to the radiographic image
what does the changes in the graph represent?
- changes in the y-axis indicate changes in quantity
- changes in the x-axis indicate changes in quality
what are five factors that changes the appearance of the x-ray emission?
- mA, kVp, tube filtration, generator type, and target material.
How does mA impact the x-ray graph?
- Changes in mA affect beam quantity.
- an increase in mA increases the amplitude of both the continuous and discrete portions of the spectrum
- increases the quantity of x-rays produced
how does kVp impact the x-ray graph?
- Changes in kVp affect beam quality and quantity
- increase in kVp increases the amplitude of both continuous and discrete portions of the spectrum and shifts the right side of the curve to the right along the x-axis.
- more photons (quantity) are produced
- increases the amplitude of the spectrum and higher-energy photons (quality)
how does filtration impact the x-ray graph?
- removes low-energy photons from the beam.
- an increase in tube filtration causes a decrease in quantity and an increase in quality.
how does generator types change the x-ray graph?
- change the x-ray production efficiency of the machine
- High-frequency units are much more efficient in producing x-rays than single-phase units
- represented by an increase in amplitude and average energy.
- Improving the efficiency of the generator increases x-ray beam quantity and quality
define classical interactions
- also known as coherent scattering or Thomson scattering
- deals with low-energy photons
- no ionization
- atom absorbs the energy and releases it to a new direction
- occupational exposure
define compton scattering
- involves moderate energy x-ray photons
- outside of the tube
- hits an outer shell
- ionization occurs
- main feature of occupational exposure
- it contributes no useful information to the image and only results in image fog
- we want to minimize as much as possible
define photoelectric
- the primary photon hits an electron from the inner shell
- secondary photon becomes really weak
- contributes to patient dose
- secondary photon is VERY weak and therefore stay inside the patient
- ionization occurs
- cascade reaction occurs
define transmission
- x-ray photons that pass through the body and hit the IR
- when photons reach the IR, it creates a black dot (adds black shades)
define absorption
- photons that are attenuated by the body and do not reach the IR
- since it doesn’t reach the IR, it results in lighter shades
