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X-Ray Tube Interactions, Increased kVp, Increased Target Material (Z#),…
X-Ray Tube Interactions
Majority of x-rays in primary beam
Bremsstrahlung Interactions
Dependent on KE of incident electrons & Binding energy of the electron shell of target atoms
Negative electron vs. Positive nucleus
"Braking"
Interaction with the electrostatic force (field) of nucleus
"Lost" energy turns into x-rays
Close to Nucleus
More Kinetic Energy (KE) lost
Higher energy photon created
Direct impact with nucleus
All energy lost and unlikely to happen
Produces a maximum energy photon
Far from Nucleus
Low energy x-ray photons created
Less Kinetic energy (KE) lost
Responsible for heterogeneous (Polyenergetic) nature of x-ray beam
Forms different elements due to the loss of a proton
Type of radioactive decay
Energy Level of an individual Brems photon is unpredictable
Interaction with an orbital electron
Characteristic Interactions
Electrons transfer KE to the shell of electrons of the target atom
Incident Electron does this
Electron interacts with an inner shell electron and ejects it from its shell leaving a hole
The Ionized atom now seeks equilibrium
Characteristic Cascade
A electron from a high shell moves inward to fill the void
Energy difference of shells is emitted as a characteristic x-ray photon
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Characteristic radiation
About 1% is an X-ray and the rest is mostly heat
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Octet Rule
The ejected electron can cause additional interactions until all Kinetic Energy (KE) is used up
The energy level of an individual characteristic photon is extremely predictable
Set/Limited to specific values
The Spike is Characteristic Radiation
Conditions needed to produce x-rays
Acceleration of the electrons
A sudden stoppage of high speed of the electrons
A source of elecrons
99% of KE is heat and Less than 1% produces x-rays
Happens when electron energy is transferred to the anode target
Incident electrons strike the anode
Target Materials = Anode
Tungsten & Rhenium
High Z#
More electron colisions occur
More x-rays produced
Amplitude of curve is increased
Higher energy Characteristic x-rays are produced
Similar Electron Binding Energies
Molybdenum
Lower Z#
Ideal for soft tissue of breast
80-100 kVp range
90% of the beam is Brems
10% of the beam is Characteristic
Exposure Factors Change
mA or mAs
Increased mA
Change Amplitude but No Change in Characteristic Peak energy levels
Increases the amount of X-ray photons
Only Increases Beam Intensity/Amount
Doubling mAs
A 100% increase in beam intensity
Beam Quality is NOT affected
kVp or keV
Increased kVp
More Bremsstrahlung interactions
Makes Amplitude larger and longer
No change in characteristic interaction energy levels
No increase in electrons striking the target
Increase kVp to 70-90
Increases the Kinetic Energy (KE) provided to the incident electrons
Increases the Quality (Penetration) and Quantity (Intensity/Amount) of x-ray photons
Quality = Only higher Energy electrons reach the IR
Quantity = More electrons reach the IR because they have higher energy to penetrate
Increasing kVp 15%
Increases beam intensity up to 40%
The average keV is approximately 1/3 of the selected kVp
Within the 70-90 kVp Range
Increasing kVp by 15% or Doubling mAs produce similar increases to IR exposure
Tube Output (beam intensity) directly determines patient skin dose
Top or height of Arch is Amount of Photons = Amplitude
Photon Intensity or "How Many"
End/bottom of the Chart is the maximum amount of kVp = Photon Energy
No x-rays are produced above the elected kVp
Filtration absorbs most of the very low x-ray energies
Gives it the bell shape
The Apex of the arch is where filtration of bremsstrahlung becomes apparent
L,M,N,O,P Shells will be removed from the primary beam by filtration
Affects the Amount (Amplitude) and Energy level of the emission spectrum
Average energy quality is increased
Linear - Double X-Axis = Double Y-Axis
Non-Linear - Double X-Axis = No change in Y-Axis
Threshold - Point where a response is found
Non-Threshold - The point right before a response happens
The average photon energy is approximately 1/3 of the selected kVp
Remnant Beam and Remnant Radiation are the same thing - Radiation that comes out of the patient
Generators
Higher-Frequency Generators
More Efficient
More kVp
Higher # of X-rays
Single Generators
Less efficient
Increased kVp
Increased Amplitude Size
Increased Average Energy
Increased Length
Increased Target Material (Z#)
Increased Amplitude size
Increased Average Energy
Increased Characteristic X-Ray Energy
Increased Binding Energy
Characteristic Interactions
69 kVp or more
Seeks Equilibrium = Octet Rule
Shells electrons move up to fill a void
Characteristic Cascade
Increased Filtration
Increased Average Energy
Decreased Amplitude Size
Increased Generator Frequency
Increased Amplitude Size
Increased Average Energy
Bremsstrahlung Interactions
Close to Nucleus = High energy photons
Far from Nucleus = Low energy photons
Increased mA
Increased Amplitude Size
