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Radiology Exam 1 NotesDr. Osher
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Ionizing Radiation
Ionizing Radiation
Energy is always transferred to any material withwhich it interacts
Process where an atom GAINS or LOSES electrons inthe outer shell
Results in a net charge
Positive Ions=Cations
Negative Ions=AnionsX-rays have enough energy to cause atoms to ionize
Is harmful for DNA and such
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Ionizing Radiation
Biologic Effects of Ionizing radiation are short andlong-term
May disrupt atomic structure
Can cause Temporary or permanent cellular damage
Can penetrate matter
Causes some materials to flouresce
Reacts with Silver Halide of film
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Electricity and
Magnetism2 Types of ElectricityStatic ElectricityElectric Charge at Rest (In Coulombs)
CurrentMoving Electric Charges (In Amperes)
Ohms Law= V=IR
Direct CurrentFlow of electrons in ONE direction ONLYStraight line
Alternating CurrentElectrons flow in ALTERNATE OPPOSITE directionsSinusoidal wave
Flow from negative to positive (also vice versa)
Each change from negative to positive, or positive to negative, results in ONEPULSE
2 pulses= one cycle
Equates to Power coming out of the wall
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AC and DC Current
A steady DC voltage delivers more power than ACvoltage source of the same peak voltage
Amplitude of a sinusoidal AC voltage must be thesquare root of 2 times greater than the steady valueof DC current to perform the same amount ofworkRMS voltage
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X-Ray Basics
X-ray Machine Components
Generator
X-Ray Tube
Control Panel
X-ray Energy is from 10^4 to 10^5 Electron volts
Tungsten= main material in Anode of X-ray
High melting point
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X-Ray Machine
CANNOT USE AC CURRENT DIRECTLYpulsating X-ray tube
Is not safe
Produces poor imagessoft radiation: contributes todosage the patient is getting ONLY
Hard on tube
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Parts of the X-ray
MachineX-Ray GeneratorSupplies Electric Power to the X-ray tube
Needs to beTransformed,
Rectified (goes in one directionusing diodes)Smoothed out
Begins with a source of electrical energyWall Plug115 or 230 V
60Hz AC is standard in US
Modified to meet tube requirements
Filament heating requires 10Vproduces electrons
Electron acceleration requires between 40-150 kVpMachines here are 60000-70000 V
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Parts of the X-ray
MachineX-ray GeneratorProduces smooth, high voltage AC current out of low-voltage AC current by
Transforminglow-voltage AC current to high-voltage ACcurrent
Either increases or decreases voltage
Rectifyhigh-voltage AC current with diodes
Makes it go all in one direction
Smooth voltage dips with capacitive filter, offset circutry,or increases frequency
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Parts of the X-ray
MachineX-ray GeneratorTransformers
Magnets are not the only source of Magnetic fields
Right-hand rulecurrent in a wire capable of generating a magneticfield B
Current in coil of wire creates a weak magnetic fieldcreates asolenoid
If iron core placed in center of solenoid, the magnetic field becomesmore intensebecomes an electromagnet
A wire carrying current experiences a force in a magnetic field
This force CANNOT be parallel to the magnetic field, B
F=LIBB=magnetic field
I=current (in A)
L=length of wire
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Parts of the X-ray
MachineX-ray GeneratorTransformers
A changing magnetic field produces a transient electric field
A changing electric field produces a transient magnetic field
Induced EMFsBasis of the Transformer: Current flow through one coil cancause mutual inductance in a 2ndcoil wrapped around the sameiron core or rod
Induced EMFs exist in the coil only if flux through the coil ischanging
EMF= N x Change in flux (per unit time)N=number of coils
If there are more coils on the battery sidevoltage steps down
If there are less coils on the battery sidevoltage steps up
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Parts of the X-ray
MachineX-ray GeneratorTransformer
When an AC current flows through the primary coil, itcreates a changing magnetic field within the core
This field induces a current in the secondary coil
When battery is plugged up into the wall
There is no current flow when B is stable
This is why we cant use DC current
In AC current, the voltage changes continuouslythereforeit cycles
Current flow in one direction while voltage is positive
Flows in opposite direction while voltage is negative
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Parts of the X-ray
MachineX-ray GeneratorTransformer
Law #1 of transformers
Np/Ns=Vp/Vs
Law #2 of transformers
A transformer cannot create energyVp x Ip=Vs x Is
Step up transformer= Makes X-rays
Fewer turns on the primary side than the secondary side
Step down transformer=X-ray tube filament transformer
Heats filament
Steps down from left to right
Voltage In secondary will be less than primary
Auto-Transformerdetermines how much voltage will go into the step-up transformer
2V/turn of wire
Allows you to control primary voltage
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Parts of the X-ray
MachineCurrent RectificationAllows the current to flow in one direction
Uses Diodes
DiodeEliminates AC flow1 pulse out of 2 gets cut out
Cathode (-) and Anode (+)
Has a Space chargeelectrons boil out of the wire here
AC changes the polarity of the cathode and anode to
complete the circuit to get opposite charges to attractOne pulse gets cut outallows current to flow in onedirection
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Parts of the X-ray
MachineCurrent RectificationFull-Wave Rectificationneeds 4 diodes
Diodes allow current in ONE directionare one way
systemsWith Full-wave rectification, both halves of thealternating voltage are used to produce x-rays
Half-wave rectification= 1 diode
60 pulses/second
Full-wave rectification= 4 diodes120 pulses/second
Smoother result
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Parts of the X-ray
MachineSmoothing it OutDisadvantages of Full-Wave Rectification
Tube pulsates and the anode receives rapidly varyingamounts of energy
Intensity of X-ray beam varies over each half cycleThe quality of the beam varies over each half cycle
Increased patient dose via soft radiationpulsating tube
(This is why we cant use DC current)
Capacitoris used to smooth out bumps in Full-waverectification
Capacitorstores chargeQuickly charge (lots of current coming in) and discharge(current comes out)
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Parts of the X-ray
MachineSmoothing it outRipple factor--the variation in the voltage across the x-ray tube
Expressed as a percentage of its maximum value
Ripple Factors
Unfiltered= 100%=No capacitor
Filtered=less=Capacitor
Smaller ripple factors=betterFull-wave filtered=best ripple factor
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Parts of the X-ray
MachineX-ray Tube HeadEvacuated glass envelope and Cathode Ray Tube
CathodeTungsten=Negatively charged
Has Coiled FilamentsAnodeCopper= Positively Charged
Has an Embedded tungsten target
Window
Added filtration
Beam-limiting device
Cone/ collimating shutters
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X-Ray Generation
X-Ray Generation (in the X-ray tube)
Electrons thermoionically boil-off filament embedded in thecathode(-)
Tungstenboiled off electrons leave wire
Electrons shot (accelerated) at anode (+) target (made oftungsten) by applying a STRONG POTENTIAL DIFFERENCE (kVp)
High KE electrons interact with target atoms to producephotons in the x-ray wavelengthProduces X-rays in theAnode
Electrons in the anode are conducted away by the copperanode to complete the circuit
Cathode emits electronshits target and produces x-rayradiation
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X-Ray Generation
X-Ray Generation
Electrons all acquire about the same high terminal KE
Monochromatic keV
Over a very short distance (1-3 cm)
Is about velocity of light
X-ray beam is polyenergeticphotons are comprisedof varied energies (spectrum)
X-rays directed toward window and filter
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X-Ray Generation
X-Ray Generation
Not all X-rays are alike
Faster moving electrons produce higher energy,
shorter wavelength photonsSlower moving electrons produce Low energy andhigh wavelength photons
Electrons have about the same average KE, and still
produce a varied X-ray spectrum
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X-Ray Tube Details
Cathodes
Emits electronsproduces the electrons
Helps generate a strong potential difference across a
small evacuated gap which has the anode (+)Focusing cup (-) surrounds coil and Tungsten filament
Current applied to Tungsten filament
Attains approx 2000 C
Units are Amps (A)
Electrons boil off of coil and form a negatively chargedelectron cloudThermionic emission
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Cathode Assembly
Cathode Assembly
Dual Focal Spot
Focusing cup and Filaments
Unit becomes electronegative
Electrons go towards anode--divergence is limited by thefocusing cup
Without focusing cupdivergent cloud of electrons
With focusing cupelectrons go towards tungstentarget
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Cathode Assembly
Filament Circuit
Current flow is high4A
Voltage across filament is 10V
Power dissipated40W (P=VI)
High resistance in filament causes the temperature toriseThermionic emission of electrons
Filament Circuit Requires step-down transformer
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X-ray tube Current
Electrons emitted from filament forms a negative cloudAKA theSpace charge
The Space Charge prevents further electron emission
Electrons are attracted to anode when the increase in potential is
applied to the anodethis is how you produce X-rays
Tube current is measured in Milliamps (mA)the flow of electronsacross the vaccum gap from filament to anode completes thecircuit
Increase in attraction=Increase in X-rays produced
If force of attraction is large, no cloud exist and cant form an X-raythis is around 40 kVp or greater
If voltage difference between cathode and anode is greater than 40kVp, the space charge dissipates, and there is no X-ray formed
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Space Charge Effect
Space Charge Effect
The space charge is an electron cloudand it iselectronegative
Via electrostatic repulsion, the space charge makes itdifficult for subsequent electrons to be emitted fromthe cathode filament
Residual space charge acts to limit the number of
electrons availableThis limits current flow in the x-ray tube
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X-Ray Tube Output and
CurrentX-ray tube output and currentTube output is proportional to Tube Current
At Low kVp, the tube current is Space Charge LimitedkVp
is controlledAfter 40 kVP, the prime determinant of X-ray production isfilament heating
At saturation voltage, all electrons are pulled away from thefilament, and tube current is maximized
Saturation Voltage= 40 kVpTube current is now largely controlled by Filament Heating
More electrons=more x-rays
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X-Ray Tube Output and
CurrentTube Output and CurrentOnce saturation voltage has been attained, current isdetermined by the number of electrons available byfilament heating
Emission or temperature limited
kVp affects the tube current for a given filament current
Space charge effect
At low peak voltages (less than 40 kVP), the potential
difference is insuffient to cause electons to be pulled awayfrom filamentthus a residual space charge remains
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X-Ray Tube and Anode
The Copper Anode Contains the Tungsten Target
Focal spot= Target area bombarded by electrons
Embedded target material= Tungsten
High melting pointHigh atomic number is more efficient in X-ray production(Z=74)
Tube Circuit= Low current, High Voltage
Filament Circuit=Low voltage, High Current
Target=embedded AnodeThe thing that produces X-rays
Is the Focal Spot
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Anode Designs
2 Basic Anode DesignsStationary Anode
Has an angled face
Rotating Anode
Has a motor attached to the anodeGoes up to high speed before taking an X-ray
Increased surface area is used to dissipate heatmoreefficient
Anode is angled to decrease focal spot size
Line-focus principalSmaller focal spotsharper images **sharper x-ray beams**
Shallow anglessharper images
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Anode Designs
Effective focal spot
This is what the patient experiences
The area/shape of the beam projected onto the patient
and image receptorBy angling anode target, the effective focal spot ismuch smaller than the actual focal spot
This is what comes out of the anode towards the patient
Larger anode angle=larger effective focal spot
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Anode Designs
Dual Focal SpotAnode
Produces a narrow beam (used for detail) and a widerbeam
Anode Heel absorbs more radiationHeel Effectis the rate limiting factor in X-ray tubedesigns
Non-uniform beam from center out to edges=Heel Effect
Decrease Anode angle (Narrow Focal Spot)= Increase HeelEffect
From the center to the anode, the beam intensity falls off
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Anode Designs
Heel Effect
X-ray beam intensity is NOT uniform
X-rays produced within the anode are attenuated as
they pass out of the anodeThe effect is more pronounced with decreased (steep)anode angles
Higher intensity on the cathode side
Thicker body parts should be positioned towards the
cathode, and thinner body part towards the anodeAny photons directed along the heel plane are lessintense
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Anode Designs
Heel Effect
Beam fluence= # of photons per unit area
Because fluence is more uniform near the central ray, the
heel effect is not a concern whenSID (FFD) is increased
Collimation decreases field size for small anatomic areas(ex: foot)
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Filtration
FiltrationIs required by law for patient safety
Filters out long wavelength and lower energysoftradiation
This hardens the beamIs measured in mm/s of actual or equivalent aluminumthickness
There is Inherent Filtration and Added filtrationTotal Filtration=Added + Inherent
We want to filter the low energy photons before they hitthe patient
Increase Aluminum Filtration= Decrease X-ray exposure topatient
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Filtration
2 Types of Filtration
Inherent Filtrationtotal filtering equivalent inherentin any X-ray tube head
0.9-1.0 mm Al equivalentAdded FiltrationRequired by law!
Measured in actual or equivalent Aluminum Thickness
50-70 kVp range requires 1.5mm aluminum filtration (0.5
added)Total filtration= 2.5mm Al
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Filtration
Inherent FiltrationEquivalent aluminum filtration effect of inner X-ray tube headmaterials
Results when X-rays pass through
Glass envelope
Insulating oil surrounding tube
Window (bakelite, etc)
Range0.9- 1.0 mm Al equivalent
Components
Inherent FiltrationThinned wall of glass envelope of X-ray tube insert
Insulating oil
Aluminum added filtration
Thin metal mirror of collimatoroffers additional filtration
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Types of Filters
Added Filters
Attenuate via Photoelectric Reactions
Absorber placed in path of exiting X-rays
Aluminum is an excellent filter for low energy radiation
Compound filterscombine layered Al (Z=13) andCopper (Z=29) to cut down filter thickness for higherenergy beams
Copper faces X-ray beam
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Types of Filters
Compensating Filters
Compensate for part density variation
Changes the shape of the filter to allow a more unified
beamWedge filergreat for foot
Thick part is towards toes
Trough/bilateral wedge filterfor chest
The thin/central part is positioned over the mediastinum
Thicker lateral portions shadow aerated lung fieldstowards toes
Step-wedge filter
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Anode Interactions
Basic Anode Interactions
99% of interactions give useless infrared radiation (akaHeat) via outer orbital, non-ionizing electron excitation
1% of all anode interactions produce useful X-raysThree Basic Anode Interactions
Infrared Radiation99%
Bremsstrahlung Radiation0.9%
Characteristic Radiation0.1%
B t hl
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Bremsstrahlung
RadiationBremsstrahlung RadiationBraking RadiationElectrons do not collide with Tungsten anode atoms ortheir componenets
Diverted from original course due to opposing nuclearforces
Each deflection=braking effect
Each deflection yields a photon of radiation
Greater Deflection=Greater Energy
Kinetic energy lost by electrons through the Brakingeffect is converted to photons of equivalent energy
B t hl
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Bremsstrahlung
RadiationBremsstrahlung RadiationElectrons enter with similar Kinetic Energy
Incoming electrons from the cathode may undergo
many anode reactions before coming to restElectrons can penetrate thru many anode layers beforegiving up their total Kinetic energy
Exiting photons have many different energy values
Faster moving electrons produce higher energy,
shorter wavelength photonsSlower moving electrons produce lower energy,longer wavelength photons
B t hl
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Bremsstrahlung
RadiationBremsstrahlung RadiationBraking radiation is a wide distribution of energy inthe polyenergetic spectrum that is produced with
Bremsstrahlung Radiation
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Characteristic Radiation
Characteristic RadiationX-rays are characteristic of material used
Gives the spikes on the Bremsstrahlung curvearound 68 kVp
Discrete energy bands within the beam
Electrons bombarding target able to knock out inner orbital electronsIncoming electron energy is greater than or equal to atomic shellbinding energy of emitted electron
Incoming Electron Energy Atominc Shell Binding Energy
(+) charged target atom returns to normal energy state by emitting X-ray radiation characteristic of Tungsten
Tungsten is at a higher energy state
Electron drops from L to K: produce photon equal to binding shelldifference58 kEv
M to K drop down: 67 kEv
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Electron Binding Energy
Atomic electrons held by electrostatic pull of positivelycharged nucleus
The work required to remove the electron from theatom=binding energy
Bound particles always have negative potential energyTo freean electron from an atom, energy must be raised to0 or a positive value
The positively charged (ionized) tungsten anode atomreturns to its normal energy state by emitting radiation in
the X-ray wavelengthsContribution of Characteristic Radiation to X-ray beam isfrom 10%-28%--80-150 kVp
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The X-Ray Beam
Units of X-ray beam intensity (Exposure)Product of number of photons and their average photonicenergy
Intensity= Quantity x Quality
Unit of Measurement of Exposure= Roentgen (R)Amt of radiation needed to liberate a charge of .000258 C per Kg ofair
ExposureA source related term used to express intensity of an X-ray beam
Total charge liberated per unit air mass
Units of Exposure=Coloumbs per KgSi system
Roentgens (R)non SI units: 2.58 x 10^-4 C
4 Factors affecting the
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4 Factors affecting the
Quantityof X-Ray BeamPhotonsMilliamperage x Time (mAs)
Kilovoltage (kVp)
Distance
Filtration
Q tit f X R B
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Quantity of X-Ray Beam
PhotonsMilliamperageQuantity= area under the curve
Double mA=double the number of photons=doubles numberof emitted X-rays
Directly affects the number of photonsrecruits more orless photons
recruits more cars
Milliamperage x time= mAs
Beam intensity and mAs are directly proportional
Directly increases the area of Bremsstrahlung curve
DOES NOT change energy distribution
Q tit f X R B
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Quantity of X-Ray Beam
PhotonsKilovoltage (kVp)Beam intensity in direct proportions to kVp squared
Defines the QUANTITATIVE effect
Doubling kVp increases beam intensity x 4
This affects X-ray beam quality
Overall effect on film blackening is equal to the 4thpower
kVp usually stays constant
15% RuleTo maintain constant film density, and increase of the kVp by 15% shouldbe accompanied by a 50% Decrease in mAs
If you increase kVP, you must decrease the mAs by 50%Film density=degree of blackness produced by radiation
Optical density
High kVPsare safer than lower kVps
Q antit of X Ra Beam
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Quantity of X-Ray Beam
PhotonsDistanceInverse-Square Lawradiation intensity varies inverselywith the distance squared from the source
Results from X-ray beam divergence
Non-linear beam fall off with distanceEx:
Doubling distance from X-ray source DECREASES the intensityby a factor of 4
Increase distance= Decrease intensity
2x
3x1/94x1/16
Decrease Distance=Increase intensity
Quantity of X Ray Beam
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Quantity of X-Ray Beam
PhotonsFiltrationAttenuates X-rays of all energies
Results in a higher percentage of low-energy X-rays
Decreased area beneath Bremsstrahlung curve, alongwith a Right Shift
Increases effective beam energy
Beam Hardeningpreferential loss of lower energy
photonsDoubling filter thickness results in More energetic photonsvia Right Shift
2 Factors Affecting
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2 Factors AffectingQualityof X-Ray Beam
PhotonsKilovoltage (kVp)
Filtration
Quality of X Ray Beam
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Quality of X-Ray Beam
PhotonsX-Ray beam QualitySpecifies as the thickness of an Aluminum absorber thatreduces the beam intensity by 50%--called the Half ValueLayer
Half-Value LayerLower HVL means that the beam has too many low energyphotons
At 70-80 kVp, the legal minimum X-Ray beam HVL is 2.5-3.0mm Al
75 KvP is 2.8 HVLHVL increases with increasing filtration
Increase in filtration increases beam quality
Quality and Quantity of
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Quality and Quantity of
X-Ray Beam PhotonsSummaryAn Increase in
Kilovolt PeakIncreases Quantity and Quality
Milliampere-SecondIncreases the Quantity/Does notchange the quality
MilliamperageIncreases the Quantity/ Does not changethe Quality
Exposure TimeIncreases the Quantity/Does not changethe Quality
DistanceDecreases the Quantity/Does not change theQuality
FiltrationDecrease the Quantity/ Increases the Quality
Quality and Quantity of
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Quality and Quantity of
X-Ray Beam PhotonsIncrease in Quality with Increase in FactorKilovolt Peak
Milliampere-Seconds
Milliamperage
Exposure Time
Increase in Quality and Quantity with increase in factorKilovolt Peak
Decrease in Quantity with Increase in FactorDistance
Decrease in Quantity/Increase in Quality with Increase in FactorFiltration
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Matter Interactions
Practical Considerations
Interactions with AirIonizes Airbasis for Roetegns(R)
Interactions with PatientInteraction with image receptors
Film
Screens
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Matter Interactions
Interactions with Matter
PenetratePhotons pass through unaffected
No Deposition of Energy
AbsorbedPhotons transfer energy to absorbing medium
Energy deposited into bodyBAD
ScatteredPhotons change direction and possibly loseenergy
May or may not deposit energy
Interactions with Ionizing RadiationPhotons which are either absorbed or scattered ionize thepatients atoms
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Matter Interactions
Basic Interactions with MatterCoherent Scatter (5%)Insignificant
No energy deposiited
Not significant
Energy stays the samePhotoelectric AbsorptionSignificant
Compton ScatterSignificantIncident X-Ray comes in, and a photon is absorbed
Electron Cloud is excited
Photon is emitted
Increase in Atomic Number= Increase in Probability of comptonScatter
K-shell electron has to be equal to binding energy
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Photoeletcric Reaction
Photoelectric ReactionInteraction with matter where the incident X-ray is ABSORBEDnot Scattered
An electron escapes with Kinetic Energy equal to the difference between theenergy of incident X-ray and Electron Binding Energy
This yields weak characteristic Radiation in biologic systems
There is a vacancy in the K or L orbital that must be filledOne of the electrons from the outer orbital drops to the void
As the electron drops to the void, it may shed its excess energy as a secondaryphoton
3 Products of the Photoelectric Effect
Photoelectron
Characteristic Radiationweak and characteristic of atoms of body
Positive Ionatom is ionizedHigher Atomic Numbers are more likely to undergo the photoelectric effect
Not that Safewant to minimize these reactions for the patient
Photoelectric Effect
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Photoelectric Effect
ProbabilitiesThe incident photon must have sufficient energy to overcome theBinding Energy of the electronPhotoelectric Reaction most likely occurs when the photon energyand the Electron Binding Energy are nearly the same
The Photoelectric effect is more likely the tighter the electron isbound in orbit
Increase in atomic number= Increase in electron binding=Increase inPhotoelectric Effect
Increase in kVp= Decrease in photoelectric interactions to the thirdpower
Photoelectric effect allows better contrastDecrease kVpBasis for Mammography
Great for Viewing the Toes in Podiatry
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Compton Scatter
Compton effectGreatest risk to the X-ray operator
The photon interacts with an outer orbital electron, imparting some of itsenergy to the electron ejecting it from orbitionizes patients atoms
The ejected electron leaves the atom with an energy equal to the excessimparted by the photon
The photon continues on an altered path
Angle of deflection determines the energy of the Compton Photon (scatteredphoton)
Is scattered with less energy and longer wavelength than before the collision
Energy is Deposited--Can leave patients body and hit the operator
If it hits the film, it darkens the film in a random patternnot ideal
Thicker body parts= more scattered radiation= Increase in kVPIncrease in KvP= Decrease in Photoelectric Effect
Increase in KvP= Increases Compton Scatter80 kVp
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Compton Scatter
Increase in KvP= Decrease in Photoelectric Effect
Increase in KvP= Increases Compton Scatter80 kVp
Thicker body parts scatter more radiation= Higher
KvP= Increased Scattered Radiation
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Attenuation
4 Factors that Affect Attenuation:
Attenuation= Lessen in Intensity
KilovoltageInverse Square Law
DensityAtomic Number (Z)
Increase in Atomic Number=Increase in AttenuatingPower
Electrons per Gram of Tissue
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Attenuation
Attenuation--s the gradual loss in intensity of anykind of flux through a medium
Attenuation is Exponential
Monoenergetic Attenuationneed 3-4 half valuelayers to get to 1000 photons
Every centimeter is a Half-Value Layer
Polyenergetic AttenuationHalf value layer increasesto get to 62.5
Functionally Monoenergetic Attenuation after 3-4 HalfValue Layers (Required)
Units of Radiation
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Units of Radiation
Deposition and SafetyRadiation Detection and MeasurementAbsorbed Dose (D)Measures the amount ofradiation energy (E) absorbed per unit mass (M) of the
absorbing mediumAbsorbed Dose
D=E/MDose=Radiation Energy/Mass
Units
Gray (Gy)SI system
Radsnon SI units
Absorbed dose is not source related
Units of Radiation
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Units of Radiation
Deposition and SafetyAbsorbed Dose1 Gray= 1J of energy/kg
1 Rad=100 ergs of energy deposited/gram
1 Gray=100 rads1 Rad= 10 mGy
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Linear Transfer Energy
Linear Transfer Energy (LET)
Energy absorbed by the medium per unit length oftravel (keV per micrometer)
LET is proportional to Particle Charge squaredLET is inversely related to particle Kinetic Energy
Photons, electrons, gamma, and X-rays= Low LET
Neutrons, protons, and alpha particles= High LET
High LET=increase in biological damageNeutrons are used in cancer therapy
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Dose Equivalent
Dose Equivalent (H)Attempts to quantify biologic damage from deposition ofradiation in the tissues
Dose Equivalent=absorbed dose x quality factor
H=D x QFX-Rays, Gamma Rays, Electrons, Beta particles have a QualityFactor= 1.0
Neutrons and Protons= 5.0
Alpha Particles=10.0
Quality factor depends on the LET value
1 rad= 1 rem in diagnostic RadiologyQuality factor may be as high as 20 for alpha particles andheavy nuclei
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Dose Equivalent
Dose Equivalent
Units
Sievert (Sv)SI system
Rem (radiation equivalent man)non SI
1 Sv= 100 Rem
1 Rem= 10 mSV
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F-Factor Conversion
F-Factor converts exposure(X) and absorbed dose(D)
Roentgen to Rad conversion factor
D= f x XAt diagnostic X-ray energies, f-Factor for soft tissues isclose to 1.0
f-Factor for bone is 4 at Low kvP
F-factor for bone is 1 at High kVp
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Interactions With Film
A Latent image is formed
Heavily irradiated areas turn black
Ionic Ag +1 is reduced to metallic Ag 0
Image must then be developed
Complete attenuation of X-rays leaves the film clear
No radiation passes through
Partial attenuation/Transmission= Film is GraySome radiation passes through and some doesnt
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Interactions With Film
Emulsion contains Crystalline Silver-Halide GrainBromine and Iodine are halides
10^9 grains/cm3
Can be sensitized to radiation or light to hold a latent image
Latent image must then be developed
Atomic arrangement inside hexagonal film crystal is cubic
Sensitivity Speck is AgS surface defect
Non-rigid crystal with negative surface chargeAtoms and electrons may migrate
Absorbed photons liberate halide electrons within the grain
P oton Interact ons
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P oton Interact onswithin Silver-Halide
CrystalPhotoelectrons and Compton Electrons are producedthat migrate throughout the crystaldislodging
other electronsSome are trapped by the Ag+ sensitivity speck
Turns silver black when bromine interacts with Ag
Sensitivity speck ultimately becomes electronegative
Electrons are attracted towards the sensitivity speckturns sensitivity speck black
Photon Interactions within
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Photon Interactions withinSilver-Halide Crystal
In each crystal, less than 10 silver atoms are deposited atthe sensitivity speckwhich is the latent image center
They are not apparent microscopically, and are ultimately
developed into black grainsCrystal that have not been irridated will remain crystallineand inactive
Development process converts silver ions on sensitivity
speck to grainsDeveloper makes electrons available to silver on the filmrandomlyturns black
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End Exam 1 Material