radio exam 1 material

8/10/2019 Radio Exam 1 Material

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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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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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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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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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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



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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

radio exam 1 material

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