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TRANSCRIPT
3/3/2017
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Equipment Operation
and Quality Control
Daw n Couch Moore, M.M.Sc., RT (R)
Assistant Professor and Director
Emory University
Medical Imaging Program
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ARRT Specifications
• Safety
– Principles of Radiation Physics 11
• Image Production
– Equipment Operation and QA 29
• Imaging Equipment
• Quality Control / Accessories
3
Principles of Radiation Physics
• X-ray Production
• Target Interactions
• X-ray Beam
X-ray Production
• Primary beam
• Secondary beam
• Remnant beam
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5
X-ray Production
• X-ray s are produced
whenev er high speed
electrons are suddenly
decelerated.
6
X-ray Production
• Source of electrons
• Acceleration of electrons
• Deceleration of electrons
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X-ray Production
• Focusing of electrons
• Vacuum
• Heat remov al mechanism
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Processes in X-ray Production
• Bremsstrahlung
• Characteristic
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Bremsstrahlung
(Brems)
• Electron-nuclear f ield interaction
• Electron loses kinetic energy and changes direction
• Lost KE appears as an
x-ray photon Carlton & Adler, 2006
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Bremsstrahlung
(Brems)
• Produces heterogeneous
beam
• Comprises 70-90% of
beam (kVp > 80)
• Maximum energy photon
= kVp lev elBushong, 2004
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Characteristic
• Electron-orbital electron interaction
• X-ray s are produced by electron transition
• Photon energy = dif f erence in shell binding
energies
Carlton & Adler, 2006
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Characteristic
• Produces a discrete
spectrum
• Only k-characteristic
photons are usef ul
• Comprises 10-30% of
beam (kv p > 80)
Bushong, 2004
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Emission Spectrum
• Composite of Brems and
Characteristic radiation
• Poly energetic
• Heterogeneous Bushong, 2004
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Emission Spectrum
• Quantity
– mAs
– kVp
– Filtration
– “Z” of target
– Distance
• Inverse Square Law
– Voltage Wav ef orm
• Quality
– kVp
– “Z” of target
– Filtration
• Amount
• Atomic Number
– Voltage Wav ef orm
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Emission Spectrum(mAs: mA and Time)
Carlton & Adler, 2006
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Emission Spectrum(kVp)
Carlton & Adler, 2006
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Emission Spectrum(Atomic # of Target)
Bushong, 2004
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Emission Spectrum(Filtration)
Bushong, 2004
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Emission Spectrum
(Distance)
• Distance
– Inv erse Square Law 40”
72”
Bushong, 2004
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Emission Spectrum(Voltage Waveform)
Carlton & Adler, 2006
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Fundamental Properties
of X-rays
• Electromagnetic radiation
– High Energy
– High Frequency
– Short Wav elength
• 0.1-0.5 A
– Constant v elocity
• 3 x 108 m/sCarlton & Adler, 2006
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Fundamental Properties
of X-rays
• Travel in straight lines
• Cause biological damage
– Ionization
• Photoelectric Effect
• Compton Scatter
– Excitation
• Cause phosphorescence
Carlton & Adler, 2006
Fundamental Properties
of X-rays
• Undetectable by
human senses
• Electrically neutral
• Cannot be focused
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Imaging Equipment
• Types of Radiographic Units
• Components of Radiographic Units
• X-Ray Generator, Transformers, and
Rectif ication System
• Components of Fluoroscopic Units
• Components of Digital Imaging Units
• Accessories
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Types of Units
• Stationary
– Radiographic
– R & F
• Mobile
– Radiographic
– Fluoroscopic (C-arm)
• Specialized/ Dedicated
– Chest units
– Dental units
– Mammography
– Bone Densitometry
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Basic Radiographic Units
• X-ray Tube
• Control Console
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X-ray Tube Design
• Basic Components
– Env elope
– Cathode Assembly
– Anode Assembly
– Induction Motor
• Held within the Tube
Housing
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Tube Housing
• Provides mechanical support for x-ray tube
• Absorbs leakage radiation
• Protects against electric shock
• Aids in heat dissipation
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Envelope
• Py rex Glass / Metal
• Vacuum Tube
• Port WindowCarlton & Adler, 2006
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Cathode Assembly
• Negativ e electrode
• Components:
– Filaments
– Electrical connections
– Focusing cup
Carlton & Adler, 2006
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Anode Assembly
• Positiv e electrode
• Decelerates projectile
electrons
• Ty pes:
– Stationary
– Rotating
Carlton & Adler, 2006
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Anode Assembly
• Designed according to
the Line Focus Principle
– Large actual area f or
heat dissipation
– Small projected area
f or improv ed detailCarlton & Adler, 2006
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Induction Motor
• Two parts:
– Stator (external)
– Rotor (internal)
• Rotation speed
– Normal 3000-3600 rpm
– High Speed 10,000 rpm
Carlton & Adler, 2006
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Control Console
• kVp selector
• mA selector
• Time selector
• Rotor Switch
• Exposure Switch
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Control Console
• kVp Selector:
– Sets v oltage dif f erence
between cathode and
anode
– Controls kinetic energy
of projectile electrons
– Controls beam quality
Carlton & Adler, 2006
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Control Console
• mA Selector:
– Sets f ilament current
– Controls heating of the
f ilament and thermionic
emission
• (# of electrons
av ailable f or x-ray
production)
– Controls beam quantity
Carlton & Adler, 2006
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Control Console
• Time Selector:
– Sets length of exposure
– Controls how long electrons are allow ed to
f low from the cathode to the anode
– Controls beam quantity
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Control Console
• Rotor Sw itch
– Brings rotor up to speed
– Triggers f ilament heating
– Triggers grid in Bucky (if activ ated)
• Exposure Sw itch
– Completes circuit
– Initiates kVp production
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Circuit Components Associated
with Control Panel
• kVp Selector
– Autotransf ormer
• mA Selector
– Rheostat
• Time Selector
– Timer circuit
• Rotor Switch
– Stator of induction
motor
• Exposure Switch
– Remote switch
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Timer Circuit
• Manual
– Mechanical
– Sy nchronous
– Electronic
– mAs timers
• AEC / AED
– Automatic Exposure
Control / Dev ice
– Automatically
terminates exposure
af ter a preset amount
of radiation has
reached the image
receptor
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AEC /AED
• Utilizes a f lat, parallel
plate ionization chamber
• Minimum response time
– 1 mSec
Carlton & Adler, 2006
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AEC / AED Detectors
• Must select correct photocells
• Must set optimum kVp lev el
• Must set backup timer
– 150% of expected time
– 600 mAs
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AEC / AED Density Control
• -3, -2, -1, 0, 1, 2, 3
• Changes mAs
– 25-30% (Papp)
– 12-15% (Carlton & Adler)
• Changes OD
– 0.1 (Bushong)
– 0.15 (Carlton & Adler)
– 0.2 –0.25 (Papp)
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X-ray Tube Operation
• Warm-up Procedures
• Heat Unit Calculations
• Tips for Extending Tube Life
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Tube Warm-up Procedures
• Prevents thermal shock
– Cracking of a cold anode
• Refer to manufacturer’s guidelines
– Several moderate exposures
– Automated series of exposures
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Heat Unit Calculations
• HU= kVp * mA * Time * Generator Factor
• Generator Factors:
– Single Phase: 1.0
– Three Phase, 6-pulse: 1.4
– Three Phase, 12-pulse: 1.4
– High Frequency: 1.4
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Tips for Extending Tube Life
• Warm up the anode.
• Don’t hold the rotor sw itch unnecessarily.
• Use low er mA stations w hen possible.
• Use low er rotor speed w hen possible.
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Tips for Extending Tube Life
• Don’t make repeated exposures near the tube
loading limit.
• Don’t use the tube w hen you hear loud rotor
bearings.
• Use the appropriate operational charts.
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Tips for Extending Tube Life
• Know the heat capacity of the anode.
– 70,000 - 400,000 HU
• Know the heat capacity of the tube housing.
– 1 - 1.5 Million HU
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X-ray Generation and
Rectification
• Basic Electronics
• Transformers
• Rectif ication
• X-ray Circuit
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Simple Electric Circuit
• Components
– Conductor
– Voltage Source
– Resistor
Carlton & Adler, 2006
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Circuit Factors
• Current (I)
– Unit: Ampere
• Voltage (V)
– Unit: Volt
• Resistance (R)
– Unit: Ohm Carlton & Adler, 2006
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Ohm’s Law
• I = V/R
• The current f low in a circuit is directly proportional to the v oltage and inv ersely proportional to the resistance.
Carlton & Adler, 2006
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Types of Circuits
• Series Circuit
• Parallel Circuit
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Series Circuit
• All components are
connected in a row on the
main conductor.
Carlton & Adler, 2006
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Effect of Series Circuit on
Circuit Factors
• It = I1 = I2 = I3
• Vt = V1 + V2 + V3
• R t = R1 + R2 + R3
Carlton & Adler, 2006
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Parallel Circuit
• Components are
connected on separate
branches of the circuit.
Carlton & Adler, 2006
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Effect of Parallel Circuit on
Circuit Factors
• It = I1 + I2 + I3
• Vt = V1 = V2 = V3
• 1/R t = 1/R1 + 1/R2
Carlton & Adler, 2006
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Transformers
• Principle of operation
– Electromagnetic Induction
• Effect on circuit factors
– Voltage
– Current
• Types:
– Fixed Ratio
– Variable Ratio
Carlton & Adler, 2006
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Transformer Construction
Carlton & Adler, 2006
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Transformer Laws
• Transformer Ratio = # of secondary turns
# of primary turns
*TR > 1: step-up transformer
TR < 1: step-dow n transformer
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Transformer Laws
• Vsecondary / Vprimary = Nsecondary / Nprimary
• Isecondary / Iprimary = Nprimary / Nsecondary
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Transformer Placement in Circuit
Carlton & Adler, 2006
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Rectification
• Def inition
• Dev ices
• Cy cle Modif ications
• Voltage Ripple
Carlton & Adler, 2006
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Rectification
• The process of
conv erting AC to
pulsating DC f or more
ef f icient x-ray tube
operation.
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Types of Rectifiers
• Solid State Dev ices
– No f ilament
– More Compact
– Produce less heat
– No separate power source required
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Cycle Modifications
• 1 Ø, Full Wav e
• Inv erts the negativ e
alteration to produce 2
electrical pulses/cy cle
• 100% v oltage ripple
Carlton & Adler, 2006
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Cycle Modifications
• 3 Ø, 6-pulse
• Sy nony mous with 3 Ø,
half -wav e rectif ication
• 13-25% v oltage ripple
Carlton & Adler, 2006
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Cycle Modifications
• 3 Ø, 12 pulse
• Sy nony mous with 3 Ø,
f ull-wav e rectif ication
• 4-10% v oltage ripple
Carlton & Adler, 2006
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Cycle Modifications
• High Frequency
Generators
– 500-5000 Hz
– < 1% v oltage ripple Bushong, 2004
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Cycle Modifications
Carlton & Adler, 2006
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Completed X-ray Circuit
Carlton & Adler, 2006
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Quality Control
• Beam Restriction
• Recognition and Reporting of Malfunctions
• Shielding Accessories
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Beam Restriction
• Beam Restriction
– Light Field/ Radiation
Field Alignment:
+/- 2% of SID
– PBL: +/- 2% of SID
• Central Ray Alignment
– 1% v ariance
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Radiographic Unit Maintenance
• Equipment Calibration
– kVp
– mA
– Timer
– SID
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Equipment Calibration
• kVp: +/- 5% or +/- 4 kVp
• mAs
– Linearity: +/- 10%
– Reproducibility: +/- 5%
– Reciprocity: +/- 10%
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Equipment Calibration
• Timer accuracy :
– +/- 5% > .01s
– +/- 20% < .01s
• SID: +/- 2%
Equipment Calibration
• HVL
– Beam quality
– Must exceed the
required minimum
• 2.0 mm AL @ 70
kVp (3 Ø)
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Equipment Calibration
• Focal Spot Size
– 50% variance
• Tests
– Pinhole camera
– Slit camera
– Star Test Pattern
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Shielding Accessories
• Lead Apparel Check
– Bi-annually
– Fluoroscope/
Radiograph
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Be A Professional Radiographer
• Be an expert in equipment operation!
• Understand technical factor
selection and the impact on:
– Beam quantity
– Beam quality
– Image quality
• Provide high quality care!