Flashcards
Imaging Ch 5 & 6
Cards in this deck (135)
- 1Three main components of an x-ray systemTube
Operating console
High-voltage generator - 2What material are x-ray tables made of?Carbon fiber
- 3Ancillary equipment for tablesShoulder, foot supports
Hand grips
Compression bands - 4Most flexible type of tube supportCeiling mounted
- 5Amount of Hz coming into incoming line current60 Hz
- 6Amount of voltage coming into incoming line current220-240 volts
- 7Amperage in filament current3-8 amps
- 83 main conditions for x-ray productionHigh number of electrons
High voltage/potential difference
Direct current - 9Two sections of x-ray circuitMain circuit
Filament circuit - 10What two sections does the main circuit contain?Primary/low voltage side
Secondary/high voltage side - 11What two features are in the filament circuit?Filament
Rheostat - 12What does the filament do?Provides a high number of electrons
- 13RheostatVariable resistor - adjusts amperage by varying resistance
- 14What components are located on the control console?kVp
mA
time
rotor switch
exposure switch - 15Exposure switch is designed to prevent exposure beforeThe anode is up to speed
- 16What does the filament circuit do?Modifies current to filament in tube
Heats filament to boil off electrons
Controls mA of tube current - 176 components of filament circuit (in order)Incoming power
Circuit breaker/main switch
Line monitor and compensator
Rheostat
Focal spot selector
Filament transformer - 18What do the line monitor and compensator do?Adjust for fluctuations in incoming power
Tube needs exactly 220 or 240 volts - 19Focal spot selectorEnergizes small or large filament which determines small or large focal spot
- 20Filament transformer - step up or step down?Step down
- 21Filament transformer increases _______ and decreases _________Increases amperage
Decreases voltage - 22Components of main circuit - primary sideIncoming power
Circuit breaker, main switch
Line compensator and monitor
Autotransformer (kVp selector)
kVp meter
Timer - 23Is autotransformer step-up or step-down?Can be either, it's a variable transformer
- 24Turns ratio for filament transformerAlways <1
- 25Turns ratio for autotransformerVariable, can be <1 or >1
- 26Does the kVp meter register kVp before or after exposure?Before
- 27kVp meter displaysVoltage at secondary side of autotransformer
Displays kilovolts as a result of step-up transformer - 28What does the timer do?Controls duration of exposure
- 29Where is timer located in main circuit?Between autotransformer and high-voltage transformer
- 30What is the first component of the secondary/high-voltage side of the main circuit?High-voltage transformer
- 31Turns ratio of high-voltage transformerFixed ratio of either 500:1 or 1000:1
- 32When you select kVp, what two devices transform the incoming voltage into the kVp you selected?kVp selector/autotransformer
High-voltage transformer - 33Where is the mA meter located in the main circuit?Between high-voltage transformer and x-ray tube
- 34AEC registers mAs before or after exposure?After
- 35RectifierChange AC to DC before it reaches tube
- 36Where is rectifier located?Between high-voltage transformer and x-ray tube
- 37Transformer needs __ current; tube needs __ currenttransformer - AC
tube - DC
(this is why rectifier is located between transformer and tube) - 38X-ray generator is a term for all components of the circuit that:Provide electrical power to the x-ray tube
- 395 types of generatorsSingle-phase; 2 pulse
Three-phase; 6 pulse or 12 pulse
High frequency power generator
Falling load generator
Mobile unit generators - 40Single-phase generator - pulses per second120 pulses per second
- 41Average voltage produced by single-phase generator70% of kVp
- 42Voltage ripple of single-phase generator100%
(drops all the way to zero) - 43Dead zoneLow or no power
Only occurs in single-phase
Occurs 120 times per second - 44Three-phase power, 6 pulse3 separate sine waves generated in 3 separate phases
- 45Pulses per second in three-phase, 6 pulse360 pulses per second
- 46Voltage ripple in three-phase, 6 pulse13 - 25%
- 47Three-phase, 6 pulse produces _____% more x-ray photons than single-phase35%
- 48Pulses per second in three-phase, 12 pulse720 pulses per second
- 49Three phase, 12 pulse produces ___% more x-ray photons than single-phase41%
- 50Voltage ripple in three-phase, 12 pulse4-10%
- 51Advantages of 3Φ over 1ΦShorter exposure time
Higher average kVp
Greater x-ray photon energy
Greater x-ray photon production efficiency - 52Disadvantage of 3Φ compared to 1ΦMore costly
- 53Pulses per second in high-frequency generatorUp to 12,000 pulses per second
- 54Voltage ripple in high-voltage generatror3-4%
or >1??
Very small - 55High-voltage generators produce ___% more energy than single-phase45%
- 56Advantages/disadvantages of high-frequency generatorsAdvantages:
Small
More efficient; almost constant kVp
Increased radiation quality/quantity
Disadvantage: expensive - 57Less voltage ripple =Higher x-ray quality and quantity
- 58Single-phase tube generation factor (energy)1.0
- 593Φ6P; 3Φ12P; and High-frequency tube generation factor (energy)1.4
- 60Falling load generatorused with mAs timers
mA falls during exposure
automatically uses highest possible mA and shortest time - 61Advantages of falling load generatorGuaranteed shortest exposure time
Simpler, use with AEC - 62Disadvantages of falling load generatorShortens tube life due to filament wear
- 632 types of mobile x-ray generatorsCapacitor-discharge
Battery powered - 64CapacitorDevice that accumulates and stores an electrical charge
- 65Insulator material inside capacitorsDielectric
- 66Capacitor-discharge generatorDischarges all power completely during one exposure
- 67Advantages of capacitor-discharge generatorSmaller
- 68Disadvantages of capacitor-discharge generatorVoltage falls throughout exposure
Limited mAs
Long exposure times
Must be charged after every exposure - 69How does a capacitor store energy?When connected to DC current, electrons flow into the capacitor and are collected and stored on the negative place
- 70What rate does voltage fall at in a capacitor-discharge unit1kV/mAs
Ex: 20mAs @ 70kV
kV would drop by 20 (70 to 50kV) by end of exposure - 71Battery-powered generatorGenerator powered by bank of batteries that is charged from AC wall outlet
- 72What are batteries in battery-powered generator made of?Nickel-cadmium
- 73Advantages/disadvantages of battery-powered generatorsAdvantages:
Constant voltage & mAs during exposure
Disadvantages:
Larger and heavier than capacitor-discharge units - 74Power rating equation for three-phase and high frequencykW = (mA x kVp)/1000
- 75Power rating equation for single phasekW = (mA x kVp x 0.7)/1000
[mult. by 0.7 because of dead zone] - 76Characteristics of synchronous timersin sync with 60 Hz generator
must be reset after each exposure
minimum exposure time is 1/60s - 77Electronic timerMost common and most accurate
Wide range of settings, as small as 1ms - 78mAs timerTerminates when desired mAs is reached
Automatically provides shortest exposure time at largest mA - 79Automatic exposure controlAEC/AED/AECD
Measures radiation at the IR and terminates exposure when AEC receives preset amount of radiation - 802 types of AECPhototimer
Ionization chambers - 81PhototimerLocated under IR
Uses photomultiplier
Light sensitive - 82Ionization chambersLocated between patient & IR
Radiation sensitive - 83Minimum reaction or response time1ms
Minimum time needed for AEC to respond to radiation
determined by manufacturer - 84AEC/AED Back up timeManual exposure time set in case AEC fails
Set at 1.5-2 times the expected mAs - 85What does the x-ray tube consist of?Anode and cathode enclosed in a vacuum glass envelope and protective housing
- 86What is required in order to produce xrays?Source of electrons (filament)
Target material (anode)
High voltage
Vacuum tube - 87Parts of cathodeFilament
Focusing cup
Grid-biased tube - 88Functions of cathodeProduce thermionic cloud
Focus electron stream
Conduct voltage between anode & cathode - 89What is the filament?Small coil of thorium tungsten wire that produces an electron cloud
- 90What temperature does thermionic emission occur at?2200°C
- 91Melting point of tungsten3370°C
- 92Focusing cupShallow nickel depression housing filaments
- 93What does the focusing cup do?Narrows the thermionic cloud
Focuses electrons
Has a negative charge - 94Space-charge effectPoint at which no more electrons can be boiled off the filament
- 95Saturation currentPoint at which all available electrons in electron cloud have been sent across the tube
- 96Grid biased tubeA third wire adds a low current, positive charge to the focusing cup
- 97What does the filament current do?Creates electron cloud or space charge
- 98What does the tube current do?Draws electrons to anode
- 99Parts of the anodeFocal spot
Stator
Rotor - 100What is a stationary anode made of? What is the target angle? Where are they used?Tungsten in copper
45°
Used in dental units & low mA machines - 101Other terms used for targetFocus, focal point, focal spot, focal track
- 102Why is tungsten used in the target?High melting point, dissipates heat well
- 103How fast do rotors spin?3600rpm
High speed rotors can spin up to 10,000rpm - 104What is the rotating anode disk made of?Molybdenum, backed with graphite
- 105What is the target made of?Tungsten with rhenium
- 106What is the shaft/neck made of?Molybdenum
- 107What is the rotor made of?Copper
- 108Line focus principleUsed to reduce effective focal spot and control mA
As angle of target decreases, focal spot size and field size decrease - 109What is the focal spot size determined by?Filament size/length
Larger filament creates large focal spot; smaller filament creates small focal spot - 110What degree are most targets angled at?12°
- 111Advantages/disadvantages of large focal spotAdvantages: allows use of higher exposures, allows greater amount of heat
Disadvantages: Decreased spatial resolution (decreased image quality) - 112Advantages/disadvantages of small focal spotAdvantages: Increased spatial resolution
Disadvantages: Limited to lower mA due to concentration of heat in a smaller area - 113Anode heel effectRadiation intensity is greatest towards cathode side of tube
- 114Cathode end produces ___% more photons, while anode end produces ____% lessCathode - 20% more photons
Anode - 25% less photons - 115What can decrease the anode heel effect?Increased anode angle (focal spot)
- 116How would a smaller focal size effect anode heel effect?Smaller focal size would increase anode heel effect
- 117How does SID affect the anode heel effect?Increased SID decreases anode heel effect
Decreased SID increases anode heel effect - 118What is the stator composed of?Induction motor
Electromagnets - 119Where is the stator located?OUTSIDE the glass housing
- 120What is the rotor made of and where is it located?Copper and iron
Located inside tube - 121What are the two stages that occur when you press the exposure button?First stage - rotor accelerates, filament heats to thermionic emission
Second stage - voltage applied to tube, electrons accelerated and slammed into anode, x-rays photons produced - 122EnvelopePyrex glass that encloses cathode and anode (NOT stator)
Creates vacuum for electrons to flow with little friction
Contains a window or thinner area for electrons to exit the tube - 123Function of protective housingControl radiation leakage, protect against electrical shock, dissipate heat
- 124What is protective housing made of?Lead, filled with dielectric oil
- 125Useful beamX-rays emitted from window of tube that are used to produce the image
- 126Leakage radiationX-rays that escape the housing
- 127Off-focus radiationExtra focal radiation not produced at the focal spot
- 128Heat unit equationHU = mAs x kVp x tube generator factor x number of exposures
- 129Causes of tube failureAnode cracking
Ball bearing heat damage in rotor
Tube arcing
Filament breakage due to vaporization - 130What causes anode cracking?Overheated or near max exposure on a cold anode
- 131What causes ball bearing damage in the rotor?Overheated ball bearings warp and cause rotor to rotate improperly (wobbly rotor)
- 132What causes tube arcing?Tungsten vaporization - tungsten evaporates and deposits on the side of the tube
- 133What is a gassy tube?Evaporated tungsten on the inside of a tube - gassy tubes are no longer vacuums
- 134What is anode pitting?Anode focal track becomes roughened due to vaporization
- 135What is anode melting?Induction motor fails and rotor stops rotating
Entire exposure now hits one spot on the anode and melts it
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- Flashcards on Imaging Ch 5 & 6, created by Haley Cordova on 23/02/2016.
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- Haley Cordova
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