4618462
Description
Flashcards by Haley Cordova, updated more than 1 year ago
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Created by Haley Cordova
almost 10 years ago
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| Question | Answer |
| Three main components of an x-ray system | Tube Operating console High-voltage generator |
| What material are x-ray tables made of? | Carbon fiber |
| Ancillary equipment for tables | Shoulder, foot supports Hand grips Compression bands |
| Most flexible type of tube support | Ceiling mounted |
| Amount of Hz coming into incoming line current | 60 Hz |
| Amount of voltage coming into incoming line current | 220-240 volts |
| Amperage in filament current | 3-8 amps |
| 3 main conditions for x-ray production | High number of electrons High voltage/potential difference Direct current |
| Two sections of x-ray circuit | Main circuit Filament circuit |
| What two sections does the main circuit contain? | Primary/low voltage side Secondary/high voltage side |
| What two features are in the filament circuit? | Filament Rheostat |
| What does the filament do? | Provides a high number of electrons |
| Rheostat | Variable resistor - adjusts amperage by varying resistance |
| What components are located on the control console? | kVp mA time rotor switch exposure switch |
| Exposure switch is designed to prevent exposure before | The anode is up to speed |
| What does the filament circuit do? | Modifies current to filament in tube Heats filament to boil off electrons Controls mA of tube current |
| 6 components of filament circuit (in order) | Incoming power Circuit breaker/main switch Line monitor and compensator Rheostat Focal spot selector Filament transformer |
| What do the line monitor and compensator do? | Adjust for fluctuations in incoming power Tube needs exactly 220 or 240 volts |
| Focal spot selector | Energizes small or large filament which determines small or large focal spot |
| Filament transformer - step up or step down? | Step down |
| Filament transformer increases _______ and decreases _________ | Increases amperage Decreases voltage |
| Components of main circuit - primary side | Incoming power Circuit breaker, main switch Line compensator and monitor Autotransformer (kVp selector) kVp meter Timer |
| Is autotransformer step-up or step-down? | Can be either, it's a variable transformer |
| Turns ratio for filament transformer | Always <1 |
| Turns ratio for autotransformer | Variable, can be <1 or >1 |
| Does the kVp meter register kVp before or after exposure? | Before |
| kVp meter displays | Voltage at secondary side of autotransformer Displays kilovolts as a result of step-up transformer |
| What does the timer do? | Controls duration of exposure |
| Where is timer located in main circuit? | Between autotransformer and high-voltage transformer |
| What is the first component of the secondary/high-voltage side of the main circuit? | High-voltage transformer |
| Turns ratio of high-voltage transformer | Fixed ratio of either 500:1 or 1000:1 |
| When you select kVp, what two devices transform the incoming voltage into the kVp you selected? | kVp selector/autotransformer High-voltage transformer |
| Where is the mA meter located in the main circuit? | Between high-voltage transformer and x-ray tube |
| AEC registers mAs before or after exposure? | After |
| Rectifier | Change AC to DC before it reaches tube |
| Where is rectifier located? | Between high-voltage transformer and x-ray tube |
| Transformer needs __ current; tube needs __ current | transformer - AC tube - DC (this is why rectifier is located between transformer and tube) |
| X-ray generator is a term for all components of the circuit that: | Provide electrical power to the x-ray tube |
| 5 types of generators | Single-phase; 2 pulse Three-phase; 6 pulse or 12 pulse High frequency power generator Falling load generator Mobile unit generators |
| Single-phase generator - pulses per second | 120 pulses per second |
| Average voltage produced by single-phase generator | 70% of kVp |
| Voltage ripple of single-phase generator | 100% (drops all the way to zero) |
| Dead zone | Low or no power Only occurs in single-phase Occurs 120 times per second |
| Three-phase power, 6 pulse | 3 separate sine waves generated in 3 separate phases |
| Pulses per second in three-phase, 6 pulse | 360 pulses per second |
| Voltage ripple in three-phase, 6 pulse | 13 - 25% |
| Three-phase, 6 pulse produces _____% more x-ray photons than single-phase | 35% |
| Pulses per second in three-phase, 12 pulse | 720 pulses per second |
| Three phase, 12 pulse produces ___% more x-ray photons than single-phase | 41% |
| Voltage ripple in three-phase, 12 pulse | 4-10% |
| Advantages of 3Φ over 1Φ | Shorter exposure time Higher average kVp Greater x-ray photon energy Greater x-ray photon production efficiency |
| Disadvantage of 3Φ compared to 1Φ | More costly |
| Pulses per second in high-frequency generator | Up to 12,000 pulses per second |
| Voltage ripple in high-voltage generatror | 3-4% or >1?? Very small |
| High-voltage generators produce ___% more energy than single-phase | 45% |
| Advantages/disadvantages of high-frequency generators | Advantages: Small More efficient; almost constant kVp Increased radiation quality/quantity Disadvantage: expensive |
| Less voltage ripple = | Higher x-ray quality and quantity |
| Single-phase tube generation factor (energy) | 1.0 |
| 3Φ6P; 3Φ12P; and High-frequency tube generation factor (energy) | 1.4 |
| Falling load generator | used with mAs timers mA falls during exposure automatically uses highest possible mA and shortest time |
| Advantages of falling load generator | Guaranteed shortest exposure time Simpler, use with AEC |
| Disadvantages of falling load generator | Shortens tube life due to filament wear |
| 2 types of mobile x-ray generators | Capacitor-discharge Battery powered |
| Capacitor | Device that accumulates and stores an electrical charge |
| Insulator material inside capacitors | Dielectric |
| Capacitor-discharge generator | Discharges all power completely during one exposure |
| Advantages of capacitor-discharge generator | Smaller |
| Disadvantages of capacitor-discharge generator | Voltage falls throughout exposure Limited mAs Long exposure times Must be charged after every exposure |
| How does a capacitor store energy? | When connected to DC current, electrons flow into the capacitor and are collected and stored on the negative place |
| What rate does voltage fall at in a capacitor-discharge unit | 1kV/mAs Ex: 20mAs @ 70kV kV would drop by 20 (70 to 50kV) by end of exposure |
| Battery-powered generator | Generator powered by bank of batteries that is charged from AC wall outlet |
| What are batteries in battery-powered generator made of? | Nickel-cadmium |
| Advantages/disadvantages of battery-powered generators | Advantages: Constant voltage & mAs during exposure Disadvantages: Larger and heavier than capacitor-discharge units |
| Power rating equation for three-phase and high frequency | kW = (mA x kVp)/1000 |
| Power rating equation for single phase | kW = (mA x kVp x 0.7)/1000 [mult. by 0.7 because of dead zone] |
| Characteristics of synchronous timers | in sync with 60 Hz generator must be reset after each exposure minimum exposure time is 1/60s |
| Electronic timer | Most common and most accurate Wide range of settings, as small as 1ms |
| mAs timer | Terminates when desired mAs is reached Automatically provides shortest exposure time at largest mA |
| Automatic exposure control | AEC/AED/AECD Measures radiation at the IR and terminates exposure when AEC receives preset amount of radiation |
| 2 types of AEC | Phototimer Ionization chambers |
| Phototimer | Located under IR Uses photomultiplier Light sensitive |
| Ionization chambers | Located between patient & IR Radiation sensitive |
| Minimum reaction or response time | 1ms Minimum time needed for AEC to respond to radiation determined by manufacturer |
| AEC/AED Back up time | Manual exposure time set in case AEC fails Set at 1.5-2 times the expected mAs |
| What does the x-ray tube consist of? | Anode and cathode enclosed in a vacuum glass envelope and protective housing |
| What is required in order to produce xrays? | Source of electrons (filament) Target material (anode) High voltage Vacuum tube |
| Parts of cathode | Filament Focusing cup Grid-biased tube |
| Functions of cathode | Produce thermionic cloud Focus electron stream Conduct voltage between anode & cathode |
| What is the filament? | Small coil of thorium tungsten wire that produces an electron cloud |
| What temperature does thermionic emission occur at? | 2200°C |
| Melting point of tungsten | 3370°C |
| Focusing cup | Shallow nickel depression housing filaments |
| What does the focusing cup do? | Narrows the thermionic cloud Focuses electrons Has a negative charge |
| Space-charge effect | Point at which no more electrons can be boiled off the filament |
| Saturation current | Point at which all available electrons in electron cloud have been sent across the tube |
| Grid biased tube | A third wire adds a low current, positive charge to the focusing cup |
| What does the filament current do? | Creates electron cloud or space charge |
| What does the tube current do? | Draws electrons to anode |
| Parts of the anode | Focal spot Stator Rotor |
| What 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 |
| Other terms used for target | Focus, focal point, focal spot, focal track |
| Why is tungsten used in the target? | High melting point, dissipates heat well |
| How fast do rotors spin? | 3600rpm High speed rotors can spin up to 10,000rpm |
| What is the rotating anode disk made of? | Molybdenum, backed with graphite |
| What is the target made of? | Tungsten with rhenium |
| What is the shaft/neck made of? | Molybdenum |
| What is the rotor made of? | Copper |
| Line focus principle | Used to reduce effective focal spot and control mA As angle of target decreases, focal spot size and field size decrease |
| What is the focal spot size determined by? | Filament size/length Larger filament creates large focal spot; smaller filament creates small focal spot |
| What degree are most targets angled at? | 12° |
| Advantages/disadvantages of large focal spot | Advantages: allows use of higher exposures, allows greater amount of heat Disadvantages: Decreased spatial resolution (decreased image quality) |
| Advantages/disadvantages of small focal spot | Advantages: Increased spatial resolution Disadvantages: Limited to lower mA due to concentration of heat in a smaller area |
| Anode heel effect | Radiation intensity is greatest towards cathode side of tube |
| Cathode end produces ___% more photons, while anode end produces ____% less | Cathode - 20% more photons Anode - 25% less photons |
| What can decrease the anode heel effect? | Increased anode angle (focal spot) |
| How would a smaller focal size effect anode heel effect? | Smaller focal size would increase anode heel effect |
| How does SID affect the anode heel effect? | Increased SID decreases anode heel effect Decreased SID increases anode heel effect |
| What is the stator composed of? | Induction motor Electromagnets |
| Where is the stator located? | OUTSIDE the glass housing |
| What is the rotor made of and where is it located? | Copper and iron Located inside tube |
| What 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 |
| Envelope | Pyrex 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 |
| Function of protective housing | Control radiation leakage, protect against electrical shock, dissipate heat |
| What is protective housing made of? | Lead, filled with dielectric oil |
| Useful beam | X-rays emitted from window of tube that are used to produce the image |
| Leakage radiation | X-rays that escape the housing |
| Off-focus radiation | Extra focal radiation not produced at the focal spot |
| Heat unit equation | HU = mAs x kVp x tube generator factor x number of exposures |
| Causes of tube failure | Anode cracking Ball bearing heat damage in rotor Tube arcing Filament breakage due to vaporization |
| What causes anode cracking? | Overheated or near max exposure on a cold anode |
| What causes ball bearing damage in the rotor? | Overheated ball bearings warp and cause rotor to rotate improperly (wobbly rotor) |
| What causes tube arcing? | Tungsten vaporization - tungsten evaporates and deposits on the side of the tube |
| What is a gassy tube? | Evaporated tungsten on the inside of a tube - gassy tubes are no longer vacuums |
| What is anode pitting? | Anode focal track becomes roughened due to vaporization |
| What 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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