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LPT Chapter 6
| Question | Answer |
|---|---|
| x-ray circuit divided into what 3 parts? | low-voltage circuit, high-voltage circuit and filament circuit |
| low voltage circuit is circuit between what? | AC power supply and primary input side of high-voltage (step-up) transformer |
| All devices of low-voltage circuit are found where? | in control console |
| What is the control console? | unit where exposure technique like kVp, mA, and exposure time are selected |
| Voltage of power supply supplied to facilities? Usually? | 220 V |
| What current comes into the facility? | AC |
| Main switch controls | power to control console |
| Voltage compensator does what? | Monitors minor changes in incoming 220 V of room because it could cause large variations of kVp to tube. |
| What type of coil is autotransformer? | single-coil transformer |
| Autotransformer's primary purpose? | vary the boltage to the pirmary side of the stepup transformer |
| 3 functions of autotransfromer? | 1) kVp selection 2) compensations for fluctuations in line voltage 3) power to other parts of circuit |
| How is varying the voltage to primary side of stepup transformer accomplished? | kVp selector |
| What side of autotransformer is the kVp selector on? | secondary output side |
| How does autotransformor vary kVp to tube? | by controlling the input to the step-up transformer |
| What does exposure switch do? | allows electric current to flow through primary side of step up transformer and induce current to flow through secondary side of transformer creating voltage across the x-ray tube |
| What does exposure switch do? | terminates the exposure and is set by the operator on the control console |
| Parts of the low-voltage circuit? | main switch, auto transformer, kVp selectors, exposure switch, exposure, line monitor |
| Primary purpose of the filament circuit? | supply a low current tot heat the x-ray tube filament for thermionic emission of electrons |
| Filament circuit is activated when? | any time the operator adjusts the mA on the generator |
| Step-down transformer does what? | reduces the voltage on secondary side providing an appropriate current to heat the filament |
| mA selector controls? | amperage in the filament circuit # of electrons at x-ray tube filament mA in the high-voltage circuit |
| High-voltage circuit begins and ends with? | step-up transformer (secondary side) |
| High-voltage circuit includes? | x-ray tube and rectifier unit |
| Current flows in high voltage circuit only during? | an exposure |
| Step-up transformer also called? | high-voltage or high tension transformer |
| Primary purpose of high-voltage circuit is to? | supply x-ray tube with voltage high enough to creat x-rays |
| What is rectification? | process of changing AC to DC so it flows in one direction only. |
| 3 ways current is rectified? | half-wave rectification and full-wave rectification and self-rectification (not used) |
| What is a diode? | electronic device, only permits current to flow in 1 direction only |
| how many diodes used in half-wave rect? | 2 |
| What is half-wave rectification? | negative cycle of AC canceled y a diode. x-rays pulse on and off at a rate of 60 pulses/sec |
| Full-wave rectification uses how many diodes? | 4 |
| What is full-wave rectification? | negative impulses from AC are tuned positive using the entire electric cycle |
| How many pulses per second with full wave rectification? | 120 |
| Full wave rectification _____ x-ray output | doubles |
| All modern general purpose x-ray machines use what kind of rectification? | full-wave |
| What is the main advantage of full-wave rectification? | exposure time is cut in half because of doubling in s-ray output compare with half-wave rectification |
| single phase x-ray generators are powered by a ____ source of AC current | single |
| Single phase current results in ___ x-ray beam | pulsating |
| What is a three-phase x-ray generator? | powered by 3 separate sources of AC current at the same time |
| Does three-phase current with full-wave rectifiaction there are ____ pulses of electricity per second? | 360 |
| Major advantages of 3-phase current? | more efficient, produces ~ 40% more x-rays than single-phase current, less exposure time by 40 % |
| What is most frequent generator used today? | high-frequency x-ray generator |
| What is primary function of high frequency circuity? | the 60 Hz full-wave rectified circuit is converted to a higher frequency of about 6,000 Hz (or higher!) |
| How many sources of AC with High frequency generator | 1 source |
| High frequency produce _____ amount of x-rays | greatest, near constant voltage |
| What is a synchronous exposure timer? | controlled by small electric motor rotating at 60 revs/sec each of 60 impulses can be used as an exposure time 17 msec is shortest time. stated in fractions. |
| What is an electronic exposure timer? | timer capable of short expostures 1 msec or less, more accurate, used with 3-phase and high-frequency |
| What is automatic exposure control (AEC)? | terminates exposure time when a certain quantity of radiation has been detected by IR |
| With AEC the exposure time is ______ determined? | automatically |
| AEC senses photons using ______? | phototimers and ionization chambers |
| The sensors for AEC are located between? | grid and IR |
| When using an AEC ____ must be absolutely accurate? | patient positioning |
| Density control selections? | enables by preset amounts used only after image is made |
| Back-up timer? | timer set manually if automated system fails |
| Back-up timer set to ______ % more than anticipated exposure? | 150 |
| Law states that generators must terminate at ______ mAs for exposrues over 50 kVp | 600 |
| What is anatomically programmed radiography (APR) | By selecting 1 or 2 controls the other exposure factors are automatically chosen |
| What is a rotor switch? | rotates anode, heats filament says ready for exposure |
| When the tube is ready, the limited operator initiates the exposure by continuing to hold _____ and also pressing ______ | rotor switch; exposure switch |
| Premature release of either the rotor switch or the exposure switch will _____ the exposure before it complete | abort |
| What can cause the anode to expand too rapidly and crack and fail? | excessive exposure on a cold tube |
| What is a good warm-up procedure? | 30 sec apart, 3 exposures, 200 mA, 0.5 second, 80 kVp |
| What can damage the tube by melting the tungsten surface of the focal track? | a rapid series of large exposures |
| tube rating chart is? | a chart for maximum tube capacity for a single exposure below line is safe exposure |
| What are heat units (HU)? | max heat capacity of anode |
| What are formulas for Heat Unit factors for single phase, three phase and high frequency? | single phase: HU = mA x time x kVp three phase: HU = mA x Time x kVp x 1.35 high frequency: HU = mA x Time x kVp x 1.40 |
| Do not activate the rotor switch before? | before you are completely ready to make an exposure |
| _______ anode according to the manufacturers instructions | Warm-up |
| Do not hold down the rotor switch.... | for long periods of time |
| Use _____ mA settings whenever possible | low |
Created by:
Cjenki10