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Dx Imaging (X-Ray Imaging System)
Terms in this set (16)
What is needed fro x-rays to be produced?
Fast moving electrons slam into a metal object.
What are the 3 principle parts of the x-ray unit?
- X-ray tube
- Operating console
- High voltage generator
What controls the number of photons in the x-ray beam?
Number of x-rays or intensity of x-ray beam measured in mAs
What is the energy of the x-ray beam? What determines the energy of the beam?
Penetrability of the x-ray beam or energy of the beam, measured in kVP.
What is the tube current and what is its unit of measurement?
Milliamperes (mA) or Coulombs/sec
How is the tube current selected by the operator?
What type of current must be applied to the X-ray tube for t to operate?
What device ensures that electrical current only travels in one direction across the X-ray tube?
Rectifier that changes AC to DC.
Describe the x-ray output for half-wave rectification:
- Only uses electrons half the time
- Inverse voltage is removed from the supply to the x-rays tube by rectification.
- Represents a condition in which the voltage is not allowed to swing negatively during the negative half of the cycle.
- X-ray out put is pulsing at 60 per second.
- Waste half the power cycle and exposure take.
- Circuit allows only one half-cycle of the AC voltage waveform to be applied to the load, resulting in one none-alternating polarity across it.
Describe the x-ray output for full wave rectification. What happens to the exposure time, compared to half wave rectification.
- Use both positive and negative sine curve.
- Reduces exposure time by 1/2 over half-wave rectification.
- All waveform is used.
- Contains 4 diodes arranged in bridge configuration.
- X-ray tube bias/polarity remains the same.
- Creates 120 pulse/sec.
- Does NOT waste any input source so no gaps in output waveform.
- The negative half cycle corresponding to the inverse voltage is reverse so that a positive is always directed across the X-ray tube.
- Exposure time = decreasing half.
- Full Wave Rectification - have positive and negative.
- 1/2 Wave Rectification - more efficient.
What is the difference in single phase and three phase powers?
- Results in pulsating x-ray
- 1 wave you are dealing with
3 Phase powers
- Multiple voltage waveforms are superimposed on one another which results in a waveform that maintains a nearly constant voltage.
- Waves that are together but don't move at the same patter (3 different phases) —> 3 sets of waves.
Compare/contrast the voltage and ripple across the X-ray tube for single phase, 3 phase 6 pulse, 3 phase 12 pulse, and high frequency?
- 100% voltage ripple
3 Phase 6 Pulse
- 1/6 os (14% ripple)
- Better and more consistent x-rays than single phase.
3 Phase 12 Pulse
- 1/12 os (4%)
- <11% —> high energy in the beam.
- High voltage and low ripple.
How does voltage ripple affect the quantity and quality of the x-ray beam.
It increases quantity and quality. Decrease in ripple will increase quality and quantity.
What makes or breaks the high voltage across the X-ray tube?
What is the automatic exposure control (AEC)?
Measures the amount of radiation that passes through the patient and terminates when enough photons pass through patient to produce image.
What backup time should be set when using AEC, to protect the patient in case of malfunction?
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