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The x-ray tube is housed in an envelope made of glass or metal that provides a sealed atmosphere which allows air to be removed from the tube. Why is that important?
The vacuum removes unnecssary atoms from the air that might interact with the electron stream as it move sfrom cathode to anode.
It also increases tube efficiency
Why is tungsten mostly used for the creation of the anode?
Tungsten is used because it disspitates heat, resists melting and produces quality x-rays.
What is the focal spot?
The area of the anode where x-ray is produced.
What is the differenc between anode and cathode?
Cathode is the negative part of the tube while Anode is the positive side.
Is the filament part of the cathode or anode?
The filament is part of the cathode.
What charge does the filament have?
Rotors can spin the anode up to how many RPM's?
The rotor cna spin the anode from 3600 RPM to 12,000 RPM.
What is thermionic emission? What is the result of this?
When electrons boil off the cathode creating the high number of electrons needed to produce x-rays.
What does the molybdenum do?
It helps reduce the amount of heat that is trasnferred from the anode to the rest of the x-ray tube.
X-ray beam can be altered or manipulated by adjusting Five Major Factors. They are...
- - Milliamperage (mA)
- - Exposure Time (seconds)
- - Kilovolatage Peak (kVp)
- - Beam Filtration
- - Generator Waveform
What does mAs control?
It controls the amount of x-ray photons that are emitted from the x-ray tube.
An increase in mAs does what to the amount of x-ray photons emitted?
Increase in mAs increases the amount of x-ray photons emitted.
What does the kVp determine?
- Kvp determines the strength/energy of the x-ray photons.
How does a higher kVp affect the energy of the x-ray photon?
- An increase in kVp increaes the x-ray photons energy.
- Since the x-ray photons will have more energy, it will have the ability to be able to penetrate through objects better.
What is the reason we used filtration? What happens to patient dose with added filtration?
- To remove weaker x-rays that the beam produces in x-ray tubes.
- With added filtration, it decreases patient dose.
The type of generator power supplying the x-ray tube influences the production of the x-ray beam
- Single Phase
- 3-phase six pusle
- 3-phase twelve pulse
- High Frequency generators.
Whats the difference between them? How does increasing or decreasing generator efficiency affect beam intensity? ( primary signal intensity )
The difference between these generators is that everytime you use higher frequency generators such as going from single phase to 3 Phase/6 pulse generators, youre going from less efficient generators to more efficient generators.
When you move to mroe efficient generators you are able to produce more x-rays with the same technical factors.
Increasing generator efficiency will increase beam intensity.
Decreasing generator efficiecny will decrease beam intensity.
What is quantum noise? How does the strength of the beam affect this? ( Primary Signal Strength )
Quantus noise is the noise present due to the amount of primary signal intensity interacting with the image receptor.
The lower the strength of the beam, the greater noise is present on the image.
True or false:
Increasing kVp increases the number of x-rays that the x-ray tube emits.
- Increasing kVp increases the number of interactions that occur inside the anode of the x-ray tube. This creates more x-ray photons. The photons that are created also have increased energy.
What is the primary reason filtration is added to the x-ray beam?
Filtration is added in order to decrease patient dose.
How does an increase in SID affect beam intensity?
An increase in SID decreases beam intensity.
Doubling the SID affects beam intensity how?
Doubling the SID would decrease the radiation youre getting by a factor of 4.
How does SID affect magnification?
Higher SID decreases magnification.
What is the primary reaseon why the x-ray beam loses its intensity as it travels away from the x-ray tube?
The primary reasonw hy the x-ray beam lsoes its intesntiy is because of the divergence of the beam.
What are the two major techniques used in reducing scatter radtiation?
The two major techniques used are collimation and the use of anti-scatter grids.
How does collmation reduce scatter radiation?
- Collimation reduces scatter radiation because if you increase collimation, you reduce the area of the patient and the volume of tissue being exposed.
- The more tissue you are exposing, the higher the amoutn of scatter radiation.
How does scatter affect density?
When there's more scatter, density is increased.
How does collimation affect contrast?
Reducing the amount of scater radiation produced increases contrast of image.
Why should you erase a casette if they're not used within 24-48 hours?
You should erase them because the plate may be exposed to scattered radiation from x-ray tubes as well as background radiation that the plate is exposed to.
These types of radiation can affect the image you take when you take an x-ray.
Does using a grid reduce the production of scattered radiation?
- Using a grid does NOT reduce production of scattered radiation.
- But grids do reduce the amount of scattered radiation reaching the image receptor.
Approximately how much of scattered radiation does grids remove?
80 percent to 96 percent
What is grid ratio?
Relationship of height of thes trips to the distance between them.
What is grid radius?
A definition appleid to focused grids and is the distance from the surface of the grid to the ponit above the grid where all the strips would meet. ( This is also known as focal distance )
What is grid frequency?
Grid Frequency is the measure of the number of lead strips occuring for a given unit of measure.
How does grid ratio affect contrast?
The higher grid ratio, the more improvement on contrast.
When would you use a grid with higher ratio?
When x-raying anatomical parts with bigger mass/volume, you should use a grid with higher ratio because more mass/volume, more scatter.
What are the grid conversion factors?
- No grid = 1
- 5:1 = 2
- 6:1 = 3
- 8:1 = 4
- 12:1 = 5
- 16:1 = 6
Whats the grid conversion factor for no grid?
Whats the grid conversion factor for a ratio that has 5:1 ?
A grid ratio of 5:1 has a ratio of 2
What is the grid conversion factor for a grid that has a 6:1 ratio?
What is the grid conversion factor for a grid with a 8:1 ratio?
What is the grid conversion factor for a grid with a 12:1 ratio?
What is the grid conversion factor for a grid with a 16:1 ratio?
True or False:
The main purpsoe of a grid is to improve radigraphic contrast?
True or false:
Grids transmit approximately 96% of the primary beam.
False. Approximately 60% of the priamry beam is transmitted through an anti scattered grid. For this reason radiographic techniques must be increased when using them.
Generally, when should a grid be used? Whats the only exception to this rule?
A grid should be used whenever a body part measured 12 cm or more.
The only exception to this is in chest imaging where a grid is used only when the chest measures more than 26 cm because of the air in the lungs.
Whats the diffeerence between a short dimension grid and a long dimension grid?
Short dimension grids run the short way ( If 14 x 17 casette, it runs across the 14 inch way )
Long dimension grids urn the long way ( In 14 x 17, it runs long wise the 17 inch way. )
True or False:
Grid lines are less of a problem in digital radiography imaging than in analog imaging.
- because digital systmes are able to produce diagnostic quality films with shorter exposure times in certain situations, grid lines can become more of a problem when they are used.
True or False:
Grid cut-off increases the amount of primary radiation that reaches an image receptro.
When grid cut-off occurs primary radiation is absorbed by the lead strips of the grid and less of the primary signal reaches the image receptor.
What is the Moire pattern?
Its a grid artifact where you see the grid lines run across the x-ray ( Running left and right )
Which one has more of a possibility to demonstrate the moire effect? Short dimension grids or long dimension grids?
Short dimension grids are more likely to demonstrate the moire effect.
True or False
The most intense aspect of an x-ray beam is located on the cathode side.
- X-rays that exit the teu bre on the anode side must navigate through a portion of the anode material. This weakens the anode side of the x-ray beam.
True or False:
X-rays are a type of electromagnetic radiation.
- X-rays are found in the electromagnetic spectrum and travels in waves much like light photons.