10. X-RAYS: QUALITY ASSURANCE Flashcards

1
Q
  1. What influences the quality of the Radiation?
A
  • the beam’s overall energy
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2
Q
  1. What influences the intensity of the beam?
A
  • the number of X-Ray photons
  • determined by the mass or the Kilovolts
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3
Q
  1. What does the intensity of the beam represent?
A
  • the quantity of the radiation produced
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4
Q
  1. What can be said about the height of the Bremsstrahlung curve?
A
  • it is directly proportional to the intensity of the X-Ray
    beam
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5
Q
  1. What does the quality of the X-Ray beam measure?
A
  • it measures how readily the beam will penetrate any
    given material
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6
Q
  1. What does HVT stand for?
A
  • the Half- Value Thickness of a beam of radiation
  • this is also known as the Half- Value Layer (HVL)
  • it affects the quality of the beam
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7
Q
  1. What is the Half-Value thickness of a beam of radiation?
A
  • it is the amount of a given material that will reduce
    the intensity of the X-Ray beam by 50%
  • it is the amount that will half the quality of the beam
  • it affects the energy and the penetrability of the beam

THE MEASURE OF THE HVT:
- provides a guide to the penetrating power of the
beam

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8
Q
  1. What is Beam Attenuation?
A
  • it is the change in the number of photons as a beam
    passes through a medium of material

IT IS DESCRIBED BY THE EQUATION:
N = N₀ x e to the power of µx

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9
Q
  1. In the equation, what is µ?
A
  • this is the linear attenuation coefficient
  • this is the fraction of the photons that interact per unit
    thickness of the attenuator
  • this coefficient exists to describe how different materials
    can absorb radiation differently
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10
Q
  1. In the equation, what is N?
A
  • this is the number of photons after they have passed
    through the material
  • it is the intensity of the beam after it has passed through
    the material
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11
Q
  1. In the equation, what is N₀e?
A
  • this is the number of photons before they have passed
    through the material
  • it is the intensity of the beam before it has passed through
    the material
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12
Q
  1. In the equation, what is x?
A
  • the thickness of the material
  • this is in metres or millimetres
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13
Q
  1. How do we work out the HVL?
A
  • this is the Half-Value Layer
  • it is a special thickness that attenuates the beam to
    50%
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14
Q
  1. What is the quality of any beam of X-Rays proportional to?
A
  • the HVT for any given material
  • the maximum beam energy is often referred to as E-Max

IN DIAGNOSTIC X-RAY BEAMS:
- the E-Max will always be equal to the generating voltage
(kVp) of the X-Ray beam
- the generating voltage is the voltage that the operator
gives to the voltage supply

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15
Q
  1. What is the mA?
A
  • it is the measure of the current flowing across the X-Ray
    tube
  • this is often called the Tube Current
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16
Q
  1. What is current?
A
  • this is the flow of electrons
  • its value is in mA
  • this is determined by the number of electrons flowing per
    unit time
17
Q
  1. What happens to the number of electrons if we double the current from 200 to 400 mA?
A
  • there will be twice as many electrons making up the tube
    current
18
Q
  1. What does it mean for the electron that it is subjected to the same potential difference?
A
  • it will have the same chance of creating an X-Ray Photon

THIS MEANS THAT DOUBLING THE MA (CURRENT)
- will double the number of X-Rays produced
- this will not affect the energy range of the X-Rays
- this means that it does not affect the quality of the
X-Ray beams

19
Q
  1. What would happen if the mA was halved?
A
  • the number of X-Rays would be halved

THE ASSOCIATION BETWEEN THE mA AND THE X-RAY BEAM
- the beam intensity is proportional to the mA (current)
- the beam quality is unaffected by changes in the mA

20
Q
  1. What will an increase in the mAs (current per second) result in?
A
  • this would increase the background blackness
  • this would increase the image contrast
21
Q
  1. What does the X-Ray tube voltage (keV) determine?
A
  • it determines the potential difference between the
    cathode and the anode of the X-Ray tube
  • this determines the kinetic energy that is acquired by each
    of the electrons as the current flows across the X-Ray tube
22
Q
  1. What is the Peak-Kilovoltage (kVp)?
A
  • this is the maximum cathode-anode voltage
  • it is measured in Kilovolts
23
Q
  1. What can be inferred if kVp is equal to 150 kV?
A
  • the electrons will have a kinetic energy that is equal to 150
    keV just before they hit the anode
24
Q
  1. What happens as the keV is increased?
A
  • the speed a which the electrons impact on the target
    anode is increased
  • there are more opportunities for the conversion of energy
    into X-Rays and heat
25
25. What will happen when we have more energy available at the interaction process at the anode?
1. The maximum photon energy achievable will increase 2. There will be an increase in the average energy of each photon of X-Rays 3. If the total number of photons increases: - the intensity of the X-Ray beam must increase
26
26. How can we mathematically write down the associations between beam quality, beam intensity and keV?
- Beam Quality ∝ (keV)² - Beam Intensity ∝ keV
27
27. Does this graph make sense?
- yes
28
28. Does this image make sense?
- yes WHEN WE DECREASE THE KVP: - the photoelectric effect is reduced
29
29. Does this diagram make sense?
- yes AN INCREASE IN KVP LEADS TO AN INCREASE IN PENETRANCE: - this leads to a decrease in Contrast