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MED 107- MEDICAL PHYSICS II > 7. X-RAYS: TUBE INSERT > Flashcards

7. X-RAYS: TUBE INSERT Flashcards

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1
Q
  1. What is this image showing?
A
  • the insert
  • this is found inside the X-RAy Tube
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2
Q
  1. Provide the labels for the parts numbered 1-6.
A
  1. Cathode Assembly
  2. Vacuum
  3. Anode Disk
    (the electrons travel towards the Anode)
  4. Anode Stem
  5. Rotor
  6. HT Connection
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3
Q
  1. Provide the labels for the parts numbered 7-12.
A
  1. HT Cable
  2. Rotor Support
  3. Bearings
  4. Focal Track
  5. Filament
    (set in focusing)
  6. Glass Envelope
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4
Q
  1. What does the Insert maintain?
A
  • it maintains a vacuum for the X-Ray Production
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5
Q
  1. What does the Insert contain?
A
  • the Anode Assembly
  • the Cathode Assembly
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6
Q
  1. What happens to the Metal Component of the Insert?
A
  • it is Earthed
  • this is so that there is no build up of static
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7
Q
  1. What fixes the anode and the cathode assembly to the Insert?
A
  • the envelope
  • it supports the two electrodes
  • it keeps them at the correct distance away from each
    other
  • it aligns them correctly
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8
Q
  1. How are the seals and the metal poles chosen?
A
  • they are chosen carefully
  • this is to match the expansion coefficients (heat) of the
    different parts
  • this reduces the risk of damage to the insert during the
    Operation
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9
Q
  1. What do these images show?
A
  • The Anode Assembly
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10
Q
  1. What does the Anode Assembly consist of?
A
  1. the Anode Disc
  2. the Focal Track
  3. the Rotor Assembly
  4. the HT Connection for the positive side of the Tube
    Circuit
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11
Q
  1. What materials make up the Rotating Anode?
A
  • a Tungsten Rhenium Disc
  • this typically is 90-150mm in diameter
  • this makes this a large rotating disc
  • this increases the tube rating and the thermal capacity
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12
Q
  1. What can be said about the content of the Anode Disc?
A
  • it may be a composite disc
  • it has either a Tungsten or a Rhenium focal track
  • it has either a Graphite or Molybdenum backing
  • it has bevelled edges
  • these form the Anode Angle and the Focal Track
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13
Q
  1. Why does the Anode Angle exist?
A
  • it decreases the size of the apparent focal spot

AN INCREASE IN THE ANODE ANGLE:
- increases the size of the focal spot
- this increases the heat capacity

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14
Q
  1. What is the Typical Angle for the rotating X-Ray tubes?
A
  • between 16° and 20°
  • this produces a better quality of the image
  • this results in better spatial resolution
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15
Q
  1. What is the Anode attached to?
A
  • the Molybdenum Stem
  • this connects it to the rotors
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16
Q
  1. What can be said about the contents of the Anode Stem?
A
  • it has a small cross-section
  • the anode stem is as long as possible
  • it is connected to the Copper Rotor Assembly
17
Q
  1. Why is the Anode Stem as long as it can possibly be?
A
  • this restricts the conduction of heat to the bearing
    assembly
18
Q
  1. What do the Rotors do to the Anode?
A
  • they rotate the Anode at speeds of 3000-9000 r.p.m
    during exposures
  • they do this using induction
19
Q
  1. What is this image showing?
A
  • the Cathode Assembly
  • this is negatively charged
20
Q
  1. Write down the labels for the parts numbered 1-3.
A
  1. Focusing Cup
  2. Wire Filament for the Small Focal Spot
  3. Wire Filament for the Large Focal Spot
21
Q
  1. Does this diagram make sense?
A
  • yes
22
Q
  1. What does the Cathode Assembly consist of?
A
  1. the Filaments
    (fine and broad)
  2. the Focusing Cup
    (this is negatively charged)
  3. Electrical supplies and Connections
23
Q
  1. What are the Electrical Supplies and Connections related to the Cathode Assembly?
A
  1. The Filament Supply
    • this is the current
    • it defines the intensity of the X-Ray Beam
    • it defines the number of Photons and Electrons in the
      X-Ray beam
  2. The HT Supply
    • to the negative side of the X-Ray Tube Circuit
    • this is the voltage supply
    • it is connected to the Cathode
24
Q
  1. What is the purpose of the Cathode?
A
  • to produce a thermionic emission of electrons
  • these can be focused
  • they can be attracted to the anode
25
Q
  1. How is Thermionic Emission achieved?
A
  • it is achieved by supplying a variable (mA/current)
  • this heats up the filament
26
Q
  1. How is the filament positioned?
A
  • it is tightly coiled
27
Q
  1. What does an increase in the mA (current) result in?
A
  • an increase in the temperatures of the filament
  • this increases the number of electrons in the electron
    cloud
28
Q
  1. What is the mathematical relationship between the current and the number of electrons?
A
  • mA (current) is directly proportional to the number of
    X-Rays produced

∴ DOUBLING THE CURRENT (mA) FROM 100 TO 200:
- double the number of electrons

29
Q
  1. What is the Filament of the Cathode Focusing Cup encased in?
A
  • it is encased in a Nickel Housing
    (this can also be stainless steel in some occasions)
30
Q
  1. What is the function of the Filament’s Nickel Housing?
A
  • it focuses the electrons on to the focal track of the
    anode
  • this is achieved by it have sharp edges to the Focusing
    Cup
  • these edges become negatively charged when the tube
    voltage is applied
31
Q
  1. What does the sharp edge of the Nickel Housing of the filament do?
A
  • it concentrates the negative charge
  • it narrows the electron beam directly towards the
    anode

MED 107- MEDICAL PHYSICS II (108 decks)

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