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1. Medical Radiation Sciences > 6. The X-ray Tube (P2) > Flashcards

6. The X-ray Tube (P2) Flashcards

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USMLE® Step 1 flashcards
1
Q

What prime factor controls the limits of the focusing cup?

A

mA

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2
Q

What is the role of focusing cups?

A

To focus the electrons produced by the tungsten filament coils to the focal spot

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3
Q

What are some characteristics of the focusing cup? ei; materials, conductivity, charge, thermal energy

A
  1. Made of nickel
  2. Conductor
  3. Negatively charged
  4. Not a good thermionic emitter (not going to release its own e-)
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4
Q

Why is it important that the filaments are a good thermionic emitter?

A

Because the filaments are responsible for producing the electrons by heating the coil to energize and release them

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4
Q

What are the pros and cons of a larger focal spot?

A

Pros: Larger mA, better heat dissapation
Cons: Lower resolution (focal spot blooming), decreased SR

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5
Q

What type of relationship does mA and the filaments have?

A

A direct relationship

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6
Q

What does increasing the kVp do to the photons?

A

Increases their energy

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7
Q

What are the 3 functions of the anode?

A
  1. Supports the target
  2. Conducts current
  3. Dissipates heat
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8
Q

With a stationary anode would you need a higher or lower mA and kVp? Why?

A

Lower, because you are localized to one area

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9
Q

What is the unit for tungsten? What is its atomic number?

A

W…yes, just W….nothing else
Atomic #: 74

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10
Q

Does tungsten have a high or low binding energy? Why?

A

It has a high binding energy which is because it causes high energy to be released

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11
Q

What is the stem made out of in a stationary anode?

A

Copper

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12
Q

What are 4 characteristics that a stationary anode has?

A
  • High conductivity
  • Low melting point
  • Tungsten Target
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13
Q

What is the atomic number of tungsten?

A

74

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14
Q

What are four characteristics of tungsten?

A
  • High melting point
  • High thermal conductivity
  • Low vaporization
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15
Q

What is unequal thermal expansion and contraction called?

A

Pitting

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16
Q

What are the 3 tube ratings?

A
  1. mA
  2. Time
  3. kVp
17
Q

What are the 5 parts of the spinning anode?

A
  1. Disc
    2. Focal track
    3. Stem
    4. Rotor=inside
    5. Stator=outside
18
Q

What makes up the focal track?

A

Focal spot + rotation

19
Q

Why is a spinning anode better in terms of heat?

A

It allows for better heat dissipation (Looses heat when its spinning so it doesn’t get hot)

20
Q

What material is the spinning anode made of?

A
  • Made of Tungsten and 10% Rhenium
21
Q

What are the layers of behind the tungsten?

A
  • Molybdenum
    • Carbon (graphite)
22
Q

What is the stem in a spinning anode and what is it made of?

A

It connects disc to rotator, is thin and made of molybdenum

23
Q

What is the rotor and what is it made of?

A

-Rotates on bearings
-High conductivity
-Made of copper

24
Q

How fast does the anode rotate?

A

> 3000rpm up to 12000

25
Q

What is the function of the stator and what is it made of?

A

-Causes rotor to spin, but is stationary itself
- Is an Induction motor
-Keeps alternating where the current runs through
-Current that is created in the copper is the same polarity of what is in the coil

26
Q

What 4 parts of the tube are most likely to wear down?

A
  1. Filament-space charge created here
  2. Anode
  3. Bearings-helps our disc spin
  4. Housing wear
27
Q

What is filament wear caused by?

A

-High mA
-Longer prep-when your holding halfway (building space charge and rotate anode)

28
Q

What is anode wear caused by?

A
  • Uneven thermal expansion
  • High exposure ratings
29
Q

What is bearing wear caused by?

A

-Heavy use (higher techniques)
-Longer prep

30
Q

What is housing wear caused by?

A

-Physical Damage
-Overheating

31
Q

What are the consequences of filament wear?

A

-Tungsten plating on tube-tungsten vaporizing (builds up metallic substance on tube)
-Arcing- attracts electricity to the tungsten plating
-The filament may break due to arcing over time

32
Q

What are the consequences of anode wear?

A

Pitting=Unequal x ray intensity

33
Q

What are the consequences of bearing wear?

A
  • Slower rotation
  • More pitting
  • Grinding noise
34
Q

What are the consequences of housing wear?

A

Oil leakage=leads to more heat

35
Q

What are 3 ways to prevent tube wear?

A
  1. Lower techniques
  2. Shorter preps
  3. Tube warm up-prevents cracking the target
    • Helps prevent anode damage
36
Q

What is the purpose of the rating charts? Why is there two?

A

-Shows safe and unsafe combinations of kVp and mA
-2 charts for the two different focal spots, for different phase generators, rotation speed

37
Q

What are the 6 factors that affect tube rating?

A
  1. FS size
  2. Rotation speed
  3. Disk Diameter
  4. Waveform
  5. Segmented/Grooved anode-gives room for expansion
  6. Metal tube-can control the potential of the tube
38
Q

What is heat storage capacity?

A

How many exposures you can do without cooling
(Refers to the bearings)

39
Q

What are the consequences of composition?

A

-Differing expansion
-Differing conduction
-Damage to the bearings

40
Q

What does it mean by heat units/second

A

-Amount of e- emitted and hitting the target per second
(refers to filament and target)

41
Q

What are anode cooling charts?

A

-Shows heat capacity of anode and length of time to completely cool after its received a certain amount of heat
-Only one chart per machine

1. Medical Radiation Sciences (18 decks)

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