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Radiologic Physics > Chapter 5 > Flashcards

Chapter 5 Flashcards

1
Q

What is the tube housing usually made from?

A

Metal with a lining of lead

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2
Q

What kind of radiation does the tube housing protect from?

A

Leakage radiation

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3
Q

How much leakage radiation is allowable from the tube?

A

1 mGy/hr at 1 meter

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4
Q

Where are x-rays made?

A

The actual focal spot

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5
Q

What is isotropic?

A

X-rays go everywhere with high intensity in all directions

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6
Q

What is inside the x-ray tube?

A

Anode and cathode

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7
Q

What is the function of di-electric oil?

A

Located outside of tube for heat distribution absorption

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8
Q

What can cause tube arc or failure?

A

Tube gasification from the tungsten filament

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9
Q

What is the useful beam?

A

Where xrays come from the tube window out onto the patient

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10
Q

What are the primary parts of the cathode?

A

Filament (large and small)
Focusing cup
Filament wires

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11
Q

What is filament made of?

A

Thoriated Tungsten

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12
Q

What is the high melting point of tungsten?

A

3400 degrees celcius
6152 degrees F

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13
Q

What is saturation current?

A

Filament emits electrons when heated, to the point it can’t produce anymore electrons

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14
Q

What is thermionic emission?

A

Electons are boiled off

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15
Q

What charge does filament carry?

A

Negative

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16
Q

Where do electrons hang out in the focusing cup?

A

Space charge (electron cloud)

17
Q

What is the anode made of?

A

Target - tungsten (w/ rhenium)
Neck and base - molybdenum or graphite

18
Q

How does the anode rotate?

A

Induction motor

19
Q

Why is a rotating anode better than stationary?

A

Good thermal dissipater
Gets rid of heat
Allows for more tungsten to be hit by electrons

20
Q

What 4 things are needed to produce xrays?

A
  1. Source of free electrons
  2. Means to accelerate them (kVp)
  3. Decelerate them (tungsten)
  4. Angle them down - actual focal spot
21
Q

What is atomic number for Tungsten?

A

74

22
Q

What is the Line Focus Princple?

A

Anode has different angles for small and large focal spot sizes.

23
Q

What is the relationship between anode angle size and heel affect?

A

Smaller the angle, the greater heel effect
(more electrons get caught in heel of focal point)

24
Q

What is the relationship between the anode angle and spatial resolution?

A

The smaller the angle, the better the spatial resolution

25
Q

What is the equation for heat load capacity?

A

kVp x mAs x c x # of exposures

26
Q

How does inherent filtration affect beam?

A

Makes beam stronger by eliminating weak photons

27
Q

What are the generator correction factors?

A

Single phase - 1.0
Three phase, 6 pulse - 1.35
Three phase, 12 pulse - 1.41
High frequency - 1.45

28
Q

What are the 3 types of heat produced?

A

Radiation
Conduction
Convention

Radiologic Physics (9 decks)

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