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Radiologic Physics > Chapter 6 > Flashcards

Chapter 6 Flashcards

1
Q

What does mA control?

A

Size of the filament, focal spot size, size of the beam, and the resistance

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2
Q

How does mA effect resistance?

A

The higher the mA, the bigger the electron beam, the less the resistance

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3
Q

What is saturation current?

A

Filament is heated with mA and there is no more electrons to boil off

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4
Q

What is Thermionic Emission?

A

Electrons boil off

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5
Q

Where do electrons hang out after boiling off the filament?

A

Space charge

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6
Q

What charge does the focusing cup have?

A

Negative

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7
Q

What causes the electrons to move from the cathode to anode?

A

kVp
Electric potential
Potential difference

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8
Q

What charge does the Anode have?

A

Positive

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9
Q

Where are Xrays and heat made?

A

The focal spot

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10
Q

What are the 2 interactions within the tube?

A

Characteristic
Brems

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11
Q

When does a Charactertistic interaction happen?

A

When incoming electron is at least 69.5 keV

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12
Q

If kVp is less than 70, then all photons will be:

A

Brems

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13
Q

What happens during a Brem’s interaction

A

Filament electron misses tungsten electrons and gets attracted to the nucleus

The stronger the attraction, the more energy the filament loses when it breaks and the stronger the brems photon

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14
Q

What is the average energy of Brems?

A

1/3 of the kVp selected

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15
Q

What is the beam before filtration?

A

Heterogenous

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16
Q

What is the beam after filtration?

A

Homongenous

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17
Q

What does total filtration need to be a minimum off?

A

2.5mm of Al

18
Q

Why do we use filtration?

A

To take out any weak photon that would only contribue to patient dose, they are undiagnostic

19
Q

How much Al is inherent filtration?

A

.5mm

20
Q

What is total filtration?

A

Inherent + added

20
Q

What is Beam hardening?

A

Filtration takes away weak photons and increases the overall average energy of the beam

21
Q

What are compensation filters?

A

Used to compensate for vatiations in patient thickness and will create a more uniform exposure

22
Q

How should a wedge filter be used?

A

Thick part of wedge over thin part of patient

23
Q

What is HVL?

A

Amount of Al necessary to reduce the beam to 1/2 its intensity

24
Q

What is the normal HVL?

A

3-5mm Al

25
Q

How does HVL effect beam quality and quantity?

A

Increases quality
Decreases quantity

26
Q

What is beam quantity?

A

The number of x-rays in a beam

27
Q

What is beam quantity affected by?

A

mAs
kVp
Distance
Filtration
Grid

28
Q

How does beam quantity affect radiation dose to the patient?

A

An increase in quantity, increases the radiation dose

29
Q

What type of relationship does mAs have with beam quantity?

A

Direct

30
Q

How does a 15% change in kVp affect quantity of Xrays?

A

Halving or doubling the quantity of xrays reaching the IR

31
Q

What is the main control to change quantity?

A

mAs

32
Q

How does beam quantity vary with distance?

A

Intensity of the beam gets less over large distances (inverse square law)

33
Q

How does distance affect divergence?

A

As distance increase, beam divergence decreases

34
Q

What is beam quality?

A

Strength or penetrating ability of the photons transmitted through the body

35
Q

What color is created when then photons reach the IR?

A

Black

36
Q

What color is created when the photons don’t reach the IR?

A

White

37
Q

What is the relationship between kVp and quality?

A

The higher the kVp, the higher the quality of the beam

38
Q

Other names for beam quantity?

A

Patient dose
Rate
Amount
Number
Quantity

39
Q

How does SID affect beam divergence?

A

The greater the SID, the less the beam divergence

40
Q

How does FSS affect beam divergence?

A

The greater the FSS, the greater the beam divergence

41
Q

How does collimation affect beam divergence?

A

The greater the collimation, the less the beam divergence

Radiologic Physics (9 decks)

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