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Radiology > Production of X-rays > Flashcards

Production of X-rays Flashcards

1
Q

What is the atomic number?

A

number of protons
what determines identity of atom

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2
Q

What is the atomic mass?

A

protons + neutrons

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3
Q

What is the binding energy?

A

minimal amount of energy required to remove an electron from its shell

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4
Q

Which shell is the most tightly bound?

A

K

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5
Q

How much energy does it take to remove a K shell electron in Tungsten?

A

70,000 eV // 70 keV

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6
Q

How is electron binding energy related to atomic number?

A

proportionally: higher atomic number = more protons –> higher atomic binding energy

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7
Q

What describes creating a positive & negative ion by removal of an electron from a neutral atom?

A

ionization

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8
Q

What is the transmission of energy through space in a vacuum & matter?

A

radiation

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9
Q

What are the two forms of radiation?

A

wave & quantum

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10
Q

Describe properties of the wave theory.

A

explains propagation of radiation
radiation in form of waves
no mass
speed of light

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11
Q

Describe properties of quantum theory.

A

explains the interaction of radiation with matter
considers radiation small bundles of energy called photons: mass & travel in straight/diverging lines at speed of light

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12
Q

What is high energy radiation?

A

high frequency & short wavelength

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13
Q

What is low energy radiation?

A

low frequency & long wavelength

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14
Q

How are frequency & wavelength related in wave theory?

A

inversely proportional

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15
Q

Where does the electromagnetic spectrum become ionizing?

A

blue light (ultraviolet spectrum)

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16
Q

List the electromagnetic spectrum from lowest energy to highest.

A

radio, micro, infrared, visible, ultraviolet, x-ray, gamma

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17
Q

In the quantum theory of radiation are the particles charged?

A

they can be, but neutrons & x-rays are not

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18
Q

What is the heaviest & most charged particle of radiation?

A

alpha

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19
Q

What is the linear energy transfer (LET)?

A

ionizing rate: low LET for x-rays allows particles to move through tissue easily to reach receptor

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20
Q

How is contrast created when considering the particle theory?

A

some energy/x-rays remain in tissue…cannot penetrate & remain trapped

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21
Q

What particle has the highest LET and why?

A

alpha: electrical charge & weight

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22
Q

What are the factors that lead to higher LET?

A

low velocity, higher charge, bigger size –> less penetration because lose energy over short distances

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23
Q

US law states that x-ray machines must have what features?

A

dead-man type exposure button
indicator light
audible sound

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24
Q

What is located inside the tube head?

A

power supply & x-ray tube

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25
Q

Where is the step up transformer?

A

anode end

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26
Q

Where is the step down transformer?

A

cathode end

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27
Q

What charge are the cathode & anodes?

A

cathode = negative
anode = positive

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28
Q

Where are the electrons produced?

A

cathode

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29
Q

What is the purpose of the aluminum filter?

A

filters non-useful x-rays so only the ones that will create an image exit the tube head

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30
Q

What is in the cathode?

A

focusing cup (Mb) negatively charged
filament (tungsten)

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31
Q

Where is the source of electrons?

A

filament

32
Q

How are electrons produced?

A

thermionic emission

33
Q

How do we make the filament hotter to create more electrons?

A

increase the voltage/energy

34
Q

Which transformer heats up the filament?

A

low energy / step-down

35
Q

What is at the anode end?

A

tungsten target & copper stem

36
Q

How efficient is the tungsten target at transferring kinetic energy of the e- into x-rays?

A

highly inefficient: only 1% become x-rays

37
Q

What is the purpose of the copper stem?

A

works as a thermal conductor to remove heat & prevent target from melting

38
Q

Where is the source of x-rays?

A

focal spot

39
Q

What happens if the target melts?

A

vapors/materials enter the x-ray tube & it is no longer a vacuum

40
Q

Why is a vacuum needed?

A

we do not want x-rays to interact with anything & want the full energy of them to create our radiographs

41
Q

Why is tungsten a good target material?

A

high atomic number
high melting point
high thermal conductivity
low vapor pressure

42
Q

The low voltage current heats up the _____ resulting in ______.

A

tungsten filament
separation of outer shell e- from atom

43
Q

How many volts does the low-voltage/step-down transformer produce?

A

6-12 volts

44
Q

How many volts are required to remove a k shell electron of tungsten?

A

70kp

45
Q

How is the focal spot related to spatial resolution?

A

smaller focal spot = higher resolution

46
Q

How do we avoid heat accumulation on the focal spot?

A

line-focus principle

47
Q

How does the line-principle work?

A

angling of target creates smaller effective focal spot compared to actual focal spot…results in sharper resolution, while maintaining original surface area of target for heat dissipation

48
Q

The step down transformer is regulated by what switch?

A

mA

49
Q

Increasing mA setting will increase what?

A

number of electrons emitted

50
Q

The step UP transformer is regulated by what switch?

A

kV setting

51
Q

Increasing kV will increase the ?

A

energy of the electrons traveling from the cathode to the anode

52
Q

If you increase the exposure time, how does that effect the amount of xrays produced?

A

increases…proportional

53
Q

What term means flow of electrons through an electrical conductor?

A

electricity

54
Q

What term means the amount of electrons flowing through a conductor per second?

A

current

55
Q

what is current measured in?

A

mA

56
Q

What is the path of electrical current?

A

circuit

57
Q

What is the difference in electrical potential energy between 2 points in an electrical circuit?

A

voltage (potential difference)

58
Q

What is voltage measured in?

A

kVp

59
Q

In the USA how many cycles per second?

A

60

60
Q

T/F During each cycle there is a phase where the anode is positive & attracts e- and a phase where the anode is negative & repels e-?

A

true

61
Q

T/F the current is constant?

A

false

62
Q

During what part of the cycle are x-rays produced?

A

when the anode is positive & attracts e-

63
Q

Why does the current have to be alternating?

A

because direct current cannot pass through the transformer

64
Q

Why do we need direct current?

A

once we pass through the transformer we want direct current to ensure that the flow of e- is in one direction towards the anode

65
Q

What device converts the current from alternating to direct?

A

rectifier

66
Q

How do we create a nearly constant potential?

A

give multiple pulses after rectification so that the amount of energy/volts stays nearly constant between cathode & anode

67
Q

Why do we want the higher voltage to be constant?

A

more efficient at producing x-rays & the x-rays will have higher energy

68
Q

Constant potential & direct current means that we can have…?

A
  • shorter exposure times
  • more consistent beam of intensity
  • higher mean energy of beam
  • decreased radiation dose
69
Q

How are x-rays actually produced ?

A

when the high-speed e- suddenly stop/decelerate close to the nuclei of a high Z # absorbing material (tungsten)

70
Q

What are the 2 mechanisms for x-ray formation?

A
  • Bremsstrahlung
  • Characteristic
71
Q

Which mechanism describes an e- to nucleus interaction?

A

Bremsstrahlung

72
Q

Which mechanism describes an e- to e- interaction?

A

characteristic

73
Q

Describe the spectrum of x-ray energy for Bremsstrahlung radiation?

A

all the way to max if head on collision occurs (wide distribution/heterogenous)

74
Q

Describe the type of energy emitted by an e- in characteristic radiation?

A

energy is equivalent to the difference in binding energies of the 2 shells/orbitals

75
Q

Majority of x-ray beams are produced in which way?

A

Bremsstrahlung radiation

76
Q
A

Radiology (4 decks)

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