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Image Characteristics > X-ray production > Flashcards

X-ray production Flashcards

1
Q

How is X-radiation created?

A

Taking energy from electrons and converting it into photons with appropriate energies

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2
Q

Where does energy conversion take place?

A

Within x-ray tube

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3
Q

How can the quantity (exposure) and quality (spectrum) of the x-radiation produced be controlled?

A

Adjusting the electrical quantities (KV,MA) and exposure time,S, applied to the tube

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4
Q

What is an x-ray tube?

A

energy converter

Receives electrical energy and converts it into two other forms: x-radiation and heat

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5
Q

What is heat?

A

undesirable byproduct

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6
Q

What are x-ray tubes designed and constructed to maximize?

A
  1. X-ray production

2. Dissipate heat as rapidly as possible

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7
Q

What does x-ray tube consist of?

A
  1. it is a simple electrical device

2. two principle elements: a cathode and anode

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8
Q

What is the process of x-radiation?

A

As the electrical current flows through the tube from cathode to anode, the electrons undergo an energy loss

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9
Q

What is anode?

A

The component in which the x-radiation is produced

2, large piece of metal that connects to the positive side of the electrical circuit

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10
Q

What are two primary functions of anode?

A
  1. convert electronic energy into x-radiation

2. dissipate the heat created in the process

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11
Q

what does the fraction of the total electronic energy that is converted into x-radiation depend on?

A
  1. Atomic number (Z) of the anode material

2. Energy of the electrons

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12
Q

What do most x-ray tubes use as the anode material?

A
  1. tungsten

2. atomic number: 74

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13
Q

What are several characteristics of tungsten?

A
  1. Maintain strength at high temperatures
  2. High melting point
  3. Relatively low rate of evaporation
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14
Q

What is the shape of anode?

A

Beveled disks

Attached to the shaft of an electric motor that rotates them at relatively high speeds during x-ray production process

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15
Q

What is the focal spot?

A

Radiation produced in a very small area on the surface of anode

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16
Q

What is the dimension of the focal spot determined by?

A

Dimension of electron beam arriving from the cathode

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17
Q

In most x-ray tubes, what is the focal spot approx?

A

rectangular

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18
Q

What are the dimension of the focal spot?

A

Usually range from 0.1mm to 2mm

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19
Q

What is x-ray tubes designed to have?

A

Specific focal spot sizes

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20
Q

What does small focal spots produce?

A

less blurring

better visibility of detail

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21
Q

What does large focal spots have?

A

greater heat-dissipating capacity

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22
Q

What is the basic function of the cathode?

A

Expel electrons from the electrical circuit and focus them into a well-defined beam aimed at the anode

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23
Q

What does the typical cathode consist of?

A

small coil of wire (a filament) recessed within a cup-shaped region

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24
Q

What happens to electrons that flow through electrical circuit?

A

cannot generally escape from the conductor material and move into free space

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25
Q

Where is anode and cathode contained in?

A

Airtight enclose or envelope

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26
Q

What is referred to as the tube inset?

A

The envelope and its contents

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27
Q

what is the tube insert?

A

part of the tube that has a limited lifetime and can be replaced within the housing

28
Q

What are the primary functions of the envelope?

A

provide support and electrical insulation for the anode and cathode assemblies and to maintain a vacuum in the tube

29
Q

What does the presence of gases in the x-ray tube allow for?

A

electricity to flow through the tube freely, rather than only in the electron beam

  1. interfere with the x-ray production and possibly damage the circuit
30
Q

What does the x-ray tube housing provide?

A

several functions in addition to enclosing and supporting the other components

31
Q

What is the function of x-ray tube housing?

A

functions as shield and absorb radiation

32
Q

What is the circuit connected to?

A

source of electrical energy

33
Q

What does the generator receive?

A

Electrical energy from the electrical power system and converts it into the appropriate form to apply to the x ray tube

34
Q

What does the generator provide?

A

The ability to adjust certain electrical quantities that control the x-ray production process

35
Q

What are the three electrical quantities that can be adjusted?

A
  1. KV (voltage or electrical potential applied to the tube)
  2. MA (the electrical current that flows through the tube)
  3. S (duration of the exposure or exposure time)
36
Q

What is the circuit?

A

A circulatory system for electrons

pick up energy as they pass through the energy and transfer to the x-ray tube anode

37
Q

What happens as electrons pass through the x-ray tube?

A

undergo two energy conversion

  1. the electrical potential energy is converted into kinetic energy
  2. then converted into x-radiation and heat
38
Q

What is the amount of energy carried by each electron determined by?

A

Voltage or KV between anode and cathode

39
Q

What are two types of interactions that produce radiation?

A
  1. Interaction with electron shells produces characteristic x-ray photons
  2. Interactions with atomic nucleus produce Bremsstrahlung x-ray photons
40
Q

What do electrons within atom each have a specific amount of?

A

Binding energy that depends on the size (atomic number, Z) of the atom and the shell in which the electron is located

41
Q

What is the binding energy?

A

Energy that would be required to remove an electron from the atom
It is an energy deficit

42
Q

What is the interaction that produces the most photons?

A

Bremsstrahlung process

‘’ braking radiation’’

43
Q

What is the production process of Bremsstrahlung?

A

Electrons that penetrate the anode material and pass close to the nucleus are deflected and slowed down by the attractive force from the nucleus

44
Q

What does KV (kilovoltage) establish?

A

Energy of the electrons as they reach the anode

No x-ray photon can be created with an energy greater than that of the electrons

45
Q

What is the maximum photon energy determined by?

A

Maximum or peak voltage during the voltage cycle

46
Q

What does characteristic radiation involve?

A

Collision between high-speed electrons and orbital electrons in the atom

47
Q

How can the characteristic radiation occur

A

If the incoming electron has a kinetic energy greater than the binding energy of the electron within the atom

48
Q

How can anode material give rise to several characteristic x-ray energies?

A

Electrons at the different energy levels can be dislodged by the bombarding electrons and the vacancies can be filled from different energy levels

49
Q

What does subscript alpha (a) denote?

A

Filling with an L shell electron

50
Q

What does subscript beta indicate?

A

Filling from either the M or N shell

51
Q

What does the characteristic radiation produce?

A

Line spectrum with several discrete energies

52
Q

What does the Bremsstrahlung produce?

A

Continuous spectrum of photon energies over a specific range

53
Q

Why is the number of photons created at each characteristic energy different?

A

The probability for filling a K-shell vacancy is different from shell to shell

54
Q

What does the Molybdenum anode tube produce?

A
  1. used for mammography

2. Produce two intense characteristic x-ray energies: K-alpha radiation (17.9 keV) and K-beta (19.5 keV)

55
Q

Why is anodes that have dual surface areas, molybdenum and rhodium, useful?

A

Operator can select a spectrum that is more optimized for different breast sizes and densities

56
Q

When is No characteristic radiation produced?

A

If KV is less than the binding energy of the K-shell electrons

57
Q

What is the relative composition of an x-ray spectrum with respect to Bremsstrahlung and characteristic radiation depend on?

A
  1. Anode material
  2. KV
  3. Filtration
58
Q

What is the efficiency of the x-ray production defined as?

A

Total x-ray energy expressed as a fraction of the total electrical energy imparted to the anode

59
Q

What are the two factors that determine production efficiency?

A
  1. Voltage applied to the tube
  2. Atomic number of the anode, Z

2.Efficiency = KV x Z x 10-6.

60
Q

What is the consequence of increasing KV?

A

The quantity of radiation produced per unit of heat is significantly increased

61
Q

What is the x-ray efficacy of the x-ray tube defined as?

A

the amount of exposure, in milliroentgens, delivered to a point in the center of the useful x-ray beam at a distance of 1 m from the focal spot for 1 mAs of electrons passing through the tube

62
Q

What does the efficacy value express?

A

The ability of a tube to convert electronic energy into x-ray exposure

63
Q

Why is KV very useful?

A

Controlling the radiation output of an x-ray tube

64
Q

What is radiation output?

A

proportional to the square of KV

65
Q

What does waveform describe?

A

The manner in which KV changes with time during the x-ray production process because of the cyclic nature of the electrical supply

66
Q

What is the most effective x-ray producer?

A

The waveform with the least KV variation during the exposure

Image Characteristics (8 decks)

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