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SEM II - Rad Physics > X-ray Tube, Housing, & Collimater > Flashcards

X-ray Tube, Housing, & Collimater Flashcards

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0
Q

Cathode rays

A

Electrons emitted by a cathode and propelled across a vacuum tube from cathode to anode

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1
Q

The early X-ray tubes

A

Had no cathode filament, incomplete vacuum chamber

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2
Q

Cathode tube

A

Hot filament utilizes the process of thermionic emission to provide a source of free electrons.

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3
Q

The Coolidge tube was produced by

A

GE in 1936 and sold for a price of $40

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4
Q

3 things for X-ray production

A

Source of free electrons

Acceleration of free electrons

Abrupt halting of high speed electrons

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5
Q

Dense anode target material

A

Made of tungsten

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6
Q

Primary components of X-ray tube

A

Cathode
Anode
Glass envelope
All above encased in a protective housing

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7
Q

Why a glass envelope?

A

To maintain a vacuum within

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8
Q

Why a vacuum

A

So that electrons accelerated from cathode to anode don’t “bump” into anything and be deviated or lose kinetic energy, also to prevent the filament from burning as it heats up.

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9
Q

Mammographic tubes

A

Can also be composed of metal or ceramic, however these are rare.

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10
Q

The cathode

A

The negative side of the X-ray tube whose function is to emit electrons.

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11
Q

The cathode consists of

A

Filament(s)

Focusing cup

Associated wiring

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12
Q

Filament

A

Most X-ray tubes are dual focus (two filaments - large and small).

Only one filament is used at a given time.

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13
Q

Filament size corresponds to

A

Focal spot size

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14
Q

Filaments undergo

A

Thermionic emission

- electron emission from a heated source

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15
Q

Tungsten is the primary component of the filament, why?

A

Heat resistance, over 6,000 degrees.

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16
Q

Thermionic emission

A

Electron emission from a heated source

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17
Q

Thermionic emission source

A

Filament of cathode

  • tungsten wire with very narrow diameter
  • as diameter decreases resistance increases
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18
Q

Electrical resistance

A

= heat

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19
Q

Thermionic emission produces free electrons for

A

X-ray production

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20
Q

As mA increases, the rate of thermionic emission

A

Increases

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21
Q

Electrons hover off of the

A

Filament

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22
Q

The collection of electrons is referred to as the

A

Electron cloud or space charge

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23
Q

mA =

A

The number of electrons thermionic ally emitted per second

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24
Q

mA Stations

A

Selected by technologist at the control console.
Controls amperage to cathode filament.
- this controls rate of thermionic emission

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25
Q

mA

A

The number of electrons thermionically emitted per second.

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26
Q

Routine radiography is done between

A

100 to 400 mA

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27
Q

MAS

A

mA and S combined

The number of X-rays in beam - has primary control of image density

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28
Q

Density

A

Overall image blackness

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29
Q

Focusing cup

A

Metallic cup that encases the filaments, composed of nickel or molybdenum; given a negative charge.

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30
Q

Focusing cup keeps emitted electrons in a tight fist until

A

Accelerated to anode.

31
Q

Electrons impact the anode

A

In the smallest area possible - minimizes focal spot

32
Q

Mutual repulsion

A

Negative repels negative

- this is how focusing cup works

33
Q

Anode

A

Positive side of the X-ray tube whose function is to receive stream of john speed electrons

34
Q

Anode consists of

A

Anode
Stator
Rotor
Associated wiring

35
Q

Types of anodes

A

Stationary anodes

Rotating anodes

36
Q

Stationary anodes

A

Anode stationary as electrons impact to produce X-ray

Tungsten button in a copper core

Dental X-ray, limited medical machine

37
Q

Rotating anode

A

Anode rotates as electrons impact to produce X-ray.

Capable of higher technical factors

38
Q

Rotating anode spreads heat

A

Over a larger area, heat due to impact of high speed electrons

39
Q

Composition of anode

A

Tungsten - able to withstand great amounts of heat
High melting point - 6192*f
High atomic number - 74
Good conductor of heat/electricity

40
Q

Line focus principle

A

The effective focal spot will always be smaller than the true/actual focal spot.

41
Q

Anode face is angled

A

7-15 degrees is typical - 12 degrees is standard

42
Q

True/actual focal spot

A

Area of electron impact

43
Q

Effective focal spot

A

True focal spot projected towards the patient.

44
Q

Focal spot sizes are measured by

A

The effective focal spot

45
Q

Anode heel effect

A

Construction of the anode results in a disparity of X-ray intensity from cathode to anode.

There will be more X-rays on the cathode side of the tube than the anode side.

46
Q

Stator

A

Induction motor that turns the anode disk located on the outside of the glass envelope and tube housing. No physical contact between stator and anode

47
Q

Rotor

A

Rotates, located inside the glass envelope connected to disk by shaft of molybdenum.
Can be noisy and can continue to spin long after exposure

48
Q

Rhenium

A

Blended in Tungsten for additional strength

49
Q

Other metals anode/cathode

A

Graphite - substrate of anode disk (weight)

Molybdenum - stem/neck of anode (light weight and strong)

Copper -rotor portion of anode (good heat/electric conductor)

Iron - rotor portion of anode (responds to magnetic field of stator)

50
Q

Composition of X-ray tube housing

A

Metallic housing, usually lead lined

51
Q

Functions of X-ray tube housing

A

Protects X-rays tube within
Absorb unusable X-ray
Protect from unnecessary radiation
Protect from electrical risk (high voltage/amperage)

52
Q

Oil found within the X-ray tube housing

A

Sometimes called dielectric oil, located between glass envelope and metal housing.

53
Q

Functions of the oil

A

Absorb unusable X-ray
Electrically insulate
Conduct heat away from X-ray tube

54
Q

X-ray proceeds isotropically from

A

The point of origin, originates at anode focal spot

55
Q

Most of the X-ray created is

A

Unusable, only tiny portion of X-ray that happens to travel toward patient are useful in creating am image

56
Q

Leakage radiation

A

Radiation that leaves the tube housing at a point other than the tube window.

Must be less than 100mR/hr at 1 meter

57
Q

X-ray tech controls

A

When X-rays are created (exposure switch)
Strength of X-rays created (KVP adjustment)
How many X-rays created (mAs adjustment)
How long X-rays created (exposure timer)

58
Q

How X-rays are created

A

X-ray machine is a device that converts one form of energy that we have in abundance into the form of energy we want.

59
Q

Electrical energy into electromagnetic energy as X-ray

A 
Electrical energy
Thermal energy
Potential energy
Kinetic energy 
Electromagnetic energy
60
Q

X-ray production begins and ends with

A

Electrical energy

61
Q

Properties of electricity

A

Voltage (the force/strength of electron propulsion)

Amperage (the number of electrons in motion)

62
Q

The properties of X-ray are similar to

A

The properties of electricity (kilovoltage and miliamperage seconds)

63
Q

X-ray photons are produced on demand when

A

Electrons are made available by thermionic emission of the cathode filament (these electrons possess potential energy)
OR
Electrons boiled off the filament are accelerated toward the anode disk up to half the speed of light and collide with the positive anode.

64
Q

Incident electrons

A

Possess massive kinetic energy

65
Q

When incident electrons strike the anode target

A

Electrons come to an abrupt halt, kinetic energy is lost

66
Q

Lost kinetic energy must take new energy forms:

A

Heat (thermal energy)

Electromagnetic (in the form of X-ray)

67
Q

X-ray production is a very inefficient process

A

99% heat

1% X-ray

68
Q

X-ray exposure switches are two stage

A

Pushing the prep button

  • thermionic emission occurs (boiled electrons float in vacuum as a space charge)
  • anode rotates in preparation for electrons (anode rotates to spread heat over larger area)
69
Q

Pushing the exposure button

A

Kilovoltage is applied

  • boiled off electrons are accelerated from cathode to anode
  • these electrons possess massive kinetic energy
70
Q

Primary beam/useful beam

A

Polyenergetic/heterogeneous in nature - exists in a variety of strengths - from 1kv to KVP

71
Q

Primary beam exits tube housing

A

At tube window, proceeds toward patient, passes through colimator

72
Q

Collimater function

A

Control size and shape of primary beam, minimize the amount of tissue irradiated and amount of scatter produced.

73
Q

Centering light

A

With “crosshairs” for central ray, visible light bounced off mirror, mirror acts as X-ray filter

74
Q

Colimator contains

A

2 sets of lead shutters within

Scaled colimator dial

75
Q

3 things for X-ray production

A 
All come together in the X-ray tube...
High amperage for thermionic emission
 - source of free electrons
 - delivered by filament/step down transformer
High voltage/kiliovoltage
 -acceleration of free electrons
 -delivery of high voltage/step up transformer
Dense anode target material
 -abrupt halting of high speed electrons
 -Tungsten

SEM II - Rad Physics (6 decks)

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