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Oral Radiology > Production of X-Rays Part I > Flashcards

Production of X-Rays Part I Flashcards

1
Q

what is on the control panel

A
  • exposure time, kVp, and mA selectors
  • exposure button
  • indicator light and audible signal
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2
Q

what makes up the tube head

A

power supply and x ray tube

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3
Q

where is the insulating oil located

A

outside the X ray tube and transformers

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4
Q

what is inside the xray tube

A

a vacuum

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5
Q

what is in the tube head

A
  • glass envelope
  • insulating oil
  • metal housing
  • tube window
  • aluminum filters
  • lead collimator
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6
Q

what does the aluminum filter do

A

filters X ray and removes low energy X rays from the whole beam, so only those that have sufficient energy can exit the tube head

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7
Q

what is the x ray tube made of

A

glass

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8
Q

what is the tube head made of

A

metal

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9
Q

what does the oil do

A

dissipates the heat generated in the tube head

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10
Q

what is in the cathode

A

filament and focusing cup

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11
Q

what is the filament made of

A

tungsten

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12
Q

what is the source of electrons

A

the filament

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13
Q

how are electrons emitted from the cathode

A

filament is heated with a low voltage source and emits electrons at a rate proportional to its temperature - called thermionic emission

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14
Q

what is the focusing cup made of

A

molybdenum

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15
Q

what is the charge of the focusing cup

A

negative

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16
Q

what does the focusing cup do

A

focuses the electrons into a narrow bean directed to the focal spot

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17
Q

what charge is the focal spot

A

positive

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18
Q

what is in the anode

A

tungsten target and copper stem

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19
Q

what does the tungsten target do

A
  • transform the kinetic energy of the colliding electrons into Xray photons
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20
Q

how efficient is the tungsten target

A

very ineffective. produced 99% heat and 1% Xrays

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21
Q

what does the copper stem do

A

works as a thermal conductor to remove the heat from the tungstem avoiding target melting

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22
Q

why is tungsten a good target material

A
  • high atomic number: efficient production of X rays
  • high melting point - 3422 C- to withstand heat in tube
  • high thermal conductivity: to dissipate the heat produced away from the target
  • low vapor pressure: helps maintain vacuum in the tube at high temperatures
  • cheap
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23
Q

what are the conditions necessary for X ray production

A
  • separation of electrons
  • production of high speed electrons
  • concentration of electrons
  • sudden stoppage of electron steam
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24
Q

what happens in separation of electrons

A
  • thermionic emission
  • step down transformer provides the voltage
25
Q

how much voltage is supplied from the step down transformer

A

6-12 volts

26
Q

describe the production of high speed electrons

A
  • high potential difference is produced between the cathose and anode by applying a high voltage between them
  • electrons are accelerated to approximately 1/2 speed of light
27
Q

what does the kVp stand for

A

difference between the anode and the cathose

28
Q

what is usually the kVp

A

60-90

29
Q

describe the concentration of electrons

A
  • electron beam is focused by the focusing cup (negative charge) and directed towards the focal spot
30
Q

describe the sudden stoppage of electron steam

A
  • upon striking the focal spot in the anode the electron steam is stopped and kinetic energy of the electron steam undergoes conversion to greater than 99% heat and less than 1% x-radiation
31
Q

what removes the heat from tungsten

A

copper stem

32
Q

the smaller the focal spot the _____ of the image

A

higher resolution

33
Q

what is the focal spot

A

the area of the target to which the focusing cup directs the electrons and from which the xrays are produced

34
Q

the smaller the focal spot the more ___ accumulates

A

heat

35
Q

what are 2 ways to overcome heat accumulation with a smaller focal spot

A
  • rotating anodes
  • stationary anodes - line focus principle
36
Q

what does the rotating anode do and where is it found

A
  • allows heat at the focal spot to spread out over a large surface
  • medical devices
37
Q

what is the line focus principle (stationary anode)

A
  • angling the target to achieve a smaller effective focal spot than the actual focal spot
38
Q

what does a stationary anode result in

A

sharper radiographic image while maintaining the original surface area of the target for heat dissipation

39
Q

what is the actual focal spot

A

the projection of the focal spot perpendicular to the target

40
Q

what is the effective focal spot

A

the projection of the focal spot perpendicular to the electron beam

41
Q

how does the effective focal spot compare to the actual focal spot in size

A

the effective is always smaller

42
Q

what are the 2 functions of the power supply

A
  • provide a low voltage current to heat the x ray tube filament - step down transfomer
  • generate a high potential difference to accelerate electrons from the cathose to the focal spot of the anode- step up transformer
43
Q

what is the transformer

A

electromagnetic device that either increases or decreases the voltage in a circuit

44
Q

what are the 3 types of transformers in the xray unit

A
  • step down transformer - filament transformer
  • step up transformer - high voltage
  • autotransformer
45
Q

what does the mA control

A

the amount of energy in the step down transformer

46
Q

what happens if you increase the mA

A

more energy through the transformer the higher voltage through the filament and the higher number of electrons -> modifies the AMOUNT of X rays produced

47
Q

what does the kVp modify

A

step up transformer and ENERGY of the X ray

48
Q

what happens if you increase kVp

A

greater difference between anode and cathose -> electron will be more attracted to the anode -> electron has more energy -> Xray will be more energetic -> modified ENERGY of X ray

49
Q

what does the step down transformer do

A

used to convert 110 volts to 3-5 volts to heat the filament

50
Q

what does the step up transformer do

A

used to convert 110 volts to 60,000-100,000 volts to move the electrons across the tube

51
Q

what does the exposure timer determine

A

amount of time the high voltage circuit is applied across the x ray tube- amount of time x rays are produced

52
Q

what is the time delay circuit

A

delay of 1/2 second to heat the filament

53
Q

what is the timing circuit

A

actual time of exposure

54
Q

what affects number of X rays

A

time and mA

55
Q

what affects energy of x rays

A

kVp

56
Q

what does kV control

A

the acceleration of electrons from cathode to anode

57
Q

what does mA control

A

the heating of the filament

58
Q

what does exposure time control

A

the time in which xrays are produced

59
Q
A

Oral Radiology (26 decks)

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