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radiology > X-ray Tube > Flashcards

X-ray Tube Flashcards

1
Q

what are the parts of a dental X-ray tube

A 
Control Panel
Extension Arm
Tubehead
PID (the tube)
BAsic parts: tube head and control pannel
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2
Q

what does PID stand for

A

position indicating device

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3
Q

what does the tube head contain

A

X ray tube and Position indicating device

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4
Q

how is the tubehead suspended

A

from a flexible extension arm

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5
Q

why is the extension arm hollow

A

enables wires to pass through

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6
Q

what is found on the control panel of a dental radiographic machine

A

On/off switch
exposure botton with indicator light and audible signal
expose time, KvP and mA selection

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7
Q

where is the control panel mounded

A

Wall or portable control box

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8
Q

what does the control panel do

A

turs on machine and adjusts settings (Kilovolts, Milliampers, exposure time)

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9
Q

what does federal laq require the exposure button be connected to

A

Indicator light and audible signal

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10
Q

what happens when the exposure button is depressed

A

Indicator light and sound is activited

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11
Q

what type of switch is the exposure button

A

Dead man type(switch works only with continuous pressure)

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12
Q

how long do you hold the exposure button down

A

Until the sound is over and the light is off

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13
Q

what are the 4 conditions for the production of X-rays

A
  • Separation of electrons from tungsten filament at cathode
  • production of high speed electrons to ensure enought KE needed for the production of X-rays
  • focusing of electrons on a small region on the anode
  • sudden stopage of electrons creating x-ray photons
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14
Q

why do electrons repel each other

A

negative charge

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15
Q

where are electrons focuesed

A

On the focal spot of the anode

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16
Q

what does the anode do to the electrons

A

stops and slows electrons

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17
Q

what types of interactions form when an electron slows

A

Bremsstrahlung

Characteristic

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18
Q

how are electrons originally separated

A

By the formation of an electron cloud by heating of tungsten filament at low voltage

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19
Q

is the anode or cathode the source of electrons

A

Cathode

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20
Q

what is the cathode made of

A

tungsten

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21
Q

what voltage is used to heat the cathode

A

6-12 volts

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22
Q

what is the process of using heat to produce electrons

A

Thermionic emission

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23
Q

what provides the necessary current to the tungsten filament

A

Step down transform

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24
Q

why is tungsten used in the cathode

A

High Z number

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25
Q

what is the voltage difference between cathode and anode

A

1000 times higher than 110 volt wall outlet

65000-90000 volts

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26
Q

what provides the necssary voltage between the cathode and anode

A

step up transformed

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27
Q

how fast are electrons accelerated

A

.5 times the speed of light

28
Q

what doe the High Voltage difference do to the electrons

A

Lead to high Kinetic energy and high speed

29
Q

what is used to focus the electons

A

A Molybdenum focusing cup at the cathode

30
Q

what is the target made of for the electron beam

A

Tungsten(anode)

copper stem

31
Q

why is tungsten used as the Anode

A

High Atomic number
High melting point
Low VP

32
Q

efficiency of X-ray production

A

99% of electron energy transformed as heat, 1% converted to X-rays

33
Q

why is the tungsten target embeeded in a copper stem

A

Need a good thermal conductor to dissipate heat

34
Q

what fills the X-ray tube

A

Nothing, it is a vaccume

35
Q

why does a metal housing surround the glass X-ray tube

A

Protect tube from accidental damage

prevents overheating by giving a potential space to fill with oil

36
Q

what determines the current of the X-ray tube

A

By the Low voltage side

37
Q

High current X-ray tubes do what to Xrays

A

create lots of X-rays

38
Q

High voltage difference does what X-rays

A

X-rays are higher energy

39
Q

problem with placing metal in a vaccum

A

Metal must not vaporize(good cuz tungsten has low vapor pressure)

40
Q

How “pure” is the beam of X-rays leaving the tube

A

Different wavelengths with Different enegy

41
Q

what does filtration of X-rays do

A

preferentially removes low energy X-ray photons from beam, reducing dose to patient

42
Q

what is inherent filtration

A

The glass covering and oil in the tube that stops low energy X-rays

43
Q

What is total filtration

A

Aluminum and inherent Filtration

44
Q

what is the Aluminum equivalent

A

The thickness of aluminum (in mm) which gives the same filtration as the inherent filtering material (glass and oil) of x-ray tubehead under same conditions

45
Q

how much total filtration must be used if 50-70KVp

A

1.5mm total (inherent +AI)

46
Q

How much total filtration must be used above 70KVp

A

2.5mm total(inherent +Al)

47
Q

why is the tube placed in oil

A

Insulationa nad heat

48
Q

What does filtration do to exposure time and skin dose

A

INcreases exposure time up to 50% to account for loss inintensity
reduces patient skin exposure as much as 80%

49
Q

what do you do if you use an Xray machine below 60KVP

A

don’t use it, need to overexpose patient to produce an acceptable radiograph

50
Q

what are the facotrs that control the X-ray beam

A 
Tube Voltage 
Exposure time
Tube current
Filtration
Collimation
Distance
51
Q

what does A high amount of voltage do number and energy of photons

A

More photons(higher quantity( and higher energy(higher quality)

52
Q

what does KVp control in an electron

A

Control the speed (KE) of each electron) leading to higher energy photons and X-rays

53
Q

what is the Rule of Thumb for KVP

A

an increase in 15% in KvP should be followed by a reduction in 1/2 mAs

54
Q

what happens to the expsore timeif you increase by 15kVP to get the same density

A

1/2 exposure time

55
Q

what happens to the exposure time if you decrease by 15kVP to get the same density

A

double exposure time

56
Q

why does low KVP lead to less dense images

A

longer wavelengths and lower energy so less penetration

57
Q

what does Increaseing exposure time do

A

INCresaes the amount of x rays produced

58
Q

what does an increase in current ddo to the x-rays

A

Increases the quantiy of x-rays produced

59
Q

what one factor determines the total number of x-ray photons produced in the beam

A

miliamp seconds

60
Q

what should remain constant for a particular exposure

A

miliamp seconds(increase time, decrease miliamps

61
Q

what does Collimation do

A

Minimizes the amount of radiation to patients and reduces scatter, protecteing patient from unnecessary radition

62
Q

what is the most effective beam limiting device

A

Collimator

63
Q

do all X-ray tubes have collimators

A

Yes, made of lead

64
Q

what does Federal law require that a collimator should restrict a beam to

A

no more than 7cm(2.75 inches) at the skin surface of the patient when making an intraoral dental radiograph

65
Q

what is the relationship between intesnity of radiation and distance

A

Inverse square(intensity decreases inversly as the square of the source film distance)

radiology (10 decks)

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