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202 MEDIMAGE > 1. X-Ray Production > Flashcards

1. X-Ray Production Flashcards

1
Q

How are x-rays produced in the x-ray tube

What happens on the cathode side

A

the tungsten filament is heated and produces e- through thermionic emission

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2
Q

How are x-rays produced in the x-ray tube

What happens on the anode side

A

e- produced at the anode side accelerate towards the anode and hits the metal target

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3
Q

what type of electrode is the cathode

what is the role of the cathode in x-ray production

A

its a negative electrode

its the source of e-

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4
Q

what type of electrode is the anode

what is the role of the anode in x-ray production

A

positive electrode

e-s attracted to the positive charge and accelerate towards it where they are stopped/decelerated

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5
Q

what occurs at the anode in terms of energy that produces x-rays

what else does the process produce

A

kinetic energy of e- transferred to the anode (when e- strike target it loses energy which is the kinetic energy)

x-rays and heat are produced

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6
Q

what material is the center of the anode made of

A

tungsten

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7
Q

where do the x-rays leave the x-ray tube from

A

the window

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8
Q

what does the vacuum in the x-ray tube prevent and do

A

it makes sure that the e- energy is undissipated so produces x-rays and prevents energy from being lost as heat

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9
Q

what are the 2 types of anodes

A

stationary and rotating

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10
Q

what is the limitation of the stationary anode and what is the benefit of the rotating anode

A

stationary = compact but wears and creates heat

rotating = larger and longer life as can tolerate higher mAs and dissipate more heat

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11
Q

what 2 components make up the cathode

A

filament (large and small) and focusing cup

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12
Q

what is the filament and what is its role in x-ray production

A

coiled tungsten wire

source of e- during x-ray production

filament current heats the tungsten filament and causes thermionic emission

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13
Q

what is the focusing cup and what is its role in x-ray production

A

surrounds filament and open at one end to allow e- to flow from cathode to anode

purpose is the focus the e- stream, it does this with its negative charge which prevents the filaments emitted e- from spreading apart

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14
Q

what are the 3 components of the rotating anode and how are they arranged in a x-ray tube

A

target, stator and rotor

rotor attached to target and the stator is found either side of the rotor

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15
Q

what is the purpose of the anode target

A

metal that abruptly decelerates/stops e- in the tube current

either rotational or stationary

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16
Q

what is the purpose of the stator and rotor

A

electric motor that turns the rotor

the rotor is connected to the target through the molybdenum anode stem

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17
Q

what components of the x-ray tube prevent overheating

A

insulating oil

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18
Q

which 2 types of interactions produce x-ray photons

A

bremsstrahlung and characteristic interactions

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19
Q

in terms of the incident e- and x-ray production what occurs in bremsstrahlung interactions

A

incident e- is attracted to the nucleus but doesnt eject any e-s

incident e- loses energy and changes direction

excess energy is emitted as a photon

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20
Q

which 2 factors impact the photon energy produced from a bremsstrahlung interaction

A

proximity to nucleus

atomic number

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21
Q

how does increased proximity of the incident e- to the nucleus impact the photon energy produced from a bremsstrahlung interaction

A

closer = incr attractive forces = more energy lost = incr photon energy

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22
Q

how atom size impact the photon energy produced from a bremsstrahlung interaction

A

larger atom = incr attractive force = incr photon energy

23
Q

is the range of energy produced for photons from bremsstrahlung interactions discrete or continuous

A

continuous

24
Q

what is a bremsstrahlung interaction

A

projectile e- completely avoids the orbital e- of the tungsten atom and travels very close to its own nucleus

the strong electrostatic force of the nucleus causes the e- to slow down

e- loses energy and change direction and energy lost produces an x-ray photon

25
Q

in the diagnostic energy range most of the interactions are characteristic/bremsstrahlung

A

bremsstrahlung interaction

26
Q

in terms of the incident e- and x-ray production what occurs in characteristic interactions

A

incident e- removes an e- from the inner k shell of the orbit via repulsion

other e-s in the orbit falls form outer shell to inner shell to replace the removed e-

x-rays are emitted in this process due to the energy difference created

27
Q

is the range of energy produced for photons from characteristic interactions discrete or continuous

A

discrete specific energies due to specific orbits

28
Q

Is there a difference in x-rays produced by bremsstrahlung and characteristic interactions at the same energy level

A

no they are the same simply produced by different processes

29
Q

the x-ray spectrum has what on its y and x axis

A

y = x-ray intensity

x = energy (keV)

30
Q

what is the x ray quantity and how is this show on the spectrum

A

total number of x-ray photons

area under whole curve

31
Q

what is x-ray quality

A

average energy of x-ray photons contained in x-ray beam/spectrum

32
Q

is the x-ray spectrum representative of the average energy

A

no

33
Q

why is there a lower and upper limit on the bremsstrahlung interactions on the x-ray spectrum

A

upper = cant produce more energy than it had to start with (need to apply more voltage to increase the upper limit)

lower = doesnt go to 0 as its filtered by the x-ray tube and the tube components

34
Q

what is the tube current

A

the mA is the current of e- flowing from cathode to anode in the x-ray tube

35
Q

what is the space charge effect

A

e- from the filament during thermionic emission form a cloud around the filament called space charge

tendency to prevent more e- boiled off the filament (number of e- is limited)

36
Q

what aspect of the e- in the tube current does kV control

A

speed at which they move

37
Q

in terms of quality and quantity what does the kV affect and how

A

quantity and quality

higher quality = high energy and greater penetrability

38
Q

in terms of quality and quantity what does the mA affect and how

A

quantity, doesnt affect quality or energy

more e- in the tube current the more x-ray produced

39
Q

what effect does exposure time have on the x-ray quantity

A

longer exposure time results in more e- moving in the tube current from cathode to anode

more x-rays produced

40
Q

what is the anode heel effect

A

x-ray beams have higher intensity (number of x-rays) on cathode side but lower intensity on anode side

41
Q

why is the anode heel effect present

A

the x-rays produced leave in many directions and the x-rays produced at the anode side have further to travel and some are absorbed by the anode itself

this reduces the x-ray numbers compared to the to photon produced in the direction of the cathode

42
Q

how can the anode heel effect be used advantageously

A

place cathode over thicker anatomy to produce a more even exposure

43
Q

what is the line focus principle

A

relationship between the actual focal spot and the effective focal spot

by angling the anode target the actual focal spot can remain large and effective fs can be reduced in size (greater heat capacity and greater image quality achieved)

44
Q

what is the actual focal spot and what does it depend on

A

size of area on anode target that is exposed to e- from tube current

depends on the filament size producing the e- stream

45
Q

what is the effective focal spot

A

focal spot size as measured directly under the anode target

46
Q

what is the difference between using small and large focal spots in terms of quality and exposures

A

large fs can withstand large exposures

small fs can give better image quality

47
Q

the larger the anode angle, the larger/smaller the effective focal spot

A

larger

48
Q

In terms of the line focus principle what does biased and non biased mean for the voltage

A

Biased = voltage applied

Non-biased = same voltage everywhere

49
Q

Effective focal spot is smaller/bigger near cathode & smaller/bigger near anode

A

cathode = bigger

anode = smaller

50
Q

the smaller the anode target angle the smaller/bigger the effective focal spot size

A

smaller

51
Q

Total filtration in the x-ray beam includes which 2 types of filtration

A

inherent and added filtration

52
Q

the intensity of the x-ray beam is greater on the ___ side of the tube

A

cathode

53
Q

the clouds of e- that forms before x-ray production is referred to as ___ ____

A

space charge

54
Q

what % of kinetic energy is converted to heat when moving e-strike the anode target

A

99%

202 MEDIMAGE (18 decks)

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