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Radiation Therapy > Physics Chapter 4 powerpoint > Flashcards

Physics Chapter 4 powerpoint Flashcards

1
Q

What are the two types of medical uses of x ray tubes?

A

Diagnostic

Therapy

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2
Q

Superficial and Orthovoltage are associated with what kind of medical use of x ray tubes?

A

Therapy

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3
Q

What is the type of energy input of an x ray tube?

A

electrical energy

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4
Q

What are the type of output energies for x ray tube?

A

heat 99%

x-rays

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5
Q

What are the two types of photons emitted from the x ray tube?

A

bremmstrahlung

characteristic x rays

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6
Q

What are the problems that heat production from the x ray tube can cause?

A

limited beam intensity

limited throughput

x ray tube death

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7
Q

Where does the glass vacuum tube sit?

A

inside the metal housing of the x ray tube

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8
Q

What is the housing of the x ray tube?

A

The visible part of the x ray tube

it is filled with oil

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9
Q

What is another name for the glass vacuum tube?

A

insert

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10
Q

X rays are created in the ____________ portion of the x ray tube.

A

glass vacuum insert

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11
Q

What is the function of oil in the tube housing?

A

conduct heat for cooling

electrical insulation

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12
Q

What part of the x ray tube is electrically grounded and has its inside wrapped with lead?

A

tube housing

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13
Q

What does the tube housing shield against?

A

high voltage

leakage radiation

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14
Q

What two things are located inside the glass insert?

A

filament (usually tungsten)
(cathode)

tungsten target
(anode)

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15
Q

Why is the tungsten block sometimes inserted in copper?

A

for heat removal

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16
Q

Why is tungsten used as the target material?

A

high melting point

high atomic number (more efficient for producing x rays)

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17
Q

What is thermionic emission?

A

The boiling off of electrons from a filament

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18
Q

What is another name for thermionic emission?

A

Edison Effect

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19
Q

____________ is the source of electrons.

A

filament

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20
Q

__________ provides energy for electrons to escape filament.

A

heat

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21
Q

_________ voltage is applied to the anode (target).

A

positive

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22
Q

When electrons strike the target __________ energy is converted to heat and x rays.

A

kinetic

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23
Q

What is tube m(A)?

A

rate of electron flow from filament to target

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24
Q

What are the units of tube current?

A

milliamperes (mA)

also expressed in electrons per second

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25
Q

True or false: tube current is the same as filament current.

A

False

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26
Q

Output radiation is ____________ to mA.

A

proportional

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27
Q

What two types of electrical requirements are there for production of x rays?

A

filament voltage

high voltage

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28
Q

What is the focal spot?

A

the portion of the anode struck by the electron stream. It is the place from which x rays are emitted

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29
Q

What is responsible for affecting resolution and maximum intensity?

A

focal spot size

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30
Q

The larger the focal spot, the more it will _______ a tiny place on the patient.

A

blur

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31
Q

The larger the area the electron beam hits, the more ________ the beam can be without melting the target.

A

intense

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32
Q

What is the angle that exists between the target and the perpendicular tube axis?

A

target angle

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33
Q

What is the typical target angle range?

A

7-15 degrees

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34
Q

From what perspective is the actual (true) focal spot seen?

A

as seen from the filament

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35
Q

The apparent (effective, projected) focal spot is from the perspective of the:

A

patient or tube port

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36
Q

Large target angles have ________ heat ratings but _______ field coverage.

A

worse

better

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37
Q

Small target angles have _______ heat ratings but __________ field coverage.

A

optimized

limited

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38
Q

True or false: Large and small target angles can have different (actual focal spot sizes) but the same (apparent focal spot sizes)

A

True

39
Q

What is the heel effect?

A

intensity of the x ray beam is significantly reduced on the anode side of the target because it partially travels through the target.

40
Q

Stationary anodes are used in ________ tubes.

A

therapy

rarely for diagnostic

41
Q

What is the disadvantage and advantage of rotating anodes?

A

Have much better heat ratings

but

much more expensive

42
Q

Diagnostic x ray tubes operate at about 40-150 kVp, while therapy tubes operate at more than ______ kVp.

A

200

43
Q

What are three things that a therapy tube has that diagnostic tubes don’t?

A

larger focal spot size

no rotating anode

hooded anode

44
Q

Why do therapy tubes have larger focal spots?

A

they don’t need to image

their focal spot is about 5 mm

45
Q

What kind of anode is designed to run continuously and have cooling oil channels?

A

stationary anode

46
Q

What is the purpose of a hood on an anode?

A

prevent secondary electrons and x rays that would interfere with the electron beam focus

47
Q

What provides electricity for an x ray tube?

A

x ray generator

48
Q

What controls exposure timing?

A

x ray generator

49
Q

What is kilovoltage peak?

A

the maximum high voltage applied between cathode and anode

50
Q

What is exposure time?

A

the length of time high voltage is applied

51
Q

What is mAs?

A

mA multiplied by exposure time

52
Q

What is beam intensity the product of?

A

number of photons in a beam

energy spectrum

53
Q

What are the units of beam intensity?

A

roentgens (R) per unit of time

54
Q

What factors does beam intensity depend on?

A

kVp
mA
target material
filtration

55
Q

What is beam intensity PROPORTIONAL to?

A

exposure time
mA
mAs

kVp squared -kVp cubed approximately

56
Q

What provides high voltage to the therapy tube?

A

x ray generator

57
Q

High voltage from a x ray generator to a therapy tube gives the same maximum ______.

A

kVp

58
Q

Exposure timing can be _______ or ________________.

A

manual

automatic

59
Q

What is automatic exposure timing?

A

equipment measures radiation

exposure is terminated when designated radiation is measured

compensates for differences in the patient

60
Q

Where is the photo timing’s radiation detector located?

A

between the grid and the image receptor

61
Q

True or false: the target can be damaged from a single exposure by melting.

A

True

62
Q

True or false: housing of the tube cannot overheat from repeated long exposures.

A

False

63
Q

What is a single exposure tube rating chart?

A

A chart that indicates heat load limit for tube for a single exposure

maximum time for a given kVp and mA

64
Q

What is a cumulative heat curve chart?

A

maximum time of continuous exposure at a given kVp and mA

The maximum heat for multiple single exposures or a continuous exposure

65
Q

What are tube rating charts?

A

charts built into modern equipment to prevent tube damage

66
Q

What kind of imaging are grids used in?

A

in most diagnostic

67
Q

What are grids?

A

directional filters for photons

68
Q

How do grids achieve their purpose?

A

by passing all primary photons (photons coming from focal spot)

blocking secondary photons (scattered photons that change directions and did not come from the focal spot.

69
Q

What material is used in grids?

A

lead (thin, upright strips of foil)

70
Q

What is interspace of a grid?

A

the material between the lead strips that keep the lead in place.

they can be made of fiber, wood, or aluminum

71
Q

What are the two grid styles?

A

parallel and focused

72
Q

True or false: grids remove all secondary x rays perfectly and allow all primary to pass.

A

False

some primary blocked

some bad pass

73
Q

What is the disadvantage of a grid? slide 46

A

It can increase the patient dose 3-6 times

74
Q

What are the. layers of an x ray film from superficial to deep?

A

supercoating

emulsion layer

adhesive layer

film base

adhesion layer

emulsion layer

supercoating

75
Q

What does the film base allow?

A

structural support for fragile emulsion

76
Q

What part of the x ray film contains gelatin, allows penetration of processing solutions, and is made from cattle bones?

A

emulsion

77
Q

What is the purpose of the adhesive layer of an x ray film?

A

attaches the emulsion layer to the base

78
Q

What is the supercoating of an x ray film?

A

a thin supercoating that protects from mechanical damage and makes the film smooth and slick

79
Q

True or false: an x ray film can be used as a dosimeter

A

true

80
Q

Why do x ray films have poor efficiency?

A

most photon energy is lost

81
Q

What is an intensifying screen?

A

a film used for virtually all diagnostic film imaging

82
Q

Why are intensifying screens better than direct film exposure?

A

decreases patient dose by hundreds

much shorter exposure time

83
Q

What is the structure of an intensifying screen?

A

a film between two cassettes

84
Q

What do intensifying screens do?

A

convert x rays to light

85
Q

True or false: a single x ray produces many light photons through an intensifying screen.

A

True

86
Q

What is the purpose of a radiographic cassette?

A

tight container for film that increase imagine sharpness by preventing gaps

87
Q

What is computed radiography (CR)?

A

re usable metal imaging plates that replaced film and cassette

uses conventional Bucky and x ray equiment

88
Q

What is digital radiography?

A

electronic digital receptor

89
Q

Stimulable Phosphor receptor is associated with what kind of imaging?

A

CR

90
Q

How does CR work?

A

radiation causes electrons to move to a higher energy state (excitation). They then become trapped by a photostimulable phosphor plate, which forms the latent image

a laser then releases the electrons causing them to emit visible light energy (the intensity indicates a measure of radiation)

the plate is moved through the laser beam by rollers, and the light emitted by the plate is measured by a photomultiplier tube and recorded by a computer

91
Q

How is a CR plate erased?

A

the plate is erased using a bright light

92
Q

What is a receptor able to do in digital radiography?

A

provide direct digital output immediately because no processor/ reader is required

93
Q

What are the two types of DR receptors?

A

direct conversion

indirect conversion

94
Q

what is the difference between direct conversion and indirect conversion in DR receptors?

A

direct conversion uses a-Selenium before the thin film transistor array

indirect conversion uses a scintillator to visible light to photodiode (a-Silicon) to the thin film transistor array

Radiation Therapy (26 decks)

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