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1
Q

what is tube current

A

the flow of electrons from cathode to anode

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2
Q

what is tube current measured in

A

milliamps

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3
Q

what is filament current

A

electron flow through the cathode

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4
Q

what is filament current measured in

A

amperes

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5
Q

how are tube current and filament current related

A

tube current is adjusted by controlling the filament current

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6
Q

what is the cathode

A

negative side of tube; 2 parts: filament and focusing cup

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7
Q

what is the anode

A

positive side of tube; conducts electricity and radiates heat and contains target

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8
Q

what does the mAs timers do

A

automatically picks high mA and short exposure time

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9
Q

what is rectification

A

convert AC to near DC

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10
Q

what is resiprocity

A

when the mAs are the same

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11
Q

1/2 wave, single phase= _____ pulses

A

60

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12
Q

full wave, single phase=______pulses

A

120

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13
Q

how far does the supply to the tube fall away from maximum (peak) between impulses/cycles for single phase, half wave

A

100%

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14
Q

single phase, full wave

A

100%

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15
Q

three phase, 6 pulse

A

14%

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16
Q

three phase, 12 pulse

A

4%

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17
Q

high frequency

A

1%

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18
Q

what is an example of a capacitor discharge unit

A

portable

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19
Q

the source of energy from a capacity discharge unit is

A

battery

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20
Q

what declines as the exposure is made on a capacitor discharge unit

A

kvp

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21
Q

what is a regular x-ray tube called

A

diode

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22
Q

why use a grid controlled tube

A

because photon emission could continue after the exposure is terminated for a capacitor discharge unit

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23
Q

What does a grid controlled tube do

A

terminates exposure precisely (pt. dose and image quality related)

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24
Q

how does a “grid” work

A

a grid is placed between the cathode and anode and is negatively charged to terminate the flow of electrons at the precise time photon generation should stop.

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25
Q

how do you calculate power ratings

A

(mA*kVp)/1000= kW

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26
Q

how many electrodes does a diode have

A

2

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27
Q

why is the glass or metal envelope thin

A

for least attenuation possible

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28
Q

what does the protective house do

A
  1. protect from leakage radiation

2. protect from electric shock

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29
Q

what is isotropic x-ray emission

A

when x-rays are emitted equally and in all directions

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30
Q

what is the window of the x-ray tube

A

only use x-rays emitted throught the window

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31
Q

there can be no leakage greater than what

A

100 mR/hr at 1 meter

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32
Q

what are filaments made of and why

A

thoriated tungsten; high melting point and low vaporization

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33
Q

what is the most common cause of tube failure

A
  1. abrupt tube failure

2. chronic use

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34
Q

once you go above saturation current, increasing kVp does what to tube current or quantity of x-rays produced

A

nothing

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35
Q

what does mAs control

A

quantity

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36
Q

what does kv control

A

quality

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37
Q

the rotation of the anode is based on what

A

induction motor

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38
Q

what is the stator

A

part of induction motor; outside the glass or metal enclosure; series of electromagnets equally spaced around the neck of the tube

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39
Q

what is the rotor

A

part of induction motor; inside glass; shaft made of bars of copper and soft iron fabricated into one mass

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40
Q

how does an induction motor work

A
  1. stators are energized in sequence
  2. rotor attempts to align with magnetic fields sequentially
  3. when exposure terminates order of stator activation is reversed to slow dow rotation
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41
Q

what is space charge effect

A

cloud of negatively charged electrons around filament discourages further thermionic emission by electrostatic repulsion (makes it harder for electrons to boil off wire)

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42
Q

what is the focusing cup

A

negatively charged to condense/repel electrons toward anode

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43
Q

what are the two types of anodes

A

stationary and rotating

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44
Q

which type of anode gives more surface area for heat loading by providing an increased target area

A

rotating.

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45
Q

what material is the anode typically made of

A

needs to be a good electrical and thermal conductor-copper

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46
Q

what is the target

A

specific area of the anode where electrons interact to produce x-rays

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47
Q

why is tungsten metal a good target

A
  1. high atomic number (so high energy x-rays)
  2. thermal conductivity (dissipates heat produced)
  3. high melting point (can stand high tube current without melting)
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48
Q

what is saturation current

A

the point at which all electrons go

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49
Q

what is the line focus principle

A

get effective focal spot size smaller than actual electron beam due to angled anode.

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50
Q

the smaller the anode angle, the _____effective focal spot

A

smaller

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51
Q

what is the anode heel effect

A

reduced intensity on anode side of beam due to absorption of photons in ‘heel’ of anode.

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52
Q

in theory the _____should be placed over the thick/dense portion of the patient to produce more uniform density on resulting image

A

cathode

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53
Q

an an anode heel increases, there is ____ significant anode heel effect

A

less

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54
Q

the more electrons sent off the cathode, the ______ x-rays recieved

A

more

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55
Q

what is the anode cooling for a H.U. production

A

mAtimekVp

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56
Q

what is the anode cooling for a three phase/six pulse

A

mAtimekVp*1.35

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57
Q

what is the anode cooling for a three phase/twelve pulse

A

mAtimekVp*1.41

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58
Q

what can be determined from an anode cooling chart

A
  1. tells maximum heat for tube and how long to completely cool
  2. calculates required “wait” between exposures
  3. partial cooling between exposures
59
Q

tube “warm up” prevents what

A

damage to cold anode from high heat unit exposures

60
Q

what does a radiographic rating chart determine

A

the safety of a single exposure for a specific x-ray tube.

61
Q

what does the radiographic rating chart contain

A

proper filament size, anode rpm, target angle, rectification method

62
Q

kVpl time, mA combinations which intersect ______ curve in question are safe

A

below

63
Q

Even though quantity does not change above saturation current, what happens to density

A

it goes up as kVp goes up

64
Q

when tube current increases, quantity of x-rays ____, quality ______, when all electrons go

A

increase, increase

65
Q

what is saturation current

A

specific kVp at which all space charge electrons are immediately propelled to anode every exposure

66
Q

what happens above saturation current

A

mA is a function solely of filament temp. (increasing kV doesn’t increase tube current)

67
Q

What happens below saturation current

A

space charge limited region- not all electrons at cathode went to anode on exposure so changes in kV change the tube current (mS is influenced by kVp)

68
Q

what is the only thing that changes above saturation current

A

mAs

69
Q

What is the most common energy in any beam

A

1/3 operation

70
Q

what is the common saturation current

A

115 kVp

71
Q

most projectile electrons have insufficient energy to ionize the target atoms, therefore

A

excitation occurs instead, thus the heat

72
Q

to ionize the electron, the projectile electron must have

A

energy greater than the binding energy of the electron

73
Q

what are the two types of production

A

characteristic and brems

74
Q

which type of production runs around nucleus

A

brems

75
Q

which type of production ionizes the target

A

characteristic

76
Q

what percentage of x-rays produced are characteristic

A

10%

77
Q

what percentage of x-rays produced are brems

A

90%

78
Q

a photon that loses energy is what type of production

A

brems

79
Q

describe characteristic production

A
  1. when projectile electrons from cathode have sufficient energy to ionize an inner shell target electron at the anode
  2. the ionization leaves a “hole” which is filled by an electron from a more distant shell
  3. x-ray produced during this trasition has energy equal to the differetnce in binding energy between the shells involved
80
Q

describe brems production

A
  1. negative electron from the cathode comes under the influence of the positive nucleus of the target material at the anode
  2. unlike charges attract
  3. the electron leaves the target atom with reduced energy in new direction
81
Q

what is a discrete spectrum represent

A

characteristic x-rays

82
Q

the vertical line at specific energies is related to

A

electron binding energy of the target

83
Q

the hights of the discrete spectrum relate to

A

quantity of photons at that energy-intensity-frequencey-number of photons at this energy

84
Q

what changes the location of the discrete spectrum

A

atomic number

85
Q

the lower the atomic number, the further______the discrete spectrum

A

left and vice versa

86
Q

on a combined emission spectrum graph, amplitude is

A

quantity

87
Q

energy is

A

position

88
Q

the continuous spectrum represents

A

brems

89
Q

the greatest number of photons (highest amplitude of curve is approximately

A

1/3 of maximum

90
Q

area under curve represents

A

total number of x-rays

91
Q

to move the discrete spectrum left or right, nedd new

A

target material

92
Q

the discrete spectrum has the ______ energy all the time

A

same

93
Q

change in kVp

A

shift of spectrum left and right and amplitude (gets more or less photons

94
Q

shift of the continuous spectrum to the right means

A

greater effective energy when kVp in increased

95
Q

changing mA changes

A

amplitude of curve of both discrete and continuous BUT position of neither.

96
Q

long scale

A

lots of gray

97
Q

compton interactions have what scale of contrast

A

long scale (lots of gray)

98
Q

what is increase filtration

A

reduces amplitude of curve, more on left (low energies)

99
Q

what happens to contrast when you significantly increase filtration?

A

fewer energis to work with so shorter scale of contrast.

100
Q

when you increase mA or mAs

A

amplitude of curve changes up and down (quantity of x-rays up or down)

101
Q

changes in atomic number of the target material changes

A

the amplitude of the entire curve

102
Q

atomic number of target material change results in

A

amplitude (discrete and continuous) and shifting of the discrete spectrum (energy of characteristic x-rays produced changes)

103
Q

full wave rectification to 3-phase

A

the amplitude increases and continuous spectrum shifts to the right. The amplitude of the discrete spectrum increases (but at same energy, so the location does not move)

104
Q

if you increase kVp by 15% you

A

reduce mAs by 50% to maintain image density

105
Q

Increaseing the kVp does not double the number of photons. it

A

increases the number of photons with sufficient energy to reach the film

106
Q

if you decrease kVp by 15%, you

A

double your mAs to maintain image density.

107
Q

for long scale contrast, kVp is ______, grid ratio is ______, film screen (system speed) is _______

A

increased, decreased, increased

108
Q

shortest wavelength photons are associated with

A

maximum energy (controlled by kV operation)

109
Q

wavelength min in angstroms =

A

12.4/kVp

110
Q

quantity is effected by

A

mAs, mA, time, distance, voltage, waveform, filtration

111
Q

quality is effected by

A

kVp

112
Q

HVL

A

amount of absorbing material needed to cut beam in half

113
Q

what is the minumum requirement for inherent filtration of a general purpose x-ray tube

A

.5 mm Al equivalent

114
Q

x-ray quantity is proportional to

A

mAs; kVp^2

115
Q

x-ray quantity is inversely proportional to

A

distance^2

116
Q

increased filtration

A

removes soft photons from the beam; fewer photon energies means shorter scale of contrast

117
Q

x-ray production is

A

at the target

118
Q

x-ray interaction is

A

with matter, outside the tube

119
Q

alpha and beta particles are interactions based on

A

electric charge on particle; mass of particle

120
Q

x-ray and gamma photon interactions are based on

A

energy of photon; type of matter

121
Q

types of photon interaction

A
  1. transmitted through matter unchanged
  2. change direction with no energy lossed
  3. change direction and lose energy
  4. deposit all energy in the matter
122
Q

a photon interaction that changes direction with no energy loss is

A

classical scattering

123
Q

a photon interaction that change direction and loses energy is

A

compton scattering

124
Q

a photon interaction that deposits energy in the matter is

A
  1. photoelectric effect
  2. pair production
  3. photodisitegration
125
Q

pair production

A

only happens at extremely high energys and does not happen in diagnostic; 1.02 Mev to happen

126
Q

photodisintegration

A

10MeVto happen

127
Q

describe classical scattering (aka coherent or elastic)

A
  1. low photon energy (less than 10 KeV) enters atom
  2. atom excited by photon
  3. releases photon of same keV and wavelength
  4. new photon travels in different direction from original photon but usually forward (small scatter angle)
128
Q

Describe photoelectric effect (total absorption)

A
  1. photon ejects an inner shell electron
  2. photon loses all energy
  3. characteristic radiation emitted when hole filled
  4. there is a cascade of photons until atom is neutral again
129
Q

what are the results of the photoelectric effect

A
  1. photon disappears
  2. atom is ionized
  3. characteristic photon is emitted
130
Q

the liklihood of the photoelectric effect decreases as

A

energy increases

131
Q

probablility of the photoelectric effect is about

A

z^3

132
Q

describe compton scatterint (partial absorption)

A
  1. photon changes direction with decreased energy
  2. original atom is ionized
  3. contributes to personnel/patient exposure; film fog (decreased contrast)
133
Q

what is the probability of compton interactions happening

A

atomic number (Z) is independent

134
Q

as energy increases both PE and Compton ______

A

decrease; PE more rapidly than compton

135
Q

describe pair production (total absorption)

A
  1. photon interacts with nuclear force field
  2. uses 1.022 MeV to produce pair of electron like particles
  3. photon ceases to exist; 2 photons of .511 MeV emitted
136
Q

Describe photodisentegrtion (total absorption)

A
  1. high photon energy (greater than 10 MeV)
  2. photon absorbed by nucleus
  3. nucleus excited
137
Q

photon attenuation

A

removal of photons from primary beam; interactions are total or partial absorption

138
Q

photon transmission

A

incident photons that do not interact

139
Q

differential absorption

A

the difference between those x-rays absorbed photoelectrically in the patient and those transmitted to the image receptor.

140
Q

What are 3 factors that influence differential absorption

A
  1. beam energy
  2. atomic number
  3. mass density of matter
141
Q

beam energy

A
  • DA increases as E increases
  • due to increase probability of PE at low E
  • increase in patient dose
142
Q

atomic number

A
  • DA increases as Z increases
  • probablility of PE increases with Z increases
  • REMEMBER compton is not influenced by Z
143
Q

Mass Density of Matter

A
  • DA increases as density increases
  • quantity of matter per unit volume
  • increase matter/volume = increase interactions
  • important since tissue densities cary more widely than Z

Physics Test 3 (1 decks)

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