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Radiologic Physics > Final exam > Flashcards

Final exam Flashcards

1
Q

Rectifier

A

allows current to flow only in one direction

electrons travel from cathode to anode and can’t be reversed

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2
Q

rectification

A

the process of converting alternating current to direct current

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3
Q

Diode

A

electronic device that contain two electrodes
cathode and anode
same thing as rectifier

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4
Q

2 types of rectifiers

A
  1. valve tubes/vacuum tubes

2. solid state rectifiers

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5
Q
  1. valve tubes/vacuum tubes
A

used in older xray imaging systems

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6
Q
  1. solid state rectifiers
A

replaced the valve tubes
in use today
conduct electric current in only one direction

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7
Q

symbol for rectifier

A

the arrowhead indicates the direction of conventional electric current
its the opposite to the flow of electrons

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8
Q

where are rectifiers located

A

high voltage section

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9
Q

2 ways of rectifying high voltage AC

A
  1. half wave rectification

2. full wave rectification

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10
Q
  1. half wave rectification
A

gets rid of the negative swing
left with half the sine wave
the inverse voltage (negative portion) to the x ray tube is removed by rectification
contains 1 or 2 diodes
produces 60 x ray pulses each second
during the positive portion of the AC waveform the rectifier allows electric current to pas through the x ray tube
during the negative portion of AC waveform rectifier does not conduct and no electric current flows

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11
Q

disadvantages of half wave rectification

A

not so great because loses some of the power due to the gaps

requires twice the exposure time

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12
Q

full wave rectification

A

change the negative half cycle to a positive one
now all waveforms are positive and going in one direction
produce a pulsating direct current
has 4 diodes
rectifies the entire AC waveform
occurs 120 times per second

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13
Q

diodes opposite one another…

A

work together

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14
Q

full wave rectification advantage

A

exposure time is cut in half

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15
Q

space charge

A

cloud of electrons forming around the filament

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16
Q

space charge effect

A

as more and more electrons build up around the filament they start to repel one another
can limit the mA

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17
Q

space charge compensator

A

automatically lowers the filament current to just the right amount as the kVp is raised

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18
Q

motor

A

device that converts electrical energy to mechanical energy

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19
Q

electric motor

A

uses direct current
electric energy is supplied to current loop
will produce a mechanical motion or rotation of the loop in the magnetic field
converts electrical energy to mechanical energy

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20
Q

Ohm’s law

A

voltage = current * resistance
V=IR
use the triangle

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21
Q

anmeter

A

measures current in amperes

used in series circuit

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22
Q

voltmeter

A

measures potential difference in volts

used in parallel circuit

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23
Q

power

A 
P=IV
power = current * voltage 
measured in watts
P=I^2R
P=V^2/R
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24
Q

self induction

A

when you change the current in a coil of wire the magnetic field it produces will change
this will change the magnetic flux and produce a voltage across the coil
used in autotransformer

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25
Q

mutual induction

A

2 coils placed in proximity and a varying current of the 1st coil induces a similar flow in the second
in step up and step down transformer in high voltage section

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26
Q

Alternating current motor

A

incoming current switches direction

uses slip rings

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27
Q

2 major types of AC motors

A
  1. synchronous

2. induction

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28
Q

Rotor

A

bars of copper around an iron core
moves
on the inside

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29
Q

stator

A

electromagnets arranged around the motor
stays stationary
on the outside

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30
Q

induction motor

A

utilize a rotor coil with exterior magnetic field producing a strong magnetic field
increases power of the motor and permits it to run at any desired speed
produced by induction

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31
Q

T or F inducing an EMF allows rotor to spin

A

True

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32
Q

turns ratio

A

the # of turns/coils in the secondary to the number of turns/coils in the primary
Ns/Np

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33
Q

transformer law

A

the change is directly proportional to the ratio of # of turns of secondary coil to the number of turns in primary coil
twice the amount of coils twice the amount of energy
Vs/Vp = Ns/Np

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34
Q

step up transformer

A

more coils
in high voltage transformer
more coils in the secondary coil than in the primary coil

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35
Q

step down transformer

A

if voltage is less in the secondary coil than in the primary coil
in the filament transformer

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36
Q

voltage vs. current in step up and step down transformers

A

voltage goes up amperage goes down

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37
Q

transformer law for current

A

Is/Ip = Vp/Vs

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38
Q

losses in power are caused by 3 things

A
  1. copper losses
  2. hysteresis
  3. eddy currents
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39
Q
  1. copper losses
A

loss of electrical power due to the resistance of the coils

can be reduced by using a copper wire of adequate diameter

40
Q
  1. hysteresis
A

magnetic fields rearranging themselves produce heat in core of transformer wasting electrical power
loss of heat due to rearranging of magnetic fields
corrected by laminating the core

41
Q
  1. eddy currents
A

alternating magnetic flux in transformer core induces electrical eddy currents (swirling currents)
produce heat in the core wasting electric power

42
Q

4 types of transformers

A
  1. air core
  2. open core
  3. closed core
  4. shell type
43
Q
  1. air core
A

two coils side by side

44
Q
  1. open core
A

2 coils side by side with iron core inserted into coil
iron core intensifies the magnetic flux
leakage flux

45
Q
  1. closed core (donut)
A

coils wound around a square or circular iron ring

continuous path for magnetic flux so only small amount of magnetic energy is lost to leakage

46
Q
  1. shell type
A

most advanced
laminated core
highly insulated
higher efficiency

47
Q

minimum response time

A

the length of time necessary for the AEC to respond to the radiation and the generator to terminate the exposure

48
Q

exposure switch

A

remote control switch that permits current to flow in the circuit

49
Q

filament circuit

A

modifies incoming line power to produce thermeonic emissions from filament of x ray tube

50
Q

advantages of 3 phase equipment

A

most efficient method of xray production

higher x ray quantity and quality

51
Q

disadvantage of 3 phase equipment

A

initial cost is the main disadvantage

52
Q

amps needed for heating of the filament

A

3-6 amps

53
Q

volts needed for heating of the filament

A

4-12 volts

54
Q

what comprises the high voltage generator

A

step up transformer
step down transformer
diodes

55
Q

voltage ripple

A

how much the voltage drops in between each crest

the smaller the ripple the more efficient/powerful

56
Q

single phase voltage ripple

A

voltage ranges from 0 to the maximum value so it has a 100% voltage ripple

57
Q

half wave voltage ripple

A

100%

58
Q

full wave voltage ripple

A

100%

59
Q

3 phase 6 pulse voltage ripple

A

13%

60
Q

3 phase 12 pulse voltage ripple

A

4%

61
Q

high frequency voltage ripple

A

less than 1%

62
Q

capacitor

A

a device capable of accumulating and storing an electrical charge
stores energy
2 insulated metal plates with opposite charges

63
Q

current

A

The quantity or number of electrons flowing
Amount of electrons burning off= current or amperage
Unit is the ampere
Symbol is I
Coulombs per kilogram

64
Q

voltage

A

Joule per coulomb
Amount of energy per unit of charge
10 volts = 10000 kV

65
Q

resistance

A

opposition to the flow of current/electrons

66
Q

Generator

A

converts mechanical energy to electrical energy by electromagnetic induction

67
Q

2 components needed in a generator

A
  1. electromagnet

2. armature/conductor

68
Q

AC generator

A

uses slip rings
need alternating current to do mutual induction
single coil
flows positive to negative

69
Q

DC generator

A

adds a comutator ring to replace slip rings.

only flows in positive direction

70
Q

Multiple coil DC generators

A

more coils you have the more efficient your machinery will be/more energy you’ll have

71
Q

Basic x ray circuit is divided into

A
  1. main circuit - produces x ray

2. filament circuit - creates themionically emitted electron cloud

72
Q

most x ray equipment operates on

A

240 V or 220 V

73
Q

line compensator

A

compensates for the fluctuation in voltage

located on the primary side of the autotransformer

74
Q

falling load generator

A

the exposure begins at a maximum mA which drops as the anode heats
will give you a minimum exposure time
very high mA short exposure time

75
Q

thermionic emission

A

as current increases filament becomes hotter and more electrons are released
boiling off of electrons

76
Q

backup time

A

the maximum length of time the x ray exposure will continue when using an AEC system
may be set or controlled automatically
acts as a safety mechanism
protects the patient from unnecessary exposure

77
Q

Automatic exposure control (AEC)

A

measures the quantity of radiation reaching the IR
used to eliminate the need for the RT to set an exposure time
saves time, avoids repeats

78
Q

2 types of AEC systems

A
  1. photomultiplier tubes (not common)

2. ionization chambers (more popular)

79
Q
  1. photomultiplier tubes
A

1st generation of AEC’s
converts visible light energy into electrical energy
exit type device since detectors are behind the cassette
radiation mush exit casette before its measured by detectors
under the IR

80
Q
  1. Ionization chamber
A

flat parallel plate is placed between the patient and the IR
entrance type device because detector are in front of the cassette
radiation interacts with detectors before the IR
is radioluscent so it doesn’t interfere with the image

81
Q

what is the most critical element in using AEC

A

Exact positioning

need to position properly over AEC cells

82
Q

operating console

A

RT’s can control the kVp, mA, and exposure time, exposure switch, line compensation

83
Q

5 types of timers

A
  1. mechanical
  2. synchronous
  3. electronic
  4. mAs
  5. automatic exposure control
84
Q
  1. mechanical timer
A

no longer used

preset exposure time dialed by turning a knob that winds a spring

85
Q
  1. synchronous timer
A

designed to drive a shaft at precisely 60 revolutions per second
requires too much time and needs to be re set after each exposure

86
Q
  1. electronic timer
A

most sophisticated, accurate and complicated
can select from a wide range of timing intervals
for rapid exposures

87
Q
  1. mAs timer
A

monitors product of mA and time

provides highest safe tube current for shortest exposure

88
Q
  1. Automatic exposure control
A

measures the quantity of radiation reaching the IR

eliminates the need to set an exposure time

89
Q

spinning top test

A

for single phase generators

used to test the timer

90
Q

synchronized spinning top test

A

used for 3 phase or high frequency

91
Q

transformers only operate on

A

alternating current

92
Q

primary current is measured in

A

amps

93
Q

secondary current is measured in

A

miliamps

94
Q

rheostat

A

Responsible for varying current

Same thing as a variable resistor

95
Q

Turns ratio

A

Vs/Vp=Ns/Np=Ip/Is

Radiologic Physics (3 decks)

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