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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
mutual induction
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
26
Alternating current motor
incoming current switches direction | uses slip rings
27
2 major types of AC motors
1. synchronous | 2. induction
28
Rotor
bars of copper around an iron core moves on the inside
29
stator
electromagnets arranged around the motor stays stationary on the outside
30
induction motor
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
31
T or F inducing an EMF allows rotor to spin
True
32
turns ratio
the # of turns/coils in the secondary to the number of turns/coils in the primary Ns/Np
33
transformer law
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
34
step up transformer
more coils in high voltage transformer more coils in the secondary coil than in the primary coil
35
step down transformer
if voltage is less in the secondary coil than in the primary coil in the filament transformer
36
voltage vs. current in step up and step down transformers
voltage goes up amperage goes down
37
transformer law for current
Is/Ip = Vp/Vs
38
losses in power are caused by 3 things
1. copper losses 2. hysteresis 3. eddy currents
39
1. copper losses
loss of electrical power due to the resistance of the coils | can be reduced by using a copper wire of adequate diameter
40
2. hysteresis
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
3. eddy currents
alternating magnetic flux in transformer core induces electrical eddy currents (swirling currents) produce heat in the core wasting electric power
42
4 types of transformers
1. air core 2. open core 3. closed core 4. shell type
43
1. air core
two coils side by side
44
2. open core
2 coils side by side with iron core inserted into coil iron core intensifies the magnetic flux leakage flux
45
3. closed core (donut)
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
4. shell type
most advanced laminated core highly insulated higher efficiency
47
minimum response time
the length of time necessary for the AEC to respond to the radiation and the generator to terminate the exposure
48
exposure switch
remote control switch that permits current to flow in the circuit
49
filament circuit
modifies incoming line power to produce thermeonic emissions from filament of x ray tube
50
advantages of 3 phase equipment
most efficient method of xray production | higher x ray quantity and quality
51
disadvantage of 3 phase equipment
initial cost is the main disadvantage
52
amps needed for heating of the filament
3-6 amps
53
volts needed for heating of the filament
4-12 volts
54
what comprises the high voltage generator
step up transformer step down transformer diodes
55
voltage ripple
how much the voltage drops in between each crest | the smaller the ripple the more efficient/powerful
56
single phase voltage ripple
voltage ranges from 0 to the maximum value so it has a 100% voltage ripple
57
half wave voltage ripple
100%
58
full wave voltage ripple
100%
59
3 phase 6 pulse voltage ripple
13%
60
3 phase 12 pulse voltage ripple
4%
61
high frequency voltage ripple
less than 1%
62
capacitor
a device capable of accumulating and storing an electrical charge stores energy 2 insulated metal plates with opposite charges
63
current
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
voltage
Joule per coulomb Amount of energy per unit of charge 10 volts = 10000 kV
65
resistance
opposition to the flow of current/electrons
66
Generator
converts mechanical energy to electrical energy by electromagnetic induction
67
2 components needed in a generator
1. electromagnet | 2. armature/conductor
68
AC generator
uses slip rings need alternating current to do mutual induction single coil flows positive to negative
69
DC generator
adds a comutator ring to replace slip rings. | only flows in positive direction
70
Multiple coil DC generators
more coils you have the more efficient your machinery will be/more energy you'll have
71
Basic x ray circuit is divided into
1. main circuit - produces x ray | 2. filament circuit - creates themionically emitted electron cloud
72
most x ray equipment operates on
240 V or 220 V
73
line compensator
compensates for the fluctuation in voltage | located on the primary side of the autotransformer
74
falling load generator
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
thermionic emission
as current increases filament becomes hotter and more electrons are released boiling off of electrons
76
backup time
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
Automatic exposure control (AEC)
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
2 types of AEC systems
1. photomultiplier tubes (not common) | 2. ionization chambers (more popular)
79
1. photomultiplier tubes
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
2. Ionization chamber
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
what is the most critical element in using AEC
Exact positioning | need to position properly over AEC cells
82
operating console
RT's can control the kVp, mA, and exposure time, exposure switch, line compensation
83
5 types of timers
1. mechanical 2. synchronous 3. electronic 4. mAs 5. automatic exposure control
84
1. mechanical timer
no longer used | preset exposure time dialed by turning a knob that winds a spring
85
2. synchronous timer
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
3. electronic timer
most sophisticated, accurate and complicated can select from a wide range of timing intervals for rapid exposures
87
4. mAs timer
monitors product of mA and time | provides highest safe tube current for shortest exposure
88
5. Automatic exposure control
measures the quantity of radiation reaching the IR | eliminates the need to set an exposure time
89
spinning top test
for single phase generators | used to test the timer
90
synchronized spinning top test
used for 3 phase or high frequency
91
transformers only operate on
alternating current
92
primary current is measured in
amps
93
secondary current is measured in
miliamps
94
rheostat
Responsible for varying current | Same thing as a variable resistor
95
Turns ratio
Vs/Vp=Ns/Np=Ip/Is

Radiologic Physics (3 decks)

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