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RT 209 > 6. X-ray Circuit > Flashcards

6. X-ray Circuit Flashcards

1
Q

Primary Circuit

A

Main power switch, circuit breakers, the autotransformer, the timer circuit, primary side of the step-up transformer

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2
Q

Secondary Circuit

A

Secondary side of the step-up transformer, the milliampere meter, a rectifier bank, and the x-ray tube (except for the filaments)

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3
Q

Filament Circuit

A

Rheostat, step-down transformer, the filaments

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4
Q

incorporates a meter to measure the voltage provided to the x-ray machine and a control to adjust that voltage to precisely 220 volts

A

Line Compensator

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5
Q

included in the primary circuit to protect against short circuits and electric shock

A

Circuit Breakers

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6
Q

is an adjustable transformer controlled by the kVp selector on the operating console

A

Autotransformer

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7
Q

operators in the principle of self-induction

A

Autotransformer

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8
Q

Autotransformer sometimes called the

A

kVp selector

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9
Q

primary purpose is to provide a voltage that will be increased by the step-up transformer to produce the kilovoltage selected at the operating console

A

Autotransformer

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10
Q

the radiographer controls the ______ through the kVp selector on the operating console, and through this directly determines the voltage applied to the x-ray tube to produce x-rays

A

Autotransformer

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11
Q

when a radiographer selects a kVp setting, he or she determines the number of turns on the _______ to be included in the circuit element and with it the output voltage

A

secondary side

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12
Q

used to increase the voltage from the autotransformer to the kilovoltage necessary for x-ray production

A

Step-up Transformer

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13
Q

not adjustable and increases the voltage from the autotransformer by a fixed amount

A

Step-up Transformer

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14
Q

consists of mechanical and electronic devices whose action is to “make” and “break” the high voltage across the x-ray tube

A

Timer Circuit

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15
Q

cause the x-ray to emit x-rays for a specific time as determined by the radiographer or by AEC

A

Exposure Timers

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16
Q

controls the length of exposure

A

Exposure Timers

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17
Q

simple devices use in some portable and dental units

A

Mechanical Timers

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18
Q

operates by clockwork

A

Mechanical Timers

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19
Q

inexpensive but not very accurate

A

Mechanical Timers

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20
Q

exposure times greater than 250 ms

A

Mechanical Timers

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21
Q

minimum exposure time possible 1/60 second (17 ms)

A

Synchronous Timers

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22
Q

most sophisticated, most complicated, most accurate

A

Electronic Timers

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23
Q

used for rapid serial exposures

A

Electronic Timers

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24
Q

exposure time as small as 1 ms

A

Electronic Timers

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25
wide range of time intervals
Electronic Timers
26
based on the time it takes to charge a capacitor through a variable resistor
Electronic Timers
27
designed for accurate control of tube current and exposure time
mAs Timers
28
terminated the exposure once desired mAs is attained
mAs Timers
29
located in the secondary circuit
mAs Timers
30
automatically terminates the exposure when sufficient radiation to provide the required optical density has reached the image receptor
Automatic Exposure Control
31
method used to check the accuracy of exposure timer
Spinning Top Test
32
is a device placed in the secondary circuit that monitors x-ray tube current
mA meter
33
____ rectifiers are commonly used
solid-state
34
is responsible for converting the low voltage from the electric power company into a kilovoltage of proper waveform
High-Voltage Generator
35
High-voltage generator contains the following three primary parts:
* High-voltage transformer * Filament transformer * Rectifiers
36
is a step-up transformer
High Voltage-transformer
37
The secondary voltage is greater than the primary voltage because the number of secondary windings is greater than the number of primary windings
High Voltage-transformer
38
the ratio of the number of secondary windings to the number of primary windings
Turns Ratio
39
is the process of converting alternating voltage to direct voltage and therefor alternating current to direct current
Rectification
40
property of an x-ray tube which means that it acts as a valve permitting the flow of current in only one direction, from the cathode to the anode
Self-rectification
41
represents condition in which the voltage is not allowed to swing negatively during the negative half of its cycle
Half-wave rectification
42
contain zero, one, or two diode
Half-wave rectification
43
x-ray output is pulsating, with 60 x-ray pulses per second
Half-wave rectification
44
in a full-wave rectified circuit the negative half cycle corresponding to the inverse voltage is reversed so that a positive voltage is always directed across the x-ray tube
Full-wave rectification
45
contains at least 4 diodes
Full-wave rectification
46
x-ray output – 120 x-ray pulses per second
Full-wave rectification
47
results in pulsating x-ray beam
Single-Phase Power
48
alternate swing from zero to maximum potential 120 times per second
Single-Phase Power
49
low energy, low penetrability, low diagnostic value
Single-Phase Power
50
generated three simultaneous voltage waveforms out of step with one another
Three-Phase Power
51
voltage across x-ray tube is nearly constant and never drops to zero during exposure
Three-Phase Power
52
requires additional size and cost
Three-Phase Power
53
can be place in the x-ray tube housing
High-Frequency Generator
54
produce nearly constant potential
High-Frequency Generator
55
improves image quality
High-Frequency Generator
56
lower patient dose
High-Frequency Generator
57
are high-speed switches, or choppers, that convert DC into a series of square pulses
Inverter Circuits
58
used by a high-frequency voltage generation
Inverter Circuits
59
Capacitor Discharge Generator uses ____ battery
nickel-cadmium (NiCd)
60
during capacitor discharge, the voltage falls approximately
1 kV/mAs
61
delivers the maximum possible mA for the selected kVp by considering the instantaneous heat load characteristics of the x-ray tube
Falling-load capability
62
This delivers the desired amount of radiation to the image receptor in the shortest possible exposure time
Falling-load capability
63
works on the principle that a small current is drawn from the mains to charge a capacitor before the x-ray exposure, and this capacitor is allowed to discharge through the x-ray tube during exposure
capacitor discharge mobile
64
is the variation in peak voltage waveform
Voltage Ripple
65
100% voltage ripple
Single-phase Generator
66
the voltage varies from zero to its maximum value
Single-phase Generator
67
3-phased, 6 pulse generator = ___ voltage ripple
13%
68
3-phased, 12-pulse generator= ___ voltage ripple
4%
69
High-Frequency Generator less than ___ voltage ripple
3%
70
POWER RATING
``` Power = current x potential Watts = amperes x volts ```
71
when specifying high-voltage generators, the industry standard is to use the maximum tube current (mA) possible at 100 kVp for an exposure of 100 ms
Maximum Available Power
72
a variable resistor controlled by the mA selector on the operating console
Rheostat
73
when the radiographer adjusts milliamperage on the operating console, he or she is adjusting the _____ and ultimately the amount of current applied to the filament (filament current) in the x-ray tube
rheostat
74
the higher milliamperage station number, the _____ resistance
lower
75
the goal of the filament circuit is to literally boil electrons out of the filament wire
Filament Circuit
76
normally, a rather large filament current of _____ is required to produce a tube current in the range of milliamperes
5 to 7 amperes
77
controls filament temperature
rheostat
78
used in filament circuit to increase the current by reducing the voltage that is applied to the filament
Step-down Transformer
79
the purpose is to control the degree and duration that the filament is heated, which in turn controls the number of electrons boiled off that will ultimately become the tube current
Filament Circuit
80
represented on the operating console by the “large focal spot” and “small focal spot”
Filaments
81
PRINCIPLES OF CIRCUIT OPERATION
* The kVp selected adjusts the autotransformer and determines the number of turns on the secondary side necessary to produce a voltage, through self-induction, that will be sent to the step-up transformer * The step-up transformer increases this voltage by a fixed amount and, through mutual induction, produces the kilovoltage selected on the operating console * This kilovoltage must be rectified * The filament circuit draws electricity from the autotransformer, which then travels to the rheostat * The selected mA station sets the resistance in the filament circuit * From the rheostat, electricity travels to the step-down transformer * The kilovoltage applied to the x-ray tube creates a large positive charge on the anode and a large negative charge in the cathode
82
Allows radiographer to control the x-ray tube current and voltage so that the useful x-ray beam is of proper quality and quantity
Operating Console/Control Panel
83
refers to the number of x-rays or intensity of the beam usually expressed in mR or mR per mAs
Quantity
84
refers to the penetrating qualities of the x-ray beam an is expressed by kVp or HVL
Quality
85
FACTORS THAT AFFECT X-RAY QUANTITY
* mAs * kVp * Distance * Filtration
86
FACTORS THAT AFFECT X-RAY QUALITY
* kVp | * Filtration
87
Some Basic Controls for Every Panel
* On/off switch * mAs selection * kVp selection * Table or wall unit activation * Exposure switch * mAs and kVp meters
88
EXTENDING TUBE LIFE
* X-ray tube life may be extended by using minimum radiographic factors of ma, kVp, and exposure time appropriate for each examination * Use of faster image receptors * Excessive heat results in reduced x-ray tube life
89
WARM UP PROCEDURES
* Prepares the x-ray tube to receive high heat load * An example of a warm-up technique is an initial exposure of 50 kVp, 100 mA, at 1/30 second followed by a second exposure in which the mA is raised to 200
90
OTHERS WAYS OF EXTENDING TUBE LIFE
* Minimize filament boost (preparation) time * Limit rotor/start/stop operations * Use lower tube current (mA) * Do not make a high mA exposure on a cold tube * Adhere to rating charts and anode heating and cooling curves * Limit operations to 80% of maximum single exposure ratings * Do not exceed the anode thermal capacity or dissipation rate of the target * Do not rotate the tube housing rapidly from one position to another * Avoid long intervals between spot-films
91
X-RAY TUBE AGING
1. Deposition of Filament Tungsten 2. Produces Gas (Gassy Tube) 3. Punctured Tube 4. Careless 5. Damages to Anode 6. Damages to Rotor and Bearings 7. Damages to Filament 8. Damages to Tube Housing 9. Damages to Stator

RT 209 (11 decks)

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