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IMAG 311- Med Img Fundmts & Physics > Ch. 8 and 17 > Flashcards

Ch. 8 and 17 Flashcards

1
Q

What are the three main parts of the x-ray unit?

A
  • The tube
  • The operating console
  • The high-voltage genertor
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2
Q

Operating Console

A

Allows you to control x-ray tube current and voltage

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3
Q

The Quantity of beam is controlled by what?

A

mAs (current)

-refers to the number of x-rays

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4
Q

The Quality of the beam is controlled by what?

A

kVp (voltage)

-refers to the penetrability of the beam

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5
Q

Quality refers to what regarding x-ray/

A

The penetration

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6
Q

Why is compensation needed?

A

Needed to keep voltage from fluctuating

-Any fluctuation in voltage will affect the x-ray tube function

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7
Q

Properties of a Transformer

A
  • Used to vary voltage of AC electricity
  • Uses two coils, one primary and one secondary
  • operates by electromagnetic induction
  • Current applied to primary circuit induces current in the secondary circuit
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8
Q

What is the main function of a transformer?

A

To vary voltage (kVp) or keV

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9
Q

Autotransformer

A

Provides x-ray machines high-voltage circuit w. precise/constant voltage

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10
Q

Autotransformers can be 2 kinds of transformers…what are they?

A

-Step-up or Step-down

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11
Q

What is a step-up transformer

A
  • When the voltage increases in the secondary coil decreases the current
  • Turns ratio is greater than 1
  • less coils in primary, more coils in secondary
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12
Q

What is a step-down transformer?

A
  • When the voltage decreases in the secondary coil, and the current increases (Amperage)
  • Turns ratio is less than 1
  • More coils in primary, less coils in secondary
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13
Q

Important aspects of Autotransformers (3)

A
  • They can increase or decrease voltages in the low voltage range
  • have a single winding core and can connect to primary or secondary
  • Are capable of doubling the voltage
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14
Q

More turns in the secondary results in what?

A

Results in the Autotransformer functioning as a step-up transformer, which increases voltage

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15
Q

One the Autotransformer adjusts voltage, what does the step-up transformer do?

A

It increases the voltage to kilovaults (kV)

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16
Q

High voltages are applied between what?

A

Between the cathode (filament) and the anode (target)

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17
Q

What voltage is typically used in radiography equipment?

A

220 V

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18
Q

What are the operations of the Autotransformer?

A
  • Works on the principles of electromagnetic induction (self induction)
  • Has one winding and one core
  • can either increase or decrease the voltage to the x-ray machines high-voltage transformer
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19
Q

What are the components of a High-voltage Generator?

A
  • High-voltage transformer (step-up)
  • Filament transformer (step down)
  • Rectifiers
  • *All parts are immersed in oil as an electrical insulator
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20
Q

What does the primary connector on winding do for a Autotransformer and where is it located?

A

-They are located along its length and conduct the input power to the autotransformer

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21
Q

What do the secondary connectors on winding do for an Autotransformer and where are they located?

A

-They are located throughout the winding and conduct the output power form the autotransformer

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22
Q

If an Autotransformer has extra coils, what does it act as, a step-up or step-down transformer?

A

Step-up transformer

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23
Q

What does the primary connector on winding do for an Autotransformer and where is it located?

A

-They are located along its length and conduct the input power to the autotransformer

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24
Q

If an Autotransformer has less coils, what does it act as, a step-up or step-down transformer?

A

Step-down transformer

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25
What is the transformer Law?
Vs / Vp = Ns / Np
26
Rectifiers act like what?
A one way street or a stop sign; used for direct current on the secondary side of the transformer
27
Rectifiers act like what?
A one way street or a stop sign; used for direct current on the secondary side of the transformer -Rectifiers stop currents we don't want or redirect them
28
The High-voltage transformer is what type of a transformer?
A step-up transformer with a turns ratio normally between 500:1 and 1000:1
29
How are voltage and current related?
They are inversely related. so that when one increases the other decreases
30
In a step-up transformer, the secondary voltage is greater or lower than the primary?
GREATER | -Due to the # of secondary windings vs. primary windings
31
Turns ratio
of secondary windings : # of primary windings
32
High-Voltage Transformer operates on what current?
AC, sinusoidal
33
Rectification
The process in which alternating current is redirected to form directing current so that electrons in the x-ray tube can flow in one direction (from the cathode to the anode)
34
Key principle behind the transformer?
-If the secondary coil has more turns (windings) than the primary coil, voltage is increased proportionately in the secondary coil
35
What are the Four Factors of Faraday's Law?
- Strength of magnetic field - Speed of motion between lines of force and conductor - Angle between lines of flux and conductor - Number of turns in conductor
36
Mutual Induction
Has two magnetic fields, varying current supplied to primary coil--induces current in secondary coil
37
Transformer Law (in word form)
Voltage induced in the secondary coil is directly related to the number of turns in the secondary coil
38
How is the current (I) and the # of turns (N) of a coil related?
Current is inversely proportional to the # of turns (N)
39
What is Amplitude?
Amplitude is the difference between primary and secondary waveform
40
How many Vp is equal to 1 kVp?
1,000 Vp
41
What does a kVp minor and major allow for a technologist?
To select the exact kVp to use for an exam
42
What does the Filament Temperature control?
Controls the number of electrons emitted | *Temp. is controlled by the current supplied to the tube
43
As filament temperature increases, what else increases?
The number of electrons emitted increases as well
44
Tube current is controlled by what?
Filament circuit
45
Voltage from Autotransformer is reduced by what?
Precision resistors
46
As voltage decreases the current increases proportionally to what?
The turns ratio (# of secondary windings to primary windings)
47
What type of a transformer is the Filament transformer?
Step-down transformer (voltage decreases and current increases)
48
Single Phase Power results in what?
Results in a pulsing x-ray beam due to AC from zero to peak
49
Half-way rectified wave- Single Phase
- 1 pulse/cycle | - 60 cycles/sec
50
Full-wave rectified wave-Single Phase
-2 pulses/cycle -60 cycles/sec 120 pulses/sec
51
Three-Phase Power
Where three wave forms re generated, out of synch, and prevent kV from reaching 0
52
Full wave rectified-Three Phase
- 6 pulses/cycle - 60 cycles/sec - 360 pulses/sec
53
3 Phase-12 pulse
- 12 pulses/cycle - 60 cycles/sec - 720 pulses/sec
54
4 properties of High Voltage Transformer
- step up transformer - increases V to kV - changes amplitude of the wave - # of turns is larger in secondary connection
55
What is a High voltage generator consist of?
- High voltage transformer (step-up) - Filament transformer (step-down) - Rectifiers *All parts are immersed in oil as an electrical insulator
56
High Voltage Transformer?(3 things)
- Step-up - secondary voltage greater than primary due to the greater # of windings in the secondary - Operates on AC, sinusoidal
57
Line Compensation
Provides 220V for equipment, and prevents variation of incoming Voltage
58
AutoTransformer (2)
Provides exact/constant voltage to equipment, 1 winding and 1 core, * primary connectors- input power * secondary connectors- output power * can increase or decrease voltage
59
kVp Meter
Located within autotransformer, measures Voltage and reads them out as kV
60
mA meter
In tube current, where voltage is 0 (safe place)
61
Tube current is controlled by what circuit?
Filament circuit
62
how many amperes (range) does the filament in the x-ray tube need in order to emitt electrons through a process called thermionic emission?
3-5 amperes | **Best answer is between those two numbers
63
Where is the rectification circuit located?
Between the step-up transformer and the x-ray tube
64
Voltage in the x-ray circuit is adjusted where?
In thee Autotransformer
65
Mechanical Timer
Used in portable units and dental units | -only for times > 250 ms
66
Synchronous Timer
Electric motor, time intervals are mulitples of 60, times > 1/60 s
67
Most accurate timer, times ~ 1 ms, and can be used for rapid exposure
Electronic Timer
68
mAs Timer
Designed for highest mA and lowest sec stting possible
69
AEC Timer
Automatic Exposure Control - Measures the quantity of radiation (mAs) and adjusts the time accordingly to patients' body thickness/thinness -ionization chambers are usd (placed between patient and receptor)
70
What is the electrical device used to adjust the mA station ?
Precision resistor
71
Power rating
Expressed in kW (kilowatts) | Power = Current (mAs) * Potential (kVp)
72
What is the space charge effect?
When most electrons emitted by the cathode are driven back to the cacthode by repulsion of the cloud of electrons in its neighborhood
73
Filtration
Reduces quantity while increasing average quality | -usually placed between the tube and the patient
74
Off Focus Radiation
When x-rays are produced by stray electrons that interact @ positions on the anode other than the focal spot

IMAG 311- Med Img Fundmts & Physics (6 decks)

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