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

Ch. 8 and 17 Flashcards

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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
Q

What is the transformer Law?

A

Vs / Vp = Ns / Np

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26
Q

Rectifiers act like what?

A

A one way street or a stop sign; used for direct current on the secondary side of the transformer

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27
Q

Rectifiers act like what?

A

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

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28
Q

The High-voltage transformer is what type of a transformer?

A

A step-up transformer with a turns ratio normally between 500:1 and 1000:1

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29
Q

How are voltage and current related?

A

They are inversely related. so that when one increases the other decreases

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30
Q

In a step-up transformer, the secondary voltage is greater or lower than the primary?

A

GREATER

-Due to the # of secondary windings vs. primary windings

31
Q

Turns ratio

A

of secondary windings : # of primary windings

32
Q

High-Voltage Transformer operates on what current?

A

AC, sinusoidal

33
Q

Rectification

A

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
Q

Key principle behind the transformer?

A

-If the secondary coil has more turns (windings) than the primary coil, voltage is increased proportionately in the secondary coil

35
Q

What are the Four Factors of Faraday’s Law?

A
  • 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
Q

Mutual Induction

A

Has two magnetic fields, varying current supplied to primary coil–induces current in secondary coil

37
Q

Transformer Law (in word form)

A

Voltage induced in the secondary coil is directly related to the number of turns in the secondary coil

38
Q

How is the current (I) and the # of turns (N) of a coil related?

A

Current is inversely proportional to the # of turns (N)

39
Q

What is Amplitude?

A

Amplitude is the difference between primary and secondary waveform

40
Q

How many Vp is equal to 1 kVp?

A

1,000 Vp

41
Q

What does a kVp minor and major allow for a technologist?

A

To select the exact kVp to use for an exam

42
Q

What does the Filament Temperature control?

A

Controls the number of electrons emitted

*Temp. is controlled by the current supplied to the tube

43
Q

As filament temperature increases, what else increases?

A

The number of electrons emitted increases as well

44
Q

Tube current is controlled by what?

A

Filament circuit

45
Q

Voltage from Autotransformer is reduced by what?

A

Precision resistors

46
Q

As voltage decreases the current increases proportionally to what?

A

The turns ratio (# of secondary windings to primary windings)

47
Q

What type of a transformer is the Filament transformer?

A

Step-down transformer (voltage decreases and current increases)

48
Q

Single Phase Power results in what?

A

Results in a pulsing x-ray beam due to AC from zero to peak

49
Q

Half-way rectified wave- Single Phase

A
  • 1 pulse/cycle

- 60 cycles/sec

50
Q

Full-wave rectified wave-Single Phase

A

-2 pulses/cycle
-60 cycles/sec
120 pulses/sec

51
Q

Three-Phase Power

A

Where three wave forms re generated, out of synch, and prevent kV from reaching 0

52
Q

Full wave rectified-Three Phase

A
  • 6 pulses/cycle
  • 60 cycles/sec
  • 360 pulses/sec
53
Q

3 Phase-12 pulse

A
  • 12 pulses/cycle
  • 60 cycles/sec
  • 720 pulses/sec
54
Q

4 properties of High Voltage Transformer

A
  • step up transformer
  • increases V to kV
  • changes amplitude of the wave
  • # of turns is larger in secondary connection
55
Q

What is a High voltage generator consist of?

A
  • High voltage transformer (step-up)
  • Filament transformer (step-down)
  • Rectifiers

*All parts are immersed in oil as an electrical insulator

56
Q

High Voltage Transformer?(3 things)

A
  • Step-up
  • secondary voltage greater than primary due to the greater # of windings in the secondary
  • Operates on AC, sinusoidal
57
Q

Line Compensation

A

Provides 220V for equipment, and prevents variation of incoming Voltage

58
Q

AutoTransformer (2)

A

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
Q

kVp Meter

A

Located within autotransformer, measures Voltage and reads them out as kV

60
Q

mA meter

A

In tube current, where voltage is 0 (safe place)

61
Q

Tube current is controlled by what circuit?

A

Filament circuit

62
Q

how many amperes (range) does the filament in the x-ray tube need in order to emitt electrons through a process called thermionic emission?

A

3-5 amperes

**Best answer is between those two numbers

63
Q

Where is the rectification circuit located?

A

Between the step-up transformer and the x-ray tube

64
Q

Voltage in the x-ray circuit is adjusted where?

A

In thee Autotransformer

65
Q

Mechanical Timer

A

Used in portable units and dental units

-only for times > 250 ms

66
Q

Synchronous Timer

A

Electric motor, time intervals are mulitples of 60, times > 1/60 s

67
Q

Most accurate timer, times ~ 1 ms, and can be used for rapid exposure

A

Electronic Timer

68
Q

mAs Timer

A

Designed for highest mA and lowest sec stting possible

69
Q

AEC Timer

A

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
Q

What is the electrical device used to adjust the mA station ?

A

Precision resistor

71
Q

Power rating

A

Expressed in kW (kilowatts)

Power = Current (mAs) * Potential (kVp)

72
Q

What is the space charge effect?

A

When most electrons emitted by the cathode are driven back to the cacthode by repulsion of the cloud of electrons in its neighborhood

73
Q

Filtration

A

Reduces quantity while increasing average quality

-usually placed between the tube and the patient

74
Q

Off Focus Radiation

A

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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