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RT: 34 > Circuitry > Flashcards

Circuitry Flashcards

1
Q

What are the 3 main parts of the x-ray imaging system

A
  1. Operating console
  2. High Voltage generator
  3. X-ray Tube
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2
Q

Where is the ____ located at:

  1. Operating console
  2. High voltage generator
A
  1. Inside the room but outside the radiation area

2. Adjacent to the x-ray tube in a cabinet or closet

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3
Q

What is the function that all diagnostic x-ray imaging systems perform?

A

Provide ionizing radiation for medical imaging

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4
Q

Most imaging systems operate at ____ kVp and ____ mA?

A
  1. 25-150 kVp

2. 100-1200 mA

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5
Q

What is between the operator and the radiation area?

A

Leaded wall equipped with leaded glass

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6
Q

The operating console provides control for:

A
  • is a Low voltage circuit*
    1. Line compensation
    2. kVp
    3. mA
    4. Exposure time
    5. AEC controls
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7
Q

All of the circuits withing the console are ______ to protect us from electric shock

A

Low voltage

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8
Q

What are 3 functional parts of the x-ray circuit

A
  1. Primary Circuit
  2. Secondary Circuit
  3. Filament Circuit
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9
Q

Describe the primary circuit

A
  1. Consists of:
    - Console panel
    - Auto transformer
    - kVp selector
    * * It is low voltage circuit*
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10
Q

Describe what the secondary circuit houses (5)

and what side of the tube does it enter

A 
= High voltage circuit
Houses:
1. Step up transformer
2.Rectifier 
3.mA meter
4.Ground
5.Focal spot selector ( it only houses, Function is part of the filament circuit)

It Enters anode side of tube

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11
Q

Describe what the filament circuit consists of

  • What is its function:
A
  1. mA selector
  2. Focal spot selector
  3. Step down transformer
  4. Resistors

Function:

  • Controls current
  • Controls temp to filament
  • determines level of thermionic emission
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12
Q

Define line compensator

A

Measures and adjust the voltage to 220 V

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13
Q

Supplied voltage from the power company can vary by ____ %, Which is why line compensatory measure and regulate voltage

A

5%

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14
Q

If the power supply from the wall can vary up to 5%, what are the repercussions of the variance?

A

Beam intensity will vary by 5% which can affect the image quality leading to repeats.

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15
Q

220 V are supplied from the wall but ____ is needed when we create x-ray

A

kilo volts (kV)

  • So the power supply (V) must go through the auto-transformer to convert V into kV
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16
Q

Describe autotransformers

A
  • Consists of a single winding and single core
  • Operates on self induction
  • Supplies regulated voltage to : Filament circuit & High voltage circuit
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17
Q

The power supplied to the x-ray imaging system is delivered first to the ____

A

Auto transformer

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18
Q

Auto transformers are designed to “step up” the voltage approx. ____ the input voltage

A

2x’s

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19
Q

Primary voltage comes from ____

A

Input voltage from the wall

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20
Q

secondary voltage comes from?

A

Output voltage from the auto transformer

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21
Q

Describe the primary side of the main x-ray circuit

A
  • Located on the console panel
  • Consists of:
  • *preselected kVp meter
  • *auto transformer
  • *Line compensator
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22
Q

_____ on the primary side of the main x-ray circuit , “reads the output voltage”

-Why does the meter scale register in kV

A

kVp meter

– Measure in kV because it is programmed with the turn ratios across the auto transformer

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23
Q

What are the 3 types of timer selectors (circuits)

A
  1. Electronic timer:
    (most common & accurate to 1 ms)
  2. mAs timer:
    (Located on secondary side to monitor tube current)
  3. AEC timer:
    ( it is time dependant on proper amt. of radiation hitting the chambers
    - It is back up electronic timer)
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24
Q

What is the function of the mAs timer

A

made to operate highest tube current for short exposure

25
Q

The number of electrons emitted by the filament is determined by the ___ ??
It is controlled by the -?

A

1.temperature of the filament

(thermionic emission)

  1. Controlled by current (Amperes)
    ( current increases , then temp increases which results in more “boiling off of electrons)
26
Q

Define thermionic emission

A

emission of electrons from a heated surface

27
Q

What stops exposure in

  1. X-ray
  2. Fluor
A
  1. Radiographer starts & the Console stops

2. Radiographer starts and stops the exposure in fluoro

28
Q

What is the exposure back up set at?

A

max. mAs = 600 mAs

or 6s ( whichever comes first)

29
Q

What does the filament circuit control

A

Controls:

  • Current (A)
  • # of electrons emitted by filament
  • these circuits normally bump up amps
30
Q

filament circuit bumps up amps to ___- ___ A.

How ?

A
  1. 3-6 Amps

2. It is done by step down transformer which decreases volts and therefore increases amps

31
Q

What type of “step” transformer is the filament transformer

  • What is its purpose
  • and voltage it supplies
A

Step down transformer
= provides current to the heat filament
= Decreases Voltage to 12 V, increases A

32
Q

Describe the voltage path from the auto transformer to the filament circuit

A

Voltage is supplied to the mA selector from the secondary connections of the auto transformer

  • Then the voltage travels to the filament switch
  • Then to the filament transformer ( this is where the voltage is decreased to 12 v)
33
Q

The filament circuit enters which side of the x-ray tube

A

cathode side

34
Q

Which circuit is :

  1. Low voltage
  2. High voltage
A
  1. Primary circuit ( operating console)

2. Secondary circuit
High voltage generator

35
Q

____ of the x-ray imaging system is responsible for increasing the output voltage from the auto transformer to the kV necessary for x-ray production

A

High voltage generator

36
Q

In which part of the circuitry is the focal spot selector located in

A

Located in the high voltage side ( secondary circuit) but is part of the filament circuit

37
Q

The high voltage generator consists of 3 parts:

A
  1. High voltage transformer
  2. Filament transformer
  3. Rectifiers
38
Q

In regards to Filament components:

The primary circuit houses the : ___
&

The secondary circuit houses the: ___

A
  1. mA selector

2. Focal spot selector
3.Step down transformer
slide 41

39
Q

Why is the filament circuit separate from the primary and secondary circuits?

A

Because it’s components lie in both primary and secondary circuits

40
Q

Which circuit is a “step up transformer” and why?

A

Secondary circuit is a “step Up transformer” because it converts the voltage received from the auto transformer into kV

41
Q

____ is the process of converting AC to DC.

Why is it needed

A

= Rectification

  • needed to ensure electrons travel one way once they reach they reach the x-ray tube ( From cathode to anode)
42
Q

Describe the difference between old rectifiers and new ones

A

Old rectifiers were vacuum tubes called “Valve tubes”

Current rectifiers = solid state diodes made of silicon

43
Q

____ conduct electricity in one direction

A

Rectifiers

44
Q

___ is an electronic device that contains 2 electrodes

A

Diodes

  • arrowhead of the diode symbol indicates the direction of the current ( opposite of electron flow)
45
Q

What does the filament circuit consists of?

A
  • mA selector
  • Focal spot selector
  • Step down filament transformer
46
Q

Describe un-rectified voltage

A

Located on the secondary side of high voltage step up transformer

-Wave form looks the same as the primary side except that the amplitude is larger

47
Q

Describe half wave rectification

A

=Voltage can not swing negatively during the negative half of the cycle ( bottom part of wave)
Therefore:

  • only 1/2 the supply power is used
  • Takes twice the exposure time
  • Consists of 0,1 or 2 diodes
  • X-ray pulse 60 times/s
48
Q

Describe full wave rectification

A
  • Entire AC wave is rectified
  • Contains at least 4 diodes
  • Exposure time is cut in half
  • X-ray pulse 120/s
49
Q

Which generator do we use today to produces a nearly constant potential voltage waveform, improving image quality at lower dose

A

High frequency generators

50
Q

Name advantages of the high frequency generator

A

-Smaller than single phase & three phase

  • less costly
  • More efficient
51
Q

High frequency generators are used in which exams:

A
  1. Mammograhy
  2. Portable units
  3. CT
52
Q

____ is the measure of variation in voltage waveform

A

Voltage ripple

53
Q

What is the voltage ripple for:

  1. Single phase waveform:
  2. 3 phase, 6 pulse wave form
  3. 3 phase, 12 pulse waveform:
  4. High frequency generator:
A
  1. 100%
    - This is because voltage varies from 0 to its max value
  2. 14%
    - Voltage never falls below 0.

3.4%
4. 1%
= constant exposure

54
Q

less voltage ripple results in ___?

A

increase x-ray quantity & Quality

55
Q

Which generator is used in portable x-ray machines

A

High frequency because them are much more compact and less costly.

56
Q

We use ____ rectification with _____ generation in almost all stationary x-ray imaging systems today

A
  1. Full wave rectification
  2. High frequency voltage generator

= Ensures integrity of power is constant

57
Q

What is the purpose of a capacitor

A

stores high voltage then discharges

1 kV/mAs during exposure

58
Q

During exposure the capacitor discharge generator discharges ____ during exposure

A

1 kV/mAs

59
Q

The secondary circuit enters the _____ side of the tube

A

Anode

RT: 34 (8 decks)

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