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Concepts of Image > Chapter 5 > Flashcards

Chapter 5 Flashcards

1
Q

Within a vacuum tube, high energy electrons are converted to

A

X-ray photons

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2
Q

Energy changes in form - kinetic to

A

X-ray

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3
Q

4 Conditions Necessary for the Production of X-rays

A

• A source of electrons that will be converted to x-ray photons.
• Focusing of the electrons to the anode.
• Production of High Speed Electrons. By using the laws of electricity, electrons are put into motion.
• Sudden stopping of the Electrons

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4
Q

Cathode Assembly has what 3 things

A

o Filament
• Focusing cup
• Associated wiring

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5
Q

Cathode Function

A

• Produces a thermionic cloud
• Conducts high voltage to the gap between the cathode and anode
• Focuses the electron stream as it heads towards the anode

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6
Q

Source of ElectronsCathode • FILAMENT

A

current flows through the wire, heating it and causing electrons to “boils off”

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7
Q

Source of Electrons

A

• FILAMENT
• THERMIONIC EMISSION

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8
Q

current flows through the wire, heating it and causing electrons to “boils off”.

A

FILAMENT

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9
Q

Filament is made with

A

Tungsten and Rhenium and molybdenum

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10
Q

Within a vacuum tube, high energy electrons are converted to

A

X-ray photons

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11
Q

created in a vacuum tube

A

X-rays

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12
Q

Energy changes in form - kinetic to

A

X-ray

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13
Q

4 Conditions Necessary for the Production of X-rays

A

• A source of electrons that will be converted to x-ray photons.
• Focusing of the electrons to the anode.
• Production of High Speed Electrons. By using the laws of electricity, electrons are put into motion.
• Sudden stopping of the Electrons

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14
Q

Cathode Assembly

A

o Filament
• Focusing cup
• Associated wiring

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15
Q

Cathode Function
• Produces a

A

thermionic cloud

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16
Q

Cathode Function
• Conducts high voltage to the gap between the

A

cathode and anode

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17
Q

Cathode Function
• Focuses the __ as it heads towards the anode

A

electron stream

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18
Q

Tungsten selected due to:

A

High melting point
• Difficult to vaporize

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19
Q

*Filament length and width impact

A

recorded detail

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20
Q

Focusing Cup is
Composed of
Compresses
And

A

Composed of nickel
• Compresses thermionic cloud
• Grid-biased focusing cup
• Space charge effect
• Saturation current

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21
Q

directs the electrons towards the anode.

A

FOCUSING CUP -

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22
Q

• Regulates the flow of electrons, producing x-ray photons

A

Grid-biased (more negative charge)

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23
Q

• Precise control of thermionic cloud
• Permits very short, rapid sequencing of exposures

A

Grid-biased (more negative charge)

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24
Q

Grid biased is used when

A

• Angiography
• Pulsed fluoroscopy

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25
Q

The electrons will hang around the filament in a __ until they are put in motion or until the filament cools when they will settle back on the wire.

A

“space cloud” or “space charge”

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26
Q

As kVp increases, a greater percentage of the __ are driven toward the anode.

A

thermionically emitted electrons

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27
Q

Because electrons are electrically negative and the cathode becomes strongly negative, the electrons speed away from it. The strong positive attraction of the anode put them in __

A

motion at the speed of light

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28
Q

ANODE - The high speed electrons slam into the anode at the

A

target track.

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29
Q

It is at this point that x-rays are created. When the electrons interact with the__ material a transfer of energy takes place and the electron __ is converted into __. Electrons are converted into X-ray photons.

A

target

kinetic energy

x-ray energy

30
Q

• Serves as the target surface for high voltage electrons from the filament.

A

Anode Functions

31
Q

Conducts the high voltage from the cathode back into the x-ray generator circuitry.

A

Anode

32
Q

Serves as the primary thermal conductor.

A

Anode

33
Q

Anode
assembly consists
a specific area where the electrons hit The angle (and the size of the filament) will

A

• assembly consists of anode, stator and rotor
• Anodes can be rotating or stationary.
• Regardless of the type, each have a target track - a specific area where the electrons hit
• They may have different angles.
• The angle (and the size of the filament) will control the detail that is created on the x-ray.

34
Q

Material used for Rotating Anode

A

Molybdenum with tungsten target tract.

35
Q

For a Rotating Anode the material used is Molybdenum with tungsten target tract. These two materials are used because:

A

High atomic number
•High melting point
• Greater conductivity of heat

36
Q

Stationary Anode

A

• Static target area
• Smaller target area
• Low power, used mainly in dental units

37
Q

Anode Heat Loading
• Rotating anode

A

Revolutions per minute (rpm)
• Diameter of disk

38
Q

ANODE ANGLES

A

• Most common 12 degrees
• Diagnostic 7 - 17 degrees

39
Q

Anode Angles give a FS size of 0.1mm to 3.0mm
• The smaller the FS size, the greater the

A

image detail

40
Q

The smaller the tube angle….

A

the smaller the FS size
• the more detailed the resultant image

41
Q

The Larger the FS size

A

• the greater the heat capacity.
• the greater thermal conductivity
•which lessens the chance of tube damage
• the lesser the capability of demonstrating image detail.

42
Q

used to reduce the effective area
of the actual focal spot because of the anode angle.

A

Line Focus Principle-

43
Q

Effective focal spot (projected area of x-ray beam) Controlled by:

A
  • Actual focal spot (physical portion of focal track being hit by electrons)
    -Target angle
44
Q

Anode Heel Effect
• Radiation intensity is greater on the __ side of the x-ray beam, due to the geometry of the anode.

A

cathode

45
Q

Due to the anode heel effect, the __ portion of the body should be placed at the cathode

A

thicker

46
Q

X-RAYS are emitted

A

isotropically

47
Q

ANODE HEEL EFFECT
• Less radiation intensity on the __ side of the x-ray beam.

A

anode

48
Q

PREVENT TUBE DAMAGE

A

Warm-up Anode
• Test exposures to heat anode
• Refer to Rating Charts and Cooling Curves
• Protective Housing

49
Q

Warm-Up Procedure is to prevent

A

Gradually warms anode
• Prevents cracking
• Helps maintain vacuum
• Stress relieved anode-feature that allows efficient heat dissipation and doesn’t require an elaborate warmup procedure

50
Q
  • produce magnetic field
A

Stator

51
Q

Stator- produce magnetic field
Located
Bank of
Failure Results in

A

• Located outside envelope
• Bank of electromagnets
• Stator failure
• Results in suboptimum anode rotation speed

52
Q

Anode cooling is

A

rapid at first then gradually slows

53
Q

Anode cooling Most integrated into

A

generator software controls

54
Q

Tube rating charts
• Designed to

A

protect
X-ray tube and lengthen tube life

55
Q

Tube rating charts Any combo of kVp and mAs __ are safe for the x-ray tube

A

at or under the red curve

56
Q

Collimator
• Lead strips used to

A

restrict the primary beam (exit)

57
Q

Off-Focus Radiation is Undesirable part of the beam; because

A

photons not produced at the focal spot

58
Q

Contributes up to 25 percent of total primary beam

A

Off focus radiation

59
Q

Produces “ghosting” of image and reduces image quality

A

Off focus radiation

60
Q

Can change histogram during post processing in digital radiography

A

Off focus radiation

61
Q

Protective Housing
• Controls

A

leakage and scatter radiation

62
Q

• Additional lead at cathode end because of

A

direction of photons

63
Q

photons that escape from the protective housing except at the port.

A

Leakage radiation-

64
Q

Provides means to cool tube

A

-Contains dielectric oil which insulates and absorbs heat
-Small air fan

65
Q

maintains the vacuum between the cathode and anode

A

Glass Envelope-

66
Q

The glass envelope is made of

A

Made of (pyrex) glass or metal (eliminates the occurrence of tungsten vaporization)

67
Q

The glass envelopes contains

A

Contains the cathode and anode assemblies except the stator

68
Q

Copper cylinder connected to anode disk by

A

molybdenum stem

69
Q

Rotator Turns when

A

stator is energized

70
Q

• Bearing failure due to

A

excessive heat, lubricant break down & friction

Concepts of Image (4 decks)

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