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SEM II - Exposure > Fluoroscopy/Heat Units > Flashcards

Fluoroscopy/Heat Units Flashcards

0
Q

Fluoroscopy

A

Real time dynamic imaging produced on a glass plate covered by a layer of phosphor material (emit light when stimulated). Require dark environment to view dim images

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1
Q

Fluoroscopy development

A

Thomas Edison - 1896

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2
Q

Image intensification

A

Few X-ray photons converted to any visible light photons.

- flux gain

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3
Q

Image intensifier

A 
Like an X-ray tube containing:
Glass envelope
Input phosphor
Photocathode
Focusing lense
Anode
Output phosphor
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4
Q

Glass envelope (image intensifier)

A

Maintains the vacuum within

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5
Q

Input phosphor

A

Cesium iodide

  • efficient at converting X-ray energy to visible light
  • needle like crystals
  • X-ray is “coming in” to the fluoroscopy tube
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6
Q

Photocathode

A

Antimony

Light to electron

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7
Q

Focusing lenses

A

Electrostatic - mutual repulsion

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8
Q

Anode

A

Positive charge, attracts electrons (shaped like a donut)

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9
Q

Cathode

A

Negative charge

- emits electrons

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10
Q

Output phosphor

A

Zinc cadmium sulfide

  • efficient at converting electron energy to visible light
  • last stage of the fluoroscopy tube
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11
Q

Conversion of energies across the image intensifier

A

X-ray to light (input phosphor)
Light to electron (photocathode)
Electron to light (output phosphor)
Resulting in 1 X-ray photon amplified to many light photons (the image is intensified)

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12
Q

Flux gain

A

The increase in light photons due to the conversion efficiency of the output phosphor.
Measures the electron to visible light conversion by the zinc cadmium sulfide.

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13
Q

Good news - flux gain

A

One electron will produce dozens of visible light photons

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14
Q

Bad news - flux gain

A

Visible light in the image formation process always results in decreased resolution due to light divergence.

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15
Q

As flux gain increases

A

Visible light image becomes brighter

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16
Q

Mutual repulsion

A

Using something negative to push (repel) something negative away

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17
Q

How many light photons are created by each photoelectron that strikes the output phosphor

A

50-75 (flux gain)

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18
Q

Electrons are accelerated from cathode to anode in the fluoro tube by

A

Kilovoltage (25-30kv)

Higher KV=higher electron energy=light photons

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19
Q

Minification gain

A

The result of many electrons leaving the relatively large input phosphor/photocathode impacting the relatively small output phosphor

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20
Q

Standard input phosphor/photocathode sizes are

A

6, 9, or 12 inches

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21
Q

Standard output phosphor size

A

1 inch

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22
Q

Mini fixation gain formula

A

Minification gain =
input phosphor diameter2/output phosphor diameter2

As minification gain increases the visible image becomes brighter

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23
Q

Total brightness gain

A

He much the image has been intensified by the image intensifier tube (output phosphor intensity measured in candela)

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24
Q

Brightness gain

A

= minification gain x flux gain

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25
Q

ABC

A

Automatic brightness control

- maintains a preset brightness level by automatically adjusting the exposure factors to compensate for varying subject

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26
Q

Fluoro imaging techniques

A

Very low mA (.5-5mA)

Higher KVP utilized

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27
Q

SSD (source to skin distance) in fluoro

A

Must be at least 15 inches for fixed fluoro
- minimize skin exposure/dose

Must be at least 12 inches for mobile fluoro
- c-arms for surgery/mobile have higher patient does

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28
Q

Quantum mottle - fluoroscopy

A

Can be a problem caused by not enough X-rays (mAs); image not fully formed.
Not enough photons hitting the input phosphor
Increasing KVP makes it MUCH worse

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29
Q

Magnification tubes

A

Visible voltage to electrostatic focusing lense
- as voltage increases the electrons are pushed closer to the input phosphor causing the image to be magnified to output phospho

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30
Q

Magnification formula

A

=total input phosphor diameter/diameter of input phosphor used

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31
Q

TV camera

A

Placed adjacent to the output phosphor I order to capture and transmit the output intensified image. Radiologist no longer has to view image directly from phosphor screen or be in the path of the primary beam

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32
Q

Two basic types of cameras in use

A

Vidicon

Plumbicon

33
Q

Vidicon

A

Camera used with general fluoro

34
Q

Plumbicon

A

Camera used with interventional fluoro

35
Q

Splitter

A

Able to split signal from output phosphor to multiple components:

  • monitor
  • video
  • digital video
  • hard film
36
Q

Changes in voltage o the electrostatic focusing lenses causes

A

The electrons to narrow of widen their stream

37
Q

Common field sizes for angio

A

35/25/15 cm

The smaller the mode the more magnified the image
Mag modes increases scatter

38
Q

Common field sizes for general

A

25/17 cm

The smaller the mode the more magnified the image
Mag modes increases scatter

39
Q

Multiple imaging devices on fluoro

A

TV camera, spot films, cine camera, cassette

  • all use the image as displayed on the output phosphor
40
Q

Fluoro patient radiation protection

A

Exposure dose should not exceed 10R/min - typical range is from 1-3R/min

41
Q

5 minute timer

A

Units must alarm at 5 minute intervals to alert radiologist/surgeon

42
Q

Magnification fluoro

A

Causes increased dose.

As you magnify the image, patient does goes up

43
Q

Occupational exposure

A

Fluoro is a techs #1 source of exposure
- scatter from patient

Lead aprons must be worn

44
Q

Lead aprons fluoro

A

At least .5mm lead equivelant

45
Q

Bucky slot cover/lead drapes

A

Must be at least .25mm lead equivelant

46
Q

3 things for X-ray production

A

Source of free electrons

Acceleration of free electrons

Abrupt halting of high speed electrons

47
Q

As high speed electrons are abruptly halted by dense anode target, their kinetic energy converts to:

A

Heat as thermal energy (99%)

Xray as electromagnetic energy (1%)

48
Q

Heat

A

The kinetic energy of molecules (rapid motion = heat)

49
Q

The enemy of electrical components which make them wear out

A

Heat

50
Q

Calorie

A

The unit of heat.

The amount if heat required to raise the temperature of 1 gram of water 1 degree Celsius

51
Q

Heat is transferred by 3 means

A

Conduction

Convection

Radiation

52
Q

Conduction

A

The transfer of heat through a material by touching of ohysical contact of solid objects

53
Q

Convection

A

The transfer of heat by the mixing of molecules in a liquid or gas

54
Q

Radiation

A

The transfer of heat by the emission of infrared radiation

X-ray tubes are cooled primarily by radiation

55
Q

X-ray tubes are cooled primarily by

A

Radiation

56
Q

Modern X-ray machines are controlled to not allow overheating by

A

Computerized control

57
Q

Older X-ray machines require a

A

Manual heat calculation

58
Q

Heat units are found by the formula

A

KVP x MA x Time x rectification constant

59
Q

Rectification constant

A

Voltage waveform

60
Q

A more efficient voltage waveform produces what

A

More heat

61
Q

Actual focal spot

A

Aka true focal spot

Area that high speed electrons strike the anode

62
Q

Effective focal spot

A

Actual focal spot projected towards patient

63
Q

Line focus principle

A

Effective focal spot will always be smaller than true

64
Q

The modern standard anode angle is

A

12 degrees

65
Q

As focal spot increases

A

Penumbra increases

66
Q

Penumbra

A

Loss of detail

67
Q

Small focal spot

A

Maximum image detail

68
Q

Large focal spot

A

Decreased image detail

69
Q

Focal spots are measured as

A

Effective focal spot

Approximate sizes are .5mm up to 2.0mm

70
Q

Blooming of focal spot

A

Enlargement of the electron stream as it travels from cathode to anode

Due to mutual repulsion of electrons

71
Q

Blooming increases as

A

mAs increases and vice versa

72
Q

Why not always use a small focal spot

A

They correspond to the size of cathode filaments

Small filaments are mA limited

Sometimes we need a higher mA station

73
Q

Tests to determine focal spot size

A

Line pair resolution

Star pattern test

Pinhole camera test

74
Q

Effective focal spots up to .8mm

A

+/- 50%

75
Q

Effective focal spots between .8 - .15mm

A

+/- 40%

76
Q

Effective focal spots greater than 1.5mm

A

+/- 30%

77
Q

Anode heel effect

A

Disparity of X-ray intensity

  • more X-rays to cathode side, larger effective focal spot
  • fewer X-rays to anode side, smaller effective focal spot
78
Q

Maximum image detail is found where

A

At the anode side of the cray tube - smaller effective focal spot

79
Q

Once heat units are calculated the tube rating chart tells you

A

How much time for tube to cool down

How long you have to wait before you can safely take the next exposure

80
Q

Heat units

A

= KVP x mAs x rectification factor

SEM II - Exposure (6 decks)

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