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SEM II - Exposure > Fluoroscopy/Heat Units > Flashcards

Fluoroscopy/Heat Units Flashcards

(81 cards)

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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
Brightness gain
= minification gain x flux gain
25
ABC
Automatic brightness control | - maintains a preset brightness level by automatically adjusting the exposure factors to compensate for varying subject
26
Fluoro imaging techniques
Very low mA (.5-5mA) | Higher KVP utilized
27
SSD (source to skin distance) in fluoro
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
28
Quantum mottle - fluoroscopy
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
29
Magnification tubes
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
30
Magnification formula
=total input phosphor diameter/diameter of input phosphor used
31
TV camera
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
32
Two basic types of cameras in use
Vidicon Plumbicon
33
Vidicon
Camera used with general fluoro
34
Plumbicon
Camera used with interventional fluoro
35
Splitter
Able to split signal from output phosphor to multiple components: - monitor - video - digital video - hard film
36
Changes in voltage o the electrostatic focusing lenses causes
The electrons to narrow of widen their stream
37
Common field sizes for angio
35/25/15 cm The smaller the mode the more magnified the image Mag modes increases scatter
38
Common field sizes for general
25/17 cm The smaller the mode the more magnified the image Mag modes increases scatter
39
Multiple imaging devices on fluoro
TV camera, spot films, cine camera, cassette - all use the image as displayed on the output phosphor
40
Fluoro patient radiation protection
Exposure dose should not exceed 10R/min - typical range is from 1-3R/min
41
5 minute timer
Units must alarm at 5 minute intervals to alert radiologist/surgeon
42
Magnification fluoro
Causes increased dose. | As you magnify the image, patient does goes up
43
Occupational exposure
Fluoro is a techs #1 source of exposure - scatter from patient Lead aprons must be worn
44
Lead aprons fluoro
At least .5mm lead equivelant
45
Bucky slot cover/lead drapes
Must be at least .25mm lead equivelant
46
3 things for X-ray production
Source of free electrons Acceleration of free electrons Abrupt halting of high speed electrons
47
As high speed electrons are abruptly halted by dense anode target, their kinetic energy converts to:
Heat as thermal energy (99%) Xray as electromagnetic energy (1%)
48
Heat
The kinetic energy of molecules (rapid motion = heat)
49
The enemy of electrical components which make them wear out
Heat
50
Calorie
The unit of heat. The amount if heat required to raise the temperature of 1 gram of water 1 degree Celsius
51
Heat is transferred by 3 means
Conduction Convection Radiation
52
Conduction
The transfer of heat through a material by touching of ohysical contact of solid objects
53
Convection
The transfer of heat by the mixing of molecules in a liquid or gas
54
Radiation
The transfer of heat by the emission of infrared radiation X-ray tubes are cooled primarily by radiation
55
X-ray tubes are cooled primarily by
Radiation
56
Modern X-ray machines are controlled to not allow overheating by
Computerized control
57
Older X-ray machines require a
Manual heat calculation
58
Heat units are found by the formula
KVP x MA x Time x rectification constant
59
Rectification constant
Voltage waveform
60
A more efficient voltage waveform produces what
More heat
61
Actual focal spot
Aka true focal spot Area that high speed electrons strike the anode
62
Effective focal spot
Actual focal spot projected towards patient
63
Line focus principle
Effective focal spot will always be smaller than true
64
The modern standard anode angle is
12 degrees
65
As focal spot increases
Penumbra increases
66
Penumbra
Loss of detail
67
Small focal spot
Maximum image detail
68
Large focal spot
Decreased image detail
69
Focal spots are measured as
Effective focal spot Approximate sizes are .5mm up to 2.0mm
70
Blooming of focal spot
Enlargement of the electron stream as it travels from cathode to anode Due to mutual repulsion of electrons
71
Blooming increases as
mAs increases and vice versa
72
Why not always use a small focal spot
They correspond to the size of cathode filaments Small filaments are mA limited Sometimes we need a higher mA station
73
Tests to determine focal spot size
Line pair resolution Star pattern test Pinhole camera test
74
Effective focal spots up to .8mm
+/- 50%
75
Effective focal spots between .8 - .15mm
+/- 40%
76
Effective focal spots greater than 1.5mm
+/- 30%
77
Anode heel effect
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
Maximum image detail is found where
At the anode side of the cray tube - smaller effective focal spot
79
Once heat units are calculated the tube rating chart tells you
How much time for tube to cool down How long you have to wait before you can safely take the next exposure
80
Heat units
= KVP x mAs x rectification factor

SEM II - Exposure (6 decks)

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