Fluoroscopy

1
Fluoroscopy

• Ch 24

2
Fluoroscopy

• A dynamic type of imaging modality
• Invented by Thomas Edison in 1896
• Utilizes image intensification to increase
  visualization of images

3
Demands of Fluoroscopy

• Illumination
• The principal advantage of image intensified
  fluoro is an increased brightness
• Sometimes requires that the room be dark so that
  the image can be visualized better

4
Human vision

• Structures designed for vision
• Rods
• Sensitive to low light levels
• Cones
• Sensitive to bright light levels

5
Fluoroscopic technique

• Maximum detail is desired
• Image brightness must be high
• Controlled by automatic brightness control (ABC)
• Generally high kVp and low mA are preferred
• kVp relates to the body part being examined
• mA is around 5
• Much lower than hundreds of mA usually used for
  static imaging

6
Components of the image intensifier tube

• Input phosphor
• Glass envelope
• Photocathode
• Electrostatic lenses
• Anode
• Output phosphor

7
Glass envelope

• Surrounds all of the components and provides
  mechanical support of internal components
• Has a vacuum tube

8
Input phosphor

• Receives incident x-rays from the x-ray tube and
  converts them into light
• Composed of cesium iodide

9
Photocathode

• Attached to the input phosphor by an adhesive
  layer
• Converts light from input phosphor to electrons
  by photoemission
• Negative portion of the tube

10
Anode

• Positive portion of the tube
• A circular plate with a hole in it in which
  electrons are focused to which goes to the output
  phosphor

11
Electrostatic focusing lenses

• Focuses electron path form photocathode to anode
  by means of repulsion

12
Output phosphor

• Converts electrons from anode to light

13
Flux Gain

• The ratio of the number of light photons at the
  output phosphor to the number of x-rays at the
  input phosphor
• Flux gain number of output light photon
• number of input x-ray photons

14
Brightness Gain

• The ability of the image intensifier to increase
  illumination level of the image
• Brightness gain minification gain x flux gain

15
Minification gain

• The ratio of the square of the diameter of the
  input phosphor (Di) to the square of the diameter
  of the output phosphor (Do)
• Minification gain (Di)2
• (Do)2

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Multifield Image Intensification

• Gives the fluoroscopist the ability to magnify
  the video image of the body part examined
• Sometimes referred to as a Mag view
• Electrostatic focusing lenses focus electrons in
  a smaller area on the output phosphor which makes
  the resulting image larger than the original

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Magnification Factor for Fluoro

• Ratio of the original diameter of the input
  phosphor to the new diameter of the input
  phosphor
• Dual field tubes
• 25/17
• Tri-field tubes
• 25/17/12
• Magnification factor original input diameter
• new input diameter

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Television monitoring

• Types of TV Camera Tubes
• Videcon
• Plumbicom

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Coupling Devices

• Fiber optic coupling
• Uses fiber optic materials to tie the TV camera
  tube with the image intensifier tube
• Advantage small, compact and rugged
• Disadvantage cannot use with anything but spot
  film devices

20
Coupling devices

• Lens coupling
• Uses lenses and mirrors to split the incoming
  signal into two signals and connect the output
  phosphor of the IIT to the TV CT
• Advantage can be used with digital and camera
  imaging
• Disadvantage large, very fragile

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TV Camera Components

• Electron gun
• Control grid
• Steering coil
• Glass envelope
• Target assembly

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Glass envelope

• Surrounds all of the components and provides
  mechanical support of internal components
• Has a vacuum tube

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Electron Gun

• The converted light from the output phosphor
  heats up a filament that supplies a constant
  electron current to the target assembly

24
Control grid

• Starts the focusing of the electrons from the
  electron gun by repulsion

25
Steering coil

• Also known as deflection coils, focusing coils
  and alignment coils
• Focuses the electron beam by means of repulsion
  toward the target

26
Target assembly

• Face plate or window
• Signal plate
• Target or photoconductive layer

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Face plate

• The outside layer of the target

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Signal plate

• Coated on the inside of the window
• Composed of a thin layer of metal or graphite
• Conducts video signals out of the tube into the
  external video circuit

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THE END
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Target of photoconductive layer

• Located on the inside of the signal plate
• The electron beam interacts with this layer and
  becomes illuminated

31
TV picture tube

• Also called the Cathode Ray Tube (CRT)
• Components
• Glass envelope
• Electron gun
• Control grid
• Focusing coil
• Deflection coil
• Anode
• Output phosphor

32
Television Image

• Raster pattern
• Active trace
• The movement of the electron beam from upper left
  to right portion of the screen
• Horizontal retrace
• After the active trace a time for beam to go back
  to upper left right portion
• Vertical retrace
• After horizontal retrace is complete, the process
  begins again in between the active traces
• Interlace
• Combining the two fields together to form one TV
  frame

33
Fluoroscopic recording

• Cassette-loaded spot film
• The spot film is positioned between the patient
  and the image intensifier. During exposure the
  image intensifier exposes the film
• Photospot camera
• Similar to a movie camera but can only expose one
  frame at a time