1. Fluoroscopic Unit
Thomas Edison 1896

4. Fluoroscopy Dynamic imaging Spot films 3-5 mA
kVp and mA determine brightness level
Automatically adjusted during fluoro by automatic brightness control (ABC)

5. Image Intensifier Electronic vacuum tube
Converts the remnant beam to light, then to electrons, then back to light
Remnant beam-light electrons light
light intensity in the process
Parts
Input Phosphor
Photocathode
Electrostatic focusing lenses
Accelerating anode
Output phosphor

7. Input Phosphor Made of Cesium iodide
Absorbs the remnant x-ray photon energy and emits light in response
Side toward the tube
Side toward the patient
Bonded to the curved surface of the tube

8. Photocathode Made of cesium and antimony compounds
These metals emit electrons in response to light stimulus in a process called Photoemission
Bonded directly to the input phosphor
Curved so that all of the electrons emitted travel the same distance to the output phosphor

9. Electrostatic Focusing Lens
Negatively charged plates along the length of the image intensifier tube
Repel the electron stream, focusing it on the small output phosphor

10. Accelerating Anode
Sets the electron stream in motion at a constant velocity
Maintains constant potential of 25kV

11. Output Phosphor Silver-activated zinc cadmium sulfide
Absorbs electrons and emits light in response
End result
An increase in image intensity and brightness

12. Magnification Mode Focal point is shifted farther from output phosphor
Voltage to electrostatic focusing lenses is increased. The increase tightens the diameter of electron stream and focal point is shifted
Increase in pt dose
Spatial Resolution is improved
Smallest structure that may be detected
Measure in line pairs/mm
Magnification
If fewer electrons are incident on the output phosphor , the output intensity decreases
What does the ABC do to compensate? (increase radiation)
What does this do to pt dose? (increase)

13. Magnification
9-inch Input” button, you’ll see that an image of the figure appears smaller and inverted near the output phosphor – this simulates a normal mode in fluoroscopy.
When you click on the “6-inch Input” button, the input phosphor size is reduced, the output phosphor size remains the same and the image is magnified.

15. Intensification Principles
Brightness gain(Conversion Factor)
Ability of image intensifier tube to convert x-ray energy into light energy & increase the brightness of the image
Minification gain x flux gain
Flux gain
Ratio of #light photons at the output phosphor to the # of light photons emitted in the input phosphor
Represents the tubes conversion efficiency
Conversion factor
Luminance at output phosphor input exposure rate
Appears brighter because the same # of electrons are being concentrated on a smaller surface area
What do you think happens to the brightness as the tube ages? (deteriorates)
How do you compensate for the decrease in brightness? (use more radiation)
What happnes to pt dose? (increase)

16. image appears brighter
Minification gain – the brightness gain caused from a decrease in size from the input to the output phosphor
image appears brighter
Input phosphor daimeter2 / output phosphor diameter2

17. Automatic Brightness Control (ABC)
Adjusts and maintains the overall image density and contrast during fluoroscopy
Determined by the brightness control setting that the radiographer sets
Contrast and density
By automatically adjusting kVp and mA or both

18. Distortion Misrepresentation of true size or shape of an object
Caused by the curved shape of the photcathode
Inaccurate control or focusing of electrons released at photocathode
Pincushion appearance
Vignetting-loss of brightness around the edge of the fluoroscopic image caused by the curve of the photocathode
Loss of brightness

19. Viewing Systems
The signal is sent to a television monitor for viewing through the Vidicon tube
Diode tube in a glass envelope
Connected to the output phosphor
Digital fluoroscopy
Computerized images from output phosphor
No need for overhead/spot films

20. Camera Tube

21. Cathode Cathode Electron gun Provides continuous stream of electrons
Control grid
Forms the electron stream into a beam

22. Anode
Anode
Face plate
Signal plate
Target