1. Fluoroscopy – Viewing Systems Optical Mirrors TV Camera & TV Camera Tubes Charge Coupled Devices (CCD)
Based on:
Principles of Radiographic Imaging, 3rd Ed.
By: R. Carlton & A. Adler
Radiologic Science for Technologists, 8th Ed.
By: S. Bushong
Syllabus on Fluoroscopy Radiation Protection, 6th Rev.
By: Radiologic Health Branch – Certification Unit
PPT created by Jed Miles, BSRS, RT(R), CRT-CA

2. Video Viewing System
Closed circuit video with TV monitor is the most commonly used fluoroscopic viewing system
Contained system, eliminates outside and background broadcast interference
System includes:
Video camera attached to the output side of the II
Camera Control Unit
Amplifies the video signal
Synchronizes video signal between the TV camera and TV monitor
Display monitor
Cathode Ray Tube (CRT) or LCD
Associated cabling

3. Video (TV) Camera Tubes
Several types of camera tubes, main difference is the phosphor used as the target material
Vidicon tube
Most often used in fluoroscopic imaging chains
Relatively slow response time, produces image lag
Less quantum mottle due to lag producing signal averaging
Plumbicon tube
Less often used (mainly used in cardiac cath labs)
Faster response time and low lag
Produces better contrast
More quantum mottle – low lag does not provide signal averaging from previous frame
Image-Orthicon: very expensive – rarely used
Charged Coupled Device (CCD)
Solid-state semiconductor – not a vacuum tube

4. Charge-Coupled Devices (CCD)
Semiconducting device capable of storing a charge from light photons striking a photosensitive surface
When light strikes the photoelectric cathode of the CCD, electrons are released proportionally to the intensity of the incident light
Advantages:
Extremely fast discharge time – no image lag
Useful for high speed imaging applications
More sensitive than video tubes – operate at lower voltages – prolongs useful life
Acceptable resolution
Not prone to damage from rough handling

5. Video (TV) Camera Tubes
Camera tubes contain:
Cathode with a control grid
Series of electromagnetic focusing coils
Series of electrostatic deflecting coils
Anode with face plate
Signal plate
Target

6. Video Camera Tubes – Cathode End
Electron Gun - Consists of heated filament assembly that supplies a constant electron current across the tube via thermionic emission
Thermionic emission is flow of electrons from a metal or metal oxide surface, caused by thermal energy
Control grid – shapes the electrons into a stream or beam
Also helps accelerate electrons to anode end of tube
Electrostatic Grids - further accelerate and focus the electron beam toward anode end
Focusing Coils – focus the electron beam into a pencil point stream
Deflecting coils (in pairs) deflect pencil beam to scan target in path known as a raster pattern

7. Video Camera Tubes – Anode End
Beam is decelerated by wire mesh-like structure in front of the target assembly
This arrangement brings the electron beam to a near standstill where it is straightened to strike the target in a perpendicular fashion

8. Video Camera Tubes – Target Assembly
Consists of three layers sandwiched together
Face plate or window – is the thin part of the glass envelope closest to the output phosphor of the image intensifier
Signal plate – consists of a thin film of metal or graphite charged with a positive voltage
Is thin enough to transmit light from intensifier
Yet thick enough to conduct an electronic signal
Target or photoconductive layer – a photoconductive layer coated on the inside surface of the signal plate

9. Target Assembly - Construction
Target or Photoconductive layer
Consists of a thin insulating mica coating in which globules of a light sensitive photoconductive material are suspended in a matrix
Vidicon tubes use antimony trisulfide (Sb2S2)
Plumbicon tubes use lead oxide (PbO)
Globules approximately inch (0.025 mm) in diameter
Size of globules determines resolving power of camera tube (smaller = increased resolution)
Light photons interacts with this layer
When illuminated becomes photoconductive and releases electrons - when dark acts as an insulator

10. Target Assembly – How it Works
Light from output phosphor of image intensifier tube arrives, transmitted through window and signal plate to target material
Antimony trisulfide (or lead oxide) globules absorbs light photons from II output screen and emit electrons
Light is absorbed by globules, electrons released to anode and removed from tube (equivalent to intensity of absorbed light)
Loss of electrons creates positive charge at globule
Electron gun’s beam scans target, discharges globules, causing current flow in signal plate
Sequential charging and discharging of globules results in modulated current flow in signal plate creating varying amplitudes of video signal

11. Target Assembly

12. Another Way of Stating it…
As electron beam is incident on a globule some of its electrons will be conducted through target to signal plate and conducted out of tube as video signal
If area (globule) of target is dark (i.e. bone attenuated the x-ray beam) there will be less video signal
Magnitude of video signal is proportional to intensity of light from the intensifier
Sequential discharging of the globules releases signal plate’s charge as a pulsed signal
This “pulsing” is the varying amplitude of the video signal
Full explanation (click link)

13. What’s Next?
Please close this PowerPoint presentation, and then click Topic 2 to continue.