1. Fluoroscopy: Viewing Systems
Optical Mirrors TV Camera & TV Camera Tubes Charge Coupled Devices (CCD)

2. Video Viewing System System includes:
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
Display Monitor
Cathode ray Tube (CRT) or LCD
Camera Control Unit
Amplifies the video signal
Synchonizes video signal between the TV camera
and TV monitor
Associated cabling

3. Video (TV) Camera Tubes
There are several types of camera tubes.
The 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
Photoelectric cathode
When light strikes the photoelectric cathode of the CCD…
Electrons are released proportionally to the intensity of the incident light
Extremely fast discharge time with no image lag
Useful for high speed imaging applications
More sensitive than video tubes that operate at lower voltages
which prolongs useful life
Acceptable resolution
Not prone to damage from rough handling
Advantages

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

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

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
Video camera tubes consist of three layers sandwiched together:
Face Plate (or window)
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
Is thick enough to conduct an eletronic signal
Target Layer (or photoconductive layer)
A photoconductive layer coated on the inside surface of the signal plate

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

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

11. Target Assembly
Magnitude of video signal is proportional to intensity of light from the intensifier
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

12. Target Assembly Click for full explanation
Sequential discharging of the globules releases signal plate’s charge as a pulsed signal
This pulsing is the varying amplitude of the video signal
Pulsed signal
Click for full explanation

13. Scanned Raster Pattern
A closed circuit television systems picture is a series of scanned lines of the video camera’s target which are projected fast enough on a TV monitor to
create movie-like fluid motion
ecx.images-amazon.com
1 frame = 525 scanned lines, each scan line consists of thousands of dots
To avoid flicker, each frame is divided into
two halves or fields:
1st half scans even-numbered lines
2nd half scans odd-numbered lines

14. Interlaced Scans
Electron beam scans diagonal lines as active traces while horizontal lines are inactive retraces to position for next active trace
Thus, 2 interlaced scans (or fields) produce
1 complete frame
262.5 lines scanned every 1/60 second,
Entire 525-line raster pattern scanned
every 1/30 second
30 frames per second =
15,7000 scanned lines per second

15. Progressive Scan Analog commercial television uses a
525 horizontal raster line pattern per frame
(2 x 262½ fields)
Progressive raster pattern scans sequentially from top to bottom (no interlacing)
High resolution video systems now offer over 1,000 lines per frame
Provides increased resolution

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What’s Next?
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Presented by
Based on:
Principles of Radiographic Imaging, 4th 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