This document discusses fluoroscopy, including conventional fluoroscopy units and modern fluoroscopic units. It describes the key components of a fluoroscopic unit, including the image intensifier, vidicon camera, and TV monitor. It also discusses factors that influence fluoroscopic image quality such as radiation dose rates, image resolution both vertically and horizontally, and techniques to reduce image noise like frame averaging.

1. FLUOROSCOPY

2. Conventional Fluoroscopy

3. Conventional Fluoroscopic Unit

4. Photons used: Fluoro vs Radiography
Spotfilm Fluoroscopy
kVp: 85 85
mA: 200 3
Time (sec): 0.3 0.2*
mAs: 60 0.6
Ratio: 100 1

5. Conventional Fluoroscopy

6. Light Levels and Fluoroscopy

7. Modern Fluoroscopic Unit

8. Fluoroscopic Image Receptors

9. Image Intensifier

10. Functioning of Image Intensifier

11. Intensifier Flux Gain

12. Intensifier Performance
Conversion factor is the ratio of output phosphor
image luminance (candelas/m2) to x-ray exposure
rate entering the image intensifie (mR/second).
 Very difficult to measure: access to output phosphor
 No absolute performance criteria

13. Intensifier Brightness Gain (BG)
BG = Minification Gain x Flux Gain
 Minification gain (MG): The ratio of the squares of
the input and output phosphor diameters. This
corresponds to “concentrating” the light into a
smaller area, thus increasing brightness
MG = (Input Diamter )2 / (Output Diameter)2

14. Intensifier Brightness Gain (con’t)
 Flux Gain (FG): Produced by accelerating the
photoelectrons across a high voltage (>20 keV), thus
allowing each electron to produce many more light
photons in the output phosphor than was required
to eject them from the photcathode.
 Summary: Combining minification and flux gains:

15. Intensifier Brightness Gain (con’t)
 Example:
Input Phosphor Diameter = 9”
Output Phosphor Diamter = 1”
Flux Gain = 75
BG = FG x MG = 75 x (9/1)2 = 6075
 Typical values: a few thousand to >10,000 for
modern image intensifiers

16. Fluoroscopic Noise (Quantum
Mottle)
Fluoroscopic image noise can only be reduced
by using more x-ray photons to produce
image. Can possibly accomplish in 3 ways:
 Increase radiation dose (bad for patient dose)
 Frame-averaging:
– forms image using a longer effective acquis time
– Can cause image lag (but modern methods good)
 Improve Absorption Efficiency of the input
phosphor

17. Conventional Input Phosphor

18. Cesium Iodide (CsI) Phosphor

19. Viewing Fluoroscopic Images

20. Automatic Brightness Control
 Monitoring Image Brightness
– Photocell viewing (portion of) output phosphor
– TV signal (voltage proportional to brightness)
 Brightness Control: Generator feedback loop
– kVp variable
– mA variable/kV override
– kV+mA variable
– Pulse width variable (cine and pulsed fluoro)

21. Fluoroscopic Dose Rates

22. Intensifier Format and Mag Modes

23. Intensifier Format and Modes

24. Vidicon (tube) TV Camera

25. Video Field Interlacing

26. Vidicon Target Assembly

27. TV Monitor

28. Synchronization (Sync Signals)

29. TV RESOLUTION-Vertical
 Conventional TV: 525 TV lines to represent
entire image. Example: 9” intensifier (9” FOV)
1) 9” = 229 mm
2) 525 TV lines/229 mm = 2.3 lines/mm
3) Need 2 TV lines per test pattern line-pair
4) (2.3 lines/mm) /2 lines/line-pair = 1.15 lp/mm
 Actual resolution less because test pattern bars
don’t line up with TV lines. Effective resolution
obtained by applying a Kell Factor of 0.7.
Example: 1.15 x 0.7 Kell Factor = 0.8 lp/mm

30. TV RESOLUTION-Horizontal
 Along a TV line, resolution is limited by how fast
the camera electronic signal and monitor’s electron
beam intensity can change from minimum to
maximum. This is bandwidth. For similar horiz
and vertical resolution, need 525 changes (262 full
cycles) per line. Example (at 30 frames/second):
262 cycles/line x 525 lines/frame x 30 frames/second
= 4.2 million cycles/second or 4.2 Megahertz (MHz)