1. Appendix H: Chapter 40: Fluoroscopy

2. Spot film camera
(Photospot)
(105 mm in
this case)
Cine (35 mm)
camera
Video
camera
Spot film
device
Image intensifier

3. A C-arm fluoroscope X-ray tube Patient table Image intensifier
Video
camera
or CCD
Image intensifier
Cine
camera
Cine film. Rolls of 35mm film, hundreds
of feet long, typically contained multiple
projections of the coronary arteries and
often the left ventricle.
Though most institutions have gone digital,
many will still have cans of film and a cine
projector stashed in an archive.
X-ray
tube
Patient table

4. The transfer of energy through the fluoroscopic imaging chain
The three major pieces
of equipment in the
fluoroscopic imaging
chain are the:
1. image intensifier,
2. the video camera, and
3. the CRT monitor

5. How a Fluoroscopic Image Gets Intensified and Digitized
6. Video
camera (old)
or CCD
(microchip, like in home
camcorders)
translates
image into
electrical
(video) signal
7. Computer assigns
pulses from video signal values in binary code (0s and 1s) and stores them as image data
8. Displayed
on monitor
Video signal
Video signal
5. Optical lens
focuses light
Image
Intensification
tube
4. Electrons are accelerated toward a tiny fluorescent screen
at other end of image intensifier. Concentration of
electrons and added kinetic energy make image tens of
thousands of times brighter.
3. Light stimulates a photoemissive material to
liberate electrons. Image pattern is maintained
2. X-rays excite atoms of a fluorescent screen, light
is given off. This is fluoroscopy in its simplest
form but the image is very dim.
1. X-rays pass through the body or are attenuated, thus
forming a pattern (aerial image) of the anatomy they pass through.
Photons from the X-ray tube

6. Image Intensifier (II)
Output Phosphor
Zinc Cadmium Sulfide
Anode
25,000 V
Electrostatic focusing
lens
Glass envelope
Photocathode
Cesium & Antimony
Concave surface so all electrons arrive at the output screen at the same time, but causes vignetting.
Input Phosphor
CsI

7. The transfer of energy through the fluoroscopic imaging chain
3000 light photons
at the output phosphor
Focal Point
50 Photoelectrons
at the photocathode
1000 light photons
at the input phosphor
For every one incident X-ray photon

8. (zinc-cadmium sulfide)
Anode
25kV + potential
Flux Gain
Output Phosphor
(zinc-cadmium sulfide)
Electrostatic focusing
lens
Photocathode
Electrons accelerated across the tube gain kinetic energy from the
attractive force of the anode (conversion efficiency). The collision at
the output screen liberates that energy in the form of more light photons

9. (zinc-cadmium sulfide)
Minification Gain
1” diameter
Output Phosphor
(zinc-cadmium sulfide)
The ratio of the areas of the input
and output screens is expressed as
the minification gain. 92 12
= 81 times
Input Phosphor
(CsI)
9” diameter

10. Total Brightness Gain The product of the flux gain
and the minification gain is
the total brightness gain.
If the flux gain were 70, and
the brightness gain 81
70 x 81 = 5670 total brightness gain
,000 is the range

11. Quantum Mottle Conversion factor
Because the image intensifier makes the image
on the output screen thousands of times
brighter than the image on the input screen,
much less radiation is needed.
If too few photons are used, the
image becomes grainy and
unacceptable for diagnostic purposes.
Generally speaking a better image is always
obtained by using more photons, but the price
is paid in patient dose.
Conversion factor
The intensity of illumination at the output phosphor (candela per
meter squared) to the radiation intensity that produced it (mR/s)
Typical conversion factors of 50 to 300 relate to the ,000 BG

12. Veiling Glare
Scatter radiation from
x-ray, electrons, and light

13. (As opposed to increased OID magnification)
Multifield (Duel focus) Electronic Magnification
(As opposed to increased OID magnification)
By increasing the positive charge on the electrostatic focusing lens,
the convergence (focal) point
is changed (further
from out put screen). } 7” } 9” }
7” mode
11” mode
11”

14. } } } Duel focus or Electronic Magnification
When the convergence point is further from the output screen, (blue) the photoelectrons have further to diverge, and the image
arriving at the output screen is larger.
Electronic magnification
creates better resolution
But patient dose is
increased. } 7” } 9” }
7” mode
11” mode
11”

15. Automatic Brightness Control
(ABC)
While doing fluoroscopy the .5 to 5 mA, and the kVp will be automatically adjusted to compensate for changes in part thickness, composition of the part as the fluoro tube is being moved. ABC adjusts the mA. Lag is evident, especially if the tube is moving fast.
ABC also increases patient dose
when using electronic
magnification

16. Resolution Measured in line pairs.
Measuring the resolving power of imaging equipment using a line pair test tool
Measured in line pairs.
One line and one space is a line pair
1 mm
= 1 line pair per millimeter
of spatial resolution

17. A Line Pair Test Tool
(for Testing Spatial Resolution)
The Test Tool provides line pairs of various sizes to measure spatial resolution
1 mm
1 mm
1 mm
1 mm
1 mm

18. Vidicon and Plumbicon camera tubes

19. Vidicon Camera Window Signal Plate Tube Target Anode Electron gun
(cathode)
Globules
Video Signal
(from signal
plate)
Control grid
Steering and
deflecting coils

20. The transfer of energy through the fluoroscopic imaging chain
Optical lens
to focus
light from II

21. Coupling of the II to
the camera
* Fiber optics
* Lens coupling
* Beam splitting
mirror allows
photospot and
camera filming

22. The transfer of energy through the fluoroscopic imaging chain
Optical lens
to focus
light from II No
signal
High
intensity
Low
intensity
Modulation

23. Interlaced Scanning 262 1/2 Odd Lines scanned first = Field 1
262 1/2 Even Lines scanned first = Field 2
2 Fields = 1 Frame

24. Radiography (Film or digtal) On Fluoro
Why are densities reversed on the fluoro monitor
* Low atomic densities =
* Low attenuation =
* Input phosphor glows brightly
* Camera target highly excited.
* Video signal is strong
* Light area on monitor
* Low atomic densities =
* Low attenuation =
* Many photons interact with IR =
* Dark area on image
Comparison of the low
density (air filled)
maxillary sinus as seen
on film or digital monitor,
and in standard
fluoroscopic mode.
Radiography (Film or digtal) On Fluoro

25. The transfer of energy through the fluoroscopic imaging chain
Optical lens
to focus
light from II No
signal
High
intensity
Low
intensity

26. Question: How is a conventional fluoroscopic, analog imaging chain converted to digital?
ADC 1
ALU CU
Primary
Memory
Secondary
(RAM)
DAC

27. Spot films recorded on a spot film device
* Both are taken during fluoroscopy 4 on 1
* Both are radiographic exposures
* Both are 9 x 9 inch films made
especially for this purpose, (though
some fluoroscopes use standard
size cassettes) 1 on
* Both were filmed using the same
device, but in different formats.

28. Spot film camera
(Photospot)
(105 mm in
this case)
Cine (35 mm)
camera
Video
camera
Spot film
device
Image intensifier
35 mm cine film. Real
time motion, projected
on a projector.

29. Spot films (Photospots) recorded on a spot film (photospot) camera
105 mm
identifiable
by sprockets
that drives
the roll of
film that is
unique for
this size
* Both were taken during fluoroscopy
* Both are fluoroscopic exposures (i.e.
taken off the output phosphor of the II.)
* Both are serial films (not designed to be
projected as a moving image, but taken
in rapid sequence such as 1, 2, or 4 a
second
105 mm
* Both are filmed by the same camera
but are different sizes.
90 mm (cut film)

30. Flat Screen Monitors