2. Fluoroscopy
Purpose
To visualize, in real time:
organ motion
ingested or injected contrast agents
insert stents
cathetarize small blood vessels
REAL TIME IMAGING 2
3. X-rays were discovered because of
there ability to cause fluorescence .
Thefirst x-ray image of human part was
observed fluoroscopically-Dr. Glasser.
3
4. THE FLUOROSCOPE
First generation fluoroscopes consisted of an x-ray
tube, an x-ray table and a fluoroscopic screen.
The fluorescent material used in screen was copper
activated zinc cadmium sulfide that emitted light in
yellow-green spectrum.
A sheet of lead glass covered the screen, so that
radiologist could stare directly into the screen with out
having the x-ray beam strike his eyes.
Screen fluoroscence was very faint so, the
examination was carried out in a dark room by the
radiologist who had to adapt his eyes by wearing red
goggles for 20-30 mins prior to the examination
technique is now obsolete & gone. 4
6. Photograph
shows an early
(1933)
fluoroscopic
system in use
before the
development
of image
intensification.
An actual
fluoroscopic
examination
with this
device would
have occurred
in a darkened
room. 6
7. IMAGE INTENSIFIER DESIGN
Image intensifier was discovered in 1950s-to
produce an image bright enough to allow cone
vision without giving the pt an excess radiation
exposure.
The components of an x-ray image intensifier
The tube itself is an evacuated glass
envelope ,a vacuum tube containing-
1.input phosphor and photocathode .
2.electrostatic focusing lens.
3.accelerating anode.
4.out put phosphor. 7
8. After an x-ray beam passes the pt it enters the image
intensifier tube the input fluorescent screen absorbs
x-ray photons and converts their energy into light
photons.
The light photons strike the photo cathode, causing it
to emit photoelectrons these electrons are
immediately drawn away from the photocathode by
the high potential difference betn it &the accelerating
anode.
As the electrons flow from the cathode towards the
anode, they are focused by an electrostatic lens which
guides them to the output fluorescent screen without
distorting their geometric configuration.
8
9. The electrons strike the output screen, which
emits the light photons that carry the
fluoroscopic images to the eye of the observer.
In intensifier tube, the image is first carried by
the x-ray photons, then by the light photons,
next by the electrons &finally by the light
photons.
9
12. INPUT PHOSPHOR & PHOTO CATHODE:
The input fluorescent screen in image intensifiers is
cesium iodide (CsI). (older intensifier- silver activated
zinc cadmium sulfide).
CsI is deposited on a thin aluminum substrate by a
process called “vapor deposition”. an interesting &
useful characteristic of CsI is that during the
deposition process the crystals of CsI grow in tiny
needles perpendicular to the substrate. There by
reducing scattering.
12
13. INPUT PHOSPHOR & PHOTO CATHODE:
Image quality is dramatically better with CSI input
screen than it was with zinc cadmium sulfide screens.
Three physical characteristics of CsI make it superior.
1. vertical orientation of the crystals.
2. A greater packing density &
3. A more favorable effective atomic number.
Phosphor thickness have been reduced comparably
from app. 0.3mm with Zn-Cd su to 0.1mm with CsI. The
principal advantage of thinner phosphor layer combined
with needle shaped crystals is improved resolution.
13
14. PHOTO CATHODE:
The photo cathode is a photoemissive metal
(commonly a combination of antimony & cesium
compounds).
When the light from the fluorescent screen strikes the
photo cathode, photo electrons are emitted in numbers
proportional to the brightness of the screen.
The photo cathode is applied directly to the CsI input
phosphor.
The photoelectrons thus produced has to be moved to
the other end of the image intensifier. This can be
done using an electrostatic focusing lens and an
accelerating anode.
14
15. ELECTROSTATIC FOCUSING CUP:
The lens is made up of a series positively charged
electrodes that are usually plated on to the inside surface
of the glass envelope.
These electrodes focus the electron beam as it flows from
the photocathode toward the output phosphor.
Electron focusing inverts & reverses the image which is
called “point inversion” because all the electrons pass
through a common focal point on their way to output
phosphor.
The input phosphor is curved to ensure that electrons
emitted at the peripheral regions of the photocathode
travel the same distance as those emitted from the
central region.
The image on the output phosphor is reduced in size
,which is one of the principle reasons why it is brighter.
15
16. ACCELERATING ANODE :
The anode is located in the neck of the image tube.
Its function is to accelerate electrons emitted from the
photocathode towards the output screen. the anode has a
+ve potential of 25 to 35 kv relative to the photocathode,
so it accelerates electrons to a tremendous velocity.
OUTPUT PHOSPHOR:
The output fluorescent screen of image intensifiers is
silver activated zn-cd sulfide, the same used in Ist
generation input phosphor.
Crystal size and layer thickness are reduced to maintain
resolution in the minified image.
A thin layer of aluminum is plated onto the fluorescent
screen prevent light from moving retrograde through
the tube & activating the photocathode.
16
17. The glass tube of the image intensifier is abt 2 to 4mm
thick &is enclosed in a lead lined metal container
protects the operator from stray radiation.
The output phosphor image is viewed either directly
through a series of lenses and mirrors or indirectly
through closed circuit TV.
BRIGHTNESS GAIN:
Two methods are used to evaluate the brightness gain
of image intensifiers. the first compares the luminance
of an intensifier output screen to that of a Patterson
type B2 fluoroscopy screen when both are exposed to
same quantity of radiation.
The brightness gain is the ratio of the two
illuminations.
Brightness gain=intensifier luminance/Patterson b-2
lumin.
17
18. Another way of evaluation of brightness gain is called as
“conversion factor”
Conversion factor =cd/m2 by mR/sec
Output screen luminance is measured in candelas.
Radiation quality & output luminance are explicitly
defined, so the method is accurate & reproducible.
The brightness gain tends to deteriorate as the image
intensifier ages. ie the pt dose with an older image
intensifier tends to be higher than with a new intensifier
of the same type.
The brightness gain of an imag inten comes from 2
completely unrelated sources called minification gain
&flux gain.
18
19. MINIFICATION GAIN:
The brightness gain from minification is produced by a
reduction in image size.
The quantity of gain depends on the relative areas of
input &output screens. coz the size of the intensifier is
usually indicated by its diameter, so minif gain is
expressed as MG=(d1/d0)2.d1=diameter of input
screen,d0=diameter of output screen.
Most img inten have an input screen from 5 to9 in.& an
output screen of app 1in in diameter.
Theoretically minification can be increased indefinitely
as we can see from above formula, but as the
minification is increased the image becomes smaller.-
disadvantage.
Hence image has to be magnified and viewed which will
result in reduce brightness & precipitous drop in
resolution. 19
20. FLUX GAIN:
FLUX gain increases the brightness of the fluoroscopic
image by a factor of app 50.
The total brightness of an imag intes is product of
minification & flux gain: ie
Brightness gain =minification gain x flux gain.
20
21. MULTIPLE-FIELD IMAGE INTENSIFIERS
Dual field or triple field imsg intes attempt to
resolve the conflicts btn image size & quality.
They can be operated in several modes, including
the 4.5in, a 6in, or a 9in mode. the 9in mode is
used to view large anatomic areas. When size is
unimportant the 4.5in or 6in mode is used coz of
better resultant image quality.
Field size is changed by a simple electronic
principle: the higher the voltage on the
electrostatic focusing lens, the more the electron
beam is focused. 21
22. This figure shows this principle
applied to a dual field imag
intes.
In the 9in mode, the
electrostatic focusing voltage is
decreased. the electrons focus to
a point or cross, close to the
output phosphor & the final
image is actually smaller than
the phosphor.
In 6in mode the electrostatic
focusing voltage is increased &
the electrons focus farther away
from the output phosphor. after
the electrons cross they diverge,
so the image on the output
phosphor is larger than in the 22
23. Optical coupling
Optical system transmits the output of the image
intensifier to the light sensitive area of the video
camera
The optical distributor include beam-splitting
mirror, which directs a portion of the light from
the image intensifier output window to an
accessory device for image recording and passes
the remainder to the video camera.
Two lenses are mounted in tandem
The II and the vidicon are placed at the focal
planes of the two lenses
23
25. Closed-circuit Television System
used to view the image intensifier output image
Consists of
1)Television camera
2) Camera control unit
3) Monitor
The television system allows for real-time
viewing of the fluoroscopic image by several
people at once from one monitor or multiple
monitors
25
26. Television Camera Tube
Output phosphor is directly coupled to a TV
camera tube
Plumbicon
Vidicon
CCD
26
27. The basic video camera consists of
1) vacuum tube cylinder (approximately 2.5 cm in
diameter) surrounded by electromagnetic focusing
coils ,2 pairs of electrostatic deflecting coils
2) photoconductive target
3) a scanning electron beam
Target assembly:
a) Glass plate assembly
b) signal plate
c) Target
27
29. Target
Functionally most important i n tube
Thin film of photoconductive material, antimony sulfide
suspended as globules in mica matrix.
The optical coupling lens focuses the image intensifier output
image onto the target, forming a charge image within the
photoconductive layer
This latent image is read out by the electron beam, which
scans across the target in a series of horizontal raster lines.
As the scanning electron beam moves across the target, a
current signal is produced that represents the two-dimensional
image as a continuous series of raster lines with varying
voltage levels.
29
30. Video signal
When globules absorbs light ,photoelectrons are
emitted
The globule becomes positively charged
The electron beam scans the electrical image stored
on the target & fills in the holes left by the emitted
photoelectrons, discharging the tiny globular
capacitors
When the electrons in beam neutralize the positive
charge in the globules , the electrons on the signal
plate leave the plate via resistor
These moving electrons form a current flowing
through a resistor and voltage across the resistor
This voltage ,when collected for each neutralized
globule, constitutes the video signal
30
32. Television monitor
The video signal produced by the video camera is converted into a visible
image by the monitor
Contains picture tube & controls for regulating brightness & contrast
Picture tube contains-
Electron gun
control grid
anode
focusing coil, deflecting coil-control the electron beam
synchrony with the camera tube
Control grid-receive video signal from Camera control unit ,uses this signal
to regulate the no. of electrons in electron beam
Anode –carries higher potential (10,000V) accelerates the electron beam to
much higher velocity
The electron Strike the fluorescent screen ,emit large number of light
photons.
32
34. Image Recording
Two modes of recording th flouroscopic
image -
1) light image from output phosphor of II
recorded on film with a photospot camera
or cine camera
2) electrical signal generated by TV camera-
includes magnetic tape, magnetic discs &
optical discs
34
35. DIRECT FILM RECORDING
SPOT FILM DEVICES:
Fluoroscopic systems designed for gastrointestinal imaging
are generally equipped with a spot film device.
The spot film device allows exposure of a conventional
screen-film cassette in conjunction with fluoroscopic
viewing. This rather familiar system, located in front of the
image intensifier, accepts the screen-film cassette and
"parks" it out of the way during fluoroscopy
Cassettes may be loaded from the front or rear depending on
the design of the system.
35
36. Standard spot film
imaging configuration
typical of
gastrointestinal
fluoroscopy equipment.
The screen-film cassette
is parked out of the x-
ray field until the spot
film trigger is pressed,
causing both the
cassette and the
formatting mask to
move into position.
36
37. The x-ray field size is also reduced automatically by the
collimators at the time of exposure to minimize scattered
radiation and patient radiation dose.
The fluoroscopist can override this automatic collimation to
further reduce the x-ray field.
Spot film imaging uses essentially the same technology as
conventional screen-film radiography.
Differences and limitations of spot film imaging
compared with general radiography.
One major limitation is the range of film sizes available for
spot film imaging. Although some older fluoroscopy
equipment is limited to a single size, usually 24 x 24 cm,
current equipment allows a range of film sizes to be used,
from 20 x 25 cm to 24 x 35 cm.
Spot film devices usually allow more than one image to be
obtained on a single film.
Formats typically include one, two, three, four, or six images
on a film.
37
38. Moving the spot film device closer to the patient
reduces the amount of magnification and decreases
the patient radiation dose.
A number of factors affect patient doses in spot film
imaging.
The source-to-skin distance is shorter in spot film imaging
than in general radiography.
Although the automatic exposure control system fixes the
exposure to the screen, the shorter source-to-skin distance
increases the inverse square reduction in radiation intensity
as it passes through the patient.
This increase tends to make the skin entrance exposure
higher.
The field size in spot film imaging is generally smaller than
that used in general radiography.
This smaller field size reduces scatter and therefore tends to
reduce dose. For the same reason, grids used in fluoroscopy
generally have a lower grid ratio and therefore a smaller
Bucky factor, which also leads to lower dose.
These effects tend to offset each other to a large extent. 38
39. One of the major shortcomings of conventional spot
film devices is the delay involved in moving the
cassette into position for exposure.
In gastrointestinal imaging, this delay can be
overcome by using photofluorography.
In vascular imaging, more rapid film movement is
achieved with automatic film changers.
39
40. AUTOMATIC FILM CHANGERS
The automatic film changers used in vascular imaging are
also screen-film systems.
They can be found in several varieties. Some are large,
floor-mounted boxes, but systems more commonly used
today mount on the image intensifier
The system consists of a supply magazine for holding
unexposed film, a receiving magazine, a pair of
radiographic screens, and a mechanism for transferring the
film.
When an exposure is required, the screens are mechanically
separated, the film is pulled into place between them, and
they are closed.
After the film is exposed, the screens separate again.
The film is moved to the receiver, and another film is pulled
into place for the next exposure.
The number of films and filming rates must be
preprogrammed for proper operation.
40
41. Photospot camera
Records the the image output of an II on a film
Film – role film/cut film(10 cm)
Advantage –1)reduction in pt exposure
2)film does not have to be changed
b/w exposures
3)exposure times are shorter-motion is less
likely problem
4)films can be taken more rapidly
5)possible to record & view image at same
time
41
42. Framing with spot film cameras:
Framing –utilisation of available area on film
The output phosphor of II tube is round,
shape of film is square
4 framing patterns
1) Exact framing
2) Equal area framing
3) mean diameter framing
4) total area framing
Equal area framing or mean diameter framing
is recommended for most clinical situations.
42
44. Cineflourography
Process of recording fluoroscopic images on
movie (cine) film
Two film sizes- 16 mm, 35 mm
Cine camera-components are lens, iris
diaphragm, shutter, aperture, pressure plate, pull
down arm & film transport mechanism
44
46. TV image recorders :
3) TAPE RECORDER : used for both recoding& playback
• as a recorder receives video signal from camera
control unit
• for playback transmits the signal to one or more
several TV monitors
Components:1)magnetic tube
2)writing head
3) tape transport system
Writing head converts an electrical signal in to magnetic
field for recoding & converts magnetic signal to electric
signal for replay
46
49. DIGITAL FLUOROGRAPHY
Digital charge-coupled device (CCD) TV cameras are
rapidly replacing conventional TV cameras in fluoroscopic
systems.
An analog, high-resolution (1,023-line) TV camera has
a vertical resolution of about 358 line pairs.
A high-resolution CCD camera with a 1,024 x 1,024
matrix will provide equivalent vertical resolution. However,
the digital camera will have the same vertical and
horizontal resolution, whereas the horizontal resolution of
the analog camera is defined by its electronic band-pass.
49
50. For a 15-cm-diameter intensifier input, the
limiting resolution of the CCD camera would be
358 lp/150 mm or 2.4 lp/mm. This result is about
half the resolution of a photospot film. This
resolution loss is made up for by the ability to
digitally increase display contrast, reduce noise,
and enhance the edges of digital images.
There are several other advantages to digital
photospot images. Mechanical devices are not
needed for film transport. Film processing is not
required. Images can be viewed immediately. The
linear response of the digital system makes it very
forgiving of under- or overexposure.
50
51. Fluoroscopic Equipment Configurations
The basic configurations include radiography/fluoroscopy (R/F) tables with
either an under-table or over-table x-ray tube and fixed C-arm, mobile C-arm,
and mini C-arm
R/F Units with Under-Table X-ray Tube:
most common fluoroscopic equipment configuration
The x-ray tube and collimator are mounted below the tabletop with the image
intensifier tower mounted above the table on a carriage that can be panned
over the patient.
In addition to the standard fluoroscopic imaging chain, R/F systems include
an overhead x-ray tube that can be used for regular radiography with a Bucky
incorporated into the table.
Other common features include a tilting table and image recording devices.
51
52. Under-table x-ray tube R/F system. Photograph shows an example of an
R/F table that includes a spot film device and side-mounted video camera.
52
53. R/F Units with Over-Table X-ray Tube
x-ray tube mounted over the table with the
image intensifier below.
this configuration results in increased patient
access, which is helpful for interventional
procedures.
Radiography can be performed with the same x-
ray tube and a Bucky incorporated into the table.
The x-ray tube can be angled to acquire
angulated projections or tomograms.
53
54. Over-table x-ray tube R/F system. Photograph shows a sample system
that can be controlled from within the procedure room with the pedestal
control panel (left) or from outside the room from the remote desk controls
(right).
54
55. SUMMARY:
Early fluroscopy was accomplished by
radiologists looking directly at a fluoroscopic
screen.
The image on the screen was only 0.0001 as bright
as the image of a routinely viewed radiograph, so
dark adaptation of eyes was required.
In 1950s the image intensifier alleviated this
situation by producing an image bright enough to
be viewed with cone vision.
The input phosphor of modern image intensifier
is CsI; the output phosphor is zinc cadmium 55
56. Brightness gain is the product of minification gain and
flux gain.
Imaging characteristics important in the evaluation of
image intensifier fluoroscopy include contrast, lag and
distortion.
Large field of view image intensifier tubes are available
to fill special needs, such as digital and spot film
angiography.
Most image intensifiers allow dual field or triple field
imaging.
56
57. Output phospher image is processed by television
camera tube (vidicon, plumbicon, CCD)
The image is displayed on TV monitor
Standard x-ray closed-circuit television uses
525x525 format with 5-MHZ band pass
Vertical resolution limited by scan line format,
horizontal resolution is a function of band pass
Light image is recorded by photo spot camera or
cine camera
57
