Fluroscopy

1. Rakesh C A

2. Fluoroscopy: a “see-through” operation with
motion
 Used to visualize motion of internal
fluid, structures
 Operator controls activation of tube
and position over patient
 Modern systems include image
intensifier with television screen
display and choice of recording
devices

3. Purpose
To visualize, in real time:
– organ motion
– ingested or injected contrast agents
– insert stents
–
–
–
–
–
– (endless)

4. CONVENTIONAL FLUOROSCOPY
INVENTED BY THOMAS EDISON (1896)

5. Early Fluoroscopy
 Early fluoroscopy = the
image was viewed
directly – the xray
photons struck the
fluoroscopic screen –
emitting light.

6. Direct Fluoroscopy: obsolete
In older fluoroscopic examinations
radiologist stands behind screen and view
the picture

7. Conventional Fluoroscopic Unit
Consisted of:
x ray tube
x ray table
fluoroscopic screen

8. Activated zinc cadmium sulfide

9. Conventional Fluoroscopy systems 9
30 min for dark adaptation

10. 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

11. Older Fluoroscopy
• DISADVANTAGES:
– ROOM NEED
COMPLETE DARKNESS
– PATIENT (&
RADIOLOGIST) DOSE
WAS VERY HIGH
– ONLY ONE PERSON
CAN VIEW IMAGE
11

12. Visual Physiology
Fluoroscopic Image
viewing based on
Human Vision
Rods
Cones
There are more than 100000
rods and cones per
square millimetre of
retina.

13. Cones = Photopic (daylight) Vision
• cones are less sensitive
to light
• concentrated on the
center of the retina in
an area called fovea
centralis
• capable of responding
to intense light levels
• threshold is about
5x10-1 mL

14. • Cones are better at visualizing small detail than rods
• ability to perceive fine detail is called visual acuity
• cones are better at detecting differences in
brightness levels than rods (contrast perception)
• cones are sensitive to a wide range of wavelengths
but rods are essentially colour blind

15. Rods = Scotopic (night) Vision
• sensitive to light and are used
during dim light situations
• located on the periphery of
the retina
• No rods in fovea; so scotopic
vision is entirely peripheral
vision
• The density of rods is less over
the remainder of the retina
than the density of cones in
fovea.
• threshold for rod vision is
10-6 mL (milliLambert)

16. • Scotopic (rod) vision is
less acute than photopic
(cone) vision
• Rods are most sensitive to
blue-green light –
daylight levels reduce the
sensitivity to low
illumination levels –
hence the need for dark-adaptation
with red
goggles (to filter out blue
green wavelengths)

17. • The dim fluroscopic vision required use of rod
vision, with its poor visual acuity and poor
ability to detect shades of gray (contrast).
• What was needed:
– Image bright enough to allow cone vision
– Without excess radiation exposure

18. Image Intensifier

19. Modern fluoroscopic system components

20. IMAGES ARE VIEWED ON A TV
SCREEN/MONITOR

21. Basic Components of “Imaging Chain”
Fluoro
TUBE
Primary
Radiation
PATIENT
EXIT
Radiation
Image
Intensifier
ABC
Image
Recording
Devices
Fiber Optics
OR
Photospot
CINE
Cassette
VIDICON
Camera Tube
CONTROL
UNIT
TV
LENS
SPLIT

22. Basic Components of “Imaging Chain”
Fluoro
TUBE
Primary
Radiation
PATIENT
EXIT
Radiation
Image
Intensifier
ABC
Image
Recording
Devices
Fiber Optics
OR
Photospot
CINE
Cassette
VIDICON
Camera Tube
CONTROL
UNIT
TV
LENS
SPLIT

23. X-ray tube
• Similar to diagnostic tubes except:
– Designed to operate for longer periods of time at
much lower mA i.e. fluoroscopic range 0.5-5 mA
– tube target must be fixed
– Fluoroscopic tube can operate by foot switch
– Equipped with electrically controlled shutter

24. Fluoroscopy mA
Low, continuous
exposures
0.05 – 5 mA
(usually ave 1 – 2 mA)
Radiographic Exposure
(for cassette spot films)
100 – 200 mA

25. FLUORO TUBES
TUBE ABOVE THE TABLE TUBE UNDER THE TABLE

26. Basic Components of “Imaging Chain”
Fluoro
TUBE
Primary
Radiation
PATIENT
EXIT
Radiation
Image
Intensifier
ABC
Image
Recording
Devices
Fiber Optics
OR
Photospot
CINE
Cassette
VIDICON
Camera Tube
CONTROL
UNIT
TV
LENS
SPLIT

27. Image Intensification Tubes
• Developed in 1948
• Is designed to
amplify the
brightness of an
image
• New II are capable
of increasing image
brightness 500-8000
times

28. Image intensifier - Components
• protective vacuum case
• input window,
• input phosphor
• input photocathode
• electrostatic focussing
lens
• accelerating anode
• output phosphor

29. Vacuum Case
• When the image intensifier
was first introduced, it had
a small input size and a
glass vacuum case.
• Modern image intensifiers
have input field sizes up to
57 cm in diameter with little
image distortion, and the
vacuum cases are usually
made of metal.
• Encased in Lead housing =
2mm Pb

30. Input Screen

31. Input screen
Input screen consists of
four layers:
• The vacuum window
(thin Al window that is
part of the vacuum
bottle)
• A support layer (also
thin Al), curved for
accurate electron
focusing
• The input phosphor
(CsI in thin, needle-like
crystals)
• The photocathode (a
thin layer of antimony
and alkali metals, such
as Sb2S3) that emits
electrons when struck
by visible light

32. 33

33. Cesium Iodide (CsI) Phosphor
on Input Phosphor
• CsI crystals grown linear and
packed closely together
• The column shaped “pipes”
helps to direct the Light
with less blurring
• Converts x-ray photons to
visible light

34. Cesium Iodide (CsI) Phosphor
on Input Phosphor

35. Conventional Input Phosphor

36. Input Screen
Input phosphor and
photocathode are kept in
close contact so that there
is no loss in resolution

37. For undistorted focussing,
all photoelectrons must
travel the same distance.
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.

38. • 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.
• It also gives the image
intensifier better
mechanical strength
under atmospheric
pressure.

39. Thickness of the input phosphor layer
Advantages
• higher x-ray absorption
efficiency  more x-ray
photons can be absorbed
and converted to light
photons in the phosphor
layer.
• requires fewer x-ray
photons to generate the
same amount of light
photons at the image
intensifier output window,
thus reducing patient dose.
Disadvantages
• light photons are scattered
laterally within the
phosphor layer, thus
reducing the spatial
resolution.
• Currently, the thickness of an input phosphor layer is a compromise between
spatial resolution and x-ray absorption efficiency and typically measures between
300 and 450 mm

40. Input phosphor material
• To maximize the conversion efficiency from x ray
photons to photoelectrons, the mass attenuation
coefficient of the input phosphor material should
be matched with the spectrum of the x rays
emerging from the patient.
• Ideally, the light spectrum of the input phosphor
should also match the sensitivity profile of the
photocathode.

41. Input phosphor material
• The initial phosphor used in early image
intensifiers was zinc-cadmium sulfide (ZnCdS),
• The current phosphor of choice is cesium
iodide (CsI:Na).

42. Why CsI:Na??

43. 1. The mass attenuation peaks in CsI:Na, compared with those of
ZnCdS,are more closely matched to the transmitted xray spectrum,
thus increasing the absorption of the transmitted x-ray photons.
Increasing the absorption efficiency decreases the patient’s dose.

44. Why CsI:Na??
2. It has a high atomic number from Cs (Z = 55)
and I (Z = 53),which also results in higher x-ray
absorption.
• CsI screens absorbs 2/3 rd of the incident
beam as compared to less than 1/3 rd for zinc
cadmium sulfide.

45. Why CsI:Na??
3. K-edge energies for CsI is in the diagnsotic
range 36keV for Cs and 33 keV for I

46. Why CsI:Na??
4. CsI:Na can be
evaporated onto
the substrate in
crystal needle
form.
These needles act like
light pipes, in a
manner similar to the
light propagation in a
fiber-optic faceplate,
thus reducing cross
scatter inside the
phosphor screen and
yielding better spatial
resolution.

47. Photocathode material
• The photocathode layer is made of antimony
cesium (SbCs3).
• To maximize the conversion efficiency from
light photon to photoelectron, light emitted
from the input phosphor should match the
sensitivity spectrum of the photocathode.

48. CsI:Na has a better spectral match to the antimony-cesium compound
(SbCs3).

49. Image Intensifier
• The input phosphor
converts x-ray to light
• Photocathode turns
light into electrons
(called photoemission)
• Now we have electrons
that need to get to the
anode……….. this is
done by the
electrostatic lenses

50. Electrostatic Focussing Lens
• Photoelectrons are
accelerated from the
photocathode to the output
phosphor by the anode
• These are positively
charged electrodes that are
placed inside the glass
envelope.
• These lenses help in
preventing the diverging
of the x-ray beams as they
travel from cathode to
anode.
• Electron focussing inverts
and reverse the image ,this
is called as point inversion,
because all electrons pass
through a common focal
point .

51. Accelerating Anode
• Located in the neck of
the II tube
• The potential applied
at the anode is +25 to
+35 kv more as
compared to the
cathode.
• This results in gain of
kinetic energy by the
electrons .

52. When the resulting high energy electrons strike
the output phosphor produces more number of
light photons and hence there is increase in the
brightness of the image.

53. Output Phosphor
• Typically is called P20,
• Materials used: ZnS:CdS: Ag
activated
• converts electrons into visible
light
• smaller than the input
phosphors (to 1 inch)
• Crystal size and layer thickness
are reduced to maintain
resolution in minified image.
• photo e- have much higher
energies than when they were
emitted from input screen
• can produce more light photons
than the initial photo e- (increase
app 50 folds)
Electrons
Light
photons

54. Output phosphor
• Anode is a very thin (~0.2 m) coating of aluminum on the
vacuum side of the phosphor

55. Output phosphor
• On the vacuum side of the
output phosphor surface,
the anode of the electron
optics system has a thin
aluminum film coating.
• This aluminum film allows
electrons to pass through,
but it is opaque to light
photons generated on the
fluorescent screen.
• It stops these photons
from being scattered back
into the image intensifier
and exposing the
photocathode. (prevents
retrograde)
• The film also serves as a
reflector to increase the
output luminance.
Electrons Light
photons

56. WE WILL HAVE TO DRAW THIS!!!
58

57. IMAGE INTENSIFIER PERFORMANCE

58. Image Intensifier Performance
Brightness Gain Conversion Factor

59. Brightness gain or Intensification factor
• Definition:
– output luminance level (or brightness) of an image intensifier divided
by the output luminance level of a Patterson B-2 fluoroscopic screen
when both are exposed to the same quantity of radiation.
Brightness Gain =
푰풏풕풆풏풔풊풇풊풆풓 풍풖풎풊풏풂풏풄풆
푷풂풕풕풆풓풔풐풏 푩−ퟐ 풍풖풎풊풏풂풏풄풆
• The Patterson B-2 fluoroscopic screen was typically used for fluoroscopy before
image intensifiers intensifiers were introduced.
• Drawback: lack of reproducibility
• Typical values: a few thousand to >10,000 for modern image
intensifiers

60. Conversion Factor (ICRU)
• Definition:
– the output luminance level of an image intensifier divided by its
entrance exposure rate.
• It is a measure of how efficiently an image intensifier
converts the x rays to light.
Conversion Factor =
푳풖풎풊풏풂풏풄풆 풐풇 풐풖풕풑풖풕 풑풉풐풔풑풉풐풓
푰풏풑풖풕 푬풙풑풐풖풓풆 푹풂풕풆
=
푐푑/푚2
푚푅/푠푒푐

61. Conversion Factor
• With age  Brightness Gain 
Patient Dose 
• The higher the conversion factor, the more
efficient the image intensifier.

62. Minification gain
• Definition:
– the ratio of input area to the output area of the image
intensifier.
Minification Gain =
퐴푟푒푎 표푓 푖푛푝푢푡 푠푐푟푒푒푛
퐴푟푒푎 표푓 표푢푡푝푢푡 푠푐푟푒푒푛
=
푑2
푖
푑표
2
• A smaller output window size will just compress more
photons into a smaller area, producing a smaller but
brighter image.
• Because the number of photoelectrons leaving the
photocathode is equal to the number striking the output
phosphor, the number of photoelectrons per unit area
at the output phosphor increases.

63. Minification gain
• The minification gain does not improve the
statistical quality of the fluoroscopic image.
• It will not change the contrast of the image,
but it will make the image appear brighter.

64. Flux gain
• Definition:
– The ratio of the number of light photons striking
the output screen to the ratio of the number of x-ray
photons striking the input screen.
• The flux gain results from the acceleration of
photoelectrons to a higher energy so that
they generate more fluorescent photons at
the output phosphor.

65. FLUX GAIN
• 1000 light photons at the
photocathode from 1 x-ray
photon
• photocathode decreased
the number of electrons
so that they could fit
through the anode
• Output phosphor = 3000
light photons (3 X more
than at the input
phosphor!)
• This increase is called the
flux gain
• Flux gain is almost
always 50

66. Brightness Gain
and Conversion Factor
• The brightness gain comes from two sources
that are completely unrelated:
– the minification gain
– the flux gain.
• Brightness Gain = 푀푖푛푖푓푖푐푎푡푖표푛 퐺푎푖푛 × 퐹푙푢푥 퐺푎푖푛

67. IMAGING CHARACTERISTICS

68. 1. Contrast
The contrast ratio of an image intensifier is defined as
• the brightness ratio of the periphery to the center of
the output window when the center portion of an
image intensifier entrance is totally blocked by a lead
disk.
• The contrast ratio is typically specified in two ways:
large area and small detail area.

69. • The large area or 10% area contrast ratio is
measured by putting a lead disk, which has a
surface area equal to 10% of the useful entrance
area of the image intensifier, at the center of the
input surface of the image intensifier.
• The small detail, or 10-mm area contrast, is
measured by putting a 10-mm lead disk at the
center of the input surface of the image
intensifier.

70. • Measurements are made at 50 kVp without
additional filtration.
• Currently, new image intensifiers have
contrast ratios in the range of
– 10:1 to 30:1 for the 10% area contrast ratios.
– 15:1 to 35:1 for the 10-mm area contrast ratios.

71. Two factors diminish contrast
First:
• input screen does not absorb all the incident
photons
• some of the transmitted ones can be
absorbed by the output phosphor
• photons increase the brightness at the output
phosphor but does not contribute to image
formation

72. Two factors diminish contrast
Second:
• light flow from the output phosphor to the
photocathode (retrograde)
• light flow generates more photo e- and also
increases the brightness but does not
contribute to the real image
• Contrast deteriorate as intensifier ages.
• Both mechanisms result in a brighter fog, thus
reducing contrast

73. 2. Sideways Light Scattering
Unsharpness due to the lateral diffusion of light
after being produced by the input phosphor
before reaching the photo cathode.
So keep both as close as possible

74. 3. Geometric unsharpness
Can be avoided by placing the image intensifier
as close to the patient body as possible.

75. 4. Lag
• Persistence of
luminescence after x-ray
stimulation has been
terminated.
• Lag degrades the
temporal resolution of
the dynamic image.
• usually of short duration-older
tubes(30-40 ms)
with CsI tubes-1ms.

76. • lag in modern fluoroscopic systems is more
likely caused by the closed-circuit television
system than the image intensifier.
example:
ZnS:CdS:Ag fluorescent screen 1% of the
image luminance remains after 0.1 s and
about 0.1% remains after 0.5 s

77. Artifacts
• Image intensifiers come with a variety of
imperfections or artifacts
– pincushion distortion
– S distortion
– vignetting
– veiling glare
• Some of these artifacts are caused by improper
calibration and can usually be corrected.

78. Pincushion Distortion
• Pincushion distortion is a
geometric, nonlinear
magnification across the
image.
• Appearance of straight
lines curving towards the
edges
• The distortion is easily
visualized by imaging a
rectangular grid with the
fluoroscope.

79. S Distortion
• Electrons within the image
intensifier move in paths
along designated lines of
flux.
• External electromagnetic
sources affect electron
paths at the periphery of
the image intensifier more,
than those nearer the
center.
• This characteristic causes
the image in a fluoroscopic
system to distort with an S
shape

80. • Larger image intensifiers
are more sensitive to the
electromagnetic fields
that cause this distortion.
• Manufacturers include a
highly conductive mu-metal
shield that lines
the case in which the
vacuum bottle is
positioned to reduce the
effect of S distortion.

81. Vignetting
• A fall-off in brightness
at the periphery of an
image is called
vignetting.
• As a result, the center
of an image intensifier
has better resolution,
increased brightness,
and less distortion.

82. Veiling Glare
• Scattering of light and the defocusing of
photoelectrons within the image intensifier are
called veiling glare.
• Veiling glare degrades object contrast at the output
phosphor of the image intensifier.
• X-ray, electron, and light scatter all contribute to
veiling glare.

83. MULTI FIELD IMAGE INTENSIFIERS
• In this type either
the central part
of the image can
be viewed or the
whole image.
• This can be
brought about by
increasing the
charge of the
focusing lens.

84. Magnification Tubes
• Greater voltage to electrostatic lenses
– Increases acceleration of electrons
– Shifts focal point away from anode
• Dual focus
– 23/15 cm 9/6 inches
• Tri focus
– 12/9/6 inches

85. Intensifier Format and Modes
Note focal point
moves farther from
output in mag
mode

87. MAG MODE VS PT DOSE
• MAG USED TO ENLARGE
SMALL STRUCTURE OR TO
PENETRATE THROUGH
LARGER PARTS
• PATIENT DOSE IS
INCREASED IN THE MAG
MODE
DEPENDANT ON SIZE OF INPUT PHOSPHOR

88. MAG MODE VS PT DOSE
% mag =
퐼푃 표푙푑 푠푖푧푒
퐼푃 푛푒푤 푠푖푧푒
Pt dose =
퐼푃 표푙푑 푠푖푧푒2
퐼푃 푛푒푤 푠푖푧푒2

89. Viewing the Fluroscopic Image

90. Basic “Imaging Chain”

91. Basic Components of “Imaging Chain”
Fluoro
TUBE
Primary
Radiation
PATIENT
EXIT
Radiation
Image
Intensifier
ABC
Image
Recording
Devices
Fiber Optics
OR
Photospot
CINE
Cassette
VIDICON
Camera Tube
CONTROL
UNIT
TV
LENS
SPLIT

92. We have stopped at the output phosphor

93. Viewing Fluoroscopic Images

94. Fluoroscopic Image monitoring
• Optical Coupling:
The light output from the II needs to directed to a
video camera and then to a television screen.
There are two ways of coupling the output window
to the input of a video camera;
- Lens coupling
- Fibre optic coupling

95. Lens coupling
- uses a pair of optical lens and
a “beam splitting mirror” (to
enable other accessories like
spot film camera or cine
camera) and an aperture.
- loss of image brightness due
to lens system and beam
splitting.
- Aperture controls the
amount of light passes through
to the TV camera.

96. Lens coupling
- A wide aperture will allow
most light on to the video
camera, thus reducing
patient dose but the image
will have high noise.
- A narrow aperture will
allow only a fraction of the
light on to the video camera,
thus increasing patient dose
but reducing the image
noise.

97. Fibre optic coupling
• Uses fibre optic cables thus reducing light loss
from the II to video camera
• Prevents any additional accessories being
used.
• Preserves better spatial resolution

98. What’s our final aim?
TV
image

99. TV Image
• Composed of discrete horizontal scan
lines
• No of lines independent of monitor size
• broadcast TV standard
– 525 lines
• High definition
– 1025 lines
– becoming more popular
– more expensive

100. Viewing system
• It is development of the image from output screen to
the viewer these include video, cine and spot film
systems
• Most commonly used is video as closed circuit
through cables to avoid broadcast interference

101. TV Camera
• Converts light to coded
electrical signal
• Camera Tube
– vidicon
• cheapest / compact / laggy
– plumbicon
• enhanced vidicon / less lag
– CCD
• Semiconductor
• not a tube
TV
electrical
signal
Camera
Light

102. Vidicon TV Pick-up Tube

103. Vidicon (tube) TV Camera

104. Video camera Tubes
• Video camera;
– is a cylindrical glass tube
of 15 mm diameter and
25 cm long
– contains a target
assembly, a cathode &
electron gun,
electrostatic grids and
electromagnetic coils for
steering and focusing of
electron beams

105. Cathode
• Is an electron gun which
emits electrons by heat
(thermoionical) and shaped
by the grid
• Electron accelerated toward
the target
• Focusing coil bring the
electron to a point to
maintain resolution
• Pair of deflecting coils serve
to cause the electron beam
to scan the target in a path
as a raster pattern

106. Vidicon Target Assembly
The target assembly contains 3 layers - the face plate, signal plate and photo-conductive
layer.
Vidicon tubes use antimony trisulfide (Sb2S3) (photo-conductive) while PlumbiconTM use lead
oxide (PbO) in mica matrix
The globules are approx 0.025 mm in diameter
Each globule capable of absorbing light photons and releasing electrons equivalent to
intensity of the absorbed light

107. Vidicon Target Assembly

108. 1980
CCD REPLACED THE CAMERA IN
VIDEO SYSTEM
Video Camera Charge Coupled Device

109. Semiconductor Video Cameras
• These cameras are based on
the charged coupled device
(CCD) technology
• CCDs consist of a
semiconductor chip which is
sensitive to light – not
vacuum tubes
• The chip contains many
thousands of electronic
sensors which react to light
and generate a signal that
varies depending on the
amount of light each
receives.
• When the light photon
strikes the photoelectric
cathode of CCD electrons
are released

110. CCDs have been developed primarily for the domestic
video camera market
They are:
• Compact
• lightweight
• possess improved camera qualities compared to
photoconductive cameras.

111. CCD SYSTEM ADVANTAGE OVER
CAMERA SYSTEM
• LOW LEVEL OF ELECTRONIC NOISE
• HIGH SPATIAL RESOLUTION
• NO LAG OR BLOOMING
• NO MAINTENANCE
• UNLIMITED LIFE
• UNAFFECTED BY MAGNETIC FIELD
• LINEAR RESPONSE
• LOWER DOSE
• A scanning electron beam in an evacuated environment
is not required,
The image is read by electronic means.

112. Basic Components of old fluoroscopic
“Imaging Chain”
Fluoro
TUBE
Primary
Radiation
PATIENT
EXIT
Radiation
Image
Intensifier
ABC
Image
Recording
Devices
Fiber Optics
OR
Photospot
CINE
Cassette
VIDICON
Camera Tube
CONTROL
UNIT
TV
LENS
SPLIT

113. Basic Componets of “NEW DIGITAL”
Fluoro“Imaging Chain”
Fluoro
TUBE
Primary
Radiation
PATIENT
EXIT
Radiation
Image
Intensifier
ABC CCD
Analog to
Digital
Converter
ADC
TV

114. I.I. AND CCD
LIGHT
SIGNAL

115. FUTURE – CCD REPLACED BY
SILICON PIXEL DETECTORS

117. Video Signal
• Voltage level indicates brightness
• Blanking during non-video
– retrace

118. Video Monitor
• A video monitor is used to display
images acquired by the video
camera of a fluoroscopy system.
- The image is described as a
“softcopy”
- The video monitor is similar to
an oscilloscope, ie, a scanning of
the electron beam but in a raster
fashion.

119. Video Monitor
• It is an evacuated glass tube
which contains an electron
gun, a number of focussing &
steering electrodes and a
phosphor screen.
• The electron gun forms the
cathode and the electrons are
accelerated by a high voltage
towards the phosphor screen.
• The impact of the electrons on
the screen causes it to
fluoresce and the resulting
light forms the image.

120. Video Monitor
• Video monitors generally have two
viewer adjustable controls;
contrast - controlled by the
number of electrons in the
electron beam
brightness - controlled by the
acceleration of the electrons in
the tube
These have a strong influence on
the quality of displayed images.

121. CRT

122. Television Scanning
• beam scanning for standard TV
– 525 lines in total image
– 30 images (frames) scanned per second
• Oscillators
– Vertical
– Horizontal
Vertical
(Slower)
Horizontal
(Faster)

123. • Eye can detect flashes – upto 50 pulses per
second
• TV monitor only displays – 30 frames per
second
FLICKER

124. Video Field Interlacing

125. Progressive Scanning
• progressive scanning
– used on newer systems, lines scanned in order
– no interlacing

126. Synchronization (Sync Signals)

127. Synchronization
• TV Camera & Monitor must be
synchronized
– In phase with each other
• Camera Control Unit adds special sync
pulses sent at end of each horizontal line
& vertical field – Horizontal and Vertical
Syncronization Pulses
• Generated during retrace
– horizontal retrace
• beam returned to left side of screen
– vertical retrace
• beam returned to the top of screen
– Turns off video during retrace
Horizontal Retrace
Vertical Retrace

128. Vertical Resolution
• proportional to number of vertical
scan lines
• theoretic maximum
– half number of visible scan lines
– black lines alternate with white
• max. line pairs = video lines / 2

129. Vertical Resolution
• actual limit lower than theoretical
~ 10% of lines occur during retrace
• returning beam from bottom to top of image
– scan lines may not perfectly synchronize to
high resolution object
• typically 525 lines yield ~ 370 lines (185
line pairs)

130. Bandwidth (Bandpass)
• Varying frequency  varying video signal
• The frequency range that the electronic
components of the video system must be
designed to transmit.
•  sound (16Hz to 30,000Hz)
• no sharp frequency cutoff
– not all frequencies transmitted or displayed with
same quality
– Gradual degrading

131. Bandwidth (Bandpass)
• What it means for video
– camera
• how fast camera can turn electrical signal on &
off
– monitor
• how rapid a change in incoming electrical
signal monitor can display

132. Horizontal Resolution
Bandwidth = [Horizontal Resolution] X [Video Lines] X [Frame Rate]
cycles
------------
scan line
lines
---------
frame
frames
---------
sec
cycles
----------
sec
= X X
Bandwidth
[Horizontal Resolution] = -------------------------------------------
[Video Lines] X [Frame Rate]
Frequency of
video signal
525 30
$$$$

133. Resolution Summary
• Vertical resolution depends on
Number of scan lines
• Horizontal resolution depends on
– bandwidth
– number of scan lines
– frame rate
• Systems designed to yield approx. equal
horizontal & vertical resolution
~ 4.5 MHz typical bandwidth for 525 line system

134. Television Image Quality
• Depends upon:
– Resolution
– Contrast
– Lag

135. (1)Fluoro Resolution On TV Depends Upon
• TV resolution
– total lines
– Frame rate
– bandwidth
• Size of imaged field

136. Overall TV Resolution (Example)
• typical 9” image tube
• typical 185 line pairs for 525 line TV system
185 line pairs 1 inch
------------------- X -------------- = .8 line pair / mm
9 inches 25.4 mm
• Higher number is better

137. Conventional TV Systems
• Fluoro Resolution
– 9 inch mode => 0.8 line pairs / mm
– 6 inch mode => 1.2 line pairs / mm
– 4 inch mode => 1.6 line pairs / mm

138. (2) Overall System Contrast
• Vidicon reduces contrast by about 20%
• monitor enhances contrast by up to 2X
– adjustable by operator
– brightness & contrast controls
• Plumbicon does not cause any decrease in
image contrast.

139. ABC FEEDBACK LOOP
Generator
Exposure
Control
KVp
mA
Automatic
Brightness
Control Sensor
Light
Intensity

140. ABC
• When the ABC mode is selected, the ABC
circuitry controls the X-ray intensity measured at
the Image-Intensifier so that a proper image can
be displayed on the monitor.
• ABC mode was developed to provide a
consistent image quality during dynamic
imaging
• The ABC compensates brightness loss caused by
decreased I-I radiation reception by generating
more X-rays (increasing mA) and/or producing
more penetrating X-rays (increasing kVp).
• Conversely, when the image is too bright, the
ABC compensates by reducing mA and
decreasing kVp.

141. • Brightness Control: Generator feedback loop
– kVp variable
– mA variable/kV override
– kV+mA variable
– Pulse width variable (cine and pulsed fluoro)

142. The top curve increases mA more rapidly than kV as a function of patient thickness, and
preserves subject contrast at the expense of higher dose.
The bottom curve increases kV more rapidly than mA with increasing patient thickness,
and results in lower dose, but lower contrast as well.

143. Recording the Fluroscopic Image

144. Types
• Direct film recording
• Indirect recording
• Recording motion.

145. Direct Film Recording

146. Spot Film Devices

147. • 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 (Fig 1).
• One major limitation is the range of film sizes
available for spot film imaging.
• Spot film devices usually allow more than one
image to be obtained on a single film.
• Slightly more magnification

148. • Source to skin distance is shorter – skin
entrance exposure higher
• The field size in spot film imaging is generally
smaller than that used in general radiography.
- reduces scatter - tends to reduce dose.
• Grids used in fluoroscopy generally have a
lower grid ratio and therefore a smaller Bucky
factor, which also leads to lower dose.

149. • One of the major shortcomings of
conventional spot film devices is the delay
involved in moving the cassette into position.
• In gastrointestinal imaging, this delay can be
overcome by using photofluorography.
• In vascular imaging, more rapid film
movement is achieved with automatic film
changers.

150. Automatic Film Changers

151. Automatic Film Changers
• used in vascular imaging
• The number of films and filming rates must
be preprogrammed for proper operation.
• limits the automatic changer to one film size,
usually 35 x 35 cm.
• The typical film changer holds up to 30 films in
the receiving magazine.

152. Indirect Recording

153. Photofluorography

154. Photofluorography
• More rapid filming - as many as 200 films
• The film is cheaper and needs less storage space
than radiographic film. There is less delay
between fluoroscopy and filming.
• Higher frame rates and longer runs are possible.
• It is possible to view the images on the TV
monitor as they are being produced. Doses can
be reduced.
• The disadvantages are poorer resolution and
viewing a less than full-size image.

155. Digital Fluorography
• Digital charge coupled device (CCD) TV cameras are
rapidly replacing conventional TV cameras in
fluoroscopic systems.
• 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.
• Digital CCD cameras offer a compromise between
radiation dose and image quality, with the added
advantages of digital image manipulation and storage.

156. Recording Motion
Cine Fluorography
Videotape Recording
Magnetic Disc Recorders
Optical Discs

157. Cine Fluorography