A fluoroscope uses x-rays and a fluorescent screen to enable direct observation of internal organs. It consists of an x-ray tube, table, and image intensifier. The image intensifier converts x-rays into visible light images and amplifies them for viewing. It works by accelerating photoelectrons emitted from a photocathode onto a phosphor screen, producing light photons and gaining brightness. Newer generations of image intensifiers use additional electron multiplication for higher sensitivity. Fluoroscopy provides real-time moving images for procedures while fluorography captures still diagnostic images.
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FLUOROSCOPIC IMAGING.ppt
1.
2. Fluoroscope
– – A fluorescent screen for observing the
shadows cast by objects placed in the path of the
x- -rays
– – An x- -ray machine that combines an x- -ray
source and a fluorescent screen to enable direct
observation of internal organs
-- Examination of an organ or body structure
using a fluoroscope is FLUOROSCOPY
3. FLUOROSCOPY
Refers to use of low (i.e. 0.5 to 2
mA), continuous x-ray exposures.
The resultant images have a relatively
low signal-to-noise ratio (SNR), because of
the low XRT current, but are of sufficient
quality for applications such as patient
positioning or monitoring catheter
placement.
4. FLUOROGRAPHY
Refers to the use of relatively intense
(e.g.50 to 500 mA or greater), pulsed
exposures.
The pulses are typically of short
duration and are applied at, for example,
1 to 12 pulses per second. The resultant
images have a relatively high SNR and are
used for diagnostic purposes.
5. HISTORY
Fluoroscopy was done for the first time
by Dr.W.C. Roentgen when he first
discovered the new kind of rays in 1895
Thomas Edison is credited with the
designing and producing of the first
commercially available fluoroscope
1950’s ----- introduction of Image
Intensifiers
9. IMAGE INTENSIFIER TUBE
PARTS
INPUT PHOSPHUR AND THE PHOTO CATHODE
ELECTROSTATIC FOCUSING LENS
ACCELERATING ANODE
OUTPUT PHOSPHUR
10.
11. INPUT PHOSPHUR
CESIUM IODIDE
VERTICAL ORIENTATION OF CsI CRYSTALS
Vapour deposited on thin aluminium substrate --
0.5 micrometre thick
CsI grow as tiny needles 150 to 400 micrometre
high and 5 micrometer in diameter
Grow perpendicular to the substrate
Prevent lateral diffusion of light
13. GREATER PACKING DENSITY
CsI HAS 3 TIMES MORE PACKING
DENSITY WHEN COMPARED TO Zn
Cd sulphide
REDUCE PHOSPHUR LAYER
THICKNESS
IMPROVE RESOLUTION OF THE
IMAGE
THE RESOLUTION OF CsI IMAGE
INTENSIFIER IS ABOUT 4 lp/mm
14. FAVOURABLE ATOMIC NUMBER
ATOMIC NUMBER OF CESIUM IS 55
K EDGE OF Cs IS 36keV AND THAT OF IODIDE IS
33.2keV
CLOSE TO THE MEAN ENERGY OF X RAY BEAM
USED IN FLUOROSCOPY i.e 30 to 40 keV
FOR MAXIMUM PHOTOELECTRIC ABSORPTION
THE K EDGE SHOULD BE AS CLOSE TO THE KV
OF THE X RAY BEAM AS POSSIBLE
16. LIGHT FROM INPUT PHOSPHUR >>>>
PHOTOCATHODE >>>>>
PHOTOELECTRONS ARE EMITTED
NO: OF ELECTRONS EMITTED IS
PROPORTIONAL TO BRIGHTNESS OF
SCREEN
17.
18. ACCELERATING ANODE
HAS POSITIVE POTENTIAL OF 25 TO 35 kV
RELATIVE TO PHOTOCATHODE
ACCELERATE ELECTRONS
BECAUSE OF THE POTENTIAL
DIFFERENCE THE ELECTRONS ARE
ACCELERATED TO VERY HIGH VELOCITY
19. ELECTROSTATIC FOCUSING
LENS
SERIES OF POSITIVELY CHARGED
ELECTRODES
JOB- TO FOCUS BEAM OF ELECTRONS
POINT INVERSION- ALL ELECTRONS
PASS THROUGH A COMMON FOCAL
POINT ON THEIR PATHWAY
20. OUTPUT PHOSPHUR
SILVER ACTIVATED ZINC CADMIUM SULPHIDE
HAS DIAMETER OF ½ TO 1 INCH
SINCE ELECTRONS ARE ACCELERATED >>>
MORE LIGHT PHOTONS ARE EMITTED FOR
EVERY ELECTRON.
NO: OF LIGHT PHOTONS ARE INCREASED 50
FOLD
24. EACH POINT IN INPUT PHOSPHUR IS
FOCUSED ON A SPECIFIC POINT ON THE
OUTPUT PHOSPHUR
FOR UNDISTORTED FOCUSSING OF THE
IMAGE
25. INPUT PHOSPHUR IS CURVED SO THAT
ELECTRONS EMITTED FROM THE
PERIPHERY ALSO TRAVELS THE SAME
DISTANCE
OUTPUT IMAGE IS SMALLER IN SIZE
>>>> MORE BRIGHTNESS
26. THIN LAYER OF ALUMINIUM ON THE INSIDE
SURFACE OF OUTPUT PHOSPHUR
JOB--- TO PREVENT RETROGRADE
PASSAGE OF LIGHT FROM THE OUT PUT
PHOSPHUR TO PHOTOCATHODE
28. MINIFICATION GAIN
PRICE PAID FOR INCREASED
BRIGHTNESS IS THAT THE IMAGE IS
CORRESPONDINGLY SMALLER
THE QUANTITY OF THIS GAIN DEPENDS
ON DIAMETER OF THE INPUT AND
OUTPUT SCREENS
29. THE DIAMETER OF THE OUTPUT SCREEN
IS ABOUT ONE FIFTH AS THAT OF THE
INPUT SCREEN
THE PHOTONS THAT MAKE UP THE IMAGE
ON BOTH SCREENS ARE THE SAME
THE PHOTONS ARE COMPRESSED
TOGETHER ON A SMALLER SCREEN>>>>
BRIGHTER IMAGE
32. FLUX GAIN/ ELECTRON GAIN
RATIO OF NUMBER OF LIGHT PHOTONS AT
THE OUTPUT PHOSPHUR TO THE NUMBER
OF X RAY PHOTONS AT THE INPUT
PHOSPHUR
INCREASAE BRIGHTNESS BY A FACTOR
OF 50
33. BRIGHTNESS GAIN
THE TOTAL BRIGHTNESS GAIN OF AN
IMAGE =
MINIFICATION GAIN X FLUX GAIN
TENDS TO DETERIORATE AS THE IMAGE
INTENSIFIER AGES
THEN THE PATIENT DOSE WILL BE
HIGHER
DETERIORATON AT THE RATE OF 10 %
PER YEAR
34. CONVERSION FACTOR
RATIO OF THE LUMINANCE OF THE OUT
PUT PHOSPHUR TO THE INPUT XRAY
EXPOSURE RATE
LUMINANCE IS MEASURED IN candelas
{cd}
CONVERSION FACTOR =
37. 1
THE INPUT PHOSPHUR DOES NOT
ABSORB ALL THE INCIDENT PHOTONS
SOME OF THE TRANSMITTED ONES CAN
BE ABSORBED BY THE OUPUT
PHOSPHUR
38. THESE PHOTONS INCREASE THE
BRIGHTNESS AT THE OUTPUT PHOSPHUR
BUT DOESN’T CONTRIBUTE TO IMAGE
FORMATION
THESE PHOTONS WILL PRODUCE A
BACKGROUND OF FOG AND WILL REDUCE
THE CONTRAST
39. RETROGRADE FLOW OF LIGHT PHOTONS
FROM THE OUTPUT PHOSPHUR
MOST OF THESE ARE BLOCKED BY THE
THIN ALUMINIUM LAYER
2
40. THESE PHOTONS REACH THE
PHOTOCATHODE WHICH THEN EMITS
PHOTOELECTRONS WHICH AGAIN COME
AND STRIKE THE OUTPUT PHOSPHUR
THEY INCREASE THE BRIGHTNNESS BUT
PRODUCE FOG SINCE THE DISTRIBUTION
OF THE ELECTRONS BEARS NO
RELATIONSHIP TO THE PRINCIPAL IMAGE
42. LAG
PERSISTENCE OF LUMINESCENCE AFTER
TERMINATION OF OF X RAY STIMULATION
PERSISTENCE OF IMAGES
USUALLY OF SHORT DURATION
DOESN’T INTERFERE WITH THE ACQUISITION
OF IMAGES
43. Eg :
FOR ZINC CADMIUM SULPHIDE 1% OF
IMAGE RETAINS AFTER 0.1 sec AND O.1%
IMAGE AFTER 0.5 sec
FOR CsI THE LAG TIMES ARE AROUND 1
ms
44. IMAGE DISTORTION
PIN CUSHION EFFECT
APPEARANCE OF STRAIGHT LINES
CURVING TOWARDS THE EDGES
THE ELECTRONS IN THE PERIPHERY OF
THE BEAM FLARE OUT FROM THE IDEAL
COURSE
THE ELECTRIC FIELD CAN ACCURATELY
CONTROL THE ELECTRONS IN THE
CENTRE OF THE IMAGE BUT NOT THOSE
IN THE PERIPHERY
45. EFFECT
FLARING OUT OF THE ELECTRONS
CAUSE UNEQUAL MAGNIFICATION >>>>
PERIPHERAL DISTORTION
EFFECT IS MORE WITH LARGE
INTENSIFIERS
46.
47. VIGNETTING
FALL OFF IN BRIGHTNESS AT THE
PERIPHERY OF IMAGE
UNEQUAL MAGNIFICATION PRODUCE
UNEQUAL ILLUMINATION
THE CENTER OF THE OUTPUT SCREEN IS
BRIGHTER THAN THE PERIPHERY
48. PERIPHERAL IMAGE DISPLAYED OVER A LARGE
AREA OF THE OUT PUT SCREEN
BRIGHTNESS GAIN FROM MINIFICATION IS LESS
THAN AT THE CENTER
50. MULTIPLE FIELD IMAGE
INTENSIFIERS
ALWAYS BUILT-IN IN DIGITAL UNITS
ALLOW FOCAL POINT CHANGE TO
REDUCE FIELD OF VIEW AND MAGNIFY
IMAGE
DONE BY CHANGING THE VOLTAGE OF
THE ELECTROSTSATIC FOCUSING LENS
51. MULTIFIELD IMAGE INTENSIFIERS
SMALLER DIMENSIONS – VOLTAGE OF
THE FOCUSING LENS IS INCREASED
ELECTRON FOCAL SPOT MOVES AWAY
FROM THE OUT PUT SCREEN
AS THE ELECTRONS CROSS THEY WILL
DIVERGE---- RESULTS IN MAGNIFIED
IMAGE
52. ONLY THE ELCTRONS FROM THE CENTER
OF THE INPUT WILL STRIKE THE OUTPUT
SPATIAL RESOLUTION IS BETTER
LOW NOISE
HIGH CONTRAST RESOLUTION
54. SEVERAL MODES 4.5” , 6” , 9”
LARGE ANATOMICAL AREAS --- 9”
WE REDUCE THE VOLTAGE OF THE FOCUSING
LENS
THE ELECTRONS FOCUS OR CROSS OVER AT A
POINT CLOSE TO THE OUTPUT PHOSPHUR
FINAL IMAGE IS SMALLER
55. MULTIFIELD IMAGE
INTENSIFIERS
NO CHANGE IN THE PHYSICAL SIZE OF THE
INPUT AND OUT PUT SCREENS
CHANGE IS ONLY IN THE SIZE OF THE OUTPUT
IMAGE
DISADV: AS MAGNIFICATION THE
BRIGHTNESS
TO COMPENSATE , HAVE TO INCREASE mA
INCREASE PATIENT DOSE
56. 1st generation
Utilize only a single potential difference to
accelerate electrons from the cathode to the
anode (screen). Focusing is achieved by two
methods:
by placing the screen in close proximity to the
photocathode (proximity diode)
by using an electron lens to focus electrons
originating from the photocathode onto the screen
(inverter diode)
57. 2nd generation
The major difference between first and second
generation tubes is the use of electron multipliers
Not only the energy but also the number of
electrons between input and output is significantly
increased.
Multiplication is achieved by use of a device
called PHOTOELECTRON MULTIPLIER TUBES ---
MICRO CHANNEL PLATE DETECTORS
59. PHOTOMULTIPLIER TUBE
A photomultiplier tube is useful for light
detection of very weak signals
These detectors work by amplifying the
electrons generated by a photocathode
exposed to a photon flux.
60. Consists of
A TYPICAL PMT TUBE is a vaccum tube
PHOTOEMISSIVE CATHODE
FOCUSING ELECTRODES
ELECTRON MULTIPLIER
ELECRON COLLECTOR -- ANODE
61. WHEN LIGHT ENTERS PHOTOCATHODE
>>> PHOTOELECTRONS ARE EMITTTED
INTO THE VACCUM
THESE ELECTRONS ARE FOCUSED BY
FOCUSING ELECTRODE TOWARDS THE
ELECTRON MULTIPLIER
CONSISTS OF A SERIES OF METAL
CHANNEL ELECTRODES – DYNODES --
EACH MAINTAINED AT A MORE POSITIVE
POTENTIAL
62. 14 TO 16 DYNODE ELEMENTS IN A PMT TUBE
FOCUSING ELECTRODE DIRECT THE
PHOTOELECTRONS ON TO THE 1ST DYNODE
THIS WILL INVOKE THE RELEASE OF
ADDITIONAL ELECTRONS THAT ARE
ACCELERATED TOWARDS THE NEXT DYNODE
AND SO ON…
SECONDARY EMISSION
THESE ELECTRONS ARE THEN COLLECTED BY
THE ANODE AS AN OUTPUT SIGNAL
63.
64. THE SURFACE COMPOSITION AND THE
GEOMETRY OF THE DYNODES DETERMINE
THEIR ABILITY TO SERVE AS ELECTRON
MULTIPLIERS
GAIN VARIES WITH THE VOLTAGE ACROSS THE
DYNODES AND THEIR TOTAL NUMBER
ELECTRON GAINS OF 10 MILLION ARE POSSIBLE
IF 12 TO 14 DYNODE ELEMENTS ARE EMPLOYED
71. MICROCHANNEL PLATE
CONSISITS OF MILLIONS OF MICRO GLASS
TUBES FUSED IN PARALLEL WITH EACH OTHER
THESE TUBES CONTAIN SECONDARY ELECTRON
EMITTTER ON THEIR INNER WALLS eg: CESIUM
IODODE ; COPPER IODIDE
EACH CHANNEL ACT AS AN INDEPENDENT
ELECTRON MULTIPLIER
72. ELECTRONS GENERATED BY THE PHOTOCATHODE
ARE DRIVEN THROUGH THE CHANNELS BY A
CONSTANT FIELD FROM VOLTAGE 600 TO 900
VOLTS APPLIED TO THE MCP
THE ACHIEVABLE IMAGE RESOLUTION AND
DYNAMIC RANGE ARE LESS WHEN COMPARED TO
1ST GEN. INTENSIFIERS.
BUT LUMINOUS GAIN IS TREMENDOUSLY
INCREASED
76. OPTICAL SYSTEM
USED TO COUPLE XII TO PHOTOGRAPHIC
DEVICES AND / OR A VIDEO CAMERA
TWO METHODS :
LENS COUPLING
FIBRE OPTIC COUPLING
77. LENS COUPLING
USUALLY COMPLEX ARRANGEMENTS OF LENSES
AND PRISMS
LIGHT FROM THE OUTPUT PHOSPHUR IS
COLLECTED BY THE LENS SYSTEM ; CONVERTED
INTO A PARALLEL BEAM AND TRANSMITTED TO
THE LENS SYSTEM OF VIDEO CAMERA FOR
FOCUSSING ONTO ITS TARGET
ADVANTAGE OF LENS COUPLING IS THAT IT
CAN BE USED TO ACCOMMODATE MORE THAN ONE
CAMERA
78. APERTURE OR IRIS : IS USED TO
COLLIMATE THE OPTICAL IMAGE AND
TO CONTROL THE EXPOSURE OF CAMERA
LOW INPUT EXPOSURE – OUTPUT
LUMINANCE LOW – AMOUNT OF LIGHT
AVAILABLE TO THE CAMERA IS LOW –
WIDE APERTURE TO OPTIMISE THE
LIGHT STRIKING THE CAMERA
79. SEMI- TRANSPARENT MIRROR
PLACED BETWEEN THE APERTURE AND THE
CAMERA LENSES
ACTS AS A BEAM SPLITTER WHICH DISTRIBUTES
THE LIGHT FROM THE OUT PUT PHOSPHUR TO A
CINE OR SPOT FILM CAMERA AND A VIDEO
CAMERA SIMULTANEOUSLY
80.
81. FIBRE OPTIC COUPLING
A fibre-optic bundle relays the
light from the output phosphor
directly to the video camera.
Consists of a coherent bundle of
glass fibre light guides; each fibre
around 10 micrometer in diameter
Advantages
a smaller sized coupling system
increased efficiency and improved
image quality relative to lens-based
coupling
84. VIDEO CAMERA TUBES
Translate the output image from an x-ray image
intensifier (XII) into an electronic signal which can
be:
displayed on a video monitor,
recorded by a video tape or disc recorder,
fed to a computer for manipulation, analysis
and storage.
Convert a two-dimensional spatial image
distribution to a one-dimensional temporal, voltage
distribution.
85. TYPES OF VIDEO CAMERA
Two types
PHOTOCONDUCTIVE CAMERAS –
Vaccum tube TV Cameras
SEMI CONDUCTOR VIDEO CAMERAS --
CCD Cameras, CMOS cameras
BOTH PRODUCE VIDEO SIGNAL BUT IN SUBSTANTIALLY
DIFFERENT WAYS
86. CAMERA TUBES
VIDICON– USUALLY EMPLOYED
Good resolution , moderate lag and low image distortion
SEVERAL OTHER TYPES:
PLUMBICON – trade mark of Philips
high performance tube ,very high resolution and low lag.
particularly suited to use with X-ray image intensifiers in
digital subtraction and angiographic applications.
CHALNICON -- trade mark of Toshiba
SATICON -- trade mark of Hitachi
87. CAMERA TUBE
SMALL ELECTRONIC VACCUM TUBE
1 inch in diameter and 6 inches in length
MAINLY 4 PARTS
o CATHODE
o CONTROL GRID
o ANODE
o TARGET ASSEMBLY
ELECTROMAGNETIC FOCUSING COILS
ELECTROSTATIC DEFLECTING COILS
88.
89. VIDICON CAMERA
CATHODE – AT THE OPPOSITE END OF THE
TUBE FROM TARGET
HEATED INDIRECTLY BY INTERNAL ELECTRIC
COILS – ELECTRONS ARE EMITTED ----
THERMIONIC EMISSION
ANODE – EXTENDS ACROSS THE TARGET END
OF THE TUBE AS A THIN WIRE MESH
HAS A POSITIVE POTENTIAL OF OF ABOUT
250 V WITH RESPECT TO THE CATHODE
91. SIGNAL PLATE
LOCATED ON THE INNER SURFACE OF
THE FACE PLATE
THIN TRANSPARENT FILM OF GRAPHITE
POSITIVE POTENTIAL OF 25 V
92. TARGET
THIN FILM OF PHOTOCONDUCTIVE MATERIAL–
ANTIMONY SULPHIDE
ANTIMONY SULPHIDE SUSPENDED AS TINY GLOBULES
IN MICA MATRIX
EACH GLOBULE IS ABOUT 0.001 inch IN DIAMETER
GLOBULES ARE INSULATED FROM ITS NEIGHBOURS
AND FROM THE SIGNAL PLATE BY THE MICA MATRIX
IN PLUMBICON – LEAD MONO OXIDE
93. ELECTRONS EMITTED FROM CATHODE
FORMED INTO A BEAM BY CONTROL GRID
GRID INITIATE ACCELERATION OF THE
ELECTRONS TOWARDS TARGET
ELECTRONS MOVE INTO THE
ELECTROSTATIC FIELD OF THE ANODE
94. DUE TO THE 250 V POTENTIAL DIFFERENCE
THE ELECTRONS ARE ACCELERATED TO VERY
HIGH VELOCITY
THE ANODE WIRE MESH AND THE SIGNAL PLATE
SET UP A DECCELERATING FIELD FOR THE
ELECTRONS
THE ELECTRON BEAM IS DEFLECTED SLIGHTLY
UPWARDS AND VELOCITY DECREASES
95. COMES TO A NEAR STAND STILL AS THEY
REACH THE TARGET
THE DECCELERATING FIELD STRAIGHTENS THE
FINAL PATH OF ELECTRON BEAM SO THAT THEY
STRIKE THE TARGET PERPENDICULARLY
ELECTROMANETIC COILS KEEPS THE BEAM OF
ELECTRONS IN A NARROW BUNDLE
96. THE ELECTRONS PROGRESS IN A SERIES OF
OSCILLATING SPIRALS AND STRIKE THE
TARGET AS A NARROW BEAM
DEFLECTING COILS - 2 PAIRS
VERTICAL – MOVES BEAM UP AND DOWN
HORIZONTAL – MOVES BEAM SIDE TO SIDE
97.
98. FORMATION OF VIDEO SIGNAL
THE FLUOROSCOPIC IMAGE FROM THE XII IS
MADE TO FOCUS ONTO THE TARGET ASSEMBLY
GLOBULE ABSORBS LIGHT >>>>
PHOTOELECTRONS ARE EMITTED >>>>
GLOBULES BECOME POSITIVELY CHARGED
SINCE INSULATED FROM EACH OTHER AND FROM
THE SIGNAL PLATE IT BEHAVES LIKE HALF
OF A TINY CAPACITOR >>>> DRAWS
CURRENT ONTO THE SIGNAL PLATE
THIS CURRENT IS IGNORED… NOT RECORDED
99. VIDEO SIGNAL
THIS CHANGE IS OCCURING OVER THE ENTIRE
TARGET PLATE SURFACE
A BRIGHTER AREA IN THE LIGHT IMAGE EMITS
MORE PHOTOELECTRONS WHEN COMPARED TO A
DIM AREA >>> PRODUCES A STRONGER
CHARGE ON THE TINY CAPACITORS
A MOSAIC OF CHARGED GLOBULES THAT STORE
AN ELECTRICAL IMAGE WHICH IS AN EXACT
REPLICA OF THE LIGHT IMAGE FOCUSED ON TO
THE TARGET
100. ELECTRON BEAM SCAN THE ELECTRONIC IMAGE
STORED ON THE TARGET >>> HOLES
LEFT BY THE EMITTED PHOTOELECTRONS GET
FILLED >>> NEUTRALISE / DISCHARGE
THE TINY GLOBULE CAPACITORS
ELECTRONS IN THE SIGNAL PLATE NO LONGER
HAVE ELECTROSTATIC FORCE TO HOLD THEM ON
TO THE PLATE >>> THEY LEAVE THE
PLATE VIA THE RESISTOR >>>
PRODUCING A CURRENT
101. THIS VOLTAGE WHEN COLLECTED FOR EACH
NEUTRALISED GLOBULE CONSTITUTES A
VIDEO SIGNAL
EACH INSTANT ONLY A DOT IS GETTING
DISCHARGED >>> THEN THE BEAM MOVES
ON TO THE NEXT DOT
SERIES OF VIDEO PULSES >>> EACH PULSE
CORRESPONDS TO EXACT LOCATION ON THE
TARGET
102.
103. TV MONITOR
REASSEMBLING OF VIDEO PULSES BACK TO
LIGHT IMAGE IS DONE BY THE TV MONITOR
MAIN PART IS THE PICTURE TUBE
ELECTRONIC VACCUM TUBE
ELECTRON GUN [ CATHODE + CONTROL GRID]
ANODE– 10, 000 V
FLUORESCENT SCREEN
FOCUSING COILS
DEFLECTING COILS
104. THE VIDEO SIGNAL IS RECEIVED BY THE
CONTROL GRID
THE BRIGHTNESS OF THE INDIVIDUAL DOTS IS
REGULATED BY THE CONTROL GRID
LARGE NUMBER OF ELECTRONS --- BRIGHTER
AREA OF IMAGE
COILS CONTROL THE ELECTRON BEAM IN
EXACT SYNCHRONY WITH THE CAMERA TUBE
105. ELECTRONS STRIKE THE FLUORESCENT SCREEN
>>> EMITS LIGHT PHOTONS >>> VISIBLE
TELEVISION IMAGE
COLOUR MONITOR
3 ELECTRON GUNS
3 FLUOROSCENT MATERIALS
RED BLUE YELLOW
106. TELEVISION IMAGE QUALITY
RESOLUTION : depends on the size of the
input image
525 line TV SYSTEM with total resolution of
185 lp/ mm
LAG : when camera moved rapidly –
‘stickiness of image’ = image blur
Time for the image to build up and decay on
the vidicon target
107. TELEVISION IMAGE
BRIGHTNESS :
AUTOMATIC BRIGHTNESS CONTROL
AUTOMATIC GAIN CONTROL
: VARYING THE GAIN OF
TELEVISION AMPLIFICATION SYSTEM
108. AUTOMATIC BRIGHTNESS CONTROL
An optical sensor - called the ABC sensor is
used in a feedback loop to the x-ray generator to
automatically adjust the radiation exposure in order
to maintain a constant image brightness
This small photodetector senses the output
luminance and its output is used to appropriately
adjust the kVp, the mA or both factors, when the XII
is moved to screen a different part of the body.
109. In fluorography, it can be used to
terminate an exposure pulse and to set an
appropriate kVp and mAs for the next
image.
The ABC sensor is also useful when the
XII field size is changed so that, for
example, the exposure factors can be
increased automatically when a smaller
field size is chosen.
111. SEMICONDUCTOR CAMERAS
CHARGED – COUPLED DEVICES
Small photoelectronic imaging device
(typically 1.5 cm square) made from a crystal
of silicon in which numerous (at least
250,000) individual light-sensitive picture
elements (pixels) have been fabricated.
These pixels are tiny capacitors
Each pixel (less than 0.03 mm in size) is
capable of storing electronic charges created
by the absorption of light
112.
113. Extraction of the locally stored charges from
each pixel, is done by transferring or "coupling"
charges from one pixel to the next by the
controlled collapse and growth of adjacent
storage sites or potential wells
Each well is formed inside the silicon crystal by
the electric field generated by voltages applied
to tiny, semi-transparent metallic electrodes on
the CCD surface--- CLOCKING GATES.
114. An image is projected by a lens on the capacitor array,
causing each capacitor to accumulate an electric
charge proportional to the light intensity at that
location.
Once the array has been exposed to the image, a
control circuit causes each capacitor to transfer its
contents to its neighbour.
The last capacitor in the array dumps its charge into
an amplifier that converts the charge into a voltage
115. The control circuit converts the entire contents
of the array to a varying voltage, which it
samples, digitizes and stores in memory.
Stored images can be transferred to a printer,
storage device or video display.
116.
117. CMOS CAMERAS
COMPLEMENTARY METAL- OXIDE SEMICONDUCTOR
DEVICES
Eg : flat panel detectors
LARGER PIXEL SIZE
ALL CIRCUITARY WITHIN CHIP
CREATES DIGITAL SIGNAL ON THE CHIP
119. TWO METHODS
DIRECT METHODS : USE THE LIGHT IMAGE
FROM THE OUTPUT PHOSPHUR OF THE IMAGE
INTENSIFIER
SPOT FILM RECORDER
CINEFLUOROGRAPHY
INDIRECT METHODS : USE THE ELECTRICAL
SIGNAL FROM THE TV CAMERA
TAPE RECORDER
DIGITAL FLUOROSCOPY
120. SPOT FILM RECORDING
THIS ALLOWS A CONVENTIONAL SCREEN FILM
CASSETTE EXPOSURE IN CONJUNCTION WITH
FLUOROSCOPIC VIEWING
AN X RAY FILM CASSETTE IS INTERPOSED
BETWEEN THE X RAY BEAM AND IMAGE
INTENSIFIER TUBE
CONDUCTED AT ABOUT 80 TO 90 kVp and
1 to 3 mA of TUBE CURRENT
THERE IS A PHOTO TIMER THAT CONTROLS THE
LENGTH OF EXPOSURE
121. DIFFERENCES FROM GENERAL RADIOGRAPHY
LIMITATION IN THE FILM SIZES – USUALLY
USE 10”- 8” FILM
SPOT FILMS ALLOW MORE THAN ONE IMAGE TO
BE OBTAINED ON A SINGLE FILM
SCREEN FILM COMBINATIONS WITH A SPEED OF
AROUND 400 ARE USED
SLIGHTLY MORE MAGNIFICATION OF PATIENTS
FEATURES
122. CINE FLUOROGRAPHY
PROCESS OF RECORDING
FLUOROSCOPIC IMAGES ON A MOVING
FILM
2 FILM SIZES ARE USED , 16 MM AND 35
MM
35 mm USED FOR CARDIAC CINE
FLUOROGRAPHY