x ray fluoroscopy

1. FLUOROSCOPY
DR PRAKHAR SIHARE

2.  Conventional xray radiographs are used for static imaging.
 For dynamic studies or for real time imaging of the anatomical structures
we need to use the fluoroscopy.
 It is based on the principle that Xrays are able to produce fluorescence.

3. Conventional Fluoroscopy or first
generation fluoroscopy
 Consists of an Xray tube
Xray table
Fluoroscopic screen
 Sheet of Lead glass covers the screen – can be read directly.
 Carried out in a dark room due to faint fluorescence.
 Dark adaptation by wearing red goggles is required 20-30 mins prior.
• Copper activated zinc sulphide used in screen.
• Emits light in yellow green spectrum, thus the name
green screen.

5.  The results obtained from these conventional systems were of low quality
because of :
1. Poor light output by the fluorescent screen.
2. Low efficiency of the light conversion mechanism.
3. Poor spatial resolution.
 Also high radiation dose to the operator is there.
 To improve image quality Image Intensifiers were designed.

6. VISUAL PHYSIOLOGY
 Rods and cones in the retina are responsible for the vision.
 Cones for day/phototopic vision
Situated more centrally on retina
Number is more tha rods
Have better visual acuity and contrast perception
 Rods for night/scotopic vision
situated peripherally
Less in number
Sensitive to low intensity light
Sensitive to green spectrum of light
 Since the conventional fluoroscopy was carried out in dark rooms i.e. dependent
on rods a new system was built to overcome the pitfalls of conventional system.

7. Fluoroscopy with image intensifiers
 In order to produce a bright image without excessive radiation exposure
Image Intensiifers were developed.
 Image Intensifier is a complex electronic imaging device that receives the
remnant beam and converts it to light and increases the intensity.
 The tube is contained in a glass envelope in a vaccum and consists of four
components :
1. Input phosphor and photocathode
2. Electrostatic focusing lens
3. accelerating anode
4. Output phosphor

9.  After an xray beam passes through patient it enters the image intensifier
tube.
 The INPUT PHOSPHOR absorbs xray photons and convert their energy
into light energy.
• The input fluorescence screen is made of Cesium iodide.
• The crystals of Cs I grow as tiny needles perpendicular to the substrate
and are tightly packed with a favourable effective atomic number.
• Resulting in little dispersion and improved spatial resolution.
• Std size is 10 – 35 cms.
• No active binder is required.

10.  The light then falls onto PHOTOCATHODE emitting photoelectrons – number
of electrons is proportional to brightness of screen.
 A series of ELECTROSTATIC LENSES are placed inside the tube to maintain
proper focus of the photoelectrons emitted from the photocathode.
• Made of Photoemissive metal (Sb and Cs compounds)
• Applied directly to Cs I input phosphor improving the resolution.
• Made of positively charged particles.
• Placed along the length of tube.
• Assist in maintaining the kinetic energy of electrons to Output
Phosphor.
• Point Inversion : inverts and reverses the image as all the electron
passes through a common focal point.

11.  Then photoelectrons then fall onto ACCELERATING ANODE which then
accelerates electron towards the output screen.
 The electrons then interact with OUTPUT PHOSPHOR producing light.
• Consists of circular plate with a hole in middle.
• Situated in the neck region.
• Has a potential of 25-35 kV.
• Made of Zinc Cadmium Sulfide Crystals.
• Crystal size and layer thickness are reduced to improve resolution of
minified image.
• Diameter of output screen varies from ½ to 1 inches.

12.  Due to acceleration of the electrons, the number of light photons are increased
approximately 50 fold.

13.  To prevent light from moving retrograde through the tube and in turn activating
the photocathode, a thin layer of aluminium is plated onto the fluorescent
screen.
 The output phosphor image is viewed either directly through a series of lenses
and mirrors or indirectly through closed TV circuit.


14.  Image intensifier with TV Coupling
1. Using Lens 2. Using Fibre Optic

15.  BRIGHTNESS GAIN :
- The ability of the image intensifier to increase the illumination level
of the image is called as brightness gain.
- Two methods are used :
In the second method the radiation quality and optical luminance
are explicably defined, so accurate and reproducible.
Compares the luminance of an intensifier
output screen with that of a Patterson type B2
fluoroscopy screen when both are exposed to
same quantity of radiation
Conversion factor : compares the luminance
of output phosphor with that of input exposure
rate.

16.  Luminance is measured in Candela per meter squared i.e. cd/m2 and
radiation intensity in milliroentgens per second i.e. mR/sec.
 The conversion factor is approximately 0.01 times the brightness gain
calculated by first method.
 As image intensifier ages the brightness gain decreases as patient dose is
higher than with a new intensifier.
 Brightness gain can also be defined as –
Minification gain Flux gain
Square of the Input Phosphor
diameter
Square of the Output
Phosphor diameter
No of light photons at the
Output Phosphor No
of Xrays at the Input
Phosphor

17. MULTIPLE – FIELD IMAGING INTENSIFIERS
 Dual field or triple field image intensifier ttempts to resolve the conflict between
image size and quality.
 They can be operated in several modes – including 4.5 in, 6 in or a 9 in mode to
view the anatomic areas. 4.5 or 6in mode is used for better resultant image
quality.
 Field size is changed by a simple electronic method – higher the voltage on
electrostatic lenses more the focussing of electron beam is there.
 For ex :
- in a 9 in mode – electrostatic focussing voltage is decreased
the electrons focus to a point close or cross, to the Output Phosphor
the image is smaller than the phosphor.
- In a 6 in mode, electrostatic focusing voltage is increased the
electrons focus farther away from the output phosphor after crossing
they diverge and final image is larger than that of 9in mode.

18. Advantages :
1. Magnifies anatomy
2. Improved spatial resolution
Disadvantages ;
1. Smaller field of view
2. Increased radiation
intensity
- Decreased minification
gain

19. Optical coupling
 Optical system transmits the output of the image intensifier to the light sensitive
area of the video camera.
 The optical distributor includes beam splitting mirror, which directs portion of the
light from the image intensifier output window to an accessory device for image
recording and passes the remainder to video camera.
 Two lenses are mounted in tandem.
 The image intensifier and the television camera are placed at the focal point of the
two lenses.

21. FLUROSCOPIC DATA ACQUISITION
– IMAGE INTENSIFIED SYSTEM

22.  Two methods are used to electronically convert the visible image on the output
phosphor of image intensifier into the electrical signal :
1. Thermoionic Television Camera Tube
2. The solid state charged coupled device
• A semiconductor device that can store charge in local areas.
• On appropriate signal transfer the charge to readout point.
• CCD + Photocathode = Video camera
• Difference from vidicon is :
- store charges in negative form
- in reaout process the charge is moved from one bucket to next
until reaches the edge of CCD where it forms electrical signal.
• No electron beam or controlling coils are required.
• Can be used with a digital imaging system.

23.  The practical and efficient viewing system was employed because of the limitations
of the mirror optic viewing system.
 TV Monitors :
1. Enables viewing by multiple persons
2. Monitors may be located in remote locations other than radiographic
system.
3. Image brightness and contrast can be manipulated.
4. Images may be stored on different medium for reviewing at a later
time.

24. CLOSED CIRCUIT TELEVISION
SYSTEM
 Used to view image intensifier output image.
 Consists of : 1. Television camera
2. Camera control unit
3. TV Monitor
 The television system allows for the real time viewing of the fluoroscopic
image by several people at once from one monitor or multiple monitors.

26. TELEVISION CAMERA
 Output Phosphor is directly coupled to TV camera tube
Plumbicon
Vidicon
CCD

27.  The basic video camera consists of
1. Vaccum tube cylinder ( of approx. 2.5cm in size) surrounded by
electromagnetic focussing coils, 2 pairs of electrostatic deflecting signals
2. Photoconductive target
3. A scanning electron beam
 Target assembly
1. Glass plate assembly
2. signal plate
3. target

28.  TARGET is functionally most important.
 Image Output from image intensifier reaches to optical Coupling lens.
 On interacting with target, a charge image is formed within photoconductive
layer.
 The latent image is read by electron beam
 Scanning electron beam moves across the target producing a current signal
which represents the 2D image with varying voltage levels.
• Thin film of photoconductive material
• Antimony sulphide suspended in mica matrix as globules.
• Each globule diameter is 0.001
• Insulated from neighbour and signal plate by the mica matrix.
• Globules behave as tiny capacitors.

29. VIDEO SIGNAL
 When the globule absorbs light, photoelectrons are emitted
making the globules positively charged.
 The electron beam scans the electrical image sytored on the
target.
 Fills in the holes left behind by the emitted photoelectrons,
discharging the tiny globular capacitors.
 As the electrons neutralizes the positive charge in globules,
the electrons on signal plate will leave via the resistor
producing current and voltage.
 Thus the video signal produced is converted into image by
monitor.

30. TELEVISION MONITOR
 The video signal produced by the video camera is converted into a visible image
by the monitor.
 Contains picture tube and controls for regulating brightness and contrast.
 Picture tube contains :
- Electron gun
- Control grid
- Anode
- Focussing Coil, Deflecting Coil – which control the electron
beam synchrony with the camera tube.

32.  Control grid receive the signal from
camera control unit, uses the signal to
regulate the no of electrons in electron
beam and thus the brightness.
 Anode- carries higher potential(10000V)
accelerates the electron beam to much
higher velocity towards the fluorescent
screen.
 The electrons strike the fluorescent
screen emitting much larger number of
light photons image on television
monitor.

33. Image Recording
 Two main methods are there ;
1. Light image from output phosphor of Image intensifier recorded
on film with a photospot camera or cine camera
2. Electrical signal generated by TV camera includes magnetic
tape, magnetic discs and optical discs.

34. Direct film recording
SPOT FILM DEVICES
 Fluoroscopic systems designed for GI imaging are generally equipped with a spot
film device.
 The spot films allows exposure of a conventional screen film cassette in
conjuction with fluoroscopic viewing.
 Similar 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.
 The xray field size is reduced automatically by the collimators at the time of
exposure to minimixe scattered radiation and patient radiation dose.

35.  The fluoroscopist can further reduce xray fileld after overriding the automatic collimator.
 Moving the spot device closer to the patient reduces the amount of magnification and
decrease the patient radiation dose
 Limitation :
- Limited range of film sizes available for spot film imaging
- Delay involved in moving the cassette into the position for exposure.
 Difference from conventional radiography and Factors affecting patient dose in a spot
film imaging
- More than one image can be obtained on a single film
1. the source to skin distance is shorter in spot film imaging than in generl
radiography
2. above mentioned distance increases the inverse square reduction in
radiation intensity as it passess through patient.
3. Making skin entrance exposure higher.
4. the field size is smaller than in general radiography
5. the smaller field size reduces scatter and therefore tends to reduce dose

36. AUTOMATIC FILM CHANGERS
 The automatic film changers used in vascular imaging are also screen film
systems.
 Various varieties such as large, floor mounted boxes but systems more commonly
used today are mounted on image intensifier.
 System consists of – Supply magazine for holding unexposed film
- a receiving magazine
- a pair of radiographic screens
- mechanism for transferring film
 When an exposure is required machine are mechanically separated, the film is
pulled into space between them and they are closed.
 After the film is exposed the screen separates again.
 The film is moved to the receiver and another film is pukled into place for the next
exposure.
 The number of films and filming rates must preprogrammed for proper operation.

37. PHOTSPOT CAMERA
 Records the image output of an image intensifier on a film.
 Film can be roll film or cut film (10cm)
 Advantage :
1. reduction in patient exposure
2. film does nnot have to be changed between exposures.
3. exposure times are shorter - motion is lesss likely to be a p[roblem.
4. films can be taken more rapidly.
5. possible to record and view image atr the same time.

38.  Framing with Spot film cameras.
 Framing – utilisation of the available area on film.
 The output phosphor of image intensifier tube is round, shape of the film is
square.
 4 framing pattern are there :
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

40. CINEFLUOROGRAPHY
 Process of recording fluoroscopic images on movie(cine) film.
 Two film sizes – 16mm, 35mm
 Cine camera – components are lens, iris, diaphragm, shutter, aperture, pressure,
plate, pull down arm and film transportation mechanism.
 Light enters the camera through lens restricted by aperture – which defines
the configuration of image reaching the film.
 Shutter is located in front of aperture and when it rotates it interrupt the light flow
into camera.
 The pressure plate holds the film so it is located in the proper image plane.
 An electric driver motor advances the film past the aperture to the take reel.
 The xray pulses and shutter opening are synchronized by electrical signal from the
driver motor.

41.  The combination of framing frequency and shutter opening determines the
amount of time available for exposure and pulldown.
 For ex – with 180degree shutter opening and 60 frames per second, the time
available for both exposure and pulldown is 1/120 sec.

42. TAPE RECORDER
 Used for both recording and playback
- As a recorder receives video signal from camera control unit.
- For playback transmits the signal to one or more several TV monitors.
 Images are stored on ½, ¾, 1 or 2 inch wide polyester based tape, coated on
one side by magnetic film.
 Components :
1. Magnetic tube
2. Writing head – converts an electrical signal in to a magnetic field for
recoding and converts magnetic signal to electric signal for replay.
3. Tape transport system

44.  The MAGNETIC LAYER of tape is composed of oxides of magnetic material.
 Each molecule behaves like a tiny magnet called DIPOLES – arranged randomly
on unrecorded tape.
 As a tape moves past writing head the dipoles get arranged in the direction of
magnetic field impressed on them while passing through the gap.
 The alignment is proportional to the strength of magnetic field.
 Playback is reverse of the recording process.
 Partially aligned dipoles have a magnetic field of their own and when passing
through the gap in writing head induces a magnetic field at core
producing electrical signal in wire coils.

46.  The WRITING HEAD consists of magnetic core made of iron-nickel alloy wrapped
with two coils of wire.
 A gap is cut from the core and the coils are wired together so that there magnetic
fields reinforce each other.
 Changing electric current moves through the coil producing changing
magnetic field in the gap.

47.  Every component of video signal must be recorded on a different portion of the
magnetic tape.
 In order to achieve this the tape must move at a high velocity.
 This is accompolished by moving both tape and writing head at the same time.
 The tape moves diagonally and in opposite direction past paired writing heads,
mounted on either side of drum.
 At a time only one head is recording the signal and the tape moves just fast
enough to separate the tracks of two heads.
 Limitations :
1. The data recording is limited by the speed of tape movement.
2. Retrieveing a stored image can take a very long time if stored far from
the starting of the tape.
3. Tape wear and degradation is another factor.

48. MAGNETIC DISC RECORDERS
 Similar to tape recorder but different function.
 Disc recorders are designed to show stationary images rather than video as in
tape recorders much like a spot camera.
 The video tracks are laid in preset groove which is complete separate track.
 One picture frame is recorded in a single track.
 Advantages :
1. random access can be done – the video grooves are numbered and recorder
can go directly to the required number.
2. no physical wear
3. digital and analog signals, both can be recorded.
 Used for proper approach in invasive procedures such as angiography, arterial
embolization and hip pinning.

51. FLUOROSCOPY TYPES
1). An Over The Table –
 when the x-ray tube is placed over the table top
 Image intensifier under the table surface.

52. 2) An Under The Table Model –
 the xray tube is placed under the table surface
 image intensifier is placed over the table top.

53. 3). Single Or Biplanar Cine-fluoroscopy Model
 Xray tube and image intensifier are fixed to the C arms.
 Mostly used in surgical theatres.

56.  An analog high resolution camera (1023 line) has a vertical resolution of
about 358 line pairs and the horizontal resolution is defined by electronic
bandpass.
 A high resolution CCD camera (1024 * 1024 matrix) will provide equivalent
vertical resolution
 The resolution of a CCD is half than that of a photospot camera but it has
ability to digitally increase the display contrast, reduce noise and enhance
the degree of digital images thus overcoming the decreased resolution
point.

57. THANK
S