Flouroscopic imging


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Flouroscopic imging

  1. 1. Dr.V.Ramana reddy 1
  2. 2. FluoroscopyPurposeTo visualize, in real time: organ motion ingested or injected contrast agents insert stents cathetarize small blood vessels REAL TIME IMAGING 2
  3. 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. 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. 6. Photographshows an early (1933) fluoroscopic system in use before the development of imageintensification. An actual fluoroscopic examination with this device would have occurred in a darkened room. 6
  7. 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. 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. 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
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  12. 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. 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 comparablyfrom app. 0.3mm with Zn-Cd su to 0.1mm with CsI. Theprincipal advantage of thinner phosphor layer combinedwith needle shaped crystals is improved resolution. 13
  14. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
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  25. 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. 26. Television Camera Tube Output phosphor is directly coupled to a TV camera tube Plumbicon Vidicon CCD 26
  27. 27.  The basic video camera consists of1) vacuum tube cylinder (approximately 2.5 cm in diameter) surrounded by electromagnetic focusing coils ,2 pairs of electrostatic deflecting coils 2) photoconductive target3) a scanning electron beamTarget assembly:a) Glass plate assemblyb) signal platec) Target 27
  28. 28. PICK UP TUBE 28
  29. 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. 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
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  32. 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
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  34. 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. 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. 36.   Standard spot film imaging configuration typical of gastrointestinalfluoroscopy 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. 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. 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. 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. 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. 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. 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
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  44. 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
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  46. 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 monitorsComponents:1)magnetic tube 2)writing head 3) tape transport systemWriting head converts an electrical signal in to magnetic field for recoding & converts magnetic signal to electric signal for replay 46
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  49. 49. DIGITAL FLUOROGRAPHY Digital charge-coupled device (CCD) TV cameras arerapidly replacing conventional TV cameras in fluoroscopicsystems. An analog, high-resolution (1,023-line) TV camera hasa vertical resolution of about 358 line pairs. A high-resolution CCD camera with a 1,024 x 1,024matrix will provide equivalent vertical resolution. However,the digital camera will have the same vertical andhorizontal resolution, whereas the horizontal resolution ofthe analog camera is defined by its electronic band-pass. 49
  50. 50. For a 15-cm-diameter intensifier input, thelimiting resolution of the CCD camera would be358 lp/150 mm or 2.4 lp/mm. This result is abouthalf the resolution of a photospot film. Thisresolution loss is made up for by the ability todigitally increase display contrast, reduce noise,and enhance the edges of digital images. There are several other advantages to digitalphotospot images. Mechanical devices are notneeded for film transport. Film processing is notrequired. Images can be viewed immediately. Thelinear response of the digital system makes it veryforgiving of under- or overexposure. 50
  51. 51. Fluoroscopic Equipment ConfigurationsThe basic configurations include radiography/fluoroscopy (R/F) tables witheither an under-table or over-table x-ray tube and fixed C-arm, mobile C-arm,and mini C-armR/F Units with Under-Table X-ray Tube:most common fluoroscopic equipment configurationThe x-ray tube and collimator are mounted below the tabletop with the imageintensifier tower mounted above the table on a carriage that can be pannedover the patient.In addition to the standard fluoroscopic imaging chain, R/F systems includean overhead x-ray tube that can be used for regular radiography with a Buckyincorporated into the table.Other common features include a tilting table and image recording devices. 51
  52. 52. Under-table x-ray tube R/F system. Photograph shows an example of anR/F table that includes a spot film device and side-mounted video camera. 52
  53. 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. 54. Over-table x-ray tube R/F system. Photograph shows a sample systemthat can be controlled from within the procedure room with the pedestalcontrol panel (left) or from outside the room from the remote desk controls(right). 54
  55. 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. 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. 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
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