Flouroscopic imaging
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1. Fluoroscopy uses real-time x-ray imaging to visualize organ motion, injected contrast agents, stent placement, and small blood vessels. 2. Early fluoroscopes used faint fluorescent screens viewed in dark rooms, requiring adapted vision. Image intensifiers were developed in the 1950s to produce brighter images without excess radiation. 3. Modern fluoroscopy uses cesium iodide screens, electron optics, and closed-circuit television for real-time multi-viewer imaging while reducing patient radiation exposure.
Flouroscopic imaging
- 2. 2 Fluoroscopy PPuurrppoossee TToo vviissuuaalliizzee,, iinn rreeaall ttiimmee:: oorrggaann mmoottiioonn iinnggeesstteedd oorr iinnjjeecctteedd ccoonnttrraasstt aaggeennttss iinnsseerrtt sstteennttss ccaatthheettaarriizzee ssmmaallll bblloooodd vveesssseellss REAL TIME IMAGING
- 3. 3 X-rays were discovered because of there ability to cause fluorescence . The first x-ray image of human part was observed fluoroscopically-Dr. Glasser.
- 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. PPhhoottooggrraapphh sshhoowwss aann eeaarrllyy ((1993333)) fflluuoorroossccooppiicc ssyysstteemm iinn uussee bbeeffoorree tthhee ddeevveellooppmmeenntt ooff iimmaaggee iinntteennssiiffiiccaattiioonn.. AAnn aaccttuuaall fflluuoorroossccooppiicc eexxaammiinnaattiioonn wwiitthh tthhiiss ddeevviiccee wwoouulldd hhaavvee ooccccuurrrreedd iinn aa ddaarrkkeenneedd 6 rroooomm..
- 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
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- 12. IINNPPUUTT PPHHOOSSPPHHOORR && PPHHOOTTOO CCAATTHHOODDEE:: 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. IINNPPUUTT PPHHOOSSPPHHOORR && PPHHOOTTOO CCAATTHHOODDEE:: 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. PPHHOOTTOO CCAATTHHOODDEE:: 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 aannooddee.. 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 15 it is brighter.
- 16. AACCCCEELLEERRAATTIINNGG AANNOODDEE :: 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. OOUUTTPPUUTT PPHHOOSSPPHHOORR:: TThhee oouuttppuutt fflluuoorreesscceenntt ssccrreeeenn ooff iimmaaggee iinntteennssiiffiieerrss iiss ssiillvveerr aaccttiivvaatteedd zznn--ccdd ssuullffiiddee,, tthhee ssaammee uusseedd iinn IIsstt ggeenneerraattiioonn iinnppuutt pphhoosspphhoorr.. CCrryyssttaall ssiizzee aanndd llaayyeerr tthhiicckknneessss aarree rreedduucceedd ttoo mmaaiinnttaaiinn rreessoolluuttiioonn iinn tthhee mmiinniiffiieedd iimmaaggee.. AA tthhiinn llaayyeerr ooff aalluummiinnuumm iiss ppllaatteedd oonnttoo tthhee fflluuoorreesscceenntt ssccrreeeenn pprreevveenntt lliigghhtt ffrroomm mmoovviinngg rreettrrooggrraaddee tthhrroouugghh tthhee ttuubbee && aaccttiivvaattiinngg tthhee pphhoottooccaatthhooddee.. 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. BBRRIIGGHHTTNNEESSSS GGAAIINN:: 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. MMIINNIIFFIICCAATTIIOONN GGAAIINN:: 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 FFLLUUXX GGAAIINN:: 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.
- 21. MMUULLTTIIPPLLEE--FFIIEELLDD IIMMAAGGEE IINNTTEENNSSIIFFIIEERRSS 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 9in mode.
- 23. 23 OOppttiiccaall ccoouupplliinngg OOppttiiccaall ssyysstteemm ttrraannssmmiittss tthhee oouuttppuutt ooff tthhee iimmaaggee iinntteennssiiffiieerr ttoo tthhee lliigghhtt sseennssiittiivvee aarreeaa ooff tthhee vviiddeeoo ccaammeerraa TThhee ooppttiiccaall ddiissttrriibbuuttoorr iinncclluuddee bbeeaamm--sspplliittttiinngg mmiirrrroorr,, wwhhiicchh ddiirreeccttss aa ppoorrttiioonn ooff tthhee lliigghhtt ffrroomm tthhee iimmaaggee iinntteennssiiffiieerr oouuttppuutt wwiinnddooww ttoo aann aacccceessssoorryy ddeevviiccee ffoorr iimmaaggee rreeccoorrddiinngg aanndd ppaasssseess tthhee rreemmaaiinnddeerr ttoo tthhee vviiddeeoo ccaammeerraa.. TTwwoo lleennsseess aarree mmoouunntteedd iinn ttaannddeemm TThhee IIII aanndd tthhee vviiddiiccoonn aarree ppllaacceedd aatt tthhee ffooccaall ppllaanneess ooff tthhee ttwwoo lleennsseess
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- 25. Closed-circuit Television System used to view the iimmaaggee iinntteennssiiffiieerr oouuttppuutt iimmaaggee CCoonnssiissttss ooff 25 11))TTeelleevviissiioonn ccaammeerraa 22)) CCaammeerraa ccoonnttrrooll uunniitt 33)) MMoonniittoorr TThhee tteelleevviissiioonn ssyysstteemm aalllloowwss ffoorr rreeaall--ttiimmee vviieewwiinngg ooff tthhee fflluuoorroossccooppiicc iimmaaggee bbyy sseevveerraall ppeeooppllee aatt oonnccee ffrroomm oonnee mmoonniittoorr oorr mmuullttiippllee mmoonniittoorrss
- 26. TTeelleevviissiioonn CCaammeerraa TTuubbee Output phosphor is directly coupled to a TV camera tube 26 Plumbicon Vidicon CCD
- 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 27 Target assembly: a) Glass plate assembly b) signal plate c) Target
- 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.
- 30. 30 Video signal When globules absorbs light ,,pphhoottooeelleeccttrroonnss aarree eemmiitttteedd TThhee gglloobbuullee bbeeccoommeess ppoossiittiivveellyy cchhaarrggeedd TThhee eelleeccttrroonn bbeeaamm ssccaannss tthhee eelleeccttrriiccaall iimmaaggee ssttoorreedd oonn tthhee ttaarrggeett && ffiillllss iinn tthhee hhoolleess lleefftt bbyy tthhee eemmiitttteedd pphhoottooeelleeccttrroonnss,, ddiisscchhaarrggiinngg tthhee ttiinnyy gglloobbuullaarr ccaappaacciittoorrss WWhheenn tthhee eelleeccttrroonnss iinn bbeeaamm nneeuuttrraalliizzee tthhee ppoossiittiivvee cchhaarrggee iinn tthhee gglloobbuulleess ,, tthhee eelleeccttrroonnss oonn tthhee ssiiggnnaall ppllaattee lleeaavvee tthhee ppllaattee vviiaa rreessiissttoorr TThheessee mmoovviinngg eelleeccttrroonnss ffoorrmm aa ccuurrrreenntt fflloowwiinngg tthhrroouugghh aa rreessiissttoorr aanndd vvoollttaaggee aaccrroossss tthhee rreessiissttoorr TThhiiss vvoollttaaggee ,,wwhheenn ccoolllleecctteedd ffoorr eeaacchh nneeuuttrraalliizzeedd gglloobbuullee,, ccoonnssttiittuutteess tthhee vviiddeeoo ssiiggnnaall
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- 32. 32 TTeelleevviissiioonn mmoonniittoorr 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.
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- 34. 34 IImmaaggee RReeccoorrddiinngg 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
- 35. DIRECT FILM RECORDING 35 SPOT FILM DEVICES: FFlluuoorroossccooppiicc ssyysstteemmss ddeessiiggnneedd ffoorr ggaassttrrooiinntteessttiinnaall iimmaaggiinngg aarree ggeenneerraallllyy eeqquuiippppeedd wwiitthh aa ssppoott ffiillmm ddeevviiccee.. TThhee ssppoott ffiillmm ddeevviiccee aalllloowwss eexxppoossuurree ooff aa ccoonnvveennttiioonnaall ssccrreeeenn--ffiillmm ccaasssseettttee iinn ccoonnjjuunnccttiioonn wwiitthh fflluuoorroossccooppiicc vviieewwiinngg.. TThhiiss rraatthheerr ffaammiilliiaarr ssyysstteemm,, llooccaatteedd iinn ffrroonntt ooff tthhee iimmaaggee iinntteennssiiffiieerr,, aacccceeppttss tthhee ssccrreeeenn--ffiillmm ccaasssseettttee aanndd ""ppaarrkkss"" iitt oouutt ooff tthhee wwaayy dduurriinngg fflluuoorroossccooppyy CCaasssseetttteess mmaayy bbee llooaaddeedd ffrroomm tthhee ffrroonntt oorr rreeaarr ddeeppeennddiinngg oonn tthhee ddeessiiggnn ooff tthhee ssyysstteemm..
- 36. SSttaannddaarrdd ssppoott ffiillmm iimmaaggiinngg ccoonnffiigguurraattiioonn ttyyppiiccaall ooff ggaassttrrooiinntteessttiinnaall fflluuoorroossccooppyy eeqquuiippmmeenntt.. TThhee ssccrreeeenn--ffiillmm ccaasssseettttee iiss ppaarrkkeedd oouutt ooff tthhee xx-- rraayy ffiieelldd uunnttiill tthhee ssppoott ffiillmm ttrriiggggeerr iiss pprreesssseedd,, ccaauussiinngg bbootthh tthhee ccaasssseettttee aanndd tthhee ffoorrmmaattttiinngg mmaasskk ttoo mmoovvee iinnttoo ppoossiittiioonn.. 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 41 likely problem 4)films can be taken more rapidly 5)possible to record & view image at same time
- 42. FFrraammiinngg wwiitthh ssppoott ffiillmm ccaammeerraass:: FFrraammiinngg ––uuttiilliissaattiioonn ooff aavvaaiillaabbllee aarreeaa oonn ffiillmm TThhee oouuttppuutt pphhoosspphhoorr ooff IIII ttuubbee iiss rroouunndd, 42 sshhaappee ooff ffiillmm iiss ssqquuaarree 44 ffrraammiinngg ppaatttteerrnnss 11)) EExxaacctt ffrraammiinngg 22)) EEqquuaall aarreeaa ffrraammiinngg 33)) mmeeaann ddiiaammeetteerr ffrraammiinngg 44)) ttoottaall aarreeaa ffrraammiinngg EEqquuaall aarreeaa ffrraammiinngg oorr mmeeaann ddiiaammeetteerr ffrraammiinngg iiss rreeccoommmmeennddeedd ffoorr mmoosstt cclliinniiccaall ssiittuuaattiioonnss..
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- 44. 44 CCiinneefflloouurrooggrraapphhyy PPrroocceessss ooff rreeccoorrddiinngg fflluuoorroossccooppiicc iimmaaggeess oonn mmoovviiee ((cciinnee)) ffiillmm TTwwoo ffiillmm ssiizzeess-- 1166 mmmm, 3355 mmmm CCiinnee ccaammeerraa--ccoommppoonneennttss aarree lleennss, iirriiss ddiiaapphhrraaggmm, sshhuutttteerr, aappeerrttuurree, pprreessssuurree ppllaattee, ppuullll ddoowwnn aarrmm && ffiillmm ttrraannssppoorrtt mmeecchhaanniissmm
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- 46. TV image recorders : 1) TAPE RECORDER : used for both recoding& playback • as a recorder receives video signal from camera 46 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
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- 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 49 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.
- 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 sshhoowwss aann eexxaammppllee ooff aann RR//FF ttaabbllee tthhaatt iinncclluuddeess aa ssppoott ffiillmm ddeevviiccee aanndd ssiiddee--mmoouunntteedd vviiddeeoo ccaammeerraa.. 52
- 53. RR//FF UUnniittss wwiitthh OOvveerr--TTaabbllee XX--rraayy TTuubbee xx--rraayy ttuubbee mmoouunntteedd oovveerr tthhee ttaabbllee wwiitthh tthhee iimmaaggee iinntteennssiiffiieerr bbeellooww.. tthhiiss ccoonnffiigguurraattiioonn rreessuullttss iinn iinnccrreeaasseedd ppaattiieenntt aacccceessss,, wwhhiicchh iiss hheellppffuull ffoorr iinntteerrvveennttiioonnaall pprroocceedduurreess.. RRaaddiiooggrraapphhyy ccaann bbee ppeerrffoorrmmeedd wwiitthh tthhee ssaammee xx-- rraayy ttuubbee aanndd aa BBuucckkyy iinnccoorrppoorraatteedd iinnttoo tthhee ttaabbllee.. TThhee xx--rraayy ttuubbee ccaann bbee aanngglleedd ttoo aaccqquuiirree aanngguullaatteedd pprroojjeeccttiioonnss oorr ttoommooggrraammss.. 53
- 54. Over-table x-ray tube R/F system. Photograph sshhoowwss aa ssaammppllee ssyysstteemm tthhaatt ccaann bbee ccoonnttrroolllleedd ffrroomm wwiitthhiinn tthhee pprroocceedduurree rroooomm wwiitthh tthhee ppeeddeessttaall ccoonnttrrooll ppaanneell ((lleefftt)) oorr ffrroomm oouuttssiiddee tthhee rroooomm ffrroomm tthhee rreemmoottee ddeesskk ccoonnttrroollss ((rriigghhtt)).. 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 sulfide
- 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 iiss pprroocceesssseedd bbyy tteelleevviissiioonn ccaammeerraa ttuubbee ((vviiddiiccoonn,, pplluummbbiiccoonn,, CCCCDD)) TThhee iimmaaggee iiss ddiissppllaayyeedd oonn TTVV mmoonniittoorr SSttaannddaarrdd xx--rraayy cclloosseedd--cciirrccuuiitt tteelleevviissiioonn uusseess 552255xx552255 ffoorrmmaatt wwiitthh 55--MMHHZZ bbaanndd ppaassss VVeerrttiiccaall rreessoolluuttiioonn lliimmiitteedd bbyy ssccaann lliinnee ffoorrmmaatt,, hhoorriizzoonnttaall rreessoolluuttiioonn iiss aa ffuunnccttiioonn ooff bbaanndd ppaassss LLiigghhtt iimmaaggee iiss rreeccoorrddeedd bbyy pphhoottoo ssppoott ccaammeerraa oorr cciinnee ccaammeerraa 57
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