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Dr.V.Ramana reddyDr.V.Ramana reddy

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Fluoroscopy

PurposePurpose

To visualize, in real time: To visualize, in real time: organ motion organ motion ingested or injected contrast ingested or injected contrast

agents agents insert stents insert stents cathetarize small blood vessels cathetarize small blood vessels

REAL TIME IMAGING

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X-rays were discovered because of there ability to cause fluorescence .

The first x-ray image of human part was observed fluoroscopically-Dr. Glasser.

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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.

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FLUOROSCOPEFLUOROSCOPE

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PhotograpPhotograph shows an h shows an

early early (1933) (1933)

fluoroscopifluoroscopic system in c system in use before use before

the the developmedevelopment of image nt of image intensificatintensificat

ion. An ion. An actual actual

fluoroscopifluoroscopic c

examinatioexamination with this n with this

device device would have would have occurred occurred

in a in a darkened darkened

room. room.

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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.

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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.

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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.

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IMAGE INTENSIFIER

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INPUT PHOSPHOR & PHOTO CATHODEINPUT 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.

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INPUT PHOSPHOR & PHOTO CATHODEINPUT 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 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.

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PHOTO CATHODEPHOTO 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.anode.

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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.

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ACCELERATING ANODEACCELERATING 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:OUTPUT PHOSPHOR: The output fluorescent screen of image The output fluorescent screen of image

intensifiers is silver activated zn-cd sulfide, the intensifiers is silver activated zn-cd sulfide, the same used in Ist generation input same used in Ist generation input phosphor.phosphor.

Crystal size and layer thickness are reduced to Crystal size and layer thickness are reduced to maintain resolution in the minified image.maintain resolution in the minified image.

A thin layer of aluminum is plated onto the A thin layer of aluminum is plated onto the fluorescent screenfluorescent screen prevent light from moving prevent light from moving retrograde through the tube & activating the retrograde through the tube & activating the photocathode. photocathode.

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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: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.

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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.

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MINIFICATION GAIN: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.

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FLUX GAIN: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.

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MULTIPLE-FIELD IMAGE MULTIPLE-FIELD IMAGE INTENSIFIERSINTENSIFIERS

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.

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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.

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Optical couplingOptical coupling Optical system transmits the output of Optical system transmits the output of

the image intensifier to the light the image intensifier to the light sensitive area of the video camerasensitive area of the video camera

The optical distributor include beam-The optical distributor include beam-splitting mirror, which directs a portion splitting mirror, which directs a portion of the light from the image intensifier of the light from the image intensifier output window to an accessory device output window to an accessory device for image recording and passes the for image recording and passes the remainder to the video camera. remainder to the video camera.

Two lenses are mounted in tandemTwo lenses are mounted in tandem The II and the vidicon are placed at the The II and the vidicon are placed at the

focal planes of the two lensesfocal planes of the two lenses

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Closed-circuit Television System

used to view the image intensifier used to view the image intensifier output image output image

Consists ofConsists of 1)Television camera1)Television camera 2) Camera control unit2) Camera control unit 3) Monitor3) Monitor The television system allows for real-The television system allows for real-

time viewing of the fluoroscopic time viewing of the fluoroscopic image by several people at once from image by several people at once from one monitor or multiple monitorsone monitor or multiple monitors

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Television Camera TubeTelevision Camera Tube

Output phosphor is directly coupled to a TV camera tube

Plumbicon Vidicon CCD

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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 Target assembly: a) Glass plate assembly

b) signal plate c) Target

28PICK UP TUBE

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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.

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Video signal When globules absorbs light ,photoelectrons are When globules absorbs light ,photoelectrons are

emittedemitted The globule becomes positively chargedThe globule becomes positively charged The electron beam scans the electrical image stored The electron beam scans the electrical image stored

on the target & fills in the holes left by the emitted on the target & fills in the holes left by the emitted photoelectrons, discharging the tiny globular photoelectrons, discharging the tiny globular capacitorscapacitors

When the electrons in beam neutralize the positive When the electrons in beam neutralize the positive charge in the globules , the electrons on the signal charge in the globules , the electrons on the signal plate leave the plate via resistorplate leave the plate via resistor

These moving electrons form a current flowing These moving electrons form a current flowing through a resistor and voltage across the resistorthrough a resistor and voltage across the resistor

This voltage ,when collected for each neutralized This voltage ,when collected for each neutralized globule, constitutes the video signalglobule, constitutes the video signal

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Television monitorTelevision 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.

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Image RecordingImage 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

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      DIRECT FILM RECORDING

SPOT FILM DEVICES: Fluoroscopic systems designed for Fluoroscopic systems designed for

gastrointestinal imaging are generally gastrointestinal imaging are generally equipped with a spot film device.equipped with a spot film device.

The spot film device allows exposure of a The spot film device allows exposure of a

conventional screen-film cassette in conventional screen-film cassette in conjunction with fluoroscopic viewing. This conjunction with fluoroscopic viewing. This rather familiar system, located in front of the rather familiar system, located in front of the image intensifier, accepts the screen-film image intensifier, accepts the screen-film cassette and "parks" it out of the way during cassette and "parks" it out of the way during fluoroscopy fluoroscopy

Cassettes may be loaded from the front or Cassettes may be loaded from the front or rear depending on the design of the system. rear depending on the design of the system.

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    Standard spot Standard spot film imaging film imaging configurationconfiguration

typical of typical of gastrointestinal gastrointestinal

fluoroscopy fluoroscopy equipment. The equipment. The

screen-film screen-film cassette is parked cassette is parked

out of the x-ray out of the x-ray field until the spot field until the spot

film trigger is film trigger is pressed, causing pressed, causing both the cassette both the cassette

and the and the formatting mask formatting mask

to move into to move into position.position.

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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.

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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.

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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.

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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.

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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

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Framing with spot film cameras:Framing with spot film cameras: Framing –utilisation of available area Framing –utilisation of available area

on filmon film The output phosphor of II tube is The output phosphor of II tube is

round, shape of film is squareround, shape of film is square 4 framing patterns4 framing patterns 1) Exact framing1) Exact framing 2) Equal area framing2) Equal area framing 3) mean diameter framing3) mean diameter framing 4) total area framing4) total area framing Equal area framing or mean diameter Equal area framing or mean diameter

framing is recommended for most framing is recommended for most clinical situations. clinical situations.

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Cineflourography Cineflourography

Process of recording fluoroscopic Process of recording fluoroscopic images on movie (cine) filmimages on movie (cine) film

Two film sizes- 16 mm, 35 mmTwo film sizes- 16 mm, 35 mm Cine camera-components are lens, Cine camera-components are lens,

iris diaphragm, shutter, aperture, iris diaphragm, shutter, aperture, pressure plate, pull down arm & film pressure plate, pull down arm & film transport mechanismtransport mechanism

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TV image recorders : 1) 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 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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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 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.

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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.

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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.

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Under-table x-ray tube R/F system. Photograph shows Under-table x-ray tube R/F system. Photograph shows an example of an R/F table that includes a spot film an example of an R/F table that includes a spot film device and side-mounted video camera. device and side-mounted video camera.

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R/F Units with Over-Table X-R/F Units with Over-Table X-ray Tuberay Tube

x-ray tube mounted over the table with x-ray tube mounted over the table with the image intensifier below. the image intensifier below.

this configuration results in increased this configuration results in increased patient access, which is helpful for patient access, which is helpful for interventional procedures.interventional procedures.

Radiography can be performed with the Radiography can be performed with the same x-ray tube and a Bucky same x-ray tube and a Bucky incorporated into the table.incorporated into the table.

The x-ray tube can be angled to acquire The x-ray tube can be angled to acquire angulated projections or tomograms. angulated projections or tomograms.

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Over-table x-ray tube R/F system. Photograph shows a Over-table x-ray tube R/F system. Photograph shows a sample system that can be controlled from within the sample system that can be controlled from within the procedure room with the pedestal control panel (left) or procedure room with the pedestal control panel (left) or from outside the room from the remote desk controls from outside the room from the remote desk controls (right).(right).

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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

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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.

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Output phospher image is processed by Output phospher image is processed by television camera tube (vidicon, television camera tube (vidicon, plumbicon, CCD)plumbicon, CCD)

The image is displayed on TV monitorThe image is displayed on TV monitor Standard x-ray closed-circuit television Standard x-ray closed-circuit television

uses 525x525 format with 5-MHZ band uses 525x525 format with 5-MHZ band passpass

Vertical resolution limited by scan line Vertical resolution limited by scan line format, horizontal resolution is a function format, horizontal resolution is a function of band passof band pass

Light image is recorded by photo spot Light image is recorded by photo spot camera or cine cameracamera or cine camera

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