Fluoroscopy

 Adapted by:-

KAMARUL AMIN BIN ABDULLAH What is Fluoroscopy?

 A type of radiographic study  Provides a dynamic imaging source  Allows the observer to visualize motility of organs  Films provide a static image  Contrast media is generally used in conjunction with fluoroscopy  Static images are obtained on a spot film C-Arm Diagram History Of Fluoroscopy

 Invented in 1896 by Thomas Edison  Original phosphor was zinc-cadmium sulfite  The screen was placed above the patient, the image was observed by viewing the screen  Dark adaptation was necessary to view images  This type of fluoroscopy was adapted to mirror optics but only one person could view at a time  In the 1950’s, image intensification was developed  In the 1990’s, digital fluoroscopy was developed and is widely used today Conventional Fluoroscopy Illumination During Fluoroscopy

 Fluoroscopy is generally visualized in dimly lit rooms  Capable of limited brightness levels  Image-intensified fluoroscopy is much brighter than conventional fluoroscopy  Illumination levels are measured in lamberts  II levels are about the same brightness as viewing radiographic films Visual Physiology

 Two structures  Path of light through the responsible for vision eye – Light incident first passes – Rods and cones through cornea – Located in the center of – Through the lens retina called fovea – Light is focused onto the centralis retina – Between cornea and lens is the iris  Controls the amount of light to enter eye Rod And Cone Vision

 Rods  Cones – Sensitive to low light – Less sensitive to light – Used for night vision – Capable of responding to brighter light – Scotopic vision – Used for daylight vision – Do not perceive color as readily as cones – Photopic vision – Able to perceive fine detail – Able to distinguish between brightness levels Properties Of Vision

 Ability to perceive fine detail – Visual acuity  Ability to detect differences between light levels – Contrast perception Image Intensifier Tube

 Receives remnant radiation  Converts it to light  Increases the light intensity  Similar to x-ray tube – Contains a vacuum – Mounted in a metal container to protect it Image Intensifier Tube Parts Of The II Tube

 Input phosphor  Photocathode  Electrostatic lenses  Accelerating anode  Output phosphor Input Phosphor

 Made from cesium iodide  X-ray conversion to visible light takes place here – Similar to the intensifying screen Photocathode

 Coupled to input phosphor  Emits electrons when stimulated by light  The number of electrons emitted is directly proportional to the light intensity hitting photocathode Electrostatic Lenses Accelerating Anode

 Lenses – Positively charged electrodes – Plated on inside surface of glass – Used to precisely focus electrons from photocathode toward the output phosphor  Anode – Positively charged – Located in neck of imaging tube – Accelerates electrons toward the output phosphor Output Phosphor

 Made from zinc cadmium sulfite  Converts electrons from photocathode to light photons Summary Of Image Intensification

 Remnant radiation hits input phosphor  Converted to light photons  Light produced is proportional to beam intensity  Light photons hit photocathode  Converted to photoelectrons equal to light intensity  Photoelectrons accelerated and focused to output phosphor  Light photons multiplied at output phosphor  Result is much brighter image Flux Gain

 Flux gain = Number of output light photons Number of input x-ray photons  Compares the number of light photons at output phosphor to number of x-rays at input phosphor  Represents the conversion of x-rays to light  The number of light photons will always be higher than incident x-rays Flux Gain Brightness Gain

 Ability of the II to increase the light level  Brightness gain = minification gain X flux gain Minification Gain

 Compares the size of input and output phosphor  Improves image detail  Input phosphor is always larger than output phosphor  The image is minified for better detail  Ratio of the square of diameter of input phosphor to that of the output phosphor Multifield Image Intensification

 The magnification mode  Used to make the image appear larger  Comes in dual or trifield  Can change from 9 inch to 6 inch field or:  From 9 - 6 - 3 inch field  Raises patient dose Accomplishing Multifield II

 Fields of view are selected at touch of a button  The numbers represent diameter used of input phosphor  e.g. If 9 in. is selected, photoelectrons from entire phosphor are accelerated to O.P.  If 3 or 6 in. is selected, only photoelectrons from that section are accelerated to O.P. Dual Field Image Intensifier Multifield Image Intensification What’s Happening?

 Voltage on electrostatic lenses is increased  Electron focal point moves further from O.P.  Field of view is reduced  Image appears magnified  How much more magnified? – MF = ODP/NDP Magnification And Patient Dose

 Minification gain is reduced  Fewer photoelectrons on O.P.  Brightness is reduced  X-ray tube current is increased to maintain image brightness  This is automatic, patient dose is increased  This increase improves image quality Determining Patient Dose Increase

 To determine increase in dose  New dose = OPD²/NPD² Magnification And Resolution

 Patient dose is increased  Brightness is increased  Less noise/Higher contrast resolution  Only central region of input phosphor is used  Spatial resolution is improved  Vignetting – Dimness around the periphery – Loss of focus at periphery of input phosphor Brightness Controls

 mA or kVp control brightness  The size of the anatomic part also controls density  High kVp and low mA are preferred  Tube current is low, generally .5 - 5 mA – Generally 1 - 3mA Image Quality

 Contrast  Resolution  Distortion  Quantum Mottle Quantum Mottle Fluoroscopy Equipment

 Tube and film alignment are maintained  Allows for spot films  Table allows for special positioning  Image intensifier can be under or over table Viewing Systems

 Image produced at output phosphor is much smaller, brighter image  Could be viewed directly off output phosphor – Mirror optics  Finally updated to a television monitor – Closed circuit monitor system

Television Monitoring

 Output phosphor is coupled directly to a television camera tube  Vidicon is most often used  Light image is converted to an electronic signal  Brightness and contrast can be controlled electronically  Several observers can view image at the same time Television Camera

 Plumbicon and vidicon are most often used – Plumbicon - Best for imaging moving organs, i.e., heart – Vidicon - Best for imaging stationary organs  A typical vidicon is contained in a glass envelope with a vacuum  Internal components:  Electron gun – Cathode  Electrostatic grids  Target assembly – Anode Television Camera Tube How The Vidicon Works

 Light image from II is converted to electric signal  Varying light intensity is received at target assembly  Electrons are emitted - number depends on light intensity received by the target assembly  The electron gun supplies electrons to fill any deficiency Vidicon (Continued)

 This causes a current to flow  Causes a varying voltage across the tube  This is the video signal  The video signal pulses are reassembled into a visible image by the image monitor Image or TV Monitor

 The final component in the II system  Converts the varying voltage from the Vidicon into a visible image  Elements of the TV Monitor – Cathode ray tube – Electron gun – Focusing coils – Control grids Television Monitor Tube Image Monitor (Continued)

 Electron gun emits electron toward a fluorescent screen, (TV screen) of the monitor  Electrons emitted are in synchronicity with the signal being emitted by vidicon Image Production

 Formed similar to a mosaic, hundreds of thousands of tiny dots of varying degrees of brightness  These patterns are scan lines  A typical US fluoroscopic tube uses 525 scan lines  Electron gun in tube scans from top to bottom in 1/60 sec. Image Production (Continued)

 Each scan is a field  Contains 262 ½ horizontal scan lines  One frame is two fields or 525 scan lines  Two fields take 1/30 second  This is about 30 scans per second  Less than this cause flicker  Interlace methods is better – First the even numbered lines are scanned – Then the odd numbered lines are scanned Interlace Method Coupling Of The Television Camera

 Two methods:  Fiber optics – Cassette loaded spot films are necessary  Lens coupling – Cine – Spot film camera Video Display System Recording The Fluoroscopic Image

 Dynamic Systems – Cine Film Systems – Videotape Recording  Static Systems – Spot Film Devices - Cassettes – Spot Film Devices – Camera (Photofluorography) – Automatic Film Changers – Video Recorders – Digital Fluoroscopy Cine Film Systems

 Uses a 16 - 35mm movie camera  Image quality is better with 35mm  Patient dose is higher with 35mm  Patient dose is higher with cine than regular fluoro - requires higher mA  Cine camera is driven by an electronic synchronous motor Cine Film Systems (Cont..d) Cine Film Systems (Continued)

 Number of frames/second based on 60 Hz cycle  Framing frequencies are divisible by 60  Radiation dose increases with increased frame rate  Radiation is pulsed to be synchronous with camera shutters Videotape Recording

 Can record image from TV monitor  Uses VHS ½ in. or U-matic ¾ in recorder  Does not exhibit high resolution  Can provide instant playback of examination  Does not provide additional dose to patient Spot Film Devices - Cassettes

 High image quality  High patient dose  Delay of two seconds is required before cassette can be exposed  Multiple images can be exposed on one cassette  Provides a familiar format, therefore, most popular Spot Film Devices – Cassettes (Cont..d) Spot Film Devices – Cameras (Photofluorography)

 Also called millimeter and photospot cameras  Similar to movie cameras, but only expose one frame  Image comes directly from output phosphor  This requires less heat loading, lower mA, shorter interruption of exam  Used with a beam splitting mirror  Available in 70 and 105mm  70 mm can expose up to 12 frames/sec

105 Spot Films Automatic Film Changers Automatic Film Changers (Cont..d)

 are also screen-film systems.  consists of a supply magazine for holding unexposed film, a receiving magazine, a pair of radiographic screens, and a mechanism for transferring the film.  Approximately 20 films are held in the supply magazine. During exposure, a film is advanced between the high-speed screens, exposed, and removed to the receiving magazine. Video Recorders

 Uses a magnetic disk  Usually records single frames  Has a playback mode Digital (Computerized) Fluoroscopy

 Developed in late 70’s  Images are taken directly from output phosphor  A video camera and digital image processor are used to obtain images  The image is converted from analog to digital  A dynamic recording can be made  Image can be manipulated in many ways  Less radiation is used Digital Fluoroscopy Chain of Events Mobile Fluoroscopy

 Can provide both static and dynamic images  Usually connected to a video disk  Can do everything that a fixed unit can  Generally used in critical care areas and surgery Mobile Fluoroscopy