Fluoroscopy Dynamic Image Recording Systems Based on: Principles of Radiographic Imaging, 3rd Ed. By: R. Carlton & A. Adler Radiologic Science for Technologists, 8th Ed. By: S. Bushong Syllabus on Fluoroscopy Radiation Protection, 6th Rev. By: Radiologic Health Branch – Certification Unit PPT created by: Jed Miles, BSRS, RT(R), CRT-CA

Recording the Fluoroscopic Image Many types of recording systems have been developed to record the fluoroscopic image The image viewed during fluoroscopy can be recorded in either a dynamic or static method Dynamic (motion) image recording Video tape recording Cinefluorography Static recording Radiographic cassette Photospot camera Video disc

Modern Viewing Systems Output phosphor of intensification tube coupled with input side of camera by either fiber optics or optical lens coupling system Permits light photons from the intensifier to be transmitted to a TV camera and/or optical recording devices

Fiber Optic vs. Lens Coupling Fiber optics: simplest most direct method of coupling output phosphor to TV camera input Consists of a fiber-optic bundle which contains thousands of glass fibers per square millimeter Advantages: small, compact, and rugged Disadvantage: does not permit auxiliary photographic imaging devices such as cine or photospot cameras to be attached to the fluoro tower For cine and/or photospot cameras to be attached, optical lens coupling is required Accomplished with use of beam splitting mirrors or an intercept mirror

Beam Splitting Mirror Beam splitting mirror allows image to be recorded while being viewed Partially silvered Allows both transmission and reflection of fluoro image Gray shaded area is the visible image present on the output phosphor

Beam Splitting Mirror System Beam Intercept mirror reflects all light from output phosphor to image receptor (cine or photospot device) Fully silvered Advantages: allows recording of fluoro image at reduced dose rate Disadvantage: large size, easily knocked out of alignment

Dynamic Recording – Video Tape Logical method to record closed-circuit TV system fluoro images Uses magnetic tape Same as analog home video recorders Recording media 1/2 inch VHS 1/2 inch S-VHS or VHS-S VHS-S requires high resolution camera, recorders, tape and monitors VHS-S offers a significant increase in resolution 3/4 inch U-matic

Video Tape Recording – How it Works Magnetic recording and playback heads produce and read a pattern of magnetic particles on the tape, which produce a pulsed video signal Only the video track is used Audio and synchronization tracks are left empty or blank Advantages Available for instant replay w/o any intermediate processing Patient exposure is not increased Disadvantages Lower resolution than cinefluorography Fixed framing rate at 30 frames/sec

Cine or Cinefluorography Cinematic /cine film/cinefluorography consists of cine (movie) camera positioned to intercept image produced by output screen of image intensification tube Requires about 90% of output image intensity for proper exposure levels 16mm & 35mm format Dramatically increased resolution compared to other dynamic image recording systems Patient exposure significantly greater than with other types of image recording systems 35mm requires an increased dose compared to 16 mm – will also produce a higher quality image

Cinefluorography Camera

Cardiac Cath Lab with 35mm Cine Camera Film Magazine Image Intensifier Grid Controlled X-ray Tube

Cinefluorography – How It Works Cine cameras record a series of static images at high speed When images are projected at same high speed, eye becomes incapable of differentiating separate images and perceives them as a single image in motion (i.e. a movie) Cine film can be viewed as both a movie or in stop-action (single frame or frame-by-frame)

Cinefluorography – Movie Viewing Eyes can perceive flicker up to 50 frames/sec If projector shows each frame once (most common) Framing at 30 frames/sec will show flicker Framing at 60 frames/sec will be perceived as continuous motion without flicker Some movie projectors operate at 24 frames/sec and show each frame twice, thus pulsing light 48 times/second to eliminate flicker Display playback rate can be slowed to 16 frames/sec (16 x 2 = 48 frames /sec = smooth action motion without noticeable flicker

Cinefluorography – How It Works - cont Generator and x-ray tube must be able to handle high heat loading Exposure per frame may be minimal but at 30 or 60 frames/sec, x-ray tube heat loading builds rapidly Radiation dose at tabletop for 35 mm cine fluorography approximately 10 times greater than routine fluoroscopy Dose per frame is minimal but cumulative dose builds rapidly when framing at 60 frames/sec

Processor used to develop, fix, and dry cine film Cine Film Processor Cine film is wet chemical developed using a cine film processor – similar to what is used at Wal-Mart or CVS for developing rolls of 35mm color film Exposed cine film is attached to a leader which is pulled through processor Processor used to develop, fix, and dry cine film

Cine Film Movie Projector Projected single frame of Left Coronary Artery obtained during a cardiac catheterization

Cine - Synchronization Operation of camera shutters at same frequency as x-ray pulses Cine camera shutter speed must be synchronized with pulsed radiation (pulse synchronization) Grid Biased Tube Controls radiation pulse rate Negatively charged grid (screen) across cathode focusing cup Grid voltage on hold: Electrons are held in check at cathode thus no radiation production even though tube is held at peak kilovoltage Grid voltage off: results in electron flow from cathode to anode with resultant x-ray production

Synchronization of Exposure to Film

Cine – Framing Frequency Framing frequency (rates) are derivatives of 60 Hz Synchronization is driven by synchronous motors controlled by the frequency of line voltage (60 Hz) 7.5, 15, 30, 60, 90, and 120 frames / second Frequency utilized determined by physiological motion More motion requires higher framing frequency Example: pediatric coronary angio = 60 f/s Higher framing rate = higher radiation dose

F-number of an Optical System Speed of camera system = lens’ “f-number” Concentration dependent on amount of available light and area upon which it falls Optical lens characteristics Diameter Focal length

Cinefluorography – Camera Lenses F-number is dependant on focal length and diameter Analogous to f-stop in photography Lower f-number = more light = faster lens Faster lens (lower f-number) = less exposure required Example F-number = focal length / lens diameter = 100 mm / 15 mm = 6.6 A faster system requiring less exposure would be = 50 mm / 15 mm = 3.3 Due to shorter focal length lens at same diameter

Framing Framing refers to available film area used for image capture Primary X-ray beam must be restricted to match framing method If beam is not restricted (collimated), areas of patient are exposed to radiation but not recorded as an image Iris or diaphragm located between camera lens and shutter Restricts divergence of light from lens Controls amount of light reaching film

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