Fluoroscopy: Dynamic Imaging Systems

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 Cinefluorgraphy 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 intensifer to be transmitted to a TV camera and/or optical recording device

Fiber Optic vs. Lens Coupling Fiber optics is the simplest, most direct method of coupling output phosphor to TV camera input 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 Consists of a fiber-optic bundle with 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

Red area is the visible image present on the output phosphor Beam Splitting Mirror Beam splitting mirror allows image to be recorded while being viewed Partially silvered Allows both transmission and reflection of fluoro image Red 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 ADVANTAGE 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 like analog home video recorders Recording media: ½ inch S-VHS or VHS-S Requires high resolution camera recorders, tape and monitors Offers a significant increase in resolution ½ inch VHS ¾ 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 Pulsed video signal is produced Only the video track is used, audio and synchronization tracks are left empty or blank ADVANTAGES Available for instant replay without 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 16mm & 35mm format Requires about 90% of output image intensity for proper exposure levels 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 and produces a higher quality image 16mm

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 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 some 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

Cinefluorography – How It Works - cont Radiation dose at tabletop for 35mm 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 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

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 Synchronization is the operation of camera shutters at the same frequency as x-ray pulses 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 on 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 7.5 15 30 60 90 120 Frames per second: Synchronization is driven by synchronous motors controlled by the frequency of line voltage (60 Hz) Frequency utilized is 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 Lens’ “f-number” = Speed of camera system Concentration is dependent on amount of available light and area upon which it falls Optical Lens Characteristics: Diameter Focal Length

Cinefluorography – Camera Lenses F-number is dependent on focal length and diameter (analogous to f-stop in photography) Lower f-number = More light = Faster lens Faster lens means less exposure is required F-number = Focal length / Lens diameter A lens with the same diameter but with a shorter focal length yields a faster lens and thus requires less exposure. Example F-number = 100 mm / 15 mm = 6.6 F-number = 50 mm / 15 mm = 3.3

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

Framing and Patient Dose The term ‘framing’ also refers to the use of the available film area used for image capture UNDERFRAMING Maximum size of Fluoro image is smaller than smallest dimension of the frame. Underframing should be avoided. EXACTFRAMING Diameter of intensifier image at the output phosphor and the smallest dimension of the frame (18mm) are the same. No part of the image is lost but only 58% of the cine film is used. OVERFRAMING Diameter of circular image from optical system is larger than shortest dimension of film. Part of the image is lost. TOTAL OVERFRAMING Diameter of circular image from optical system is equal to diagonal measurement of rectangular aperture (30 mm). All of the film is used but 39% of the image is wasted.

Please close this PowerPoint presentation, and continue the lesson. What’s Next? Please close this PowerPoint presentation, and continue the lesson. Presented by Based on: Principles of Radiographic Imaging, 4th 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