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

Dynamic Recording Systems Recording of “dynamic” fluoroscopic images can be accomplished by: Video tape Cine film (cinefluorography) Laser or magnetic video disc Digital video (newest method)

Dynamic Recording – Video Tape Video tape recording is a logical method to recording closed-circuit TV system fluoro images Videotape recorders use 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 a cine (movie) camera positioned to intercept the image produced by the output screen of the image intensification tube Requires about 90% of the output image intensity for proper exposure levels 16mm & 35mm format Dramatically increased resolution as compared to other dynamic image recording systems Patient exposure in cinefluorography is 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 operate by recording a series of static images at high speed When images are projected at the same high speed, the eye becomes incapable of differentiating the separate images and perceives them as a single image in motion (i.e. a movie) In cinefluorography the following are very important Synchronization Framing frequency F-number of the optical system Framing and patient radiation dose

Cine - Synchronization Synchronization is the operation of the camera shutters at the 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 the 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 is determined by physiological motion… More motion requires higher framing frequency Example: pediatric coronary angio = 60 f/s Higher the framing rate = higher the radiation dose

F-number of an Optical System The speed of any given camera system depends on the ability of its lens to concentrate light on a given area Denoted by the lens’ “f-number” Concentration is dependent on the amount of available light and the area upon which it falls Optical lens characteristics Diameter Determines how much light will flow through lens large diameter will allow more light to be transmitted than a small one Focal length Refers to the distance between the lens and image plane (film surface) Determines the amount of magnification and consequently the area (size) of light distribution Short focal length = less magnification = increased light concentration at the image plane (film surface)

Focal Length Diagram

Cinefluorography – Camera Lenses F-number is dependant on the focal length and diameter It is analogous to the f-stop in photography The lower the 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 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 Exact framing: 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

Framing cont & Iris Primary X-ray beam must be also restricted to match the framing method used If beam is not restricted (collimated), areas of patient are exposed to radiation but not recorded as an image An “iris” or diaphragm is located between the camera lens and shutter Restricts the divergence of light from the lens Controls amount of light reaching the film

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 The radiation dose at the tabletop for 35 mm cine fluorography is approximately 10 times greater than routine fluoroscopy Again, the dose per frame is minimal but framing at 60 frames/sec, the cumulative dose builds rapidly

Cinefluorography – How It Works - cont Cine film can be viewed as both a movie or in stop-action (single frame or frame-by-frame) Viewing as movie 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 then be slowed to 16 frames/sec (16 x 2 = 48 frames /sec = smooth action motion without noticeable flicker

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 Pharmacy 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

Video Disc Recording Video disc recorders are used to record Single field Single frame Short sequence Last image hold / freeze or “sticky fluoroscopy” When foot switch is depressed a real-time fluoro image is displayed When foot switch is released, the last full frame of a fluoro sequence is recorded and displayed as ‘last image hold’ After several sequences, previous last image holds can be reviewed one image at a time

Video Disc Recording Electronic radiography Is the term used when a video disc recorder is interfaced with the fluoroscope Use of this method permits fluoro radiation to continue only long enough to build a useful image on the output phosphor & camera, then stored as a single frame on the video disc recorder Process can be completed from 1/3 sec to 5 ms A 95% exposure reduction can be achieved using this method

Video Disc Recording Video disc frame rates or speeds vary from 1 image per sec to 30 images per second Frequency used is determined by the physiological motion of organ being imaged An additional benefit is the video recorder being capable of storing images for later review, photographing and printing as a permanent record Both magnetic and laser video disc equipment is available for either digital or analog recording Magnetic format uses an arrangement of magnetized particles on a moving disc, causing a magnetic field to fluctuate and produce a video signal Laser format uses a laser light to scan the disc surface, causing the light to be reflected to a photodiode to produce the video signal

Next up… Static Image Recording Systems