1. Fluoroscopy: Dynamic Imaging Systems

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Cinefluorography Camera

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

12. 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)

13. 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

14. 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

15. 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

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

17. 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

18. Synchronization of Exposure to Film

19. 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

20. 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

21. 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

22. 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

23. 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.

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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