1. 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

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
Cinefluorography
Static recording
Radiographic cassette
Photospot camera
Video disc

3. 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)

4. 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

5. 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

6. 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

7. Cinefluorography Camera

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

9. 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

10. 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

11. Synchronization of Exposure to Film

12. 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

13. 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)

14. Focal Length Diagram

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

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

22. 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

23. 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

24. 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

25. Next up… Static Image Recording Systems