Fluoro: Image recording systems
Video disc frame rates vary from
1 image/sec to 30 images/sec
35mm vs 16mm format
35mm requires more dose but has a higher image quality
How much output image intensity does it require for proper exposure levels
90%
How much exposure reduction is achieved using video disc recording
95%
the image viewed during fluoro can be recorded in what 2 ways?
Dynamic or Static
Disadvantages of video tape recording
Lower resolution than cinefluorography and fixed framing rate at 30 frames/sec
How is a video signal produced from the video tape?
Recording and playback heads magnetically arrange and read a pattern of ferrous particles on the surface of a tape
Important factors in cinefluorography
Synchronization, framing frequency, F-number of the optical system, and framing and patient radiation dose
Types of Static recording
Video Disc, Radiographic cassette (film/sceen or CR), Photospot camera (roll or chip film) and charged-coupled devise (CCD)
sensitive component of the CCD
a layer of crystalline silicone
What is a CCD
a semiconducting device capable of storing a charge from light photons striking a photosensitive surface
Computerized fluoroscopy captures images using
an analog video camera and a digital image processor
Video signal must be converted by
an analog-to-digital (ADC) converter
Where is the CCD mounted
at the output phosphor of the image intensifier tube and is coupled by either fiber optics or a lens system
Advantages of video tape recording
available for instant replay w/o any intermediate processing, patient exposure is not increased, and can be viewed in slow motion or stop frame
Where is the "iris" or diaphragm located
between the camera lens and shutter
Which recording mediums causes the single highest dose rate
cassette recording
spot filming is accomplished by
cassettes, 100 or 105 mm chip film (cut film, sheet film) and 70 or 100 mm roll film (long roll of film)
Cinefluorography
consists of a cine (movie) camera positioned to intercept the image produced by the output screen of the image intensification tube
Grid Biased Tube
controls radiation pulse rate
Total over framing
diameter of circular image from optical system is equal to diagonal measurement of rectangular aperture (30mm) all of the film is used but 39% of image is wasted
Over framing
diameter of circular image from optical system is larger than shortest dimension of the film part of the image is lost
Exact framing
diameter of intensifier image at the ouput phosphor and the smallest dimension of the frame (18mm) are the same no part of the image is lost but only 58% of the film is used
Data is converted back to an analog image by
digital-to-analog (DAC) converter
What happens when ligh strikes the crystalline silicone (photoelectric cathode) of the CCD
electrons are released proportionally to the intensity of the incident light
What is the advantage of the CCD having a linear response curve
enables imaging with low light levels (less dose) possible with retained contrast resolution
Patient exposure with cinefluorography
exposure is significantly greater than with other types of image recording systems
Diameter of the optical lens determines?
how much ligh will flow through the lens
where is the cassette stored
in a lead lined compartment in the fluoro carriage
Increasing the frame rate does what to dose
increases the dose due to dose accumulation
Shorter focal length equals?
less magnification and increased light concentration at the image plane (film surface)
Video tape Recording
logical method to record closed-circuit TV system fluoro images.
Under Framing
maximum size of fluoro image is smaller than smallest dimension of the frame should be avoided
The lower the f-number means
more light and a faster lens and therefore less exposure is required
Larger optical lens diameter will allow?
more light to be transmitted than a small one
Cone camera shutter speed must be sychronized with?
pulse radiation (pulse synchronization)
Cine cameras operate by
recording a series of static images at high speed
Framing
refers to the use of the available film area used for image capture
First CCD
replaced the TV camera in a video system in 1980s
Resolution in Cinefluorography
resolution is dramatically increased compared to other dynamic image recording systems
What does the "iris" or diaphragm do?
restricts the divergence of light from the lens and controls the amount of light reaching the film
Length of the optical lens determines?
the amount of magnification and consequently the area (size) of light distribution
Length of the optical lends refers to?
the distance between the lens and image plane (film surface)
F-number is dependent on?
the focal length and diameter
Synchronization
the operation of the camera shutter at the same frequency
Frequency used in video disc recording is determined by
the physiological motion of organ being imaged
Types of Dynamic (motion) image recording
video tape recording, cinefluorography, and digital video
When do static images become necessary
when a permanent record of the fluoroscope exam is required