Image Recording & Storage Devices Flashcards
Why are recording devices important?
- Rad is not always present
- Required for teleradiography
- Images can be used for later comparison
What are the types of film that can be used to capture images? (3)
- Transparency film
- Polaroid film
- Paper film
Are polaroids and transparency film positive or negative?
Transparency = Negative Polaroid = Positive
What was the most common type of recording medium and why?
Transparency film
- Several year shelf life
- Infinite resolution
What are the disadvantages of film? (4)
- Storage space
- Ease of retrieval for viewing
- Cost
- Not environmental
How is film constructed?
Layers with an acetate base topped with an emulsion layer that contains silver bromide crystals and a suspension of gelatin that is porous to liquids
How does film work?
Light strikes the crystals to form the latent image and are converted to silver grains via chemical processing
How does a film image become darker?
As the exposure to light increases more silver grains are activated (image becomes darker)
What is film speed?
How fast the film darkens
What must film speed and contrast be matched to?
The monitor that is used for exposure
How is film quality ensured?
Regular testing
How was film processed historically and how long did it take?
Manually
1 Hour per film
What were the steps processing of film?
- Development
- Fixing
- Washing
- Drying
What were the disadvantages of film processing?
- Variations in density/contrast of processing
- Chemicals were expensive
- Chemicals were not environmental
- Time to process
What is a multi-format camera?
One of the most common devices used to expose transparency film, essentially a CRT that could fix an image onto the film
What were the advantages of a multi-format camera?
- Excellent grayscale
2. Used a shutter and lens to control the exposure time and position
How fast was automatic processing of film and how was it done?
Rollers move the film through the steps in 1-2 mins
What was important about processing film from a multi-format camera?
The film was sensitive to light and had to be processed in a dark room with “wet” processing.
What were the disadvantages of the multi-format camera starting with the biggest? (4)
- One camera per machine
- CRT’s have curved screens which could distort the image
- High quality lens was needed and expensive
- Dust
- Bumping wrecked alignment
What replaced the multi-format camera?
The laser camera
What is laser an acronym for?
Light Amplification by Stimulated Emission of Radiation
What was improved with the laser camera? (Advantages)
- Intensity and size of beam are precisely controlled to improve contrast and detail resolution
- Many machines/modalities could be accommodated with one camera
Was the film for laser cameras sensitive to light?
No
How did the laser camera film work?
The film contains a laser sensitive carbo layer that when activated by heat cause the carbon to stick and the back can be peeled off
What was the advantage to polaroid film?
- No special processing
2. Inexpensive
What was the disadvantage to polaroid film?
Poor spatial resolution
How did b&w polaroid film work?
The exposure to light created white on the film using silver halide crystals
How did the colour polaroid film work?
The film had 3 layers (RGB) that were activated with exposure
How did the video thermal printer compare to the multi-format or laser printer?
Good quality but not as good
How did the video thermal printer work?
A video signal is stored in the memory and transferred to a thermal printing mechanism, the heat sensitive paper is passes along the mechanism and the heat creates gray scale
What does the gray scale correspond to in a video thermal printer?
The shade of gray corresponds to the amount of heat produced
What was the advantage to the video thermal printer?
Images were available instantly
What were the disadvantages to the video thermal printer? (3)
- Big issue with archival stability
- Exposed film could not be placed by any heat source
- Image degraded over time
How did the colour video printer work?
Similar to video thermal, used a dye on paper. No dye = white, mix of RGB = black.
What was the disadvantage of colour video printer?
The printing requires a single pass of each colour which increased the printing time
What did the magnetic tape recorder allow?
Ability to capture video instead of just a still image
What was the format of the magnetic tape recorder?
VHS (Video Home System)
What were the VHS tapes from the magnetic tape recorder played in?
VCR (Video Cassette Recorder)
What type of VHS was preferred and why?
S-VHS (Super VHS) because it had better spatial resolution.
How did the magnetic tape recorder work?
The tape contains magnetic dipoles that can be aligned in a magnetic field where the strength of the signal determines the alignment
How were the magnetic tape recorder tapes played back?
The tape is passed by the “read head” and the fluctuating magnetic field produces a video signal
What was an advantage to the magnetic tape recorder?
An audio track could be included in sync with the video signal
What was the difference in spatial resolution between the VHS and the S-VHS?
VHS = 240 lines on the monitor SVHS = 400 lines (greater spatial resolution)
How did the playback differ between VHS and SVHS?
Both VHS and SVHS could be played in a SVHS machine but SVHS could not be played in a VHS which posed compatibility issues
How were magneto-optic disks different?
They combined two technologies (magnetics and optics)
What were the advantages to magneto-optic disks? (3)
- Relatively large memory space
- Were rewritable
- Not susceptible to magnetic damage
How were magneto-optic disks used to record?
A laser heats the disk part its Curie point so that the magnetic crystals can be realigned when placed in a magnetic field
How were magneto-optic disks read?
A weaker laser scatters light off the disk and the intensity is read to create the signal
What was a disadvantage to magneto-optic disks?
They could hold hundreds of MB but suffered with a lack of compatible drives
What is PACS an acronym for?
Picture Archiving Communication System
What are the advantages of PACS? (6)
- Storage
- External viewing
- Connection to other modalities
- Web access
- Image Quality
- Time factor (no processing)
How does PACS work?
Digital data is electronically transferred from a machine to a work station and can be sent anywhere in the world via the internet
What was the challenge of PACS?
The manufacturers all used different programming and coding to digitize their images.
What is DICOM?
Digital Imaging and Communications in Medicine is the universal standard in compressing images
What did DICOM allow?
The images from any machine (by any manufacturer) to be sent to the workstations for tech and physicians to access
What are the disadvantages to PACS? (2)
- Large investment (but saves cost of film/chemicals/etc.)
2. The complexity of the equipment requires additional staff to upkeep, maintain and troubleshoot.
