Pacs-Storage Devices

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Image Storage Devices

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Magnetic:magnetic disc, magnetic tape
Optical: optical disc, CD-ROM, CD-R, CD-RW, drivers, DVD, USB Electronic: RAID, PACS

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Magnetic Disc

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A memory device such as a floppy disk. It is a flat disc covered with a magnetic coating containing magnetic domains. Digital information is stored on this coating in the form of microscopically small, magnetized needles. When the domains are subjected to a magnetic field, they will align with that field. Then, an electrical current is applied to change the polarity of the domains. When this is removed, the magnetic domains will remain in alignment.

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Magnetic tape

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A medium for magnetic recording. They work similar to a magnetic disc, but with larger domains and smaller storage capacity. It is made of thin magnetizable coating on a thin, narrow strip of plastic.

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Optical Disc

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An optical disc is a Compact Disc or "CD." A CD contains a plastic coated surface and stores data as tiny pits etched in the disc surface. A laser is used to read the data by scanning the surface.

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CD-ROM

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Read only memory, contains data accessible to, but not writable by a computer for data storage. These are popularly used to distribute software. The data is already pressed into the polycarbonate layer in the form of bumps and troughs. The aluminum is then laid over this to reflect the laser to the optical pickup. This information is permanently stored and cannot be over written, destroyed or altered. When scanned, the bumps and troughs reflect differently and correspond to 0s and 1s.

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CD general structure

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A thin film of aluminum sandwiched between a piece of clear polycarbonate and a film of acetate in the shape of a disc 120mm x 1.2mm.

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CD-R

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CD-R's contain a layer of dye between the aluminum and the polycarbonate. When data is written to the CD, a high power laser heats the area to be recorded and turns the dye black. This serves the same purpose as the bumps in the CD-ROM. Once the dye has been "burnt," the info is permanently recorded.

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CD-RW

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This utilizes a mixture of metals -- antimony, indium, silver and tellurium. When heated to different temps, this layer is either reflective or dull. The dull areas do not reflect the light. To re-write, the crystals are reheated.

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Drivers

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A program that determines how a computer will communicate with a peripheral device. The program needed to allow reading and writing of a CD-R/RW

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DVD

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Digital Versatile Disc. Similar to a CD-ROM, but a DVD can store more data on the same surface area. The size of the tracks that are encoded is much smaller. A DVD has two layers of pits and bumps to allow double the surface area for recording. Some DVD's are also double sided for even further storage capacity. The DVD utilizes a finer wavelength laser meaning that a finer track can be created with smaller pits and bumps.

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USB

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Universal Serial Bus. A connection device that allows very rapid transfer of data between the main computer system and a peripheral device. Flash drive, thumb drive. Solid state storage device with static memory.

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RAID

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Redundant array of Independent discs. Several magnetic discs or hard discs that link together to form an array. Memory on a RAID ranges from several hundred GB to several TB. Capable of short or long term storage. Long term storage is less expensive using a RAID than other storage types, however, it is not ideal.

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RAID-short term storage types

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1. Information is "striped" across several discs
2. Duplicate discs created
3. "Striped" across all but one disc that contains all information. This disc is referred to as the "parity."

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PACS

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Picture Archiving and Communication System. This is the in-house image storage system that allows easy access to image data. Costs can be high depending on needs of the department.

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ASP

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Application Service Provider. This is an outside company providing archiving and management options for image storage. Short term archive may be supplied on site, while long term archive is kept off site. ASP allows access to equipment at a lower cost. ASP also accounts for disaster recovery by storing copies of data off site.

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Care of CD/DVD

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-Do not stack
-Do not touch under the surface
-Do not eat, drink or smoke around discs
-Do not expose to excessive heat
-Hold edges when transferring
-Keep in the jewel case

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USB flash drive

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Consists of a flash memory data storage device integrated with a USB interface. They are removable and rewritable and have storage capacities up to 256 GB.

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DICOM-File based storage

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Software on the computer system used for storage.

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DICOM-database based storage

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Information is sent to a database for storage. This type of storage allows for manipulation of data for easier access (query, sort, etc). It is also more expensive to maintain and if the database goes down, no one has access to the information.

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DICOM-mixed PACS storage

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With a mixed storage system, data is segmented into chunks before storing. This may create issues when trying to view images on other systems that "don't know" how to put the chunks together.