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What
size of archive do I need ?
In the " Telemis Newsletter 8 ", we had touched
upon the archival question with regards to hardware options.
But the question of archival strategy needs to be asked as
well : how many " on-line " images should we keep,
what about " near-line " or " off-line "
?
The answer to these questions may vary according to the type
of project and to the phasing of a project.
An example of project may be teleradiology between several
sites wishing to cooperate for emergency cases. The A&E
(Accident and Emergency) application defines the specific
needs of such a project and it won't necessarily be useful
to keep images for very long. A classical system will provide
about 80 GB of hard disk space, allowing for storage of 30
to 120 days of imaging data.
Another example could be to strive for a " film-less
environment " for new imaging studies done. In this case
a fully digital solution must be found for all users that
received film before. Moreover the digital system will become
very central and a back-up procedure must be analysed in depth.
The analysis of hardware requirements will typically become
more important and will combine different levels of data
storage:
1- Recent data defined as " current ", requested
in over 90% of the cases (6 to 12 months of image production),
and readily available on hard disk
2- Back-up of recent data, to be available on robust media
and different from the existing hard disk, ideally in a different
location
3- Archival of "older " data on resilient media,
able to contain typically 5 to 7 years of image production
.
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Dr Lebon, one of the promoters of a digital hospital at the
CHR Namur (Belgium).
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The
phasing of a project may also command a phased approach
for ordering the equipment. In fact, a hospital may
choose to equip a limited number of users in the beginning
of the project in order to test the acceptance of viewing
on digital screens. This means that both film and digital
image viewing will be used for the duration of this
initial phase. The hardware requirements for this initial
phase may be quite minimal and hence rather cheap. When
decision is taken to extend the use of the digital system
to all medical doctors and stop the film prints, the
hardware requirements will have to be reconsidered.
This particular approach has been chosen by the "CHR
de Namur" hospital. It started on-screen diagnosis
in 2002 and feels more comfortable to prepare the passage
to the digital hospital on the whole site.
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