Travels are controlled in x and y by a ball on an air-cus-
hion and in z by a large drum-shaped roller. Fine markers in the middle of
the screen allow precise plottings in the stereomodel (in real-time and
X-y-Zz true coordinates).
b) an electronics compartment
It consists of several systems ensuring slaving and acquisi-
tion : they correspond to the travel axes of the photo stages, of the
drawing table and the automatically-controlled tool-holder.
c) a mini computer 16 bits NOVA 4 (manufactured by DATA GENE-
RAL) with 32 kwords RAM memory.
It runs computer programs that can be classified in 3 catego-
ries
- a driving software piloting orders to electronics in or-
der to control
. the photo stages, according to a mathematical model
computed during the model orientation
. the drawing-table after adjustment to the stereomo-
del
- the automatically-controlled tool-holder according to
the parameters of a previously defined trajectory.
- the "standart-traster" software : it includes the diffe-
rent tasks directly connected to photogrammetry (plotting, relative and ab-
solute orientations).
- the application software : it manages the ressources of
the system in order to help the surgeon to define, as easily and accurately
as possible, the parameters of a surgical operation of the brain.
In other words it allows
. to replace corresponding points on the different pe-
ripheral units (especially drawing table and graphic
display terminal)
- to choose target points and trajectories leading to
the targets
. to build a "patient file" with which the intervention
will be able to be planned and simulated.
2 - Drawing table
A series of stereotactic frontal and lateral angiograms
shall be disposed on the drawing table showing arteries, veins, cerebral
cavities. After an accurate adjustment on the stereomodel it will complete
the information available from the stereoscopic pair. This real-time driving
of the table will allow to replace any point of the model into its vascular,
and venticular contexts.
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