The appearance of analytical stereoplotters with large possibili- 
ties of application software further development should allow to combine 
easiness of use and great accuracy in measurements, both conditions being 
necessary to provide a good knowledge of intracranial vasculature. 
B) COMPLEMENTARITY OF THE 3 SOURCES OF INFORMATION 
  
It has been widely pointed out in literature ; but it is necessa- 
ry to develop a coherent system to analyse these data : a referential devi- 
ce should lead to this coherence. 
A multitude of systems have been described [ 1,2,3,4,7] . 
Whatever the method, the purpose is always the same one : it is 
the transfer of topographic co-ordinates x,y,z from scanner to the stereo- 
tactic system, as accurately as possible. 
Once you have got over this problem of coherence between the dif- 
ferent sources of information available (Scanner, Stereotaxis, Stereosco- 
Py), the interchanging of these information has to be studied. 
It can be carried out by dedicated software on the computer of 
the stereoplotter L5] - This software allows to plot and check correspon- 
ding points on C.T. slices and radiograms. Thus with this methodology, each 
point of the cerebral space can be replaced into its C.T. Scanner, stereo- 
tactic and stereoscopic contexts. (fig.6). 
II - COHERENCE OF THE 3-D INFORMATION ANALYSIS SYSTEM - REFERENTIAL DEVICE 
  
Thanks to the device that we have constructed* we may deter- 
mine the C.T. Scanner cross-sectional plane in relation to the stereotactic 
frame, taken as a reference (fig. 3-4). 
We can distinguish two parts : 
   
Fig.3 (left) : Referential device 
and fixation system. 
Fig.4 (right) : Referential device 
on the patient's head in the ste- 
reotactic frame. 
* A. QUEQUINER INSA RENNES 
228