2 - Stereotactic radiograms 
  
The morphological and functional approach to brain structures 
provides an excellent practical use for stereotactic methodology (develop- 
ped in France by Talairach and Coll). Of course, it cannot be used in every 
Case, nor in every way ; for this reason a first selection of patients to 
whom this kind of approach could be applied is now ensured bv C.T.. scan~ 
ning. 
The stereotactic frame is in fact the most important factor and 
will allow for a very precise 3-D approach and also provides the plane of 
reference which is necessary for the use of an entire series of instru- 
ments. 
Stereotactic neuroradiology involves the use of a focus-film dis- 
tance which allows for maximum reduction of magnification of the radiologi- 
cal image. A distance of 5 meters was chosen. Furthermore, the axis of the 
X Rays must be perpendicular to the plane of the film and must pass through 
the median planes of the retention system. 
This technique allows us to obtain the radiological morphogram 
which can be defined in this way : a collection of vascular, ventricular 
cerebral unmagnified and undistorted data, all superimposable, carried out 
in one session (fig.l). 
With this information, a whole series of investigations can be 
safely and preciselv carried out during this examination or later on 
implantation of electrodes, staggered stereotactic biopsies, puncture and 
visualization of a cyst, implantation of radioactive bodies in a deep 
inoperable tumour. 
At the end of this procedure, the therapeutic attitude can be 
easily worked out and the choice will be facilitated by this collection of 
data. 
The works of our laboratory are described and illustrated in a 
monograph entitled "Stereotactic approach to diagnosis and treatment of 
cerebral tumours".[6] 
In spite of all the advantages of this approach (which has proven 
very complementary of CT Scan examination) we must point out the difficul- 
ty of a really three-dimensional analysis, in particular of intracranial 
vessels as only two series of frontal and lateral projections of a very 
complicated network are available : this 3-D analysis requires a third 
source of information : stereoscopy. 
3 - Pair of stereoscopic angiograms 
  
Using 2 stereoscopic angiograms (2 lateral or frontal views, 
taken in stereotactic conditions, making a stereo angle of 6 degrees) the 
technics of photogrammetry enable to visualize the opacified vessels in the 
stereoscopic field and to get quantitative information about their 3-D 
topography (fig. 2). 
J. VIGNAUD [8] and Coll. have already shown what could be done 
with such a method but, because of a lack of stereocomparators adapted to 
medical constraints, it has not had any further development so far. 
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