Computer calculations of target parameters for a stereotactic apparatus

Abstract

SummaryI~iechert and Mundinger's stereotactic apparatus (1956) has been modified and partly reconstructed so that the parameters of different target points, adopted during a single procedure, can be immediately calculated by a computer. The mathematicM foundations and derivations are given.The expansion of clinical information regarding stereotaetic brain operations employing multiple target points during one operation provides an opportunPuy to include computer calculations in the operative procedure 5. Moreover, Modell II. (developed in 1951) of the stereotactic apparatus of Rieehert and Mundinger 6, 7, s has boon so modified that a computer calculation of the focus parameters can be performed. The obvious advantages for clinical use are described elsewhere 1,3,3,4 Two points are fundamental: the target point, which will be reached by the probe, and the trepanation point where the probe will enter the skull.If the calculations are to be performed with the coordination of these two points, it is then necessary to appreciate the principles of construction of our current stereotactic apparatus (Figs. 1 and 2): G is the basal ring which is fixed temporarily onto the patient's head. B is the target arc which, by pivoting the X-axis, produces a partial sphere with radius R ----g. ~ and t are the target and the trepanation point; the angles ~, ~, 9, ~, and the penetration depth T have to be determined.The ~ point is next calculated, by an equation which relates the line of approach through ~ and t to the spherical shell:

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