Objective: Defining the best lead trajectory (Arc; Ring) with a computational 3D stereotactic model of the Globus Pallidus internus (GPi) and investigating the influence of electrical field and voltage values.

Background: It is well known that the position of the leads within the GPi is a key issue in improving continuous electrical neuromodulation therapy in movement and behavioural disorders. A standard trajectory has not been yet established. The choice of the trajectory depends on the neurosurgeon and is essentially based on anatomical criteria. However, the use of a 3D stereotactic model of the GPi shows that the trajectory must also depend on the anatomy of the target itself. In our centre, leads are routinely implanted under a stereotactic procedure based on magnetic resonance imaging alone through a coronal transfrontal approach in such a way that no vessels or sulci are encountered.

Methods: We modelled a surgical case with a normal right GPi. Modelled electrical parameters were: contacts 1 and 2 negative (C+, 1-, 2-). The isofield lines (ISL) were configured to 0.2V/mm. The intersection between the electrical field volume and GPi volume was processed for voltage ranging from 0.5 to 2.0V. Both ring and arc values ranged from 90 to 45 degrees, bearing in mind that it is quite rare to end up with angle values of less than 70 degrees. Eventually, angle values from primo-implantation type surgery over one year were collected with the aim of comparing them with the optimal values found.

Results: Maximal overlapped volume appeared when: the arc value was between 90 and 80 degrees; and ring value was between 50 and 60 degrees. Arc value decreased with an increase in voltage intensity. In contrast, ring value increased with an increase in voltage intensity. In this surgical case, the lead path chosen by the neurosurgeon was defined with 88.3 degrees as the arc value and 74.6 degrees as the ring value. Over one year, we implanted leads with arc values within the [92; 71] range, with a mean value of 80.9, and ring values within the [89; 59.5] range with a mean value of 75.4.

Conclusions: The anterior-lateral path proved to be the optimal trajectory. This is confirmed by results over one year of procedures which were close to the results of our proposed model. This study shows that it is possible to associate the theoretical optimal electrical field overlapping with a safe trajectory.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/finding-an-optimal-lead-trajectory-for-a-better-stimulated-volume-in-movement-disorder-therapy/