Individual localization of thalamic contacts
Thalamic contacts were localized by using the procedure described below
(see also Simor et al. 2021). In order to individually localize the
thalamic contacts preoperative MRI and postoperative CT images were
co-registered using tools available in the FMRIB Software Library (FSL,
Oxford, FLIRT, linear registration, 6 degrees of freedom). Threshold was
applied on the co-registered CT scans to achieve the desired level of
density for proper identification of the lead, thus removing the
surrounding brain tissue. Coordinates of the most distal point of the
lead were identified and a more proximal point was selected along the
line of the contacts to mathematically reconstruct the coordinates of
the center point of each contact using Euclidean distance in three
dimensional space. These points superimposed over the T1 MRI image
provided a guideline for contact localization by examining their
location to the anatomical boundaries of the ANT. Anatomical positions
according to standard coordinates of the contacts were double-checked by
using the mamillothalamic tract as an anatomical guide to localize the
ANT. In case of convergent results of these two methods, the ANT (for 15
patients) and MD (for 10 patients) contacts were considered as subjects
for further digital signal processing in the present study.