Article
Deep brain stimulation: the variability of atlas based targets in relation to surrounding major fiber tracts
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Published: | May 13, 2014 |
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Objective: In essential tremor (ET) the main target for deep brain stimulation (DBS) is the thalamic ventralis intermedius nucleus (Vim). This target cannot be identified on conventional MR imaging. Therefore targeting depends on probabilistic coordinates derived from stereotactic atlases. The goal of our study was to investigate the variability of atlas based Vim targets in relation to surrounding major fiber tracts.
Method: In 10 patients who underwent DBS atlas based Vim targets were determined in both hemispheres. In addition, we have performed deterministic fiber-tracking based on diffusion tensor imaging (DTI) of the dentato-rubro-thalamic tract (DRTT), pyramidal tract (PT) and lemniscus medialis (LM) in all 20 hemispheres. Standardized regions of interest and DTI parameters were used in all cases. Subsequently we measured the distance from the atlas based Vim target to each tract along the medial/lateral (x-coordinate), anterior/posterior (y-coordinate) and superior/inferior axis (z-coordinate).
Results: 17 out of 20 DRTTs could be depicted with our standardized DTI/fiber tracking parameters. The PT and the LM could be displayed in all 20 hemispheres. The projection of the atlas based Vim target was found medial (n=2), lateral (n=4) and inside the DRTT (n=11) (concerning the x-coordinate) with a mean distance of 2.1mm. Along the y-axis atlas targets were positioned anterior (n=1), posterior (n=11) and inside the DRTT (n=5) with a mean distance of 2.8mm. 3 targets were located superior, 4 inferior and 10 inside the DRTT concerning the z-axis (mean distance = 2.0mm). A similar variability of positions of the atlas targets was found regarding the PT and LM.
Conclusions: We found a considerable variability of the locations of atlas-based target points of the ventralis intermedius nucleus in relation to neighboring major fiber tracts in individual patients. These results suggest that DTI based fiber tracking might help to individualize targeting to structures not directly visible on conventional MRI.