Letter of response to “Individualization of deep brain stimulation targets for movement disorders”

Dear Editor, We would like to thank Josue M. Avecillas-Chasin for his appreciation of our study BThe variability of atlas-based targets in relation to surrounding major fibre tracts in thalamic deep brain stimulation^ [1] and for his valuable comments on the study. We fully agree with the concerns regarding the limitations of tractography, as already discussed in our article [1] and earlier reports by our group [2, 6, 10]. His own work constitutes a further valuable contribution to the topic [3]. Several studies in the past have used diffusion tensor imaging (DTI) and tractography to visualise fibre tracts in the region of the ventro-lateral thalamus [5, 7, 8, 11]. However the reliability of the depicted connections is yet unclear. First approaches to comparing diffusion tensor imaging-based fibre tracts with clinical effects have been made [3–5, 10] and have shown promising results. But, as demanded by Avecillas-Chasin, the method needs to be optimised and standardised. Optimal parameters for data acquisition (number of read-out directions, field strengths of MR scanner or voxel size) have to be generated, as well as optimal algorithms such as a mixture of tensors, Q-ball imaging, diffusion spectrum imaging and others [10]. As also mentioned by Avecillas-Chasin, it will be necessary in the future to compare deterministic algorithms with the probabilistic method, especially in tracts such as the dentate-rubro-thalamic tract (DRTT) that intersect regions with multiple fibre orientations. Furthermore, different software packages lead to different results in the depiction of chosen fibre tracts [6]. We are aware that the used method of DTI with deterministic tractography has its limitations and is not yet elaborate and reliable enough for implementation in routine clinical use as a standard tool. Therefore, today we still depend on neurophysiological and clinical information for targeting by means of micro-electrode recording (MER) and clinical testing in the setting of awake-surgeries [9].