Sweetspot mapping in deep brain stimulation: Strengths and limitations of current approaches

Abstract

Objective: Open questions remain regarding the optimal target, or sweetspot, for deep brain stimulation (DBS) in e.g. Parkinson's Disease. Previous studies introduced different methods of mapping DBS effects to determine sweetspots. While having a direct impact on surgical targeting and postoperative programming in DBS, these methods so far have not been investigated in ground truth data. Materials & Methods: This study investigated five previously published DBS mapping methods regarding their potential to correctly identify a ground truth sweetspot. Methods were investigated in silico in eight different use case scenarios, which incorporated different types of clinical data, noise, and differences in underlying neuroanatomy. Dice coefficients were calculated to determine the overlap between identified sweetspots and the ground truth. Additionally, out of sample predictive capabilities were assessed using the amount of explained variance R-squared. Results: The five investigated methods resulted in highly variable sweetspots. Methods based on voxel-wise statistics against average outcomes showed the best performance overall. While predictive capabilities were high, even in the best of cases Dice coefficients remained limited to values around 0.5, highlighting the overall limitations of sweetspot identification. Conclusions: This study highlights the strengths and limitations of current approaches to DBS sweetspot mapping. Those limitations need to be taken into account when considering the clinical implications. All future approaches should be investigated in silico before being applied to clinical data.

The Contribution of Subthalamic Nucleus Deep Brain Stimulation to the Improvement in Motor Functions and Quality of Life

“…In the past, different methods to calculate sweet spots for clinical outcomes have been used (references9 and 43‐46 ; for an overview, see reference 47). Here, we chose a comparatively simple weighting method (by calculating t scores against zero) but used it to cross‐predict out‐of‐sample results not observed by the model (leave‐one‐out cross‐validation design).…”

“…New methods of sweet spot calculation have recently been proposed, and future studies may further refine our findings and compare statistical methods to the one applied here. Statistically, a t test model comparing to zero has been criticized, in the past, because most patients improve and, therefore, t ‐values will always be positive 47 . However, because we used the t ‐values only as a surrogate parameter for our maps and not as an indicator of voxel‐wise statistical significance, this problem is only of little importance.…”

Predicting Outcome in a Cohort of Isolated and Combined Dystonia within Probabilistic Brain Mapping

“…Some questions remain regarding the optimal DBS target for dystonia in the pallidal region 24 . Previously published approaches result in a variety of different DBS “hotspots” when used in the same dataset.…”

“…Previously published approaches result in a variety of different DBS “hotspots” when used in the same dataset. The most recent models, which employed voxel‐wise statistics comparing the outcomes of each voxel against an average of other outcomes in the dataset, explained substantially greater response variance compared to classically‐described target locations 11,24–27 . These voxel‐wise models provide the highest accuracy and predictive capabilities between detected and predefined outcome maps.…”

A randomized crossover trial of short versus conventional pulse width DBS in Parkinson’s Disease

“…[1][2][3] However, postoperative outcomes critically depend on lead locations and stimulation settings. [4][5][6][7] While titration of the stimulation amplitude and choice of the active contact are usually individual, stimulation frequency and pulse width are typically set to standard values of 130Hz and 60µs. This standard value emerged from a previous study, demonstrating that a pulse width of 60µs enlarges the therapeutic window.…”