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OBJECTIVEDespite the widespread use of deep brain stimulation (DBS) for movement disorders such as Parkinson's disease (PD), the exact anatomical target responsible for the therapeutic effect is still a subject of research. Intraoperative stimulation tests by experts consist of performing passive movements of the patient's arm or wrist while the amplitude of the stimulation current is increased. At each position, the amplitude that best alleviates rigidity is identified. Intrarater and interrater variations due to the subjective and semiquantitative nature of such evaluations have been reported. The aim of the present study was to evaluate the use of an acceleration sensor attached to the evaluator's wrist to assess the change in rigidity, hypothesizing that such a change will alter the speed of the passive movements. Furthermore, the combined analysis of such quantitative results with anatomy would generate a more reproducible description of the most effective stimulation sites.METHODSTo test the reliability of the method, it was applied during postoperative follow-up examinations of 3 patients. To study the feasibility of intraoperative use, it was used during 9 bilateral DBS operations in patients suffering from PD. Changes in rigidity were calculated by extracting relevant outcome measures from the accelerometer data. These values were used to identify rigidity-suppressing stimulation current amplitudes, which were statistically compared with the amplitudes identified by the neurologist. Positions for the chronic DBS lead implantation that would have been chosen based on the acceleration data were compared with clinical choices. The data were also analyzed with respect to the anatomical location of the stimulating electrode.RESULTSOutcome measures extracted from the accelerometer data were reproducible for the same evaluator, thus providing a reliable assessment of rigidity changes during intraoperative stimulation tests. Of the 188 stimulation sites analyzed, the number of sites where rigidity-suppressing amplitudes were found increased from 144 to 170 when the accelerometer evaluations were considered. In general, rigidity release could be observed at significantly lower amplitudes with accelerometer evaluation (mean 0.9 ± 0.6 mA) than with subjective evaluation (mean 1.4 ± 0.6 mA) (p < 0.001). Of 14 choices for the implant location of the DBS lead, only 2 were the same for acceleration-based and subjective evaluations. The comparison across anatomical locations showed that stimulation in the fields of Forel ameliorates rigidity at similar amplitudes as stimulation in the subthalamic nucleus, but with fewer side effects.CONCLUSIONSThis article describes and validates a new assistive method for assessing rigidity with acceleration sensors during intraoperative stimulation tests in DBS procedures. The initial results indicate that the proposed method may be a clinically useful aid for optimal DBS lead placement as well as a new tool in the ongoing scientific search for the optimal DBS target for PD.

International audience; Introduction:Deep brain stimulation (DBS) is a common neurosurgical procedure for relieving movement related disorders such as Parkinson’s disease. DBS presents uncertainties associated with suboptimal target selection, partially due to incomplete knowledge of the optimal stimulation site in the brain and suboptimal exploitation of the intra-operatively obtained patient data in general. Our aim was to evaluate the feasibility to objectively assess clinical effects obtained during intraoperative test stimulation based on acceleration measurements.Methods:Two patients referred for bilateral DBS-implantation for the treatment of Parkinson’s disease were included in the study. For one patient, rigidity was evaluated by fixing a 3-axis accelerometer on the neurologist’s wrist during intraoperative test stimulation. While the intensity of stimulation current was increased, the neurologist continuously moved the patient’s wrist to determine the moment of and the amplitude at rigidity release (“stimulation threshold”). For the other patient, tremor was evaluated by fixing the accelerometer on the patient’s wrist during stimulation. In this case, the neurologist evaluated the stimulation threshold based on visual examination of variation in tremor. In both cases, for each test stimulation position, different mathematical features were determined and statistically compared a) for the time period before reaching the stimulation threshold identified by the neurologist and b) after reaching the threshold. We then statistically identified the stimulation thresholds that would have been chosen based on the acceleration signal alone and compared them to the ones subjectively identified by the neurologist.Results:A statistical significant change in rigidity (p

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Poster; International audience; Background: Deep brain stimulation (DBS) is a common neurosurgical treatment for the tremor of Parkinson’s disease, essential tremor, and tremor of other causes. The outcome depends on optimal placement of the permanently implanted electrode. Many centers perform DBS surgery under local anesthesia in order to confirm the therapeutic effect with intraoperative stimulation testing. Visual inspection—the method generally used to rate changes in tremor during stimulation testing – is subjective, and its accuracy depends on the evaluator’s experience. This study presents the results of quantitatively estimating improvement in tremor during intraoperative stimulation tests in 15 patients. In addition, its influence on identifying the final position of the permanently implanted electrode is described.Method: We designed a 3D acceleration sensor system that is attached to the patient’s forearm during surgery. During intraoperative stimulation tests, at each different position, accelerometric data are synchronously recorded with the changing stimulation current amplitude. The method was applied in 15 DBS procedures in 2 centers (University Hospital Bern, Switzerland & University Hospital Clermont-Ferrand, France); the data were analyzed offline to assess improvements in tremor and to identify tremor-suppressing stimulation current-amplitudes. For correlation analysis, the quantitatively and visually determined improvements in tremor were categorized into: no improvement, low improvement, average improvement, high improvement and tremor arrest. The quantitatively identified tremor-suppressing currentamplitudes were compared to those identified by visual inspection, in order to determine the influence these findings would have had on the position chosen for permanent electrode implantation if they had been used for intraoperative decision-making. As this was a purely observational study, the accelerometric measurements werenot, in fact, allowed to alter the surgical procedures in any way.Results: A total of 359 evaluations were available for a comparison of the improvement in tremor identified by accelerometry vs. visual inspection. Of these evaluations, 156 (43.5%) were assigned the same categorie by both methods; 296 (82.5%) fell in the same or neighboring categories; and 63 (17.5%) were at least 2 categories apart. The quantitatively identified tremor-suppressing current-amplitudes were significantly lower than the visually identified ones (1.13 ± 0.8 mA vs. 1.7 ± 0.8 mA [mean ± SD]). Of the 26 finally chosen positions for permanent lead implantation, 15would have been different had the accelerometric data been considered.Discussion and Conclusion: The improvement of tremor brought about by test stimulation was rated in the same category by visual inspection and by quantitative measurement (accelerometry) in only 43.5% of the evaluations that we made in this study. In some of the evaluations where there was only mild tremor at baseline, the stimulation-induced improvement in tremor was classified by visual inspection as tremor arrest, while accelerometry revealed a very mild residual tremor. This fact explains many of the instances in which the tremor ratings obtained by the two methods were only 1 category apart, but it cannot account for the 17.5% of evaluations that were 2 or more categories apart. The quantitative assessment of tremor as performed here yields different findings from assessment by visual inspection alone. The tremor-suppressing stimulation current-amplitudes are lower, and this, in turn, can often affect the chosen site for permanent electrode implantation. Thus, quantitative tremor assessment can affect, and perhaps improve, targeting in DBS without altering the routine surgical procedure. This tentative conclusion awaits confirmation by further studies. Moreover, aside from its potential direct clinical utility, quantitative tremor assessment DBS surgery might be a useful adjunct to the clinical testing of new types of DBS electrode.

Poster; International audience; Introduction: The outcome of deep brain stimulation (DBS) depends heavily on the position of the implanted lead. After a preoperative anatomical planning, most groups collect numerous intraoperative data such as therapeutic effects induced by stimulation tests. To choose the final implant position, physicians “mentally” visualise all available data. The aim of the present work was to develop a method visualising intraoperative stimulation test results, patient’s images, electric field (EF) simulations for the patient-specific stimulation conditions and the corresponding therapeutic effects quantitatively evaluated by accelerometry. The application to five essential tremor (ET) patients should give a first idea about the optimal target position. Methods: In Clermont-Ferrand University Hospital the anatomic target structure and the neighbouring structures were manually outlined, a target and a trajectory defined and two parallel trajectories per hemisphere intraoperatively evaluated. Stimulation tests were performed at 7 to 8 positions per trajectory and several stimulation current amplitudes. The therapeutic effect was evaluated using a previously published method based on accelerometry. Finite element models and simulations were performed for up to three stimulation amplitudes per position and EF isosurfaces (0.2V/mm) were extracted. For the 3D visualization of the numerous overlapping isosurfaces, we generated “improvement maps” by assigning to each voxel within the isosurfaces the highest tremor improvement. Those maps were visualized together with anatomical images, delineated structures and trajectories (Paraview, Kitware Inc). The method was applied to 5 ET patients implanted in the ventro-intermediate nucleus of the thalamus (VIM). Results were analysed by the neurosurgeon regarding the optimal implant position. Results: The clinical teams were able to identify the optimal implant position for all patients with more ease and in less time compared to the routine discussion using pen and paper. Additionally, for 7 of the 9 improvement maps, the highest improvement region was found to be in the posterior subthalamic area, inferior and posterior to the VIM. Conclusion: Improvement maps assist the clinicians in determining the optimal implant location of the chronic DBS lead. Results support findings of other studies that the fibre tracts in the posterior subthalamic area like prelemniscal radiations may be responsible for alleviating tremor in ET patients.