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Deep brain stimulation (DBS), an effective surgical treatment for Essential Tremor (ET), requires test stimulations in the thalamus to find the optimum site for permanent electrode implantation. During these test stimulations, the changes in tremor are only visually evaluated. This, along with other parameters, increases the subjectivity when comparing the efficacy of different thalamic nuclei. We developed a method to quantitatively evaluate tremor during the test stimulations of DBS surgery and applied to 6 ET patients undergoing this treatment. From the quantitative data collected, we identified effective stimulation amplitudes for every test stimulation position and compared it with the ones identified visually during the surgery. We also classified the data based on the thalamic nuclei in which the center of the stimulating contact was present during test stimulations. Results indicate that, to achieve the same reduction in tremor, on average, the stimulation amplitude identified by our method was 0.6 mA lower than those identified by visual evaluation. The comparison of the different thalamic nuclei showed that stimulations in the Ventro-oral and the Intermediolateral nuclei of the thalamus result in higher reduction in tremor for similar stimulation amplitudes as the frequently targeted Ventrointermediate nucleus. We conclude that our quantitative tremor evaluation method is more sensitive than the widely used visual evaluation. Using such quantitative methods will aid in identifying the optimum target structure for patients undergoing DBS.

International audience; Deep brain stimulation (DBS) surgery is extensively used in the treatment of movement disorders. Nevertheless, methods to evaluate the clinical response during intraoperative stimulation tests to identify the optimal position for the implantation of the chronic DBS lead remain subjective. In this paper, we describe a new, versatile method for quantitative intraoperative evaluation of improvement in tremor with an acceleration sensor that is mounted on the patient's wrist during surgery. At each anatomical test position, the improvement in tremor compared to the initial tremor is estimated on the basis of extracted outcome measures. This method was tested on 15 tremor patients undergoing DBS surgery in two centers. Data from 359 stimulation tests were acquired. Our results suggest that accelerometric evaluation detects tremor changes more sensitively than subjective visual ratings. The effective stimulation current amplitudes identified from the quantitative data (1.1 ± 0.8 mA) are lower than those identified by visual evaluation (1.7 ± 0.8 mA) for similar improvement in tremor. Additionally, if these data had been used to choose the chronic implant position of the DBS lead, 15 of the 26 choices would have been different. These results show that our method of accelerometric evaluation can potentially improve DBS targeting.

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

International audience; Introduction:DBS is a routinely performed surgical procedure for treatment of movement disorders like Essential Tremor (ET). However, the target selection in DBS is not fully optimized. Incomplete knowledge of the mechanisms of action being one of the reasons, we believe, suboptimal usage of information during surgery is another. We have previously demonstrated the use acceleration sensors to quantify changes in patient tremor during deep brain stimulation surgery. In this paper, we would like to analyze the correlation of the acceleration data results with the different deep brain structures. We present in this paper the result from 5 ET patients implanted in the VIM. Methods: A 3 axis acceleration sensor was used to record and quantify changes in the patient's tremor while test stimulations were performed during DBS surgery using the method described previously. During surgery, for every test stimulation position, the maximum change in patient's tremor and the stimulation amplitude at which it was observed subjectively were noted. As the acceleration data was continuously recorded, it was possible, from offline analysis, to find stimulation amplitudes for changes in statistical features equal to those found subjectively. Additionally, the stimulation amplitudes at which acceleration data suggested maximum change in tremor were also identified for every test stimulation position. For the anatomical analysis, the surgical team carefully identified the anatomical location of the electrode and attributed one thalamic sub-structure to it. Based on this information, the change in tremor and its corresponding stimulation amplitude were grouped into respective sub-structures. For the identification of most effective anatomical sub-structures, we checked for higher reduction in tremor at lower amplitude, both for subjective evaluations and acceleration data analysis. This method was applied to acceleration data collected from 5 Essential tremor patients under a clinical study in University Hospital in Clermont-Ferrand France. A total of 107 test stimulations were analyzed. The different sub-structures of the thalamus have been named according to the previously published nomenclature. Results: The 107 different test stimulation positions were found to be distributed in different parts of the thalamus: Intermedio-Lateral (InL, n=20), Ventro-Oral (VO, n=16), VIM (n=37), Ventro-Caudal-Lateral (VCL, n=2), Central-Medial (CM, n=3), Ventro-Caudal-Medial (VCM, n=23) and the PreLemniscal Radiations (PLR n=6). As the number of test stimulations in the VCL, CM and PLR is low, the significance of the results is very low.For the other structures, the effective stimulation amplitudes for the same clinical effect were lower for acceleration data than the subjective ones (p75%) was on average lower in the VO (1.8 mA) and in VCM (1.9 mA) as compared to the VIM (2.5 mA) and in InL (2.5 mA). Conclusion:The use of sensitive acceleration measurements during the surgery introduces a new approach to analyze the effectiveness of stimulation in different target structures. Our results suggest that the VCM is a better target than the VIM. This information should be considered during the planning of the exploration paths to have more contacts in the effective thalamic area. However, the current analysis does not take into considerations stimulation induced side effects. Those influence the final implant position significantly and can alter our conclusion. Also, attributing one stimulation position to just one structure considering it as a point is suboptimal. A better approach would be to simulate the stimulated volume by using electric field simulations. Along with additional analysis of the results with reference to the known mechanisms of actions of DBS they may result in increasing our understanding of DBS efficiency.

Objective The aim of the present study was to evaluate the feasibility to objectively assess clinical effects on rigidity obtained during intraoperative test stimulation based on acceleration measurements. Background Deep brain stimulation (DBS) has few uncertainties associated with suboptimal target selection. The feasibility of using acceleration measurements to evaluate tremor quantitatively during DBS surgery has been shown earlier (1). However to be able to quantitatively evalute the clinical effects of intraoperative stimulation on Parkinson's disease patients it is important to take rigidity as a symptom into consideration. Methods 3 patients referred for bilateral sub thalamic nucleus DBS implantation were included in the study. To quantitatively evaluate rigidity a 3 axis acceleration sensor was fixed to the neurologist's wrist during the evaluation of the patient. Accelerometer data was post operatively analyzed statistical features were extracted similar to those in (1) with the same method but with different cut off frequencies for the filters. The effective stimulation amplitudes (thresholds) were identified. Wilcoxon two sided rank test was used to identify the significance of changes in the statistical features 1) before and at thresholds identified by medical experts and 2) those before and at thresholds found using acceleration data alone. Results Out of the calculated statistical features standard deviation signal energy and peak frequency amplitude were the most sensitive to changes in patient rigidity. The changes in the features when compared to baseline were in the range of 0 40. The thresholds identified based on acceleration data were lower in 40 of the cases compared to the one chosen by the neurologist. The results of the statistical test showed higher significance for the changes at the acceleration thresholds than the ones identified subjectively. Conclusion The results of this study suggest that acceleration measurements of the neurologist's wrist can be used to quantitatively evaluate the changes in patient's rigidity. This simple method may provide additional support to the neurosurgeon in selecting the optimal target even if identified changes (0 40) are less significant than for tremor (0 99).

International audience; Objective Deep brain stimulation (DBS), a routine neurosurgical treatment for movement related disorders, has few uncertainties associated with suboptimal target selection. Our aim is to evaluate the feasibility to objectively assess clinical effects on tremor obtained during intraoperative test stimulation based on acceleration measurements. Methods Five patients (1 Parkinson's disease and 4 Essential Tremor) referred for bilateral DBS-implantation were included in the study. Tremor was evaluated by fixing a 3-axis accelerometer on the patient's wrist during intraoperative test stimulation. The accelerometer data was post-operatively analyzed, statistical features were extracted and effective stimulation amplitudes (thresholds) identified (Fig 1). Wilcoxon two sided rank test was used to identify significance of changes in the statistical values before and at thresholds identified by medical experts and those before and at thresholds found using acceleration data alone. Results Out of the statistical features identified, the standard deviation, signal energy and peak frequency amplitude were the most sensitive to changes in patient tremor. The thresholds identified based on acceleration data were lower in 65% of the cases compared to the one chosen by the neurologist. The results of the statistical test showed higher significance for the changes at the acceleration thresholds than the ones identified subjectively.

International audience; Deep Brain Stimulation (DBS) surgery is used increasingly as a symptomatic treatment for patients with movement related neuro-degenerative disorders. However, the method of intraoperative symptom evaluation is subjective. This paper proposes a method to quantitatively evaluate tremor by measuring the acceleration of the patient's wrist during the surgery. The results of applying the method to 2 patients suggest that the acceleration measurements are very sensitive to the change in the tremor and that they can be used to identify clinically effective stimulation amplitudes. By collecting acceleration data from DBS surgeries for many patients, we hope to add more knowledge to the mechanisms of deep brain stimulation.

The use of Deep Brain Stimulation (DBS) surgery is increasing as a treatment for movement related disorders. One of the important areas of improvement is the target selection procedure. To do so we measured the acceleration of tremor by sensors in 6 patients during their DBS surgeries to evaluate the changes quantitatively. The post operative data analysis revealed that acceleration measurements are very sensitive to the changes in tremor and that they can be used to identify clinically effective stimulation amplitudes. With the aim to increase objectivity in symptom evaluation we intend to introduce real time analysis so as to provide more information to the neurosurgeon to aid him in his target selection during the surgery. © 2013 by Walter de Gruyter.

International audience; Deep brain stimulation (DBS) of basal ganglia using surgically implanted electrodes is now an effective and widely-used method to treat neurological movement related disorders such as Parkinson's Disease (PD) and Essential Tremor (ET). The mechanism of action of DBS is not fully understood; optimal target definition is difficult and thus most groups use complementary intraoperative methods. Intraoperative stimulation tests are performed along the predetermined trajectories to evaluate the clinical effects on tremor while gradually increasing the stimulation parameters (voltage/current), determining the thresholds for clinical effects (subjective threshold) and side effects at each anatomical measurement position. Currently, these evaluations are performed semi quantitatively by the neurosurgeon or the neurologist. Our method intends to improve the targeting procedure and make it more objective by measuring the acceleration of the patient's wrist.

International audience

Introduction Deep brain stimulation (DBS) is a common neurosurgical procedure for relieving movement related disorders such as Parkinson’s disease. DBS extends uncertainties associated with suboptimal target selection. Our aim was to evaluate the feasibility to objectively assess clinical effects obtained during intraoperative test stimulation based on acceleration measurements of the neurologist’s wrist. Methods One patient referred for bilateral DBS-implantation for the treatment of Parkinson’s disease was included in the study. A 3-axis accelerometer was fixed on the neurologist's wrist during intraoperative test stimulation. While the intensity of electric current used for stimulation was increased , the neurologist continuously moved the patient's wrist to determine the moment of and the amplitude at rigidity release ("stimulation threshold"). For each test stimulation position, differrent mathematical features were determined and statistically compared a) for the time period before re aching the stimulation threshold that had been identified by the neurologist and b) after reaching the threshold. We then visually 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

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

National audience

National audience

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.