Erik Schkommodau

A method to quantitatively evaluate changes in tremor during deep brain stimulation surgery

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 patients 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.

Using acceleration sensors to quantify symptoms during deep brain stimulation surgery.

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.

A novel assistive method for rigidity evaluation during deep brain stimulation surgery using acceleration sensors

OBJECTIVE Despite the widespread use of deep brain stimulation (DBS) for movement disorders such as Parkinsons 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 patients 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 evaluators 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. METHODS To 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. RESULTS Outcome 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. CONCLUSIONS This 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.

Optimization of deep brain stimulation surgery for Parkinson’s disease with quantitative rigidity evaluation

Background Deep brain stimulation (DBS) is now a widely accepted surgical treatment for Parkinsons disease (PD). Electrodes are implanted in the patients brain after intraoperative test stimulation. Changes in parkinsonian rigidity during test stimulation are detected by an evaluator, usually a neurologist, by identifying changes in the resistance of the patients arm to a passive movement. We hypothesised that at the moment of reduction in rigidity, the speed with which the evaluator moves the patients arms increases and that this change and its amplitude can be detected with an acceleration sensor. The aim of the present study was to test this hypothesis by collecting data during DBS surgery. Furthermore, to know more about the optimal stimulation target, these quantitative data were categorized based on the anatomical location of the electrode during test stimulation. Discussion: The additional acceleration measurements during the surgery did not increase operation time or the patients discomfort. Higher sensitivity when using the accelerometer recording system; effective stimulation amplitudes were found for 33 additional test stimulations. Conventionally targeted STN requires the lowest stimulation amplitude to reduce rigidity, but has significantly higher chances of side effect occurrence. The Fields of Forel have slightly higher stimulation amplitudes but have much lower change of causing side effects. Sufficient baseline data is necessary for proper identification of BQAs. There is an inherent subjective component in the acceleration analysis because the evaluation is done by the neurologist. Conclusion • Changes in rigidity of PD patients can be quantified during passive movements by measuring data from the evaluator. • Acceleration measurements confirm the subjective evaluation, but they seem to be more sensitive (Fig 4). • STN may not be the most efficacious target structure. The patient may benefit from an electrode placed closer to the Fields of Forel.

Use of quantitative tremor evaluation to enhance target selection during deep brain stimulation surgery for essential tremor

Abstract 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.

Intraoperative optical flow based tremor evaluation - a feasibility study

Deep brain stimulation as treatment for movement related disorders is a common neurosurgical procedure. Nevertheless the targeting procedure can still be optimized as the clinical outcome resulting from intraoperative test stimulation is in general subjectively evaluated. The aim of the present study was to analyse the feasibility of objective tremor evaluation based on optical flow analysis in videos and to compare the results with in parallel performed acceleration measurements. The results demonstrate the feasibility but as well limitations of the applied setup. Solutions to increase the quality in the future are proposed.

Repositioning Precision of EEG-Caps – A Preliminary Study

In this study the possibility to mount an EEG cap to a predefined position is investigated and the influence to the measured electrode position and the measured EEG signals was studied in a Brain Computer Interface application. A P300 spelling device was used to compare the performance of 4 probands after replacing the cap with or without tracking by an Optotrak device. We found that the tracking system allows for precise replacement of the cap and the electrodes. The success rates of the spelling experiment correlates well to the mounting accuracy. These findings offer the possibility to continue EEG sessions without the need of reclassification.