Simone Hemm-Ode

High-Resolution Laser Doppler Measurements of Microcirculation in the Deep Brain Structures: A Method for Potential Vessel Tracking

Background: Laser Doppler flowmetry (LDF) can be used to measure cerebral microcirculation in relation to stereotactic deep brain stimulation (DBS) implantations. Objective: To investigate the microcirculation and total light intensity (TLI) corresponding to tissue grayness in DBS target regions with high-resolution LDF recordings, and to define a resolution which enables detection of small vessels. Methods: Stereotactic LDF measurements were made prior to DBS implantation with 0.5-mm steps in the vicinity to 4 deep brain targets (STN, GPi, Vim, Zi) along 20 trajectories. The Mann-Whitney U test was used to compare the microcirculation and TLI between targets, and the measurement resolution (0.5 vs. 1 mm). The numbers of high blood flow spots along the trajectories were calculated. Results: There was a significant difference (p < 0.05) in microcirculation between the targets. High blood flow spots were present at 15 out of 510 positions, 7 along Vim and GPi trajectories, respectively. There was no statistical difference between resolutions even though both local blood flow and TLI peaks could appear at 0.5-mm steps. Conclusions: LDF can be used for online tracking of critical regions presenting blood flow and TLI peaks, possibly relating to vessel structures and thin laminas along stereotactic trajectories.

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.

Influence on Deep Brain Stimulation from Lead Design, Operating Modeand Tissue Impedance Changes â A Simulation Study

Background: Deep brain stimulation (DBS) systems in current mode and new lead designs are recently available. To switch between DBS-systems remains complicated as clinicians may lose their reference for programming. Simulations can help increase the understanding. Objective: To quantitatively investigate the electric field (EF) around two lead designs simulated to operate in voltage and current mode under two time points following implantation. Methods: The finite element method was used to model Lead 3389 (Medtronic) and 6148 (St Jude) with homogenous surrounding grey matter and a peri-electrode space (PES) of 250 μm. The PES-impedance mimicked the acute (extracellular fluid) and chronic (fibrous tissue) time-point. Simulations at different amplitudes of voltage and current (n=236) were performed using two different contacts. Equivalent current amplitudes were extracted by matching the shape and maximum EF of the 0.2 V/mm isolevel. Results: The maximum EF extension at 0.2 V/mm varied between 2-5 mm with a small difference between the leads. In voltage mode EF increased about 1 mm at acute compared to the chronic PES. Current mode presented the opposite relationship. Equivalent EFs for lead 3389 at 3 V were found for 7 mA (acute) and 2.2 mA (chronic). Conclusions: Simulations showed a major impact on the electric field extension between postoperative time points. This may explain the clinical decisions to reprogram the amplitude weeks after implantation. Neither the EF extension nor intensity is considerably influenced by the lead design. However, the EF distribution is affected by the larger contact of Lead 6148 generating an electric field below the tip.

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.

Optical Measurements during Deep Brain Stimulation Lead Implantation: Safety Aspects

Background: Intracerebral hemorrhage (ICH) is the most feared complication in deep brain stimulation (DBS) surgery. The aim of the study was to evaluate patient safety and outcome using laser Doppler flowmetry (LDF) as guidance tool during DBS implantations. Methods: An LDF probe adapted for the stereotactic system was used as guide for creation of the trajectory. The microcirculation along 83 preplanned trajectories was measured with the guide during DBS surgery for movement disorders. The microvascular blood flow levels were investigated for all measurement positions. Medical record and postoperative radiology were retrospectively reviewed. Results: Of 2,963 measurement positions, 234 (7.9%) showed at least a doubled blood flow compared to the surrounding tissue. Of these 2.2% had a more than 5 times higher blood flow in front of the probe tip. Along 1 trajectory, a small ICH was detected during surgery. Increased blood flow was more common close to sulci and verticals. Conclusion: Real-time LDF measurement of the microcirculation using a forward-looking probe during DBS surgery can detect blood flow peaks and further minimize the risk of developing ICH. No separate guide tube is necessary as the probe also creates the trajectory for the DBS lead.

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.

Correlation between laser Doppler measurements and anatomy during deep brain stimulation surgery

IntroductionIn Deep Brain Stimulation (DBS) the save, accurate and precise electrode implantation is essential. We have previously presented an optical technique for intra-operative measurements du ...