Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> OBINSON et al. 6 have recently shown t h a t measuremen t of brain tissue impedance and phase angle by means of a roving electrode is a useful me thod in locat ing deep cerebral s t ructures in laborato ry animals. T h e y also recorded impedance and phase angle in the dead h u m a n brain. T h e y considered the method safe and useful for h u m a n stereotaxic use. Dur ing 1965, we recorded the impedance and phase angle of brain tissue in 65 pat ients undergoing stereotaxic surgery for various conditions. I n this paper we report our technique and discuss the results and value of this me thod as a locating aid in stereotaxic surgery. <s> BIB001 </s> Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> In evaluating the success of deep brain stimulation (DBS), the benefit for the patient is the most important criteria. Nevertheless, correct placement of electrodes should also be determined in terms of their anatomic position. Therefore, we propose a suite of different imaging modalities and further processing, which leads to an exact anatomic and statistically comparable documentation of electrode localization. Forty-three consecutive patients with a total of 85 implanted DBS electrodes were evaluated with respect to postoperative imaging. T1-weighted magnetic resonance imaging (T1-MRI) was performed in all patients, 34 patients received T2-MRI, in 18 patients stereotactic X-ray of the scull was performed in anteroposterior and lateral projections, whereas 6 patients were additionally evaluated by pre- and postoperative MR-image fusion between T1-data sets and calculation of coordinates for electrode contacts. In T1-MRI, the artefacts of each electrode contact could be delineated in relation to anatomic reference structures, whereas T2-MRI allowed reproducibly for delineation of electrode artefacts within subthalamic nucleus or globus pallidus pars interna. By MR-image fusion it could be shown that the difference between planned target coordinates and coordinates of the active electrode contact ranged below 1 mm except for the z axis. The comparison with values obtained from stereotactic X-ray confirmed these results. The sequential and complementary use of the described imaging modalities and further image processing provide clinically reliable and statistically comparable results to prove the exact anatomic electrode positioning in DBS in addition to the objective and subjective improvements of the patients' symptoms. <s> BIB002 </s> Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> We present a method of constructing a database of intraoperatively observed human subcortical electrophysiology. In this approach, patient electrophysiological data are standardized using a multiparameter coding system, annotated to their respective magnetic resonance images (MRIs), and nonlinearly registered to a high-resolution MRI reference brain. Once registered, we are able to demonstrate clustering of like interpatient physiologic responses within the thalamus, globus pallidus, subthalamic nucleus, and adjacent structures. These data may in turn be registered to a three-dimensional patient MRI within our image-guided visualization program enabling prior to surgery the delineation of surgical targets, anatomy with high probability of containing specific cell types, and functional borders. The functional data were obtained from 88 patients (106 procedures) via microelectrode recording and electrical stimulation performed during stereotactic neurosurgery at the London Health Sciences Centre. Advantages of this method include the use of nonlinear registration to accommodate for interpatient anatomical variability and the avoidance of digitized versions of printed atlases of anatomy as a common database coordinate system. The resulting database is expandable, easily searched using a graphical user interface, and provides a visual representation of functional organization within the deep brain. <s> BIB003 </s> Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> The long term objective of our research is to develop a system that will automate as much as possible DBS implantation procedures. It is estimated that about 180,000 patients/year would benefit from DBS implantation. Yet, only 3000 procedures are performed annually. This is so because the combined expertise required to perform the procedure successfully is only available at a limited number of sites. Our goal is to transform this procedure into a procedure that can be performed by a general neurosurgeon at a community hospital. In this work we report on our current progress toward developing a system for the computer-assisted pre-operative selection of target points and for the intra-operative adjustment of these points. The system consists of a deformable atlas of optimal target points that can be used to select automatically the pre-operative target, of an electrophysiological atlas, and of an intra-operative interface. The atlas is deformed using a rigid then a non-rigid registration algorithm developed at our institution. Results we have obtained show that automatic prediction of target points is an achievable goal. Our results also indicate that electrophysiological information can be used to resolve structures not visible in anatomic images, thus improving both pre-operative and intra-operative guidance. Our intra-operative system has reached the stage of a working prototype that is clinically used at our institution. <s> BIB004 </s> Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> The vast majority of centers use electrophysiological mapping techniques to finalize target selection during the im- plantation of deep brain stimulation (DBS) leads for the treat- ment of Parkinson's disease and tremor. This review discusses the techniques used for physiological mapping and addresses the questions of how various mapping strategies modify target selection and outcome following subthalamic nucleus (STN), globus pallidus internus (GPi), and ventralis intermedius (Vim) deep brain stimulation. Mapping strategies vary greatly across centers, but can be broadly categorized into those that use microelectrode or semimicroelectrode techniques to optimize position prior to implantation and macrostimulation through a macroelectrode or the DBS lead, and those that rely solely on macrostimulation and its threshold for clinical effects (benefits and side effects). Microelectrode criteria for implantation into the STN or GPi include length of the nucleus recorded, pres- ence of movement-responsive neurons, and/or distance from the borders with adjacent structures. However, the threshold for the production of clinical benefits relative to side effects is, in most centers, the final, and sometimes only, determinant of DBS electrode position. Macrostimulation techniques for map- ping, the utility of microelectrode mapping is reflected in its modification of electrode position in 17% to 87% of patients undergoing STN DBS, with average target adjustments of 1 to 4 mm. Nevertheless, with the absence of class I data, and in consideration of the large number of variables that impact clinical outcome, it is not possible to conclude that one tech- nique is superior to the other in so far as motor Unified Parkinson's Disease Rating Scale outcome is concerned. More- over, mapping technique is only one out of many variables that determine the outcome. The increase in surgical risk of intra- cranial hemorrhage correlated to the number of microelectrode trajectories must be considered against the risk of suboptimal benefits related to omission of this technique. © 2006 Move- ment Disorder Society <s> BIB005 </s> Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> Background: Brain shift may occur during deep brain stimulation (DBS) surgery, which may affect the position of subcortical structures, compromising target localization. Methods: We retrospectively evaluated pre- and postoperative magnetic resonance imaging in 50 Parkinson’s disease patients who underwent bilateral subthalamic nucleus (STN) DBS. Patients were separated into two groups: group A – those with <2 mm cortical displacement (66 leads) and group B – those with ≧2 mm cortical displacement (34 leads). Pre and post-op coordinates of anterior (AC) and posterior commissures (PC), as well as the boundaries of red nucleus (RN) were compared. Results: AC-PC shortening due to posterior displacement of AC correlated with cortical displacement (p < 0.02) and was significantly greater in group B (0.41 ± 0.68 mm) than A (0.04 ± 0.76 mm; p < 0.005). Posterior shift of AC and RN’s center positively correlated (p < 0.0001). Shift appeared to impact the number of microelectrode tracks made to optimize STN targeting. AC-PC shortening also correlated with age (p < 0.003) and duration of surgery (p < 0.04). Conclusions: Subcortical structures shift during DBS surgery. This shift appears to be gravity-dependent since structures only shifted posteriorly, and patients were primarily in the supine position. Posterior shift of RN may indicate STN displacement. Such positional change may compromise target localization, requiring multiple microelectrode adjustments. This may provide indirect justification for the necessity of microelectrode recordings during DBS surgery. <s> BIB006 </s> Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> Deep brain stimulation (DBS) surgery can significantly improve the quality of life for patients suffering from movement disorders, but the success of the procedure depends on the implantation accuracy of the DBS electrode array. Pre-operative surgical planning and navigation are based on the assumption that the brain tissue is rigid between the time of the acquisition of the pre-operative image set and the time of surgery. A shift of deep brain structures by only a few millimeters can potentially increase the number of required microelectrode and/or macroelectrode tracks and decrease implantation accuracy. We studied 25 subjects that underwent DBS surgery and analyzed brain shift between pre-operative and post-operative 3D MRI scans. Brain shift of up to 4 mm was observed in deep brain structures. On average, the recorded shift was in the direction of gravity, with deeper structures experiencing smaller shift than more superficial structures. The main conclusion of the study is that the brain shift is comparable to the size of the targets in deep brain stimulation surgery and should not be ignored. Techniques that minimize the amount of brain shift may therefore lead to increased accuracy of DBS lead implantation. <s> BIB007 </s> Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> Objective:To assess the role of age in the results of bilateral deep brain stimulation in the subthalamic nucleus (DBS-STN), we carried out a study of two groups of patients regarding age at time of surgery. Methods:We compared, up to 2 years after surgery, the clinical effects, safety, and quality of life in parkinsonian patients younger than 65 years old (young patients) vs parkinsonian patients 65 years old or older (old patients). Results:The mean age was 57.4 ± 4.9 years (n = 53) in young patients and 68.8 ± 2.8 years (n = 34) in old patients. A dramatic improvement in motor complications was equally observed in both groups of patients. There was no significant difference between the groups regarding acute effects of DBS-STN on the motor score of the Unified Parkinson's Disease Rating Scale part III (UPDRS III). Time course evolution of UPDRS the motor score (p < 0.0001) and axial score (p = 0.0001) assessed postoperatively in “on” medication and “on” stimulation conditions appeared worse in old patients as compared to young patients. Improvement in the Schwab and England Scale score was better in young patients in “on” (p < 0.0003) and “off” state (p < 0.001). Quality of life assessed with the 39-item Parkinson's Disease Questionnaire showed an improvement in subscales evaluating mobility (p < 0.0001), activities of daily life (p < 0.0001), emotion and stigma (p = 0.0004), cognition (p < 0.0074), and communication (p = 0.0029) in young patients as compared to old patients. Side effects were similar in the two groups. Conclusions:Although deep brain stimulation in the subthalamic nucleus reduces motor complications equally in both groups of patients, postoperative quality of life improved only in young patients. <s> BIB008 </s> Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> The accuracy and precision of frameless neuronavigation as compared to conventional frame-based stereotaxy for implantation of deep brain stimulation (DBS) electrodes were studied in 14 patients with essential tremor. DBS electrodes were implanted bilaterally in the ventrolateral thalamus [ventrointermediate nucleus (VIM)] in one procedure. Frameless neuronavigation was used on one side and the conventional frame-based technique on the other. Targeting was guided by MRI and CT imaging. Intraoperative stereotactic plain X-ray verified final electrode positions and electrode deviations from the planned target were measured. Clinical outcome was evaluated with the Essential Tremor Rating Scale. Thirteen of the patients were eligible for measuring electrode deviations and 10 of them were available for a clinical follow-up. Electrode deviations from target were larger using the frameless technique in the medial-lateral (x: 1.9 +/- 1.3 mm) and anterior-posterior (y:0.9 +/- 0.8 mm) directions as compared to the frame-based technique (x: 0.5 +/- 0.5 and y: 0.4 +/- 0.4 mm) but similar in the superior-inferior direction (z). The vector of deviation was 2.5 +/- 1.4 mm with the frameless technique and 1.2 +/- 0.6 with the frame-based technique. The differences were statistically significant (p < 0.05-0.001). The dispersion was larger with the frameless technique as represented by the larger standard deviations in all three planes. At clinical follow-ups, tremor reduction was similar irrespective of the implantation technique. It is concluded that conventional frame-based stereotaxy has higher accuracy/precision for hitting a small brain target than the frameless technique. However, the difference is relatively small and does not influence the clinical result of DBS electrode implantations in the VIM when treating tremor. <s> BIB009 </s> Stereotactic implantation of deep brain stimulation electrodes: a review of technical systems, methods and emerging tools <s> Surgical procedure <s> AIMS ::: Spectral analysis of local field potential (LFP) recorded by deep brain stimulation (DBS) electrode around the subthalamic nucleus (STN) in patients with Parkinson's disease was performed. ::: ::: ::: METHODS ::: The borders of the STN were determined by microelectrode recording. The most eligible trajectory for the sensorimotor area of the STN was used for LFP recording while advancing the DBS electrode. ::: ::: ::: RESULTS ::: The low-frequency LFP power (theta- to beta-band) increased from a few millimeters above the dorsal border of the STN defined by microelectrode recording; however, the low-frequency power kept the same level beyond the ventral border of the STN. Only high beta-power showed close correlation to the dorsal and ventral borders of the STN. ::: ::: ::: CONCLUSIONS ::: A spectral power analysis of LFP recording by DBS electrode helps with the final confirmation of the dorsal and ventral borders of the STN of Parkinson's disease in DBS implantation surgery. <s> BIB010
The second part of the procedure is the intervention itself. It can be performed under local or general anaesthesia depending on if the patient's feedback is needed for specific testing or not. In the first case, supplementary techniques are used to get additional information about the target area; in the latter, the DBS electrode is directly implanted at the target chosen during the preoperative planning phase. For a number of reasons, including individual variability regarding brain anatomy, several problems may arise during a DBS implantation. One of these is the ''brain shift'' that occurs in conjunction with trepanation. It can cause a deviation from the pre-planned target coordinates resulting in suboptimal anatomical location with side disorders or with haemorrhage if the stereotactic probe injures a blood vessel BIB006 BIB007 . This is one of the reasons in addition to the varying brain anatomy why intraoperative measurements are often performed. Such complementary intraoperative data acquisition methods can be for example impedance measurements while creating the trajectory for the DBS electrode, giving an idea of the surrounding structures passed BIB001  . Another often used method is microelectrode recording (MER) which is based on registering neuronal activity BIB008 BIB005 . Registration is recorded along 1-5 trajectories in the volume of interest to identify the different structure boundaries. In general, these measurements are performed in millimetre steps before reaching the target and often measurements even go beyond the target structure. Most centres using microelectrode recording perform, as well, intraoperative stimulation along the trajectory using the microelectrodes stimulating in the microampere range BIB004 BIB003  or macroelectrodes stimulating in the milliampere range for example using RF-or DBS stimulation electrodes BIB009 BIB010  . In general, this is done at the same measurement points as for MER to evaluate the clinical effects with increasing stimulation current and to determine symptom reduction, the clinical therapeutic and side effect thresholds at each measurement point. The interpretation of all the intraoperative data in order to take a decision on the final surgical target is in general done by the neurosurgeon or neurologist by ''mental imagination'', i.e. interpreting mentally and combining the anatomic position of each measurement value with the results of MER and test stimulation including clinical efficacy, therapeutic stimulation threshold, side effects and stimulation range. During the surgery, some groups perform an intraoperative position control in order to check the absence of deviation of the electrode from the planned trajectory. This can be an intraoperative conventional 2D-X-Ray or a fluoroscopic control  BIB008 BIB002 . Some groups do compensation due to their experience.