Juergen Schlaier

Magnetic Resonance Imaging Diffusion Tensor Tractography: Evaluation of Anatomic Accuracy of Different Fiber Tracking Software Packages

BACKGROUND Diffusion tensor imaging (DTI)-based tractography has become an integral part of preoperative diagnostic imaging in many neurosurgical centers, and other nonsurgical specialties depend increasingly on DTI tractography as a diagnostic tool. The aim of this study was to analyze the anatomic accuracy of visualized white matter fiber pathways using different, readily available DTI tractography software programs. METHODS Magnetic resonance imaging scans of the head of 20 healthy volunteers were acquired using a Siemens Symphony TIM 1.5T scanner and a 12-channel head array coil. The standard settings of the scans in this study were 12 diffusion directions and 5-mm slices. The fornices were chosen as an anatomic structure for the comparative fiber tracking. Identical data sets were loaded into nine different fiber tracking packages that used different algorithms. The nine software packages and algorithms used were NeuroQLab (modified tensor deflection [TEND] algorithm), Sörensen DTI task card (modified streamline tracking technique algorithm), Siemens DTI module (modified fourth-order Runge-Kutta algorithm), six different software packages from Trackvis (interpolated streamline algorithm, modified FACT algorithm, second-order Runge-Kutta algorithm, Q-ball [FACT algorithm], tensorline algorithm, Q-ball [second-order Runge-Kutta algorithm]), DTI Query (modified streamline tracking technique algorithm), Medinria (modified TEND algorithm), Brainvoyager (modified TEND algorithm), DTI Studio modified FACT algorithm, and the BrainLab DTI module based on the modified Runge-Kutta algorithm. Three examiners (a neuroradiologist, a magnetic resonance imaging physicist, and a neurosurgeon) served as examiners. They were double-blinded with respect to the test subject and the fiber tracking software used in the presented images. Each examiner evaluated 301 images. The examiners were instructed to evaluate screenshots from the different programs based on two main criteria: (i) anatomic accuracy of the course of the displayed fibers and (ii) number of fibers displayed outside the anatomic boundaries. RESULTS The mean overall grade for anatomic accuracy was 2.2 (range, 1.1-3.6) with a standard deviation (SD) of 0.9. The mean overall grade for incorrectly displayed fibers was 2.5 (range, 1.6-3.5) with a SD of 0.6. The mean grade of the overall program ranking was 2.3 with a SD of 0.6. The overall mean grade of the program ranked number one (NeuroQLab) was 1.7 (range, 1.5-2.8). The mean overall grade of the program ranked last (BrainLab iPlan Cranial 2.6 DTI Module) was 3.3 (range, 1.7-4). The difference between the mean grades of these two programs was statistically highly significant (P < 0.0001). There was no statistically significant difference between the programs ranked 1-3: NeuroQLab, Sörensen DTI Task Card, and Siemens DTI module. CONCLUSIONS The results of this study show that there is a statistically significant difference in the anatomic accuracy of the tested DTI fiber tracking programs. Although incorrectly displayed fibers could lead to wrong conclusions in the neurosciences field, which relies heavily on this noninvasive imaging technique, incorrectly displayed fibers in neurosurgery could lead to surgical decisions potentially harmful for the patient if used without intraoperative cortical stimulation. DTI fiber tracking presents a valuable noninvasive preoperative imaging tool, which requires further validation after important standardization of the acquisition and processing techniques currently available.

Deep Brain Stimulation for Essential Tremor: Targeting the Dentato-Rubro-Thalamic Tract?

The aim of our study was to evaluate the influence of the stimulation site relative to the dentato‐rubro‐thalamic tract (DRTT) on the alleviation of tremor in deep brain stimulation.

The variability of atlas-based targets in relation to surrounding major fibre tracts in thalamic deep brain stimulation

BackgroundIn essential tremor (ET), the main target for deep brain stimulation (DBS) is the thalamic ventralis intermedius nucleus (Vim). This target cannot be identified on conventional magnetic resonance imaging (MRI). Therefore, targeting depends on probabilistic coordinates derived from stereotactic atlases. The goal of our study was to investigate the variability of atlas-based Vim targets in relation to surrounding major fibre tracts.MethodsWith the MRI and computed tomography (CT) scan data of ten patients who underwent DBS, we planned atlas based Vim targets in both hemispheres. We also performed deterministic fibre-tracking with diffusion tensor imaging (DTI) of the dentato-rubro-thalamic tract (DRTT), pyramidal tract (PT) and lemniscus medialis (LM) in all 20 hemispheres. Subsequently, we measured the distance from the atlas-based Vim target to each tract along the medial/lateral (x-coordinate), anterior/posterior (y-coordinate) and superior/inferior axis (z-coordinate).ResultsSeventeen out of 20 DRTTs could be depicted with our standardised DTI/fibre-tracking parameters. The PT and the LM could be displayed in all 20 hemispheres. The atlas-based Vim target was found inside the DRTT in 11 (concerning the x-coordinate) and 10 hemispheres (concerning the z-coordinate). Regarding the anterior/posterior direction, the target was posterior to the DRTT in 11 cases. In 19 hemispheres the Vim target was located medial and superior to the PT and in 17 hemispheres posterior to it. Concerning the LM, the Vim target was found inside the LM in 16 (regarding the x-coordinate) and in 14 cases (regarding the z-coordinate). In eight cases it was located inside and in 12 cases anterior to the LM concerning the y-coordinate.ConclusionsWe found a considerable variability of the location of atlas-based target points of the ventralis intermedius nucleus in relation to neighbouring major fibre tracts in individual patients. These results suggest that individualised targeting to structures not directly visible on conventional MRI is necessary.

The influence of intraoperative microelectrode recordings and clinical testing on the location of final stimulation sites in deep brain stimulation for Parkinson’s disease

BackgroundThe goal of our study was to investigate the influence of intraoperative microelectrode recordings and clinical testing on the location of the final stimulation site in deep brain stimulation in Parkinson’s disease.MethodsIn 22 patients with Parkinson’s disease we compared magnetic resonance imaging (MRI)-based and atlas-based targets with the adjusted stimulation sites after intraoperative, multitrack microelectrode recording (MER) and intraoperative and postoperative clinical testing. The investigation included 176 target/stimulation sites in 44 subthalamic nuclei (STNs), which were related to a standardised three-dimensional, MRI-defined STN.ResultsAtlas-based targets were positioned more superior and more medial than the MRI-based targets, which were located in the centre of the MRI-STN. The optimal stimulation sites, found intraoperatively after MER and clinical testing, were located more lateral and slightly more superior than both planned targets. In the majority of the cases the location of the active contact was the most superior and most lateral of all target sites. The differences in the distributions of those four targets reached statistical significance. However, final active contacts were distributed throughout the MRI-defined STN and its immediate surroundings.ConclusionsThe adoption of microelectrode recordings and extensive clinical testing allows the adjustment of anatomical targeting even to unexpected stimulation sites in and around the MRI-defined STN.

Acute urinary retention in two patients after subthalamic nucleus deep brain stimulation (STN-DBS) for the treatment of advanced Parkinson's disease

Chorea-acanthocytosis (ChAc) is a hereditary neurodegenerative disease characterized by hyperkinesias, peripheral neuropathy, and erythrocyte acanthocytosis. ChAc belongs to the group of neuroacanthocytosis syndromes, including ChAc, McLeod syndrome, Huntington’s disease-like 2 and pantothenate kinase associated neurodegeneration. ChAc diagnosis can be confirmed by the absence of chorein in western blot of erythrocyte membranes. Medical treatment (botulinum toxin A injections, tetrabenazine and atypical neuroleptics) is only partially effective. Functional surgery has been tried in ChAc with variable results. We report a case of ChAc treated with bilateral deep brain stimulation (DBS) of the internal globus pallidum (GPi) with positive results. The patient is a 35-year-old woman without family history of movement disorders. At 25, she began to note tongue and lip biting, movement disorders and mild loss of postural reflexes. On examination she had dysarthria, oromandibular dystonia, mild chorea, and irregular choreic gait with occasional flexor truncal spasms. Further neurological examination was unremarkable except for hyporeflexia. She was cognitively intact, save for moderate impairment to solve problems as showed in the Tower of Hanoi test. Performance in orientation, attention, language, visuospatial abilities and executive functions was within normal limits. Laboratory tests revealed acanthocytosis (up to 20%) and increased creatine kinase. Electromyography showed axonal neuropathy in the lower limbs. CT and MRI scans showed mild dilatation of lateral ventricles and slight atrophy of the head of the caudate nucleus. Genetic testing for Huntington’s disease was negative. The clinical diagnosis was confirmed by the absence of chorein in western blot of erythrocyte membranes. The patient was treated first with olanzapine, then with tetrabenazine, amantadine and clozapine with transient benefit. With the passage of time, her chorea gradually worsened and the trunk spasm increased in frequency and severity. After discussing different options with the patient, she opted for DBS. After written consent was obtained, she underwent bilateral implantation of a quadripolar electrode (DBS 3387, Medtronic) into the GPi under generalized anaesthesia. Image study included CT/MRI fusion imaging coupled with a stereotaxic atlas map. Targeting and electrode implantation were performed according to previously described methods. Initial coordinates were 3 mm in front of midcomisural point; 21 mm lateral from midline, and 4 mm ventral to AC-PC line. For physiological verification we used microelectrode recording, visual evoked potentials and macrostimulation. Postoperatively, the benefit was rapidly evident with marked improvement in both dystonia and chorea. Chorea responded faster than dystonia. The patient was able to walk independently and her truncal spasms almost disappeared, but dysarthria did not improve. Two months postoperatively the improvement was confirmed (video). Chorea-dystonia items (motor section) of Unified Huntington’s Disease Rating Scale (UHDRS) scored 24 in the preoperative evaluation, and 14 in the 2 month postoperative evaluation. Over the subsequent 2 years, she needed a progressive increase in electrical parameters to maintain her improvement since the trunk spasms reappeared although not with the same severity; in addition, she developed occasional freezing of gait. At present electric parameters are as follows:

The impact of sedation on brain mapping: a prospective, interdisciplinary, clinical trial.

BACKGROUND During awake craniotomies, patients may either be awake for the entire duration of the surgical intervention (awake-awake-awake craniotomy, AAA) or initially sedated (asleep-awake-asleep craniotomy, SAS). OBJECTIVE To examine whether prior sedation in SAS may restrict brain mapping, we conducted neuropsychological tests in patients by means of a standardized anesthetic regimen comparable to an SAS. METHODS We prospectively examined patients undergoing surgery either under total intravenous anesthesia (TIVA) or under regional anesthesia with slight sedation (RAS). The tests included the DO40 picture-naming test, the digit span, the Regensburg Word Fluency Test, and the finger-tapping test. Each test was conducted 3 times for every patient in the TIVA and RAS groups, once before surgery and twice within about 35 minutes after the end of sedation. Patients undergoing AAA were examined preoperatively and intraoperatively. RESULTS In the AAA group, no significant difference was found between preoperative and intraoperative test results. In the TIVA and RAS groups, postoperative tests showed worse results than preoperative tests. In most tests, patients improved from the first to the second postoperative test. CONCLUSION Cognitive and motor performance were significantly influenced by prior sedation in the TIVA and RAS groups, but not in the AAA group. Therefore, prior sedation may be assumed to cause a change in the baselines, which may compromise brain mapping and thus endanger a patients neurological outcome in the case of an SAS.

Distance between Active Electrode Contacts and Dentatorubrothalamic Tract in Patients with Habituation of Stimulation Effect of Deep Brain Stimulation in Essential Tremor

Background Some patients under thalamic deep brain stimulation (DBS) for essential tremor (ET) experience habituation of tremor reduction. The nucleus ventralis intermedius (Vim) is the current main target side for ET in DBS. However, the dentatorubrothalamic tract (DRTT) is considered the relevant structure to stimulate. We investigated the distance between the active contact of the DBS electrode and the DRTT and compared this distance in patients with habituation of tremor reduction and good responders. Material and Methods In this retrospective study, we performed deterministic fiber tracking of the DRTT in 6 patients (12 hemispheres) with ET who underwent DBS in the Vim. We subsequently measured the distance between the active contact of the electrode and the ipsilateral DRTT in both hemispheres. The clinical tremor response of those 6 patients was analyzed accordingly. Results The distance between the active contact and the DRTT in patients with better and constant clinical tremor reduction was shorter (mean distance: 2.9 ± 2.2 mm standard deviation [SD]) than in patients who showed habituation of their response (mean distance: 6.1 ± 3.9 mm SD). After re‐placement of a thalamic electrode inside the DRTT in one patient who experienced unsatisfying tremor reduction due to habituation of stimulation, the tremor alleviation was significant and persistent at a 13‐month follow‐up. Conclusion This retrospective analysis suggests that recurrence of ET tremor under chronic DBS might be associated with a larger distance between the DRTT and the active lead contact, in comparison with the smaller distances in patients with persistently good tremor control.

Relevance of correction for rotational targeting error in functional neurosurgery

Objective: A prospective study is presented on the amount of targeting error that is due to rotational deviations between the atlas and the stereotactic coordinate system. Materials and Methods: We investigated 14 volunteers with a stereotactic frame fixed to their heads by tight adhesive bands. Sagittal, coronal and axial T2-weighted MRI scans, as well as MPRage sequences, were performed. The anterior and posterior commissures and one additional point on the midline (the septum pellucidum) were determined on the axial T2-weighted images. Bilateral atlas coordinates for the subthalamic nucleus (STN), globus pallidus pars interna (GPi) and nucleus ventralis intermedius (Vim) were transformed to stereotactic frame coordinates, either without correction or by 2-point or 3-point correction. A total of 896 coordinates (x, y, z for the STN, GPi and Vim in both hemispheres) were calculated. Results: Although the mean differences between the two algorithms (0.24 ± standard deviation of 0.33 mm) were within the range of system-immanent inaccuracies in MRI-guided stereotaxy, deviations of up to 2.8 mm occurred. No significant correlation was found regarding the amount of rotational angle and the differences in x-, y-, or z-coordinates when 2-point and 3-point transformations were compared. Conclusions: The reliability of meticulous trajectory planning might be compromised significantly by using only 2-point-based correction or no calculations at all.

Probabilistic vs. deterministic fiber tracking and the influence of different seed regions to delineate cerebellar-thalamic fibers in deep brain stimulation

This study compared tractography approaches for identifying cerebellar‐thalamic fiber bundles relevant to planning target sites for deep brain stimulation (DBS). In particular, probabilistic and deterministic tracking of the dentate‐rubro‐thalamic tract (DRTT) and differences between the spatial courses of the DRTT and the cerebello‐thalamo‐cortical (CTC) tract were compared. Six patients with movement disorders were examined by magnetic resonance imaging (MRI), including two sets of diffusion‐weighted images (12 and 64 directions). Probabilistic and deterministic tractography was applied on each diffusion‐weighted dataset to delineate the DRTT. Results were compared with regard to their sensitivity in revealing the DRTT and additional fiber tracts and processing time. Two sets of regions‐of‐interests (ROIs) guided deterministic tractography of the DRTT or the CTC, respectively. Tract distances to an atlas‐based reference target were compared. Probabilistic fiber tracking with 64 orientations detected the DRTT in all twelve hemispheres. Deterministic tracking detected the DRTT in nine (12 directions) and in only two (64 directions) hemispheres. Probabilistic tracking was more sensitive in detecting additional fibers (e.g. ansa lenticularis and medial forebrain bundle) than deterministic tracking. Probabilistic tracking lasted substantially longer than deterministic. Deterministic tracking was more sensitive in detecting the CTC than the DRTT. CTC tracts were located adjacent but consistently more posterior to DRTT tracts. These results suggest that probabilistic tracking is more sensitive and robust in detecting the DRTT but harder to implement than deterministic approaches. Although sensitivity of deterministic tracking is higher for the CTC than the DRTT, targets for DBS based on these tracts likely differ.

Deep Brain Stimulation for Obsessive Compulsive Disorder Reduces Symptoms of Irritable Bowel Syndrome in a Single Patient

Irritable bowel syndrome (IBS) is a frequent gastrointestinal disorder that is difficult to treat. We describe findings from evaluation of a woman (55 years old) with obsessive compulsive disorder, which was treated with bilateral deep brain stimulation in the anterior limb of the internal capsule, and IBS. After the brain stimulation treatment she reported substantial relief of her IBS symptoms. This reduction depended on specific stimulation parameters, was reproducible over time, and was not directly associated with improvements in obsessive compulsive disorder symptoms. These observations indicate a specific effect of deep brain stimulation on IBS. This observation confirms involvement of specific brain structures in the pathophysiology of IBS and shows that symptoms can be reduced through modulation of neuronal activity in the central nervous system. Further studies of the effects of brain stimulation on IBS are required.