| 1. |
- Fytagoridis, Anders, et al.
(författare)
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Surgical Replacement of Implantable Pulse Generator in Deep Brain Stimulation : Adverse Events and Risk Factors in a Multicenter Cohort
- 2016
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Ingår i: Stereotactic and Functional Neurosurgery. - : S. Karger AG. - 1011-6125 .- 1423-0372. ; 94:4, s. 235-239
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Tidskriftsartikel (refereegranskat)abstract
- Background: Deep brain stimulation (DBS) is a growing treatment modality, and most DBS systems require replacement of the implantable pulse generator (IPG) every few years. The literature regarding the potential impact of adverse events of IPG replacement on the longevity of DBS treatments is rather scarce. Objective: To investigate the incidence of adverse events, including postoperative infections, associated with IPG replacements in a multicenter cohort. Methods: The medical records of 808 patients from one Australian and five Swedish DBS centers with a total of 1,293 IPG replacements were audited. A logistic regression model was used to ascertain the influence of possible predictors on the incidence of adverse events. Results: The overall incidence of major infections was 2.3% per procedure, 3.7% per patient and 1.7% per replaced IPG. For 28 of 30 patients this resulted in partial or complete DBS system removal. There was an increased risk of infection for males (OR 3.6, p = 0.026), and the risk of infection increased with the number of prior IPG replacements (OR 1.6, p < 0.005). Conclusions: The risk of postoperative infection with DBS IPG replacement increases with the number of previous procedures. There is a need to reduce the frequency of IPG replacements.
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| 2. |
- Rejmstad, Peter, et al.
(författare)
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Oxygen saturation estimation in brain tissue using diffuse reflectance spectroscopy along stereotactic trajectories
- 2017
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:7, s. 8192-8201
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Tidskriftsartikel (refereegranskat)abstract
- Diffuse reflectance spectroscopy (DRS) can be used to estimate oxygen saturation (SO2) of hemoglobin and blood fraction (fB) in brain tissue. The aim of the study was to investigate the SO2 and fB in different positions along deep brain stimulation (DBS) trajectories and in specific target regions using DRS and a novel algorithm. DRS measurements were done at 166 well-defined anatomical positions in relation to stereotactic DBS-implantation along 20 trajectories toward 4 DBS targets (STN, Vim, GPi and Zi). The measurements were dived into groups (gray, white and light gray matter) related to anatomical position, and DBS targets, before comparison and statistical analysis. The median SO2 in gray, white and light gray matter were 52%, 24% and 20%, respectively. Median fB in gray matter (3.9%) was different from values in white (1.0%, p < 0.05) and light gray (0.9%, p < 0.001) matter. No significant difference in median SO2 and fB was found between DBS target regions. The novel algorithm allows for quick and reliable estimation of SO2 and fB in human brain tissue.
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| 3. |
- Tapper, Sofie, 1989-, et al.
(författare)
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A pilot study of essential tremor: cerebellar GABA+/Glx ratio is correlated with tremor severity
- 2020
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Ingår i: Cerebellum & ataxias. - : BioMed Central. - 2053-8871. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Essential tremor is a common movement disorder with an unclear origin. Emerging evidence suggests the role of the cerebellum and the thalamus in tremor pathophysiology. We examined the two main neurotransmitters acting inhibitory (GABA+) and excitatory (Glx) respectively, in the thalamus and cerebellum, in patients diagnosed with severe essential tremor. Furthermore, we also investigated the relationship between determined neurotransmitter concentrations and tremor severity in the essential tremor patients.
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| 4. |
- Tapper, Sofie, 1989-
(författare)
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Neurotransmitter Imaging of the Human Brain : Detecting γ-Aminobutyric Acid (GABA) Using Magnetic Resonance Spectroscopy
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Introduction: In this thesis, MEGA-edited Magnetic Resonance Spectroscopy (MRS) has been used for the purpose of non-invasive detection of !- aminobutyric acid (GABA) within the brain. GABA is the main inhibitory neurotransmitter in the human central nervous system, and glutamate is the corresponding main excitatory neurotransmitter. A balance between GABA and glutamate is crucial for healthy neurotransmission within the brain, and regional altered concentrations have been linked to certain neurological disorders. However, it is challenging to measure GABA, and special editing approaches are needed in order to allow reliable quantification. In addition, the GABA measurement is further complicated due to disturbances such as movements during the acquisition that may lead to artifacts in the resulting spectrum. This thesis can be divided into two sections, where the first section focuses on three clinical applications (narcolepsy, irritable bowel syndrome (IBS), and essential tremor (ET)), which were all investigated using MEGA-edited single- voxel spectroscopy (SVS). The second section focuses on method development, where two statistical retrospective approaches were investigated for the purpose of improving MEGA-edited data. In addition, a new MRS imaging (MRSI) pulse sequence with the purpose of GABA detection using a high spatial resolution, short acquisition time, and full brain coverage was also investigated.Materials and Methods: In total, 164 participants were included and 272 MRS measurements were performed with the voxel placed in the medial prefrontal cortex (mPFC, 136), thalamus (32), and cerebellum (104) using two different but “identical” MR systems. Nineteen narcolepsy patients and 21 matched healthy controls performed an fMRI working memory task using a simultaneous EEG followed by an mPFC GABA-edited MRS measurement. Sixty-four IBS patients and 32 matched healthy controls underwent an mPFC GABA-edited MRS measurement followed by resting state fMRI. In addition, psychological symptoms were assessed using questionnaires. Ten ET patients and six matched healthy controls underwent four GABA-edited MRS measurements with the voxels placed in the thalamus and cerebellum. In this study, the symptom severity was investigated using the essential tremor rating scale (ETRS). All clinical MRS datasets were analyzed using conventional methods for post-processing and quantification. Furthermore, 12 volunteers were recruited for the purpose of investigating statistical retrospective approaches for artifact detection and elimination of MRS data. Each participant underwent three reference measurements and three measurements with induced head movements conducted according to a movement paradigm. Order statistic filtering (OSF) and jackknife correlation (JKC) were investigated as regards to the elimination of artifact-influenced spectra and reliability of the resulting concentrations. Finally, phantom measurements were performed for the purpose of investigating MEGA-edited MRSI.Results: In narcolepsy, a trend-level association was observed between the mPFC MRS concentrations and increased deactivation within the default mode network during the working memory task. A significantly higher mPFC GABA+ concentration was observed in IBS patients with a high severity of comorbid anxiety. In ET, a positive correlation was observed between cerebellar GABA+/Glx ratios and tremor severity. Moreover, movements during the measurement decreased the concentration estimates due to signal loss in the spectra. Both OSF and JKC resulted in trend-level improvement of the signal- intense metabolites in spectrum when artifacts were present in the data, while performing equally as well as conventional analysis methodology when no intentional movements were present in the data. Finally, using the fast MEGA- edited multi-voxel sequence developed for a conventional clinical scanner, our phantom measurements showed that GABA was detectable using a 1:45 min acquisition time and an MRSI voxel size of 1 mL.Discussion: Several challenges such as time constraints, large voxel sizes, and protocol design were encountered when performing SVS MEGA-PRESS in the clinical research settings. In addition, artifacts in the MRS data originating for example, from motions, negatively impacted the resulting averaged spectra, which was evident in both data from clinical populations and healthy controls. In the presence of artifacts in the data, both OSF and JKC improved the SVS MEGA-edited spectra. In addition, the implemented JKC method can be used not only for artifact detection, but also as a generally applicable retrospective technique for the quality control of a dataset, or as an indication of whether a shift in voxel placement occurred during the measurement. Using the MEGA-edited MRSI pulse sequence, there are many technical challenges, including detrimental effects from eddy currents, spurious echoes, and field inhomogeneities. Even though there are many technical challenges when using MEGA-edited MRSI, an optimized version of the MRSI sequence would be extremely valuable in clinical research applications where high spatial resolution and short acquisition times are highly desired.Conclusions: OSF and JKC improved the metabolite quantification when artifacts were present in the data, and JKC was preferable. Although there are many technical challenges, MEGA-edited MRSI with full brain coverage in combination with a minimal voxel size for the purpose of GABA detection, would be extremely useful in clinical research applications where disorders such as narcolepsy, IBS, or ET, are investigated.
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| 5. |
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| 6. |
- Wårdell, Karin, et al.
(författare)
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High-Resolution Laser Doppler Measurements of Microcirculation in the Deep Brain Structures : A Method for Potential Vessel Tracking.
- 2016
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Ingår i: Stereotactic and Functional Neurosurgery. - : S. Karger. - 1011-6125 .- 1423-0372. ; 94:1, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
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| 8. |
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| 9. |
- Alonso, Fabiola, 1980-, et al.
(författare)
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Influence of Virchow-Robin spaces in the Electric Field Distribution in Subthalamic Nucleus Deep Brain Stimulation
- 2019
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Konferensbidrag (refereegranskat)abstract
- Objectives: Previous investigations have shown the appearance of cysts i.e. Virchow-Robin spaces (VR) in the basal ganglia and their relationship with parkinsonian symptoms [1-3]. Simulations [4]using the finite element method (FEM) suggests that VR affects the electric field around deep brain stimulation (DBS) electrodes. The aim of the study was to evaluate how the electric field is modified by the presence of cysts in the STN. Methods: The effect of cysts on the electric field around the DBS lead placed in the STN was evaluated using FEM. 3D patient-specific brain models were built with COMSOL 5.2 (COMSOL AB, Sweden) and an in-house developed software [5] to convert a T2 weighted MRI of Parkinsonian patients (ethics approval no: 2012/434-3) into electrical conductivity matrix readable by FEM software. VR was classified as CSF [6]assigning a high electrical conductivity (2.0 S/m). The stimulation amplitudes were set to the clinically programmed values. Depending on the lead used, the stimulation was set to voltage control (3389) or current control (6180, ring mode). The coordinates corresponding to the lowest (first) electrode and the third higher up in the lead, taken from the postoperative CT electrode artefact, were used to localize the leads in the brain model [7]. The electric field was visualized with a 0.2V/mm isosurface. Results: Simulations showed that the electric field distribution is affected by the cysts. The higher conductivity at these regions in the vicinity of the electrode redistributes the electric field pushing it away from the cyst. The same effect occurs regardless of the operating mode or the lead design as long as the directional lead is configured in ring mode. Conclusions: The use of patient-specific models has shown the importance of considering nuances of the patients’ anatomy in the STN. This information can be used to determine the stimulation parameter and to support the analysis of side effects induced by the stimulation. The potential advantage of directional leads can also be assessed by including in the model patient-specific data.
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| 10. |
- Alonso, Fabiola, et al.
(författare)
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Influence of Virchow-Robin spaces on the electric field distribution in subthalamic nucleus deep brain stimulation
- 2021
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Ingår i: Clinical neurology and neurosurgery. - : Elsevier. - 0303-8467 .- 1872-6968. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- Patient MRI from DBS implantations in the subthalamic nucleus (STN) were reviewed and it was found that around 10% had Virchow-Robin spaces (VRS). Patient-specific models were developed to evaluate changes in the electric field (EF) around DBS leads. The patients (n = 7) were implanted bilaterally either with the standard voltage-controlled lead 3389 or with the directional current-controlled lead 6180. The EF distribution was evaluated by comparing simulations using patient-specific models with homogeneous models without VRS. The EF, depicted with an isocontour of 0.2 V/mm, showed a deformation in the presence of the VRS around the DBS lead. For patient-specific models, the radial extension of the EF isocontours was enlarged regardless of the operating mode or the DBS lead used. The location of the VRS in relation to the active contact and the stimulation amplitude, determined the changes in the shape and extension of the EF. It is concluded that it is important to take the patients? brain anatomy into account as the high conductivity in VRS will alter the electric field if close to the DBS lead. This can be a cause of unexpected side effects.
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