| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
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| 5. |
- Bobinski, L, et al.
(författare)
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Leptomeningeal cyst due to vacuum extraction delivery in a twin infant
- 2007
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Ingår i: Acta Neurochirurgica. - : Springer Science and Business Media LLC. - 0001-6268 .- 0942-0940. ; 149:3, s. 319-323
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Tidskriftsartikel (refereegranskat)abstract
- A rare case of a leptomeningeal cyst is reported in a twin male neonate delivered using a vacuum extractor, who presented a huge, non-pulsating, oedematous mass overlying the frontal fontanelle after birth. The mass was initially diagnosed as a cephalo haematoma. Ultrasonography indicated intracranial bleeding and a subsequent CT scan revealed an intraparenchymal bleeding above the left frontal horn, combined with a thin, left-sided, subdural haematoma and subarachnoid haemorrhage in the left Sylvian fissure. Apart from a bulging soft and round formation (2 × 2 × 3 cm) next to the anterior fontanel growing since birth, the neurological development of the infant was normal. MRI examination at the age of 7 months revealed that it consisted of a cystic mass (leptomeningeal cyst) connected to the left frontal horn, stretching right through the brain and also penetrating the dura mater. No signs of the perinatal haematomas were observed at this time. Surgical treatment, with fenestration of the cyst into the frontal horn and a watertight duraplasty with a periosteal flap and thrombin glue covered by small bone chips, was performed at 9 months of age. Due to a residual skull bone defect a second cranioplasty with autologous skull bone was performed three and half years later. During a follow-up period of 12 years the neurological and psychological development of the boy has been indistinguishable to that of his twin brother, indicating the satisfactory outcome of the treatment. © 2007 Springer-Verlag.
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| 6. |
- Boström, Sverre, 1948-, et al.
(författare)
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A new scaled microgauge for use in neurosurgery
- 2005
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Ingår i: Acta Neurochirurgica. - : Springer Science and Business Media LLC. - 0001-6268 .- 0942-0940. ; 147:12, s. 1281-1282
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Tidskriftsartikel (refereegranskat)abstract
- A new scaled microgauge is described for measuring anatomical structures during microsurgery. The instrument has a tip marked in millimetres, which can be positioned in any desired angle enabling measurement in confined areas. © Springer-Verlag 2005.
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| 7. |
- Fytagoridis, Anders, et al.
(författare)
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Funktionell neurokirurgi möjlig hjälp vid svåra neurogena tillstånd
- 2023
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Ingår i: Läkartidningen. - : Sveriges Läkarforbund. - 0023-7205 .- 1652-7518. ; 120
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Forskningsöversikt (refereegranskat)abstract
- Funktionell neurokirurgi är ett samlingsnamn för en bred arsenal av neurokirurgiska metoder för att lindra besvär vid olika neurogena tillstånd. Syftet är genomgående att förbättra livskvalitet, och verksamheterna präglas av ett uttalat multidisciplinärt och tvärprofessionellt samarbete. Detta underlättar en god patientselektion, vilket är helt avgörande för att uppnå ett lyckat resultat. Med rätt urval och uppföljning erbjuder dessa ingrepp säker och effektiv lindring eller till och med bot för notoriskt svårbehandlade och ofta starkt funktionsnedsättande tillstånd.
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| 8. |
- Göransson, Nathanael, et al.
(författare)
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Postoperative lead movement after deep brain stimulation surgery and changes of stimulation area
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- IntroductionLead movement after deep brain stimulation (DBS) may occur and influence the area of stimulation. The cause of the displacement is not fully understood. The aim of the study was to investigate differences in lead position between the day after surgery and approximately one month postoperatively and also simulate the electric field (EF) around the active contacts.Methods23 patients with movement disorders underwent DBS surgery (37 leads). CT at the two time points were co-fused respectively with the stereotactic images in Surgiplan. The coordinates (x, y, z) of the lead tips were compared between the two dates (paired t-test). 8 of these patients were selected for the EF simulation in Comsol Multiphysics.ResultsThere was a significant discrepancy (mean ± s.d.) on the left lead: x (0.44 ± 0.72, p < 0.01), y (0.64 ± 0.54, p < 0.001), z (0.62 ± 0.71, p < 0.001). On the right lead, corresponding values were: x (-0.11 ± 0.61, n.s.), y (0.71 ± 0.54, p < 0.001), z (0.49 ± 0.81, p < 0.05). No correlation was found between bilateral (n =14) vs. unilateral DBS, gender (n = 17 male) and age < 60 years (n = 8). The lead movement affected the EF spread (Fig. 1).ConclusionThe left lead tip displayed a tendency to move lateral, anterior and inferior and the right a tendency to move anterior and inferior. Lead movement after DBS can be a factor to consider before starting the stimulation. The differences in the area of stimulation might affect clinical outcome.
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| 9. |
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| 10. |
- Liew, Bernard X. W., et al.
(författare)
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Clinical predictive modelling of post-surgical recovery in individuals with cervical radiculopathy : a machine learning approach
- 2020
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Prognostic models play an important role in the clinical management of cervical radiculopathy (CR). No study has compared the performance of modern machine learning techniques, against more traditional stepwise regression techniques, when developing prognostic models in individuals with CR. We analysed a prospective cohort dataset of 201 individuals with CR. Four modelling techniques (stepwise regression, least absolute shrinkage and selection operator [LASSO], boosting, and multivariate adaptive regression splines [MuARS]) were each used to form a prognostic model for each of four outcomes obtained at a 12 month follow-up (disability-neck disability index [NDI]), quality of life (EQ5D), present neck pain intensity, and present arm pain intensity). For all four outcomes, the differences in mean performance between all four models were small (difference of NDI<1 point; EQ5D<0.1 point; neck and arm pain<2 points). Given that the predictive accuracy of all four modelling methods were clinically similar, the optimal modelling method may be selected based on the parsimony of predictors. Some of the most parsimonious models were achieved using MuARS, a non-linear technique. Modern machine learning methods may be used to probe relationships along different regions of the predictor space.
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