| 1. |
- Akram, Harith, et al.
(författare)
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Subthalamic deep brain stimulation sweet spots and hyperdirect cortical connectivity in Parkinson's disease
- 2017
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Ingår i: NeuroImage. - : Elsevier. - 1053-8119 .- 1095-9572. ; 158, s. 332-345
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Firstly, to identify subthalamic region stimulation clusters that predict maximum improvement in rigidity, bradykinesia and tremor, or emergence of side-effects; and secondly, to map-out the cortical fingerprint, mediated by the hyperdirect pathways which predict maximum efficacy.Methods: High angular resolution diffusion imaging in twenty patients with advanced Parkinson's disease was acquired prior to bilateral subthalamic nucleus deep brain stimulation. All contacts were screened one-year from surgery for efficacy and side-effects at different amplitudes. Voxel-based statistical analysis of volumes of tissue activated models was used to identify significant treatment clusters. Probabilistic tractography was employed to identify cortical connectivity patterns associated with treatment efficacy.Results: All patients responded well to treatment (46% mean improvement off medication UPDRS-III [p < 0.0001]) without significant adverse events. Cluster corresponding to maximum improvement in tremor was in the posterior, superior and lateral portion of the nucleus. Clusters corresponding to improvement in bradykinesia and rigidity were nearer the superior border in a further medial and posterior location. The rigidity cluster extended beyond the superior border to the area of the zona incerta and Forel-H-2 field. When the clusters where averaged, the coordinates of the area with maximum overall efficacy was X = -10(-9.5), Y = -3(-1) and Z = -7(-3) in MNI(AC-PC) space. Cortical connectivity to primary motor area was predictive of higher improvement in tremor; whilst that to supplementary motor area was predictive of improvement in bradykinesia and rigidity; and connectivity to prefrontal cortex was predictive of improvement in rigidity.Interpretation: These findings support the presence of overlapping stimulation sites within the subthalamic nucleus and its superior border, with different cortical connectivity patterns, associated with maximum improvement in tremor, rigidity and bradykinesia.
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| 2. |
- Cottaar, Michiel, et al.
(författare)
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Improved fibre dispersion estimation using b-tensor encoding
- 2020
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- Measuring fibre dispersion in white matter with diffusion magnetic resonance imaging (MRI) is limited by an inherent degeneracy between fibre dispersion and microscopic diffusion anisotropy (i.e., the diffusion anisotropy expected for a single fibre orientation). This means that estimates of fibre dispersion rely on strong assumptions, such as constant microscopic anisotropy throughout the white matter or specific biophysical models. Here we present a simple approach for resolving this degeneracy using measurements that combine linear (conventional) and spherical tensor diffusion encoding. To test the accuracy of the fibre dispersion when our microstructural model is only an approximation of the true tissue structure, we simulate multi-compartment data and fit this with a single-compartment model. For such overly simplistic tissue assumptions, we show that the bias in fibre dispersion is greatly reduced (~5x) for single-shell linear and spherical tensor encoding data compared with single-shell or multi-shell conventional data. In in-vivo data we find a consistent estimate of fibre dispersion as we reduce the b-value from 3 to 1.5 ms/μm2, increase the repetition time, increase the echo time, or increase the diffusion time. We conclude that the addition of spherical tensor encoded data to conventional linear tensor encoding data greatly reduces the sensitivity of the estimated fibre dispersion to the model assumptions of the tissue microstructure.
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| 3. |
- Ligneul, Clémence, et al.
(författare)
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Diffusion-weighted MR spectroscopy : Consensus, recommendations, and resources from acquisition to modeling
- 2024
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Ingår i: Magnetic Resonance in Medicine. - 0740-3194. ; 91:3, s. 860-885
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Tidskriftsartikel (refereegranskat)abstract
- Brain cell structure and function reflect neurodevelopment, plasticity, and aging; and changes can help flag pathological processes such as neurodegeneration and neuroinflammation. Accurate and quantitative methods to noninvasively disentangle cellular structural features are needed and are a substantial focus of brain research. Diffusion-weighted MRS (dMRS) gives access to diffusion properties of endogenous intracellular brain metabolites that are preferentially located inside specific brain cell populations. Despite its great potential, dMRS remains a challenging technique on all levels: from the data acquisition to the analysis, quantification, modeling, and interpretation of results. These challenges were the motivation behind the organization of the Lorentz Center workshop on “Best Practices & Tools for Diffusion MR Spectroscopy” held in Leiden, the Netherlands, in September 2021. During the workshop, the dMRS community established a set of recommendations to execute robust dMRS studies. This paper provides a description of the steps needed for acquiring, processing, fitting, and modeling dMRS data, and provides links to useful resources.
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| 4. |
- Nagy, Zoltan, et al.
(författare)
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Structural Correlates of Preterm Birth in the Adolescent Brain
- 2009
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Ingår i: Pediatrics. - : American Academy of Pediatrics. - 0031-4005 .- 1098-4275. ; 124:5, s. e964-e972
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: The Stockholm Neonatal Project involves a prospective,cross-sectional, population-based, cohort monitored for 12 to17 years after birth; it was started with the aim of investigatingthe long-term structural correlates of preterm birth and comparingfindings with reports on similar cohorts.METHODS: High-resolution anatomic and diffusion tensor imagingdata measuring diffusion in 30 directions were collected byusing a 1.5-T MRI scanner. A total of 143 adolescents (12.18–17.7years of age) participated in the study, including 74 formerlypreterm infants with birth weights of 1500 g (range: 645–1486g) and 69 term control subjects. The 2 groups were well matchedwith respect to demographic and socioeconomic data. The anatomicMRI data were used for calculation of total brain volumes andvoxelwise comparison of gray matter (GM) volumes. The diffusiontensor imaging data were used for voxelwise comparison of whitematter (WM) microstructural integrity.RESULTS: The formerly preterm individuals possessed 8.8% smallerGM volume and 9.4% smaller WM volume. The GM and WM volumesof individuals depended on gestational age and birth weight.The reduction in GM could be attributed bilaterally to the temporallobes, central, prefrontal, orbitofrontal, and parietal cortices,caudate nuclei, hippocampi, and thalami. Lower fractional anisotropywas observed in the posterior corpus callosum, fornix, and externalcapsules.CONCLUSIONS: Although preterm birth was found to be a risk factorregarding long-term structural brain development, the outcomewas milder than in previous reports. This may be attributableto differences in social structure and neonatal care practices.
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