Optimization of proprioceptive stimulation for echo-planar and inverse magnetic resonance imaging

In echo-planar imaging (EPI), the optimal passive movement parameters (rate and duration) for studying proprioceptive brain responses are unknown. The aim of this thesis was to test the effect of stimulus rate on brain responses evoked by proprioceptive stimulation in EPI. In addition, we attempted to develop a measurement protocol for experiments focused on proprioception in ultrafast inverse magnetic resonance imaging (InI) and investigate the amplitude of blood oxygen level-dependent (BOLD) signal at varying stimulus duration. This experimental setup was supposed to be applied in future connectivity studies of the proprioceptive brain network. We found that the optimum rate for right index finger proprioceptive stimulation in EPI varies from 3 to 6 Hz. While we managed to sample the BOLD responses every 100 ms (a 20-fold increase in temporal resolution compared to EPI), the experimental design in InI is challenging due to methodological constraints. Thus, the appropriate stimulation parameters for InI still remain a topic for further research

List of Artefacts Observed in Magnetic Resonance Imaging

Import 22/07/2015Obrazové artefakty vznikající při zobrazování pomocí magnetické rezonance představují komplikaci při investigaci patologických nálezů u vyšetřovaných pacientů. Artefakt lze definovat jako nežádoucí zobrazení ve výsledném MR obrazu, většinou neodpovídající reálnému prostorovému rozložení tkání uvnitř organismu. Nejčastější příčiny jejich vzniku jsou variace intenzity magnetického pole, fyzikálně-chemické vlastnosti tkání pacienta či relikty signálového zpracování. Artefakty lze rovněž rozdělit dle schopnosti předcházet jejich vzniku či omezení dopadu na výsledný obraz. Ve snaze eliminovat tyto artefakty bylo vytvořeno uživatelské prostředí v programu C#, umožňující na základě aplikace příslušných filtračních metod pro zpracování obrazu zlepšit parametry při zachování diagnosticky významných oblastí snímků. Podpůrnou složkou tohoto softwaru je podrobná katalogizace MR artefaktů s detailním popisem problematiky jednotlivých skupin a online přístupem ve formě výukového materiálu.Artefacts in MRI represent complications in diagnostics of pathological findings in examined patients. An artefact can be defined as an undesirable image component in final MR images, predominantly incommensurate with the real spatial distribution of tissues inside an organism. The most frequent causes of their occurrence are represented by magnetic field variability or by physical properties of patients’ tissues; however, artefacts can be divided according to the feasibility of their elimination or the limitation to their impact on image quality. Pursuing the elimination of artefacts, an interactive user interface has been developed in C# programme allowing to improve the quality and preserve the diagnostically important regions of the images based on appropriate application of genuine filtering methods. Included as a supportive element of this software is a detailed catalogue of MR artefacts providing circumstantial account of all artefact groups in conjunction with its online implementation in the form of an educational environment.450 - Katedra kybernetiky a biomedicínského inženýrstvívýborn

Multi-level fiber tracking: evaluation on clinical data

Conventional deterministic fiber tractography approaches commonly used in clinical applications are prone to generating false-negative reconstructions, which might influence further decision-making related to treatment and repeated surgery in patients with brain tumors. Surgery-related effects, such as blood inflow into white matter and edema, further distort the diffusion signal, complicating the task of tractography. We evaluated a novel multi-level fiber tractography approach on data of subjects who had undergone tumor resection. A comparison with conventional deterministic approaches is performed. The results were correlated with the reported motor-function deficit grades. ( Abstract #1746

Functional traits trade-offs define plant population stability scross different biomes

Ecological theory posits that temporal stability patterns in plant populations are associated with differences in species’ ecological strategies. However, empirical evidence is lacking about which traits, or trade-offs, underlie species stability, especially across different biomes. We compiled a worldwide collection of long-term permanent vegetation records (greater than 7000 plots from 78 datasets) from a large range of habitats which we combined with existing trait databases. We tested whether the observed inter-annual variability in species abundance (coefficient of variation) was related to multiple individual traits. We found that populations with greater leaf dry matter content and seed mass were more stable over time. Despite the variability explained by these traits being low, their effect was consistent across different datasets. Other traits played a significant, albeit weaker, role in species stability, and the inclusion of multi-variate axes or phylogeny did not substantially modify nor improve predictions. These results provide empirical evidence and highlight the relevance of specific ecological trade-offs, i.e. in different resource-use and dispersal strategies, for plant populations stability across multiple biomes. Further research is, however, necessary to integrate and evaluate the role of other specific traits, often not available in databases, and intraspecific trait variability in modulating species stability