100 research outputs found
Quantitative magnetic resonance techniques in epilepsy
Get PDFEpilepsy is a chronic brain disorder characterized by unprovoked recurrent seizures that give rise to episodes of abnormal neuronal activity in the central nervous system. The most common application of magnetic resonance imaging (MRI) techniques in the epileptic brain is the identification of the underlying cause for a person’s epilepsy, and possibly the localization of the epileptic focus. In addition, quantitative magnetic resonance (MR) techniques enable examining certain relatively subtle aspects of epilepsy within the brain that go beyond the identification of seizure focus within the brain. In this thesis a number of studies are presented that investigate the application of quantitative MR techniques to epilepsy-related abnormalities of metabolism, microstructures and brain function. The research project was aimed at developing and validating quantitative MR techniques (spectroscopy, diffusion, T2 relaxometry, and functional magnetic resonance imaging) with clinical diagnostic potential. The main focus was on data acquisition and processing, and the application of this multi-modal MR approach in both patients with epilepsy and an animal model of epileptogenesis. We explored in a clinical setting how the cognitive consequences of epilepsy (either due to medication or due to seizures) may be reflected in altered MR tissue characteristics. Furthermore, using an experimental model of febrile convulsions, it was investigated whether neurological abnormalities, possibly linked with epileptogenesis and thus with epilepsy, could be detected by quantitative MR. A general introduction into quantitative MR techniques and epilepsy is given in Chapter 1. Chapter 2 describes a thorough review on absolute quantification of metabolites using spectroscopy, which can substantially improve the diagnostic utility of spectroscopy. Absolute quantification requires more time and expertise than relative quantification, as additional calibrations for concentration determination and spectrum analyses have to be performed. One can only benefit from absolute quantification if all additional reference steps are executed properly; otherwise unwanted additional errors may be introduced. Chapter 3 concerns a clinically relevant reproducibility study of several quantitative MR techniques which was performed on a 3.0 Tesla MR system. Repeated measurements in 10 healthy volunteers were used to establish the reproducibility of quantitative measures derived from different quantitative MR techniques, namely the T2 relaxation time, the apparent diffusion coefficient (ADC), the fractional anisotropy (FA), and metabolite concentrations of N-acetyl-aspartate (NAA), total creatine (tCr), choline (Cho) and myo-inositol (mI). The reproducibility of quantitative brain MR at 3.0 T appeared to be better than, or at least comparable to the reproducibility at 1.5 T. A newly developed statistical image analysis method, which offers considerably increased sensitivity for the detection of subtle signal changes in images of several neurological MR applications, is described in Chapter 4. This method, the regional false discovery rate (FDR) control, increases sensitivity by exploiting the spatially clustered nature of neuroimaging effects. The method was validated, characterized, and compared to some other commonly used methods (uncorrected thresholding, Bonferroni correction, and conventional FDR-control). It was found that the new method showed considerably higher sensitivity as compared to conventional FDR-control. Application of the method to two different neuroimaging applications, revealed substantial improvements compared to the other methods. Quantitative MR (T2 relaxation, diffusion, spectroscopy, and functional MRI) at 1.5 T and neuropsychological assessment was performed in a group of patients with localization related epilepsy and secondarily generalized tonicoclonic seizures (SGTCS) to study cognitive deterioration. Chapter 5 relates to the investigation of the effect of these seizures on microstructural and metabolic changes in brain tissue characteristics. Frontal, but not temporal, MR abnormalities were found to be related to SGTCS. These findings confirm that SGTCS do have a substantial effect on frontal brain function and on the microstructural brain tissue characteristics. This knowledge may help to obtain a better understanding and anticipatory treatment of SGTCS-related cognitive deterioration. In Chapter 6 it was investigated using functional MRI whether a higher number of SGCTS were associated with a functional reorganization of working memory. It was found that high numbers of SGTCS resulted in a decrease in intelligence scores and altered prefrontal brain activation. A shift from frontotemporal to prefrontal activation seemed to have occurred, suggesting that a functional reorganization of working memory is induced by a high number of SGTCS. It remains uncertain if this reorganization reflected compensatory mechanisms, or the underlying pathological processes of cognitive deterioration. In the same patient group it was found in Chapter 7 that the presence of a certain marker for neuronal damage in blood serum (telencephalin) correlates with a decreased frontotemporal activity during an functional MRI memory task
Editorial for "Deep Learning-Enabled Identification of Autoimmune Encephalitis on 3D Multi-Sequence MRI"
Get PDFReproducibility of quantitative cerebral T2 relaxometry, diffusion tensor imaging, and 1H magnetic resonance spectroscopy at 3.0 Tesla
No full text1H MR spectroscopy of the brain: Absolute quantification of metabolites
No full textHydrogen 1 (1H) magnetic resonance (MR) spectroscopy enables noninvasive in vivo quantification of metabolite concentrations in the brain. Currently, metabolite concentrations are most often presented as ratios (eg, relative to creatine) rather than as absolute concentrations. Despite the success of this approach, it has recently been suggested that relative quantification may introduce substantial errors and can lead to misinterpretation of spectral data and to erroneous metabolite values. The present review discusses relevant methods to obtain absolute metabolite concentrations with a clinical MR system by using single-voxel spectroscopy or chemical shift imaging. Important methodological aspects in an absolute quantification strategy are addressed, including radiofrequency coil properties, calibration procedures, spectral fitting methods, cerebrospinal fluid content correction, macromolecule suppression, and spectral editing. Techniques to obtain absolute concentrations are now available and can be successfully applied in clinical practice. Although the present review is focused on 1H MR spectroscopy of the brain, a large part of the methodology described can be applied to other tissues as well. © RSNA, 2006
Moving from talk to action: Implementing austerity-driven change
Get PDFOrganizational change is often proposed as a solution to austerity. Implementing change when there is no budget, however, is difficult. This paper explains how a major Dutch city implemented radical changes in the wake of the global financial crisis. The paper relates the change programme to eight accepted determinants of successful change. Drawing on the experience of 65 employees, the author explores three catalysts for success, which he calls ‘acts of implementation’. The paper explains why successful implementation of austerity-driven change is not just a matter of complying with eight static success conditions but also of crafting dynamic acts that fits the specific context of austerity. Implementers have to deal with politics, resistance and ambiguity to move from talk to action
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No full textDocument(en) uit de collectie Chemische Procestechnologie.DelftChemTechApplied Science
Editorial for "MRI-Based Back Propagation Neural Network Model as a Powerful Tool for Predicting the Response to Induction Chemotherapy in Locoregionally Advanced Nasopharyngeal Carcinoma"
No full textFashion, fads and the popularity of choices: Micro-foundations for diffusion consumer theory
Get PDFThis is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordKnowledge acquisition by consumers is a key process in the diffusion of innovations. However, in standard theories of the representative agent, agents do not learn and innovations are adopted instantaneously. Here, we show that in a discrete choice model where utility-maximising agents with heterogenous preferences learn about products through peers, their stock of knowledge on products becomes heterogenous, fads and fashions arise, and transitivity in aggregate preferences is lost. Non-equilibrium path-dependent dynamics emerge, the representative agent exhibits behavioural rules different than individual agents, and aggregate utility cannot be optimised. Instead, an evolutionary theory of product innovation and diffusion emerges.Engineering and Physical Sciences Research Council (EPSRC)Economic and Social Research Council (ESRC
Application of contrast-enhanced magnetic resonance imaging in the assessment of blood-cerebrospinal fluid barrier integrity
Get PDFVERHEGGEN, I.C.M., W. Freeze, J. de Jong, J. Jansen, A. Postma, M. van Boxtel, F. Verhey and W. Backes. The application of contrast-enhanced MRI in the assessment of blood-cerebrospinal fluid barrier integrity. Choroid plexus epithelial cells form a barrier that enables active, bidirectional exchange between the blood plasma and cerebrospinal fluid (CSF), known as the blood-CSF barrier (BCSFB). Through its involvement in CSF composition, the BCSFB maintains homeostasis in the central nervous system. While the relation between bloodbrain barrier disruption, aging and neurodegeneration is extensively studied using contrast-enhanced MRI, applying this technique to investigate BCSFB disruption in age-related neurodegeneration has received little attention. This review provides an overview of the current status of contrast-enhanced MRI to assess BCSFB permeability. Post-contrast ventricular gadolinium enhancement has been used to indicate BCSFB permeability. Moreover, new techniques highly sensitive to low gadolinium concentrations in the CSF, for instance heavily T2weighted imaging with cerebrospinal fluid suppression, seem promising. Also, attempts are made at using other contrast agents, such as manganese ions or very small superparamagnetic iron oxide particles, that seem to be cleared from the brain at the choroid plexus. Advancing and applying new developments such as these could progress the assessment of BCSFB integrity.Neuro Imaging Researc
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