NeuroImage
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The impact of the hemisphere affected by impairment in models of network disease is not fully understood. Among such models, focal epilepsies are characterised by recurrent seizures generated in epileptogenic areas also responsible for wider network dysfunction between seizures. Previous work focusing on functional connectivity within circumscribed networks suggests a divergence of network integrity and compensatory capacity between epilepsies as a function of the laterality of seizure onset. ⋯ We also calculated a hub disruption index for each graph metric, measuring the capacity of the brain network to demonstrate increased connectivity in some nodes for decreased connectivity in others. Our data demonstrate that the patient group as a whole is characterised by network-wide pattern of reorganization, even while global parameters fail to distinguish between groups. Furthermore, multiple metrics indicate that epilepsies with differently lateralized epileptic networks are asymmetric in their burden on functional brain networks; with left epilepsy patients being characterised by reduced efficiency and modularity, while in right epilepsy patients we provide the first evidence that functional brain networks are characterised by enhanced connectivity and efficiency at some nodes whereas reduced in others.
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Proton density and transverse relaxation (T2)-weighted fast spin echo images are frequently acquired. T2 quantification is commonly performed by applying an exponential fit to these two images, despite recent evidence that an exponential fit is insufficient to correctly quantify T2 in the presence of imperfect RF refocusing due to standard 2D slice selection or use of reduced refocusing angles. ⋯ Comparison to single spin echo is also performed in phantom experiments. The two echo method, which compensates for indirect and stimulated echoes, enables accurate quantitative T2 over a wide range of flip angle and T2 values using standard MRI methods, provided there is adequate SNR and flip angle knowledge.