Mathematical Scienceshttp://hdl.handle.net/10468/882018-01-23T15:48:02Z2018-01-23T15:48:02ZThe Gamma characteristic of reconstructed PET images: Implications for ROI analysisMou, TianHuang, JianO'Sullivan, Finbarrhttp://hdl.handle.net/10468/52452018-01-09T12:00:52Z2017-11-23T00:00:00ZThe Gamma characteristic of reconstructed PET images: Implications for ROI analysis
Mou, Tian; Huang, Jian; O'Sullivan, Finbarr
The basic emission process associated with PET imaging is Poisson in nature. Reconstructed images inherit some aspects of this—regional variability is typically proportional to the regional mean. Iterative reconstruction using expectation maximization (EM), widely used in clinical imaging now, impose positivity constraints that impact noise properties. The present work is motivated by analysis of data from a physical phantom study of a PET/CT scanner in routine clinical use. Both traditional filtered back-projection (FBP) and EM reconstructions of the images are considered. FBP images are quite Gaussian but the EM reconstructions exhibit Gamma-like skewness. The Gamma structure has implications for how reconstructed PET images might be processed statistically. Post-reconstruction inference— model fitting and diagnostics for regions of interest are of particular interest. Although the relevant Gamma parameterization is not within the framework of generalized linear models (GLM), iteratively re-weighted least squares (IRLS) techniques, which are often used to find the maximum likelihood estimates of a GLM, can be adapted for analysis in this setting. Our work highlights the use of a Gamma-based probability transform in producing normalized residuals as model diagnostics. The approach is demonstrated for quality assurance analyses associated with physical phantom studies—recovering estimates of local bias and variance characteristics in an operational scanner. Numerical simulations show that when the Gamma assumption is reasonable, gains in efficiency are obtained. The work shows that the adaptation of standard analysis methods to accommodate the Gamma structure is straightforward and beneficial.
2017-11-23T00:00:00ZThe influence of process parameters on the physical characteristics of ceramic microneedles, evaluated using a factorial designCarracedo-Taboada, MartaO'Sullivan, KathleenMcAuliffe, Michael A. P.Vucen, SonjaO'Sullivan, Carolinehttp://hdl.handle.net/10468/48512017-10-10T11:00:39Z2017-10-05T00:00:00ZThe influence of process parameters on the physical characteristics of ceramic microneedles, evaluated using a factorial design
Carracedo-Taboada, Marta; O'Sullivan, Kathleen; McAuliffe, Michael A. P.; Vucen, Sonja; O'Sullivan, Caroline
Salguero, Jorge; Ares, Enrique
The paper presents the application of the factorial Design of Experiments (DoE) to evaluate the influence of process parameters on the physical characteristics of ceramic microneedles (CMN). In this study, an understanding of the fabrication process was achieved by performing a DoE based on varying two levels of five parameters. Statistical analyses were performed on the data to investigate whether the process parameters have a significant effect on the production of a patch of 25 microneedles (MN) with sharp tips. The study showed that four out of five main effects as well as an interaction between two parameters were significant.
2017-10-05T00:00:00ZThe constrained optimisation of small linear arrays of heaving point absorbers. Part I: The influence of spacingMcGuinness, Justin P. L.Thomas, Garethhttp://hdl.handle.net/10468/48392017-10-05T18:00:22Z2017-07-18T00:00:00ZThe constrained optimisation of small linear arrays of heaving point absorbers. Part I: The influence of spacing
McGuinness, Justin P. L.; Thomas, Gareth
This paper describes the optimisation of small arrays of Wave Energy Converters (WECs) of point absorber type. The WECs are spherical in shape and operate in heave alone and a linear array of five devices is considered. Previous work is extended by considering the constrained performance of the array members, where an uaniper limit on WEC displacements is enforced. Two opimisations are performed. In each case, the objective function is defined as the mean of the averaged interaction factor ovehe non-dimensional length of the array. The first considers the array layout fixed at a geometry previously identified as optimal in an unconstrained regime and optimises the displacements of the WECs subject to constraints. The second allows both the WEC positions and displacements to vary as optimisation variables. It is shown that the optimal layout of the constrained arrays is different from the unconstrained case. Applying constrained motions results in optimal layouts that are more separated, with less grouping of WECs and this will have practical considerations. The effect of the constraints varies depending on the incident wave angle. In some cases, performance is reduced drastically and stability of performance is improved, while in other cases there is a degradation of performance. Thus, a trade-off between performance and stability of performance is seen when displacement constraints are applied.
2017-07-18T00:00:00ZModeling cortical spreading depression induced by the hyperactivity of interneuronsDesroches, MathieuFaugeras, OlivierKrupa, MartinMantegazza, Massimohttp://hdl.handle.net/10468/40182018-01-18T10:03:12Z2017-05-10T00:00:00ZModeling cortical spreading depression induced by the hyperactivity of interneurons
Desroches, Mathieu; Faugeras, Olivier; Krupa, Martin; Mantegazza, Massimo
Cortical spreading depression (CSD) is a wave of transient intense neuronal firing leading to a long lasting depolarization block of neuronal activity. It is a proposed pathological mechanism of migraine with aura. Some molecular/cellular mechanisms of migraine with aura and of CSD have been identified studying a rare mendelian form: familial hemiplegic migraine (FHM). FHM type 1 & 2 are caused by mutations of the CaV2.1 Ca2+ channel and the glial Na+ / K+ pump, respectively, leading to facilitation of CSD in mouse models mainly because of increased glutamatergic transmission/extracellular glutamate build-up. FHM type 3 mutations of the SCN1A gene, coding for the voltage gated sodium channel NaV1.1, cause gain of function of the channel and hyperexcitability of GABAergic interneurons. This leads to the counterintuitive hypothesis that intense firing of interneurons can cause CSD ignition. To test this hypothesis in silico, we developed a computational model of an E-I pair (a pyramidal cell and an interneuron), in which the coupling between the cells in not just synaptic, but takes into account also the effects of the accumulation of extracellular potassium caused by the activity of the neurons and of the synapses. In the context of this model, we show that the intense firing of the interneuron can lead to CSD. We have investigated the effect of various biophysical parameters on the transition to CSD, including the levels of glutamate or GABA, frequency of the interneuron firing and the efficacy of the KCC2 co-transporter. The key element for CSD ignition in our model was the frequency of interneuron firing and the related accumulation of extracellular potassium, which induced a depolarization block of the pyramidal cell. Our model can be used to study other types of activities in microcircuits and of couplings between excitatory and inhibitory neurons.
2017-05-10T00:00:00Z