Improving the forward model for electrical impedance tomography of brain function through rapid generation of subject specific finite element models

Electrical Impedance Tomography (EIT) is a non-invasive imaging method which allows internal electrical impedance of any conductive object to be imaged by means of current injection and surface voltage measurements through an array of externally applied electrodes. The successful generation of the image requires the simulation of the current injection patterns on either an analytical or a numerical model of the domain under examination, known as the forward model, and using the resulting voltage data in the inverse solution from which images of conductivity changes can be constructed. Recent research strongly indicates that geometric and anatomical conformance of the forward model to the subject under investigation significantly affects the quality of the images. This thesis focuses mainly on EIT of brain function and describes a novel approach for the rapid generation of patient or subject specific finite element models for use as the forward model. After introduction of the topic, methods of generating accurate finite element (FE) models using commercially available Computer-Aided Design (CAD) tools are described and show that such methods, though effective and successful, are inappropriate for time critical clinical use. The feasibility of warping or morphing a finite element mesh as a means of reducing the lead time for model generation is then presented and demonstrated. This leads on to the description of methods of acquiring and utilising known system geometry, namely the positions of electrodes and registration landmarks, to construct an accurate surface of the subject, the results of which are successfully validated. The outcome of this procedure is then used to specify boundary conditions to a mesh warping algorithm based on elastic deformation using well-established continuum mechanics procedures. The algorithm is applied to a range of source models to empirically establish optimum values for the parameters defining the problem which can successfully generate meshes of acceptable quality in terms of discretization errors and which more accurately define the geometry of the target subject. Further validation of the algorithm is performed by comparison of boundary voltages and image reconstructions from simulated and laboratory data to demonstrate that benefits in terms of image artefact reduction and localisation of conductivity changes can be gained. The processes described in the thesis are evaluated and discussed and topics of further work and application are described

Rapid generation of subject-specific thorax forward models

For real-time monitoring of lung function using accurate patient geometry, shape information needs to be acquired and a forward model generated rapidly. This paper shows that warping a cylindrical model to an acquired shape results in meshes of acceptable mesh quality, in terms of stretch and aspect ratio

Three venepuncture techniques in babies: a comparative study

Modifying hyodermic needles for blood sampling in babies is common. However, such techniques mean that medical devices are not always used as manufacturers intend and potential and actual risks associated with their use occur. A number of new devices have recently been designed to overcome safety issues. However, whether new devices are any more effective than existing modified methods is unknown. Through a randomoised controlled trial, this study attempted to compare the safety and efficacy of three blood sampling techniques in babies: (i) the 'broken' needle, (ii) the 'modified' buttrefly' and (iii) a new 'single winged' needle designed specifically for venepuncture in babies and young children. Eligibility criteria for inclusion to the study comprised: babies twelve months of age and under, weighing over 1500 grams, requiring at least three routine blood samples to monitor their condition, six hours apart. Informed, written parental consent was also required. The sample was drawn from a neonatal intensive care unit and achildren's unit in a large teaching hospital. Ethical approval for the study was gained form the local research ethics committee. Babies recruited into the study were randomised according to the order in which the three blood sampling techniques were used. Data were collected in terms of: (1) whether the blood sample had been obtained after one, two or more than two attempts; (2) whether there was clotting in the sample and (3) whether there was bruising and the extent of the bruising measured at the largest diamter of the bruise. Fourteen babies completed the study reulting in the trail being severely underpowered. Recruitment to the study was disappointing and was, in part, attributed to a number of adverse incidents that had occurred in clinical and research practices involving babies and children, that had gained much media attention, both before and during the study period

Basement-cover relations in the southeastern Cape Breton Highlands, Nova Scotia, Canada

In the southeastern Cape Breton Highlands Neoproterozoic plutonic and metamorphic rocks outcrop in upland areas whereas Carboniferous sedimentary rocks are found in the river valleys and coastal lowlands. Detailed analysis of the contacts between these two groups of rocks including mapping, geometric constructions of the contact relations, structural geological investigations, petrographic analysis and geophysical map interpretations show that the basement rocks were emplaced by a thrust fault that extends at least from the Baddeck River valley to North River, and possibly includes klippen south and east of the highlands. The thrust fault transported a slab of rock with minimum thickness of 200 m a distance of at least 8 km over Horton and Windsor group rocks. East-directed translation of the thrust block likely occurred during the Alleghanian orogeny, and appears to mirror movement previously identified in the northern and western Cape Breton Highlands, implying that much of the upland geology is allochthonous, but likely rooted in the central highlands as positive flower structure