Efficient non-linear 3D electrical tomography reconstruction

Non-linear electrical tomography imaging can be performed efficiently if certain optimisations are applied to the computational reconstruction process. We present a 3D non-linear reconstruction algorithm based on a regularized conjugate gradient solver and discuss the optimisations which we incorporated to allow for an efficient and accurate reconstruction. In particular, the application of image smoothness constraints or other regularization techniques and auto-adaptive mesh refinement are highly relevant. We demonstrate the results of applying this algorithm to the reconstruction of a simulated material distribution in a cubic volume

Optimal finite element modelling and efficient reconstruction in non-linear 3D electrical resistance tomography

Electrical Impedance Tomography can provide images with well-defined characteristics using a fully non-linear reconstruction process when appropriate constraints are imposed on the solution to allow the ill-posed inverse problem to be solved. Using appropriate finite element discretizations for forward solution and inverse problem offers additional advantages in the image reconstruction process, such as (a) inclusion of prior knowledge, (b) generic model templating to adapt to, for example, individual head shapes, and (c) obtaining accurate results without unnecessary computational overhead. We have developed an efficient 3D non-linear reconstruction algorithm based on a regularized inverse conjugate gradient solver which incorporates (a) local image smoothness constraints, and (b) a number of optimisations which reduce the computing power required to obtain an accurate solution. We show results from applying this to various problems which arise in medical resistivity reconstruction given only surface potential measurements and demonstrate the importance of the FE discretization. Keywords: 3D non-linear electrical impedance tomography, FE template modelling, optimal finite element meshes, 3D visualization, FE discretization

Efficient non-linear 3D electrical tomography and finite element optimizations for functional source imaging

An essential factor in functional source imaging is the accurate knowledge of the conducitvity dostribution inside the body. Current models for electrophysiological forward and inverse problems use tabulated conductivity values obtained from experiments. This article shows how EIT-derived conductivities can be used in EEG reconstructions of a head slice

Non-linear electrical tomography reconstruction of simple test objects and a simulated head slice

Fully non-linear reconstruction in Electrical Tomography produces images with well-defined characteristics when explicit guides are imposed on the accessible solutions. In this paper, we revisit the formulation of the problem and apply the algorithm to some simulated test objects, and to a simple 2-dimensional model of the human head. The results demonstrate the best fidelity of reconstruction which may be achieved with existing and potentially attainable levels of signal to noise. We use a finite element model with some adaptive capability so that the images generated by the chosen constraint are not perturbed by the coarseness of the mesh. The algorithm incorporates a number of optimisations to reduce the required computing power and storage space, these include:Sparse matrix storage scheme and optimised sparse numerical handlingProblem-adapted element shape and densityUsage of high quality finite element meshesPre-evaluation of used quantities and matrices and application of numerical techniques such as the Woodbury formul

Prospects for high fidelity imaging in nonlinear EIT using high performance computing

Linear image reconstruction in EIT has been widely used in medical and process applications, and nearly all of these have been based on approximately uniform distributions of the electrical conductivity in the object under study. Successful applications in medicine have been reported although the markedly non-uniform conductivity distribution in the human body, which is not known a priori, means that artefacts produced by the linear imaging approximation are difficult to exclude. It is important therefore to pursue the full nonlinear problem in order to provide a firm basis for subsequent linear treatments; we have already shown that effective nonlinear EIT can be achieved when appropriate choices are made to constrain the form of the images sought [Blott et al 1998]. In this paper we explore the image resolutions potentially achievable with the availability of improved signal-to-noise in the data. The advent of modern high performance computing allows the production of accurate reference images in practicable time scales, and these can then be used as the basis of high fidelity linear imaging systems in real-time applications. In addition, it becomes feasible to tackle the full 3-d problem

Beach-dune morphological relationships and erosion/accretion: an investigation at five sites in England and Wales using LIDAR data

Abstract The critical relationships between beach and nearshore parameters and the erosion/accretion status of frontal dunes have been investigated using LIDAR data, complemented by data obtained from conventional topographic and bathymetric surveys, at five dune systems in England and Wales. Morphometric parameters calculated from the LIDAR data demonstrate the presence of a general relationship between beach morphology, dune morphology and erosion/accretion. Eroding dunes were found to be associated wi [KEYWORDS: LIDAR ; Coastal dunes ; Beach–dune interaction ; Erosion ; Morphology

Long-term morphological change and its causes in the Mersey Estuary, NW England

Changes in the morphology of the Mersey Estuary, and their possible causes, have been investigated using Historical Trend Analysis and Expert Geomorphological Assessment. Historical bathymetric charts were digitised and analysed within a GIS to provide quantitative estimates of changes in areas and sediment volumes above and below selected elevation planes. The results show that the estuary experienced major changes over the last 150 years, notably between the late 19th century and ca. 1950. An analysis of data relating to possible natural and human factors which could have influenced these changes suggests that training wall construction and dredging in the Outer Estuary and Liverpool Bay was the most significant factor contributing to change during this period. These activities modified the hydrodynamic and sediment transport regime in a way which enhanced an existing natural tendency for movement of sediment from Liverpool Bay and the Outer Estuary into the Inner Estuary. Changes in other factors, including sea level, tidal range, wind/wave climate, freshwater flow and embanking/land reclamation, were of relatively minor importance. Between 1950 and 1977 the rate of sediment accumulation in the Inner Estuary declined as the estuary approached a new condition of dynamic equilibrium, and since 1977 there has been a slight net loss of sediment. Under these conditions the changes in natural forcing factors, such as sea level and storminess, are likely to have a relatively greater effect on the estuary than in the past. [KEYWORDS: Estuaries; Morphology ; Bathymetry ; Sedimentation ; Historical Trend Analysis ; Expert Geomorphological Assessment; Mersey]

Beach-dune morphological relationships and erosion/accretion: an investigation at five sites in England and Wales using LIDAR data

Abstract The critical relationships between beach and nearshore parameters and the erosion/accretion status of frontal dunes have been investigated using LIDAR data, complemented by data obtained from conventional topographic and bathymetric surveys, at five dune systems in England and Wales. Morphometric parameters calculated from the LIDAR data demonstrate the presence of a general relationship between beach morphology, dune morphology and erosion/accretion. Eroding dunes were found to be associated wi [KEYWORDS: LIDAR ; Coastal dunes ; Beach–dune interaction ; Erosion ; Morphology]