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Diffusion tensor magnetic resonance imaging of the heart: structural and computational studies

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We use diffusion tensor magnetic resonance imaging (DT-MRI) to examine cardiac fibre and sheet structure, and use the datasets as geometries for our computational electrophysiology models. Here we present examples from these two areas of our work.

Despite extensive effort and recent advances in imaging techniques, several opposing and non-mutually compatible models have been proposed to explain cardiac structure. These models, although limited, have advanced the study and understanding of heart structure, function and development. We present a large scale quantitative comparison of fibre orientation in two rabbit heart datasets obtained using different methods: (i) a histologically-derived dataset and (ii) a dataset obtained using DT-MRI. We compare both datasets with the previously proposed structural models. Good correspondence between the fibre helix (inclination) angles in two datasets is found, but the fibre transverse angles are markedly different. From these datasets, weaknesses in the data obtained from both methodologies are identified and discussed, we examine the validity of the different structural models, and future refinements in DT-MRI methodology are identified, particularly with respect to tissue handling and preparation.

Using our computational models, we examine the effects of cardiac geometry and architecture on the excitable media paradigm, and illustrate the effect of cardiac structure on the dynamics of arrhythmias by quantifying scroll wave filament dynamics in two biophysically-detailed, homogeneous (to remove effects of heterogeneous action potential duration) models of the human left ventricular free wall: (i) a simple cuboid model and (ii) a wedge model constructed using DT-MRI data. For any given geometry, changing the architecture (from isotropic through to anisotropic and orthotropic) results in changes to the filament meander pattern, increases in filament length, changes to the filament curvature and local filament twist, and increases in the maximum twist along a single filament. Changes to the geometry also affect scroll wave dynamics, mainly due to tissue size. We conclude that such differences in re-entrant scroll wave dynamics should be taken into account when interpreting results from simulations that use simple cardiac geometries and architectures.

This talk is part of the Isaac Newton Institute Seminar Series series.

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