Optical imaging using voltage-sensitive dyes is a commonly applied technique to investigate cardiac activity in perfused tissue preparations or whole hearts. It offers superior spatiotemporal resolution, as well as the potential of obtaining simultaneous multi-modal recordings through the combination with various other indicators (e.g. calcium).
Conventional epi-fluorescence imaging was initially considered as a surface mapping technique, but careful interpretation of epi-fluorescence signals, taking photon absorption and scattering in to account, has shown that such recordings can yield information about sub-surface wave propagation. The use of detailed bio-photonics models combined with electrophysiological models of myocardium, so-called hybrid models, has been instrumental in understanding the synthesis of cardiac optical signals.
Wave propagation in cardiac tissue and ventricular myocardium in particular, is a three-dimensional phenomenon. Building on our earlier experimental and computational work, we are currently developing novel techniques for the 3D visualization of cardiac activity using optical methods. This requires the solution of the optical inverse problem, i.e. obtaining 3D information from a limited set of optical measurements, which is, as is often the case in bio-medical imaging, ill-posed and therefore requires regularization. Hybrid models of cardiac optical signals play here too an important role as they allow to assess the accuracy of the regularization scheme, and estimate the optimal spatiotemporal resolution of the reconstruction. We present results from a recent study that showed the feasibility of 3D reconstruction of paced activity in isolated rat hearts using an optical technique called Laminar Optical Tomography. Finally, we report on recent work which has focused on increasing depth penetration to achieve 3D reconstructions in larger hearts and developing a fast acquisition system for the imaging of arrhythmias during which activity is non-repetitive.
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