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Imaging the Developing Embryonic Heart: Combining Fast Confocal Microscopes with Four-Dimensional Reconstruction Techniques

M. Liebling

Invited Talk
IPAM workshop, Heart Modeling: Image Acquisition, Segmentation, Modeling and Analysis
University of California, Los Angeles, CA, USA, February 6-10, 2006.

Abstract Studying the influence on embryonic development of fast biomechanical processes, such as those induced by blood flow in the embryonic heart, requires the ability to acquire dynamic three-dimensional data with high temporal resolution. Despite the availability of confocal laser scanning microscopes that can acquire hundreds of two-dimensional optical sections per second, direct three-dimensional imaging, which is 2-3 orders of magnitude slower, does not yield satisfactory results. However, when the motion of the studied beating heart is cyclic, a way to circumvent this problem is to acquire, successively, sets of slice sequences at increasing depths and rearrange them to recover a dynamic three-dimensional sequence. Since external gating signals (e.g., an electro-cardiogram, which is often used for other imaging modalities at macroscopic scales to achieve proper synchronization of the two-dimensional beating heart sequences) are either unavailable or cumbersome to acquire in microscopic organisms, we have developed algorithms to reconstruct volumes based solely on the information contained in the nongated image sequences. In this talk, I will present acquisition and a posteriori synchronization procedures and discuss their capabilities and limitations. The reconstruction is based on (non)uniform temporal registration algorithms, which, in turn, rely on the minimization of the intensity difference between wavelet coefficients in adjacent slice-sequence pairs. The challenges are the considerable amount of data and typical fluorescence imaging caveats (e.g. low photon count and photo-bleaching) combined with requirements for a fast and reproducible approach. By imaging and analyzing data acquired in living zebrafish embryos, we were able to extract both qualitative and quantitative information that should contribute to reach a better understanding of the mechanisms that drive heart development. This is joint work with Arian S. Forouhar, Julien Vermot, Mory Gharib, Scott E. Fraser, and Mary E. Dickinson.