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.
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