Blood flow measurement in the zebrafish heart using light sheet microscopy

The link between haemodynamics and cardiac tissue mechanics is an active area of research in developmental biology. Nevertheless, previous study of fluid-structure interaction in the developing heart was mostly confined to single projection blood flow measurements or computational fluid dynamics simulations using only the information of the heart wall structure. Hence, techniques capable of direct 3D + time resolved blood flow and heart wall motion are necessary to deepen the understanding of the cardiac function in the developing heart. This work presents an imaging system which combines selective plane illumination microscopy (SPIM), with optical gating techniques, and micro particle image velocimetry (uPIV). This combination (referred here as SPIM-uPIV) allowed non-invasively measuring blood flow in the developing zebrafish heart in a depth and time-resolved manner. Our system surpasses conventional uPIV measurement systems based on wide-field illumination which suffer from measurement errors due to volume illumination of the sample. The proposed SPIM-uPIV system was validated in a control microfluidics experiment where flow of fluorescent microspheres was measured in a 50 um diameter tube. Both qualitative and quantitative analysis was performed to compare our SPIM-uPIV against conventional brightfield-uPIV measurements. Furthermore, this work implements a different metric for “cross-correlation” which was empirically found to perform better than the traditional algorithm used in PIV analysis, when motion of large particles is measured. By implementing optical gating techniques to our analysis, 3D + time blood flow measurements in the beating hearts of 3, 4, and 5 day old zebrafish hearts were obtained. The recovered 3D + time velocity information enabled further investigation of the heart function such as the pumping efficiency which was obtained by calculating the flow rate through a section of a heart chamber. In summary, it is proposed that SPIM-uPIV system can be a useful tool for direct bloodflow measurements in transparent small-animal models. Such measurements would benefit the current knowledge of fluid-structure interaction phenomena in the developing heart, and could be used to validate previous work by other group