In-vivo Mapping of the Blood Velocity in Zebrafish with Optical Vector Field Tomography

The vascular system develops very early during vertebrate embryogenesis, since all other forming organs depend greatly on its ability to distribute oxygen and nutrients. Since long time ago, the development of the vascular system is being studied by means of ex vivo imaging, with proper staining, fluorescent markers and histological sections. Recently, the advent of Confocal Microangiography provided true advances in the field. Microangiography is the elective method for vascular system imaging in transparent embryos, because it allows one to visualize the morphology of the vessel network in 3D, with confocal resolution. However, it is an invasive technique and it is not able to give quantitative information on blood velocity and flow. Nowadays, non-invasive techniques are required in order to provide in vivo measurements over the complete development of the very same specimen. In the zebrafish, blood vessels of the trunk region are particularly important for understanding the mechanisms that drive vasculogenesis and angiogenesis during embryo development. Moreover, it has been proved that the blood flow magnitude and the shear forces applied to vessel walls have a great impact on the vascular system development. In order to provide quantitative information to be used in cardiovascular research, we developed an Optical Vector Field Tomography (OVFT) algorithm for Optical Projection Tomography (OPT) measurements. The technique is able to visualize the vascular system of the zebrafish trunk in three dimensions and to quantitatively analyze and represent in 3D the blood velocity distribution. The contrast is given by the endogenous motion of blood cells.