Analysis of microvascular trees by means of scanning electron microscopy of vascular casts and 3D-morphometry.

Arterial and capillary trees form by consecutive branching (mostly bifurcations) from a stem vessel, venous trees form by repeated merging of blood vessels. Diameters of stem (parent, mother) vessels and daughter vessels (branches), interbranching distances and branching angles between stem and daughter vessels lastly define the overall three-dimensional structure of the vascular network as well as the basic transport capacity of the system. Here we use scanning electron microscopy and 3D-morphometry to measure these variables from stereo paired images of vascular corrosion casts of the anterior cerebral artery and its main branches and from arteriolar bifurcations of the mesencephalic optic tectum in the actinopterygian fish, Acipenser ruthenus. We then calculate bifurcation indices, area ratios, asymmetry ratios and test for the optimality principles underlying the bifurcations studied. Our results show that arteriolar bifurcations in the optic tectum are in favor of the principles of minimum pumping power and minimum volume rather than the principles of minimum surface and minimum drag. We conclude that scanning electron microscopy of vascular corrosion casts in conjunction with 3D-morphometry is an excellent tool to thoroughly analyze vascular trees in healthy and diseased tissues and organs, as well as on an ontogenetic and phylogenetic scale.