Three types of capillary length estimation methods were compared:

1. Stereological methods based on a computer generation of isotropic uniform random virtual test probes in 3D, either in the form of spatial grids of virtual “slicer” planes, or spherical probes.
2. Automatic method employing a digital version of the Crofton relations using the Euler characteristic of planar sections of the binary image.
3. Interactive “tracer” method for length measurement based on a manual delineation in 3D of the axes of capillary segments. The presented methods were compared in terms of their practical applicability, efficiency and precision. 

Kubínová, L. - Mao, X. W. - Janáček, J.: Blood capillary length estimation from three-dimensional microscopic data by image analysis and stereology. Microscopy and Microanalysis (2013)