Figure 1.

“Ink drop” analogy to describe and parametrize microscopic diffusion patterns (A). When ink drops into a medium, it diffuses over time and leaves a stain (diffusion pattern), the size and shape of which are conditioned by the microstructure of the medium. Grey objects correspond to rather permeable cell membranes (B). Diffusion patterns are mathematically described by diffusion tensors D, which can be represented geometrically by glyphs (black three-dimensional objects) shaped like the corresponding diffusion patterns. In particular, the size, shape, and orientation of these glyphs are given by the trace of D, the variance of the eigenvalues of D, and the main eigenvector of D, respectively.