In the case of the inverse Edelstein effect, by looking at the section of the Dirac cone, the spin-to-charge conversion can be visualized as follows: the spin injection produces a piling up of spins of one character in one of the energy dispersion relation branches. This results in a spin unbalance due to the different branch occupations (i.e., a spin accumulation), which leads to a momentum unbalance and, therefore, to a charge current which can be electrically probed. As for the direct effect, also in the inverse Edelstein effect, the charge current can only flow on the topological insulator surfaces due to the energy band conformation. This is how the 2D spin-to-charge conversion occurs in these materials and this could allow topological insulators to be exploited as spin detectors.