Dependence of self-energy components and cross sections of nucleons in-medium on the relative momentum of nucleons in nuclear matter from different projections choices of invariant amplitudes is studied within the framework of Dirac-Brueckner-Hartree-Fock model. Special attention is paid to the discrepancy between the self-energies and cross sections for different choices in various separate chances. Our results indicate that the self-energy of nucleons in the states with spin S = 1 and isospin triplets T = 1 is larger than those with S = 0 and T = 0 at a specified relative momentum. The dependence of the self-energies of nucleons in various reaction channels on the pseudo-scalar (PS) choice are more pronounced than that on the complete pseudo vector (CPV) choice, which is mainly due to the states with smaller total momentum quantum numbers J. Results of the in-medium differential cross sections show that the difference between d/d for the neutron-proton and neutron-neutron (or proton-proton) in various choices is larger for smaller relative momentum of nucleons and smaller scattering angles in mass center reference frame However, the total cross section total in the CPV choice is always larger than that in the PS choice. All these discrepancies will disappear with increasing incident energy.