The tomography problem considered in this monograph consists of finding an essential part of information about the internal structure of an unknown medium. More particularly, the contact boundaries between various materials in the medium are sought. This investigation is implemented by studying an appropriate mathematical model, which is represented as a transport equation (linear Boltzmann's equation) together with certain boundary conditions. Both theoretical and numerical methods have been used and the results consist of proved theorems, computer testing of the corresponding algorithms, together with a number of tables.