Calculating and studying the characteristics of infrared radiation scattered by multilayer systems expands the possibilities of noninvasive diagnostics of the state of biological tissues. We present Monte Carlo simulation results of backscattering from a four-layer bio-tissue model based on the solution of the Bethe-Salpeter equation, focusing on the skin-skullcerebrospinal fluid-brain system. The calculations reveal that the angular and spatial dependences of the backscatter intensity are extremely sensitive to the penetration of blood into the cerebrospinal fluid layer, suggesting potential applications in the rapid diagnosis of head injuries.