Improved imaging techniques are being used to broaden the scope and better understanding of the complex cell behaviours in the body. Nonetheless, the migratory behavior of immune cells after CNS injury is still poorly understood. In this study, we employed four-dimensional (4D) MRI to monitor the dynamic migration of infiltrating monocytes/macrophages in the living mouse brain. Our results demonstrate the possibility of non-invasive long-term monitoring of individual live cells. Moreover, this innovative technique furthers our understanding of the cellular mechanisms occurring in the normal and injured brain tissues.