Stem-cell therapies rely on the ability of injected cells to localize in the appropriate environment after transplantation. Tracing cells after transplant in challenging. This study uses positron emission tomography (PET) along with a statistical tracking algorithm to trace the fate of cells injected into mice. The study establishes the potential of PET in offering unmatched insights into the earliest phases of cell trafficking in physiological and pathological processes and in cell-based therapies.