Tissue engineering with transplanted cells has the potential to repair and regenerate almost every tissue and organ of the body. One major obstacle of cell therapies is the inability to longitudinally assess injected cells. Non-invasive imaging with contrast-enhanced MRI is highly suited for this task but is limited with current methods. In this study, we report a novel method for producing bright endogenous cellular contrast through a genetic MRI reporter that results in the formation of in situ ferritin-manganese nanoparticles. The signal produced by these cells is significantly higher than traditional iron labelled ferritin-overexpressing cells and manganese-permeable cell lines.