Fluorine-19 MRI signal phenotype in solid tumor following in situ perfluorocarbon cell labeling

Cell tracking with perfluorocarbon (PFC) nanoemulsion (NE) and ¹⁹F MRI has been used in numerous inflammation models, including tumors. After intravenous injection, phagocytic immune cells endocytose NE droplets, producing background-free ¹⁹F images where signal foci quantify inflammation. Histology confirms tracer uptake mainly in myeloid-lineage cells. Myeloid cells - granulocytes, monocytes, and macrophages - play major roles in cancer. Tumor-associated macrophages (TAMs), which can comprise up to 60% of tumor mass, promote angiogenesis, metastasis, and immunosuppression. High TAM burden correlates with poor prognosis in several cancers and reduced responsiveness to immunotherapies. In this study, we characterize ¹⁹F MRI signals, following in situ NE labeling, in a syngeneic breast cancer model. Our goal is to validate the cell phenotype responsible for the ¹⁹F signals observed in the tumor microenvironment. We quantified ¹⁹F signal contributions from myeloid subsets using flow cytometry and ¹⁹F NMR and mapped intratumoral distributions via cryo-fluorescence tomography. These results demonstrate selective NE uptake by myeloid cells and support ¹⁹F MRI as a noninvasive biomarker for TAM burden in cancer.