OBJECTIVESTo investigate the value of R2*map for quantitatively tracing superparamgnetic ironoxides (SPIO) labeled endothelial progenitor cells (EPCs).

METHODSThe EPCs were isolated from Balb/c mice bone marrow and cultured in vitro. After 7 days, expression of acetylated low-density lipoprotein (acLDL) and Ulex europaeus agglutinin-1 (UEA-1), two markers of EPCs, was observed by double staining using fluorescence microscope, the expression of stem cell antigen-1 and vascular endothelial growth factor receptor-2 (VEGFR-2) was confirmed by flow cytometry. EPCs were labeled by incubating with 50 microg/ml SPIO and 6 microl/ml lipofectamine2000, SPIO labeled EPCs were observed under transmission electron microscope (TEM). Labeled and unlabeled EPCs were mixed with 10 g/L agarose and scanned using a 3.0T MR scanner, R2* map and R2 map images were obtained on workstation.

RESULTAfter 7 days of in vitro culture, most of the cells showed characteristics of EPCs. There was no morphological difference between SPIO labeled EPCs and unlabeled EPCs. R2* and R2 values exhibited a linear correlation with the number of labeled cells in the agarose gel. Compared to R2, R2* was a better indicator of the number of labeled cells.

CONCLUSIONMR R2* map can be used to trace SPIO labeled EPCs quantitatively.