Magnetically labeled cells can be detected by MR imaging.

To determine the feasibility of MR imaging of magnetically labeled cells, different cell lines were labeled with monocrystalline iron oxide (MION) particles. Phantoms containing MION labeled cells were then assembled and imaged by MR at 1.5 T using T1-weighted and T2-weighted pulse sequences. MION uptake ranged from 8.5 x 10(4) to 2.9 x 10(5) particles/cell for tumor cells (9L and LX1, respectively) to 1.5 x 10(6) to 4.8 x 10(8) particles/cell for "professional phagocytes" (J774 and peritoneal macrophages, respectively). On the T1-weighted images, cell-internalized MION appeared hyperintense relative to agar and similar to MION in aqueous solution. On T2-weighted images, signal intensity varied according to concentration of MION within cells. Cell-internalized MION caused similar MR signal changes of cells as did free MION; however, at a dose that was an order of magnitude lower, depending on the pulse sequence used. The detectability of MION within cells was approximately 2 ng Fe, which corresponded to 10(5) tumor cells/well or 5 x 10(3) macrophages/well. We conclude that a variety of cells can be efficiently labeled with MION by simple incubation. Intracellular labeling may be used for MR imaging of in vivo cell tracking.