ABSTRACT
The major goal of labeling cells with a paramagnetic contrast agent is to shorten the T1 relaxation properties of the intra- and extracellular water undergoing exchange across the cell membrane, resulting in an increase in signal intensity due to the labeled cells on T1-weighted magnetic resonance imaging (MRI). MR contrast agents with very high T1 relaxivity would be valuable for labeling cells, as they have the potential to retain significant detectability on MRI even in low concentrations, as well as to retain sufficiently high T1 relaxivity even at high magnetic field strengths. Josephson et al. increased the efficiency and versatility of dextran-coated monodispersed superparamagnetic iron oxide nanoparticles in labeling nonphagocytic cells by first crosslinking the dextran strands with epichlohydrin, and then covalently attaching HIV-1 Tat proteins to the surface. Determination of intracellular iron is necessary to validate findings on MRI and allow for the possible quantitation of the number of labeled cells in a region of interest.
