Positive MRI contrast enhancement in THP‐1 cells with Gd 2 O 3 nanoparticles

There is a demand for more efficient and tissue‐specific MRI contrast agents and recent developments involve the design of substances useful as molecular markers and magnetic tracers. In this study, nanoparticles of gadolinium oxide (Gd 2 O 3 ) have been investigated for cell labeling and capacity to generate a positive contrast. THP‐1, a monocytic cell line that is phagocytic, was used and results were compared with relaxivity of particles in cell culture medium (RPMI 1640). The results showed that Gd 2 O 3 ‐labeled cells have shorter T 1 and T 2 relaxation times compared with untreated cells. A prominent difference in signal intensity was observed, indicating that Gd 2 O 3 nanoparticles can be used as a positive contrast agent for cell labeling. The r 1 for cell samples was 4.1 and 3.6 s −1 m m −1 for cell culture medium. The r 2 was 17.4 and 12.9 s −1 m m −1 , respectively. For r 1 , there was no significant difference in relaxivity between particles in cells compared to particles in cell culture medium, ( p r 1 = 0.36), but r 2 was significantly different for the two different series ( p r 2 = 0.02). Viability results indicate that THP‐1 cells endure treatment with Gd 2 O 3 nanoparticles for an extended period of time and it is therefore concluded that results in this study are based on viable cells. Copyright © 2008 John Wiley & Sons, Ltd.