Intracellular and Extracellular T1 and T2 Relaxivities of Magneto-Optical Nanoparticles at Experimental High Fields

This study reports the T-1 and T-2 relaxation rates of rhodamine-labeled anionic magnetic nanoparticles determined at 7, 11.7, and 17.6 T both in solution and after cellular internalization. Therefore cells were incubated with rhodamine-labeled anionic magnetic nanoparticles and were prepared at decreasing concentrations. Additionally, rhodamine-labeled anionic magnetic nanoparticles in solution were used for extracellular measurements. T-1 and T-2 were determined at 7, 11.7, and 17.6 T. T-1 times were determined with an inversion-recovery snapshot-flash sequence. T-2 times were obtained from a multispin-echo sequence. Inductively coupled plasma-mass spectrometry was used to determine the iron content in all samples, and r(1) and r(2) were subsequently calculated. The results were then compared with cells labeled with AMI-25 and VSOP C-200. In solution, the r(1) and r(2) of rhodamine-labeled anionic magnetic nanoparticles were 4.78/379 (7 T), 3.28/389 (11.7 T), and 2.00/354 (17.6 T). In cells, the r(1) and r(2) were 0.21/56 (7 T), 0.19/37 (11.7 T), and 0.1/23 (17.6 T). This corresponded to an 11- to 23-fold decrease in r(1) and an 8- to 15-fold decrease in r(2). A decrease in r(1) was observed for AMI-25 and VSOP C-200. AMI-25 and VSOP exhibited a 2- to 8-fold decrease in r(2). In conclusion, cellular internalization of iron oxide nanoparticles strongly decreased their T-1 and T-2 potency. Magn Reson Med 64:1607-1615, 2010. (C) 2010 Wiley-Liss, Inc.