Encapsulated gadolinium and dysprosium ions within ultra-short carbon nanotubes for MR microscopy at 11.75 and 21.1 T

Single‐walled carbon nanotubes (SWNTs) have gained interest for their biocompatibility and multifunctional properties. Ultra‐short SWNTs (US‐tubes) have demonstrated high proton relaxivity when encapsulating gadolinium ions (Gd3+) at clinical field strengths. At higher field strengths, however, Gd3+ ions demonstrate decreased proton relaxation properties while chemically similar dysprosium ions (Dy3+) improve relaxation properties. This report investigates the first use of Gd3+ and Dy3+ ions within US‐tubes (GNTs and DNTs, respectively) at ultra‐high magnetic field (21.1 T). Both agents are compared in solution and as an intracellular contrast agent labeling a murine microglia cell line (Bv2) immobilized in a tissue‐mimicking agarose phantom using two high magnetic fields: 21.1 and 11.75 T. In solution at 21.1 T, results show excellent transverse relaxation; DNTs outperformed GNTs as a T2 agent with measured r2/r1 ratios of 247 and 47, respectively. Additionally, intracellular DNTs were shown to be a better T2 agent than GNTs with higher contrast percentages and contrast‐to‐noise ratios. As such, this study demonstrates the potential of DNTs at high magnetic fields for cellular labeling and future in vivo, MRI‐based cell tracking. Copyright © 2014 John Wiley & Sons, Ltd. For the first time, Dy3+ and Gd3+ encapsulated in carbon nanotubes (GNT and DNT) are evaluated as MRI contrast agents at 21.1 T.DNTs are better T2 contrast agent both in solution and in cells. Significant differences are seen in T2 contrast between DNT and GNT labeled cells and controls.