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 (Gd 3+ ) at clinical field strengths. At higher field strengths, however, Gd 3+ ions demonstrate decreased proton relaxation properties while chemically similar dysprosium ions (Dy 3+ ) improve relaxation properties. This report investigates the first use of Gd 3+ and Dy 3+ 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 T 2 agent with measured r 2 / r 1 ratios of 247 and 47, respectively. Additionally, intracellular DNTs were shown to be a better T 2 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.