Boron nitride nanotubes as magnetic resonance imaging contrast agents

In this chapter the potential use of boron nitride nanotubes (BNNTs) as agents generating positive or negative contrast in magnetic resonance imaging (MRI) is discussed. In particular, the two different kinds of BNNT-based contrast agents reported in the literature so far are described, that is, BNNTs with superparamagnetic properties arising from iron nanoparticles remaining on the nanotube tips from the synthetic procedure and BNNTs purposely doped with Gd3+ ions (Gd@BNNTs). Relaxivity properties at different magnetic fields of both kinds of systems are reported and discussed in comparison with those of commercial contrast agents of clinical use. Given the good cytocompatibility observed for these materials, the potential application in theranostics is envisaged.