Determining the relaxivity values of protein cage-templated nanoparticles using magnetic resonance imaging.The application of magnetic resonance imaging (MRI) is often limited by low magnetic relaxivity of currently used contrast agents.  The magnetic nanoparticle-protein cage composites have been reported to have high magnetic relaxivity, which implies their potential application as an MRI contrast agent.  The commonly performed techniques are field-cycling NMR relaxometry (also known as variable field relaxometry or nuclear magnetic relaxation dispersion (NMRD) profiling) and in vitro or in vivo MRI relaxometry.  Here, we describe techniques for the synthesis of nanoparticle-protein cage composite and determination of their magnetic relaxivities by in vitro MR image acquisition and data processing. 
MRI