Hyperpolarized carbon-13 MRI is a powerful emerging molecular imaging technique but it lacks tissue specificity. Selective relaxation of hyperpolarized signals by targeted gadolinium chelates has been explored to increase specificity. However, gadolinium agents have very low 13C relaxivities. We explore the use of the super paramagnetic iron oxide, ferumoxytol, by measuring the transverse and longitudinal relaxivity for two commonly imaged hyperpolarized 13C metabolites, namely [1-13C]pyruvate and [1-13C]lactate in comparison to gadopentetate. Longitudinal relaxivity of ferumoxytol is nearly 30 times higher for 13C compounds than gadopentetate. This enhanced relaxivity is expected to lead to especially low dose requirements in eventual biological translation.