Gadolinium-based carbon nanostructures are poised to make a significant impact as advanced contrast agents (CAs) for magnetic resonance imaging (MRI) in medicine. This paper reviews and forecasts gadonanotubes as synthons for the design of high-performance MRI CA probes with efficacies up to 100 times greater than current clinical CAs. This level of performance is vital for achieving the goal of cellular and molecular imaging with MRI. These new materials will be useful for in vivo MRI applications as circulating drug nanocapsules because of their low toxicities, extremely high relaxivities, and potential for cellular targeting and induced cell death by magnetic hyperthermia.