Highly sensitive and high throughput magnetic resonance thermometry using superparamagnetic nanoparticles

Magnetic resonance imaging (MRI) enables non-invasive 3D temperature monitoring during thermal ablation of tumors. While T₁ or T₂ contrast MRI are relatively insensitive to temperature, techniques with greater temperature sensitivity such as chemical shift or diffusion imaging suffer from motional artifacts and long scan times. We describe an approach for highly sensitive and high throughput MR thermometry that is not susceptible to motional artifacts. We use superparamagnetic iron oxide nanoparticles (SPIONs) to spoil T₂ of water protons.  Motional narrowing results in proportionality between T₂ and the diffusion constant, dependent only on temperature in a specific environment. Our results show, for pure water, the NMR  linewidth and T₂ follow the same temperature dependence as the self-diffusion constant of water. Thus, a T₂ mapping is a diffusion mapping in the presence of SPIONs, and T₂ is a thermometer. For pure water, a T₂ mapping in a 9.4 T MRI scanner resulted in a temperature resolution of 0.5 K for a scan time of 2 minutes.  This indicates a highly sensitive and high throughput MR thermometry technique potentially useful for monitoring of tissues during thermal therapies or for diagnosis.