Magnetic resonance imaging (MRI) enables non-invasive 3D thermometry during
thermal ablation of cancerous 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 the temperature in a specific
environment. Our results show, for pure water, the nuclear magnetic resonance
(NMR) linewidth and T2 follow the same temperature dependence as the
self-diffusion constant of water. Thus, T2 mapping is a diffusion mapping in
the presence of SPIONs, and T2 is a thermometer. For pure water, a T2 mapping
of a 64 x 64 image (voxel size = 0.5 mm x 0.5 mm x 3 mm) 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 biological tissues during thermal
therapies or for diagnosis