Highly sensitive and high throughput magnetic resonance thermometry using superparamagnetic nanoparticles

TL;DR

This paper introduces a novel MRI thermometry method using superparamagnetic nanoparticles that offers high sensitivity and fast imaging, with temperature resolution of 0.5 K in 2 minutes, suitable for thermal therapy monitoring.

Contribution

The authors develop a new MRI thermometry technique based on T2 mapping influenced by superparamagnetic nanoparticles, overcoming motional artifacts and enabling rapid, sensitive temperature measurements.

Findings

Achieved 0.5 K temperature resolution in 2 minutes.

Demonstrated T2 mapping as a diffusion-based thermometer.

Validated method on a 9.4 T MRI scanner with high spatial resolution.

Abstract

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.