Multinuclear absolute magnetic resonance thermometry

Emilia V Silletta,Alexej Jerschow,Leeor Alon,Guillaume Madelin

doi:10.1038/s42005-019-0252-3

Abstract

Non-invasive measurement of absolute temperature is important for proper characterization of various pathologies and for evaluation of thermal dose during interventional procedures. The proton (hydrogen nucleus) magnetic resonance (MR) frequency shift method can be used to map relative temperature changes. However, spatiotemporal variations in the main magnetic field and the lack of local internal frequency reference challenge the determination of absolute temperature. Here, we introduce a multinuclear method for absolute MR thermometry, based on the fact that the hydrogen and sodium nuclei exhibit a unique and distinct characteristic frequency dependence with temperature and with electrolyte concentration. A one-to-one mapping between the precession frequency difference of the two nuclei and absolute temperature is demonstrated. Proof-of-concept experiments were conducted in aqueous solutions with different NaCl concentrations, in agarose gel samples, and in freshly excised ex vivo mouse tissues. One-dimensional chemical shift imaging experiments also demonstrated excellent agreement with infrared measurements.

Highlights

Non-invasive measurement of absolute temperature is important for proper characterization of various pathologies and for evaluation of thermal dose during interventional procedures
While most magnetic resonance (MR) contrast mechanisms vary with temperature change[2,3,4,5,6,7,8], it has been shown that the proton (1H) resonance frequency (PRF) method has the highest sensitivity to thermal change in most tissues[9]
We introduce a novel multinuclear approach for absolute MR thermometry based on two endogenous types of molecules in biological tissues, water and sodium ions Naþ, as well as a general framework for absolute MR thermometry that can be used with any pair of nuclei

Summary

Introduction

Non-invasive measurement of absolute temperature is important for proper characterization of various pathologies and for evaluation of thermal dose during interventional procedures. The proton (hydrogen nucleus) magnetic resonance (MR) frequency shift method can be used to map relative temperature changes. The temperature dependence of the PRF was first discovered by Hindman when conducting nuclear magnetic resonance (NMR) experiments on intermolecular forces and hydrogen bond formation[9], and adapted to estimate temperature change through MR phase imaging measurements by Ishihara et al.[10] and De Poorter et al.[11]. The PRF method relies on the subtraction of pre- and postexposure phase images, or on the local determination of the frequency shift of protons with MR spectroscopy (MRS), to calculate temperature change due to exposure conditions[18,19], knowing that the chemical shift temperature dependence of proton is approximately −0.01 ppm/C20 in human tissues. Due to the low concentration of NAA in the brain ($10 mmol/L)[33], challenges associated with water suppression, pH-dependent separation of the NAA-water peaks, and imaging time required to obtain adequate signal-to-noise ratio (SNR), absolute thermometry via imaging of the NAA peak remains challenging[34]

Methods

Results

Conclusion