A Gadolinium(III) Zeolite-like Metal-Organic-Framework-Based Magnetic Resonance Thermometer

MRI contrast agents (CAs) feature coordinated water molecule(s) (aqua ligands), which renders them unsuitable for magnetic resonance (MR) temperature mapping because of their resulting sensitivity to metabolic and physiological changes and/or their tendency to release toxic Gd3+ cations. Herein, we introduce an approach to temperature mapping based upon a coordinatively saturated gadolinium (Gd)-based metal-organic framework (MOF) that exhibits enhanced proton relaxation and high temperature sensitivity. The stable, non-toxic Gd zeolite-like MOF Gd-ZMOF was observed to generate a large enhancement in contrast as a result of a large (70%) contribution from second-sphere water relaxivity. Temperature mapping by clinical CAs and Gd-ZMOF by means of longitudinal (T1) relaxivity was investigated. Gd-ZMOF enabled the visualization of small temperature changes, especially in the thermal therapy region (41°C–45°C). In vivo thermal imaging demonstrates the feasibility of Gd-ZMOF as an MR thermometer and as a potential theranostic.