Multi-Frequency PARACEST Agents Based on Europium(III)-DOTA-Tetraamide Ligands

摘要

Magnetic resonance imaging (MRI) is one of the most versatile and powerful diagnostic tools in modern medicine. Recently, a conceptually different approach to contrast enhancement based on chemical exchange saturation transfer (CEST) has emerged that takes advantage of slow-to-intermediate exchange conditions between two or more pools of protons (k_(ex)≤Δω). While the first reported CEST agents were diamagnetic molecules containing exchangeable NH and OH groups (Δω≤5 ppm), it was later shown that the slow water exchange characteristics of certain paramagnetic Ln~(3+) complexes of DOTA-tetraamide ligands allows selective saturation of a hyperfine shifted Ln~(3+)-bound water pool (Δω> 50 ppm) for creating CEST contrast. Radio frequency (RF) saturation of highly shifted exchange resonances in paramagnetic systems offer significant advantages over diamagnetic CEST agents with small Δω values.