Effect of lanthanide ions on dynamic nuclear polarization enhancement and liquid-state T1 relaxation

• Published in: Magnetic resonance in medicine 2012-12, Vol.68 (6), p.1949-1954
• Main Authors: Gordon, Jeremy W., Fain, Sean B., Rowland, Ian J.
• Format: Article
• Language: English
• Subjects: DNP; Ions - chemistry; Ions - radiation effects; Lanthanoid Series Elements - chemistry; Lanthanoid Series Elements - radiation effects; Magnetic Fields; Magnetic Resonance Imaging - methods; polarization; pyruvate; Solutions - chemistry; Solutions - radiation effects
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.24207

In the dynamic nuclear polarization process, microwave irradiation facilitates exchange of polarization from a radical's unpaired electron to nuclear spins at cryogenic temperatures, increasing polarization by >10,000. Doping samples with Gd3+ ions further increases the achievable solid‐state polarization. However, on dissolution, paramagnetic lanthanide metals can be potent relaxation agents, decreasing liquid‐state polarization. Here, the effects of lanthanide metals on the solid and liquid‐state magnetic properties of [1‐13C]pyruvate are studied. The results show that in addition to gadolinium, holmium increases not only the achievable polarization but also the rate of polarization. Liquid‐state relaxation studies found that unlike gadolinium, holmium minimally affects T1. Additionally, results reveal that linear contrast agents dissociate in pyruvic acid, greatly reducing liquid‐state T1. Although macrocyclic agents do not readily dissociate, they yield lower solid‐state polarization. Results indicate that polarization with free lanthanides and subsequent chelation during dissolution produces the highest polarization enhancement while minimizing liquid‐state relaxation. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.