Dynamic Nuclear Polarization with Labile Radicals

Christine Pepke Gunnarsson

Research focus 
Dissolution Dynamic Nuclear Polarization (dDNP), the transfer of the electron spin polarization to the nuclear spins using microwave (MW) radiation, is an efficient method to hyperpolarize nuclear spins and achieving dramatically enhanced magnetic resonance (MR) signals. Polarization enhancements of up to 10.000 compared to the thermal equilibrium have been reported, and with the current achievements, hyperpolarization of nuclear spins opens for the possibility of faster and more accurate cancer diagnosis through Magnetic Resonance Imaging (MRI) using the hyperpolarized sample as contrast agent. 

However, the nuclear spin polarization relaxation time is short and decays fast if the sample is moved to lower magnetic field and non cryogenic temperatures. The nuclear spins relaxes due to the electron spins. Therefore, the dissolution is performed inside the polarizer, which means that currently a polarizer is needed at every MR spectrometer. A solution to this challenge is using photo induced labile radicals which makes it possible to keep the polarization of the nuclei for a longer time. Irradiating radical precursors with UV light at cryogenic temperatures, generates radicals that can be used to polarize substrates through dDNP. The radicals are persistent at cryogenic temperatures, but annihilates if the sample temperature increases above 190 K, which is below the samples melting point (285 K). In this way, the radicals can be thermally annihilated while the sample is still a solid and the nuclear polarization can then be maintained as the solid sample is extracted from the polarizer, opening for the possibility of transportation of the hyperpolarized sample. 

The purpose of the project is to gain an understanding of the photo induced radical formation, aiming at improving the radical yield and obtaining radicals with optimal spectral properties for DNP. The properties of the generated radicals will be examined using electron paramagnetic resonance (EPR). The project will also examine the physico-chemical properties of the thermal annihilation of the radicals and investigate the relaxation mechanisms of the polarized sample. Furthermore, the project will establish conditions for storage and transportation of the hyperpolarized sample aiming at the ability to perform hyperpolarized MRI remotely from the polarizer, an achievement that will decrease the involved costs significantly.  

Scientific output 
Find Christine's publications at DTU's online research database ORBIT

The project is funded by the Independent Research Fund Denmark, Technology and Production Sciences as part of the project The "Spin Bank" – turning electron spin on and off (DFF 7017-00322B). The project is part of the HYPERMAG Center of Excellence funded by Danish National Research Foundation (DNRF124). 

Professor Jan Ardenkjær-Larsen, Postdoc Andrea Capozzi and Senior Researcher Magnus Karlsson.

Project Period 
January 2018 - December 2020 (maternity leave June 2018 - May 2019).



Christine Pepke Gunnarsson
PhD student
DTU Health Tech