In Vivo Hyperpolarized Imaging of Magnetic Resonance Biosensors with Ultra-Low Gamma Nuclei

Dissolution dynamic nuclear polarization (DNP) is a versatile hyperpolarization technique that endows high liquid-state nuclear magnetic resonance (NMR) sensitivity to a plethora of nuclei that have relatively long spin-lattice relation time T1 at physiologically-tolerable temperature. Among the nuclei, 13C (gamma γ=10.7 MHz/T) is the foremost target for hyperpolarization due to its utility in metabolic and biochemical imaging as seen in a plethora of hyperpolarized 13C MR studies using 13C-pyruvate and other 13C-labeled metabolic tracers. Although less sensitive than 13C, 15N-labeled (γ=4.31 MHz/T) biosensors have also been reported in a select number of hyperpolarized (HP) MR studies. In this presentation, ultra-low gamma nuclei are defined as nuclei with gyromagnetic ratios that are lower than that of 15N nucleus. This study reports on the feasibility of and the challenges involved in using biosensors with ultra-low gamma in in vivo hyperpolarized MR imaging, specifically with the use of 89Y (γ =2.086 MHz/T) biosensors in vivo. 89Y is a very attractive nucleus for the design of responsive MR probes e.g. pH-sensing capability using HP 89Y-EDTMP because of the sensitivity of the 89Y NMR chemical shift to changes in the coordination environment of the Y3+ ion and the relatively long T1 reported up to 600 s. The hyperpolarized 89Y data set herein will be discussed in light of current instrumental capability and limitations as well as its implications on potentially using other ultra-low gamma nuclei in HP imaging such as 106Ag, 109Ag, and other low-gamma nuclei.