Spin tagging for hyperpolarized ¹³C metabolic studies

In studies utilizing pre-polarized (13)C substrates to investigate metabolic activities in vivo, the metabolite signals observed in a region or a voxel contains a mixture of intracellular and extracellular components. This extracellular component arriving via perfusion may confound the measurements of metabolic flux or exchange rates. But if spin tagging is performed on the magnetization of the substrate, it may be possible to measure the signals of the metabolic products in the intracellular space that were derived from the tagged substrate spins locally. In this study, a spin tagging pulse sequence designed for acquiring data from spatially tagged longitudinal magnetization in hyperpolarized (13)C metabolic studies was presented and tested. Using a spectral-spatial RF pulse during the tagging preparation enabled the observation of metabolite signals derived exclusively from the tagged substrate in vivo.