Dynamic (1)H imaging of hyperpolarized [1‐(13)C]lactate in vivo using a reverse INEPT experiment

PURPOSE: Dynamic magnetic resonance spectroscopic imaging of hyperpolarized (13)C‐labeled cell substrates has enabled the investigation of tissue metabolism in vivo. Currently observation of these hyperpolarized substrates is limited mainly to (13)C detection. We describe here an imaging pulse sequence that enables proton observation by using polarization transfer from the hyperpolarized (13)C nucleus to spin‐coupled protons. METHODS: The pulse sequence transfers (13)C hyperpolarization to (1)H using a modified reverse insensitive nuclei enhanced by polarization transfer (INEPT) sequence that acquires a fully refocused echo. The resulting hyperpolarized (1)H signal is acquired using a 2D echo‐planar trajectory. The efficiency of polarization transfer was investigated using simulations with and without T(1) and T(2) relaxation of both the (1)H and (13)C nuclei. RESULTS: Simulations showed that (1)H detection of the hyperpolarized (13)C nucleus in lactate should increase significantly the signal‐to‐noise ratio when compared with direct (13)C detection at 3T. However the advantage of (1)H detection is expected to disappear at higher fields. Dynamic (1)H images of hyperpolarized [1‐(13)C]lactate, with a spatial resolution of 1.25 × 1.25 mm(2), were acquired from a phantom injected with hyperpolarized [1‐(13)C]lactate and from tumors in vivo following injection of hyperpolarized [1‐(13)C]pyruvate. CONCLUSIONS: The sequence allows (1)H imaging of hyperpolarized (13)C‐labeled substrates in vivo. Magn Reson Med 79:741–747, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.