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

Abstract

Purpose: Dynamic magnetic resonance spectroscopic imaging of hyperpolarized 13C-labeled cell substrates has enabled the investigation of tissue metabolism in vivo. Currently observation of these hyperpolarized substrates is limited mainly to 13C detection. We describe here an imaging pulse sequence that enables proton observation by using polarization transfer from the hyperpolarized 13C nucleus to spin-coupled protons. Methods: The pulse sequence transfers 13C hyperpolarization to 1H using a modified reverse insensitive nuclei enhanced by polarization transfer (INEPT) sequence that acquires a fully refocused echo. The resulting hyperpolarized 1H signal is acquired using a 2D echo-planar trajectory. The efficiency of polarization transfer was investigated using simulations with and without T1 and T2 relaxation of both the 1H and 13C nuclei. Results: Simulations showed that 1H detection of the hyperpolarized 13C nucleus in lactate should increase significantly the signal-to-noise ratio when compared with direct 13C detection at 3T. However the advantage of 1H detection is expected to disappear at higher fields. Dynamic 1H images of hyperpolarized [1-13C]lactate, with a spatial resolution of 1.25 × 1.25 mm2, were acquired from a phantom injected with hyperpolarized [1-13C]lactate and from tumors in vivo following injection of hyperpolarized [1-13C]pyruvate. Conclusions: The sequence allows 1H imaging of hyperpolarized 13C-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.