MRI of [2‐13C]Lactate without J‐coupling artifacts

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Abstract
Purpose: Imaging of [2‐13C]lactate, a metabolic product of [2‐13C]pyruvate, is over considerable interest in hyperpolarized 13C studies. However, artifact‐free imaging of a J‐coupled nuclear spin species can be challenging due to the peak‐splitting induced by the spin‐spin interactions. In this work, two new techniques resolving these J‐modulated artifacts are presented.Theory and Methods: The Product Operator Formalism (POF) of density matrix theory is used to both numerically and analytically derive the coherences arising during radiofrequency excitation and readout of a J‐coupled spin system. A combination of computer simulations and experiments with [2‐13C]lactate and 13C‐formate phantoms are then used to verify the performance of two imaging methods. In the first approach, a quadrature imaging technique is used to eliminate scalar coupling artifacts via the combination of in‐phase and quadrature images acquired at echo times differing by 1/2J with an echoplanar readout. The second approach employs a highly narrowband RF excitation pulse to image a single peak from the J‐coupled doublet.Results: Simulations using a numerical Shepp‐Logan phantom, in vitro experiments using thermally polarized [2‐13C]lactate, thermally and hyperpolarized 13C‐formate phantoms, and in vivo imaging of [2‐13C]lactate produced in rat brain following injection of hyperpolarized [2‐13C]pyruvate show artifact‐free images and demonstrate potential utility of these methods.Conclusion: The quadrature imaging and the narrowband excitation techniques resolve the J‐coupling induced ghosting and blurring artifacts present with conventional MRI of J‐coupled signals such as [2‐13C]lactate.
Funding Information
  • National Institutes of Health (P41 EB015891, R01CA176836, R01EB019018)
  • Lucas Foundation

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