<scp>Whole‐Abdomen</scp> Metabolic Imaging of Healthy Volunteers Using Hyperpolarized [<scp>1‐¹³C</scp>]pyruvate <scp>MRI</scp>

Abstract

Background Hyperpolarized 13 C MRI quantitatively measures enzyme‐catalyzed metabolism in cancer and metabolic diseases. Whole‐abdomen imaging will permit dynamic metabolic imaging of several abdominal organs simultaneously in healthy and diseased subjects. Purpose Image hyperpolarized [1‐ 13 C]pyruvate and products in the abdomens of healthy volunteers, overcoming challenges of motion, magnetic field variations, and spatial coverage. Compare hyperpolarized [1‐ 13 C]pyruvate metabolism across abdominal organs of healthy volunteers. Study Type Prospective technical development. Subjects A total of 13 healthy volunteers (8 male), 21–64 years (median 36). Field Strength/Sequence A 3 T. Proton: T 1 ‐weighted spoiled gradient echo, T 2 ‐weighted single‐shot fast spin echo, multiecho fat/water imaging. Carbon‐13: echo‐planar spectroscopic imaging, metabolite‐specific echo‐planar imaging. Assessment Transmit magnetic field was measured. Variations in main magnetic field (ΔB 0 ) determined using multiecho proton acquisitions were compared to carbon‐13 acquisitions. Changes in ΔB 0 were measured after localized shimming. Improvements in metabolite signal‐to‐noise ratio were calculated. Whole‐organ regions of interests were drawn over the liver, spleen, pancreas, and kidneys by a single investigator. Metabolite signals, time‐to‐peak, decay times, and mean first‐order rate constants for pyruvate‐to‐lactate (k PL ) and alanine (k PA ) conversion were measured in each organ. Statistical Tests Linear regression, one‐sample Kolmogorov–Smirnov tests, paired t ‐tests, one‐way ANOVA, Tukey's multiple comparisons tests. P ≤ 0.05 considered statistically significant. Results Proton ΔB 0 maps correlated with carbon‐13 ΔB 0 maps (slope = 0.93, y ‐intercept = −2.88, R 2 = 0.73). Localized shimming resulted in mean frequency offset within ±25 Hz for all organs. Metabolite SNR significantly increased after denoising. Mean k PL and k PA were highest in liver, followed by pancreas, spleen, and kidneys (all comparisons with liver were significant). Data Conclusion Whole‐abdomen coverage with hyperpolarized carbon‐13 MRI was feasible despite technical challenges. Multiecho gradient echo 1 H acquisitions accurately predicted chemical shifts observed using carbon‐13 spectroscopy. Carbon‐13 acquisitions benefited from local shimming. Metabolite energetics in the abdomen compiled for healthy volunteers can be used to design larger clinical trials in patients with metabolic diseases. Evidence Level 2 Technical Efficacy Stage 1

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