UCSF

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: T₁ -weighted spoiled gradient echo, T₂ -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 (ΔB₀ ) determined using multiecho proton acquisitions were compared to carbon-13 acquisitions. Changes in ΔB₀ 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 ΔB₀ maps correlated with carbon-13 ΔB₀ maps (slope = 0.93, y-intercept = -2.88, R²  = 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.