Design and chemical composition of a reference phantom for ¹³C metabolic MRSI

Development of a reproducible and long-term stable reference phantom for ¹³C metabolic MRSI, addressing the need for accessible calibration and quality assurance tools across sites and platforms.

The phantom was built from readily available labware (50 mL centrifuge tubes, NMR glass vials) and 3D-printed holders, designed to ensure sufficient coil loading and excellent B₀ homogeneity. ¹³C-labeled reference solutions were stabilized by argon degassing, sodium azide addition, and airtight flame sealing, with optional gadolinium doping to tune T₁/T₂ relaxation. Performance was tested at 1.4 T, 3 T, and 11.7 T using ¹H MRI, ¹³C spectroscopy, and ¹³C MRSI.

The reference solutions remained chemically and spectrally stable for up to 20 months under cooled, light-protected storage. Ethyl acetate provided a stable alternative to pyruvate, while gadolinium enabled the control of relaxation properties. Spectral assessment confirmed narrow linewidths, strong SNR, and reproducible peak separation across field strengths, validating the phantom's suitability for calibration and method development.

This low-cost, open-source design provides a durable and reproducible ¹³C phantom that complements existing dynamic and metabolite-specific models. It enables long-term standardization, supports multi-center studies, and facilitates robust quality assurance in hyperpolarized and thermal ¹³C MRSI.