A Static Phantom for Harmonization of Hyperpolarized [1-¹³C]Pyruvate Metabolic Magnetic Resonance Imaging

To develop and characterize a static, reusable ¹³C phantom designed to assess and support the harmonization of MRI setups used for hyperpolarized (HP) [1-¹³C]pyruvate imaging.

The phantom was designed as a 200-mm-diameter polycarbonate sphere filled with 8M natural abundance urea and incorporating distinct modules for assessing field and SNR homogeneity, geometric fidelity, spatial resolution, and metabolite quantification. The structural design, materials and chemical composition were selected to match the current technical requirements and capabilities in HP [1-¹³C]pyruvate MRI. The phantom was characterized on a 3T clinical MR scanner to demonstrate representative use cases.

The phantom enabled assessment of field homogeneity ( $B_0$ variation was approximately 20 Hz and $B_1^{+}$ relative flip angle was 1.0 $\pm$ 0.1) and Signal-to-Noise Ratio of the MRI setup. Spectral-spatial (SPSP) spiral imaging of the geometric module and resolution module demonstrated how post-processing pipelines can influence spatial fidelity and effective resolution. The quantification module, containing compounds with chemical shifts matching those of pyruvate and its principal metabolites and mixed in physiologically relevant ratios, enabled metabolite ratio quantification using both CSI and SPSP spiral imaging.

Initial characterization demonstrates that the proposed ¹³C phantom is a practical and versatile tool for benchmarking HP ¹³C MRI system performance, thereby supporting harmonization in multicenter clinical HP ¹³C MRI studies.