A vendor-neutral EPI sequence for hyperpolarized ¹³C MRI

Purpose: To develop a flexible, vendor-neutral EPI sequence for hyperpolarized ¹³C metabolic imaging. Methods: An open-source EPI sequence consisting of a metabolite-specific spectral-spatial RF excitation pulse and a customizable EPI readout was created using the Pulseq framework. To explore the flexibility of our sequence, we tested several versions of the sequence including a symmetric 3D readout with different spatial resolutions for each metabolite (1.0 cm³ and 1.5 cm³). A multichamber phantom constructed with a Shepp-Logan geometry, containing two chambers filled with either natural abundance ¹³C compounds or hyperpolarized (HP) [1–¹³C]pyruvate, was used to test each sequence. For experiments involving HP [1–¹³C]pyruvate, a single chamber was prefilled with nicotinamide adenine dinucleotide hydride and lactate dehydrogenase to facilitate the conversion of [1–¹³C]pyruvate to [1–¹³C]lactate. All experiments were performed on a Siemens Prisma 3T scanner. Results: All the sequence variations localized natural-abundance ¹³C ethylene glycol and methanol to the appropriate compartment of the multichamber phantom. [1–¹³C]pyruvate was detectable in both chambers following the injection of HP [1–¹³C]pyruvate, whereas [1–¹³C]lactate was only found in the chamber containing nicotinamide adenine dinucleotide hydride and lactate dehydrogenase. The conversion rate from [1–¹³C]pyruvate to [1–¹³C]lactate (k_PL) was 0.01 s⁻¹ (95% confidence interval [0.00, 0.02]). Conclusion: We have developed and tested a vendor-neutral EPI sequence for imaging HP ¹³C agents. We have made all of our sequence creation and image reconstruction code freely available online for other investigators to use.