A vendor-neutral EPI sequence for hyperpolarized 13C MRI

PurposeTo develop a flexible, vendor-neutral EPI sequence for hyperpolarized C-13 metabolic imaging. MethodsAn 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 cm(3) and 1.5 cm(3)). A multichamber phantom constructed with a Shepp-Logan geometry, containing two chambers filled with either natural abundance C-13 compounds or hyperpolarized (HP) [1-C-13]pyruvate, was used to test each sequence. For experiments involving HP [1-C-13]pyruvate, a single chamber was prefilled with nicotinamide adenine dinucleotide hydride and lactate dehydrogenase to facilitate the conversion of [1-C-13]pyruvate to [1-C-13]lactate. All experiments were performed on a Siemens Prisma 3T scanner. ResultsAll the sequence variations localized natural-abundance C-13 ethylene glycol and methanol to the appropriate compartment of the multichamber phantom. [1-C-13]pyruvate was detectable in both chambers following the injection of HP [1-C-13]pyruvate, whereas [1-C-13]lactate was only found in the chamber containing nicotinamide adenine dinucleotide hydride and lactate dehydrogenase. The conversion rate from [1-C-13]pyruvate to [1-C-13]lactate (k(PL)) was 0.01 s(-1) (95% confidence interval [0.00, 0.02]). ConclusionWe have developed and tested a vendor-neutral EPI sequence for imaging HP C-13 agents. We have made all of our sequence creation and image reconstruction code freely available online for other investigators to use.