N-15-Carnitine, A Novel Endogenous Hyperpolarized Mri Probe With Long Signal Lifetime

Purpose: The purpose of this study was to investigate hyperpolarization and in vivo imaging of [N-15]carnitine, a novel endogenous MRI probe with long signal lifetime.Methods: L-[N-15]carnitine-d(9) was hyperpolarized by the method of dynamic nuclear polarization followed by rapid dissolution. The T-1 signal lifetimes were estimated in aqueous solution and in vivo following intravenous injection in rats, using a custom-built dual-tuned N-15/H-1 RF coil at 4.7 T. N-15 chemical shift imaging and N-15 fast spin-echo images of rat abdomen were acquired 3 minutes after [N-15]carnitine injection.Results: Estimated T-1 times of [N-15]carnitine at 4.7 T were 210 seconds (in H2O) and 160 seconds (in vivo), with an estimated polarization level of 10%. Remarkably, the [N-15]carnitine coherence was detectable in rat abdomen for 5 minutes after injection for the nonlocalized acquisition. No downstream metabolites were detected on localized or nonlocalized N-15 spectra. Diffuse liver enhancement was detected on N-15 fast spin-echo imaging 3 minutes after injection, with mean hepatic SNR of 18 +/- 5 at a spatial resolution of 4 x 4 mm.Conclusion: This study showed the feasibility of hyperpolarizing and imaging the biodistribution of HP [N-15]carnitine.