SABRE-hyperpolarization dynamics of [1-13C]pyruvate monitored by in situ zero- to ultra-low field NMR

Hyperpolarized [1–¹³C]pyruvate is the leading metabolite used in the emerging field of hyperpolarization-enhanced MRI. Signal amplification by reversible exchange (SABRE) is a straight forward hyperpolarization method that has recently been shown to hyperpolarize [1–¹³C]pyruvate at low (microtesla and below) magnetic fields. Here, we show that commercial optical magnetometers with Rb-vapor media can be used to readily monitor the build-up and decay of the hyperpolarized MR signal. In addition, we measure ZULF-NMR spectra in various conditions, ranging from a J-coupling-dominated regime transitioning into a Zeeman-dominated regime when going from a sub-nT field to a µT field. The experimentally acquired spectra are matched well by numerical simulations.