Fig. 2: SOTs for SABRE hyperpolarization and measurement of chemical exchange.

phINEPT+ (A) and ESOTHERIC (B) SOT sequences and the modifications allowing investigation of chemical exchange (C, SABRE-INEPT or SABRE-ESOTHERIC). The phINEPT+ (A) and ESOTHERIC (B) sequences convert the spin order of the pH2-derived hydride ligands into transverse (X) magnetization on the 15N nuclei of the bound substrate. Adding two 90° 15N RF pulses enables the observation of chemical exchange between bound and free substrates during the mixing time τe between the pulses (C). The blue square in (C) should be substituted with an appropriate SOT sequence: here phINEPT+ or ESOTHERIC. The total phINEPT+ time ttot = 2(τ1 + τ2) and the total ESOTHERIC time ttot = 2(2τ1 + τ2).