Solid state NMR in white matter: Unconventional 31P→1H cross polarization interrogates the proton pool

Tools to better characterize myelin health are urgently needed. We demonstrate the use of the solid-state NMR techniques cross polarization (CP) and WIdeline Separation (WISE) to directly probe the phosphorous (31P) of phospholipid myelin bilayers and characterize protons (1H) involved in CP. This work demonstrates the feasibility of unconventional CP from 31P→1H in porcine spinal cord and investigates the contributing 1H. The results of this work provide crucial insight into the characteristics exploitable by CP in myelin and reinforce the potential of a two-step transfer of semi-solid 31P signals into aqueous 1H, providing a more direct and myelin-specific MRI signal.