In vivo phosphorus polarization transfer and decoupling from protons in three-dimensional localized nuclear magnetic resonance spectroscopy of human brain

Refocused insensitive nucleus enhancement by polarization transfer (RINEPT) from protons (¹H) to a J-coupled phosphorus (³¹P) has been incorporated into three-dimensional (3D) chemical-shift-imaging (CSI) sequence on a clinical imager. The technique is demonstrated on a phantom and in in vivo human brain. The polarization-transfer efficiency (~1.2) is lower than the theoretical maximum of γ¹(H)/γ³¹(P) ≃ 2.4 resulting from ¹H- ¹H homonuclear J couplings of similar magnitude competing with the ¹H → ³¹P transfer. Nevertheless, compared with direct ³¹P Ernst-angle excitation, signal gains of up to x1.8 were obtained mainly as a result of T₁ differences between ³¹P and the ¹H. Spectral interpretation is simplified by editing out all non-proton-coupled ³¹P signals. The duration, ~50 min, and power deposition, ~1 W · kg^-1, make the application suitable for human studies.