Efficient 1 H to 31 P polarization transfer on a clinical 3T MR system

Abstract

31P MR spectroscopy (MRS) in the detection of phosphocholine (PC), glycerolphosphocholine (GPC), phosphorylelthanolamine (PE), and glycerolphosphoethanolamine (GPE) compounds has shown clinical potential at 1.5T for several human diseases. The use of (1)H to (31)P polarization transfer can improve the sensitivity using a refocused INEPT method with a potential enhancement of 2.4 (gamma(1H)/gamma(31P)). However, in this method the (31)P signals of PE, PC, GPE, and GPC are strongly attenuated (50% or more) due to J-coupling between (31)P and (1)H that have similar magnitudes for homonuclear J-coupling constants in those metabolites. A method to cancel the homonuclear J-coupling effects in polarization transfer experiments is to apply frequency-selective refocusing pulses, which becomes feasible at 3T due to the increased chemical shift dispersion as compared to 1.5T. In this study, full (1)H to (31)P polarization transfer was realized using chemical shift selective refocusing pulses at 3T. T(1) and T(2) values for (1)H and (31)P spins of PE, PC, GPE, and GPC were measured in the human brain. A more than 2-fold signal-to-noise ratio (SNR) improvement was obtained compared to an optimized direct (31)P MRS method. As shifted RF pulses were used, this method can be applied on a broadband clinical MR system with a single RF system.