Sensitivity-enhanced C-13 MR spectroscopy of the human brain at 3 Tesla

Abstract

A new coil design for sensitivity-enhanced C-13 MR spectroscopy (MRS) of the human brain is presented. The design includes a quadrature transmit/receive head coil optimized for C-13 MR sensitivity. Loss-less blocking circuits inside the coil conductors allow this coil to be used inside a homogeneous circularly polarized H-1 B-1 field for H-1 decoupled C-13 MRS. A quadrature H-1 birdcage coil optimized for minimal local FIF heating makes broadband H-1 decoupling in the entire human brain possible at 3 Tesla while remaining well within international safety guidelines for RF absorption. Apart from a substantial increase in sensitivity compared to conventional small linear coils, the quadrature C-13 coil combined with the quadrature 1H birdcage coil allows efficient cross polarization (CP) in the brain, resulting in an additional 3.5-fold sensitivity improvement compared to direct C-13 measurements without nuclear Overhauser enhancement (NOE) or polarization transfer. Combined with the gain in power efficiency, this setup allows broadband H-1 to C-13 CP over large areas of the brain. Clear C-13 resonances from glutamate (Glu), glutamine (Gin), aspartate (Asp), lactate (Lac), and gamma-aminobutyrate (GABA) carbon spins in the human brain demonstrate the quality of C-13 MR spectra obtained in vivo with this coil setup.