Toward structure and metabolism of glycogen C1‐C6 in humans at 7 T by localized 13C MRS using low‐power bilevel broadband 1H decoupling

Abstract This work aims to develop and implement a pulse‐acquire sequence for three‐dimensional (3D) single‐voxel localized 13 C MRS in humans at 7 T, in conjunction with bilevel broadband 1 H decoupling, and to test its feasibility in vitro and in vivo in human calf muscle with emphasis on the detection of glycogen C 1 ‐C 6 . A localization scheme suitable for measuring fast‐relaxing 13 C signals in humans at 7 T was developed and implemented using the outer volume suppression (OVS) and one‐dimensional image selected in vivo spectroscopy (ISIS‐1D) schemes, similar to that which was previously reported in humans at 4 T. The 3D 13 C localization scheme was followed by uniform 13 C adiabatic excitation, all complemented with an option for bilevel broadband 1 H decoupling to improve both 13 C sensitivity and spectral resolution at 7 T. The performance of the pulse‐acquire sequence was investigated in vitro on phantoms and in vivo in the human calf muscle of three healthy volunteers, while measuring glycogen C 1 ‐C 6 . In addition, T 1 and T 2 of glycogen C 1 ‐C 6 were measured in vitro at 7 T, as well as T 1 of glycogen C 1 in vivo. The glycerol C 2 and C 1,3 lipid resonances were efficiently suppressed in vitro at 7 T using the OVS and ISIS‐1D schemes, allowing distinct detection of glycogen C 2 ‐C 6 . While some glycerol remained in calf muscle in vivo, the intense lipid at 130 ppm was efficiently suppressed. The 13 C sensitivity and spectral resolution of glycogen C 1 ‐C 6 in vitro and glycogen C 1 in vivo were improved at 7 T using bilevel broadband 1 H decoupling. The T 1 and T 2 of glycogen C 1 ‐C 6 in vitro at 7 T were consistent compared with those at 8.5 T, while the T 1 of glycogen C 1 in vivo at 7 T resulted similar to that in vitro. Localized 13 C MRS is feasible in human calf muscle in vivo at 7 T, and this will allow further extension of this method for 13 C MRS measurements such as in the brain.