Relaxation times of skeletal muscle metabolites at 7T

To demonstrate the feasibility of quantitatively evaluating and measuring T(1) and T(2) relaxation times of human tibialis anterior (TA) muscles metabolites in vivo at 7T and to compare these results with those of 3T.

A model lipid phantom (corn oil) and healthy volunteers (n = 4, mean +/- SD age 35.6 +/- 5.6 years) were scanned on 3T and 7T whole-body MR scanners. A voxel of 10 x 10 x 10 mm(3) was positioned on the lipid phantom and right calf TA muscles using the single-voxel stimulated echo acquisition mode (STEAM) pulse sequence. All magnetic resonance spectroscopy (MRS) data were processed with Java-based Magnetic Resonance User Interface (JMRUI) using Hankel Lanczos Singular Value Decomposition (HLSVD) filtering to remove the residual water signal.

T(1) shows a steady increase while T(2) shows a slight decrease with B(0) and the spectra show larger spectral resolution at 7T than at 3T in the lipid phantom. T(1) values of all the metabolites are higher, while T(2) values are slightly lower at 7T than those of 3T compared to reported results in TA. The maximum percentage of increase in T(1) is about approximately 488%, the maximum percentage of decrease in T(2) is about approximately 65%.

The preliminary results can potentially be used for calculating relaxation correction factors required for absolute quantitation of skeletal muscle metabolite concentrations and for further protocol and sequence optimization.