Proton diffusion tensor spectroscopy of metabolites in human muscle in vivo

Abstract

To study the apparent diffusivity and its directionality for metabolites of skeletal muscle in humans in vivo by (1) H magnetic resonance spectroscopy. The diffusion tensors were determined on a 3 Tesla MR system using optimized acquisition and processing methods including an adapted STEAM sequence with orientation-dependent diffusion weighting, pulse-triggering with individually adapted delays, eddy-current correction schemes, median filtering, and simultaneous prior-knowledge fitting of all related spectra. The average apparent diffusivities, as well as the fractional anisotropies of taurine (ADCav=0.74 × 10(-3) s/mm(2) , FA=0.46), creatine (ADCav =0.41 × 10(-3) s/mm(2) , FA=0.33), trimethylammonium compounds (ADCav =0.48 × 10(-3) s/mm(2) , FA=0.34), carnosine (ADCav =0.46 × 10(-3) s/mm(2) , FA=0.47), and water (ADCav=1.5 × 10(-3) s/mm(2) , FA=0.36) were estimated. The diffusivities of most metabolites and water were significantly different from each other. Diffusion was found to be anisotropic and the diffusion tensors showed tensor correlation coefficients close to 1 and were hence found to be essentially coaligned. The magnitudes of apparent metabolite diffusivities were largely ordered according to molecular weight, with taurine as the smallest molecule diffusing fastest, both along and across the fiber direction. Diffusivities, directional dependence of diffusion and fractional anisotropies of (1) H MRS-visible muscle metabolites were presented. It was shown that metabolites share diffusion directionality with water and have similar fractional anisotropies, hinting at similar diffusion barriers.