In Vivo Proton NMR Studies in Skeletal Musculature

Abstract

Abstract This chapter reports on non-invasive characterization of human skeletal muscle by the methods of proton NMR imaging and spectroscopy. Basic knowledge about muscle structure and function is provided, followed by examples showing the appearance of musculature in contrast to surrounding tissue using established NMR imaging sequences. Special imaging techniques for musculature are presented including a spectral–spatial technique for highly selective detection of muscular lipids and magnetization transfer imaging. Patterns of proton NMR spectra of human skeletal muscle are shown to be highly dependent on the orientation of muscle fibres in relation to the static magnetic field: bulk magnetic susceptibility effects allow the separation between intramyocellular (IMCL) and extramyocellular lipids (EMCL), dipolar coupling effects cause signal splittings for creatine and the TMA complex. The differences are shown for the tibialis anterior muscle and the soleus muscle. Methods and strategies for quantification of muscular spectra are described, focusing on the separation and assessment of IMCL and EMCL. Experiments used for measuring relaxation times, magnetization transfer rates, and diffusion coefficients of water and lipids and typical results are described. Studies on lipid metabolism in human skeletal musculature are presented with the main emphasis on the role of IMCL in the pathogenesis of insulin resistance and the regulation of IMCL by exogene interventions. Examples of findings in patients with muscle diseases (e.g., muscle dystrophies, myopathies and metabolic disorders) are reported. Finally, a brief overview on muscle NMR spectroscopy at higher field strength is given, and promising applications with other nuclei such as 31 P and 13 C are discussed.