Muscle Studies by 1 H MRS

Magnetic resonance spectroscopy (MRS) of skeletal muscle contributed significantly to our knowledge on muscle physiology in the late 1970s and 1980s, mainly by 31P-MRS in animals and human extremities. During this period, 1H-MRS was considerably less important due to limitations of the available acquisition schemes and hardware. Much-improved localization techniques and careful positioning of the selected volume reduced the vast lipid 1H signals and made investigations of small 1H resonances from other metabolites possible. It became evident that the high degree of spatial organization of skeletal muscle results in unique spectral features. Residual dipolar coupling (in particular of creatine) and susceptibility effects (resulting in a separation of intra- and extramyocellular lipids, IMCLs and EMCLs) are the major consequences of the muscular microstructure. Specific acquisition schemes allowed the observation of a series of metabolites like lactate and deoxymyoglobin, and the evaluation of diffusion, magnetization transfer, and other features of the metabolite signals in some studies with spectral and spatial resolution in multiple dimensions. The most popular applications of 1H-MRS are studies on lipid metabolism based on the link between IMCL and insulin sensitivity. In addition, measurements of various other metabolites like lactate, deoxymyoglobin, acetyl-carnitine, carnosine, and creatine are used in physiological studies.