Abstract
Skeletal muscle is a biological structure with a high degree of organization at different spatial levels. This order influences magnetic resonance (MR) in vivo—in particular ^1^H‐spectra—by a series of effects that have very distinct physical sources and biomedical applications: (a) bulk fat (extramyocellular lipids, EMCL) along fasciae forms macroscopic plates, changing the susceptibility within these structures compared to the spherical droplets that contain intra‐myocellular lipids (IMCL); this effect leads to a separation of the signals from EMCL and IMCL; (b) dipolar coupling effects due to anisotropic motional averaging have been shown for ^1^H‐resonances of creatine, taurine, and lactate; (c) aromatic protons of carnosine show orientation‐dependent effects that can be explained by dipolar coupling, chemical shift anisotropy or by relaxation anisotropy; (d) limited rotational freedom and/or compartmentation may explain differences of ^1^H‐MR‐visibility of the creatine/phosphocreatine resonances; (e) lactate ^1^H‐MR resonances are reported to reveal information on tissue compartmentation; (f) transverse relaxation of water and metabolites show multiple components, indicative of intra‐, extracellular and/or macromolecular‐bound pools, and in addition dipolar or J‐coupling lead to a modulation of the signal decay, hindering straightforward interpretation; (g) diffusion weighted ^31^P‐MRS has shown restricted diffusion of phosphocreatine; (h) magnetization transfer (MT) indicates that there is a motionally restricted proton pool in spin‐exchange with free creatine; reduced availability or restricted motion of creatine is particularly important for an estimation of ADP from ^31^P‐MR spectra, and in addition MT effects may alter the signal intensity of creatine ^1^H‐resonances following water‐suppression pulses; (i) transcytolemmal water‐exchange can be studied in ^1^H‐MRS by contrast‐agents applied to the extracellular space; (k) transport of glucose across the cell membrane has been studied in diabetes patients using a combination of ^13^C‐ and ^31^P‐MRS; and (l) residual quadrupolar interaction in ^23^Na MR spectra from human skeletal muscle suggest that sodium ions are bound to ordered muscular structures. Copyright © 2001 John Wiley & Sons, Ltd.
Abbreviations used:
ADC
apparent diffusion coefficient
BMS
bulk magnetic susceptibility
CK
creatine kinase
Cr
creatine
Cr/PCr
creatine and/or phosphocreatine
CSA
chemical shift anisotropy
EMCL
extramyocellular lipids
IMCL
intramyocellular lipids
MQF
multi‐quantum‐filtering
MRI
Magnetic resonance imaging
MRS
magnetic resonance spectroscopy
MT
magnetization transfer
PCr
phosphocreatine.