Bulk magnetic susceptibility effects on the assessment of intra- and extramyocellular lipids in vivo.

Localized proton spectroscopy provides a novel method for noninvasive measurement of lipid content in skeletal muscle. It has been suggested that the chemical shift difference between lipid signals from distinct compartments in skeletal muscle might be caused by bulk magnetic susceptibility (BMS) differences from lipids stored in intra- (IMCL) and extramyocellular (EMCL) compartments. Direct evidence is provided to confirm the theoretical prediction that compartment symmetry is responsible for discrimination between resonances of IMCL and EMCL. Phantoms imitating lipids in skeletal muscle were constructed using soybean oil to represent EMCL, and IntralipidTM, an intravenous fat emulsion of fine droplets, to represent IMCL. It was found that the chemical shift of IntralipidTM is independent of the BMS effects, while the resonance of soybean oil shifts in a predictable manner determined by the geometry of the compartment. Copyright 2002 Wiley-Liss, Inc.