In the case of muscles, NMR is used to measure the intramyocellular lipid content (IMCL). Magnetic Resonance Spectroscopy (MRS) is an analytical technique that can be used to complement the more common Magnetic Resonance Imaging (MRI) in the characterization of tissue.May 2010). In vivo (that is 'in the living organism') magnetic resonance spectroscopy (MRS) is a specialised technique associated with magnetic resonance imaging (MRI) .