Magnetic Resonance Spectroscopy Studies of Human Metabolism

Magnetic resonance spectroscopy (MRS) is a companion technique to the more familiar magnetic resonance imaging (MRI) scan. Whereas MRI determines the spatial distribution of water (and lipid) protons across a region of interest, MRS measures the chemical content of MR-visible nuclei, which include the metabolically relevant elements of hydrogen (1H), carbon (13C), and phosphorus (31P). MRS is particularly advantageous for assessing metabolism because the chemical properties and environment of each nucleus determine the frequency at which it appears in the MR spectrum, giving rise to peaks corresponding not only to specific metabolites but also to the constituent nuclei of each metabolite (Fig. 1). It is therefore a multimodal, noninvasive technique capable of measuring a broad range of biological compounds across a variety of tissues. Repeated measures of metabolite content, metabolic fluxes, and their response to an intervention are possible, characteristics that make MRS ideally suited for in vivo studies of human metabolism. An additional advantage is that MRI scans can be obtained concurrently to provide structural/anatomical information that can guide data acquisition and assist in data analysis and interpretation. In this review, we will highlight some of the applications by which MRS can be used to investigate metabolism, focusing on its application to in vivo human studies. FIG. 1. MRS measures the chemical content of MR-visible nuclei across a region of interest and provides positional information as well as content. The 13C-MRS spectrum of glutamate displays peaks corresponding to each carbon atom of the molecule. The versatility of MRS provides a hugely flexible technique capable of probing a broad range of metabolic applications across a variety of tissues. Despite its many advantages, particularly for studies of human metabolism where noninvasive techniques are at a premium, effective implementation of MRS in vivo requires consideration of its methodological limitations and …