magnetic resonance spectroscopy true true http://www.ncbi.nlm.nih.gov/pubmed/16148633 MRS A physiological assay that complements magnetic resonance imaging (MRI) as a non-invasive means for the characterization of tissue. While MRI uses the signal from hydrogen protons to form anatomic images, proton MRS uses this information to determine the concentration of brain metabolites such as N-acetyl aspartate (NAA), choline (Cho), creatine (Cr) and lactate in the tissue examined. https://www.ncbi.nlm.nih.gov/pubmed/27430454 Used to study brain function and activity. PERSON: Nicole Vasilevsky physiological assay