MR spectroscopy (MRS)

Magnetic resonance spectroscopy (MRS) uses the chemical-shift information in the MR signal to quantify tissue metabolites non-invasively, typically from a single voxel or a multi-voxel grid acquired on a standard MRI scanner. Brain 1H-MRS measures N-acetylaspartate (NAA, a marker of neuronal integrity), choline, creatine, lactate, myo-inositol, glutamate/glutamine and reduced glutathione; these are useful in tumour grading, mitochondrial disease, multiple sclerosis and neurodegenerative research. In the liver, MR proton density fat fraction (MR-PDFF), a chemical-shift-encoded MRI technique conceptually related to MRS, is the most accurate non-invasive measure of hepatic steatosis and has become the imaging endpoint of choice in MASLD/MASH trials, with good correlation to biopsy steatosis grades. MRS uses no ionising radiation; limitations include long acquisition times, susceptibility to motion and B0 inhomogeneity, modest spatial resolution and the need for specialised post-processing.