Functional magnetic resonance spectroscopy of the brain
Functional magnetic resonance spectroscopy of the brain (fMRS) uses magnetic resonance imaging (MRI) to study brain metabolism during brain activation. The data generated by fMRS usually shows spectra of resonances, instead of a brain image, as with MRI. The area under peaks in the spectrum represents relative concentrations of metabolites.
Source: Wikipedia — Functional magnetic resonance spectroscopy of the brain (CC BY-SA 4.0)