fMRS has several advantages over other functional neuroimaging and brain biochemistry detection techniques.
Unlike push-pull cannula, microdialysis and in vivo voltammetry, fMRS is a non-invasive method for studying dynamics of biochemistry in an activated brain. It is done without exposing subjects to ionizing radiation like it is done in positron emission tomography (PET) or single-photon emission computed tomography (SPECT) studies. fMRS gives a more direct measurement of cellular events occurring during brain activation than BOLD fMRI or PET which rely on hemodynamic responses and show only global neuronal energy uptake during brain activation while fMRS gives also information about underlying metabolic processes that support the working brain.
However, fMRS requires very sophisticated data acquisition, quantification methods and interpretation of results. This is one of the main reasons why in the past it received less attention than other MR techniques, but the availability of stronger magnets and improvements in data acquisition and quantification methods are making fMRS more popular.
Main limitations of fMRS are related to signal sensitivity and the fact that many metabolites of potential interest can not be detected with current fMRS techniques.
Because of limited spatial and temporal resolution fMRS can not provide information about metabolites in different cell types, for example, whether lactate is used by neurons or by astrocytes during brain activation. The smallest volume that can currently be characterized with fMRS is 1 cm, which is too big to measure metabolites in different cell types. To overcome this limitation, mathematical and kinetic modeling is used.
Many brain areas are not suitable for fMRS studies because they are too small (like small nuclei in brainstem) or too close to bone tissue, CSF or extracranial lipids, which could cause inhomogeneity in the voxel and contaminate the spectra. To avoid these difficulties, in most fMRS studies the volume of interest is chosen from the visual cortex – because it is easily stimulated, has high energy metabolisms, and yields good MRS signals.