In vivo magnetic resonance spectroscopy

In vivo (that is 'in the living organism') magnetic resonance spectroscopy (MRS) is a specialised technique associated with magnetic resonance imaging (MRI).

Magnetic resonance spectroscopy (MRS), also known as nuclear magnetic resonance (NMR) spectroscopy, is a non-invasive, ionizing-radiation-free analytical technique that has been used to study metabolic changes in brain tumors, strokes, seizure disorders, Alzheimer's disease, depression and other diseases affecting the brain. It has also been used to study the metabolism of other organs such as muscles. In the case of muscles, NMR is used to measure the intramyocellular lipids content (IMCL).

Magnetic resonance spectroscopy is an analytical technique that can be used to complement the more common magnetic resonance imaging (MRI) in the characterization of tissue. Both techniques use signals from hydrogen protons (1H), but MRI uses the information to create 2-dimensional images of the brain, while MRS uses 1H signals to determine the relative concentrations of target brain metabolites.

Both MRI and MRS are based on nuclear magnetic resonance (NMR), a technique used by chemists and physicists in the analysis and characterization of small molecules in solid, liquid, and gel-like solutions. MRS can be used to detect nuclei such as carbon (13C), nitrogen (15N), fluorine (19F), sodium (23Na), phosphorus (31P) and hydrogen (1H), however only the latter two are present in significant abundance to be detected in humans. Hydrogen is the most commonly detected nucleus due to its high natural abundance, acute sensitivity to magnetic manipulation, well known simple technique, and relatively easily discernible spectra.

Acquiring an MRS scan is very similar to that of MRI with a few additional steps preceding data acquisition. These steps include:

The more common MRI is used to detect H₂O molecules in the brain, however MRS is used to probe other molecules that are common to tumors by comparing MRS spectra with known "fingerprint" spectra.

MRS allows doctors and researchers to obtain biochemical information about the tissues of the human body in a non-invasive way (without the need for a biopsy), whereas MRI only gives them information about the structure of the body (the distribution of water and fat).

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