Magnetic Resonance Spectroscopy

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.

What is Magnetic resonance spectroscopy? #

• 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 typically acquire signal from hydrogen protons (other endogenous nuclei such as those of Carbon, Nitrogen, and Phosphorus are also used), but MRI acquires signal primarily from protons which reside within water and fat, which are approximately a thousand times more abundant than the molecules detected with MRS.

• As a result, MRI often uses the larger available signal to produce very clean 2D images, whereas MRS very frequently only acquires signal from a single localized region, referred to as a voxel.

• MRS can be used to determine the relative concentrations and physical properties of a variety of biochemicals frequently referred to as metabolites due to their role in metabolism.

Uses of Magnetic resonance spectroscopy #

• 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).

• For example, whereas MRI can be used to assist in the diagnosis of cancer, MRS could potentially be used to assist in information regarding to the aggressiveness of the tumor.

• Furthermore, because many pathologies appear similar in diagnostic imaging (such as radiation-induced necrosis and recurring tumor following radiotherapy), MRS may in the future be used to assist in distinguishing between similarly appearing prognoses.

• MRS equipment can be tuned (just like a radio receiver) to pick up signals from different chemical nuclei within the body.

• The most common nuclei to be studied are protons (hydrogen), phosphorus, carbon, sodium and fluorine.

• The types of biochemicals (metabolites) which can be studied include choline-containing compounds (which are used to make cell membranes), creatine (a chemical involved in energy metabolism), inositol and glucose (both sugars), N-acetylaspartate, and alanine and lactate which are elevated in some tumors.

• At present MRS is mainly used as a tool by scientists (e.g. medical physicists and biochemists) for medical research projects, but it is becoming clear that it also has the ability to give doctors useful clinical information, especially with the discovery that it can be used to probe the concentration of alpha-Hydroxyglutaric acid, which is only present in IDH1 and IDH2 mutated gliomas, which alters the prescribed treatment regimen.

• MRS is currently used to investigate a number of diseases in the human body, most notably cancer (in brain, breast and prostate), epilepsy, Alzheimer’s disease, Parkinson’s disease, and Huntington’s chorea.

• MRS has been used to diagnose pituitary tuberculosis.

Limitations of Magnetic resonance spectroscopy #

• The major limitation to MRS is its low available signal due to the low concentration of metabolites as compared to water.

• As such, it has inherently poor temporal and spatial resolution. Nevertheless, no alternate technique is able to quantify metabolism in vivo non-invasively and thus MRS remains a valuable tool for research and clinical scientists.

• In addition, despite recent efforts toward international expert consensus on methodological details like shimming, motion correction, spectral editing, spectroscopic neuroimaging, other advanced acquisition methods, data processing and quantification.