MR Spectroscopy (MRS): Imaging Tissue Chemistry
Instead of a picture, MRS produces a chemical fingerprint: the relative amounts of key metabolites in a chosen volume of tissue.
How it works
Rather than forming an image, MRS reads the subtle frequency differences (chemical shift) between protons in different molecules, producing a spectrum of peaks. The height of each peak reflects how much of that metabolite is present. It is most established in the brain.
The main brain metabolites
| Peak | Meaning |
|---|---|
| NAA (N-acetylaspartate) | Neuronal marker; falls with neuronal loss/injury |
| Choline (Cho) | Membrane turnover; rises in tumour and active disease |
| Creatine (Cr) | Relatively stable, so used as an internal reference |
| Lactate | Anaerobic metabolism: necrosis, high-grade tumour, ischaemia |
| Lipids | Necrosis |
The classic tumour pattern is a raised choline and reduced NAA (high Cho/NAA ratio), reflecting proliferation replacing normal neurons.
Uses
- Brain tumours: supporting grading and distinguishing tumour from non-neoplastic lesions.
- Treatment response: helping separate radiation necrosis from tumour recurrence.
- Metabolic & neonatal disease: e.g. lactate in mitochondrial disorders and hypoxic-ischaemic injury.
MRS is interpreted alongside conventional and perfusion MRI, not in isolation, and is technically demanding (voxel placement, field homogeneity).
Sources
- Horská A, Barker PB. Imaging of brain tumors: MR spectroscopy and metabolic imaging. Neuroimaging Clin N Am 2010;20:293–310.
Educational summary for clinicians; interpretation is specialist and context-dependent. Not medical advice.
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