MR Spectroscopy

MR spectroscopy (MRS) is the use of magnetic resonance to quantify various metabolites (the chemical composition of tissue) and to study their distribution in different tissues. Metabolites are displayed along a chemical-shift axis measured in parts per million (ppm), with each peak corresponding to a characteristic compound.

The 3 Main Metabolites — The Good, the Bad & the Ugly

N-Acetyl Aspartate (The Good) — NAA

• Seen at 2.02 ppm.
• Marker for neuronal health.
• Decreases in situations where neuronal damage or replacement has occurred.
• Increases in only one condition: Canavan’s disease (a defect in the breakdown of NAA).

Choline (The Bad) — Cho

• Seen at 3.22 ppm.
• Present in the cell membranes of normal brain tissue.
• Increases when there is an increased number of cells (tumors) or destruction of cell membranes with release of choline (infarction or MS); however, with the latter the increase will be transient.
• With tumors the increase in choline will be persistent.

Lactate and Lipids (The Ugly)

• Lactate is seen as two peaks close to each other (a doublet) at 1.33 ppm.
• Lipids are seen at 0.9–1.2 ppm.
• Lipids increase in situations with cell destruction (necrosis, inflammation or infection).
• Lactate increases in tissue hypoxia, either due to decreased blood supply (infarctions) or increased demand (necrotic tumors).

Other Metabolites

Creatine — Cr

• Seen at 3.03 ppm as a large peak next to choline.
• Decreases in neoplasms, tissue injury, infections or some systemic diseases.
• Absent in metastatic tumors (most metastatic tumors don’t produce creatine).

Myo-inositol — MI

• Seen at 3.56 ppm.
• Found mainly in astrocytes.
• Increases in Alzheimer’s disease, demyelinating diseases and gliosis.
• Decreases in glial tissue destruction, as in non-glial tumors, infarction and infection.

Metabolite Summary

Ahmed Koriesh, MD