In the brain, MRS is used to assess neuronal integrity, membrane turnover and energy metabolism. Metabolites such as NAA, choline, creatine, myo-inositol and lactate provide insight into tissue viability and pathology, and can reveal abnormalities before structural changes become visible on conventional MRI. Brain MRS has applications in neurology, neuro-oncology, including tumour characterization, epilepsy, metabolic disorders, neurodegeneration and inflammatory disease.
MRS also plays an important role in neonatal hypoxic-ischaemic encephalopathy (HIE). In this setting, single-voxel spectroscopy is commonly acquired in deep grey matter structures such as the thalamus or basal ganglia. A key biomarker is the lactate-to-NAA ratio (Lac/NAA), which reflects the combination of anaerobic metabolism and neuronal injury, and is widely used in studies of prognosis, therapeutic hypothermia and neuroprotection.
In practice, lactate is often assessed using a long echo time of 288 ms, which produces a positive in-phase doublet and reduces overlap from other metabolite signals. The main drawback of longer echo times is reduced signal-to-noise ratio (SNR), although this can be mitigated by improved hardware, higher field strengths and longer acquisition times.
