1HMRS

Proton magnetic resonance spectroscopy, commonly abbreviated as 1H-MRS, is a non-invasive imaging modality that uses magnetic resonance to measure concentrations of certain metabolites containing hydrogen nuclei in vivo. It is typically performed on clinical MRI scanners with localized voxel spectroscopy sequences such as Point-RESolved Spectroscopy (PRESS) or Stimulated Echo Acquisition Mode (STEAM). The technique relies on chemical shift differences of hydrogen atoms in different molecular environments, producing a spectrum where peaks correspond to specific metabolites.

Commonly detected metabolites include N-acetylaspartate (NAA) at about 2.0 ppm, total choline (tCho) around 3.2 ppm, total creatine (tCr) near 3.0 ppm, myo-inositol (mI) around 3.5-3.3 ppm, and lactate at 1.3 ppm (often inverted at TE ~ 144 ms). The signal-to-noise ratio is modest and spectra may be acquired at short echo times (TE ~ 20-35 ms) to detect multiple metabolites, or long-TE sequences (e.g., 144 ms) to emphasize lactate or to simplify the spectrum. Quantification can be relative (ratios to creatine or water references) or absolute, typically by fitting the spectrum with model basis sets (e.g., LCModel).

Applications span neurology and neuro-oncology, including assessment of epilepsy, multiple sclerosis, neurodegenerative diseases such as Alzheimer’s disease, brain tumors, and metabolic disorders. Extra-cranial uses include liver, muscle, and breast spectroscopy, though brain MRS is the most established clinical area. It provides metabolic information that complements conventional MRI, aiding diagnosis, prognosis, and treatment monitoring.

Limitations include modest signal strength and spectral overlap among metabolites, making accurate quantification challenging. Results depend on voxel placement, tissue composition, relaxation times, and scanner calibration. Lipid contamination from the scalp or skull, motion, and poor shimming can degrade data. Standardization of acquisition and analysis methods remains an active area.