18 - Magnetic resonance spectroscopy in stroke

Summary

Magnetic resonance spectroscopy (MRS) is a non-invasive method that allows the in vivo investigation of biochemical changes in both animals and humans. The application of MRS to the study of stroke has made possible dynamic studies of intracellular metabolism in cerebral ischemia. The concentration of cerebral metabolites in the brain is very low (2-20 mM) compared to that of water (41.7 M of water or 83.4 M of protons). The evoked nuclear magnetic resonance (NMR) signal from the metabolite is therefore very much smaller than the signal from water used to generate an anatomical display in magnetic resonance imaging (MRI). Hence, the minimum voxel size required for MRS is larger and data acquisition times are longer than in MRI. MRS is more sensitive to local magnetic field inhomogeneities leading to difficulties in the quantitation of peak areas. MRS has therefore been limited to use as a research tool, until the last few years. Despite the relatively low signal-to-noise ratio of spectroscopy, improvements in magnet and gradient design, and the wider availability of magnets at higher field strength (1.5T), now enable good quality brain [¹H]-MRS spectra to be recorded on most modern clinical instruments.

The original spectroscopy work in animals and humans was carried out using phosphorus [³¹P] MRS. However, not all metabolites contain phosphorus, and the MR application of this nucleus has been restricted to the study of energy and lipid metabolism.