Magnetic resonance spectroscopy in cerebral ischemia and infarction

Proton magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) are promising techniques for the noninvasive investigation of brain metabolism in vivo. They can be implemented routinely on most clinical scanners, and typically have a spatial resolution of approximately 1 to 10 cm3 with scan times of 5 to 20 minutes. Various compounds can be detected in proton MRS of the brain. Compounds that are of particular importance in cerebrovascular disease are lactate (as a marker of ischemia) and N-acetyl aspartate (NAA), which is believed to be primarily of neuronal/axonal origin. The time-course of the changes in these compounds during ischemia is blood-flow dependent and potentially could be used to stratify acute stroke patients into different treatment protocols and to monitor the effects of treatment. However, many technical challenges have to be overcome (in particular, the development of fast MRSI techniques to reduce scan times) before this goal is realized. Also, more research is required to understand the significance of spectral changes during ischemia, and to compare the relative value of MRSI with other emerging MRI techniques, such as diffusion- and perfusion-weighted MRI.