Combined magnetic resonance imaging and spectroscopy in experimental regional injury of the brain. Ischemia and impact trauma.

Combined magnetic resonance imaging (MRI) and spectroscopy (MRS) allows unique experimental insights into the central nervous system (CNS) disorders. Clinical applications are forthcoming. In order to address the potential clinical uses of MRI/MRS, experimentally induced focal brain lesions were evaluated with this modality. Focal lesions more closely mirror clinical situations than do global insults, but have rarely been the focus of MRS studies. Fluid-percussion trauma in 48 rats, focal ischemia in 18 rats and in 16 mongrel dogs were produced, with various degrees of severity. A discrepancy between temporal evolution data of MRI and MRS was found: MRI always showed an increase in lesion extension over time while 31P and 1H MRS almost always showed improvement. The severity and evolution of these MRS findings was surprising, and differed from the results reported for global brain injuries. Besides possibly reflecting real improvement in the metabolic state, other explanations for the phenomena exist. Diffusion of inorganic phosphate out of the regional site of injury and its reincorporation for more prominent lactate build-up in regional injury are possible. Therefore the use of MRS to predict metabolic and clinical outcomes of regional brain injury requires methodologic caution, but its combination to MRI offers an unprecedented tool for studies of focal CNS pathology.