Proton magnetic resonance spectroscopy (MRS) in epilepsy

Abstract

For 1H magnetic resonance spectroscopy (MRS) studies in epilepsy in vivo, the main signals of interest have been those from N-acetyl aspartate (NAA), creatine + phosphocreatine (Cr), choline-containing compounds (Cho), and lactate (Lac). Several lines of evidence have indicated that NAA is located primarily within neurons. A reduction of the NAA signal is frequently interpreted, therefore, as reflecting loss or dysfunction of neurons. Such a reduction in NAA has been found in practice in many cases where neuronal loss would be expected clinically, and such abnormalities have been shown to be present in patients with intractable focal epilepsy. The acquisition of spectroscopic data in vivo is of limited use unless the spatial origin of the signals obtained is known. It is necessary, therefore, to limit the extent of the volume from which signal is acquired and to relate this volume to the anatomy of the region under investigation. For this reason, a number of common spatial localisation techniques are outlined, and their consequences described. In vivo MRS studies in epilepsy to date have been directed largely at the temporal lobes of patients with intractable epilepsy in whom surgical treatment is under consideration. Results are presented from a number of institutions which demonstrate that 1H MRS can contribute to the lateralization of the epileptic focus and to the identification of bilateral pathology. In providing information both on static metabolic abnormalities, primarily through the NAA signal, and on dynamic changes associated with seizure activity via the lactate signal, MRS offers the possibility of obtaining information on cerebral metabolism that is likely to have significant consequences for the management of patients with epilepsy.