Imaging criteria to identify the epileptic focus. Magnetic resonance imaging, magnetic resonance spectroscopy, positron emission tomography scanning, and single photon emission computed tomography.

The use of MRI, MRSI, PET, and SPECT scanning for preoperative evaluation of patients with epilepsy is reviewed. MRI provides the best anatomic detail and contains prognostic information. PET provides useful information in some patients for whom MRI findings are absent or contradictory. Interictal SPECT scanning lacks sufficient specificity to be of use in the preoperative evaluation of refractory patients, whereas ictal SPECT appears to be useful in temporal and extratemporal lobe epilepsy. The new technique of MRSI is described.