Seizure (ICTAL, Post ICTAL and INTERICTAL) Brain Perfusion SPECT is used primarily if an MRI and EEG didn’t pinpoint the location of where the seizures are originating. There are two ways of doing the SPECT, during a seizure (ictal) and between seizures (interictal). The ICTAL SPECT provides the opportunity to image cerebral blood flow during a seizure and identify focal areas of hyperperfusion for the purpose of localization.
The INTERICTAL SPECT scan is more likely to show a region of decreased blood flow in patients with frequent seizures.

source: epilepsy.yale.edu/