Diagnosis -Ictal Brain SPECT Computerized Subtraction Imaging

In cases in which it is important to determine which part of the brain is responsible for causing seizures (e.g., in epilepsy surgery planning) it may be helpful to inject a radionucleotide at the time of a seizure. The injected substance then 'tags' the part of the brain where blood flow is increased. Blood flow increases in the area of the brain where the seizure starts thereby showing which part of the brain may be responsible for producing seizures. Ictal means during the time of a seizure and SPECT means single photon emission tomography. To inject at the time of the seizure requires that the procedure be done during epilepsy monitoring in the epilepsy monitoring unit (see under Epilepsy Monitoring Unit Evaluation). After monitoring ends, the patient returns to the hospital for a second SPECT scan at a time when seizures are not occurring. The results of the ictal SPECT and the non-ictal SPECT are then subtracted from each other and analyzed by computer to determine if an area of increased blood flow occurred during the seizure. This process is also sometimes referred to as CISCOM.