SISCOM (Subtraction Ictal SPECT with Coregistration to MRI)

Abstract

Brain single-photon emission computed tomography (SPECT) is a functional nuclear imaging technique that can provide a regional map of cerebral blood flow (CBF) changes during the interictal or ictal period in patients with epilepsy and other neurological disorders. The radiotracer for brain SPECT is rapidly taken up by the brain within 30–60 s after its injection. The radiotracer injection during seizure activity (ictal SPECT) can show a snapshot of regional CBF (rCBF) changes during seizure. The sensitivity of ictal SPECT is high in temporal lobe epilepsy but relatively lower in extratemporal epilepsy. SISCOM is an imaging technique to subtract ictal and interictal SPECT images and to coregister them on brain MRI. SISCOM significantly improves the sensitivity of ictal SPECT and can further localize epileptic focus. But the successful localization of epileptic focus can be affected by the time of radiotracer injection, seizure duration, and propagation pattern of ictal EEG. Ictal hypoperfusion as well as ictal hyperperfusion is an important finding. Thus, ictal SPECT and SISCOM should be carefully interpreted by simultaneous review with seizure semiology, clinical information, features, injection time, duration of seizure, and ictal EEG pattern at the injection times. SISCOM is also useful for localizing brain structure generating specific feature of seizures and studying propagation pathways of epileptic seizures and pathomechanism of other neurological disorders and sleep disorders.