SISCOM (Subtraction Ictal SPECT Coregistered to MRI)

Abstract

Brain single photon emission computed tomography (SPECT) is a functional imaging test that can provide a 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 CBF changes during seizure. The sensitivity of ictal SPECT is high in temporal lobe epilepsy, but relatively lower in extratemporal epilepsy. SISCOM is a subtraction technique between ictal and interictal SPECT images with coregistration on brain MRI. SISCOM significantly improved the sensitivity of ictal SPECT and can further localize epileptic focus. But according to the time of radiotracer injection, an epileptic focus can be associated with ictal hyperperfusion or hypoperfusion or mixed one. Thus, ictal SPECT and SISCOM should be interpreted carefully with clinical information, features, and duration of seizure, ictal EEG pattern at the injection time. 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.