Influence of technetium-99m-hexamethylpropylene amine oxime injection time on single-photon emission tomography perfusion changes in epilepsy.

By digitally computing perfusion changes from ictal or postictal (peri-ictal) injections referenced to those acquired interictally, an enhanced method for localizing the epileptogenic area is reported. Computer-based image processing methods for quantifying regional percent change in the brain are applied to a group of 19 epilepsy patients after the injection of technetium-99m hexamethylpropylene amine oxime (HMPAO) and after acquiring single-photon emission tomography (SPET) data. Each patient's region of epileptogenesis was independently localized through pathology and/or successful surgery. The positive and negative quantitative perfusion changes were plotted as a function of the time of the 99mTc-HMPAO ictal injection. This time scale was normalized relative to the seizure duration and is referenced to the time of seizure termination. Eight patients, injected ictally, demonstrated perfusion increases of 25%-100% in the area of known epileptogenesis. Five patients, injected immediately after seizure cessation, demonstrated excessive perfusion decreases of 30%-92% associated with the region of seizure onset. Six patients, injected well after seizure termination, demonstrated hypoperfusion changes less than 30% at the epileptogenic area. Observations on perfusion changes calculated from 99mTc-HMPAO SPET scans, as a function of normalized time, support a progression from ictal hyper- to excessive hypo-, then finally to persistent interictal hypoperfusion. By applying this perfusion pattern model and by noting the time of injection for peri-ictal images, an improved method for localizing the epileptogenic area is demonstrated.