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

By digitally computing perfusion changes from ictal or postictal (peri-icta l) injections referenced to those acquired interictally, an enhanced method for localizing the epileptogenic area is reported. Computer-based image pr ocessing methods for quantifying regional percent change in the brain are a pplied to a group of 19 epilepsy patients after the injection of technetium -99m hexamethylproylene amine oxime (HMPAO) and after acquiring single-phot on emission tomography (SPET) data. Each patient's region of epileptogenesi s 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 Tc-99m-HMPAO ictal injection. This time scale w as normalized relative to the seizure duration and is referenced to the tim e of seizure termination. Eight patients, injected ictally, demonstrated pe rfusion increases of 25%-100% in the area of known epileptogenesis. Five pa tients, injected immediately after seizure cessation, demonstrated excessiv e perfusion decreases of 30%-92% associated with the region of seizure onse t. Six patients, injected well after seizure termination, demonstrated hypo perfusion 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 per fusion pattern model and by noting the time of injection for peri-ictal ima ges, an improved method for localizing the epileptogenic area is demonstrat ed.