PRESURGICAL IDENTIFICATION OF EPILEPTIC FOCI WITH I-123 IOMAZENIL SPET - COMPARISON WITH BRAIN PERFUSION SPET AND FDG PET

Iodine-123 iomazenil (IMZ) has excellent characteristics for the quant ification of central benzodiazepine receptor (BZR) binding with single -photon emission tomography (SPET). In order to evaluate the clinical value of IMZ SPET for presurgical identification of epileptic foci in patients with medically intractable seizures, we measured the binding potential (BP) of BZR using two IMZ SPET scans and compared the result s with brain perfusion SPET and fluorine-18 fluorodeoxyglucose (FDG) p ositron emission tomography (PET). A total of ten patients with intrac table partial epilepsy were examined by electroencephalography, magnet ic resonance imaging, FDG PET, brain perfusion SPET and IMZ SPET. Afte r neuroimaging examinations, five patients underwent selective surgery , and all of them have since been free of seizures. Two SPET scans wer e performed at 15 min (early) and 3 h (late) after intravenous injecti on of I-123-IMZ (167 MBq). Parametric images of the ligand transport ( K-1) and binding potential (BP) were calculated by the table look-up m ethod, which is based on a three-compartment two-parameter model, usin g the standard arterial input function obtained by averaging of six no rmal volunteers' input functions. BP images delineated the epileptic f oci more precisely than either FDG PET or ictal perfusion SPET FDG PET showed widespread reduction, including the area surrounding the focus , and ictal increase in the cerebral blood flow was seen in possibly a ctivated areas spread from the focus. In four epilepsy cases which ori ginated from the mesial temporal lobe without lateral temporal abnorma lity there was no significant decrease in the BP images in the lateral temporal structures, which showed decreased uptake of FDG. It is conc luded that parametric images of BP with IMZ are valuable for precise p resurgical localization of epileptic foci.