Abstracts

Rationale: High resolution (3-4 mm voxel) single-photon emission computed tomography (SPECT) has been recently developed using a 72-detector focused collimator ring scanner system (inSpira, NeuroLogica Corp). The goal of this study is to demonstrate the maximal extent of transient hyperperfusion-related changes within the ictal onset zone in extratemporal epilepsy, not seen with a conventional 2-headed detector SPECT scanner (Siemens). Methods: Eight subjects with medically refractory extratemporal epileptic sources were enrolled in this investigator-initiated IRB-approved study prior to resection. Injection of SPECT radiotrace, 99mTc-HMPAO (Ceretec) was successfully completed at the ictal onset (mean time to injection from clinical or electrocerebral seizure onset = 32 sec +/-8 sec). A baseline SPECT was acquired following about a 24 hour seizure-free period. Ratio ictal SPECT co-registered to MRI (RISCOM) was performed using the SPECT datasets for each patient. The data were normalized and processed using custom software utilities. These data were co-registered to each subject's gapless SPGR MRI study using the ITK co-registration algorithm and visualized (MIM Software). Subtraction ictal SPECT co-registered to MRI (SISCOM) was also performed for each subject acquired with the inSpira scanner system and a Siemens 2-detector SPECT scanner using Analyze v10 (AnalyzeDirect). For each patient, RISCOM and SISCOM analyses of the extratemporal ictal onset zones using the 72-detector scanner were compared with datasets acquired with the Siemens SPECT scanner. These data were validated utilizing chronic electrocorticography capturing stereotypic seizures prior to resection. Results: RISCOM datasets using the 72-detector system demonstrated a concordant overlap of transient regions of hyperperfusion seen with the SISCOM data obtained with the 2-detector SPECT scanner. However, the InSpira RISCOM data demonstrated regions of hyperperfusion not seen with the SISCOM datasets. For 6 of the 8 patients, these new regions of hyperperfusion were concordant with chronic electrocorticography and included in the volume of resection. All 8 patients demonstrated an Engel's class I-II outcome after a mean of 9-12 months post-resection. Conclusions: RISCOM image processing using the 72-detector ring collimator SPECT scanner facilitated identification of the ictal onset in extratemporal epileptic circuits not visualized with conventional 2-detector SPECT scanner technology. Application of this novel SPECT technology can facilitate clarifying the extent of the ictal onset zone for strategic placement of chronic intracranial electrodes.