Abstracts

Rationale: Novel dynamic single-photon emission computed tomography (dSPECT) has been developed using a recently FDA-approved 72-detector SPECT scanner (inSpira, NeuroLogica, Corp). The goal is to demonstrate time-lapsed transient blood flow changes propagating through a temporal lobe neural circuit. The maximal extent of the circuit is activated using stimulation therapy delivered through adjacent electrode contacts on a NeuroPace responsive neurostimulator (RNS) depth lead. 'Near-real time' dSPECT data acquired during stimulation is compared with conventional static SPECT which relies on collapsing the entirety of neural activation-related blood flow changes into a single snapshot.Methods: Two subjects (TAS, SWS) with bilateral independent temporal lobe epileptic sources enrolled in this study. These subjects were previously implanted with NeuroPace 4-contact longstanding depth leads at the grey-white matter hippocampal junction. 72-scalp EEG electrodes were placed. Repetitive bipolar stimulation of two adjacent depth contacts of a paramesial depth lead was performed during peripheral intravenous administration of the SPECT radiotracer, 99mTc-HMPAO. Delivery of stimulation current was completed without recording an afterdischarge. Throughout stimulation, dSPECT scanning of an axial volume of brain was obtained during 30 sec epochs within a 600 sec imaging session using the inSpira 72-detector SPECT scanner. A baseline SPECT study was acquired following a 24 hr seizure-free period. Activated and baseline static SPECT datasets were acquired following the same radiotracer injections, respectively. dSPECT and static SPECT datasets were processed using Analyze software (Analyzedirect.com), version 9.0. Results: Transient alterations in perfusion were acquired using the inSpira SPECT scanner during delivery of 100 msec bursts of 200 Hz repetitive stimulation at 0.5 Hz with a charge density of 9.1 ?C/cm^2. An epoch temporal resolution of 5 sec was demonstrated within each of the 30 sec preset scanner imaging epochs. These time-lapsed data were compared to a single static SPECT imaging dataset of the neural response acquired 45-60 min following completion of the stimulation therapy paradigm and equilibration of radiotracer. This latter dataset is comparable to the protocol used in conventional subtraction ictal SPECT imaging. Conclusions: Such a dSPECT imaging technology and workflow can validate both the time-lapsed propagation sequence, and maximal extent of activation of a temporal lobe epileptic circuit. Applications of this technology include validating the optimal implant site for investigational direct stimulation therapy depth leads. In addition, dSPECT can be used to potentially visualize the propagation sequence of rapidly evolving subclinical partial-onset seizures.