Abstracts

IN VIVO OPTICAL SIGNAL CHANGES OBSERVED WITH OPTICAL COHERENCE TOMOGRAPHY IN A FOCAL CORTICAL SEIZURE MODEL

Abstract number : 2.238
Submission category : 5. Neuro Imaging
Year : 2014
Submission ID : 1868320
Source : www.aesnet.org
Presentation date : 12/6/2014 12:00:00 AM
Published date : Sep 29, 2014, 05:33 AM

Authors :
Jenny Szu, Melissa Eberle, Carissa Rodriguez, Mike Hsu, B. Hyle Park and Devin Binder

Rationale: Epilepsy is a chronic neurological disorder that affects approximately 2% of the population and is characterized by the unpredictable occurrence of seizures. Detection of seizures prior to their onset or spread could potentially allow therapeutic interventions to prevent and minimize their effects. Previous techniques such as intrinsic optical signal (IOS) imaging have been used to detect cortical seizures in animal models. However, these methods have limited spatiotemporal resolution and have not been shown to accurately reflect seizure onset or spread. In this study, we utilize optical coherence tomography (OCT), a minimally-invasive imaging modality capable of generating cross-sectional images with submicron resolution. Previously, we showed that functional OCT (fOCT) was able to detect changes in a generalized cortical seizure model (PTZ). In this study, we employed fOCT to characterize optical changes in a focal cortical seizure model (4-AP). Seizure generation and propagation in the cortex were evaluated together with changes in fOCT signals over time. Methods: In our focal seizure model, a one-sided hemicraniectomy was performed and animals were placed under the OCT objective for imaging (n=6). Electroencephalography (EEG) electrodes were placed in the primary somatosensory cortex and animals received intracerebral injections of 4-aminopyridine (4-AP) to reliably induce focal cortical seizures. OCT volumes were collected every 2 min. Optical attenuation coefficients were extracted during postprocessing of the OCT image datasets. The attenuation coefficient represents total light propagation losses due to absorption and scattering. Results: Focal cortical seizure activity was observed with a well-defined latency following 4-AP microinjection. The effects of seizure activity were analyzed by measuring changes in brain tissue attenuation coefficient over time. Percent changes in attenuation coefficient (Δµ) from a 90% confidence interval (C.I.) were analyzed for baseline and post-4-AP-injection temporal windows. Approximately 30 min after 4-AP injection, a maximum of 9% change in Δµ outside the C.I. was observed near the injection site while a maximum of 1% change in Δµ outside the C.I. was observed at an area distant to the injection site. We further evaluated the spatiotemporal progression of seizure activity-induced optical changes in three dimensions (3D) through the imaged tissue region of interest (ROI). Functional OCT attenuation coefficient maps were constructed voxel by voxel. Significant changes in fOCT attenuation coefficients were observed following 4-AP injection and were correlated spatially and temporally with focal EEG seizure activity. Conclusions: Our results indicate that fOCT has the capacity to detect and map optical changes occurring in response to focal seizure activity in the cortex. Further studies will need to address the mechanism of the observed fOCT changes and to validate fOCT as a minimally-invasive optical imaging technique for high spatiotemporal resolution monitoring of seizure activity.
Neuroimaging