In situ monitoring of brain tissue reaction of chronically implanted electrodes with an optical coherence tomography fiber system

Neural microelectrodes are well established tools for delivering therapeutic electrical pulses, and recording neural electrophysiological signals. However, long term implanted neural probes often become functionally impaired by tissue encapsulation. At present, analyzing this immune reaction is only feasible with post-mortem histology; currently no means for specific in vivo monitoring exist and most applicable imaging modalities provide no sufficient resolution for a cellular measurement in deep brain regions. Optical coherence tomography (OCT) is a well developed imaging modality, providing cellular resolution and up to 1.2 mm imaging depth in brain tissue. Further more, a fiber based spectral domain OCT was shown to be capable of minimally invasive brain intervention. In the present study, we propose to use a fiber based spectral domain OCT to monitor the the progression of the tissue's immune response and scar encapsulation of microprobes in a rat animal model. We developed an integrated OCT fiber catheter consisting of an implantable ferrule based fiber cannula and a fiber patch cable. The fiber cannula was 18.5 mm long, including a 10.5 mm ceramic ferrule and a 8.0 mm long, 125 μm single mode fiber. A mating sleeve was used to fix and connect the fiber cannula to the OCT fiber cable. Light attenuation between the OCT fiber cable and the fiber cannula through the mating sleeve was measured and minimized. The fiber cannula was implanted in rat brain together with a microelectrode in sight used as a foreign body to induce the brain tissue immune reaction. Preliminary data showed a significant enhancement of the OCT backscattering signal during the brain tissue scarring process, while the OCT signal of the flexible microelectrode was getting weaker consequentially.

[1]  D. Szarowski,et al.  Brain responses to micro-machined silicon devices , 2003, Brain Research.

[2]  R V Bellamkonda,et al.  Bioimpedance modeling to monitor astrocytic response to chronically implanted electrodes , 2009, Journal of neural engineering.

[3]  J. Fujimoto,et al.  In vivo endoscopic optical biopsy with optical coherence tomography. , 1997, Science.

[4]  Gereon Hüttmann,et al.  Coronal in vivo forward-imaging of rat brain morphology with an ultra-small optical coherence tomography fiber probe , 2013, Physics in medicine and biology.

[5]  Dirk Faber,et al.  Functional optical coherence tomography : spatially resolved measurements of optical properties , 2005 .

[6]  A. Rezai,et al.  A feasibility study of optical coherence tomography for guiding deep brain probes , 2006, Journal of Neuroscience Methods.

[7]  Thomas Stieglitz,et al.  In vitro evaluation of the long-term stability of polyimide as a material for neural implants. , 2010, Biomaterials.

[8]  Shashi K. Murthy,et al.  Bridging the Divide between Neuroprosthetic Design, Tissue Engineering and Neurobiology , 2009, Front. Neuroeng..

[9]  Volker Tronnier,et al.  A simple implantation method for flexible, multisite microelectrodes into rat brains , 2013, Front. Neuroeng..

[10]  David C. Martin,et al.  Chronic neural recordings using silicon microelectrode arrays electrochemically deposited with a poly(3,4-ethylenedioxythiophene) (PEDOT) film , 2006, Journal of neural engineering.

[11]  P. Tresco,et al.  Response of brain tissue to chronically implanted neural electrodes , 2005, Journal of Neuroscience Methods.