BME MS Thesis Defense - Carlos Segura

10:00 am on Tuesday, August 12, 2014
44 Cummington Mall, Room 203
Title: "Development of an Optrode for Optical Characterization of Neural Tissue-Electrode Interface"

Irving Bigio, Ph.D. (Chair, Co-Advisor)
Bryan McLaughlin, Ph.D. (Co-Advisor)
Darren Roblyer, Ph.D.

The use of implantable neural probes is becoming more popular, both for stimulation and recording, and their applications range from chronic pain treatment to implementation of brain machine interfaces (BMI). Studies have shown that signal quality of implanted electrodes decays over time mainly due to the immune response. Characterization of the tissue-electrode interface is critical for better understanding of the physiological dynamics and potential performance improvement of the electrode itself and its task. This work describes the fabrication of an implantable electrode with optical measurement capabilities for providing means to characterize the tissue-electrode interface using optical spectroscopy. The electrode has a set of waveguides embedded in its shanks, which are used to inject white light into tissue and then collect the light reflected from the tissue surrounding the shanks. The collected light is analyzed with a spectrometer and the spectra processed to detect scattering and absorption changes, information that allows to track physiological changes. Investigation of scattering and absorption coefficients in such interface and their change over time can provide useful data for modeling and determining physiological parameters like blood oxygenation while the actual shape of the acquired spectra might highlight particular phenomena that can be indicative of scaring process or hemorrhaging. Validation of this system was done using optical phantoms with known scattering coefficients and also by performing measurements on whole blood samples with various oxygenation levels. The ultimate goal of this project is to create a novel device that is capable of satisfying the unmet need of tissue characterization at the implanted electrode interface as well as a tool for the optogenetics field suitable for greater depths than those a microscope can achieve.