Time domain optical coherence tomography for compound action potential recording: computational analysis and system requirements
In the quest to understand the nervous system, electrophysiology has always been the golden standard for neural recordings. The signal observed with an electrode in close proximity of the studied tissue has an extremely high temporal and spatial resolution, and it has allowed scientists to improve our understanding of neurons. Different techniques – varying in invasiveness level – have been developed to record neural activity. To this day, however, the only accepted recording technique with
... technique with regards to the peripheral nervous system is the use of implantable electrodes, e. g. cuff electrodes. The birth and quick expansion of a new discipline, Neurophotonics, has started pushing neural recording towards a new direction. By exploiting the correlation between the electrical and optical activity of neurons, this project studies the feasibility of measuring peripheral nerve activity using light and, more specifically, using time domain optical coherence tomography. We hereby present a systematic overview of the optical techniques for neural recording proposed and tested so far, followed by a theoretical study of the forward scattering changes happening during neural activity. We have created this study to understand the order of magnitude of the expected change in refractive index (∼ one part per million of the original signal) and backscattering. We then describe the computational framework developed during this PhD project and how we used it, together with the results obtained from the theoretical model, to simulate the optical coherence tomography (OCT) signal of both functional A and structural B-scans of part of a Xenopus Laevis's sciatic nerve. Through the computational work, we have defined the theoretical minimum characteristics for an experimental setup, finally leading to a first prototype of the system. We envision that such a setup could be further developed into a minimally invasive, low cost miniaturised OCT device to detect nerve activity without damaging the fibres.