Optimizing Optode Layout for Small-scale Functional Near Infrared Spectroscopy (fNIRS)

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2019
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Swarthmore College. Dept. of Engineering
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en
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Full copyright to this work is retained by the student author. It may only be used for non-commercial, research, and educational purposes. All other uses are restricted.
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Functional near infrared spectroscopy (fNIRS) uses electromagnetic radiation in the infrared and near infrared spectrum to image the blood flow and metabolic activity of the brain in real-time. Multiple light sources and detectors are placed on the scalp around the region of interest to continuously take measurements of the light attenuation of the back-scattered light. Using the modified Beer-Lambert Law, which relates the light attenuation to the relative concentration of certain molecules, we can track the relative concentration changes of oxygenated and deoxygenated hemoglobin which corresponds directly to an increase in metabolic activity in a region of the brain. Coupling the detected brain activity with their spatial origin and mental task, we can gain a better understanding of the compartmentalized functions of the brain. For example, the frontal cortex is a core area of the brain associated with mental arithmetic tasks (Arsalidou 2018). Thus, fNIRS should indicate activity in that region while test subjects are carrying out mental math problems, with the signal-to-noise ratio increasing with penetrative depth of the light. The level of penetration, measured by the amount of light actually interacting with brain tissue, is known to have a direct relationship with the source-detector distance, and, thus, finding the optimal optode layout in which the maximum amount of light reaches the neural tissue is of increasing importance. Using Monte Carlo simulations, we studied various layouts and compared them with that of an open-source design to evaluate their efficacy in assessing frontal cortex activities.
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