Design and Fabrication of a Transmission Pulse Oximeter Device with Applications for Functional Near Infrared Spectroscopy (fNIRS)

The long-term motivation for this work is to develop a feasible prototype design to fabricate a wireless, low-cost fNIRS system. The fNIRS method, based on reflection pulse-oximetry, is becoming increasingly important for investigating in situ cerebral oxygen levels as a marker for regional brain activation during various activities. Wireless fNIRS devices allow for full portability and are commercially available, but at a high cost which is prohibitive for many research programs. As a first step toward this goal, a simple transmission mode pulse oximeter was designed and constructed with the short-term goal of gaining insight into optical techniques and theoretical constructs required to determine blood oxygenation levels. Pulse oximetry, like fNIRS, is based on the variation in light absorption between oxygenated and deoxygenated tissue. In the case of standard pulse oximetry, the tissue is arterial blood (typically in a fingernail bed), while fNIRS probes both arterial and venous blood in cortical tissue of the brain. For this work, two micro-LEDs, 660nm and 940nm, along with a silicon-based photodiode detector with a range of 350nm to 1100nm were the primary hardware. An Arduino^TM Uno was used for system interface and control of LEDs and detector. A custom Python-based code was developed to process the system output data and compute oxygen saturation. While the system is functional, reliable oxygen saturation percentage calculations have presented a challenge due to photodiode output data resolution. Current status of the device, revisions, and future plans will be discussed