A Portable Functional Near-Infrared Spectroscopy System Using 4-wavelength LEDs

Recently many countries are facing the problem of a rapid aging society. Due to the geriatric brain diseases, the research on brain imaging in a normal environment is becoming more important. Functional near-infrared spectroscopy (fNIRS) has proven its effectiveness in measuring the concentration changes of blood chromophores in the human body. In this study, we develop a light emitting diode (LED) based fNIRS instrument capable of measuring the concentration changes of multiple chromophores. We used 4-wavelength LEDs of 770 nm, 810 nm, 850 nm, and 890 nm for our system for calculating not only the concentrations of hemoglobin, but also the concentrations of oxidizing enzyme which increase or decrease during the oxygen exchange process. Along with calculating more chromophores, this device will provide more accurate oxyhemoglobin and deoxyhemoglobin values. The LED driver circuit is designed using a serial peripheral interface (SPI) based output expansion chip. Photodiode (PD) is used to measure the intensity of light after absorbing and scattering during passing through the medium. The control system is designed using the microcontroller unit (MCU) and to enable bidirectional communication with the host computer at 4 Hz by using serial communication. We used the phantom model to test the functionality of the system. We attached LED and PD to the phantom and tested it under the same conditions with actual channel configuration. The developed fNIRS system showed a total of 32 acquired constant light intensity values of 8 channels.