Design of a Novel Functional Near-Infrared Spectroscopy System for Human Brain Imaging

Many countries are facing the dilemma of ageing society and the fatality rate due to degenerative brain diseases is rising. Therefore, swift advancements in the field of neuroscience are vital to our rapidly aging society. Functional near-infrared spectroscopy (fNIRS) has become a promising neuroimaging modality for measuring the concentration changes of blood chromophores during a neuronal activity. This paper describes the development and working of our lab-developed fNIRS system which measures the concentration changes in oxyhemoglobin and deoxyhemoglobin from the optical near-infrared (NIR) light signals. 128 light emitting diodes (LEDs) consisting of two wavelengths (i.e. 735 nm and 850 nm) are used in our system. This NIR light intensity passes through the brain tissue and get absorbed and scattered, is received and measured by using only single photodiode (PD) in order to compute the desired blood chromophores. The drive circuit of LEDs was designed by using serial peripheral interface based output expansion chips. Wireless communication based on Wi-Fi was employed in the system to transfer the light intensity values to our lab-developed software running on a Windows based computer. The software has the capacity to show the data plots in real-time as well as store the information for offline evaluation. The functionality of the system was tested using a phantom of known scattering and absorption coefficients instead of human brain. The LEDs and PD were placed firmly on the phantom and different arrangements for light shooting were utilized to yield rigorous testing data. The tested system exhibited the measured optical signal intensity values for both wavelengths that are used to measure oxy and deoxyhemoglobin changes in 128 channels.