DESIGN AND DEVELOPMENT OF NEAR-INFRARED SPECTROSCOPY SYSTEM FOR MONITORING FUNCTIONAL BRAIN ACTIVITY

Near infrared spectroscopy is an optical technique which can measure the spectral absorbing molecules. Recently, it has been widely researched about its applications because the method is noninvasive and safe. The technology can measure the changes in hemoglobin concentrations in the brain. NIRS is emerging as a promising tool in the cognitive neurosciences, neuro-pathology and psychological studies. Several models of NIRS instruments have been developed, but most of them are either expensive or have safety concerns when laser sources are used. We present a simplified NIRS system using continuous, bi-color LEDs emitting light at 760/840 nm, a photodiode with on-chip transimpedance amplifier having highest responsivity for the selected wavelengths. The system is controlled by two Arduino boards, each one for light sources and photodiodes. Since Arduino microcontroller boards are interfaced with the computer, analog to digital conversion (ADC) cards are not necessary in the NIRS system. A sensor probe was designed accommodating the light sources and photodectors. In the probe, LEDs and photodiodes were arranged such that a gap of 3 cm was maintained between the LED and photodiode in order to monitor the physiological activities in the cortex by measuring the hemodynamic responses. This system has been evaluated by phantom experiment. Observations from experiments suggest that this system can be used for monitoring functional activity of the human brain.