Development of functional near infrared spectroscopy system for assessing cerebral hemodynamics of rats with ischemic stroke

The aim of this study was to develop a single-channel functional near-infrared spectroscopy (fNIRS) system by using frequency-domain method for observing the change in regional cerebral flow of ischemic stroke rats. Two laser diodes with wavelengths of 780 nm and 830 nm were driven by a 10 kHz modulated sinusoidal current source and alternately switching at 5 Hz. The optical output, detected by a high-sensitivity avalanche photodiode module, was demodulated to extract amplitude and phase parameters by using digital in-phase and quadrature demodulator. The designed fNIRS was first calibrated on a tissue-like phantom to acquire the characteristics of light source and detector for suitable configuration. After calibration, the fNIRS system was applied to study ischemic condition of stroke rats. The stroke rats were induced by the occlusion of middle cerebral artery combined with the techniques of three-vessel occlusion to observe the time-course changes of ischemia. The optical outputs of the normal side of ischemic rat were compared with those of lesion side. Our results showed that the reduction of regional cerebral blood flow in the middle regions of lesion brain was evident from the signals detected by our fNIRS system.