Research On Frequency-domain Near-infrared Spectroscopy System For Medical Use

Frequency-domain near-infrared spectroscopy(FD-NIRS) is a flourishing non-invasive, non-ionizing optical method that can be applied to early cancer diagnosis, tissue oxygenation monitoring and many other applications. This thesis mainly focuses on developing and testing a FD-NIRS system for medical use to obtain some preliminary results before its clinic applications.The FD-NIRS system studied in this thesis has four channels with four different wavelengths within the near-infrared range. Laser diodes were directly modulated with RF signals. A high speed micro-electromechanical system(MEMS) optical switch and a RF switch were used to switch from different channels in sequence. The output light was conducted into the tissue by a fiber optical sensor with two source fibers and one collection fiber. Light from the tissue collected by the collection fiber was detected and amplified by the avalanche photo diode(APD) module, followed by heterodyne detection in the network analyzer. Tissue optical characteristics, such like absorption coefficient and scattering coefficient, could be inversely extracted from the amplitude and phase shift, and hence the physiological information of tissue.Phantom experiments are commonly used to assess the performance of the system before clinic studies. Both infinite model and semi-infinite phantom experiments were conducted in order to mimic different applications. The weakest raw signals were observed to have a 7dB signal noise ratio(SNR) and a 3d B SNR for this two phantom experiments, respectively. The results of phantom experiments have showed that the system maintained a 95% accuracy under both situations. The scanning speed was also remarkable. It took only 11 seconds to run a full scanning.In order to validate the capability of the system in clinical applications, vascular occlusion test(VOT) was performed on 2 volunteers to non-invasively monitoring the change of saturated oxygenation during VOT. The monitoring curves perfectly coincided with real changes, which indicated that the system was ready for clinical studies. The works done in this thesis has significantly advanced the clinic use of FD-NIRS systems.