A Multi-wavelength Continuous-wave Functional Near-infrared Spectroscopy System Using Lock-in Photon-counting Technique

In recent years,human brain project attracts the attention of many researchers in the field of brain science research to explore the mystery of the brain.Compared with other functional neuroimaging methods,such as fMRI,EEG,MEG,etc,functional spectroscopy(fNIRS)can provide high temporal resolution and reasonable spatial resolution.fNIRS measurement system possesses the advantages of portability,noninvasiveness,available and low price.Besides,fNIRS places fewer limitations on the subjects and environment.fNIRS has played a very important role in cognitive science research,pathological diagnosis and curative effect analysis of clinical neurological or psychiatric diseases or pathological diagnosis,and other related fields.So we develop a multi-wavelength continuous-wave functional near-infrared spectroscopy system using phase-lock photon-counting technique.fNIRS reflects the brain function activity by measuring the changes in oxy-and deoxy-hemoglobin concentrations.For the purpose of eliminating the influence of water and measuring metabolism level of cerebral cortex,thus we decide using three near-infrared wavelengths.In this paper,we use three kinds of wavelength LED as the light source,also design and manufacture the LED driver circuit.We designed a novel fNIRS system,by combining the parallelization ability of the lock-in detection with the high sensitivity of the photon-counting technique innovatively.The validity and effectiveness of the proposed lock-in photon-counting based system were verified mathematically and experimentally.After that,a multiwavelength continuous-wave functional near-infrared Spectroscopy system with 20 source channel and 12 detection channel was implemented.The system achieve the light source frequency division multiplexing by modulating LED with different frequency square wave separately.Then,automatic operation as well as digital demodulation detection of the system was achieved by using Field Programmable Gate Array which is a programmable logic device.Finally,to evaluate the performance of the fNIRS system,a series of phantom experiments were conducted.The result shows that our system is capable of carrying out multi-source simultaneous excitation and multi-channel parallel measurements,and is well performed in the detection and position of heterogeneous target which has different absorptivity compared with back.Besides,the result reveals that our system can effectively reflect the variation of relevant functional brain area’s absorption coefficient while brain in resting and motion state and validly distinguish it.