Parallel Measurement Implementation Of High-Density FNIRS Imaging System Using Lock-in Photon Counting Technique

The current mainstream brain function detection technologies include:Functional Magnetic Resonance Imaging(fMRI),Electroencephalogram(EEG),Functional Near-infrared Spectroscopy(fNIRS),etc.Among them,fNIRS can take into account both time resolution and spatial resolution,with the advantages of non-invasive,low-cost,and real-time dynamic repetitive measurement,etc.This technology is very suitable for the study of brain function activities in natural situations because of its excellent motion robustness.Nowadays,most fNIRS systems based on analog detection mode use locked-in detection technology to achieve parallel measurement to improve time resolution.However,this mode is limited in sensitivity and dynamic range,which affects the improvement of the imaging quality and the realization of advanced schemes such as diffuse optical tomography(DOT).Although the traditional photon counting technology can greatly improve the sensitivity of the system,the non-parallel measurement mode of sequential source excitation it used seriously reduces the time resolution.In order to solve the above problems,this paper developed a three-wavelength(785 nm,808 nm and 830 nm),240-channel(20 source points×12 detection points)high-sensitivity,high-density(HD)fNIRS system.It combines the high-sensitivity and large dynamic range of photon counting measurement with the parallelization advantages of locked-in detection,and can effectively realize the brain functional imaging scheme based on DOT principle.For the development of the above HD-fNIRS system and the implementation of DOT measurement scheme,this paper mainly completed the following contents:Firstly,the locked-in photon-counting module was designed based on locked-in photon-counting technology in the system design.It can be used to complete the demodulation and separation of the light source signals under the parallel measurement scheme.The light intensity automatic adjustment module was designed by using the feedback adjustment scheme.Secondly,this paper also designed a man-machine interactive platform.It can realize the automatic control of the HD-fNIRS system,cooperating with other functional modules.In order to verify the reliability of the developed HD-fNIRS system,a series of systematic assessments were conducted,demonstrating appealing performances in linearity,stability,inter-channel crosstalk.According to the experimental results of the multi-source inter-channel crosstalk evaluation,a parallel scanning scheme of light sources was designed.And different scanning modes are developed based on this scanning scheme to match various excitation paradigms in the in vivo experiment.Furthermore,a series of phantom experiments,including static imaging experiments and dynamic imaging experiments,were carried out to validate the imaging capability of the system under the DOT parallel measurement scheme.The ability of the system to locate the brain excitation and track the dynamic changes of optical parameters was preliminarily verified,reflecting its potential for in vivo research and clinical applications in the future.