Research And Development Of A Brain Function Imager Based On Digital Lock-in Photon Counting

Based on functional near infrared reflectance spectroscopy(fNIRS),the brain function imager using high density diffuse optical tomography(HD-DOT)is developed,which is the main research and clinical tool for brain activity investigation.Compared with electroencephalogram(EEG)and functional magnetic resonance imaging(fMRI),HD-DOT has the advantages of being able to measure under natural conditions,simplicity,non-invasion,portability,cost-effection,and reasonable spatial-temporal resolution.So it is excellent for cognitive neuroscience research,the cause of internet addiction,the analysis of neurological etiology and curative effect.Most current imagers with analogue detection are limited by sensitivity and dynamic range.Although photon counting detection can improve detection sensitivity significantly,the intrinsic nature of sequential excitations reduces temporal resolution.To obtain HD-DOT imager with high sensitivity,large dynamic range and high temporal resolution,we develop a three-wavelength multi-channel continuous-wave(CW)imager for brain function imaging based on a novel lock-in photon counting technique with square wave mode.The imager consists of 48 Laser Device(LD)sources,a high sensitivity detection array and an automatic signal processing module combined field programmable gate array(FPGA)and LabVIEW.Thereinto,the LD sources array at three wavelengths of 785,808 and 830 nm,which are modulated by current-stabilized square-wave signals at different frequencies,and adjusted automatically by programmable digital rheostat.And the detection array is composed of 9 photon-counting photomultiplier tubes(PMT).This imager combines the ultra-high sensitivity of the photon counting technique with the simplicity parallelism of the digital lock-in technique under square wave modulation mode.The performance assessment of the imager was conducted using phantom experiments,and demonstrate its excellent measurement linearity(correlation coefficient was 0.9989),stability,negligible inter-channel crosstalk,strong noise robustness.In addition,the two layer phantom experiment using the scheme of 7-time excitation was done to prove that the imager has the ability to locate the position,describe the shape of the target accurately,and distinguish the targets with different absorption contrasts.