A Multi-wavelength,Single-pixel Spatial Frequency Domain Imaging System Based On Lock-in Photon-counting Detection

Spatial frequency domain imaging(SFDI)relies on spatial modulation technology of light to project spatially modulated illumination patterns onto the tissue surface and capture reflectance images with array detector or other imaging technique.The optical properties of tissue can be reconstructed by the spatial frequency domain demodulation algorithm and optical transmission model.SFDI is emerging as a new method in biomedical optical imaging which can provide a rapid,large-field,quantitative evaluation of the tissue.Conventional SFDI systems have certain limitations and shortcomings.First of all,the measurement under the excitation of multi-wavelength source can only be realized by time serial method,that is,switching between the wavelengths.Conventional camera could be used as detector in SFDI,it is necessary to increase the power of incident source.The high-power light source is not suitable in biomedical measurement.In addition,the camera is not conducive to the promotion due to price of camera.We present a highly-sensitive novel single-pixel SFDI system for acquiring multi-wavelength images simultaneously.The system we present herein combined the lock-in photon-counting based on time-modulated and single-pixel imaging based on two-dimensional discrete cosine transform.In the approach,three sources are temporally modulated at different frequencies,and all focused to the first digital micromirror device(DMD)to generate a wide-field sinusoidal illumination on the tissue.The reflected signal is spatially integrated by the second DMD that is coded according to the two-dimensional discrete cosine transform matrix,and fed into photomultiplier tube(PMT).Electrical pulse signal from PMT is temporally demodulated to extract the signal at each wavelength by a lock-in photon-counting module.The spatially modulated reflectance images at each wavelength are recovered by single-pixel imaging algorithm,respectively,and then used to calculate the modulation transfer function for extraction of the optical properties.To evaluate the performance of the system,the system performance evaluation and imaging experiments were conducted.Performance evaluation experiments show that the system can acquire multi-wavelength images simultaneously,and the system has good stability and negligible crosstalk.Imaging experiments demonstrate that the system has satisfactory resolution and localization ability for heterogeneous targets.