Spatial frequency domain (SFD) imaging offers a wide-field modality to effectively characterize the optical properties (absorption and scattering coefficients), and furthermore to calculate the chromophore concentrations from multiwavelength measurements, in biological tissues. Previous SFD imaging systems mostly capture the two-dimensional reflected light using an expensive charge-coupled device camera that requires switching between the multi-wavelength collections. With recent proliferation in low-cost and technology we present herein a highly-sensitive novel single-pixel SFD imaging system for simultaneous and acquisition of multi-wavelength images. In the approach, three LED-sources at 455-nm, 530-nm and 660-nm wavelengths are temporally modulated at different frequencies, and all focused to the first digital micromirror device (DMD) to generate a wide-field sinusoidal illumination on tissues. The reflected signal is spatially integrated by the second DMD that is coded according to the transform matrix, and fed into a lock-in photoncounting module and temporally demodulated to extract the signals at each wavelength. The SFD 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. The proposed system is experimentally validated on phantoms, demonstrating the system stability, measurement linearity, negligible inter-wavelength crosstalk, and recovery effectiveness.
Photodynamic therapy (PDT) has shown superiorities of noninvasiveness and high-efficiency in the treatment of early-stage skin cancer. Rapid and accurate determination of spatially distributed photon fluence in turbid tissue is essential for the dosimetry evaluation of PDT. It is generally known that photon fluence can be accurately obtained by Monte Carlo (MC) methods, while too much time would be consumed especially for complex light source mode or online real-time dosimetry evaluation of PDT. In this work, a method to rapidly calculate spatially distributed photon fluence in turbid medium is proposed implementing a classical perturbation and iteration theory on mesh Monte Carlo (MMC). In the proposed method, photon fluence can be obtained by superposing a perturbed and iterative solution caused by the defects in turbid medium to an unperturbed solution for the background medium and therefore repetitive MMC simulations can be avoided. To validate the method, a non-melanoma skin cancer model is carried out. The simulation results show the solution of photon fluence can be obtained quickly and correctly by perturbation algorithm.
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