Fast calculation of tissue optical properties using MC and the experimental evaluation for diagnosis of cervical cancer

摘要

This article aims at the development of the fast inverse Monte Carlo (MC) simulation for the reconstruction of optical properties (absorption coefficient μ_a and scattering coefficient μ_s) of cylindrical tissue ~([1]), such as a cervix, from the measurement of near infrared diffuse light on frequency domain. Frequency domain information ( amplitude and phase ) is extracted from the time domain MC with a modified method. To shorten the computation time in reconstruction of optical properties, efficient and fast forward MC has to be achieved. To do this, firstly, databases of the frequency-domain information under a range of μ_a and μ_s were pre-built by combining MC simulation with Lambert-Beer's law. Then, a double polynomial model was adopted to quickly obtain the frequency-domain information in any optical properties. Based on the fast forward MC, the optical properties can be quickly obtained in a nonlinear optimization scheme. Reconstruction resulting from simulated data showed that the developed inverse MC method has the advantages in both the reconstruction accuracy and computation time. The relative errors in reconstruction of the μ_s and μ_a are less than ±6% and ±12% respectively, while another coefficient (μ_a or μ_s ) is in a fixed value. When both μ_a and μ_s are unknown, the relative errors in reconstruction of the reduced scattering coefficient and absorption coefficient are mainly less than ±10% in range of 45<μ_s <80 cm"1 and 0.25<μ_a <0.55 cm~(-1). With the rapid reconstruction strategy developed in this article the computation time for reconstructing one set of the optical properties is less than 0.5 second. Endoscopic measurement on two tubular solid phantoms were also carried out to evaluate the system and the inversion scheme. The results demonstrated that less than 20% relative error can be achieved.