Improvement Of The Frequency-domain Inverse Monte Carlo Simulation

Measurement of near infrared diffuse light on frequency domain is a new technology for the diagnosis of early cervical cancer. Measurement of near infrared diffuse light on frequency domain is a new technology for the diagnosis of early cervical cancer. Diagnosis with NIR light produces no physical damage to biological tissues because it employs as a probing source, a near-infrared radiation in the range between 600 and 900 nm [1]. Until now, FD system has been almost the typical facility for endoscopic diagnosis using NIR light, e.g. in the detection of early cancer of cervix.Concerning the structure of and the large-scale optical properties of cervix, in this paper, MC has to be adopted for describing the forward model of photon migration in tissue. This article aims at the optical property (absorption coefficient and scatter coefficient) reconstruction from the frequency-domain (FD) near-infrared diffuse measurement on a cervix, for which inverse Monte Carlos (MC) simulation is the suitable choice. To achieve the fast and accurate reconstruction based on the inverse Monte Carlo simulation, following techniques were adopted. First, in the forward calculation, a database, which includes the frequency-domain information calculated from MC simulation for a series of optical parameters of tissue, was established with fast methods. Then, in the reconstruction procedure, Levenberg-Marquardt (L-M) optimization was adopted and Multiple Polynomial Regression (MPR) method was used to rapidly get the FD information at any optical properties by best fitting the curved surface formed by the above database. At Last, in the reconstruction, to eliminate the influence of the initial guess of optical properties on the reconstruction accuracy, cluster analysis method was introduced into L-M reconstruction algorithm to determine the region of the initial guess. The reconstruction algorithm was demonstrated with simulation data and measurement data. Simulation results showed that the relative errors ofμ_a derivation are less than 2% and those ofμsare less than 5% for the optical properties of normal and abnormal cervical tissue. It takes less than 0.5s to reconstruction one set of optical properties. Endoscopic measurements on three tubular solid phantoms were also carried out to evaluate the system and the inverse algorithm.