A Laminar Optical Tomography With Small Tilt Angle For Early Cervical Cancer Detection

Laminar optical tomography(LOT)is an emerging optical imaging system which can achieve high resolution.It is a combination of the optical structure of the confocal laser scanning optical microscopy and the image reconstruction principle of the diffuse optical tomography.In traditional LOT,the angles between the incident light as well as the returned chief light and the optical axis vary with the scanning coordinates.However,the light source model of the reconstruction algorithm of forward model doesn't change with the angle.The mismatch between the experiment model and the forward model will increase the error of image reconstruction.The purpose of this paper is to solve above problems on the premise that not to reduce the scanning speed and to modify the original optical system least.Following investigations have been conducted in this thesis:(1)With simulation,we analyze the influence of tilt angle on the distribution of light in medium,the emission light at small and large source-detection-separation,and the reconstructed absorption coefficient.(2)We have designed and built the LOT system with small tilt angle on the basis of the existing system.(3)We have proved that the developed system can improve the verticality of the incident light as well as the returned light to the detection surface by both simulation and experiments.Both simulation validation and experimental results show that the developed LOT can reduce the angle between the incident light and the normal of the detection plane to half of the traditional LOT and the angle between the returned light and the normal turns to be 1/10 of the original one.(4)An experiment is implemented and the results show that the resolution of the system reaches at least 350 micrometer under the depth of 0.5 mm.Phantom was designed for 3D image reconstructions.Results show that difference between the reconstructed absorption coefficient and the real is within 8%.The results also show that quantitative ratio of optical parameters is high and the reconstructed position and shape of the phantom match the real situation very well.The limit of absorption contrast that can be resolved by the system is verified which the feasibility of LOT to be used in detecting early cervical cancer.(5)Image experiments were also conducted on in vitro cervical tissue.The research results of this paper have significance for improving the in vivo non-invasive diagnosis of early cervical cancer.