Research On Several Key Technologies In Multi-wavelength Transillumination Of Biological Tissue

The transillumination of biological tissue has enough capacity for development by virtue of its advantages of real-time,non-invasive,low-cost,quick and convenient.However,due to the strong scattering,there has not been a widely used device based on transillumination in clinic.The strong scattering causes poor quality of transmission images,and restricts positioning of heterogeneity.Aim at the problems,we propose method of dimensionality reduction to rapid extract location information of heterogeneity,and reduce the influence of single LED on image quality.In view of the development of high power monochrome LED and the sensitivity of image sensor,we adopt the transillumination with multi-wavelength LEDs to acquire the clearer images and the more accurately positioning.The shaped-function signal is combined with frame accumulation to improve the gray resolution of images.And an optimum method adopt mutual assistance between the multi-wavelength LEDs to extend the dynamic range of transillumination system.The main contents of this thesis are follows:The application of transillumination for biological tissue in tumor screening needs to extract the location information of heterogeneity.Therefore,the method of dimension reduction for extraction the location of heterogeneity in tissue is proposed.According to the changes of the transmitted light intensity distribution curve observed by dimensional reduction method,the heterogeneity location information is extracted.Due to the influence of the position of source on the extraction of structural information,the sources are located at the multi-position to improve the extraction accuracy of the heterogeneity.Image fusion is carried out to highlight the heterogeneity.Firstly,the positional features of heterogeneity in multi-wavelength transmitted images are fused to improve positioning accuracy.Secondly,a fusion method of transmitted images is proposed based on the advantage of the information of each wavelength.The images are fused in accordance with the information of the low,intermediate and high frequency.The fusion rules and weighting factors are determined by the quality,gray reso lution and noise of the images.The fusion image improves its positioning accuracy to provide the images for tumor examination.In the transillumination system,an optimum method combined the shaped-function optical signal with the frame accumulation technique,effectively reduces the quantization noise,improves the gray resolution and increases the information of images.Compared with the equal amplitude of DC optical signal,the shaped-function optical signal reduces the radiation intensity received by the tissue per unit area per unit time.According to the response curve of image sensor,an optimization method of multi-wavelength source mutual assistance is proposed to extend the dynamic range of the transillumination system.The LED at higher camera-sensitivity area is used as the auxiliary source.The photoelectric conversion is within the linear response zone through the auxiliary source with low intensity.Thus the undetected signal can be detected and the accuracy of quantization values be improved.The experimental results show that the method improve the quality,the gray resolution of images and the accuracy of information.The Monte Carlo simulation for transmission model is studied.Firstly,considering the number of photon in simulation,an effective selection criterion is presented.It is concluded through the relationship between the simulation accuracy,geometry parameters,optical properties of tissue and the photon number.Secondly,we develop a method to optimize the MC simulation for modeling light transmission received by a fiber with the source and the receiver aligned in a straight line.It is to simplify the calculation of scattering direction and increase the constraint conditions.It improve the simulation speed and save the simulation time.