Study Of Spatially Resolved Diffuse Reflectance Of Small And Highly Absorbing Tissues

Noninvasive or minimally invasive measuring technique based on spatially resolved diffuse reflectance has a broad prospect for application. On one hand, tissue optical properties, such as scattering coefficient and absorption coefficient, can be extracted from diffuse reflectance by use of the analytic or numerical model. These optical properties are significant for diagnostic and therapeutic medicine. For example, the optimizing beam energy and photosensitize dose can be chosen with knowledge of tissue optical properties. On the other hand, spatially resolved diffuse reflectance measurements also can be used as an Optical Biopsy method to make a preliminary diagnostic for the disease. However, spatially resolved diffuse reflectance technique is based on diffuse approximation (DA) theory model is failure to describe the reflectance in the region close to the source, so it can not be applied for measurement of small and highly absorbing tissues, such as skin, mucosa and local tissue.The optical properties of small and highly absorbing tissues can be achieved by measurement of spatially resolved diffuse reflectance at short source-detector separations. To determine the optical properties, in this paper we have studied spatially resolved diffuse reflectance in the region close to the source and the works are summarized as blow.1. Influence of high-order parameters on spatially resolved diffuse reflectance is studied. The analytical expressions of sensitivities are derived from P3 approximation theory, and the complexity of diffuse reflectance close to the source is analyzed theoretically and discussed. The results show that the diffuse reflectance has very close relation with the high-order parameters. By comparison with Monte Carlo(MC)simulations, the result shows that the high-order parameters influence the diffuse reflectance close to the source by effective source terms.2. A fiber probe is designed for the use of measuring the spatially resolved diffuse reflectance of small and highly absorbing tissues. This probe is a fiber array including 12 standard fibers (62.5/125um,N.A.=0.275) and 1.5mm long, with two of which are used as illuminating fibers to illuminate the tissue and six of others are used as collecting fibers, and the other fibers are only used as filling materials. The transmittance differences of probe channels are corrected by measuring the light emitting from integrating-sphere uniformly.3. Single fiber probe and fiber array probe system are designed for measurement of spatially resolved diffuse reflectance close to the source. Tissue phantom—Intralipid is measured. By comparing with MC simulation, the reflectance data errors of single fiber probe system is tested to be considerable, and the result of fiber array probe system is tested to be well agree with that of MC simulation. Fiber array probe can measure spatially resolved diffuse reflectance in the region 0.125mm-1.25mm (resolution is 0.125mm) from the source by employing only one detector and two optical switches.4. A method for determining the optical properties of small and highly absorbing tissues from spatially resolved diffuse reflectance based on MC model is studied. In this method, MC database and artificial neural network are founded. By measuring strong absorption tissue phantom, the results show that experiment technique of measuring tissue optical properties by spatially resolved diffuse reflectance at short source-detector separations is feasible.