Optical Characteristics of Tissue and its Application for Optical CT

在医学领域，光学CT有望成为一种安全、便携的获取组织功能图像的方法。因此，在可见光和近红外光区，主要是由血红蛋白引起的吸收，而血红蛋白的吸收光谱由于氧化而发生变化。然而，由于光在组织中的强烈散射，很难区分吸收信息。首先估计组织样品的光学参数，然后研究光子在散射介质中的传播，最后估计CT图像。对于光学参数的估计，使用100 MHz的幅度调制的激光作为光源，然后测量不同厚度样品的入射光和透射光的幅度比和相位。通过这些实验，我们计算了血液、肌肉、脂肪和脂内混悬液的吸收系数、散射系数和各向异性参数。为了进行理论分析，计算机模拟的是Car…更详细地介绍了基于辐射输运理论的蒙特卡罗方法。为了实现光学CT，我们利用计算机控制的CCD摄像机搭建了实验系统，通过法布里-珀罗滤光片获得卤素灯的光通量。我们检测来自体模的散射光作为背向投影数据，并重建图像。在我们的研究中，光在人体组织中被认为是完美的散射，因此反投影数据被认为是来自体模近表面的数据。通过使用基材中具有与组织相同散射系数的吸收棒的体模进行的实验，可以分辨出体模表面以下小于3 cm处的吸收目标。用血红蛋白溶液作为吸收体的实验表明，重建的图像随波长的变化而变化；测量了血液和血红蛋白溶液的散射光的角分布，估计了光学各向异性参数。基础研究表明，在距组织表面不到3 cm的距离内，完全散射光可以获得CT图像，但利用血红蛋白的吸收特性实现血氧饱和度图像还存在许多问题。较少

In the medical field, optical CT is expected as a safe and portable methos to get functional image of tissue. Therefore in visible and near infrared light region, absorption is caused mostly hemoglobin, and the absorption spectrum of hemoglobin changes due to oxidization. However it is very difficult to distinguish absorption information, because of strong scattering of light in tissue. At first, we estimated optical parameter of tissue sample, second we investigated the photon propagation in scattering medium, and third we estimated CT image.For the estimation of optical parameter, laser beam amplitude-modulated at 100MHz was used as light source, then measured an amplitude ratio and phase between incident beam and transmitted beam through samples of various thickness. From those experiment we evaluated absorption coefficients, scattering coefficients and anisotropic parameters of blood, muscle, fat and the suspension of intralipid. For theoretical analysis computer simulation was car … More ried out by Monte Carlo method based on radiative transport theory. This results agree with results of phantom experiment.To realize optical CT,we set up experimental system using computer controlled CCD camera and light flux from halogen lamp through Fabry-Perot optical filter. We detected scattered light from phantom as back projected data, and reconstructed images. For our research light is considered as perfect scattering in human tissue, so back projected data is regarded as data from near surface of the phantom. From the experiment using the phantom which had absorbing rods in base material of the same scattering coefficient as tissue, the absorption target at less than 3cm below the surface of the phantom could be distinguished. Experiment using hemoglobin solution as absorber shows that the reconstructed image changed with the change of wavelength.We also measured angular distribution of scattered light from blood and hemoglobin solution to estimate optical anisotropic parameter.From our fundamental study, and it is shown that at less than 3cm blow from the surface of tissue it is possible to get CT image by perfect scattering light, however many problems are remained to realize the image of oxygen saturation which utilize absorption characteristics of hemoglobin. Less