Study of oxygen transport in tissue using reflection type diffuse optical tomography

研究人体内的转运现象对于理解生物体内复杂的生理机制至关重要。近年来，利用近红外（NIR）光对血流动力学进行无创监测越来越受到人们的关注。近红外光在生物组织中扩散传播，其吸收光谱随血液氧合变化。这使得我们可以用漫射光学断层扫描（DOT）来说明组织内血红蛋白浓度的空间分布。本研究旨在揭示DOT对脑和肌肉血流动力学的影响。使用连续光的简单DOT系统可以在穿透物体的透射光可检测时生成层析图像。然而，由于物体体积大，透射光无法检测，仅从反射光数据获取图像是很困难的。皮秒时间分辨测量使得从反射光获得层析图像成为可能。我们尝试使用皮秒时间分辨测量系统，用反射型DOT监测成人大脑的血流动力学，并讨论了相关问题。本研究的主要成果如下：(1)通过数值模拟和体内实验证明，在透射光无法通过成人头部等大物体的情况下，利用皮秒时间分辨测量系统可以获得反射型DOT图像。（二）发现，精确测量附着在受试者皮肤上的源探测器光纤的位置对于高质量成像至关重要。（iii）计算过程中获得额叶氧合和血容量的DOT图像。㈣发现利用反射光数据进行光学测绘受到头部结构，特别是脑脊液和颅骨层的影响。

Study of transport phenomena in human body is essential to understand the complex physiological mechanisms in living organisms. In recent years, noninvasive monitoring of hemodynamics using near infrared (NIR) light has been gaining the attention. NIR light diffusively propagates through biological tissues, and its absorption spectrum varies with blood oxygenation. These allow us Diffuse Optical Tomography (DOT) which can illustrate the spatial distribution of the hemoglobin concentrations within the tissues. This study intended to unveil the hemodynamics in the brain and muscles with DOT.Simple DOT systems using continuous-light can generate tomographic images when transmitted light through the object is detectable. However, it is difficult to obtain images only from the data of the reflected light when the transmitted light is undetectable due to the large size of the object. Pico-second time resolved measurement makes it possible to obtain tomographic images from reflected light. We attempted to monitor the hemodynamics in an adult brain with reflection-type DOT using a pico-second time-resolved measurement system, and discussed the related issues as well.The major achievements of this study are as the following :(i) It is proven by the numerical simulation and in vivo experiments that reflection-type DOT images can be obtained by a pico-second time resolved measurement system in the case of large objects such as an adult head through which the transmitted light is undetectable. (ii) It is found that the precise measurement of the positions of the source-detector optical fibers attached on the skin of the subject is essential for high-quality imaging. (iii) The DOT images of the oxygenation and blood volume in frontal lobe during calculation tasks were obtained. (iv) Optical mapping using the reflected light data is found to be affected by the structure of the head, especially by the cerebrospinal fluid and the skull layers.