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

研究人体内的输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，使用近红外（NIR）光的血流动力学的无创监测已经获得关注。近红外光在生物组织中扩散传播，其吸收光谱随血氧变化而变化。这些允许我们使用漫射光学断层扫描（DOT），其可以说明组织内血红蛋白浓度的空间分布。本研究的目的是揭示血液动力学在大脑和肌肉的DOT。简单的DOT系统使用连续光可以生成断层图像时，通过对象的透射光是可检测的。然而，当由于对象的大尺寸而无法检测透射光时，难以仅从反射光的数据获得图像。皮秒时间分辨测量使得可以从反射光获得断层图像。本文尝试了利用皮秒时间分辨测量系统对反射型DOT进行成人脑血流动力学监测，并对相关问题进行了讨论，主要研究成果如下：（1）通过数值模拟和活体实验证明，在透射光不可探测的成人头部等大物体的情况下，皮秒时间分辨测量系统可以获得反射型DOT图像。(ii)据发现，附着在受试者皮肤上的源-检测器光纤的位置的精确测量对于高质量成像是必不可少的。(iii)在计算任务中获得额叶氧合和血容量的DOT图像。(iv)发现使用反射光数据的光学映射受头部结构的影响，特别是受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.