Establishment and application of analysis of brain function by nera-infra-red light computed tomography : Estabalishment of functional light computed tomography

使用大阪大学蛋白质研究所的近红外光计算机断层扫描(NIRCT)，只有用不含血红蛋白的人造血浆置换血液后，才能获得缺血条件下大鼠脑的图像。然而，如果不用人工血浆置换血液，则无法获得清晰的脑图像，分辨率低至10 mm。解决《禁止酷刑公约》后的技术进步使以下改进成为可能。即：1)用690 nm激光分别测定血红蛋白和细胞色素氧化酶AA_3；2)对包括准直器在内的检测系统进行改造，采用考虑光散射的分析方法，为提高灵敏度和分辨率提供了可能。因此，在本研究中，我们试图通过采用考虑光散射的新的准直系统和分析方法来改进我们的NIRCT。在使用含有吸收近红外光的物质的模体的实验中，改进后的NIRCT的分辨率提高到3 mm。此外，在动物实验中，我们可以检测到注射在大鼠大脑局部的一种染料的吸收，并检测到癫痫灶区域的血红蛋白含量增加，这是通过将FeCl3注入侧脑室而不用上述人工血浆置换血液而造成的。后一个事实表明，在癫痫灶区域，血液循环增加。在未来，我们希望建立一个功能强大的CT系统，能够更有效地检测局部脑区血容量和活动的变化。

Using nera-infrared light computed tomography (NIRCT) settled in the Institute for Protein Research, Osaka University, imagings of rat brain under ischemic conditions were obtained only after displacing the blood with artificial plasma which did not contain hemoglobin. However, without displacing the blood by the artificial plasma clear image of the brain could not be obtained and the resoltion was as low as 10 mm. Technological advancement after settling of the NIRCT made following improvements possible. That is, 1) using 690nm laser light it became possible to determine hemoglobin and cytochrome oxidase aa_3 separately, 2) the reform of the detection system including collimator and adopting the analysis considering the light scattering presented a possibilty to improve sensitivity and resolution. Therefore, in this research we tried to improve our NIRCT by adopting the new collimation system and analysis method considering light scattering. In the experiment using phantoms containing a substance which absorb near-infrared light, the resolution of this reformed NIRCT was improved to 3 mm. Furthermore, in animal experiments we could detect the absorption of a dye which was injected in the localized part of the rat brain, and detected an increase in the content of hemoglobin in the area of epileptic focus which was made by administering FeCl_3 into the lateral cerebral ventricle without displacing the blood with the above artificial plasma. The latter fact suggests that in the area of the epileptic focus the blood circulation increases. In future we would like to establish a functional CT system which can detect changes in blood volume and activity in the local brain area more efficiently.