Biological observation with fluorescent X-ray CT

在当前的生物医学研究中，分子成像需要创新高对比度、高空间分辨率的新成像技术。平面模式下的荧光x射线技术是检测picogram数量级的大原子序数微量元素最灵敏的方法之一。然而，试样必须切成薄片，并用垂直于其表面的光束进行扫描。本文描述的荧光x射线CT （FXCT）方法结合了荧光x射线技术的灵敏度和CT的横截面描述。在这里，我们描述了体内FXCT成像和相关的实验结果。FXCT系统由一个硅（111）双晶单色仪、一个x射线狭缝系统、一个扫描台、两个高纯锗（HPGe）探测器和pin-二极管探测器组成。实验是在日本筑波的特里斯坦堆积环的弯曲磁束线上进行的。单色x射线能量设置为37keV，入射单色x射线准直成1 x 0.1mm^2的铅笔束，活体标本准直成1 x 0.2 mm^2的铅笔束，病理标本准直成0.5 x 0.2 mm^2的铅笔束。每个扫描步骤的数据采集时间设置为5秒。用FXCT以1mm空间分辨率和0.1 mm切片厚度清晰成像活体小鼠脑内I-127标记的IMP。透射x线CT显示颅骨几何结构，可与FXCT同时获得，便于了解解剖位置对应的功能变化。因此，在国际上首次成功实现了脑灌注的活体FXCT成像。FXCT可显示仓鼠离体脑内1-127 IMP和心肌内BMIPP的分布。因此，FXCT在体内和离体成像的成功，为生物成像研究开辟了新的途径。

In recent biomedical research, the innovation of the new imaging techniques with high-contrast and high-spatial resolution is required for molecular imaging. Fluorescent x-ray technique used in the planar mode is one of the most sensitive methods for detecting trace elements of large atomic numbers in the order of picogram. However, the specimen must be cut into thin slices and be scanned with a beam perpendicular to its surface. Fluorescent x-ray CT (FXCT) method described here combines the sensitivity of fluorescence x-ray technique and the cross-sectional description of CT. Here, we describe the in-vivo FXCT imaging and related experimental results.FXCT system consists of a silicon (111) double crystal monochromator, an x-ray slit system, a scanning table, two high purity germanium (HPGe) detectors, and pin-diode detectors. The experiment was carried out at the bending-magnet beam line of the Tristan accumulation ring in Tsukuba, Japan. Monochromatic x-ray energy was set 37keV, The incident monochromatic x-ray was collimated into a pencil beam of 1 x 0.1mm^2 for the live objects, and less than 0.5 x 0.2 mm^2 for the pathological specimens, respectively. The data acquisition time was set 5 sec for each scanning step.I-127 labeled IMP inside the brain of a live mouse was clearly imaged by FXCT at a 1 mm spatial resolution and a 0.1 mm slice thickness. Transmission x-ray CT that demonstrate geometrical structure of skull, can be simultaneously obtained with FXCT, so the anatomical position corresponding functional changes can be understood easily. Thus, in-vivo FXCT imaging of cerebral perfusion has succeeded for the first time in the world. FXCT could reveal the distribution of 1-127 IMP within ex-vivo brain and BMIPP within myocardium of hamster. Thus, the success of FXCT imaging at in-vivo and ex-vivo, allows starting new approach to bio-imaging research.