Biological observation with fluorescent X-ray CT

在现代生物医学研究中，分子成像需要高对比度和高空间分辨率的成像技术。平面模式的X射线荧光技术是检测皮克量级大原子序数微量元素的最灵敏的方法之一。然而，样品必须被切成薄片，并用垂直于其表面的光束进行扫描。本文所述的荧光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。FXCT系统由硅（111）双晶单色器、X射线狭缝系统、扫描平台、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积累环的弯曲磁铁束线上进行的。单色X射线能量设置为37 keV，入射单色X射线分别准直成1 x 0.1 mm^2的笔形射束（用于活体）和小于0.5 x 0.2 mm^2的笔形射束（用于病理标本）。每个扫描步骤的数据采集时间设定为5秒，用FXCT以1 mm的空间分辨率和0.1 mm的层厚清晰地成像活小鼠脑内的I-127标记IMP。透射X线CT能同时显示颅骨的几何结构，与FXCT同步进行，便于了解颅骨的解剖位置和相应的功能变化。因此，脑灌注的体内FXCT成像在世界上首次获得成功。FXCT可显示1-127 IMP在离体仓鼠脑内的分布和BMIPP在离体仓鼠心肌内的分布。因此，FXCT成像在体内和体外的成功，允许开始新的方法来进行生物成像研究。

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.