Development of high-speed fluorescent X-ray CT system

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。由于FXCT可以检测少量的重原子序数元素如碘，本课题组一直在开发用于分子成像的FXCT系统。在这里，我们描述了用于体内FXCT成像的高速FXCT系统的发展。FXCT系统由硅（220）双晶单色仪、x射线狭缝系统、扫描台、高纯锗（HP-Ge）探测器和pin-二极管探测器组成。为实现高速数据检测，研制了3通道型HP-Ge探测器。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射线能量设为37keV。入射的单色x射线被准直成一个铅笔束，活的物体为0.5 x 0.5mm^2，幻像和病理标本分别小于0.5 x 0.2 mm^2。每个扫描步骤的数据采集时间设置为5秒。在基础幻体实验中，在28keV的能量下，每个通道的能量分辨率约为290-310 eV。利用片束曝光法，从康普顿散射x射线中清晰地分离出碘的能谱。用FXCT以0.5 mm的空间分辨率和0.5 mm的切片厚度清晰地成像活体小鼠脑内1-127标记的IMP。透射x线CT显示颅骨的几何结构（颅骨及其周围软组织），可以与FXCT数据同时获得。这样，就可以很容易地了解解剖位置对应的功能变化。目前，由于来自物体的高光子通量导致死区时间明显增加，导致检测器系统的电子元件（ADC）过载，使得该FXCT系统不足以进行高速成像。少

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. Since FXCT can detect small amount of heavy atomic number element as iodine, our group has been developing FXCT system for molecular imaging. Here, we describe the development of high-speed FXCT system for in-vivo FXCT imaging.FXCT system consists of a silicon (220) double crystal monochromator, an x-ray slit system, a scanning table, highly purity germanium (HP-Ge) detector, and pin-diode detectors. To perform h … More igh-speed data detection, 3 channel-type HP-Ge detector was manufactured. 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 0.5 x 0.5mm^2 for the live objects, and less than 0.5 x 0.2 mm^2 for the phantom and pathological specimens, respectively. The data acquisition time was set 5 sec for each scanning step.In the fundamental phantom experiment, energy resolution of each channel was about 290-310 eV at the energy of 28keV. Using sheet beam exposure for phantom, energy spectrum of iodine was clearly separated from Compton scattering X-ray. 1-127 labeled IMP inside the brain of a live mouse was clearly imaged by FXCT at a 0.5 mm spatial resolution and a 0.5 mm slice thickness. Transmission x-ray CT that demonstrate geometrical structure of skull (skull bone, and surrounding soft tissue), can be simultaneously obtained with FXCT data. Then, the anatomical position corresponding functional changes can be understood easily. Now, this FXCT system is not sufficient to perform high speed FXCT imaging because high photon flux from object caused the significantly increased dead-time, and overflowed the electronics (ADC) of detector system. Less