Fast Energy Subtraction Using Fluorescent X-Rays Excited by Synchrotron Radiation

利用日本筑波6.5GeV同步辐射储存环研制了一种用于K边减影成像的快速开关双能荧光X射线源。荧光X射线源由一个直径为25 mm的圆柱形旋转靶框组成，其上以1 mm的距离连接一对宽度为2 - 5 mm的金属靶条。目标的表面在入射光束与光束轴相交的两个点处与入射光束成45度角。每次来自偏转磁体的入射白色x射线束（准直至1 mm × 1 mm）照射一对靶材料时，在120 rpm的旋转速率下以约10 msec的时间间隔产生两种不同能量光子的荧光x射线。通过改变靶材料可以产生范围从约20 keV到75 keV的荧光x射线。在碘造影剂的情况下，分别具有32.2和34.7 keV K X射线能量的来自Ba和De的荧光X射线可以用于具有33.17 keV的K吸收边缘的碘的K边缘减法。在钆的情况下，来自Ho和Yb的荧光X射线，分别具有47.5和52.4 keV的K X射线能量，可用于50.23 keV的钆K边缘。含有碘造影剂的体模用于K边缘能量减影对象。利用像增强器和电视系统获得的K吸收边上下两幅图像相减，得到增强的对比材料图像。目前，光子强度不足以对人体成像。由同步辐射产生的高强度荧光X射线将用于诊断放射学，例如单色射线CT、K边缘减影成像、高分辨率放大放射照相术和其他医学应用。

A fast switching dual-energy fluorescent x-ray source for K-edge subtraction imaging has been developed using a 6.5 GeV synchrotron radiation storage ring at Tsukuba (KEK). The fluorescent x-ray source is composed of a cylindrical rotating target border of 25mm in diameter on which a pair of metal target strips of 2 - 5 mm in width are attached at a distance of 1mm apart. The surface of the target is angled at 45 degrees to the incident beam at the two points where it crosses the beam axis. At each time the incident white x-ray beam from the bending magnet, collimated to 1mm x 1mm, irradiates a pair of target materials, fluorescent x-rays of two different energy photons are generated at time intervals of about 10 msec at the rotation rate of 120 rpm.Fluorescent x-rays, which range from about 20 keV to 75 keV can be generated by changing the target materials. In case of iodine contrast medium, fluorescent x-rays from Ba and De, having 32.2 and 34.7 keV K x-ray energies respectively, can be used for K-edge subtraction of iodine which has K absorption edge of 33.17 keV. In case of gadolinium, fluorescent x-rays from Ho and Yb, having 47.5 and 52.4 keV K x-ray energies respectively, can be used for gadolinium K-edge of 50.23 keV.A phantom which contains iodine contrast medium is used for K-edge energy subtraction subject. By taking subtractions between two images above and below each K absorption edge, which are obtained by using an image intensifier and TV system, enhanced contrast material images are obtained.At present, the photon intensity is not sufficient for imaging of human subjects. High intensity fluorescent x-rays generated by synchrotron radiation will be useful for diagnostic radiology such as monochromatic-ray CT, K-edge subtraction imaging, high resolution magnification radiography, and other medical applications.