The development of monochromatic X-ray computed tomography with synchrotron radiation

在生物医学诊断方面，一种新的同步辐射单色X射线CT系统正在研制中，该系统是在Tristan积累环NE-5A（6.5GeV，20 - 30 mA）的束线上建造的。该系统由旋转X光快门、硅（111）和硅（511）双单色器、X光狭缝系统、旋转载物台、X光线阵传感器系统和计算机组成。该系统可获得能量为30 ~ 52 keV的X射线图像，用于检测各种造影剂（碘、钡、钆）。X射线线阵传感器由BGO晶体管和硅光电二极管阵列组成。系统的动态范围为60000：1，空间分辨率为200 μ m。图像数据经16位A/D转换器数字化后送入计算机。每个投影的曝光时间可以从3 ms到更长。使用狭缝系统，物体的切片厚度也可以在0.1至3.2 mm之间调节。利用X射线线阵探测器获得的线阵数据，在UNIX工作站上重建SR-CT图像。该工作站利用图形加速板进行高速图像重建，利用双晶单色器消除了高次X射线污染。一种新的CCD探测器在传感器的连接处出现了一些问题，从而产生了伪影。由于1994年AR环发生机械故障，该系统的实验不能充分进行。详细的实验将于1995年进行。

For biomedical diagnosis, a new monochromatic x-ray CT system using synchrotron radiation is being developed to obtain clear images and to detect low contrast materials for quantitative functional evaluation of organs in correspondence with their anatomical structures.The SR-CT system is constructed at the beam line NE-5A of the Tristan Accumulation Ring in Tsukuba (6.5GeV,20-30mA). This system consists of a rotating x-ray shutter, a silicon (111) and silicon (511) double monochromator, an x-ray slits system, a roating object table, an x-ray linear array sensor system and a computer. By this system, the image with x-ray energy from 30 to 52 keV can be obtained to detect various contrast materials (iodine, barium and gadolinum). The x-ray linear arry sensor consists of BGO scintillators and a silicon photo-diode array. The dynamic range of the system is 60000 : 1 with 200mum of the spatial resolution. Image data was digitized by a 16 bit A/D converter and led to the computer. Exposure time of each projection can be changed from 3 ms to longer. Slice thickness of the object can be also adjustable from 0.1 to 3.2 mm using the slit system. Using a unix workstation, a SR-CT image is reconstructed from the line data obtained by x-ray linear array detector. This workstation can perform high speed image reconstruction using graphic accelerator board.Using the double crystal monochromator, the high order x-ray contamination is eliminated. A new CCD detector have some problems at the junction of sensor, and this produced the artifact. As the machine trouble of AR ring occurred in 1994, the experiments of this system could not performed sufficiently. The detailed experiment will be performed in 1995.