Fundamental Study of Heavy Radiography

对重离子放射照相的疗效进行了研究，并与x射线照相进行了比较。提示重离子造影在相对低辐射水平下对低对比肿瘤具有较好的成像效果。在重离子照相中，利用布拉格峰的远端边缘，可以在底片上记录深层组织密度的微小差异作为光密度的差异。由此可见，光密度的差异与薄膜位置处残留距离的差异有关。残差范围确定为沿粒子路径的综合停止功率。建议利用一组数据，即360度范围内不同方向的一维残差分布，计算出相对停车功率的二维分布。剩余范围确定为沿带电粒子路径的停止功率的累积效应。如果我们有一组显示360度以上不同方向的残差距离分布的图像，则可以使用停止功率公式计算电子密度的分布。本文首先从残差空间分布中得到CT图像中电子密度的计算公式入手。在以往的研究中，采用薄膜系统测定了光密度与残留范围的关系以及光密度与吸收剂量的关系，并测定了小动物各脏器处残留范围的差异。本研究采用荧光屏和带有I.I.系统的摄像机来缩短图像采集时间。通过改变移距器的厚度，实验得到了圆柱丙烯酸酯幻影投影图像的一维残差分布。

Studies of efficacy on heavy ion radiography have been performed in comparison with X-ray radiography. It was suggested that heavy ion radiography gave superior imaging for low contrast tumors at relatively low radiation levels. In heavy ion radiography, small difference of tissue density in deep seated area can be recorded on films as the difference of optical density by using a distal edge of the Bragg peak. This shows that the difference in optical density is related to the difference of the residual range at the film position. The residual range is determined as the integrated stopping power along the path of particle. It was suggested that the two dimensional distribution of relative stopping power could be calculated by the use of a set of data, namely, one dimensional (1D) residual range distributions for the different directions over 360 degrees. The residual range is determined as the accumulated effect of stopping power along the path of charged particle. If we have the set of images showing residual range distribution for the different directions over 360 degrees, the distribution of electron density could be calculated by the use of stopping power formula. This work begin with formulation of algorithm to obtain the CT image of electron density from the spatial distribution of residual range. In the previous study the relations between optical density and residual range and those between optical density and absorbed dose were determined using film system and the difference of residual ranges at each internal organ of small animal. In the present study the fluorescent screen and video-camera with I.I. system was adapted to shorten the image collection time. One dimentional distribution of residual range was obtained from the series of projection images of cylindrical aclylate phantom experimentally by changing thickness of the range shifter.