Measurement of Temperature Distribution in Phantom Body by an Ultrasonic CT Method

自从热疗在癌症治疗中出现以来，测量人体内部温度变得越来越重要。在这种治疗中，重要的是保持肿瘤的温度在42.5ºc以上，以避免正常组织的热损伤。我们期望一种间接测量人体任意横切面内部温度分布并显示图像以供监测的技术。本文研究了一种超声CT（计算机断层扫描）方法，用于间接测量从相对于幻体的几个不同方向拍摄的一系列声音投影的内部温度分布。超声CT与x线CT一样，是获取人体横向图像的主要方法之一。但它的优点是仪器简单，因为它没有x射线CT那样的辐射损伤。超声CT通过测量声波到达时间，可以得到物体内部的声速分布。本研究的目的是利用声速随温度变化的特性，从加热与不加热时的声速差来间接测量物体内部温度分布的方法。首先，我们比较了三种重建算法，以最小化所需的投影数量。其次，我们进行了温度对水中声速的依赖实验，得到了温度与水中声速的关系。然后，将琼脂制成的幻影放置在水浴中，当一对超声波探测器平移和旋转时，测量一系列的声音投影。通过加热时的声音分布减去不加热时的声音分布，可以得到精度为0.1‰的温度分布。血液、肌肉组织、脏器等含水组织的结构差异对温度分布的测量不产生影响，因为加热时的声速减去非加热时的声速即可消除。最后，我们做了一个实验，在超声测量的横切面上有一根骨头。当骨头或气体在测量区域时，投影包括数据缺失部分。实验结果表明，通过对投影进行修正，可以得到近似的重建图像，如果缺失部分较小，也可以得到温度分布。但是，如果缺失的部分很大，我们无法精确计算温度分布。少

It has been getting importance to measure the interior temperature in the body since hyperthermia appeared in treatment of cancer. In this treatment, it is important to hold the temperature of tumor over 42.5ﾟc to avoid the heat damage of normal tissue. We anticipate a technology measuring indirectly the interior temperature distribution of the arbitrary transverse section in the body and displying the image for monitoring.In this paper, An ultrasonic CT (Computed tomography) method is researched for measuring indirectly the interior temperature distribution from a series of sound projections that are taken at several different orientations relative to a phantom body. Ultrasonic CT is mainly one of the methods getting the transverse image of the body as the same as X-ray CT.But it has the advantage of simpler instrument because it doesn't have the radiation injury like X-ray CT.We can obtain the sound speed distribution within the object by measuring the arrival time of sound wave with … More ultrasonic CT.The purpose of this study is to develop the method measuring indirectly the interior temperature distribution of an object from the difference of sound speed between heating and non-heating, using the characteristics the sound speed depends on the temperature.First, we compare three reconstruction algorithms to minimize a number of required projections. Next, we make an experiment about the dependence of temperature on sound speed in water and get a relation between the temperature and the sound speed in water. Then, phantoms made of agar are placed in a water bath, and a series of sound projections is measured when a pair of ultrasonic detectors are both translated and rotated. We can obtain the temperature distribution in phantom with accuracy 0.1ﾟc by subtracting the sound distribution when non-heating from one when heating. The structure differences of watery tissue like blood, musculature, and the viscera do not effect on the measurement of the temperature distribution, because it is deleted by subtracting the sound speed when non-heating from the sound speed when heating.Lastly, We make an experiment in which there is a bone crossing the transverse section of the ultrasonic measurement. When bone or gas is in the area of measurement, the projections include a data missing part. As a result of the experiment, we could obtain approximately the reconstructed image by the modification of the projections, and the temperature distribution, too, if the missing part is small. But we can not calculate precisely the temperature distribution, if the missing part is large. Less