Noninvasive Measurement of Temperature Distribution in Tissues by Ultrasonic CT

热疗是一种治疗癌症的方法，测量热疗过程中组织的温度分布是非常必要的。我们期待着一种间接测量组织内任意横截面内部温度分布并显示图像进行监测的技术，通过超声CT测量声波的渡越时间，可以得到物体内部的声速分布。利用声速与温度有关的特性，提出了一种利用声速差间接测量组织内温度分布的方法。首先，我们在水、琼脂和几种离体组织中进行了声速与温度关系的实验，得到了温度与声速的关系。然后，我们利用声速差间接测量了组织内温度分布。最后，我们利用声速差间接测量了组织内温度分布。将琼脂制成的体模置于水浴中。用超声CT方法测量了加热前后的一系列声投影。将加热后的声分布减去加热前的声分布，得到体模中1℃以下的温差分布。但我们无法测量金枪鱼中低于1℃的温差。这是因为金枪鱼和水之间的声速差异远远超过琼脂和水之间的差异。为了获得组织中的温度分布，必须将组织置于声速接近组织声速的液体中，通过改变葡萄糖溶液的浓度，使其具有给定的声速。我们测量了葡萄糖溶液中声速随温度和浓度的变化。然后，我们进行了实验，切除金枪鱼和葡萄糖溶液具有接近金枪鱼的声速。因此，我们能够测量出金枪鱼离体的温度差小于1℃。

It is necessary to measure the temperature distributions in tissues during hyperthermia which is a treatment of cancer. We have anticipated a technology measuring indirectly the interior temperature distribution of the arbitrary transverse section in tissues and displaying the image for monitoring.We can obtain the sound speed distribution within the object by measuring the transit time of sound wave with ultrasonic CT. The purpose of this study is to develop a method measuring indirectly the temperature distribution in tissues from the differences in sound speed before and after heating, using the characteristics that sound speed depends on the temperature.The first experiment we made was about the dependence of temperature on sound speed in water, agar and several excised tissues, and we obtained some relations between the temperature and the sound speed.Then, the phantom made of agar was placed in a water bath. A series of sound projections was measured before and after heating by ultrasonic CT method. We obtained the distribution of the temperature differences below 1℃ in phantom by subtracting the sound distribution before heating from after heating.Next, we made the experiment with excised tuna in a water bath. But we were not able to measure the temperature difference below 1℃ in tuna. This is because the difference in sound speed between tuna and water is much more than the difference between agar and water. Tissue has to be placed in liquid which has the sound speed close to the sound speed in tissue in order to obtain the temperature distribution in tissue.We can make the glucose solution having a given sound speed by changing the concentration. We measured the dependence of sound speed in glucose solution on temperature and concentration. Then we made the experiment with excised tuna and glucose solution having the sound speed close to tuna's. As a result, We were able to measure the temperature difference below 1℃ in excised tuna.