Image Formation of Moisture and Temperature in a Living Body by Microwave Computed Tomography

利用多频微波透射CT和时域反射技术研究了活体内温度和湿度分布的成像。我们利用微波网络分析仪和个人计算机构建了一个简单的农产品CT系统。为了消除多径传播的影响，系统测量频率响应，将数据转换到时域，并设置对应于2个天线之间的直接路径的时间门。将门控响应转换回频域，得到直接路径响应。可以选择或组合任意频率（1GHz-3GHz）的测量数据作为投影数据.采用与X射线CT相似的方法进行图像重建，得到了包含温度和结构信息的图像。通过水瓶热模实验获得了各频率下的温度图像，但在细胞间有空隙的蔬菜情况下，结构图像比温度图像强得多.我们注意到水的衰减常数的温度系数随频率的不同而有很大的差异，因此提出了从不同频率下获得的图像之间的图像相减来提取温度分布的方法，并进行了实验。结果表明，该方法降低了体模壁和植物结构的影响，改善了温度图像。热模体的图像也是由相位常数得到的.本文尝试用时域反射法（TDR）测量粮层内的水分分布，表明TDR可以测量筒仓或大型干燥机中厚粮层的水分分布。

Image formation of temperature and moisture distribution in living body was studied using multi-frequency microwave transmission CT and TDR.1. We constructed a simple CT system for agricultural products using a microwave network analyzer and a personal computer. To eliminate the effect of multipath propagation, the system measured the frequency response, converted the data to the time domain and set the time gate corresponding to the direct path between 2 antennas. The gated response was transformed back to the frequency domain, and direct path response was obtained. Measured data at any frequency (1GHz-3GHz) could be selected or combined for projection data.2. As a result of the image reconstruction by similar same method of X ray CT, the images which included the temperature and structure informations were obtained. The temperature image at a each frequency was obtained from the experiment of thermo-phantom using a water bottle, but the structural image was much stronger than the temperature image in the case of vegetable having voids between cells.3. We noticed that the temperature coefficients of attenuation constant of water differ largely with frequencies ; thus, the method of extracting the temperature distribution from the image subtraction between the images obtainedat different frequencies, was proposed and experimented with. It became clear that the influence of the phantom wall and that of vegetable structure decreased and the temperature image improved using this method. The image of the thermo-phantom was also obtainted from phase constants.4. The measurement of moisture disribution in grain layrs using time-domain reflectometry (TDR) was attempted, and it became clear that the moisture distribution of the thick grain layrs in silo or big dryer can be measured by TDR.