Development of a chirp radar-type microwave computed tomography with the rotational scanner used for animal experiments

为实现人体温度的无创测量，研制了线性调频雷达型微波计算机层析成像(CP-MCT)原型系统。本研究将旋转扫描引入断层测量，对CP-MCT的高速成像进行了尝试。该原型系统采用1 GHz~2 GHz的线性调频脉冲信号，通过重复一对发射天线和接收天线的平移扫描和旋转扫描来采集投影数据。原型系统的空间分辨率估计约为1 cm，0.7度的温度变化已可视化，尽管数据采集需要大约100分钟。研制的旋转扫描器由发射天线和接收阵列天线组成，发射天线为介质加载发射天线，接收阵列天线由21个小偶极天线组成。将1 GHz~2 GHz的线性调频脉冲信号从发射天线照射到浸入盐水中的目标。由于介质加载的波导天线的增益方向图相当宽，因此确保了扇形波束的投影。发射天线和接收天线的距离为282 mm。每个偶极子被布置在距相邻偶极子天线14.7 mm的距离处，以减小互耦合效应。其中，扫描仪的扇角为60度。由于旋转扫描仪的采样间隔较短，所开发的扫描仪的空间分辨率与预测值相同，比原型系统的分辨率差。然而，这使得我们能够开发出具有41个小偶极天线的新型旋转扫描仪，用于动物实验。数据采集仅需90s，除了高速成像外，还利用FD-TD方法计算的点扩散函数开发了图像去模糊技术。

The prototype system of the chirp radar-type microwave computed tomography (CP-MCT) was developed for noninvasive thermometry of the human body. High speed imaging of CP-MCT has been attempted in this study by introducing the rotational scan in the tomographic measurement. The prototype system, which uses the chirp pulse signal from 1 GHz to 2 GHz, collects projection data by repeating the translational scan and rotational scan of a pair of the transmitting- and receiving-antenna. The spatial resolution of the prototype system is estimated at approximately 1cm and 0.7 degree temperature variation has been visualized, although it takes approximately 100 minutes for data acquisition.The developed rotational scanner is composed of a transmitting antenna that is the dielectric loaded transmitting antenna and a receiving array antenna, which is composed of 21 small dipole antennas. Chirp pulse signal from 1 GHz to 2 GHz is irradiated from the transmitting antenna to a target immersed in saline solution. Since gain pattern of the dielectric-loaded waveguide antenna is fairly broad so that, fan beam projection is secured. The transmitting- and receiving-antenna are facing each other at a distance of 282 mm. Each dipole is arranged at a distance of 14.7 mm from adjacent dipole antennas to reduce the mutual coupling effect. Where, fan angle of the scanner becomes 60 degrees.Spatial resolution of the developed scanner is the same value with the predicted one that is worse than that of the prototype system due to its coarse sampling interval of the rotational scanner. However, this enabled us to develop the new rotational scanner with 41 small dipole antennas for animal experiments. It requires only 90 seconds for data acquisition.In addition to high speed imaging, image deblurring technique has also been developed by using the point spread function computed by FD-TD method.