Study On Continuous-wave Terahertz Three-dimensional Imaging Techniques

Terahertz(THz)wave has many unique properties in the electromagnetic spectrum.Recently,with the development of THz generation and detection techniques,the application fields of THz technology have been expanding rapidly.Among them,THz three-dimensional imaging technique shows broad application prospects for its ability to detect the internal information of objects.In this paper,we focused on the problems encountered in the THz three-dimensional imaging of high-refractive-index samples and biological tissues.By making use of a high-power THz source,the THz computed tomography(CT)based on refractive index matching method,three-dimensional reconstruction technique based on multi-depth slices imaging and the interference elimination based on inverse image processing is studied.The main contents and innovations are as follows.1.Advances in THz imaging technique and some typical THz three-dimensional imaging techniques are summarized.THz CT technique is mainly introduced,including the development history,basic principles and the reconstruction algorithms of THz CT.2.Aiming at the problem of refractive effect in THz CT imaging of highrefractive-index samples,a THz CT imaging technique based on refractive index matching method is proposed,which can effectively eliminate the refractive effect during the scanning.Together with the data processing to eliminate the liquid absorption and to restrain the artifacts,the THz CT imaging of high-refractive-index samples are achieved successfully.3.The rat brain trauma model was established using Feeney's method,and the brain tissue slices were imaged with the THz transmission imaging system.The imaging results show that the rat brain traumatic region has lower transmittance than the normal region.The three-dimensional modeling of rat brain was realized by imaging the slices at different depths of the rat brain.The three-dimensional model clearly reflects the spatial distribution of the traumatic region inside the rat brain.4.Based on the theoretical analysis of the physical mechanism of fringes generation in various THz imaging systems,a novel image restoration approach to eliminate the interference fringes in THz imaging is proposed.The interference fringes in a simulated interference image and the original THz image are successfully eliminated.The enhancement of the peak signal-to-noise ratio(PSNR)and structural similarity index(SSIM)is achieved compared with the frequency domain filtering,which is a traditional method to eliminate the fringe noise.Moreover,the inverse image processing is performed on a THz transmission image of a fresh rat brain tissue.It presents an excellent result with accurate information for the brain tissue after interference elimination.