In this paper, we demonstrated that tumors in freshly excised whole brain tissue could be differentiated clearly from normal brain tissue using a homemade continuous terahertz (THz) wave attenuated total reflection (ATR) imaging system. The resolution of this system was about 400μm×450μm at 2.52THz. The terahertz images characters of fresh brains with tumor was studied using this THz-ATR imaging system. Tumor regions could be differentiated clearly from normal brain tissue by THz intensity imaging at different frequencies. The high absorption regions in THz images corresponded well to the tumor regions in the hematoxylin and eosin-stained microscopic images. Moreover, the morphological reconstruction method was applied to restore the blurred imaging results. The noise caused by power fluctuation in THz-ATR image was almost eliminated and the visibility of objects has been successfully enhanced. These promising results suggest that THz-ATR imaging could be used as a tool for label-free and real-time imaging of brain tumors, which would be great potential as an alternative method for the fast diagnosis tumor region during brain surgery.
Region of interest segmentation is essential for computer aided application of THz imaging. However, THz images is severely degraded by motion blur, poor resolution and noise. A robust, accurate and time-saving algorithm is in dire need for the ROI segmentation of THz images. Recently, ROI segmentation of THz-TDS images and passive THz images has been widely studied. While the ROI segmentation of THz continuous wave (CW) image is still in its infancy. In this paper, we proposed a hybrid ROI segmentation method for THz CW images. The hybrid method combines block match 3D denoising, fuzzy c-means clustering, morphology operation and canny edge detection. The hybrid method is implemented to two images acquired with a THz CW reflection imaging system. To evaluate the performance of our algorithm, we calculated the accuracy, sensitivity and specificity. As the result indicates, this hybrid ROI segmentation method performs well for THz images.
We set up the terahertz continuous reflectometry imaging system and the spatial resolution of our system was roughly 0.6×0.6mm at 2.52 THz. We also demonstrated that the paraffin embedded traumatic brain injury (TBI) in rat model sample can be differentiated clearly. The results show that the THz reflection intensity of the TBI area was lower than that of normal area. These promising results suggest that THz reflection imaging has great potential as an alternative method for the fast diagnosis of TBI.
We investigate a photonic crystal fiber (PCF) which consists of squeezed triangle lattice and elliptical air holes. Birefringence and dispersion properties of this PCF have been numerically estimated by the supercell lattice method. Numerical results show that the birefringence is on the order of 10<sup>-2</sup> over ultrabroad wavelength rang from1.3μm to 1.7μm and birefringence can be reached 1.71×10<sup>-2</sup> at the operating wavelength of 1.55μm. It is also demonstrated that two near-zero dispersion of -1.75(ps/nm/km) (x-polarized mode) and-0.33(ps/nm/km) (y-polarized mode) at 1.55μm can be achieved. Morever, the fluctuations of the dispersion with fiber parameters are very small. The simulation results show that our proposed PCF are robust to fabrication imperfections.
Photonic crystal fiber (PCF) with high birefringence and low dispersion is proposed in this work. Both two different sizes of elliptic air holes in the fiber cladding and a small elliptic air hole in the fiber core are used in our proposed PCF. The high birefringence is introduced on the combined effect of elliptical air holes and the squeezed lattice. The birefringence and the dispersion of this PCF have been numerically estimated by the supercell lattice method. The simulation results show that the high birefringence with the order of 10<sup>-3</sup>and the low dispersion of both x-polarized mode and y-polarized mode at the wavelength of 1.55μm can be obtained. The dependence of both the birefringence and the dispersion on structure parameters is analyzed. The simulation results show that flat birefringence and dispersion can be obtained.
A low-flattened index-guiding photonic crystal fiber (PCF) with high birefringence and low effective mode area is proposed. Elliptical air-holes with different diameters are distributed on the squeezed lattice. With the supercell lattice method, we simulate numerically the dispersion property and the birefringence property of the fundamental modes in this PCF. Simulation results show that the proposed PCF has a total dispersion as low as 0 ±1(ps/nm/ km) over ultra-broad wavelength band from1.3μm to1.6μm . Meanwhile, the birefringence can be reached the order of 10<sup>−3</sup> and the low effective mode area is also obtained. Moreover, the influences on the birefringence and dispersion by geometrical parameters have also been discussed in detail.