Terahertz spectral characteristics of biological tissues

Abstract

The terahertz is an electromagnetic wave with non-ionization and low average power; therefore it is thought not to be hazardous to biological tissues. The terahertz waves can excite the vibration mode and rotation mode of macromolecules, and both amplitude and phase information of samples which are detected can be gotten and contrasted. Compared with visible and infrared light, it also has the advantage of low scattering and that the surface character and depth pattern of samples can be acquired at the same time, which makes it possible to measure tissues in vivo without any damage in the field of biomedicine. In this article, THz transmission and reflection spectra of liquid and solid samples are tested and analyzed based on THz-TDS (Terahertz time Domain Spectra system), including glucose solution and different kinds of biological tissue slices, etc. The optical parameter relations of different samples are acquired. Spectrum results are contrasted and discussed for two kinds THz systems. The results show that THz spectra of different samples are differentiable, and they can be described quantitatively. EXPERIMENTThe terahertz transmission system is based on the Z-3 Time Domain Spectrometer. To eliminate the influence caused by the absorption of water vapor, the terahertz beam path is completely put into the nitrogen environment to keep a relative humidity less than 4% and enhance the SNR [1] . Terahertz reflection system is familiar with the transmission one, and the information of sample is gotten with upper reflective mode. D-(+) -glucose sample is purchased from Sigma Company. The glucose aqueous solution with different mass concentration of the glucose is configured with deionized water individually as 1%, 3%, 5%, 15%, 30%, 40%, 50%, 60% and 70%. It is appropriate for biological samples to use silicon as optical window [2][3] , because of its better penetrating characteristics and relatively more stable optical properties in THz region. The biological tissues are pork adipose, chicken, beef and pork kidney with the thickness of 40 m µ and 50 m µ respectively, and different kinds of water include de-water and some drinking waters. RESULTS AND ANALYSISThe time-domain transmission spectra of glucose aqueous solution with different mass concentration are given in Fig.1, together with one of 0.5mm thickness sample cell as reference signal. It can be seen in the waveform that the different *lwei263@263.net; phone 86 010 6890-2348