Seeing that about 70% component of fresh biological tissues is water, many scientists try to use water models to describe the dielectric properties of biological tissues. The classical water dielectric models are Debye model, Double Debye model and Cole-Cole model. This work aims to determine a suitable model by comparing three models above with experimental data. These models are applied to fresh pork tissue. By means of least square method, the parameters of different models are fitted with the experimental data. Comparing different models on both dielectric function, the Cole-Cole model is verified the best to describe the experiments of pork tissue. The correction factor α of the Cole-Cole model is an important modification for biological tissues. So Cole-Cole model is supposed to be a priority selection to describe the dielectric properties for biological tissues in the terahertz range.
As a powerful tool for the research of molecular structure, infrared absorption spectrum has been extensively studied in the field of biomedical photonics. The absorption spectrum of anhydrous glucose in terahertz region has been measured by Fourier transform infrared spectrometer (FTIR). The experimental results show that there are many characteristic absorption peaks. The origins of characteristic absorption are generally attributed to intermolecular vibrations and intramolecular torsions. CASTEP quantum chemical calculation software package was utilized to simulate the infrared spectroscopy of glucose crystal structure based on periodic boundary condition and plane wave pseudopotential method. Also, linear response approach and norm conserving pseudopotentials are essential. Besides, the performance of the generalized gradient approximation (GGA) functional has been commendably examined. The theoretical results show that the standard Perdew-Burke-Ernzerhof (PBE) approach along with its line Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm tends to be superior. We analyzed the vibration mode corresponding to each characteristic absorption peak with DFT theory. The agreement between theory and experiment indicates that the crystal simulation calculation based on solid-state density functional theory can identify absorption peaks of substance and vibration attribution accurately in terahertz region.
The water vapor noise will affect the accuracy of the extracted optical parameters based on terahertz time domain spectroscopy technology. Because vapor noise has the characteristics of wide distribution and high intensity, the existing denoising methods cannot be effectively applied to the THz signal with vapor noise. In this paper, a numerical denoising method is presented. First, based on Van Vleck-Weisskopf lineshape function and the linear absorption spectrum of water molecules in the HITRAN database, we have simulated the water vapor absorption spectrum with line width, and the continuum effect of water vapor molecules are considered in the simulation. Then, the transfer function of different humidity is constructed by the calculation of the water vapor absorption coefficient and the real refractive index; Finally, based on the propagation factor formula of the mutual effects of THz wave and water vapor, the THz signal of the Lacidipine sample containing vapor noise in the continuous frequency domain of 0.3-1.8THz is denoised by using the constructed transfer function of the water vapor; the optical parameters of the sample signal before and after denoising can be extracted. It can be seen that the optical parameters extracted from the denoised signal are close to the optical parameters in the nitrogen environment, which proves the effectiveness of denoising. Under low humidity, this method can still accurately extract the optical parameters of samples without nitrogen filling, which saves the cost, enhances the convenience of the application of terahertz time domain spectroscopy in pharmaceutical production, safety inspection, imaging etc.
We utilized terahertz time-domain spectroscopy (THz-TDS) to investigate the complex dielectric properties of solid polycrystalline material of anhydrous glucose (D-(+)-glucose with purity >99.9%). THz transmission spectra of samples were measured from 0.2 to 2.2 THz. The samples were prepared into tablets with thicknesses of 0.362, 0.447, 0.504, 0.522 and 0.626 mm, respectively. The imaginary part of the complex dielectric function of polycrystalline glucose showed that there were multiple characteristic absorption peaks at 1.232, 1.445, 1.522, 1.608, 1.811 and 1.987 THz, respectively. Moreover, for a given characteristic absorption peak, the real part of the complex dielectric function showed anomalous dispersion within the full width half maximum (FWHM) of the absorption peak. Both finite difference time-domain (FDTD) numerical simulations and experimental results showed that the complex dielectric function of anhydrous polycrystalline glucose fits well with the Lorentz dielectric mode. The plasma oscillation frequency was below the frequency of the light waves suggesting that the light waves passed through the polycrystalline glucose tablets. Calculations based on density functional theory (DFT) showed that the characteristic absorption peaks of polycrystalline glucose originated mainly from collective intermolecular vibrations such as hydrogen bonds and crystal phonon modes. The THz radiation can excite the vibrational or rotational energy levels of the biological macromolecules. This leads to changes in their spatial configuration or interactions. This study showed that THz-TDS has potential applications in biological and pharmaceutical research and food industry.
For enhance the grade ability of spherical robot, a new kind of spherical robot with climb link mechanism is
designed. This kind of spherical robot can move in traditional way by the pendulum or move across large gradient slope
by the new climb link mechanism. The mechanics model of the new spherical robot across slope by the climb link
mechanism is created. Then the model is simulated by simulation software. The simulation result verifies the mechanism
model’s accuracy. Then the mechanical model of this new spherical robot named BYQ-X was made out. The mechanical
structure and motion control system are detailed introduced. Finally, the accuracy of the mechanical model, the validity
of the climb link mechanism are verified by tests of mechanical model.
A complex filtering method for eliminating systematic and random noises of THz-TDS is proposed. This method is the combination of deconvolution and wavelet filtering algorithms. A self-reference method for extracting the complex refractive index of material accurately is also proposed in order to avoid a phase shift due to the misplacement between the surfaces of the reference and sample using the time-domain terahertz reflection spectroscopy. The basic idea of self-reference method is that the first and the second peaks of the reflection spectrum of solid pellets are regarded as the reference and sample signals, respectively. Thus more information of samples can be extracted because of a longer optical path, and meanwhile, phase error can be avoided by obtaining the reference and sample signals through a single measurement. According to the Fresnel formulas, we deduce the expression of complex refractive index and then design an iterative algorithm for solving it. We choose the glucose solid pellets as samples to test the self-reference method. After measuring the time-domain reflection spectrum, we adopted the complex filter method for filtering and utilized the self-reference method to extract the complex refractive index. Based on Density Functional Theory (DFT), the characteristic absorption spectrum of multiple glucose molecules in the THz absorption spectroscopy was obtained by the simulation analysis on the vibration of multiple glucose molecules. The results indicate that the absorption peaks appear in the absorption coefficient curves at the corresponding frequency positions which are approximately consistent with the results of the simulation based on DFT. So the methods we proposed can help improve the retrieval accuracy of complex refractive index.
The optical activity of glucose molecules is important for diagnosing and monitoring blood glucose of diabetes. In order to accurately detect the diabetes at an early stage, there is an urgent need to develop innovative detection methods. By use of Mueller matrix decomposition (MMD), we have studied the optical activity of glucose molecules in three types of turbid media—polystyrene (PST) sphere suspension, chicken blood, and the vein blood of diabetic patients. The experimental setup to obtain the Mueller matrix in the forward detection geometry has been used. The experimental results show that the rotation angle has linear relationship with the concentration of the glucose when the scattering coefficient of the PST sphere suspension remains unchanged, whereas the scattering effect enlarges the rotation angle. Furthermore, optical rotation abides by Drude’s dispersion equation. The decomposition method has also been found useful applications in quantifying the optical rotations of blood glucose in diabetic patients. The diabetic severity status can be distinguished with the rotation angle of glucose and also is in accordance with the clinical diagnosis. Thus, the method of MMD has promising applications in diabetic diagnosis and monitoring.
Optical activity is the intrinsic property of chiral molecules. Investigation of optical activity is particularly important for diagnosing and monitoring blood glucose of diabetes. The experimental setup to obtain the Mueller matrix in the forward detection geometry is used. Three kinds of chiral turbid media are selected to be studied in the experiment. The first is the tissue phantom composed of an aqueous solution of glucose mixed with PST sphere suspensions. The second is the actual chicken blood mixed with glucose solution. The last is the vein blood plasma of diabetic patients. The results presented in this study demonstrate that the method of Mueller matrix decomposition can be used to quantitatively extract the optical rotation of chiral molecule in turbid medium. The rotation angle has linear relationship with the concentration of the optical activity material when the scattering coefficient of the turbid medium maintains unchanged. The scattering effect enlarges the rotation angle. Furthermore, optical rotation abides by the Drude’s dispersion equation. The decomposition method also has been found useful applications in quantifying the optical rotations due to blood glucose in diabetic patients. The diabetic severity status can be distinguished with the rotation angle of glucose by using the decomposition method and also are in accordance with the clinical diagnosis. Thus, the method of Mueller matrix decomposition has promising applications in diabetic diagnosis.
THz transmission spectrums of different glucose solution with concentration from 1% to 70% were measured on the condition of room temperature and fewer than 4% humidity in the nitrogen environment. According to the physical model of the THz optical parameters, their refractive indexes and absorption coefficients were gotten. The results showed that with the increase of glucose concentration, the THz absorption coefficients of solution decrease linearly. The fitting relations among the refractive index, the extinction coefficient, absorption coefficient and its concentration at the frequency of 0.33, 0.6 and 0.8 THz were acquired individually. Their correlation coefficients were larger than 0.95. Analysis and discussion about them were given. The THz time domain spectroscopy technologies could realize an accuracy measurement for the concentration of glucose solution. This work was meaningful to the exploration of THz spectral response of biological samples.
It is important to measure optical properties noninvasively, quickly and accurately in vivo for disease diagnostics and
medical therapeutics. In this study, we measured the absorption coefficient and the reduced scattering coefficient of
human tissues by measuring diffuse reflectance with CCD, examined the techniques involved, such as quantization of
diffusion approximation theory, effective reverse fitting algorithm, and the data selection and processing method, and
finally concluded about the accuracy of this method. The experimental results indicate that the error is less than or equal
to 8% using the diffusion theory, under the condition that the reduced scattering coefficient is one order of magnitude
greater than the absorption coefficient. The stability and precision of optical property measurements are significantly
improved by using the multi-step iterative fitting method and using the ring areas to determine the diffuse reflectance
center. The efficiency of reverse algorithm is greatly enhanced by selecting a one-dimensional array on the straight line
crossing both the entry point and the diffusion center for fitting. The error of measured absorption coefficient and
scattering coefficient of the Intralipid solution and human forearm tissues are less than 5% with our method. These
results can provide important technical information for application of the diffusion theory.
Optical parameters of biological tissues, including absorption coefficient (μa), reduced scattering coefficient (μs') or scattering coefficient (μs), anisotropy factor (g) and refractive index (n) are investigated extensively and systemically at
wavelength of 650 nm. Intralipid solution was selected to be the tissue phantom in order to test the validity of
measurements. Considering the factors of fiber orientation and haemoglobin content, we chose some fresh bulk animal
tissues in vitro which were bovine adipose, bovine muscle, porcine adipose, porcine muscle, porcine kidney, porcine liver,
mutton and chicken breast. The basic assumption is that in vitro samples are a reasonable representation of the in vivo
situation. We have gained numbers of experimental data of Intralipid and some tissues. Particularly, we have set up the
close relationships among six optical parameters involving μa, μs', μs, g, n and μt. The experimental results show that for
animal tissues, μa, μs' or μs and n rely deeply on muscle fiber orientations. Both of μs and μt range from 10mm-1 to 20mm-1. μa ranges from 10-2 mm-1 to 10-3 mm-1 and g from 0.95 to 0.99. The results of this study will be helpful in further understanding of optical properties of tissues.
KEYWORDS: 3D image reconstruction, Polarization, Holograms, Digital holography, Tissues, Convolution, Scattering media, Metals, Composites, Signal to noise ratio
The polarization-based digital holography of Fresnel-zone-plate (FZP) convolution without motion is proposed. This
method focuses mainly on imaging of two-dimensional objects embedded in highly scattering media. The key of the
method is that the uniformly distributed light source is utilized to make many FZP projections superpose on an object in
a classical incoherent correlator. In this way a hologram of the object is obtained by convoluting its intensity distribution
with the FZP intensity distribution without relative motion. A method called composite hologram is applied to improve
the low signal-to-noise ratio due to extremely weak signals submerging in large backgrounds. Especially, the
configuration of this method is designed to avoid time-consuming. The polarization gating is used in order to extract the
weakly polarized light from the highly scattered light. In experiments, the degree of polarization of circularly polarized
light is maintained better than that of linearly polarized light in highly scattering media. Circularly polarized light is,
accordingly, used in practice. The experiments on a 0.4-mm-diameter metal wire embedded in Intralipid-1% phantom are
carried out. The outline of the metal wire can be still distinguished, although the reconstruced image becomes blurred as
the thickness of cuvett increases to 30 mm. An attempt to apply this method to image the metal wire embedded in
chicken tissue sections also be implemented. The reconstructed images can be distinguished in depth of 10 mm. The
experimental results demonstrate that the method has potential applications in imaging of objects embedded in highly
scattering media.
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