共查询到20条相似文献,搜索用时 15 毫秒
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Arunachalam K Maccarini P De Luca V Tognolatti P Bardati F Snow B Stauffer P 《IEEE transactions on bio-medical engineering》2011,58(6):1629-1636
Microwave (MW) radiometry is proposed for passive monitoring of kidney temperature to detect vesicoureteral reflux (VUR) of urine that is externally heated by a MW hyperthermia device and thereafter reflows from the bladder to kidneys during reflux. Here, we characterize in tissue-mimicking phantoms the performance of a 1.375 GHz radiometry system connected to an electromagnetically (EM) shielded microstrip log spiral antenna optimized for VUR detection. Phantom EM properties are characterized using a coaxial dielectric probe and network analyzer (NA). Power reflection and receive patterns of the antenna are measured in layered tissue phantom. Receiver spectral measurements are used to assess EM shielding provided by a metal cup surrounding the antenna. Radiometer and fiberoptic temperature data are recorded for varying volumes (10-30 mL) and temperaturesg (40-46°C) of the urine phantom at 35 mm depth surrounded by 36.5°C muscle phantom. Directional receive pattern with about 5% power spectral density at 35 mm target depth and better than -10 dB return loss from tissue load are measured for the antenna. Antenna measurements demonstrate no deterioration in power reception and effective EM shielding in the presence of the metal cup. Radiometry power measurements are in excellent agreement with the temperature of the kidney phantom. Laboratory testing of the radiometry system in temperature-controlled phantoms supports the feasibility of passive kidney thermometry for VUR detection. 相似文献
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Distribution of millimeter wavelength electromagnetic energy absorption in surface layers of biological tissue models was studied using methods of Infrared Thermography. 0.1 mm thin-layer phantoms were irradiated in the near field using different types of horn antennas in the 37-78 GHz frequency range. Heating patterns were recorded during microwave irradiation, and surface SAR distributions mere calculated. The temperature resolution was better than 0.05 K. It was found that horn antennas produced nonuniform heating patterns in irradiated objects. These nonuniform patterns were due to a geometrical resonance resulting from a secondary wave-mode interaction between an irradiated object and the corresponding critical cross-section of the horn antenna. Local SAR values in hot spots exceeded the spatially averaged values by over 10 times, and the widths of these hot spots at 5 times the average SAR were often 1 mm or less. The location, quantity, number and size of the local field absorption maxima of irradiated objects strongly depended on the frequency of electromagnetic irradiation, with equivalent Q-factors of 500 or more. These findings provide an explanation for a number of frequency-dependent effects of millimeter wave electromagnetic irradiation 相似文献
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Rastegar S. Motamedi M. Welch A.J. Hayes L.J. 《IEEE transactions on bio-medical engineering》1989,36(12):1180-1187
The role of optical properties in the distribution of laser light and the resulting thermodynamic processes in biological tissue is studied from a theoretical perspective. Light distribution is modeled by a discrete ordinate method and heat transfer and ablation is modeled by an immobilized finite element method. The effect of parametric variation of absorption, scattering anisotropicity on the dynamics of the ablation process is examined. The manifestation of higher than the ablation threshold temperature in the subsurface tissue is observed and discussed. Results indicate significant differences in the ablation behavior which may have important clinical implications. 相似文献
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农产品生物组织的光学参数测量方法研究 总被引:2,自引:0,他引:2
为解决当前近红外光谱分析技术应用于农产品品质分析时所出现的预测模型不稳定、适应性不好、预测精度难于进一步提高等问题,我们认为,研究组织内部的光学性质及其光传输规律是其关键。为此,我们首先要对农产品生物组织的光学参数进行检测研究。本文通过对生物组织光学参数目前常用的一些测量方法进行了分析研究,其中着重介绍了基于空间分辨技术、时间分辨技术和积分球技术的光学参数测量方法,并对这些方法的优缺点做了比较,为选择一种适用于农产品生物组织光学参数的测量方法提供了依据。 相似文献
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Dynamics of temperature dependent optical properties of tissue:dependence on thermally induced alteration 总被引:2,自引:0,他引:2
Agah R. Gandjbakhche A.H. Motamedi M. Nossal R. Bonner R.F. 《IEEE transactions on bio-medical engineering》1996,43(8):839-846
Thermal damage in heated bovine myocardial tissue is assessed from measured changes in total reflection and transmission of light. Mathematical expressions, based on random walk analysis of light propagation within tissue slabs, are used to relate the diffuse reflection and transmittance to the absorption coefficient, μa , and effective scattering coefficient, μ's for samples of myocardial tissue which were subjected to rapid step changes in temperature. Time-dependent changes in μ's indicate two processes, one with a fast and temperature-dependent rate the other with a slow and apparently temperature-independent rate. For final temperatures above 56.8°C and for the first 500 s after the temperature change, the optical parameters are well fit by exponential forms that exhibit temperature-dependent time constants as predicted by Arrhenius reaction rate theory of thermal damage. The scattering changes are associated with an apparent activation energy, ΔE, of 162 kJ/mole and a frequency constant, A, of 3×1023 s-1 . This method provides a means for estimating optical coefficients which are needed to assess laser tissue dosimetry 相似文献
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Garcia-Collado A.J. Molina-Cuberos G.J. Soler J.M. Nunez-Trigueros M.J. 《Latin America Transactions, IEEE (Revista IEEE America Latina)》2009,7(2):170-175
The way the energy is absorbed when skin surface is being exposed to an electromagnetic radiation, and the physical consequences involved, are essentially the purposes of this study. In particular, we are dealing with high frequency radiation. When it is directed toward the surface of the skin, energy is transmitted to its inner layers causing an increase of the temperature. This process has experimentally been proved to be beneficial in many cases. Yet theoretically there is still a slightly hollow basis about it. This study pretends to deal with that subject from its origin, and allows future study doors to tap in depth this theme. Skin tissue is actually a multilayer tissue with a different tissue in each layer. Each one of them is characterized by some parameters, such as permittivity, conductivity, density and specific heat. Two kinds of skin tissues will be analysed: a fibrous and a fatty one, each of both with different skin humidity. In a former study some parameters such a possible non-linear temporal evolution of tissue temperature and a redistribution of heat through the tissues had been neglected for simplicity. 相似文献
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Roy R Thompson AB Godavarty A Sevick-Muraca EM 《IEEE transactions on medical imaging》2005,24(2):137-154
A novel image reconstruction algorithm has been developed and demonstrated for fluorescence-enhanced frequency-domain photon migration (FDPM) tomography from measurements of area illumination with modulated excitation light and area collection of emitted fluorescence light using a gain modulated image-intensified charge-coupled device (ICCD) camera. The image reconstruction problem was formulated as a nonlinear least-squares-type simple bounds constrained optimization problem based upon the penalty/modified barrier function (PMBF) method and the coupled diffusion equations. The simple bounds constraints are included in the objective function of the PMBF method and the gradient-based truncated Newton method with trust region is used to minimize the function for the large-scale problem (39919 unknowns, 2973 measurements). Three-dimensional (3-D) images of fluorescence absorption coefficients were reconstructed using the algorithm from experimental reflectance measurements under conditions of perfect and imperfect distribution of fluorophore within a single target. To our knowledge, this is the first time that targets have been reconstructed in three-dimensions from reflectance measurements with a clinically relevant phantom. 相似文献
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《Optical Fiber Technology》2006,12(4):297-304
Novel techniques to control the effective emission cross section of a rare earth-doped optical fiber with a functional cladding structure are reviewed for applications in active fiber devices. We discuss evanescent wave filtering (EWF) technique based on the overlap in the radiative transition cross sections between the emitting ion in the core and the absorbing ion in the inner cladding. Experimental applications of EWF concept are reviewed for a composite gain medium with the erbium ions in the core and samarium ions in the inner cladding for self-gain flattening in C-band. W-type three layered fiber structure is also analyzed in terms of modal guidance and location of the LP01 mode cut-off. Its application in neodymium and thulium-doped silica fiber laser is discussed to facilitate the radiative transition near 940 and 1600 nm region, respectively. The design concepts, fabrication process, and device performances are discussed for each application. 相似文献
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Implantable luminescent sensors are being developed for on-demand monitoring of blood glucose levels. For these sensors to be deployed in vivo, a matched external hardware system is needed. In this paper, we designed a compact, low-cost optical system with highly efficient photon delivery and collection using advanced optical modeling software. Compared to interrogation with a fiber bundle, the new system was predicted to improve interrogation efficiency by a factor of 200 for native sensors; an improvement of 37?times was predicted for sensors implanted at a depth of 1?mm in a skin-simulating phantom. A physical prototype was tested using silicone-based skin phantoms developed specifically to mimic the scattering and absorbing properties of human skin. The experimental evaluations revealed that the prototype device performed in agreement with expectations from simulation results, resulting in an overall improvement of over 2000?times. This efficient system enables use of a low-cost commercial spectrometer for recording sensor emission, which was not possible using only fiber optic delivery and collection, and will be used as a tool for in vivo studies with animal models or human subjects. 相似文献
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M.E. Azim-Araghi L. Moazzami Goodarzi J. Baedi 《Materials Science in Semiconductor Processing》2013,16(6):1736-1741
We determined some optical and electrical properties of thin gold phthalocyanine films. Calculations were performed in the framework of density functional theory using the full potential linear augmented plane wave method. Studies on the density of states and band structure yielded a bandgap energy (Eg) of approximately 2 eV. Two trap energy levels were observed at 0.9 and 1.3 eV. Analysis of the dielectric function and electric loss function revealed a plasmon oscillation at 1.8 eV. In addition, we determined static refractive index values in the x, y and z directions of n0xx = 2.16, n0yy = 1.66 and n0zz = 2.07. The optical bandgap of gold phthalocyanine was estimated to be 0.97 eV. Calculations revealed strong absorption at 400–700 nm, which compares favorably with experimental results. 相似文献
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This paper outlines a framework by which the optimal illumination/collection geometry can be identified for a particular biomedical application. In this paper, this framework was used to identify the optimal probe geometry for the accurate determination of tissue optical properties representative of that in the ultraviolet-visible (UV-VIS) spectral range. An optimal probe geometry was identified which consisted of a single illumination and two collection fibers, one of which is insensitive to changes in scattering properties, and the other is insensitive to changes in the attenuation coefficient. Using this probe geometry in conjunction with a neural network algorithm, the optical properties could be extracted with root-mean-square errors of 0.30 cm(-1) for the reduced scattering coefficient (tested range of 3-40 cm(-1)), and 0.41 cm(-1) for the absorption coefficient (tested range of 0-80 cm(-1)). 相似文献