共查询到20条相似文献,搜索用时 15 毫秒
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Both the experimental and the analytical studies of the freezing/thawing process around a cryosurgical cylinder probes in a simulative biological tissue are presented in this paper. The enthalpy method and the finite element scheme are applied to solve the multidimensional phase change problems in cryosurgery. A very good agreement is found between the computed solutions and the experimental results. The influences of different cooling-warming schemes of the probe on the ice ball development, the temperature variation, the axial and the radial temperature gradients inside the tissues, and the requirement of cooling power are analyzed 相似文献
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A model is presented to simulate the cooling processes during tumor cryosurgery with different kinds of flows through the cryoprobe. The heat flux between the cryoprobe wall and the tumor, the heat transfer coefficient under different inflow conditions are obtained numerically. The impact of the inlet mass flow rate, gas volume fraction on these parameters is investigated. It is found that the heat transfer coefficient decreased significantly when inflow changed from two-phase annular flow to droplet flow, and to gas flow. The inlet gas volume fraction and flow velocity only significantly affect the freezing ability of the probe when the inflow is gas or in droplet phase. Simulation of the tumor temperature profiles under different flow conditions show that the heat transfer coefficient is a crucial parameter in temperature prediction during cryosurgery. Results indicate that when the cryoprobe wall is assumed at a constant temperature conventionally, the cooling effect could be overestimated. It would be more reasonable to use the constant wall heat transfer coefficient to simulate the cooling progress under a specific flow. 相似文献
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J.C. Gilbert B. Rubinsky M.S. Roos S.T.S. Wong K.M. Brennan 《Magnetic resonance imaging》1993,11(8):1155-1164
The inability to observe the transient, irregular shape of the frozen region that develops during cryosurgery has inhibited the application of this surgical technique to the treatment of tumors in the brain and deep in visceral organs. We used proton NMR spin-echo and spoiled gradient-echo imaging to monitor the development of frozen lesions during cryosurgery in the rabbit brain and the resulting postervosurgical changes up to 4 hr after freezing. Spoiled gradient-echo images (TE = 14 ms; TR = 50 ms) were acquired during freezing and thawing at a rate of 15 s/slice. Although the frozen region itself is invisible in MR images, its presence is distinguished easily from the surrounding unfrozen soft tissue because of the large contrast difference between frozen and unfrozen regions. T2-weighted spin-echo images (TE = 100 ms, TR = 2 s) obtained after thawing suggest that edema forms first at the margin of the region that was frozen (cryolesion) and then moves into the region's core. Histological examination showed complete necrosis in the cryolesion and a sharp transition to undamaged tissue at the margin of the lesion and its image. Blood-brain barrier (BBB) damage was investigated using gadolinium-DTPA. The region of edema in the T2-weighted spin-echo images was coincident with the area of BBB damage in the Gd-DTPA-enhanced T1-weighted spin-echo images (TE = 33 ms, TR = 400 ms) and both were distinguishable as areas of high signal relative to the surrounding normal tissue. The results of these experiments indicate that MR can both effectively monitor the cryosurgical freezing and thawing cycle and characterize the postcryosurgical changes in tissue during follow-up. 相似文献
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Temperature imaging with speed of ultrasonic transmission tomography for medical treatment control:A physical model-based method 下载免费PDF全文
《中国物理 B》2015,(10)
Hyperthermia is a promising method to enhance chemo and radiation therapy of breast cancer. In the process of hyperthermia, temperature monitoring is of great importance to assure the effectiveness of treatment. The transmission speed of ultrasound in biomedical tissue changes with temperature. However, when mapping the speed of sound directly to temperature in each pixel as desired for using all speeds of ultrasound data, temperature bipolar edge enhancement artifacts occur near the boundary of two tissues with different speeds of ultrasound. After the analysis of the reasons for causing these artifacts, an optimized method is introduced to rebuild the temperature field image by using the continuity constraint as the judgment criterion. The significant smoothness of the rebuilding image in the transitional area shows that our proposed method can build a more precise temperature image for controlling the medical thermal treatment. 相似文献
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Advances in cryosurgery since 1990 were initiated by the development of improved cryosurgical equipment and by the availability of intraoperative ultrasound to monitor the tissue-freezing process. Interest in research on the effects of freezing on tissue and on new clinical applications was then stimulated. The research led to a better understanding of the mechanisms of cryogenic injury, including cell death by apoptosis, which has emerged as a potential key to the use of adjunctive chemotherapy in the treatment of cancer. Optimization of cryosurgical technique will also improve clinical results. 相似文献
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The heating effect of urethral warming during cryosurgery has been investigated theoretically, via heat transfer simulations. Two warmer configurations have been considered: (i). the clinically available urethral warmer, which has a configuration of a counter flow fluid heat exchanger; (ii). a newly designed urethral warmer, based on a temperature controlled electrical heater, termed a "cryoheater". A dramatic effect of thermal resistance to heat transfer through the heat exchanger wall has been identified, which is absent in the cryoheater. It follows that the cryoheater is expected to be more efficient in generating an unfrozen region around the urethra. It is shown that the conventional heat exchanger may fail to prevent freezing around the urethra in a significant number of prostate cases, depending on the layout of cryoprobes around the urethra. On the other hand, clinical reports exist which suggest that the heat exchanger improves in many cases the outcome of cryosurgery, in terms of long term complications. It is speculated in the current report that the cryoheater can further improve the outcome of cryosurgery, by providing protection from freezing in a wider range of cases. It is suggested that a future study be conducted to examine the correlation between the layout of cryoprobes and surgical outcome. 相似文献
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The ability of the Antarctic nematode Panagrolaimus davidi to survive a short-term freezing stress depended upon the rate of freezing of its surroundings, measured as the duration of the sample exotherm. The freezing rate increased as the sample volume and freezing temperature decreased and resulted in fewer nematodes surviving. This appears to be due to the greater risk of physical damage by ice crystal growth at high freezing rates. Once frozen the nematodes will then survive exposure to lower temperatures. The environment of the nematode is likely to produce the slow rate of freezing of its surroundings that is necessary for its survival. 相似文献
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Yao Yang Zhensen Wu Lianxing Yao 《International Journal of Infrared and Millimeter Waves》2002,23(9):1347-1355
In traditional method of obtaining the radiance of target in infrared image, a target is often considered as an extended source. In that way, we only need the atmosphere transmittance, path radiance, and target apparent temperature to calculate the blackbody equivalent temperature of the target. However, in real infrared system imaging process, the target may be so far from the sensor that the target should be taken as a point source. In that case, the traditional data analysis method is not applicable anymore. A new method of calculating the radiance of small target is presented, which is based on the infrared system imaging theory. And the parameter needed to be input in this method is easily obtained. This method is tested by three different imaging systems. They are Thermal Vision AGEMA 900, AGEMA 1000, and Airborne Surveillance Pod Imaging System. The method is programmed into software, IRIDAS (Infrared Radiation Image Data Analysis Software) version 1.0. This software includes infrared imaging system calibration, atmosphere modification calculation, target and background selection and radiance calculation. This method can be used in infrared data anaylsis, infrared system evaluation and testing, target and background characteristics obtaining. 相似文献
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淡水资源缺乏已成为全球性问题,海水淡化方法的研究也日益引起重视。液化天然气在气化时有大量冷能可以利用,考虑到冷冻法海水淡化需要大量冷能,可以把LNG的冷能和冷冻法海水淡化结合起来,形成利用LNG能冷的冷冻法海水淡化流程。文中以间接冷冻法为例,介绍了LNG冷能在海水淡化中的利用;并针对系统中冷媒是否相变而提出了无相变流程和有相变流程,通过HYSYS软件进行模拟,比较分析了各自的优缺点。结果说明无相变流程设备简单、控制方便,但冷媒质量流量大;有相变流程冷媒质量流量小,但流程、设备与控制均较复杂,气相部分体积流量较大,使得气态管路直径较大,相应的换热器尺寸也会更大。 相似文献
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Susceptibility artifacts from magnetic resonance (MR)-compatible cryoprobes can distort MR images of iceballs. In this work, we investigate the ability of view angle tilting (VAT) to correct susceptibility induced distortions in MR images of cryosurgery. The efficacy of VAT was tested in an ex vivo bovine liver model of cryosurgery using MR-compatible cryoprobes. Artifacts on high bandwidth fast spin echo images of freezing obtained with and without VAT were compared with photographs of the actual iceball shape and size. In vivo imaging with VAT was demonstrated during percutaneous MR-guided cryosurgery of pig liver and brain. VAT was most successful in reducing probe and iceball distortions when the imaging plane was normal to the cryoprobe, and the cryoprobe was perpendicular to the main magnetic field of the scanner. VAT had the greatest benefit when used to correct MR images of freezing when the surface of the iceball was relatively near to the cryoprobe. For large iceballs, the artifact was small so the VAT correction was less important. We conclude that VAT significantly reduced distortions in the shape of the signal void corresponding to the extent of freezing visualized during MR-guided cryosurgery. This improved ability to visualize the exact location of the cryoprobe, as well as the precise shape of the iceball, particularly during initial freezing when the iceball is small, has potential to significantly improve the accuracy of MR-guided cryosurgery of small lesions, and the accuracy of MR-assisted temperature calculations that are based on precise imaging of the probe location, and boundary geometry of the iceball. 相似文献
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The model study of water mass and energy exchange between the inland water body and atmosphere 总被引:1,自引:0,他引:1
Based on a one-dimensional eddy diffusion model, a model to study the water mass and energy exchange between the water body
(such as lake and wetland) and the atmosphere is developed, which takes the phase change process due to the seasonal melting
and freezing of water and the convection mixing process of energy caused by temperature stratification into consideration.
The model uses enthalpy instead of temperature as predictive variable, which will help to deal with the phase change process
and to design an efficient numerical scheme for obtaining the solution more easily. The performance of the model and the rationality
of taking convection mixing into the consideration are validated by using observed data of Kinneret Lake in Israel and Lower
Two Medicine Lake in Montana State in America. The comparison of model results with observed data indicates that the model
presented here is capable of describing the physical process of water mass and energy between the water body (lake and wetland)
and atmosphere. Comparison of the result from wetland with shallow and deep lakes under the same forcing conditions shows
that the evaporation from wetland is much greater than that from lakes, which accords with the real observation fact and physical
mechanism.
Supported by the National Natural Science Foundation of China (Grant Nos. 40575043 and 40605024) and KZCX-sw-229 相似文献