| These days, it is well applied in clinic to treat bone tumors using interstitial microwave hyperthermia techniques. The curative effect is more notable if the therapy combines with radiotherapy and chemotherapy. The recurrence rate is slower and the function of patients recovers well after operation if it is used to treat bone tumors in early and middle stage. However, further researches on heating time, heating position, heating depth and so on is expected because of currently inadequate fundamental researches, so it often affects curative effect.More experimental studies are needed to solve this problem, which is based on heating bone tumor equivalent phantom models. The artificial models can substitute for real tissues when their electrical and heating characteristics are closely similar, so the models could simulate bone tumors when heating. The dielectric properties of phantom models must be the same as those of real tissues', which could ensure their SARs (Specific Absorption Rates) are the same. So it is one of the chief factors to set up measurement systems that can measure dielectric parameters of real tissues and equivalent phantom models, so as to carry through experimental studies.The frequency at 2450MHz is often used by microwave hyperthermia in clinic. Three measurement systems are developed in order to measure the dielectric parameters of bone tumor tissues and the equivalent phantom models at 2450MHz. 1 > Frequency conversion method is a kind of indirect way.The system is composed of three-state four-port reflectometer, standard short-circuit component (standards), power detector and sample collector, and its frequency ranges from 8.2GHz to 12.4GHz. The sample is put in a symmetric and reciprocal two-port network, and the dielectric parameters at9370MHz are measured by three-state four-port reflectometer ------three pointconversion, which are converted into the dielectric parameters at 2450MHz by empirical formulas. 2^ The fundamental of the vector network analyzer method is the same as that of the frequency conversion method. The system is composed of Wiltron 37269A vector network analyzer, standard short-circuit component (standards), waveguide-coaxial line transducer and sample collector. This method could measure the dielectric parameters of the sample at 2450MHz directly, and it is unnecessary to convert the parameters by empirical formulas. 3 > Perturbational method can calculate the dielectric parameters on the basis of minute frequency changes caused by small dielectric in the resonant cavity. The system includes AV3616X scalar network analyzer, rectangular waveguide, waveguide-coaxial line transducer, AV10314A detector and electric bridge.Of the three measurement systems, the frequency band of the frequency conversion method is much wider, but the conversion is needed when measuring the dielectric parameters of the sample at 2450MHz by using the empirical formulas, which can cause greater errors. The vector network analyzer method could measure the dielectric parameters of the sample at 2450MHz directly, which greatly decreases the errors. However, the method requires higher facture of the sample, and when the frequency changes, the hardware changes too. Perturbational method can measure dielectric parameters of the sample at 2450MHz directly also, and the precision is much higher. But it requires very precise volume value of the sample, and the frequency changes also cause the hardware changes.It is one of the important ways in the studies on biological effects and medical applications of electromagnetic field to use phantom model to carry on experimental research. Two kinds of bone tumor equivalent phantom models are put up in terms of characteristics of real tissue equivalent phantom models. The ingredients of the first include acrylamide, sodium hydrogen sulfite, carboxymethylcellulose sodium, NaCl solutions and distilled water. After measuring the dielectric parameters by virtue of measurement system, ingredients of the phantom model are changed in order to reg... |
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