射频体外加温体模内热场分布研究

Study on Thermal Map Distribution in Phantom by Short Wave Capacitance Coupled Heating

目的对于热疗,最需要解决的问题是体内的热场分布检测及其调控。本课题主要研究3MHz短波容性加温治疗时非均匀体模内热场分布之规律。用以为临床治疗提供定量依据。方法采用Maxwell方程,对非均匀模体内两及三极板射频加热条件下的电场分布特性进行了计算研究。并自制400mm×220mm×220mm肌肉等效均质体模及220mm×220mm×220mm之非均质体模。在体模内有效加温容积内垂直和水平放置100mm×25mm的猪骨各1根;并放置100mm×5.6mm的硅胶导管1根,12mm×0.7mm的订书针1根作为金属材料。用抗干扰热电偶型数字化实时测温仪进行实时动态同步测温。加热仪采用3MHz肿瘤射频热治疗仪,最大输出功率400W。结果3MHz短波容性(射频)加温治疗之治疗深度可达200mm。其电势分布表现在一是发散得很开。二是有边缘聚集效应。三是非均组织对电场有较大影响。在体模中心水平平面,有效加热范围为50%。非均匀体模内不同介质周围有不同的温升规律。结论1.在使用合适的耦合水袋时,中心温度比表面温度晚约4min达到设定温度。而水袋温度平均每4min上升1℃。因此,可通过降低表面水袋1℃的办法使得中心温度与表面温度在控温时保持一致。2.恒温后10min,金属旁2.5mm处的温度比体模中心的温度可高出约3℃。3.导管旁和骨旁的温度实际升温与中心升温基本一致。因此,在加热区域有骨或引流管时,射频热疗是安全的。4.反射波的调节能力对热场分布有决定性作用。

Objective It is very important to know the electromagnetic power deposition, and to know that if the bolus and heterogeneity materials can induce a variation in the thermal map, both superficially and deeply. The aim of this study is to evaluate the above-mentioned characteristics, in order to support basic concepts and data for clinical practice. Methods The thermal distribution generated by a capacitance coupled adiofrequency（short wave） heating machine. The frequency and the highest power applied were 3MHz and 400W. The size of self made uniformity and heterogeneity phantom were 400mm×220mm×220mm and 220mm×220mm×220mm respectively. 2 bones of pig with size of 100mm×25mm was inserted perpendicularly each other in heterogeneity phantom, 1 radix of 100mm×5.6mm silicon catheter,and 1 staple of size 12mm×0.7mm were also inserted. The way of measurement is of multi-points and online synchronization measuring. Two pairs of coupled water bags with different components were used to investigate electromagnetic match between the biological tissue and the applicator surface and to modify the skin temperature. Results The penetration depth of short wave therapy with frequency ranged between 3MHz could be reached to 200mm or more. The electric voltage field had a strong edge congregating effect. In the center horizontal plan of phantom, the effective heating area was 50% of the area of electronic pole board. Different materials had their own temperature rising laws. Conclusions For an appropriate coupled water bag, the temperature rising time at center of phantom was 4min latter than that of the superficial temperature ascending. As for superficial temperature, the rising rate was 1℃/4min .The objective or final temperature both of the center and superficial could arrive in the same time by depressing 1℃ more of the water bag. After keeping 10min of final temperature,the temperature 2.5mm away from the staple was 3℃ higher than that in the phantom center. And the rising rate of temperature for the silicon catheter and bone were the same as the rate of temperature siging in center. The adjustment of reflecting power was one of the crucial facts for deciding the shape of thermal map.