State Key Laboratory of Oncogenes and Related Genes, School of Biomedical Engineering, Med-X Research Institute, Shanghai Jiao Tong University, Shanghai, China.
Biomed Eng Online. 2013 Dec 10;12:127. doi: 10.1186/1475-925X-12-127.
Radiofrequency ablation is a promising minimal invasive treatment for tumor. However, water loss due to evaporation has been a major issue blocking further RF energy transmission and correspondently eliminating the therapeutic outcome of the treatment.
A 2D symmetric cylindrical mathematical model coupling the transport of the electrical current, heat, and the evaporation process in the tissue, has been developed to simulate the treatment process and investigate the influence of the excessive evaporation of the water on the treatment.
Our results show that the largest specific absorption rate (QSAR) occurs at the edge of the circular surface of the electrode. When excessive evaporation takes place, the water dehydration rate in this region is the highest, and after a certain time, the dehydrated tissue blocks the electrical energy transmission in the radial direction. It is found that there is an interval as long as 65 s between the beginning of the evaporation and the increase of the tissue impedance. The model is further used to investigate whether purposely terminating the treatment for a while allowing diffusion of the liquid water into the evaporated region would help. Results show it has no obvious improvement enlarging the treatment volume. Treatment with the cooled-tip electrode is also studied. It is found that the cooling conditions of the inside agent greatly affect the water loss pattern. When the convection coefficient of the cooling agent increases, excessive evaporation will start from near the central axis of the tissue cylinder instead of the edge of the electrode, and the coagulation volume obviously enlarges before a sudden increase of the impedance. It is also found that a higher convection coefficient will extend the treatment time. Though the sudden increase of the tissue impedance could be delayed by a larger convection coefficient; the rate of the impedance increase is also more dramatic compared to the case with smaller convection coefficient.
The mathematical model simulates the water evaporation and diffusion during radiofrequency ablation and may be used for better clinical design of radiofrequency equipment and treatment protocol planning.
射频消融是一种有前途的肿瘤微创治疗方法。然而，由于蒸发导致的水分流失一直是阻止进一步传输射频能量并相应消除治疗效果的主要问题。
建立了一个二维对称圆柱形数学模型，该模型耦合了电流传输、热传递和组织中的蒸发过程，用于模拟治疗过程并研究水的过度蒸发对治疗的影响。
我们的结果表明，最大比吸收率（QSAR）出现在电极圆形表面的边缘。当发生过度蒸发时，该区域的脱水速率最高，并且在一定时间后，脱水组织会阻止电能在径向传输。发现从蒸发开始到组织阻抗增加之间存在长达 65 s 的间隔。该模型还用于研究是否故意停止治疗一段时间，以使液态水扩散到蒸发区域是否有助于治疗。结果表明，这并没有明显改善治疗体积。还研究了冷尖端电极的治疗。结果发现，内部冷却剂的冷却条件对水分流失模式有很大影响。当冷却剂的对流系数增加时，过度蒸发将从组织圆柱的中心轴附近开始，而不是从电极边缘开始，并且在阻抗突然增加之前，凝固体积明显增大。还发现较高的对流系数会延长治疗时间。尽管较高的对流系数可以延迟组织阻抗的突然增加，但与较小对流系数的情况相比，阻抗增加的速度也更为剧烈。
该数学模型模拟了射频消融过程中的水蒸发和扩散，可用于更好地设计射频设备和治疗方案。
