Alba-Martínez Jose, Trujillo Macarena, Blasco-Gimenez Ramon, Berjano Enrique
Biomedical Synergy, Electronic Engineering Department, Universitat Politècnica de Valencia, Spain.
Open Biomed Eng J. 2012;6:16-22. doi: 10.2174/1874230001206010016. Epub 2012 Mar 8.
Radiofrequency cardiac ablation (RFCA) has been used to treat certain types of cardiac arrhythmias by producing a thermal lesion. Even though a tissue temperature higher than 50ºC is required to destroy the target, thermal mapping is not currently used during RFCA. Our aim was thus to develop mathematical models capable of estimating tissue temperature from tissue characteristics acquired or estimated at the beginning of the procedure (electrical conductivity, thermal conductivity, specific heat and density) and the applied voltage at any time. Biological tissue was considered as a system with an input (applied voltage) and output (tissue temperature), and so the mathematical models were based on transfer functions relating these variables. We used theoretical models based on finite element method to verify the mathematical models. Firstly, we solved finite element models to identify the transfer functions between the temperature at a depth of 4 mm and a constant applied voltage using a 7Fr and 4 mm electrode. The results showed that the relationships can be expressed as first-order transfer functions. Changes in electrical conductivity only affected the static gain of the system, while specific heat variations produced a change in the dynamic system response. In contrast, variations in thermal conductivity modified both the static gain and the dynamic system response. Finally, to assess the performance of the transfer functions obtained, we conducted a new set of computer simulations using a controlled temperature protocol and considering the temperature dependence of the thermal and electrical conductivities, i.e. conditions closer to those found in clinical use. The results showed that the difference between the values estimated from transfer functions and the temperatures obtained from finite element models was less than 4ºC, which suggests that the proposed method could be used to estimate tissue temperature in real time.
射频心脏消融术（RFCA）已被用于通过产生热损伤来治疗某些类型的心律失常。尽管破坏靶点需要高于50ºC的组织温度，但目前RFCA过程中并不使用热图谱。因此，我们的目标是开发数学模型，能够根据手术开始时获取或估计的组织特征（电导率、热导率、比热和密度）以及任何时刻施加的电压来估计组织温度。生物组织被视为一个具有输入（施加电压）和输出（组织温度）的系统，因此数学模型基于关联这些变量的传递函数。我们使用基于有限元法的理论模型来验证这些数学模型。首先，我们求解有限元模型，以确定使用7Fr和4mm电极时，4mm深度处的温度与恒定施加电压之间的传递函数。结果表明，这些关系可以表示为一阶传递函数。电导率的变化仅影响系统的静态增益，而比热变化会导致系统动态响应发生变化。相比之下，热导率的变化会同时改变静态增益和系统动态响应。最后，为了评估所获得传递函数的性能，我们使用受控温度协议并考虑热导率和电导率的温度依赖性，即更接近临床使用情况的条件，进行了一组新的计算机模拟。结果表明，从传递函数估计的值与从有限元模型获得的温度之间的差异小于4ºC，这表明所提出的方法可用于实时估计组织温度。
