Background and objectives

A constant voltage (DC voltage) is usually used in radiofrequency ablation (RFA) computer models to mimic the radiofrequency voltage. However, in some cases a low frequency sine wave voltage (AC voltage) may be used instead. Our objective was to assess the thermal impact of replacing DC voltage by low-frequency AC voltage in RFA computer modeling.

Methods

A 2D model was used consisting of an ablation electrode placed perpendicular to the tissue fragment. The Finite Element method was used to solve a coupled electric-thermal problem. Quasi-static electrical approximation was implemented in two ways (both with equivalent electrical power): (1) by a constant voltage of 25 V in the ablation electrode (DC voltage), and (2) applying a sine waveform with peak amplitude of 25√2 V (AC voltage). The frequency of the sine signal (f_AC) varied from 0.5 Hz to 50 Hz.

Results

Sine wave thermal oscillations (at twice the f_AC frequency) were observed in the case of AC voltage, in addition to the temperature obtained by DC voltage. The amplitude of the oscillations: (1) increased with temperature, remaining more or less constant after 30 s; (2) was of up to ±3 °C for very low f_AC values (0.5 Hz); and (3) was reduced at higher f_AC values and with distance from the electrode (almost negligible for distances > 5 mm). The evolution of maximum lesion depth and width were almost identical with both DC and AC.

Conclusions

Although reducing f_AC reduces the computation time, thermal oscillations appear at points near the electrode, which suggests that a minimum value of f_AC should be used. Replacing DC voltage by low-frequency AC voltage does not appear to have an impact on the lesion depth.

中文翻译：

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在射频消融计算机建模中用低频正弦波电压代替恒定电压的热影响。

背景和目标

在射频消融（RFA）计算机模型中通常使用恒定电压（DC电压）来模拟射频电压。但是，在某些情况下，可以使用低频正弦波电压（交流电压）来代替。我们的目标是评估在RFA计算机建模中用低频AC电压代替DC电压的热影响。

方法

使用由垂直于组织碎片放置的消融电极组成的2D模型。有限元法被用来解决电热耦合问题。通过两种方式（均具有相等的电功率）来实现准静态电近似：（1）通过在消融电极中施加25 V的恒定电压（DC电压），以及（2）施加峰值振幅为25的正弦波形√2V（交流电压）。正弦信号的频率（f _AC）从0.5 Hz到50 Hz。

结果

正弦波热振荡（以两倍的˚F _AC在交流电压的情况下，观察到的频率）中，除了由直流电压所获得的温度。振荡幅度：（1）随着温度增加，在30 s后保持大致恒定；（2）对于非常低的f _AC值（0.5 Hz），最高可达±3°C ；（3）在较高的f _AC值和距电极的距离处减小（对于距离> 5 mm几乎可以忽略）。最大病变深度和宽度的变化与DC和AC几乎相同。

结论

尽管减小f _AC会减少计算时间，但在电极附近的点会出现热振荡，这表明应使用f _AC的最小值。用低频交流电压代替直流电压似乎对病变深度没有影响。