Conclusion
We propose an individually-controlled multi-tined expandable electrode for the on-demand RFA lesions. The interaction between pre-curved flexible stylet and relatively stiff cannula produces various shapes of our sub-electrodes. By tuning the expanded length and expanding speed of the stylets and cannulas, diverse trajectories can be realized on demand. Along with a rationally applied energy, three individually-controlled sub-electrodes can achieve three-dimensional on-demand conformal ablation efficiently. The ex vivo RFA experiments of porcine kidney and its comparison with a commercial electrode further demonstrate the ability of electrode to ablate RFA lesions on demand. Further ultrasound-guided RFA verifies the potential of our electrode to conformally ablate in vivo target tissue with various morphologic appearances. With appropriate preoperative planning and precise control of our electrode, our device might be an important part of future intelligent surgical systems.
Experimental Section/Methods
Specification of our RFA electrode
There are three tines (sub-electrodes) within the electrode for structural simplicity, and the angle between neighboring sub-electrodes is 120°. The pre-curved stylet, which is made of nitinol, is designed to be as thin as possible for the ease of manufacturing. Therefore, the diameter of pre-curved stylet is 0.4 mm. As RFA targets for small-sized tumors (diameters less than 3 cm), the pre-curved part of stylet is designed to be a little larger, and the radius is 10 mm. Due to the fact that nitinol is hard to be weld with steel, the stylet is stuck in a small segment of steel pipe with an outer diameter of 0.7 mm. The small segment of pipe is then weld with the steel slider. To ensure that the stylet can move freely in the cannula, the inner diameter of cannula is 0.8 mm and the outer diameter is 1.0 mm. Finally, the outer diameter of steel electrode is designed to be 3.5 mm, and the electrode is electrically insulated by a Teflon sheath. The structure parameter of our electrode is illustrated in Figure 18.