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material and methods

  • We used a Berchtold® Elektrotom 106 Hitt generator and Berchtold® 16-gauge probes with 2.5 cm electrode length for creating bipolar lesions. For clinical use, the probes are inserted 3 cm apart and infused (hypertonic saline 5.85%, 50 Watt, 62 ml/ hour). Initially we created different bipolar ablation where we varied probe distance in 0.5-cm increments. We found the ideal distance (i.e., largest lesion size) at 3 cm probe distance. For interval less than 1 cm a risk of short cut and electric arc is possible. In this case, less power should be applied. For creating bipolar lesions, we attached a second probe to the generator replacing the dispersive electrode using a modified cable for connection. The control circuit varies the applied power depending on the impedance.
  • We used five ex vivo beef livers for experiments. We performed preliminary ex vivo experiments with bipolar configuration at probe distances of 4, 3.5, 3, 2.5, and 1 cm. When the distance was 4 and 3.5 cm, in some cases we found a gap of viable tissue between two lesions created by the two probes after performing ablation. Subsequently, probes were placed 3 cm apart. Both monopolar and bipolar ablations were performed for 10 min using impedance-controlled mode. After the experiments were completed, the liver was placed in 10% formalin for fixation. The lesion border was determined by optical inspection in ex vivo livers. In patients, an MR was performed 10 to 14 days after the procedure to evaluate the lesion size with dynamic sequences and injection of contrast medium. Lesion volume was computed by multiplying the lesion area of each slice-by-slice thickness, and summating results for all slices.
  • After ex-vivo experimentation we used the bipolar technique in vivo for patients in 25 cases of tumors including liver and bone. For clinical use, all procedures were performed with the patients under general anesthesia. The placement of the electrodes was guided by CT. The probes were inserted to trap the tumor in a pincer technique.

Berchtold® Radio-frequency device with injection of continuous saline. The same generator is used for bipolar technique.

 

Berchtold® Radio-frequency device: 1. Monitor of Energy and temperature. 2. Impedance control. 3. Injector for continuous injection of saline. 4. Power. 5. Timing. 6. Needle electrode input.

 

Interventional CT room.