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introduction

introduction and principle
  • Radio-frequency ablation is the most promising minimally invasive technique used for tumor ablation. Current clinical experience suggests that it is effective, safe, and relatively simple. With this method, high-frequency alternating current is delivered to the tissue via a needle electrode.
  • The electric current agitates the ions in the tissue around the tip of the electrode, creating heat, which leads to localized coagulation necrosis. The main destructive effect of this method occurs because the deposition of electromagnetic energy induces thermal injury to the tissue.

Fig 1: 1. Needle probe 2. dispersive electrode (ground pad) 3. RF field 4. RF device 5. 7. 8. saline infusion 6. closed loop

  • Basically, the term radio frequency refers not to the emitted wave but rather to the alternating electric current that oscillates in the range of high frequency (200-1,200 kHz). Schematically, a closed-loop circuit is created by placing a generator, a large dispersive electrode (ground pad), a patient, and a needle electrode in series. Both the dispersive electrode and needle electrode are active, while the patient acts as a resister. Thus, an alternating electric field is created within the tissue of the patient. Given the relatively high electrical resistance of tissue in comparison with the metal electrodes, there is marked agitation of the ions present in the tumor or liver tissue that immediately surrounds the electrode. This ionic agitation creates friction within the body and thus heat, which can be tightly controlled through modulation of the amount of radio-frequency energy deposited. The nature of the thermal damage caused by radio frequency heating is dependent on both the tissue temperature achieved and the duration of heating. Tissue and cells become more susceptible to chemotherapy or radiation when their temperature is increased to 42°C (i.e., hyperthermia), and heating tissues at 45°C for several hours produces irreversible cellular damage. Heating of tissue at 50°-55°C markedly shortens the duration necessary to irreversibly damage cells to 4-6 minutes. Near immediate coagulation of tissue is induced at temperatures between 60°C and 100°C and is manifest as irreversible damage to mitochondrial and cytosolic enzymes of the cells. At more than 100°-110°C, tissue vaporizes and carbonizes.

Fig 2: In vitro Radio frequency ablation.

Fig 3: In vitro Radio frequency ablation under MR guidance.

Fig 4: In vitro Radio frequency ablation under MR guidance. Visualization of the coagulation area

Fig 5: In vitro Radio frequency ablation under MR guidance. Visualization of the coagulation area