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FIGURE 18 ■ Percutaneous ultrasound guidance for renal radiofre-quency ablation. The radiofrequency ablation electrode is seen as a linear echogenic structure (arrow). As the procedure continues, additional bright echoes (arrowhead) obscure the renal mass.

During radiofrequency ablation, the extent of coagulation cannot accurately be predicted, and postprocedural imaging is necessary in order to assess the success of the ablation.

Patients are seen at four to six weeks after open partial nephrectomy for routine follow-up and have a physical examination, a serum creatinine level check, and an excretory urogram. Imaging with computed tomography or ultrasound is performed earlier in any patient who has clinical signs or symptoms of abscess, hematoma, urinary leak, or fistula.

shadowing does not obscure deep margin and protects the probe from the cryoablation (33). Using multiple probe positions (i.e., rotating and translating the probe along the renal surface) may be necessary to ensure complete ablation. Extension of the iceball more than 3 mm beyond the tumor margin ensures adequate freezing of the lesion for cell death (34).

During radiofrequency ablation, an electrical current flows from the tip of a needle electrode into the surrounding tissue toward grounding pads placed on the patient's thighs, and produces heat and coagulative necrosis (35). Adequate tissue treatment temperature is 70°C. When monitoring the ablation, increasing bright echoes are visualized from the electrode tip on ultrasound due to microbubble formation (Fig. 18). This provides a rough estimate of the size of the treatment area (36). Larger lesions require the use of multiple overlapping treatment zones to achieve adequate coverage for complete ablation.

During radiofrequency ablation, the extent of coagulation cannot accurately be predicted, and postprocedural imaging is necessary in order to assess the success of the ablation.

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