An adaptive microwave phased array for targeted heating of deep tumours in intact breast: animal study results.

It has previously been reported in phantoms, that an adaptive radiofrequency phased array can generate deep focused heating distributions without overheating the skin and superficial healthy tissues. The present study involves adaptive microwave phased array hyperthermia tests in animals (rabbits) with and without tumours. The design of the adaptive phased array as applied to the treatment of tumours in intact breast, is described. The adaptive phased array concept uses breast compression and dual-opposing 915 MHz air-cooled waveguide applicators with electronic phase shifters and electric-field feedback, to focus automatically by computer control the microwave radiation in deep tissue. Temperature measurements for a clinical adaptive phased array hyperthermia system demonstrate tissue heating at depth with reduced skin heating.

Radio-frequency tissue ablation: effect of pharmacologic modulation of blood flow on coagulation diameter.

PURPOSE: To determine whether vasoactive pharmacologic agents can alter radio-frequency (RF)-induced coagulation necrosis by modulating hepatic blood flow. MATERIALS AND METHODS: RF ablation was performed in normal, in vivo porcine liver with 1.5-cm internally cooled electrodes and a standardized RF application (i.e., 500 mA for 10 minutes). Ablation was performed without (n = 9) and with pharmacologic modulation of blood flow with halothane (n = 7), vasopressin (n = 6), or epinephrine (n = 7). Laser Doppler techniques were used to quantify changes in hepatic blood flow. Remote thermometry was also performed. Blood flow was correlated with both induced coagulation necrosis and tissue temperatures. RESULTS: Halothane reduced mean blood flow (+/- SD) to 46.1% +/- 8.5 of normal, and vasopressin increased mean blood flow to 132.7% +/- 13.9. Epinephrine caused increased hepatic blood flow centrally (171.1% +/- 31.7) but not peripherally (102.8% +/- 15.4). Mean coagulation diameter was 1.4 cm +/- 0.3 with vasopressin, 2.2 cm +/- 0.4 with normal blood flow, and 3.2 cm +/- 0.1 with halothane (P < .01). After epinephrine infusion, mean coagulation measured 2.3 cm +/- 0.3 peripherally and 1.4 cm +/- 0.5 centrally (P < .01). A linear correlation between coagulation diameter and blood flow was demonstrated (r2 = 0.78). Temperatures 10 and 15 mm from the electrode correlated with both blood flow and coagulation diameter (r2 = 0.65 and 0.60, respectively). CONCLUSION: The coagulation necrosis achieved for a standardized RF application correlates with relative tissue perfusion. Pharmacologic reduction of blood flow during thermally mediated percutaneous ablation may induce greater coagulation necrosis.

Benign prostatic hyperplasia: US-guided transrectal urethral enlargement with radio frequency--initial results in a canine model.

PURPOSE: To enlarge the prostatic urethra with thermal coagulation with transrectal radio-frequency (RF) application in dogs. MATERIALS AND METHODS: Eight aged dogs underwent RF ablation of periurethral prostatic tissue for 6 minutes. Eighteen-gauge electrodes were placed into the periurethral tissues with a transrectal approach and ultrasound (US) guidance. Prostatic and rectal temperatures were measured during RF application. US, conventional and computed tomographic (CT) retrograde urethrography (RUG), and CT were performed immediately (n = 8) and at 3-96 days (n = 6) after ablation. Histopathologic analysis was performed at sacrifice immediately (n = 2), at 28 days (n = 2), or at 3 months (n = 4) after treatment. RESULTS: All procedures were successful with no complications and were performed in less than 30 minutes. Rectal mucosal temperature did not exceed 38 degrees C. Immediately after treatment, CT and US demonstrated 1.2-cm foci of altered periurethral tissue that corresponded to solid coagulated tissue at histopathologic analysis. By day 3, CT, RUG, and US demonstrated that these foci had begun to cavitate, resulting in enlargement of the urethra. Complete cavitation was demonstrated by day 28. Minimal reduction in the degree of urethral enlargement was noted by day 60, but narrowing, urethral strictures, or fistulas were not observed at 3 months. At histopathologic analysis, focal cavitary enlargement with at least doubling of the urethral diameter and with normal urothelium was noted in all dogs surviving at least 28 days. CONCLUSION: Transrectal RF urethral enlargement is feasible and safe in animals and merits investigation for alleviating urethral obstruction due to benign prostatic hyperplasia.