G. Scott Gazelle

Tissue ablation with radiofrequency: Effect of probe size, gauge, duration, and temperature on lesion volume

RATIONALE AND OBJECTIVES We evaluated the parameters affecting the size and distribution of thermal tissue damage produced by radiofrequency electrodes. METHODS Thermal lesions were produced by electrodes connected to a radiofrequency generator in specimens of liver (n = 143) and muscle (n = 20). Various combinations of probe tip exposure (0.5-8 cm), gauge (12-24 gauge), duration of treatment (0.5-12 min), and temperature (80-90 degrees C) were studied. The resulting volumes of tissue coagulation were measured and compared. RESULTS Lesions equal to or less than 1.6 cm in diameter were symmetrically distributed around the electrode. Lesion diameter (but not length) increased with probe gauge and duration of treatment to a maximum of 6 min. However, lesions with mean diameters larger than 1.6 cm could not be produced using a single probe with any technique. Lesion length correlated with probe tip exposure from 1 to 8 cm (r2 = .996). Over the limited range investigated, increased temperature had minimal effects, except for tip exposures greater than 5 cm, in which larger and more uniform lesions resulted. Lesions varied equal to or less than 3 mm in diameter and equal to or less than 5 mm in length for each combination of variables. CONCLUSION Radiofrequency ablation can accurately and reproducibly cause coagulative tissue necrosis. Necrosed tissue volume increases with length of exposed probe tip, larger probes, and sessions lasting at least 6 min.

Treatment of intrahepatic malignancy with radiofrequency ablation: radiologic-pathologic correlation.

Radiofrequency (RF)‐induced tissue coagulation represents a new approach for the thermal destruction of tumors within the liver. The purpose of the current study was to 1) assess technique safety; 2) determine the extent and evolution of induced cellular damage; and 3) correlate the observed pathologic effects with radiologic studies.

Coronary CT Angiography versus Standard Evaluation in Acute Chest Pain

BACKGROUND It is unclear whether an evaluation incorporating coronary computed tomographic angiography (CCTA) is more effective than standard evaluation in the emergency department in patients with symptoms suggestive of acute coronary syndromes. METHODS In this multicenter trial, we randomly assigned patients 40 to 74 years of age with symptoms suggestive of acute coronary syndromes but without ischemic electrocardiographic changes or an initial positive troponin test to early CCTA or to standard evaluation in the emergency department on weekdays during daylight hours between April 2010 and January 2012. The primary end point was length of stay in the hospital. Secondary end points included rates of discharge from the emergency department, major adverse cardiovascular events at 28 days, and cumulative costs. Safety end points were undetected acute coronary syndromes. RESULTS The rate of acute coronary syndromes among 1000 patients with a mean (±SD) age of 54±8 years (47% women) was 8%. After early CCTA, as compared with standard evaluation, the mean length of stay in the hospital was reduced by 7.6 hours (P<0.001) and more patients were discharged directly from the emergency department (47% vs. 12%, P<0.001). There were no undetected acute coronary syndromes and no significant differences in major adverse cardiovascular events at 28 days. After CCTA, there was more downstream testing and higher radiation exposure. The cumulative mean cost of care was similar in the CCTA group and the standard-evaluation group (

PERCUTANEOUS RADIOFREQUENCY TISSUE ABLATION : DOES PERFUSION-MEDIATED TISSUE COOLING LIMIT COAGULATION NECROSIS ?

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Radiofrequency tissue ablation: Increased lesion diameter with a perfusion electrode

4,060, respectively; P=0.65). CONCLUSIONS In patients in the emergency department with symptoms suggestive of acute coronary syndromes, incorporating CCTA into a triage strategy improved the efficiency of clinical decision making, as compared with a standard evaluation in the emergency department, but it resulted in an increase in downstream testing and radiation exposure with no decrease in the overall costs of care. (Funded by the National Heart, Lung, and Blood Institute; ROMICAT-II ClinicalTrials.gov number, NCT01084239.).

American Cancer Society lung cancer screening guidelines

PURPOSE To determine, by decreasing hepatic perfusion during radiofrequency (RF) ablation, whether perfusion-mediated tissue cooling can explain the reduced coagulation observed in in vivo studies compared to that seen with RF application in ex vivo tissue. MATERIALS AND METHODS RF was applied in vivo with use of cooled-tip electrodes to normal porcine liver without (n = 8) and with balloon occlusion of the portal vein (n = 8), celiac artery (n = 3), or hepatic artery (n = 2), and to ex vivo calf liver (n = 10). In vivo trials of vasopressin (0.3-0.6 U/min) infusion during RF application with (n = 10) and without (n = 2) arterial balloon occlusion were also performed. Intraoperative RF was subsequently performed in seven patients with hepatic colorectal metastases with and without portal inflow occlusion. Remote thermometry was performed in four patients. RESULTS RF application (12 minutes) during portal venous occlusion produced larger areas of coagulation necrosis than RF with unaltered blood flow (2.9 cm +/- 0.1 vs 2.4 cm +/- 0.2 diameter; P < .01). With celiac and hepatic artery occlusion, coagulation diameter measured 2.7 cm +/- 0.2 and 2.5 cm +/- 0.1, respectively. Infusion of vasopressin without vascular occlusion reduced coagulation diameter to 1.1 cm. However, different methods of hepatic or celiac arterial balloon occlusion with simultaneous vasopressin infusion produced a mean 3.4 cm +/- 0.2 of necrosis. Coagulation in ex vivo liver was 2.9 cm +/- 0.1 in diameter. Clinical studies demonstrated greater coagulation diameter for metastases treated during portal inflow occlusion (4.0 cm +/- 1.3) than for tumors treated with normal blood flow (2.5 cm +/- 0.8; P < .05). Thermometry documented a 10 degrees C increase compared to baseline at 10 mm and 20 mm from the electrode after 5 minutes of portal inflow occlusion during constant RF application. CONCLUSIONS Perfusion-mediated tissue cooling reduces coagulation necrosis achievable with RF ablation. Reduction of blood flow during RF application increases coagulation in both an animal model and human liver metastases.

Radiofrequency tissue ablation: importance of local temperature along the electrode tip exposure in determining lesion shape and size.

RATIONALE AND OBJECTIVES We sought to induce large zones of coagulation necrosis using radiofrequency (RF) with perfusion electrodes and to define optimal parameters for this system. METHODS We developed RF electrodes with internal cannulas to enable tip perfusion. Lesions were created with monopolar RF in ex vivo and in vivo liver and muscle tissue with and without perfusion of the electrode tip using 0 degree C saline. In separate experiments, wattage, current, procedure duration, tip exposure, and perfused tip temperatures were studied. RESULTS In ex vivo liver tissue, a maximum lesion diameter of 3.1 cm without charring occurred with perfusion at 12 min and 50 W. In in vivo liver tissue with perfusion (tip temperature = 25-35 degrees C) and a 3-cm tip exposure, 80 W were deposited in muscle tissue and 65 W in liver tissue for 12 min without inducing charring. Lesion diameters were 4.5 cm and 2.4 cm, respectively. By comparison, without perfusion a maximum of 20 W could be deposited into either tissue type, resulting in 1.8-cm muscle lesions and 1.2-cm liver lesions. Tip temperatures between 45 degrees C and 55 degrees C resulted in charring. Smaller but predictable lesion diameters were created with a lower power, a shorter tip exposure, or both. Of all the parameters, diameter correlated best with the current applied. CONCLUSION Perfusion of RF electrodes with chilled saline allows for increased power deposition without tissue charring, increasing the volume of coagulation necrosis created with a single electrode insertion. Perfusion electrodes therefore might decrease the number of probe insertions required for percutaneous tumor ablation therapy or allow for the treatment of larger lesions.

Radiofrequency tissue ablation in the rabbit lung: Efficacy and complications

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PERCUTANEOUS RADIOFREQUENCY TISSUE ABLATION : OPTIMIZATION OF PULSED-RADIOFREQUENCY TECHNIQUE TO INCREASE COAGULATION NECROSIS

RATIONALE AND OBJECTIVES We determined whether heat distribution along a radiofrequency (RF) electrode would be uniform when longer tip exposures are used and whether local temperature effects would influence the shape of induced tissue coagulation. METHODS Thermistors were embedded within 18-gauge RF electrodes at both ends and in the middle of the exposed tip. The length of tip exposure varied from 1 to 7 cm. RF was applied in vitro to pig liver for 6 min using a constant tip temperature, which was varied in 10 degrees C increments from 60 degrees C to 110 degrees C. Experiments were performed in triplicate. The 3- and 5-cm probes were used at a 90 degrees C tip temperature to create lesions in live pig liver and muscle using similar parameters. Temperature was measured throughout the procedure. Observable coagulation necrosis was measured at the end of the treatment. Regression analysis was used to evaluate the local temperature-lesion diameter relationship. RESULTS Temperatures were not uniform along the tip exposure for any given trial. Temperature variation increased with higher tip temperatures and longer tip exposures. The diameter of local coagulation necrosis was a function of the local mean temperature. For in vitro trials, no coagulation was seen when the local temperature was less than 50 degrees C. Temperatures above this threshold resulted in progressively greater lesion diameter, with a minimum of 1 cm of necrosis occurring at 71 degrees C. Additional increases in lesion diameter (1.4-1.6 cm) were observed at approximately 90 degrees C. Mathematical modeling demonstrated a best-fit curve: lesion diameter (in cm) = ¿1.4 + 0.03 (tip exposure)¿ ¿1 - e [-0.067(local temp - 49.5 degrees C)]¿, r2 = .986, SD = 0.14 cm for each curve. In living tissue, less uniformity in the shape of coagulation necrosis was seen around the electrodes. Local temperature-lesion diameter data fit the same logarithmic relation, but the threshold for coagulation necrosis was 8.5 degrees C higher than for in vitro specimens. CONCLUSION Using a single-probe technique for RF-induced tissue necrosis, the diameter of tissue coagulation may be predicted by the local temperature along the exposed electrode. The uniformity of temperature decreases with increased tip exposures. This effect may be partially corrected by creating lesions at higher tip temperatures, where necrosis diameter is increased. Because effects are more pronounced in vivo, uniform volumes of tissue necrosis are limited to tip exposures of 3 cm or less.

Cost-Effectiveness of Computed Tomography Screening for Lung Cancer in the United States

RATIONALE AND OBJECTIVES We assessed the feasibility and safety of performing percutaneous radiofrequency ablation of pulmonary tissue in rabbits. METHODS Using an aseptic technique and computed tomography (CT) guidance, insulated 19-gauge aspiration biopsy needles were inserted into the right lower lobe of eight New Zealand White rabbits. Radiofrequency was applied via a coaxial electrode for 6 min at 90 degrees C. Probe-tip temperature, tissue impedance, and wattage were recorded at baseline and at 60-sec intervals throughout the procedure. CT scanning was used to assess tissue destruction and the presence or absence of pneumothorax immediately after the procedure and at 24 hr, 3 days, 10 days, 21 days, and 28 days. Three rabbits were sacrificed immediately, and the remaining rabbits were euthanized at 24 hr and at 3 days. 10 days, and 28 days (two rabbits). Gross and microscopic pathology were obtained and correlated with CT findings. RESULTS The mean initial tissue impedance was 509 +/- 197 omega, marked changes in tissue impedance were found during the procedure (240-1380 omega). Rigid temperature control required continuous manual fine-tuning of generator output. Increased respiratory rate was noted in one rabbit during the first 30 sec of radiofrequency application. Homogeneous, ovoid opacities 8.4 +/- 2.4 mm in diameter and 1.4 +/- 0.1 cm in length were found by CT scanning immediately after the procedure. These opacities showed maximal consolidation at 3 days, corresponding to coagulative necrosis and a peripheral acute inflammatory reaction. At 10 days, peripheral hyperattenuation with central hypoattenuation (early fibrosis surrounding degenerating blood products) was seen. Minimal residual fibrosis, pleural scarring, or both were noted by 28 days, suggesting a rapid, near-total recovery from the procedure. Lesion sizes were within 2 mm of gross pathologic findings. Pneumothoraces were noted in three of the eight rabbits (37.5%). CONCLUSION Radiofrequency tissue ablation was safely performed in pulmonary parenchyma via a percutaneous, transthoracic approach using a coaxial needle technique. Tissue response to thermal injury was predictable and easily monitored by CT scanning with excellent radiologic-pathologic correlation.