Hepatic hemorrhage caused by percutaneous tumor ablation: radiofrequency ablation versus cryoablation in a porcine model.

PURPOSE: To determine the extent of hepatic hemorrhage caused by percutaneous cryoablation performed with a small-diameter cryoablation probe compared with that caused by percutaneous radiofrequency (RF) ablation in a porcine model. MATERIALS AND METHODS: The study was pre-approved by the institutional research animal care and use committee, and husbandry and experiments complied with National Institutes of Health standards for care and use of laboratory animals. Percutaneous hepatic ablation was performed in 18 domestic pigs (mean weight, 45 kg) by using a 17-gauge (1.5-mm-diameter) RF electrode (n = 6), a cluster of three RF electrodes (n = 6), or a 13-gauge (2.4 mm-diameter) cryoprobe (n = 6). Ablation was performed in four sites per liver. Total blood loss, minimum lesion diameter, maximum lesion diameter, and lesion volume were determined for each group and compared by using analysis of variance. RESULTS: Mean blood loss was 11.11 mL +/- 11.47 (standard deviation), 105.29 mL +/- 175.58, and 28.06 mL +/- 30.97 with the single RF electrode, RF electrode cluster, and cryoablation probe, respectively. Mean minimum and maximum lesion diameters were largest with the RF electrode cluster (2.40 and 3.98 cm, respectively), followed by the cryoablation probe (2.38 and 3.94 cm) and single RF electrode (1.49 and 2.63 cm). Mean minimum and maximum lesion diameters were significantly different between the single RF electrode and the RF electrode cluster, as well as between the single RF electrode and the cryoablation probe (P < .001). Mean lesion volume was largest for the RF electrode cluster (24.03 cm3), followed by those for the cryoablation probe (17.46 cm3) and single RF electrode (9.05 cm3) (single RF electrode vs cryoablation probe, P < .05). Lesion volumes were not significantly different with the RF electrode cluster versus the single RF electrode (P = .052) or with the RF electrode cluster versus the cryoablation probe (P = .381). CONCLUSION: Mean blood loss from percutaneous cryoablation in this model was between that for RF ablation with the single electrode and that for RF ablation with the electrode cluster.

Microwave ablation with loop antenna: in vivo porcine liver model.

PURPOSE: To determine the effectiveness of tissue ablation with a loop microwave antenna in various configurations in porcine liver tissue. MATERIALS AND METHODS: Microwave energy was applied for 7 minutes at 60 W in six porcine livers (mean weight, 68.2 kg) by using single (n = 7) or dual 2.7-cm loop microwave probes in parallel (n = 9) or orthogonal (n = 9) configurations. Volume, diameter, shape, and temperature of the zone of necrosis and the presence of viable tissue inside the loop were determined and compared by means of factorial analysis of variance. RESULTS: Mean lesion volume and maximum diameter, respectively, were 32.2 cm(3) +/- 14.4 (SD) and 4.6 cm +/- 1.4 for lesions ablated with parallel probes (parallel lesions), 29.5 cm(3) +/- 8.1 and 4.3 cm +/- 0.6 for lesions ablated with orthogonal probes (orthogonal lesions), and 6.4 cm(3) +/- 1.9 and 3.4 cm +/- 0.62 for lesions ablated with single probes (single lesions) (P <.05, single vs parallel and orthogonal lesions). Mean minimum diameter was greatest for orthogonal lesions (3.5 cm +/- 0.53; P =.017, parallel vs orthogonal lesions). Orthogonal lesions had the highest mean internal temperature (97.2 degrees C) versus parallel (91.9 degrees C) and single (60.0 degrees C) lesions. All orthogonal lesions heated to 60 degrees C in comparison to eight of nine parallel and four of seven single lesions. The mean time to reach 60 degrees C was shortest for orthogonal lesions (93.3 seconds) versus parallel (123.8 seconds) and single (263.0 seconds) lesions. Orthogonal lesions were the most spherical. Viable tissue was present in the center of five of seven single, six of nine parallel, and zero of nine orthogonal lesions. CONCLUSION: Loop microwave antennas allow precise control and effective ablation of targeted tissue, particularly in the orthogonal configuration.

Using a saline chaser to decrease contrast media in abdominal CT.

OBJECTIVE: The purpose of this study was to compare hepatic tumor conspicuity on CT after injection of either 150 mL of contrast material or 100 mL of contrast material plus a 50-mL saline chaser. SUBJECTS AND METHODS: We evaluated 86 hypoattenuating liver metastases in 26 patients. Patients underwent CT in two sessions separated by a mean of 85 days: one time with 150 mL of contrast material and the other time with 100 mL of contrast material followed by a 50-mL saline chaser. The order of the sessions was randomized. Contrast material was administered via power injector and matched for injection rate and delay time. Attenuation values were obtained from normal liver tissue and metastases and from the spleen, kidney, aorta, and inferior vena cava. RESULTS: The 150 mL dose of contrast material caused slightly greater liver and tumor attenuation than 100 mL of contrast material with a chaser (mean hepatic attenuation, 95.6 vs 89.8 H, respectively; p < 0.03, paired t test; mean tumor attenuation, 53.2 vs 49.1 H, respectively; r = 0.71, p = 0.09). The difference in conspicuity of liver lesions was slightly greater with 150 mL than with 100 mL with a chaser (46.8 H vs 44.2 H; r = 0.46, p = 0.08, paired t test), but was of doubtful clinical significance (2.6 H). Kidney, spleen, and vascular structures enhanced more with 150 mL than with 100 mL and a chaser. CONCLUSION: Using 100 mL of contrast material and a saline chaser did not result in a meaningful difference in liver parenchyma attenuation or lesion conspicuity compared with using 150 mL of contrast medium alone. Routine use of a chaser for abdominal CT may yield cost savings and a decreased risk of contrast nephropathy.