Dynamic intrahepatic flow and cellular alterations during radiofrequency ablation of liver tissue in mice.

PURPOSE: The purpose of this study was to identify microvascular and other associated changes that occur in the liver during focal heating with monopolar radiofrequency (RF). MATERIALS AND METHODS: Intravital video microscopy was performed on exteriorized transilluminated livers of 15 live mice during RF-induced heating of liver parenchyma. Microvascular flow parameters, flow reversibility, microbubble formation, phagocytic activity, and endothelial permeability were recorded throughout a range of tip temperatures (40 degrees C-95 degrees C). RESULTS: During RF application, five discrete zones extended outward from the electrode surface: (i) tissue coagulation, (ii) cellular edema/necrosis, (iii) sinusoidal stasis, (iv) parenchymal shunting, and (v) normal liver tissue. Reversal of stasis in sinusoids and small (<25 microm) vessels occurred at tip temperatures below 50 degrees C. This zone of stasis corresponded to the hyperemic zone on histologic analysis. Although alterations in permeability and phagocytic activity were first identified at 43 degrees C, tip temperatures higher than 55 degrees C always produced local endothelial leakiness to carbon microparticles at the periphery and always inhibited phagocytic activity. At tip temperatures higher than 95 degrees C, microbubble formation occurred with bubbles ultimately tracking through necrotic tissue into patent sinusoids. Larger peripheral vessels (>30 microm) limited extension of coagulation. CONCLUSION: Although coagulation occurs at tip temperatures higher than 50 degrees C, RF heating induced reversible microvascular stasis at temperatures lower than 50 degrees C. Increased sinusoidal endothelial permeability occurs at near-coagulative temperatures. Therefore, targeted endovascular microparticle delivery through this leaky endothelium may provide an additional and complimentary adjunct for RF ablation therapy.

Percutaneous tumor ablation: increased necrosis with combined radio-frequency ablation and intratumoral doxorubicin injection in a rat breast tumor model.

PURPOSE: To determine whether a combination of intratumoral doxorubicin injection and radio-frequency (RF) ablation increases tumor destruction compared with RF ablation alone in an animal tumor model. MATERIALS AND METHODS: R3230 mammary adenocarcinoma 1.2-1.5-cm- diameter nodules (n = 110) were implanted subcutaneously in 84 female Fischer rats. For initial experiments (n = 46), tumors were treated with (a) conventional, monopolar RF (250 mA +/- 25 [SD] at 70 degrees C +/- 1 for 5 minutes) ablation alone; (b) direct intratumoral doxorubicin injection (volume, 250 microL; total dose, 0.5 mg) alone; (c) combined therapy (doxorubicin injection immediately followed by RF ablation); (d) RF ablation and injection of 250 microL of distilled water; or (e) no treatment. In subsequent experiments, amount of doxorubicin (0.02-2.50 mg; n = 40 additional tumors) and timing of doxorubicin administration (2 days before to 2 days after RF ablation; n = 24 more tumors) were varied. Pathologic examination, including staining for mitochondrial enzyme activity and perfusion, was performed, and the resultant tumor destruction from each treatment was evaluated. RESULTS: Coagulation diameter was 6.7 mm +/- 0.6 for tumors treated with RF ablation alone and 6.9 mm +/- 0.7 for those treated with RF ablation and water (P =.52), while intratumoral doxorubicin injection alone produced only 2.0-3.0 mm of coagulation (P <.001). Increased coagulation was observed only with combined doxorubicin injection and RF therapy (P <.001). Coagulation was dependent on concentration and timing of doxorubicin administration, with greatest coagulation (11.5 mm +/- 1.1) observed for doxorubicin administered within 30 minutes of RF ablation. CONCLUSION: Adjuvant intratumoral doxorubicin injection increases coagulation in solid tumors compared with RF ablation alone. Increased tumor destruction is also seen when doxorubicin is administered after RF ablation, which suggests that RF ablation may sensitize tumors to chemotherapy. Such combination therapies may, therefore, offer improved methods for ablating solid tumors.

Radio-frequency thermal ablation with NaCl solution injection: effect of electrical conductivity on tissue heating and coagulation-phantom and porcine liver study.

PURPOSE: To characterize the effects of NaCl concentration on tissue electrical conductivity, radio-frequency (RF) deposition, and heating in phantoms and optimize adjunctive NaCl solution injection for RF ablation in an in vivo model. MATERIALS AND METHODS: RF was applied for 12-15 minutes with internally cooled electrodes. For phantom experiments (n = 51), the NaCl concentration in standardized 5% agar was varied (0%-25.0%). A nonlinear simplex optimization strategy was then used in normal porcine liver (n = 44) to determine optimal pre-RF NaCl solution injection parameters (concentration, 0%-38.5%; volume, 0-25 mL). NaCl concentration and tissue conductivity were correlated with RF energy deposition, tissue heating, and induced coagulation. RESULTS: NaCl concentration had significant but nonlinear effects on electrical conductivity, RF deposition, and heating of agar phantoms (P<.01). Progressively greater heating was observed to 5.0% NaCl, with reduced temperatures at higher concentrations. For in vivo liver, NaCl solution volume and concentration significantly influenced both tissue heating and coagulation (P<.001). Maximum heating 20 mm from the electrode (102.9 degrees C +/- 4.3 [SD]) and coagulation (7.1 cm +/- 1.1) occurred with injection of 6 mL of 38.5% (saturated) NaCl solution. CONCLUSION: Injection of NaCl solution before RF ablation can increase energy deposition, tissue heating, and induced coagulation, which will likely benefit clinical RF ablation. In normal well-perfused liver, maximum coagulation (7.0 cm) occurs with injection of small volumes of saturated NaCl solution.

Perfusion of medium improves growth of human oral neomucosal tissue constructs.

Tissue engineering of the oral mucosa may be useful in congenital cleft palate repairs, defects following extirpative oncologic surgery, and periodontal disease. One of the limitations of in vitro growth of oral mucosal constructs is central necrosis of 3-dimensional tissues. We tested the hypothesis that medium perfusion would enhance oral mucosal histogenesis in vitro. Normal human oral keratinocytes were obtained from young to middle-aged adults. Porous 3-dimensional matrices were prepared from collagen and chondroitin sulfate with some crosslinked with glutaraldehyde. Each device was seeded with 5.0 x 10(5) human oral keratinocytes. The seeded matrices were cultured with or without perfusion of medium at 1.3 ml/min. Histologic analysis of samples cultured for 3, 7, or 14 days showed superior viability and proliferation when perfused. At day 7, the average number of cell layers of the neoepithelium of sponges in the perfused culture system (9.4 +/- 1.0) was 88% greater than for the nonperfused culture system (5.0 +/- 0.9, p<0.005). Glutaraldehyde crosslinking did not influence cellular proliferation or the extent of matrix's shrinkage in either culture system. This study shows that medium perfusion enhanced cell viability and proliferation of human oral keratinocytes cultured in porous 3-dimensional matrices.

Sprayed keratinocyte suspensions accelerate epidermal coverage in a porcine microwound model.

Keratinocyte suspensions can potentially treat a variety of epidermal defects, but the mechanism of action has not been fully determined. We developed a porcine model to study the effect of sprayed cell suspensions delivered on small wounds within a meshed autograft. Paired full-thickness surgically excised wounds were covered with a fully expanded 3:1 meshed split-thickness autograft. A keratinocyte cell suspension was sprayed onto half of the wounds at a seeding density of 2.8 x 10(3) cells/cm2; the remaining wounds were sprayed with cell culture medium alone. Histologic analysis at days 5 and 8 showed an increase in average epidermal thickness, confluence, keratin cysts, and blood vessels in the keratinocyte cell suspension group compared with the cell culture medium control group. Wounds sprayed with the cell suspension showed faster and better quality of epithelialization than wounds sprayed with cell culture medium alone.