Biomedical subjects
Andreas Lubienski
Publications and source records attributed to Andreas Lubienski.
Effects of vascular perfusion on coagulation size in radiofrequency ablation of ex vivo perfused bovine livers.
OBJECTIVES: A standardized perfused ex vivo bovine liver model was used to evaluate the effect of organ perfusion on coagulation size and energy deposition during radiofrequency ablation (RFA) procedures. MATERIALS AND METHODS: Bovine livers were perfused in a tank after rinsing the prepared liver vessels with anticoagulants. Tyrode's solution, oxygenated and heated to 36.5 degrees C, was used as perfusion medium. A flow and pressure controlled pump regulated Portal vein circulation; a dialysis machine provided pulsatile arterial circulation. Impedance-guided radiofrequency ablations were performed with 4-cm LeVeen electrodes with and without underlying liver perfusion. Two-dimensional diameters (Dv, Dh) of each ablation area were measured after dissecting the livers. RESULTS: In 4 bovine livers weighing 8.85 +/- 0.83 kg per organ (min, 7.7 kg; max, 9.7 kg) altogether 40 RF ablations were performed. A total of 20 ablations were generated with underlying liver perfusion (group 1) and 20 ablations with no liver perfusion (group 2). In group 1, Dv was 28.4 +/- 5.3 mm, Dh 38.6 +/- 7.8 mm, and energy deposition 36.9 +/- 18.0 kJ. The 20 ablation areas generated without liver perfusion displayed statistically significant differences, with Dv being 35.7 +/- 6.5 mm (P = 0.001), Dh 49.5 +/- 9.4 mm (P = 0.001), and energy deposition 25.5 +/- 13.0 kJ (P = 0.018). CONCLUSION: The model reproduced the cooling effect of perfused tissue during RFA. The ablation areas produced under perfusion conditions had smaller diameters despite longer exposure times and higher energy deposition.
Hepatocellular carcinoma: interventional bridging to liver transplantation.
Hepatocellular carcinoma (HCC) is one of the most common solid cancers worldwide with surgery being considered the treatment of choice. However, it is limited in view of the hepatic dysfunction and high recurrence rates associated with the disease. Liver transplantation offers the advantage of both, eradicating the tumor and treating the underlying liver disease and is the only chance for cure in patients suffering from HCC. Survival is known to reach 70% after 5 years and recurrent tumor can be found in less than 20% provided transplantation is restricted to patients with single tumors < or =5 cm or three nodules <3 cm (Milan criteria). However, donor organs are limited and the time on the transplant waiting list is up to 6 or 12 months in Europe and the United States with up to 30-40% dropouts per year. It has been demonstrated that patients with untreated HCC while on the waiting list longer than 6-10 months do not have any benefit in survival after liver transplantation. Interventional treatment options such as transarterial chemoembolization and percutaneous ablation techniques documented promising results concerning the reduction of dropouts from the waiting list and the potential risk for recurrent tumor. Mortality and morbidity were considerably low when radiological interventions had been considered as bridging therapies for liver transplantation. Percutaneous therapies come along with tumoral seeding of 0.1% to 0.6%. Adjuvant treatment with TACE, PEI, and/ or RFA in T1- and T2-staged HCC resulted in tumor-free survival after transplantation of 95.2% after 4 years and intention-to-treat survival of 94%, 85%, and 79% at 1, 2, and 3 years, respectively. Aggressive ablation therapy with a short transplant waiting time has the potential to optimize the use of liver transplantation for curative intent in selected cirrhotic HCC patients. Especially combined treatments seemed to play a key role in achieving complete tumor necrosis associated with improved disease-free survival after liver transplantation. In conclusion, no evidence based data exist in the literature supporting the efficacy of adjuvant interventional treatment modalities for HCC in patients awaiting liver transplantation. However, it has been shown that adjuvant (multimodal) interventional treatments seem a promising option for safe and effective bridging.
Radiofrequency ablation in metastatic disease.
The liver is the most common site of metastas from colorectal cancer. Hepatic metastases are the major cause of morbidity and mortality in those patients. Surgical resection provides the greatest potential for cure in patients with secondary liver tumors but can be offered to only a small number of patients (5%-20%). In selected patients image-guided radiofrequency ablation (RFA) takes over the role as curative treatment option, especially in patients who are technically not eligible for surgery. Technical aspects, criteria for patient selection, aspects concerning follow-up imaging and results of percutaneous radiofrequency ablation in liver metastases from colorectal cancer are discussed.
Experimental functional analysis of self-expanding stents using a new developed ex vivo model.
OBJECTIVE: To modify an ex vivo test procedure for balloon expandable stents as a means to evaluate the mechanical properties of self-expanding stents. METHODS: Ten stents each of 7 different stent models measuring 10 mm in diameter (LUMINEXX Vascular Stent/Memotherm-FLEXX Vascular Stent [identical to Bard], Jostent SelfX, Jostent SelfX high radial force [Jomed], sinus-Repo stent, sinus-SuperFlex stent [Optimed], S.M.A.R.T. stent [Cordis], and Easy Wallstent [Boston Scientific]) were implanted in common iliac arteries taken from cadavers (n = 35). They were randomized to either the right or left bifurcation. The vessels were then maintained at 37 degrees C for 24 hours in a special solution that inhibited autolysis, making it possible for the stents to expand. Afterward, they were filled with silicone caoutchouc. After another 24 hours, the vessel walls and stents were removed from the hardened casts. By means of fine analytic measurements, we demonstrated that the volume of a hardened cast formed in the stent cylinder is an indirect but precise measure of the radial force of a stent. Furthermore, using correlation analysis, we examined the relationship between radial force and vessel diameter as well as that between radial force and the degree of arteriosclerosis. RESULTS: The differences between the actually measured volumes, ie, radial strength, (1 cm stent length) of the various stent models (LUMINEXX/Memotherm-FLEXX: 0.6198 mL +/- 0.1537 mL; Jostent SelfX: 0.6756 mL+/- 0.1298 mL; Jostent SelfX high radial force: 0.6321 mL+/- 0.1817 mL; sinus-Repo stent: 0.5508 mL+/- 0.1485 mL; sinus-SuperFlex stent: 0.6174 mL+/- 0.0953 mL; S.M.A.R.T. stent: 0.5627 mL+/- 0.1270 mL; and Easy Wallstent: 0.5613 mL+/- 0.1019 mL) were not statistically significant (P > 0.05), but the differences to the theoretically possible volumes that we had previously calculated were highly significant (P < 0.05). Correlation and regression analyses demonstrated a significantly stronger relationship between stent volume and vessel diameter than between stent volume and degree of arteriosclerosis. CONCLUSION: The modification of our ex vivo model of balloon-expandable stents now makes it possible for researchers to obtain comparable and realistic values for both the radial force and the expansion of self-expanding stents under realistic conditions. Our methods should therefore be employed as an additional procedure to optimize the preclinical evaluation of new stent during certification.
Resistance to hoop stress in balloon expandable stents: evaluation in an ex vivo model.
RATIONALE AND OBJECTIVES: To develop a new model for a more realistic evaluation of radial strength and elastic recoil of balloon expandable stents using a new ex vivo model in human cadaver bifurcations of the aorta. MATERIALS AND METHODS: Four different stents (each group n = 10) were implanted in cadaver common iliac arteries. Randomization was performed either to right or left iliac artery. The specimens were cast filled with silicone caoutchouc and after 24 hours the vascular walls including the stents were removed from the hardened casts. The weight of the cast cylinders of the stents was measured in air and in purified water: the difference of the two values resulted in the buoyancy force and because of that the volume of the bodies as a relative degree for the radial strength could be calculated. The findings were correlated with the workbench tests of the manufacturers. RESULTS: Manufacturer's workbench tests were incomparable because of wide spread specifications. There was a significant difference between the theoretical maximal volume (0.866 mL) and the real cast volumes ( P< 0.025) that corresponds directly to the elastic recoil of the stents. The following mean real cast volumes were measured (corrected for 1 cm): Sinus-Stent 0.677 mL, Palmaz-Stent 0.708 mL, Jostent 0.715 mL, Saxx-Stent 0.732 mL, thus reflecting the various degree of radial strength; therefore, the ranking in radial strength resistance was Saxx, Jostent, Palmaz, and Sinus. CONCLUSION: High radial strength and low elastic recoil are important requirements of any stent design. Ex vivo tests unlike in vitro physical testing facilitate a realistic evaluation of the inherent stent characteristics. The model used in this study proved to be uniformly valid for physical stent design testing.
Retained surgical sponge with migration into the duodenum and persistent duodenal fistula.
Migration of a retained surgical sponge into the bowel is a rare cause of bowel obstruction. Thus far, there have not been any reports that the site of initial migration of the sponge was identified by imaging studies or surgical exploration because the onset of symptoms is usually delayed. Unique about the case presented herein is that a barium meal follow-through study revealed a duodenal fistula that had developed after uneventful cholecystectomy due to a retained surgical sponge that had migrated into the duodenum and obstructed the distal jejunum. Imaging findings are presented and discussed.
Radiofrequency ablation (RFA): development of a flow model for bovine livers for extensive bench testing.
PURPOSE: To develop a flow model for bovine livers for extensive bench testing of technical improvements or procedure-related developments of radiofrequency ablation excluding animal experiments. METHODS: The perfusion of bovine livers directly from the slaughterhouse was simulated in a liver perfusion tank developed for the experimental work. The liver perfusion medium used was a Tyrode solution prepared in accordance with physiologic criteria (as for liver transplants) which was oxygenated by an oxygenator and heated to 36.5 degrees C. Portal vein circulation was regulated via a flow- and pressure-controlled pump and arterial circulation using a dialysis machine. Flow rate and pressure were adjusted as for the physiology of a human liver converted to bovine liver conditions. The fluid discharged from the liver was returned into the perfusion system through the vena cava. Extendable precision swivel arms with the radiofrequency probe attached were mounted on the liver perfusion tank. RFA was conducted with the RF3000 generator and a 2 cm LeVeen needle (Boston Scientific, Ratingen, Germany) in a three-dimensional grid for precise localization of the generated thermolesions. RESULTS: Four bovine livers weighing 8.4 +/- 0.4 kg each were prepared, connected to the perfusion system, and consecutively perfused for the experiments. Mean arterial flow was 569 +/- 43 ml/min, arterial pressure 120 mmHg, portovenous flow 1440 +/- 305 ml/min, and portal pressure 10 mmHg. Macroscopic evaluation after the experiments revealed no thrombi within the hepatic vessels. A total of 136 RF thermolesions were generated with an average number of 34 per liver. Mean RF duration was 2:59 +/- 2:01 min:sec with an average baseline impedance of 28.2 +/- 3.4 ohms. The mean diameter of the thermolesions along the puncture channel was 22.98 +/- 4.34 mm and perpendicular to the channel was 23.27 +/- 4.82 mm. CONCLUSION: Extracorporeal perfusion of bovine livers with consecutive standardized RF ablation was feasible. The bovine liver flow model seems to allow extensive, standardized evaluation of technical or procedure-related developments of RF systems.
Radiofrequency thermal ablation: increase in lesion diameter with continuous acetic acid infusion.
PURPOSE: To evaluate the influence of continuous infusion of acetic acid 50% during radiofrequency ablation (RFA) on the size of the thermal lesion produced. METHODS: Radiofrequency (RF) was applied to excised bovine liver by using an expandable needle electrode with 10 retractable tines (LeVeen Needle Electrode, RadioTherapeutics, Sunnyvale, CA) connected to a commercially available RF generator (RF 2000, RadioTherapeutics, Sunnyvale, CA). Experiments were performed using three different treatment modalities: RF only (n = 15), RF with continuous saline 0.9% infusion (n = 15), and RF with continuous acetic acid 50% infusion (n = 15). RF duration, power output, tissue impedance, and time to a rapid rise in impedance were recorded. The ablated lesions were evaluated both macroscopically and histologically. RESULTS: The ablated lesions appeared as spherical or ellipsoid, well-demarcated pale areas with a surrounding brown rim with both RF only and RF plus saline 0.9% infusion. In contrast, thermolesions generated with RF in combination with acetic acid 50% infusion were irregular in shape and the central portion was jelly-like. Mean diameter of the coagulation necrosis was 22.3 +/- 2.1 mm (RF only), 29.2 +/- 4.8 mm (RF + saline 0.9%) and 30.7 +/- 5.7 mm (RF + acetic acid 50%), with a significant increase in the RF plus saline 0.9% and RF plus acetic acid 50% groups compared with RF alone. Time to a rapid rise in impedance was significantly prolonged in the RF plus saline 0.9% and RF plus acetic acid 50% groups compared with RF alone. CONCLUSIONS: A combination of RF plus acetic acid 50% infusion is able to generate larger thermolesions than RF only or RF combined with saline 0.9% infusion.