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A new polymer concept for coating of vascular stents using PTFEP (poly(bis(trifluoroethoxy)phosphazene) to reduce thrombogenicity and late in-stent stenosis

Objectives:We sought to evaluate the new polymer PTFEP (poly(bis(trifluoroethoxy)phosphazene) for (1) its ability to reduce thrombogenicity and late in-stent stenosis and (2) its effect on endothelialization in a rabbit iliac artery model. Materials and Methods:Nanocoated (∼50 nm) and bare stainless-steel stents were implanted bilaterally in the iliac arteries of 30 New Zealand White rabbits (1, 4, 8, 12, and 16 weeks follow-up) and evaluated by angiography, light, and scanning electron microscopy. Results:Bilateral stent placement was successful in 27 of 30 rabbits. Thrombus depositions occurred in none of the 27 coated but in 4 of the 27 bare stents (P = 0.037). A normal angiogram was obtained in 18 of 22 coated stents at risk for restenosis (follow-up ≥4 weeks) but only in 13 of 22 bare stents (P = 0.023). Marked restenosis (luminal loss >30%) was found in 6 bare stents (P = 0.011) but not in any coated stents. The neointima was 47.7–73.9 μm on coated and 66.9–115.2 μm on bare stents (statistically significant at 4, 8, and 16 weeks). Scanning electron microscopy detected full endothelialization in all stents from 4 weeks on (22 stents in both groups). Conclusion:PTFEP nanocoating successfully showed thromboresistance and reduced late in-stent stenosis. Endothelialization was equal in both stent types. Studies in more human-like models and human feasibility studies in human arteries are encouraged.

The efficacy of nanoscale poly[bis(trifluoroethoxy) phosphazene] (PTFEP) coatings in reducing thrombogenicity and late in-stent stenosis in a porcine coronary artery model.

Objectives:Previous experimental studies have demonstrated that poly[bis(trifluoroethoxy)phosphazene] (PTFEP) nanocoated stents have antithrombotic characteristics, reduce in-stent stenosis, prevent wall inflammation, and do not hamper endothelialization. This study was designed to validate these findings in a porcine coronary artery model. Materials and Methods:PTFEP-coated (n = 15) and bare stents (n= 13) were implanted in coronary arteries of 18 mini-pigs (4- and 12-week follow-up). Primary study endpoints were thrombogenicity and in-stent stenosis, secondary study endpoints were inflammatory response and re-endothelialization evaluated by quantitative angiography and light microscopy. Results:No thrombus deposition occurred on any stent. At 4 weeks follow-up, the bare stents (n = 4) had a significantly smaller neointimal area (1.93 vs. 3.20 mm2, P = 0.009). At 12 weeks, PTFEP-coated stents (n = 11) had significantly superior results in almost all parameters: neointimal area (2.25 vs. 2.65 mm2, P = 0.034), neointimal height (204.46 vs. 299.41 &mgr;m, P = 0.048), percentage stenosis (38.25 vs. 50.42%, P = 0.019), and inflammation score (0.12 vs. 0.30, P = 0.029). Complete re-endothelialization was seen in both stent types at both intervals. Conclusion:At long-term follow-up, the superior results of PTFEP-coated stents were characterized by a noteworthy reduction of neointimal growth and inflammatory response.

Quantification of Tissue Shrinkage and Dehydration Caused by Microwave Ablation: Experimental Study in Kidneys for the Estimation of Effective Coagulation Volume

PURPOSE To quantify the extent of tissue shrinkage and dehydration caused by microwave (MW) ablation in kidneys for estimation of effective coagulation volume. MATERIALS AND METHODS MW ablations were carried out in ex vivo porcine kidneys. Six study groups were defined: groups 1A, 2A, and 3A for MW ablation (90 W for 5 min, 7.5 min, or 10 min), and groups 1B, 2B, and 3B for control (without MW ablation). Pre- and postinterventional volume analyses were performed. Effective coagulation volumes (original tissue included in coagulation) were determined. Postinterventional dehydration analyses were performed with calculation of mean mass fractions of water. RESULTS Mean deployed energies were 21.6 kJ ± 1.1 for group 1A, 29.9 kJ ± 1.0 for group 2A, and 42.1 kJ ± 0.5 kJ for group 3A, and were significantly different (P < .0001). Differences between pre- and postinterventional volumes were -3.8% ± 0.6 for group 1A, -5.6% ± 0.9 for group 2A, and -7.2% ± 0.4 for group 3A, and -1.1% ± 0.3 for group 1B, -1.8% ± 0.4 for group 2B, and -1.1% ± 0.4 for group 3B. Postinterventional volumes were significantly smaller than preinterventional volumes for all groups (P < .01). Underestimations of effective coagulation volume from visualized coagulation volume were 26.1% ± 3.5 for group 1A, 35.2% ± 11.2 for group 2A, and 42.1% ± 4.9 for group 3A, which were significantly different (P < .01). Mean mass fractions of water were 64.2% ± 1.4 for group 1A, 63.2% ± 1.7 for group 2A, and 62.6% ± 1.8% for group 3A, with significant differences versus corresponding control groups (P < .01). CONCLUSIONS For MW ablation in kidneys, underestimation of effective coagulation volume based on visualized coagulation volume is significantly greater with greater deployed energy. Therefore, local dehydration with tissue shrinkage is a potential contributor.

Iodine removal in intravenous dual-energy CT-cholangiography: Is virtual non-enhanced imaging effective to replace true non-enhanced imaging?

PURPOSE To evaluate whether virtual non-enhanced imaging (VNI) is effective to replace true non-enhanced imaging (TNI) applying iodine removal in intravenous dual-energy CT-cholangiography. MATERIALS AND METHODS From April 2009 until February 2010, fifteen potential donors for living-related liver transplantation (mean age 37.6±10.8 years) were included. Potential donors underwent a two-phase CT-examination of the liver. The first phase consisted of a single-energy non-enhanced CT-acquisition that provided TNI. After administration of hepatobiliary contrast agent, the second phase was performed as a dual-energy cholangiographic CT-acquisition. This provided VNI. Objective image quality (attenuation values [bile ducts and liver parenchyma] and contrast-to-noise ratio) and subjective overall image quality (1 - excellent; 5 - non diagnostic) were evaluated. Effective radiation dose was compared. RESULTS For TNI and VNI, attenuation values for bile ducts were 16.8±11.2HU and 5.5±17.0HU (p<0.05) and for liver parenchyma 55.3±8.4HU and 58.1±10.6HU (n.s.). For TNI and VNI, contrast-to-noise ratio was 2.6±0.6HU and 6.9±2.1HU (p<0.001). For VNI, subjective overall image quality was 1 in ten datasets, 2 in four datasets and 3 in one dataset. Effective radiation dose for the dual-energy cholangiographic CT-acquisition was 3.6±0.9mSv and for two-phase single-energy CT-cholangiography 5.1±1.3mSv (p<0.001). CONCLUSION In this study on iodine removal in intravenous dual-energy CT-cholangiography, subjective image quality is equivalent, contrast-to-noise ratio is improved and effective radiation dose is reduced when VNI is performed. The differences between TNI and VNI with respect to attenuation values seem to have limited clinical relevance and therefore we consider VNI as effective to replace TNI.

Technical and clinical outcome of transjugular intrahepatic portosystemic stent shunt: Bare metal stents (BMS) versus viatorr stent-grafts (VSG)

PURPOSE To compare retrospectively angiographical and clinical results in patients undergoing transjugular intrahepatic portosystemic stent-shunt (TIPS) using BMS or VSG. MATERIALS AND METHODS From February 2001 to January 2010, 245 patients underwent TIPS. From those, 174 patients matched the inclusion criteria with elective procedures and institutional follow-up. Group (I) consisted of 116 patients (mean age, 57.0±11.1 years) with BMS. Group (II) consisted of 58 patients with VSG (mean age, 53.5±16.1 years). Angiographic and clinical controls were scheduled at 3, 6 and 12 months, followed by clinical controls every 6 months. Primary study goals included hemodynamic success, shunt patency as well as time to and number of revisions. Secondary study goals included clinical success. RESULTS Hemodynamic success was 92.2% in I and 91.4% in II (n.s.). Primary patency was significantly higher in II compared to I (53.8% after 440.4±474.5 days versus 45.8% after 340.1±413.8 days; p<0.05). The first TIPS revision was performed significantly later in II compared to I (288.3±334.7 days versus 180.1±307.0 days; p<0.05). In the first angiographic control, a portosystemic pressure gradient ≥15 mmHg was present in 73.9% in I and in 39.4% in II (p<0.05). Clinical success was 73.7-86.2% after 466.3±670.1 days in I and 85.7-90.5% after 617.5±642.7 days in II (n.s.). Hepatic encephalopathy was 37.5% in I and 36.5% in II (n.s.). CONCLUSION VSG increased primary shunt patency as well as decreased time to and number of TIPS revisions. There was a trend of higher clinical success in VSG without increased hepatic encephalopathy.

Dual-energy computed-tomography cholangiography in potential donors for living-related liver transplantation: initial experience

Objectives:To report our initial experience with dual-energy computed-tomography (CT) cholangiography in potential donors for living-related liver transplantation. Materials and Methods:Seventeen potential donors for living-related liver transplantation (6 women and 11 men; average age 37.8 ± 10.4 years) underwent contrast-enhanced dual-energy CT cholangiography. A dual-energy CT scan of the liver was carried out with acquisition of 2 raw datasets at tube currents of 140 and 80 kV, respectively. A third weighted average dataset were obtained (weighting ratio: 70% 140 kV, 30% 80 kV). Pure iodine images (fourth dataset) and contrast-optimized images (fifth dataset) were reconstructed. Analysis of all datasets comprised determination of bile duct visualization scores (on a scale of 1 to 4: 1, not visualized; 2, faintly seen; 3, identified but the origin or portions of the duct are not visualized; and 4, excellent visualization from origin to branches), maximum bile duct diameters, bile duct attenuation, and liver parenchyma attenuation as well as image noise, signal-to-noise ratio, and contrast-to-noise ratio. Results:Highest maximum bile duct diameters were detected for optimized-contrast images and the 80 kV dataset, intermediate for pure iodine images and the weighted average dataset and lowest for the 140 kV dataset with significant differences. Highest bile duct attenuation was detected for optimized-contrast images (535.7 ± 148.3 HU) and the 80 kV dataset (533.7 ± 145.9 HU) with significant differences compared with pure iodine images (344.9 ± 106.5 HU) and the weighted average dataset (355.5 ± 87.6 HU) (P < 0.001). Highest image noise was detected for the 80 kV dataset (39.3 ± 5.4 HU) with significant differences compared with the optimized-contrast images (31.5 ± 4.0) (P < 0.001). Highest signal-to-noise ratio and contrast-to-noise ratio were detected for pure iodine images (18.3 ± 7.1 and 17.6 ± 7.0) and optimized-contrast images (17.3 ± 5.8 and 14.8 ± 5.5) with significant differences compared with the 80 kV dataset (14.0 ± 5.2 and 11.8 ± 4.8) and the weighted average dataset (15.1 ± 4.4 and 12.1 ± 4.1) (P < 0.001 and P < 0.01). Conclusions:Dual-energy CT cholangiography in potential donors for living-related liver transplantation is remarkable. Pure iodine images and contrast-optimized images allow precise analysis of the biliary system with increased image quality compared with conventional images. Contrast-optimized images should be used for detection and localization of the bile ducts and pure iodine images for quantitative description of the anatomic dimensions of the biliary segments.

Irreversible electroporation of the pig kidney with involvement of the renal pelvis: technical aspects, clinical outcome, and three-dimensional CT rendering for assessment of the treatment zone.

PURPOSE To analyze irreversible electroporation (IRE) of the pig kidney with involvement of the renal pelvis. MATERIALS AND METHODS IRE of renal tissue including the pelvis was performed in 10 kidneys in five pigs. Three study groups were defined: group I (two applicators with parallel configuration; n = 11), group II (three applicators with triangular configuration; n = 2), and group III (six applicators with complex configuration; n = 3). After IRE and before euthanasia, pigs underwent contrast-enhanced computed tomography (CT). Technical aspects (radial distance of applicators, resulting mean current), clinical outcome (complications, blood samples), and three-dimensional CT rendering for assessment of the treatment zone (short axis, circularity) were assessed. RESULTS Radial distances of applicators were 14.3 mm ± 2.8 in group I, 12.3 mm ± 1.9 in group II, and 16.4 mm ± 3.5 in group III. Resulting mean currents were 25.7 A ± 6.5 in group I, 27.0 A ± 7.1 in group II, and 39.4 A ± 8.9 in group III. In group III, two perirenal hematomas were identified. There was no damage to the renal pelvis. During IRE, clinical blood parameters and cardiovascular markers did not change significantly. Short axis measurements were 20.6 mm ± 3.6 in group I, 31.9 mm ± 8.2 in group II, and 39.3 mm ± 2.4 in group III (P < .01 between groups). Circularity scores were 0.8 ± 0.2 in group I, 0.7 ± 0.1 in group II, and 0.7 ± 0.1 in group III, with a score of 1 indicating perfect roundness (P value not significant). CONCLUSIONS IRE of the pig kidney with involvement of the renal pelvis is feasible and safe. Size but not shape of the treatment zone is significantly affected by applicator configuration.

Effect of Tissue Perfusion on Microwave Ablation: Experimental in Vivo Study in Porcine Kidneys

PURPOSE To determine the effect of tissue perfusion on microwave ablation lesions in an experimental in vivo study in porcine kidneys. MATERIALS AND METHODS Twelve kidneys of six pigs were studied. In each animal, two microwave ablations were created in one kidney without limitation of tissue perfusion (group 1). In the other kidney, two microwave ablations were performed with interruption of blood flow (group 2). All microwave ablations were performed with identical system parameters (eg, temperature control mode, ablation time of 80 s, and temperature of 110°C). The animals were euthanized 3 hours later. The kidneys were harvested and cut into 2-3-mm transverse slices. Microwave ablation zone dimensions (eg, length, width, and volume) and shape (eg, sphericity ratio) and corresponding variability were compared between groups. RESULTS Microwave ablation areas were significantly longer (41.6 mm ± 4.0 vs 34.2 mm ± 5.9; P < .01) and wider (16.6 mm ± 1.2 vs 12.2 mm ± 2.1; P < .001) in group 2 than in group 1. Similarly, microwave ablation volume was significantly greater in group 2 compared with group 1 (6.7 cm(3) ± 1.0 vs 3.3 cm(3) ± 1.2; P < .001). Ablation area shapes were similar between groups (sphericity ratio, 2.57 ± 0.42 vs 2.39 ± 0.34). Ablation area variabilities were also comparable between groups (volume variance of 1.32 vs 0.93; sphericity ratio variance of 0.18 vs 0.11). CONCLUSIONS After interruption of blood flow, microwave ablation areas are significantly larger than those achieved without limitation of tissue perfusion. Microwave ablation area shape and variability were comparable between study groups.

Multimodal visibility (radiography, computed tomography, and magnetic resonance imaging) of microspheres for transarterial embolization tested in porcine kidneys.

ObjectiveThe objective of this study was to test multimodal visibility (radiography, computed tomography [CT], and magnetic resonance imaging [MRI]) of microspheres for transarterial embolization in porcine kidneys. Materials and MethodsCurrently available embolization particles (microspheres) were modified. A dense x-ray material (barium sulfate) was added to create visibility for radiography and CT. A magnetic substance (iron oxide) was additionally added to create visibility for MRI. This chemical modification was performed for particles with sizes of 100 ± 25 and 700 ± 50 &mgr;m. Three different prototypes per size class (samples A, B, and C) resulted, each with a different degree of barium sulfate but with the same degree of iron oxide. The currently available embolization particles with sizes of 100 ± 25 and 700 ± 50 &mgr;m were used as controls (sample control). Eight renal arteries of 4 pigs were embolized. Study end points were size distribution evaluated in vitro as well as qualitative and quantitative particle visibility evaluated in vivo. ResultsThe size distribution of the particles with a size of 100 ± 25 &mgr;m was between 96 ± 11 &mgr;m for sample A and 102 ± 13 &mgr;m for the sample control without significant differences (n.s.). The size distribution of the particles with a size of 700 ± 50 &mgr;m was between 691 ± 20 &mgr;m for sample A and 716 ± 34 &mgr;m for sample C without significant differences (n.s.). For radiography, the particles with sizes of 100 ± 25 and 700 ± 50 &mgr;m for samples A, B, and C were definitely visible during the embolization. The sample control was definitely not visible. For CT and MRI (T1-weighted [T1w] and T2-weighted [T2w]), the particles with sizes of 100 ± 25 and 700 ± 50 &mgr;m for samples A, B, and C were definitely visible after the embolization. The sample control was definitely not visible. For CT, the signal-to-noise ratio for samples A, B, and C increased significantly after the embolization (eg, sample A, particles with a size of 100 ± 25 &mgr;m: 66.5% ± 23.7%, P < 0.05). The signal-to-noise ratio for the sample control did not change after the embolization (eg, sample control, particles with a size of 700 ± 25 &mgr;m: −0.2% ± 15.2%, n.s.). For MRI (T1w and T2w), the signal-to-noise ratio for samples A, B, and C decreased significantly after the embolization (eg, sample B, particles with a size of 700 ± 50 &mgr;m, T1w: −72.9% ± 6.6%; P < 0.05). The signal-to-noise ratio for the sample control did not change after the embolization (eg, sample control, particles with a size of 100 ± 25 &mgr;m, T2w: 6.2% ± 16.1%, n.s.). ConclusionsIn this study, the chemical modification of the currently available microspheres for transarterial embolization resulted in a size distribution comparable with the currently available microspheres and created multimodal visibility for radiography, CT, and MRI.

Evaluation of the Plasmatic and Parenchymal Elution Kinetics of Two Different Irinotecan-Loaded Drug-Eluting Embolics in a Pig Model

PURPOSE To evaluate and compare irinotecan elution kinetics of two drug-eluting embolic agents in a porcine model. MATERIALS AND METHODS Embolization of the left liver lobe was performed in 16 domestic pigs, with groups of two receiving 1 mL of DC Bead M1 (70-150 µm) or Embozene TANDEM (75 µm) loaded with 50 mg irinotecan. Irinotecan plasma levels were measured at 0, 10, 20, 30, 60, 120, 180, and 240 minutes after completed embolization and at the time of euthanasia (24 h, 48 h, 72 h, or 7 d). Liver tissue samples were taken to measure irinotecan tissue concentrations. RESULTS The highest irinotecan plasma concentrations of both embolic agents were measured 10 and 20 minutes after embolization, and concentrations were significantly higher for DC Bead M1 versus Embozene TANDEM (P = .0019 and P = .0379, respectively). At 48 hours and later follow-up, no irinotecan was measurable in the plasma. For both embolic agents, the highest irinotecan tissue concentration was found after 24 hours and decreased in a time-dependent manner at later follow-up intervals. Additionally, SN-38 tissue levels for both agents were therapeutic at 24 hours, with therapeutic levels of SN-38 at 48 hours in one liver embolized with TANDEM particles. Histopathologic analysis revealed ischemic, inflammatory, and fibrotic tissue reactions. CONCLUSIONS Irinotecan is measurable in plasma and hepatic tissue after liver embolization with both types of irinotecan-eluting embolic agents. DC Bead M1 shows early burst elution kinetics, whereas Embozene TANDEM has a lower and slower release profile. The initial burst is significantly greater after embolization with DC Bead M1 than with Embozene TANDEM.