Silicon carbide as a heat-enhancing agent in microwave ablation: in vitro experiments.

PURPOSE: Silicon carbide (SiC) is an inert compound material with excellent microwave absorption and heat-conducting properties. The aim of our study was to investigate the heat-enhancing effects of SiC in microwave ablation in an in vitro setting. MATERIALS AND METHODS: Different concentrations of SiC powder were mixed with 2% gelatin, producing a 20-ml mixture that was then heated with a clinical microwave ablation system (5 min/45 W). Temperature was measured continuously fiberoptically. Additional heating properties were assessed for the most heatable concentrations at different energy settings (10, 20, and 30 W). As reference, 2% gelatin without SiC was heated. Statistical evaluation by analysis of variance with post hoc Student-Newman-Keuls testing was performed. RESULTS: For the different SiC concentrations, maximum temperatures measured were 45.7 ± 1.2°C (0% SiC, control), 50.4 ± 3.6°C (2% SiC), 60.8 ± 1.8°C (10% SiC), 74.9 ± 2.6°C (20% SiC), and 83.4 ± 2.5°C (50% SiC). Differences between all data points were significant (P < 0.05). Maximum temperatures that used 20% SiC were 36.3 ± 2.76°C (10 W), 48.7 ± 4.18°C (20 W), and 50.6 ± 0.68°C (30 W). The use of 50% SiC maximum temperatures resulted in values of 46.2 ± 2.52°C (10 W), 70.1 ± 0.64°C (20 W), and 83.0 ± 4.69°C (30 W). With 20% SiC and 50% SiC mixtures, the 10 W maximum temperatures were significantly lower than at all other power levels, and maximum temperatures with 20 and 30 W were significantly lower when compared with 45 W (P < 0.05). CONCLUSIONS: SiC is a nontoxic, highly effective substance for enhancing microwave-induced heating with a microwave ablation system in vitro. These data suggest its usefulness for enhancement of ablative effects in percutaneous tumor therapy. Further investigations need to be performed to evaluate the ex vivo and in vivo ablation effects and the possible methods for administration of SiC particles.

[In vitro experiments on fluid-modulated microwave ablation]. / In-vitro-Experimente zur flüssigkeitsmodulierten Mikrowellenablation.

PURPOSE: Evaluation of the enhancing or protecting effects of different fluids during microwave ablation (MWA). MATERIALS AND METHODS: 3 samples of 17 different fluids (each 20 ml) were heated using MWA at power levels of 10, 20, 30, 40 and 45 watts. Energy was applied until the temperature reached 80 degrees C or the duration of heating exceeded 10 minutes. The cooling-down process was then observed until the temperature reached 30 degrees C. RESULTS: Gastrografin needed the shortest time to be heated up to 80 degrees C (370 sec), followed by Magnograf (410 sec) and HES 10 % (420 sec). The least heatable fluids were Lipiodol (10 min -54.5 +/- 2.43 degrees C), distilled water (10 min -56 +/- 2.42 degrees C) and Glucose 5 % solution (10 min -56.6 +/- 1.69 degrees C). Fluids which could not be heated well, such as distilled water, Lipiodol or Glucose 5 % solution, had a small slope of the temperature curve as a function of the power level used (m = 0.60 - 0.73), whereas fluids which could be heated well, such as Gastrografin, Magnograf and HES 10 %, had a much steeper slope of the temperature curve as a function of the power level (m = 0.99 - 1.20). With respect to the maximum temperature, the above mentioned groups differed significantly (p < 0.05). The temperature slope correlated strongly with maximum temperatures reached (Pearson correlation coefficient: 0.97). CONCLUSION: By additionally administering a carefully chosen fluid, enhancing or protecting effects during microwave ablation can be observed. Especially Gastrografin, Magnograf and HES 10 % can be used to enhance ablation effects, whereas protective effects can be observed particularly when using Lipiodol, distilled water and Glucose 5 %-solution.

[Mono-contrast distension study of the small intestine. Comparison of conventional small bowel follow-through with enteroclysis]. / Monokontrast-Distensionsuntersuchung des Dünndarms. Vergleich mit der konventionellen MDP und dem Enteroklysma.

PURPOSE: Development of a new monocontrast examination of the small bowel. MATERIAL AND METHODS: The new examination was applied to 20 patients with suspected bowel obstruction or inflammatory bowel disease. A contrast mixture, containing gelatin, a water-soluble contrast medium (Peritrast) and water (GPW-mixture) was given over an intestinal tube. The viscosity of the new contrast mixture was measured by rotation and flow viscosimetry. The diagnostic value and the degree of small bowel distension were determined independently by 3 examiners. By comparison 20 randomized selected small bowel follow-through examinations (SBFT) and 20 small bowel enemas were examined. Special questionnaires were used to determine subjective compatibility and discomfort. RESULTS: Due to the viscosity of the new contrast medium and the administration over an intestinal tube, a good bowel distension was achieved with the GPW mixture. The bowel distension (p: < 0.01) and the diagnostic value (p: < 0.01) of the new examination in comparison to the SBFT was characterized as being significantly better. In comparison to the small bowel enema, distension was not significantly better (p: 0.31-1.0). The diagnostic value of the small bowel enema was characterized as significantly better by one of the three examiners in comparison to the new monocontrast-distenson examination (p-level < 0.01). CONCLUSION: The monocontrast-distension examination is a potential alternative in patients in whom a small bowel enema with barium sulfate is contraindicated.

Comparative examination of various rectal tubes and contrast media for the reduction of intussusceptions.

The hydrodynamic influence of different rectal tube sizes, contrast media, and heights of the fluid column on hydrostatic reduction of intussusception was analyzed in vitro. Enemas were performed in dead rabbits to compare the filling speed of bowel with a liquid and a gaseous contrast medium. For hydrostatic reduction, tubing and rectal tube with a large caliber and a low viscosity contrast medium achieved a higher filling speed of colon and are expected to provide a higher force of reduction on the intussusceptum. A rectal tube with a large caliber can be more useful than an increase of the column height. Filling bowel with carbon dioxide was approximately 7 times faster than with meglumine sodium diatrizoate. Theoretical considerations allow the hypothesis that a gaseous medium provides a faster and steadier reduction than a liquid.