It is well known that a bubble in contaminated water rises much slower than one in purified water, and the rising velocity in a contaminated system can be less than half that in a purified system. This phenomenon is explained by the so-called Marangoni effect caused by surfactant adsorption on the bubble surface. In other words, while a bubble is rising, there exists a surface concentration distribution of surfactant along the bubble surface because the adsorbed surfactant is swept off from the front part and accumulates in the rear part by advection. Owing to this surfactant accumulation in the rear part, a variation of surface tension appears along the surface and this causes a tangential shear stress on the bubble surface. This shear stress results in the decrease in the rising velocity of the bubble in contaminated liquid. More interestingly, this Marangoni effect influences not only the bubble's rising velocity but also its lateral migration in the presence of mean shear. Together, these influences cause a drastic change of the whole bubbly flow structures. In this paper, we discuss some experimental results related to this drastic change in bubbly flow structure. We show that bubble clustering phenomena are observed in an upward bubbly channel flow under certain conditions of surfactant concentrations. This cluster disappears with an increase in the concentration. We explain this phenomenon by reference to the lift force acting on a bubble in aqueous surfactant solutions. It is shown that the shear-induced lift force acting on a contaminated bubble of 1 mm size can be much smaller than that on a clean bubble.

Accurate morphological information on aortic valve cusps is critical in treatment planning. Image segmentation is necessary to acquire this information, but manual segmentation is tedious and time consuming. In this paper, we propose a fully automatic aortic valve cusps segmentation method from CT images by combining two deep neural networks, spatial configuration-Net for detecting anatomical landmarks and U-Net for segmentation of aortic valve components. A total of 258 CT volumes of end systolic and end diastolic phases, which include cases with and without severe calcifications, were collected and manually annotated for each aortic valve component. The collected CT volumes were split 6:2:2 for the training, validation and test steps, and our method was evaluated by five-fold cross validation. The segmentation was successful for all CT volumes with 69.26 s as mean processing time. For the segmentation results of the aortic root, the right-coronary cusp, the left-coronary cusp and the non-coronary cusp, mean Dice Coefficient were 0.95, 0.70, 0.69, and 0.67, respectively. There were strong correlations between measurement values automatically calculated based on the annotations and those based on the segmentation results. The results suggest that our method can be used to automatically obtain measurement values for aortic valve morphology.

A Full Eulerian Fluid-Membrane Coupling Method with a Smoothed Volume-of-Fluid Approach - Volume 12 Issue 2 - Satoshi Ii, Xiaobo Gong, Kazuyasu Sugiyama, Jinbiao Wu, Huaxiong Huang, Shu Takagi

High‐intensity focused ultrasound (HIFU) has recently been developed as a noninvasive therapeutic method. In our study, a novel noninvasive therapy with HIFU was proposed for occlusion of lower extremity varicose veins. The temperature increase caused by HIFU is used to occlude varicose veins. Occluded veins became fibrotic, resulting in complete recovery. Our final goal is the medical application of HIFU treatment for varicose veins. In this study, we attempted to occlude the veins of rabbits. Prior to venous occlusion experiments, the area heated by HIFU was investigated using bovine serum albumin (BSA) gel, which denatures at $\text{>70\hspace{0.17em}°}\mathrm{C}.$ The results indicate that the size of the heated area mainly depends on intensity at the focal point and the exposure time. A tendency was also seen for the heated area to extend toward the transducer with increasing exposure time. In animal experiments, skin burns during HIFU exposure represented a critical problem. We therefore examined the safe range of HIFU intensities in abdominal exposure experiments before conducting venous occlusion experiments. The ultrasound frequency was 1.7 MHz. Intensity at the focal point was $\text{900\hspace{0.17em}}{\mathrm{W/cm}}^2,$ and the exposure time was 20 s. Rabbits underwent chemical depilation and echo gel was applied to the exposed skin to fill the boundary gap. Target veins were compressed during HIFU exposure to avoid thermal dissipation, and hyaluronan water solution was injected between the veins and skin to maintain the distance between the skin and veins at $\text{≥5\hspace{0.17em}}\mathrm{mm}.$ Veins were then exposed to HIFU and occluded. The capability of HIFU treatment to occlude lower extremity varicose veins was verified by the present study.

HIFU treatment has been developed for various diseases because of its minimal invasiveness, and we are now developing a HIFU treatment for varicose veins of the lower extremity. Previous studies have succeeded in occluding rabbit’s veins with HIFU, but the success rate was low (about 10%). Failures were mainly caused by skin burns. When the heating lesion comes close to skin, the absorbed ultrasound energy may cause skin burns. Therefore, it is necessary to study the relationships between HIFU lesions and skin burns to improve the success rate. To visualize heating lesions from HIFU, we used tissue‐mimicking BSA gel phantoms. We tried various concentrations of BSA in gels, and determined 14% BSA as the most suitable for phantoms for experiments. The attenuation coefficient of the gel was 0.73 dB/cm, and the denaturation temperature was $\text{70\hspace{0.17em}°}\mathrm{C}.$ We put the BSA gel phantom in a water tank in which the temperature was kept at $\text{39\hspace{0.17em}°}\mathrm{C},$ and used HIFU exposures at various intensities and irradiation times. After irradiation, we measured the sizes and positions of HIFU‐induced lesions, and the results indicate that the sizes of lesion become larger when the intensitiy rises or irradiation time becomes longer. Furthermore, when the intensity rises and irradiation time becomes longer, the heating lesions move closer to upper surface of the gel, which means skin easily gets burned. Thus we have investigated relationships between HIFU parameters and heated lesions that can be used for further research into HIFU treatment of varicose veins of the lower extremity.