Yoichiro Matsumoto

Heating Location Control of HIFU Treatment Enhanced with Microbubbles

High‐intensity focused ultrasound (HIFU) treatment using ultrasound contrast microbubbles for enhancing the heating effect has been developed with the aim of realising a less invasive tumor therapy. The focused sound waves result in an increase in temperature and increased thermal absorption, which necroses tumor cells. In addition, microbubbles are used as contrast agents for ultrasound imaging, and, in a previous study, we used microbubbles to enhance the heating effect. However, when microbubbles exist in the ultrasound pathway, they disturb ultrasound propagation and distort the acoustic field. Distortion of the acoustic field leads to defocusing and causes unexpected damage to tissue in the body. The objective of the present study is to propose a method by which to destroy microbubbles in the ultrasound pathway and to focus the thermal energy only at the focal point. The proposed method consists of two steps. The first step is to use repetitive high‐intensity, short‐burst waves (20 waves) to destroy ...

A Study of Micro‐bubble Enhanced Sonoporation

Sonoporation is a recently developed system for gene induction that uses ultrasound. Micro‐bubbles are known to aid gene transfection through the introduction of genes into cells by the collapse of cavitation‐bubbles (or micro‐bubbles). However, the underlying mechanism and optimal introduction conditions have not been clarified in detail. In this research, we improved the gene introduction rate by forming DNA/Block copolymer micelles. Micelle formation compacts the DNA and enhances its stability, thereby facilitating the passage of greater amounts of DNA through holes in the cell surface and improving gene expression. Cells were exposed to ultrasonic plane waves from a piezoceramic transducer with a frequency of 2.0 MHz and a duty cycle of 10% (400/3600). Mouse fibroblast cells (NIH3T3) were cultured on the bottom of 24‐well plates. Plasmid DNA and Sonazoid® (micro‐bubbles) were added to the culture media and the cells were subsequently exposed to ultrasound. In the system described herein, micelles are ...

Surfactant effects on single bubble motion and bubbly flow structure

Surfactant effects on single bubble motion in quiescent water and upward bubbly flow in a rectangular channel are investigated. Generally, path instability of the single bubble and the bubble motion in inhomogeneous flow are sensitive to the contamination of water. Addition of surfactant in gas‐water system yields immobilization of the bubble surface due to Marangoni effect. Single bubble 3D trajectories in dilute surfactant solution are measured by two high‐speed cameras. All measured trajectories are plotted on two‐dimensional field of bubble Reynolds number Re and instantaneous boundary slip condition. In free‐slip and no‐slip condition, bubble motions are dependent on Re. However, in half‐slip condition, bubble motions are spiral and almost independent from Re. Bubbles in certain condition move along trajectories changing from spiral to zigzag. These interesting motions are caused by changing slip condition. Bubble motion in upward channel flow is also observed. The local void fraction distribution ch...

Heating Location Control of HIFU Treatment Enhanced with Microbubbles Contrast Agents

High intensity focused ultrasound (HIFU) treatment employing ultrasound contrast microbubbles for enhancing the heating effect has been developed in order to achieve a less invasive tumor therapy. The focused sound waves result in an increase of temperature, and its thermal energy increases to necrotize tumor cells. Furthermore, microbubbles are used as contrast agents of ultrasound imaging, and our previous work utilized microbubbles for enhancing the heating effect. However, when microbubbles exist on the pathway of ultrasound, the bubbles disturb ultrasound propagation and distort the acoustic field. Distortion of acoustic field leads to defocus and damage unexpected tissue in the body. The objective of present work is to propose a method to destroy microbubbles on the ultrasound pathway and to focus the thermal energy only at the focal point. The proposed method consists of two steps. The first step is irradiating repetitive high intensity short burst waves (20 waves) for destroying the microbubbles on the pathway. In the second step, weak continuous waves are sent for heating the focal point. This method was successful for a gel that contains microbubbles with the void fraction of the order of 10− 4. The results indicate that the more microbubbles were destroyed with the increased in the non-exposure time and pulse number at the first step. For applying the method to a living tissue, the optimization of pulse number is difficult because the void fraction distribution within the tissue is unclear. To overcome this problem, we suggested an advanced method, which is irradiating high intensity burst waves and weak waves in turn. This method contributes to reduce the required surgical procedure, because the destruction of microbubbles and heating the focal point is possible without optimization of burst wave number.

An Eulerian Approach to Fluid‐Structure Coupling Problems Suitable for Voxel‐Based Geometry

A new simulation method for solving fluid‐structure coupling problems suitable for voxel‐based geometry has been developed. All the basic equations are numerically solved on a fixed Cartesian grid in a finite difference scheme. An incompressible fluid flow solver is extended to the incompressible fluid‐structure system. A volume‐of‐fluid approach is applied to describing the multi‐component geometry. The temporal change in the solid deformation is described on the Eulerian frame by updating a left Cauchy‐Green deformation tensor, which expresses constitutive equations of the hyperelastic Cauchy stress for e.g. neo‐Hookean material. Two validations are made: one is a comparison with the available simulation of the solid motion in the lid‐driven flow (Zhao et al. (2008) J. Comput. Phys. 227, 3114), in which the deformed solid motion is solved in the finite element approach, the other is an examination of the reversibility in shape of the hyperelastic material under no stress situation. The present method is confirmed to well capture the material deformation and the reversal.A new simulation method for solving fluid‐structure coupling problems suitable for voxel‐based geometry has been developed. All the basic equations are numerically solved on a fixed Cartesian grid in a finite difference scheme. An incompressible fluid flow solver is extended to the incompressible fluid‐structure system. A volume‐of‐fluid approach is applied to describing the multi‐component geometry. The temporal change in the solid deformation is described on the Eulerian frame by updating a left Cauchy‐Green deformation tensor, which expresses constitutive equations of the hyperelastic Cauchy stress for e.g. neo‐Hookean material. Two validations are made: one is a comparison with the available simulation of the solid motion in the lid‐driven flow (Zhao et al. (2008) J. Comput. Phys. 227, 3114), in which the deformed solid motion is solved in the finite element approach, the other is an examination of the reversibility in shape of the hyperelastic material under no stress situation. The present method is...

Micro‐bubble Enhanced Sonoporation

A gene transfer system that uses ultrasound, known as sonoporation, has recently been developed, and it is known that micro‐bubbles can help gene transfection in this technique. However, the mechanism and optimal induction conditions have not yet been fully clarified. We examined the factors that affect the gene induction rate, and attempted to devise a method for high‐efficiency gene induction. In vitro, we inducted a GFP‐containing plasmid into fibroblast cells (NIH3T3) using an ultrasound contrast agent (Sonazoid®, or micro‐bubbles) and piezoelectric transducer. Cells were cultured on 24‐well plates. The GFP‐containing plasmid (concentration: 15 mg/ml) and Sonazoid® were mixed with the cell suspension. Ultrasound frequency was 2.0 MHz (burst wave, duty cycle: 10%), ultrasound intensity was varied from 0u2009W/cm2 to 11.0u2009W/cm2, exposure time ranged from 0 s to 120 s, and burst repetition frequency was varied from 50 Hz to 50000 Hz. Gene induction ratio was higher with stronger or longer ultrasound exposure...