Takashi Mochizuki

Production of acoustic field with multiple focal points to control high amount of microbubbles in flow using a 2D array transducer

We have newly developed a 2D array transducer to control the behavior of microbubbles, which is different from that for HIFU therapy, to emit continuous wave by designing acoustic field including multiple focal points. In the experiment using a straight path model, we have confirmed that higher concentration of acoustic energy does not result more aggregation. We also have confirmed the trapped areas of microbubbles are located not in the peak of the distribution of sound pressure, but in the middle range. The dispersion of acoustic energy is important because there was a relation in the trapping performance of microbubbles and the shape of acoustic field.

Image plane positioning by pneumatic actuators for ultrasound guidance

Image guided procedures such as percutaneous needle insertion or high intensity focused ultrasound, have become quite widespread. In images acquisition, ultrasound (US) is convenient to use in a conventional operating room, and inexpensive compared to CT and MRI. However, US requires to handle an US probe and do not have the base coordinate system. Therefore, intraoperative image position is unclear and cannot position to interested area. To address the issues, we have developed a robotic system based on US calibration and a probe scanning robot. In this study, to validate the implement system, positioning accuracy of an image plane was evaluated. Moreover, we developed an automated US guidance system with a conventional US probe. The system enables image plane positioning to visualize a therapeutic tool automatically. From the results, positioning accuracy of the image plane was 1.6 mm and 1.5 deg, maximally. In the phantom test, the error between the positions of the image plane and the mock needle was 2.5 mm and 0.9 deg. We have confirmed that the proposed system is greatly applicable for an intraoperative US guidance.

Feasibility of thin catheter manipulation in the capillary blood vessel using acoustic radiation force

This paper is to demonstrate possibility that a thin catheter less than 0.5 mm diameter could be introduced in a thin blood vessel like the capillary by using acoustic radiation force. In the experiment, a 0.4 mm diameter tube likened to the thin catheter could be controlled and introduced to the aimed flow channel of 2 mm width Y-shape bifurcation. Value of the radiation force was estimated by two methods that are cantilever method and calculation method from acoustic pressure. As a result, it was estimated that the catheter was pushed by the force of several dozens of micro Newton.

Active control of microbubbles stream in multi-bifurcated flow by using 2D phased array ultrasound transducer

We have previously reported our attempt to propel microbbles in flow by a primary Bjerknes force, which is a physical phenomenon where an acoustic wave pushes an obstacle along its direction of propagation. However, when ultrasound was emitted from surface of the body, controlling bubbles in against flow was needed. It is unpractical to use multiple transducers to produce the same number of focal points because single element transducer cannot produce more than two focal points. In this study, we introduced a complex artificial blood vessel according to a capillary model and a 2D array transducer to produce multiple focal points for active control of microbubbles in against flow. Furthermore, we investigated bubble control in viscous fluid. As the results, we confirmed clearly path selection of MBs in viscous fluid as well as in water.

Three-dimensional design of acoustic field to trap higher amount of microbubbles in flow using a matrix array transducer

We have newly developed a matrix array transducer to control the behavior of microbubbles, which is different from that for HIFU therapy, to emit continuous wave by designing acoustic field including multiple focal points. In the experiment using a straight path model, we have confirmed that higher concentration of acoustic energy does not result more aggregation. We also have confirmed the trapped areas of microbubbles are located not in the peak of the distribution of sound pressure, but in the middle range. The dispersion of acoustic energy is important because there was a relation in the trapping performance of microbubbles and the shape of acoustic field.

Active control of bubble liposome through artificial capillary by using matrix array transducer

We have ever reported our attempts to control microbubbles (MBs) using the primary and secondary acoustic force for active control in artificial blood vessels. Recently, we have demonstrated active path selection of MBs by using a matrix array transducer to produce multiple focal points. On the other hand, bubble liposomes (BLs) have an advantage in easily modifying targeting ligand. However, considering that BLs are several hundred nanometers in diameter, there were some difficulties in controllability of bubbles in blood flow under ultrasound exposure, since acoustic forces are less affected to these small bubbles. In this study, we used the liposomes (BLs) entrapping perfluoropropane gas with the average diameter of 500 nm and applied it to control the behavior in an artificial blood vessel. First, we observed aggregates formation of BLs in static water by secondary acoustic force. Next, we investigated the BLs control in multi-bifurcated flow by using a matrix array transducer. As a result, the streaming of BLs was viscously propelled to a desired path. BLs are much tied each other because of surface interaction of the lipid membrane and then caused a resistance to flow compare to MBs.