Kohji Masuda

A new robot architecture for tele-echography

This paper presents a slave robot carrying an ultrasound probe for remote echographic examination. This robot is integrated in a master-slave system called robotic tele-echography (TER). The system allows an expert operator to perform a remote diagnosis from echographic data he acquires on a patient located in a distant place. The originality of this robot lies in its architecture: the cable-driven robot is lightweight and semirigid, and it is positioned on the patient body. In this paper, we describe the clinical application, the system architecture, the second implementation of the robot, and experiments performed with this prototype.

Three dimensional motion mechanism of ultrasound probe and its application for tele-echography system

We have developed a three dimensional movable robot for an ultrasound probe for tele-echography system to apply between hospital, clinic and home. The probe movable mechanism is carefully designed not to damage the human body since miniature force sensors detect not only total contact force to the body surface but also angle of the probe to the surface. Angle and position of probe are controlled not to exceed dangerous contact force. We tried to control it via LAN and 128K ISDN by using a two-axis joystick under the Object Request Broker technique. We found that real time control was possible with an image stream. Though the delay time of the image makes the examiner stressful, we confirmed that remote diagnosis of the human abdomen is useful.

Production of Local Acoustic Radiation Force to Constrain Direction of Microcapsules in Flow

We have ever reported our attempt to control the direction of microcapsules in flow by acoustic radiation force. However, the diameter of capsules was too large to be applied in vivo. Furthermore, the acoustic radiation force affected only the focal area because focused ultrasound was used. Thus, we have improved our experiment by using microcapsules as small as blood cells and introducing a plane wave of ultrasound. We prepared an artificial blood vessel including a Y-form bifurcation established in two observation areas. Then, we newly defined the induction index to evaluate the difference in capsule density in two downstream paths. As a result, the optimum angle of ultrasound emission to induct to the desired path was derived. The induction index increased in proportion to the central frequency of ultrasound, which is affected by the aggregation of capsules to receive more acoustic radiation force.

Effect of Existence of Red Blood Cells in Trapping Performance of Microbubbles by Acoustic Radiation Force

We have proposed a method to control microbubbles by making use of acoustic radiation force, which is generated with acoustic propagation, to correspond to therapeutic applications of ultrasound. By preventing bubbles from passing through the desired target area, the local concentration of bubbles can be enhanced. However, we have never experimentally confirmed this phenomenon under in vivo conditions or close to those. Thus, we carried out an experiment to evaluate the trapping performance of bubbles using a suspension of red blood cells (RBCs) and an artificial blood vessel. By defining the trapping index to evaluate the amount of trapped microbubbles, we have confirmed that the trapping performance was enhanced according to the concentration of RBCs and the sound pressure, but not according to the central frequency of ultrasound. The results indicate that the existence of RBCs near microbubbles contributed to the increase in the size of aggregations propelled against the vessel wall.

Active Path Selection of Fluid Microcapsules in Artificial Blood Vessel by Acoustic Radiation Force

Micrometer-sized microcapsules collapse upon exposure to ultrasound. Use of this phenomenon for a drug delivery system (DDS), not only for local delivery of medication but also for gene therapy, should be possible. However, enhancing the efficiency of medication is limited because capsules in suspension diffuse in the human body after injection, since the motion of capsules in blood flow cannot be controlled. To control the behavior of microcapsules, acoustic radiation force was introduced. We detected local changes in microcapsule density by producing acoustic radiation force in an artificial blood vessel. Furthermore, we theoretically estimated the conditions required for active path selection of capsules at a bifurcation point in the artificial blood vessel. We observed the difference in capsule density at both in the bifurcation point and in alternative paths downstream of the bifurcation point for different acoustic radiation forces. Comparing the experimental results with those obtained theoretically, the conditions for active path selection were calculated from the acoustic radiation force and fluid resistance of the capsules. The possibility of controlling capsule flow towards a specific point in a blood vessel was demonstrated.

Experimental Study to Produce Multiple Focal Points of Acoustic Field for Active Path Selection of Microbubbles through Multi-bifurcation

We previously reported our attempt to propel microbubbles in a 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 the surface of the body, controlling bubbles in an against-flow was necessary. It is unpractical to use multiple transducers to produce the same number of focal points because single-element transducers cannot produce more than two focal points. In this study, we introduced a complex artificial blood vessel according to a capillary model and a two-dimensional (2D) array transducer to produce multiple focal points for the active control of microbubbles in an against-flow. From the results, about 15% more microbubbles were led to the desired path with multiple focal points of ultrasound relative to the no-emission case.

Auto-regulated osmotic pump for insulin therapy by sensing glucose concentration without energy supply

We designed an osmotic pump, using a semipermeable membrane which changes its volume according to the concentration of an outside solution. No energy supply or regulation system are required. This pump directly converts chemical potential to mechanical action without an intermediary like an electrical apparatus, called a mechanochemical actuator. This mechanism was applied to an insulin pump that works by changing the glucose concentration. We demonstrated that this pump may possibly be used in the treatment of diabetes mellitus patients.

Experimental Study of Active Path Block in a Multi-Bifurcated Flow by Microbubble Aggregation

We previously reported our attempts at the active control of microbubble aggregations using acoustic radiation force, which propels microbubbles and adjusts the size of aggregations. However, because we used simple-shape artificial blood vessels, the behavior of aggregations in a small channel, e.g., the probability to obstruct the bloodstream, and the possibility of embolization, has not been predicted. Thus, we designed and fabricated a multi-bifurcated artificial blood vessel to apply to the production and active control of microbubble aggregations. Then, we introduced two kinds of ultrasound transducers for producing and propelling aggregations. First, we produced aggregations in a flow to measure their size and investigate their variation according to the emission duration of ultrasound. Then, we control the aggregations in an artificial blood vessel to verify their controllability. When ultrasound was stopped, the aggregations flaked off the vessel wall and flowed downstream, were propelled to the desired path, and finally were caught at a narrow path. We verified the same experiment under similar parameters to calculate the probability of realizing a path block. When the flow velocity was 20 mm/s, almost 50% of the aggregations were induced to flow through the desired path and a maximum probability of realizing a path block of 86% was achieved with the formation of aggregations.

Production and validation of acoustic field to enhance trapping efficiency of microbubbles by using a matrix array transducer

We have developed a new matrix array transducer for controlling the behavior of microbubbles, which is different from that for high-intensity focused ultrasound (HIFU) therapy, in order to emit continuous wave by designing an acoustic field including multiple focal points. In the experiment using a thin-channel model, a wider acoustic field has an advantage for trapping microbubbles. In the experiment using a straight-path model, we have confirmed that a higher concentration of acoustic energy does not result in more aggregates. The dispersion of acoustic energy is important because the trapping performance is affected by the relationship between the shape of the acoustic field and the concentration of the suspension.

Experimental study of active control of microbubbles in blood flow by forming their aggregations

We have experimented a method to control behavior of microbubbles in flow using an artificial blood vessel with multiple transducers to emit ultrasonic plane wave. Microbubbules are propelled in flow owing to a primary Bjerknes force, which is a physical phenomenon where an acoustic wave pushes an obstacle along its direction of propagation. Also they form aggregation when they are put into an ultrasound field because of secondary Bjerknes force, which acts as attractive or repulsive factor among neighboring microbubbles. Thus we consider that forming bubble aggregations is effective to be propelled before entering into an ultrasound field to receive greater primary Bjerknes force. We have investigated the phenomenon of bubble aggregations and observed behavior of aggregations with and without red blood cells in artificial blood vessels under various conditions of ultrasound exposure. As the results, when microbubble aggregations were formed, the efficiency was improved more than the condition without forming aggregation. The existence of red blood cells near microbubbles contributed to the increase in the size of aggregations propelled against the vessel wall.