This paper provides a robotic ultrasound transducer positioning system for minimally invasive ultrasonic therapy by manipulating microbubbles in blood vessel, aiming at effective high-intensity focused ultrasound (HIFU) and acoustic drug/gene delivery. To realize such a technique in vivo, accurate and dynamic positioning of an ultrasound transducer is required. For this purpose, we have recently developed a robotic system with a parallel link structure. The novel system consists of the newly developed robot with an ultrasound transducer, an optical tracking device, and an ultrasound imaging device. As an interface for robot control, we have also developed a planning software to plan target position and direction on an echogram. The optical tracking device is used to integrate the robot and the echogram coordinates. To validate the system feasibility, this study evaluated the system performance by conducting experiments of microbubble manipulation in an artificial blood vessel.
For ultrasound therapy, e.g. microbubbles delivery, physical contact between therapeutic device and body surface is important. To guarantee the entire contact of the device, we propose a control method considering contact force and reaction moment using a robotic system and sensors. We used a parallel link robot, which has three links and the holder to determine position and angle of the device. First we eliminated self-weight moment of the device using the sensors. Next we established a series of surface contact controls, which consists of (a) initial contact control, (b) balance contact control, and (c) angle restoration control. Then we performed evaluation experiments using soft material and human body. Contacted area was visualized and evaluated with color ink. Convergence time to the desired position and angle was also evaluated while monitoring contact force and moment. We concluded that the determination of appropriate parameters is important and dominant for the quality of the system.
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