In 1991, we have developed a needle insertion robotic system for CT-guided stereotactic neurosurgery. The system, based on existing stereotactic frame, had six DOF of movement with minimum size to fit a CT gantry.Safety issue was carefully considered: by cutting off the power supply, all axes were held rigidly to avoid unexpected motion. A phantom study using X-ray CT showed that the overall position error was 1.0mm. This system was followed by MRI-compatible version.This paper presents the history of this system and briefly reviews other stereotactic robots.

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Since ultrasonic diagnostic equipment is small and inexpensive compared to CT or MRI, 3D-information acquiring methods by ultrasound (US) are widely studied. For that purpose, calibration for identifying of the spatial relationship between an US probe and a position tracking device is required. To apply the calibration in a clinical setting, not only the accuracy but the simplicity of a calibration phantom and procedures are important. In this study, we propose an automatic and accurate US calibration method using a metal ball marker. First, US images were captured freehand keeping the depth position of the marker. Next, an image passing through the center point of the marker was selected by comparison with mean brightness of comet-tail artifacts. Then, the center position was calculated by least-square circular fitting. When several center positions of the metal ball were obtained, the transformation matrix was determined by point-based registration. From the results, average of calibration errors was 0.26mm by a convex probe. Moreover, the calibration time including freehand image acquisition and image processing was less than 10 minutes. The results demonstrate that the proposed method is accurate and convenient for US calibration.

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Ultrasound has been widely applied to clinical purpose of therapy as well as diagnosis. For ultrasound therapy, accurate positioning of therapeutic ultrasound field is required. To address the issue, we will propose a robotic system for sound field positioning for an ultrasound guidance. The system consists of an ultrasound probe, a 6-dof robot grasping a therapeutic device, an optical tracking device, and intra-operative planning software. The robot, which was designed to form a compact parallel link structure, was composed of three serial-link manipulators and a device grasping parts. In addition, respective links and the grasping part were connected using magnetic ball joints for safety. The system enables the therapeutic device follows to a probe based on intra-operative plan on an echogram. In this paper, basic performance of the developed system was validated. The following errors and latency to the probe were 2.24 mm, 0.76 degree, and 50 ms, respectively. Also, the positioning errors between the plans and actual positions based on echograms were 2.22 mm and 0.06 degree. The results demonstrate the system has a great potential for targeting a therapeutic device under the ultrasound guidance for ultrasound therapy.

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