An embodiment in accordance with the present invention provides a robot structure that includes an MRI-Safe pneumatic stepper motor and optical encoding technologies. The present invention includes a needle guide and a needle depth limiter. The needle for biopsy is inserted through the needle guide and the depth of inserting is limited by the needle depth limiter. The robot is configured to control this procedure. The robot structure is adapted for biopsy, a novel way of setting the depth of needle insertion, image-to-robot registration. The system includes control for the robot.