A system for insertion of a surgical tool along a trajectory to a target region in a patient's tissues, under the guidance of ultrasound imaging. The system includes a hand-held robot to whose base the probe of an ultrasound system is rigidly connected. The activated platform of the hand held robot carries a surgical tool guide. The alignment of the tool guide defines the trajectory which the tool takes within the subject's body. The position of the target region seen on the ultrasound display, can be recorded, and the robot coordinate frame of reference registered thereto. The system aligns the pose of the robot such that the surgical tool is aimed directly at the target region, independently of motion of the ultrasound probe and its associated robot. An inertial measurement unit can be incorporated to provide back-up positional information if the image of the lesion is lost.
